Article

Seismic behaviour of Cross-Laminated Timber structures: A state-of-the-art review

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Abstract

Cross-Laminated Timber (CLT) structures exhibit satisfactory performance under seismic conditions. This ispossible because of the high strength-to-weight ratio and in-plane stiffness of the CLT panels, and the capacity ofconnections to resist the loads with ductile deformations and limited impairment of strength. This study sum-marises a part of the activities conducted by the Working Group 2 of COST Action FP1402, by presenting an in-depth review of the research works that have analysed the seismic behaviour of CLT structural systems. Thefirstpart of the paper discusses the outcomes of the testing programmes carried out in the lastfifteen years anddescribes the modelling strategies recommended in the literature. The second part of the paper introduces theq-behaviour factor of CLT structures and provides capacity-based principles for their seismic design.

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... Experimental local tests on mechanical connections aimed at investigating their cyclic behavior highlighted that ductile failure mechanisms can be achieved when properly designed [7,8]. Contrariwise, brittle failure mechanisms could occur if the requirements for end and edge distances are not respected [9]. Commonly, in timber practice it is assumed that ductile mechanisms are those respecting the Johansen's failure modes [10] also included in Eurocode 5 [10]. ...
... In this model, tensile-resistant contributions are provided by hold-downs (HDs) exclusively, or combining hold-downs and angle brackets (ABs) if both are assumed able to resist tensile forces [7,9,28]. Instead, compression forces are totally faced by timber-to-timber or by timber-to-RC foundation contact. ...
... The same reduction has been also applied to the tangential modulus (G) in both longitudinal and transversal direction. This material modelling gives back an acceptable representation of the material elastic properties, and is frequently adopted in literature [9,18,24,32]. ...
Conference Paper
Typically, panel-to-panel and panel-to-foundation connection zones in Cross-Laminated Tim-ber (CLT) walls consist of steel-to-timber mechanical connections (hold-downs and angle-brackets) and timber-to-timber contact. While hold-downs and angle brackets are extensively studied in literature, the role of timber-to timber contact is underestimated. The platform con-structional technology used for build CLT walls requires that the vertical timber panels com-presses the horizontal CLT floors, engaging the orthogonal to grain timber properties in the seismic response. This paper discusses a new development concerning a theoretical sectional model for CLT panels proposed by the authors in a recent work, where strength of the panels subjected to combined axial force and bending moment was studied accounting for orthogonal to grain tim-ber properties. As advancement, a theoretical moment-curvature model for CLT panels is pro-posed in this paper and the displacement capacity (i.e., ductility) is investigated. The main pa-rameters which affect the ductile behavior of the panels have been studied by means of para-metric analyses, i.e. varying cross-section dimensions, amount of axial force, and hold-downs resistance. Theoretical results have been also compared with numerical ones derived from a bi-dimensional finite element model developed by the authors and a good matching between the results has been highlighted.
... Local tests on connections showed a significant energy dissipation capacity, if (correctly) designed to prevent brittle failure modes [19][20][21][22][23]. Mechanical connections, placed in the panel to panel and panel to foundation contact zones, named as hold-down (HD) and angle brackets (AB), consist of thin steel plates nailed or screwed to timber panels and bolted to foundation: the first resist to tension forces and are used against uplift, while the second resist to shear forces and are used to withstand sliding. ...
... In fact, it has been proved that, in the case of perforated walls, a stress concentration in the corners at the interfaces between lintels and vertical panels can arise. Such stresses can be higher than the design strength values of material and lead to local brittle failure of the material in the corner region due to tension or compression [23,50,68]. ...
... According to literature, uniaxial or biaxial behavior is generally considered to simulate the connections [23,46,50,[75][76][77]. In the first case, HDs and ABs resist only in their primary direction (e.g., HDs only in tension and ABs only in shear), in the second case both HDs and ABs resist axial and shear forces simultaneously. ...
Article
Full-text available
Cross-laminated timber (CLT) buildings are recognized as a robust alternative to heavyweight constructions, because beneficial for seismic resistance and environmental sustainability, more than other construction materials. The lightness of material and the satisfactory dissipative response of the mechanical connections provide an excellent seismic response to multi-story CLT buildings, in spite of permanent damage to timber panels in the connection zones. Basically, CLT constructions are highly sustainable structures from extraction of raw material, to manufacturing process, up to usage, disposal and recycling. With respect to other constructions, the potential of CLT buildings is that their environmental sustainability in the phases of disposal and/or recycling can be further enhanced if the seismic damage in structural timber components is reduced or nullified. This paper reports a state-of-the art overview on seismic performance and sustainability aspects of CLT buildings in seismic prone regions. Technological issues and modelling approaches for traditional CLT buildings currently proposed in literature are discussed, focusing the attention on some research advancements and future trends devoted to enhance seismic performance and environmental sustainability of CLT buildings in seismic prone regions.
... In balloon-type construction, the walls are continuous over two or more storeys or even for the entire height of the building, and the floor panels are framed onto the sides of the walls at each storey. This method would therefore prevent the issue of high-accumulated compression perpendicularto-grain stress in floor panels; it also takes advantage of CLT panels being manufactured with a length up to 20 1 A number of studies on CLT structural systems undertaken in Europe, North America, and Japan have demonstrated that a CLT system can be utilized effectively as a lateral load resisting system [6]. The studies included tests on various types of connections; quasi-static and dynamic tests carried on CLT walls and assemblies; and full-scale shake table tests and/or numerical simulations on CLT buildings. ...
... where Rt is the reaction, kN, that occurs at the left corner; Ffri,vj is the friction, kN, between two panels [6], ...
... When a bi-axial (shear and tension) behaviour of the mechanical anchors is adopted, the coupled yield load is lower than the uniaxial yield load for shear and tension [6]. Therefore, a quadratic interaction relationship between shear and tension yield loads are adopted. ...
Conference Paper
In this paper, a mechanics-based analytical model was developed for predicating the deflection and resistance of balloon-type CLT walls under in-plane lateral loads. The model incorporates the contribution of the wall bending and shear deformations, contributions from the wall rocking and sliding, and contribution of the slip in the vertical joints between wall panels, if present, in the total lateral deflection. The model also assumes that the lateral resistance of this system is governed by the strength of the hold-downs, shear connector(s), wood in contact with the shear keys, and the vertical joints, if present. The model was validated against the test results of four balloon-type CLT walls in two configurations tested under monotonic and cyclic loading. The verified analytical model was used to investigate the influence of vertical load, wall aspect ratio, and vertical joints on the structural performance of balloon-type CLT walls. The developed mechanics-based model will benefit researchers and engineers to predict the strength and deflection properties of balloon-type CLT shear walls.
... In recent years, Cross-Laminated-Timber (CLT) buildings have been characterised by a fast-growing in the market of wood-based structural systems ( [1,2]). The lightness of structural panels and the capacity of mechanical connections to dissipate seismic energy make CLT buildings a valuable alternative to other traditional structural types in seismic prone areas ( [3,4]). ...
... Other authors proposed similar strategies for non-linear analyses of light-frame timber buildings [28]. However, it is noteworthy to mention that the complex implementation of these non-linear procedures and the need of input of several mechanical parameters have made these modelling strategies more suitable for research purposes rather than design practice [3]. ...
... In the upgraded model, the friction contribution is neglected as done in common practice and specified in Ref. [3] when the Force-Based Design (FBD) approach is adopted. In Refs. ...
Article
Practice-oriented finite element (FE) modelling strategies represent a fundamental tool for the seismic analysis and design of Cross Laminated Timber (CLT) structures. Although substantial research has been undertaken concerning the seismic behaviour of CLT buildings, practice-oriented FE modelling strategies are still at an early stage. This paper presents an upgrade of an existing practice-oriented FE design model for the seismic design of CLT structures. The upgrade is supported through the same modelling strategy presented by Christovasilis et al. (2020) adding some features of analytical equations models presented by Casagrande et al. (2016). 2D elements are used both for the modelling of CLT panels and for mechanical connections, which are represented by a horizontal strip with a height smaller than 7% of the height of the panel. Analytical equations for determining the elastic modulus of elasticity and the shear modulus of the horizontal strip are reported accounting for both rocking and sliding behaviour for single- and multi-panel CLT shearwalls, including the effect of the vertical loads by using a secant stiffness. The validation of the proposal is carried out in terms of the shearwall lateral stiffness through the results of experimental tests on full-scale shearwalls published by other authors and through a validation/comparison between a detailed non-linear model and the Christovasilis et al. (2020) strategy on two multi-storey seismic-resistant lateral systems configurations with different amount of vertical loads. Finally, a proposal for the initial layout of connections to reduce the iterative seismic design and analysis process for CLT buildings is presented through a case study.
... Since the spreading of Cross-Laminated Timber (CLT) as a valid alternative to engineering wood products and traditional construction materials [1,2], a remarkable number of researchers have investigated the structural performance of CLT shear walls [3][4][5]. Specifically, a significant amount of research investigated the ultimate lateral capacity of CLT shear walls [6][7][8][9]. Experimental and numerical research demonstrated that CLT panels have significant resistance to lateral loads [10][11][12], making CLT a suitable construction material, especially in earthquake-prone areas [13][14][15][16]. The scientific literature presents two approaches for predicting the lateral capacity of CLT panels [17]. ...
... The elastic displacement component is derived by the difference between the total displacement and the plastic displacement (Eq. (11) for = 1, 2, 3, 6,9,12). ...
Article
This paper investigates the effect of timber plasticization on the ultimate lateral capacity of rocking Cross-Laminated Timber shear walls with different characteristics. Simplified capacity models predict a CLT wall ultimate capacity by multiplying the hold-down ultimate resistance by its distance to an assumed pivot point, often coincident with the panel edge. However, timber plasticization at the interface with the foundation can significantly reduce the lever arm of the hold down reaction. This paper aims at assessing the effect of timber plasticization and panel characteristics (geometry, width, presence of openings, etc.) on the position of the pivot point, expressed by the dimensionless lever arm , namely the ratio between the distance of the hold-down geometrical axis from the compressed timber resultant and the distance between the hold-down geometrical axis and the panel edge. An extended covariance-based sensitivity analysis of several Finite Element (FE) models, representing all the CLT shear wall design variability was carried out. The FE model, developed in Abaqus, has been calibrated on the experimental cyclic response of a CLT wall panel. Among the chosen parameters, the sensitivity analysis proved that the most significant ones affecting are two: the ratio between the hold-down reaction and the maximum resistance of the compressed timber, and the width of the opening. Accordingly, the authors estimated an elementary empirical regression equation based on the FE model results for predicting the dimensionless lever arm () in the capacity equation of CLT panels. The use of this elementary formulation allows the designer to estimate with considerable accuracy the lateral capacity of a CLT panel given the panel geometry, the ultimate resistance of the hold-down, the compression strength of timber perpendicular to the grain and the vertical load. Almost all points used for the linear regression fall within the confidence bounds, thus proving the accuracy of the proposed empirical formula for the dimensionless lever arm.
... These research studies suggest that well-designed mass timber structures can not only exhibit satisfactory performance under seismic conditions but can outperform traditional concrete structures. The superior performance is possible because mass timber buildings are extremely lightweight compared to concrete buildings, thereby minimising inertial forces generated during an earthquake and reducing the risk of failure [46]. Additionally, the high in-plane stiffness of mass timber panels such as CLT allows the structures to resist lateral distortion and ductile connections can yield without compromising the structural integrity of the building [46]. ...
... The superior performance is possible because mass timber buildings are extremely lightweight compared to concrete buildings, thereby minimising inertial forces generated during an earthquake and reducing the risk of failure [46]. Additionally, the high in-plane stiffness of mass timber panels such as CLT allows the structures to resist lateral distortion and ductile connections can yield without compromising the structural integrity of the building [46]. Although research to date has established the viability of MTC under seismic conditions, further research is required to investigate the most appropriate seismic design for tall mass timber buildings greater than 20-storeys. ...
Article
Full-text available
The construction industry represents one of the greatest contributors to atmospheric emissions of CO2 and anthropogenic climate change, largely resulting from the production of commonly used building materials such as steel and concrete. It is well understood that the extraction and manufacture of these products generates significant volumes of greenhouse gases and, therefore, this industry represents an important target for reducing emissions. One possibility is to replace emissions-intensive, non-renewable materials with more environmentally friendly alternatives that minimise resource depletion and lower emissions. Although timber has not been widely used in mid- to high-rise buildings since the industrial revolution, recent advances in manufacturing have reintroduced wood as a viable product for larger and more complex structures. One of the main advantages of the resurgence of wood is its environmental performance; however, there is still uncertainty about how mass timber works and its suitability relative to key performance criteria for construction material selection. Consequently, the aim of this study is to help guide decision making in the construction sector by providing a comprehensive review of the research on mass timber. Key performance criteria for mass timber are reviewed, using existing literature, and compared with those for typical concrete construction. The review concludes that mass timber is superior to concrete and steel when taking into consideration all performance factors, and posits that the construction industry should, where appropriate, transition to mass timber as the low-carbon, high performance building material of the future.
... Each layer consists of adjoining solid wood boards/sheets and each layer is overlaid with adhesive at an angle of 90°. The structural properties of the CLT panels are attributed to this layout, which gives dimensional stability, reduces dispersion of the original properties of the wood, reduces or eliminates the influence of timber cracks and gives the structural element increased rigidity, parallel and perpendicular to the plane (Izzi et al. 2018). As for the mechanical properties, in addition to the intrinsic characteristics of the wood and the number of panel layers, the glue line influences the panel's resistance and performance (Betti et al. 2016;Knorz et al. 2017). ...
... There is a wide variety of standards to evaluate panels and analyse their structural performance, physical properties, durability, and the type of joints to use among other aspects (Young et al. 2016;Brandner et al. 2016;Izzi et al. 2018). Among the properties affecting CLT behaviour is glue line performance (Sikora et al. 2016), which can be evaluated at the time of panel fabrication, or while it is being used (Song and Hong 2016). ...
Article
Full-text available
Evaluation of the glue line in CLT panels and in other wood composite products in general is of great interest. Non-destructive methods such as determination of the velocity of ultrasound waves going through the materials are commonly applied to evaluate wood products. The present work is aimed at mapping ultrasound velocity (UV) to identify problems of glue line delamination in CLT panels of 3 and 5 layers made from Gmelina arborea and Tectona grandis timber. The results showed higher UV in the 3-layered panels in both timber species, and low UV and the presence of regions of low velocity in UV isocurves of the 5-layered CLT panels, due to separation of glue line, such as un-gluing and delamination. A UV reference value for glue line free of delamination problems of 927 and 1039 m/s was set for CLT panels of G. arborea of 3 and 5 layers, respectively, and of 1073 and 946 m/s for CLT panels of T. grandis of 3 and 5 layers, respectively. Values below the UV reference suggest the presence of some anomalies or problems of delamination, such as gluing defects.
... The neutral axis depth, c 1,j and c 2,j , is then iterated until force equilibrium is achieved. Note, the friction term is generally neglected [77,78] in analysing CLT structures. In this study it was considered as it was required to predict the experimental response under quasi-static loading where friction was present. ...
... The frictional force between Wall 1 and Wall 2 was calculated by F fr = ψF, where F was the ram force. Note, the friction term is generally neglected [77,78] in deflection calculation and modelling of CLT structures but this was presented for comparison to the experimental quasi-static testing results. Fig. 21 compares Test DW-2 to the coupled double wall (CDW) analytical model using both the elastoplastic and the nonlinear curve fitting model for the in-plane STS joint. ...
Article
Post-tensioned (PT) timber technology-also called Pres-Lam technology-can provide increased strength/ stiffness for mass timber seismic load resisting systems while also providing energy dissipation and re-centering capabilities. Initial experimental tests and practical implementation on PT timber structures in the past 15 years primarily utilized laminated veneer lumber (LVL), with some glulam and cross-laminated timber (CLT) prototypes and real-case applications, and their analytical prediction models were extended and adapted from precast concrete to account for unique characteristics of engineered timber. More recently, CLT has emerged into a more dominant global mass timber product. This paper presents a large-scale experimental study on 8.6 m tall PT CLT single and double wall systems. The PT double walls utilized screwed connections at the in-plane joint and U-shaped flexural plates at the foundation to provide coupling effect and energy dissipation. With screwed connections, the PT double wall partial composite action of approximately 70% was achieved and the system stiffness was almost two times that of two PT single walls without partial composite action but of equivalent length. Analytical prediction models, accounting for the peculiar controlled rocking mechanism and originally developed for PT LVL systems were adopted for PT CLT wall systems, were found to have increased compressive toe strain variability due to the increased material inhomogeneity of CLT with non-edge glued lamella. The timber compressive strains and unique 'end effect' bearing phenomenon was investigated for the first time with Particle Tracking Technology (PTT). Extensions to the existing PT double wall analytical prediction model were proposed and validated to capture the unique kinematic rocking mechanism where wall uplift occurs due to the strong and stiff screwed in-plane connection between individual walls. Free download for 50 days: https://authors.elsevier.com/a/1ehNMW4G4XR6D.
... Regardless of the technological solution adopted, the floor-to-wall connections are typically designed to transfer the shear forces coming from the upper stories. In the case of seismic capacity design, such connections are considered as non-dissipative zones and shall be consequently overdesigned [17,18]. ...
... To investigate the contribution of the floor-to-wall interaction on the rocking stiffness of CLT segmented shear-walls, the latter ones (given in Equation (1a) and (1b)) are firstly presented in dimensionless form, as percentage of the rocking stiffness of the monolithic shear-wall, see Equation (17a) and (17b). It is possible to see that the dimensionless stiffness of the segmented shear-walls can be expressed as function of the parameter α, namely the ratio between the stiffness of the wall-to-wall spring and the stiffness of the hold down, see Equation (18). Equations (17a) and (17b) are written considering the stiffness k w− w,tot , hence by taking into account the effect of the floor-to-wall interaction. ...
Article
The mechanical behaviour of Cross-Laminated Timber (CLT) buildings under lateral loads is mainly governed from the connections and is strongly influenced from the internal structure of the shear-walls, which can be monolithic or segmented. In comparison with monolithic shear-walls, segmented shear-walls have a more flexible behaviour and can dissipate higher amount of energy due to the contribution of the vertical panel-to-panel connections. However, in CLT buildings other connections, such as the connections between the wall heads and the upper floor, can influence the lateral behaviour of the shear-walls. This paper presents a study on the phenomenon of the floor-to-wall interaction and on the influence of this mechanism on the rocking behaviour of segmented CLT shear-walls. An analytical elastic model that describes the floor-to-wall interaction and allows to calculate transversal displacements and internal actions along the floor is presented and validated against numerical models developed in SAP2000. The analytical model is subsequently used for the definition of an equivalent spring, which can be used for easily taking into account the more complex phenomenon of the floor-to-wall interaction. Parametric analyses, in which different geometries and connection stiffnesses were used, showed that the floor-to-wall interaction increases the rocking stiffness of segmented shear-walls and modifies the shear-wall kinematic behaviour. The increase of rocking stiffness was found to be dependent on the floor bending stiffness as well as the withdrawal stiffness of the floor-to-wall connections.
... Cross-laminated timber (CLT) as the main structural system has seen exponential growth in the last decade worldwide, and its market share is expected to continue to grow further in the future [5] not only for lowrise, but also mid-rise and high-rise buildings including moderate and high seismic regions due to its good seismic behavior as observed in extensive experimental, analytical and numerical studies [19]. CLT has gained such popularity in construction due to numerous advantages; its low weight and high prefabrication levels reduce transportation and erection cost, enables easy handling and speed of construction, as well as reduces the size of necessary foundations. ...
... From Eqs. (17)- (19), Eq. (17) can hence be rewritten as: ...
Article
Full-text available
This paper presents a numerical and analytical study on single-storey cross-laminated timber (CLT) shear-walls with openings subjected to lateral loads. The main objective was to investigate the location and distribution of maximum values of axial and shear forces in relevant wall sections. The influence of parameters such as wall geometry (different sizes of wall openings, door openings, lintel/parapet lengths and heights, wall thickness) and different stiffness levels of mechanical anchors for CLT wall connection with floor/foundation were studied. Finite element (FE) parametric analyses were performed on a set of single-storey CLT shear-walls with door and window openings and were compared with analytical models for determination of internal forces. The importance of wall connections’ flexibility was identified, as the distribution of internal forces in walls with rigid and flexible anchors were considerably different. The obtained outcomes of this study provide a solid base for the next step, an experimental investigation of in-plane internal force distribution in CLT walls with openings, which will serve for further development of numerical, analytical and design approaches.
... Other studies have developed design guidance to estimate the in-plane resistance and deflection of shear walls in platform-type CLT buildings (Popovski et al. 2010;Gavric et al. 2015a;Pozza et al. 2018;Shahnewaz et al. 2019Shahnewaz et al. , 2020aMestar et al. 2020;Izzi et al. 2018). Popovski et al. (2010) performed quasistatic monotonic tests with vertical shear connectors and demonstrated adequate seismic performance and ductile behavior. ...
... Mestar et al. (2020) developed an equivalent-frame model for CLT shear walls with openings and evaluated the performance under lateral loading. Izzi et al. (2018) reviewed the current state of the art of seismic performance of CLT structures. All these studies confirmed that the connections between CLT shear walls and the foundation and between panels were the primary contributors to deflection and ductility and supported the implementation of design provisions for platform-type CLT construction in standards around the world (Karacabeyli and Gagnon 2019). ...
Article
This paper presents experimental investigations on the seismic behavior of cross laminated timber (CLT) shear walls in a balloon frame configuration with various ledger assemblies attached at midheight. The tested system consisted of two seven-ply 191-mm-thick CLT panels with generic hold-downs, steel angle brackets, plywood surface splines, and nails as fasteners. A 2-story system was tested with a panel aspect ratio of 3∶1 with different steel and wood ledgers under monotonic and quasistatic reversed cyclic loading. Three ledgers were subsequently tested under vertical quasistatic monotonic loading to determine their remaining load-carrying capacity. The tests showed that the shear wall displacement was due to the rocking of the wall panels, which themselves behaved as rigid bodies with negligible in-plane deformations. When compared to the monotonic tests, the strength in reversed cyclic tests was up to 21% lower. The ledger did not impede the desired rocking behavior of the wall, nor did the rocking of the wall reduce the remaining gravity load-carrying capacity of the ledgers by more than 7%. Balloon-framed CLT shear walls can be detailed and designed using the Canadian standard specifications for platform-type construction.
... The introduction of new engineered timber products, such as glue-laminated timber, Cross-Laminated Timber (CLT) and Laminated Veneer Lumber (LVL), caused a significant spread of timber-based structures in the last two-three decades also in Europe [1], not only in North Europe, which is a zone particularly devoted to the use of timber, but also in the Mediterranean area countries, like in Italy, Spain and Portugal. A massive use of timber buildings in the European market constructions has ensued, especially for CLT, light and heavy timber frame and blockhaus buildings, allowing a rapid technological progress [2][3][4]. Such progress has not been accompanied by an immediate updating of the European Standards, either at the international or national levels. ...
... Cross-Laminated Timber structures are made with CLT panels, used for both vertical shear-walls and floor slabs [3,27,28]. Shear-walls resist both vertical and horizontal loads and are used for external and internal walls of the building. Walls may be monolithic, i.e. made with a single panel including openings for doors and windows, with height equal to the inter-storey height of the building and width depending on the maximum producible and movable dimensions. ...
Article
In 2007 the Italian National Research Council published the technical document CNR-DT 206/2007 “Instructions for the design, execution and control of timber structures”, with the purpose to provide a technical support to the operators of the sector, in line with the most advanced knowledge at that time. Since then, the world of timber engineering has largely used such document, even though the instructions are not mandatory standard rules, so that they became the most common tool in Italy for the structural use of timber, opening the markets and favouring competition and new applications. In latest years new studies, researches and innovative proposals have promoted the development and the growth of timber constructions also in the civil residential field. The framework of standard rules for constructions and products, both Europeans and Italians, has evolved too. For these reasons, CNR has considered as opportune to proceed to the editing of a new version, updated and widened, namely with the acronym DT 206-R1. The document comes from the spontaneous cooperation of an open group of specialists and operators of the sector, based on a wide discussion on the common scientific and technical expertise and knowledge. The current version has already taken into account the results of the public inquiry phase (concluded by now). The paper presents the main contents of the document, evidencing the innovations.
... As a result of the development of cross laminated timber (CLT), in recent years several high-rise and complex buildings have been constructed with load-bearing elements made of wood [1][2][3]. Since CLT structures offer many advantages, such as sustainability, energy efficiency, and rapid construction, they are also becoming more common in regions prone to earthquakes [4,5]. Ductile connections play a crucial role in achieving earthquake-resistant CLT structures by ensuring the deformation capacity and energy dissipation of the structural system. ...
Article
Full-text available
This paper presents the results of an experimental campaign investigating the seismic behaviour of full-size cross laminated timber (CLT) wall systems with sound-insulated shear-tension angle brackets. The main aim of the study was to investigate the influence of more and less flexible soundproofing bedding under the CLT wall. The paper shows a comparison of lateral load-bearing capacity, displacement capacity, ductility and stiffness obtained from racking tests on uninsulated specimens and specimens with various types of bedding insulation and levels of vertical load. Moreover, an analytical procedure to estimate the lateral load-displacement response of CLT walls with bedding insulation is proposed. This model is verified by direct comparison to the experimentally determined lateral load-displacement backbone curves. The results show that the elastomeric bedding does not have a significant effect on the bearing capacity of the wall system tested, but it reduces the stiffness and increases the displacement capacity. Due to the large decrease in stiffness, the insulation causes an overall reduction in ductility. The analytical estimation proposed was able to capture the reduction in lateral stiffness and adequately predict the load-bearing capacity.
... The effectiveness of structural CLT members relies on the connections which resist large pullout type forces, the strength requirement of which increases with the square of the building's height [3]. The CLT structural system is becoming increasingly common in areas of low to moderate and even high seismicity due to its strong in-plane stiffness, inherent ductility and its comparably lighter weight compared to traditional reinforced concrete and steel frames [4]. The lightweight properties of CLT, however, result in uplift forces from lateral loads such as wind and earthquakes needing to be resisted by high-capacity connections. ...
Article
The popularity of cross-laminated timber (CLT) has increased significantly over recent years, with numerous low-to mid-rise buildings being constructed with CLT panels as the load-bearing structural system. Glued-in rods (GiR) have been used in the construction and retrofitting of timber structures and recently found its use in CLT elements. Embedded into the timber with structural grade adhesives, GiR enable stiff connections between timber and other structural members. Due to the complex force mechanisms occurring within these joints, there is yet to be consensus on a suitable method to predict their pull-out strength or failure mechanism. There is lack of experimental research on performance of GiR embedded into CLT. This paper examines previous research on glued-in rod connections as typically applied to solid timber and other engineered timber products. It aims to identify the factors contributing to the strength and failure modes of this connection, as well as the current models that are used for the analysis and design of glued-in rods. A series of 30 experiments were undertaken to investigate the load carrying capacity of single GiR bonded into CLT panels to identify the influence of (i) the bonded length of rod; and, (ii) the direction of the middle ply of the CLT panel on these results. The experimental results indicate that the pull-out strength is largely dictated by the embedment length.
... Today, wood and the modern materials derived from it can represent an optimal choice for interventions of volumetric additions (Margani et al., 2020;Valluzzi et al., 2021). Modern research and technological innovations have allowed overcoming the problems related to the anisotropy of the original material by creating a "new generation" of products and technologies that fully compete with the most commonly used materials Frunzio et al., 2021;Izzi et al., 2018;Sun et al., 2020). So, volumetric ...
... In fact, for fasteners with diameters less than 6 mm, Eurocode 5 [35] considers the embedment strength, f h , depending solely on the fastener diameter, d, and on the wood density, q, see Eq. (3), in which the subscripts k denote the characteristic values. [29] (c), rotational failure mechanism in vertical plane [14] (d), rotational failure mechanism in horizontal plane [27] (e), buckling of metal plates [10] (f). ...
Article
This paper presents an experimental study aimed at characterizing the mechanical behaviour of a new shear-tension connector for wall-to-floor connections of CLT structures. The shear-tension behaviour is reached by means of fully threaded screws inserted in the floor joint. Experimental tension, shear and inclined load tests are performed to investigate the biaxial behaviour of the connector. Results of such tests, performed in monotonic and cyclic regime, were used for the definition of force, displacement, stiffness and ductility domains. Circular experimental domains were found for all the mechanical parameters, confirming the biaxial mechanical behaviour of the connection.
... Fig. 21 presents a typical failure mode [67]. At least one plastic hinge must be developed to achieve the yielding of fasteners, where the two most desirable are timber-timber or TCC joint [67,123]. Mai et al. [6] found that the screw-type shear connector provided ductile connection mode with a large slip at failure. ...
Article
Composite construction elements are gaining extensive attention due to their high performance and reliability. Timber–concrete composite is one of the well-known engineered products of global interest. The cross-laminated timber (CLT) is a plate-like quasi-rigid composite that is usually composed of an uneven number of layers of solid timber board. The timber boards are generally placed side-by-side and arranged crosswise in CLT. The anisotropy in single timber boards is reliably adjusted, and its out-of-plane load bearing capacity is improved. The CLT members show low bending strength and resistance to global stability. The CLT–concrete composite has developed and showed approximately 3–5 times higher strength capacity than the conventional timber or concrete structures. This study aims to review the current practice and available guidelines for the CLT–concrete floor system. The basic required information on the design and construction and performance of the aforementioned system is described based on the current practices. This review can guide prospective researchers and users regarding the application of the CLT–concrete composite. The CLT–concrete elements need to be designed and constructed following the current code of practice and studies guidelines to achieve optimal performance. The design, construction, and performance of the CLT-concrete system are dependent on timber properties, connection systems, and slab details. This composite floor system possesses good performance under various loading conditions if adequately designed and constructed.
... Similar to traditional light-frame wood systems, CLT can be used to make all the components of buildings in platform-type constructions. The high strength-to-weight ratio coupled with CLT's versatile applications attracted builders to use CLT in seismic-prone areas across the world [5,6]. ...
Chapter
Ductile cross-laminated timber (CLT) shear walls can be achieved by vertically joining a series of CLT panels with ductile connectors. When such multi-panel systems have a well-defined center of rotation, the resulting kinematic behavior is termed as coupled-panel (CP). In this paper, an iterative energy-based design (EBD) method is proposed for CLT shear walls based on energy balance established on their CP kinematic. Holz-Stahl-Komposit (HSK) connectors were utilized for both hold-downs and vertical joints. The seismic energy demands were estimated from constant ductility hysteretic energy spectra established for elastic-perfectly-plastic single-degree-of-freedom oscillators. The lateral force-deformation characteristics were derived considering the CP behavior in elastic and plastic ranges. Subsequently, the ductility demand was evaluated from these force-deformation relations. The story-wise hysteric seismic energy demands were balanced by the cyclic energy supply. While the lateral yield resistances were attributed to the hold-downs and vertical joints, the lateral plastic deformations were attributed to the vertical joints. The proposed EBD method accounts for the preferred failure mode together with performance criteria derived from either target deformation limit-states or local deformation capacities of the energy dissipative components.
... Fig. 2 shows an example of commercial angle brackets used in a recently completed 10-storey Aveo Norwest CLT building in Sydney [23]. Because CLT panels have higher in-plane strength and stiffness than LTF [24], their in-plane performance is generally governed by the mechanical connection systems [25]. With commercial brackets, Flatscher et al. [26] reported that the performance of CLT LLRS was underutilized. ...
Article
Full-text available
The advent of digital fabrication technologies and mass timber products such as cross-laminated timber (CLT) have facilitated the use of traditional carpentry joints in modern mass timber construction. Through contact bearing, mortise and tenon castellated joints can also provide high shear strength and stiffness between timber members when compared to connections using mechanical connectors/fasteners. In this study, a total of 29 connection specimens using carpentry castellations and six connection specimens using commercial angle brackets were tested under monotonic loading to evaluate their structural performance. These specimens used five-ply (175 mm thick) and seven-ply (275 mm thick) CLT panels. It was found that the shear strength and stiffness of the castellated joints were 2.5 and 7 times greater than the specimens using the commercial angle brackets. A simplified component-based analytical model was also developed to predict the strength of the castellated joints loaded parallel and perpendicular to grain of the CLT outer layers. The simplified model was found to be adequate in estimating strength given the model limitations. Overall, the study showed that these castellated CLT joints can provide one effective connection type with high shear strength and stiffness for CLT structures.
... In order to achieve a resistance target, Motoshi et al. [9] conduct studies on the seismic behavior of narrow panel CLT building by a numerical model to evaluate its structural performance, and the structure behave was well during severe strong motion despite the occurrence of a compression rupture in CLT shear walls. A series of tests show that the shear damage of connections is the main failure mode of CLT wall with and without openings under cyclic loading [10,11], resulting in a decrease of bearing capacity. This failure mode could not take full use of the lateral resistance of CLT wall. ...
Article
This paper presents the results of a lateral performance study on glued-laminated timber frame (GLT) infilled with cross-laminated timber (CLT) shear walls by means of experimental method. Specially-designed steel connectors were installed at the frame-to-wall connections, which are used to provide reliable mechanism of force transmission for the structure. Lateral cyclic loading tests on this structural system were conducted, and the influences of opening size, opening form (e.g., door and window), and aspect ratio of wall panels on the lateral performance of the structural system were examined. The elastic and elastic–plastic drift ratios of the GLT frame infilled with CLT walls were defined as well. In addition, the failure mechanisms, hysteretic characteristics, lateral stiffness, energy dissipation and bearing capacities of the GLT frame with CLT shear walls were investigated in details, and the collaborative mechanism and lateral collaborative effect between GLT frame and CLT shear wall was evaluated. Results indicated that the inclusion of the CLT shear wall improved the overall stiffness and strength of the GLT frame significantly, and increments were 10.66–14.1 and 2.74–5.26 times, respectively. The CLT shear walls played an important role in dissipating a considerable portion of energy in the initial loading stage. When the overall GLT frame reaches the peak strength, observable damage appears on the walls, like cracking or squeezing deformation, but the structure is still able to withstand a substantial part of horizontal loads.
... of CLT shearwalls, e.g. [5][6][7][8][9][10][11][12][13][14][15][16]. A detailed review of these investigations is beyond the scope of this paper. ...
Article
The use of cross-laminated timber (CLT) shear walls in tall buildings poses large demands on hold-downs (HD). While commonly used HDs behave as dissipative connections, the current Canadian Standard for Engineering Design in Wood recommends designing HDs as a non-dissipative connection. To satisfy this requirement, a hyperelastic elastomeric (rubber) HD was developed. Material level tests showed that the compressive behaviour of rubber layers relied on a dimensionless geometrical shape factor (SF). Component level tests on a total of 16 different HD configurations varying the width and thickness of the rubber pads were conducted under quasi-static monotonic and cyclic loading, the latter with two different loading protocols. Under monotonic loading, the rubber HDs behaved hyperelastic without any residual inelastic deformation and no damage was observed in the CLT panels or the steel parts. The HD load-displacement behaviour was mostly influenced by SF, with smaller SF leading to lower stiffness. A power function was developed to describe the load-displacement behaviour of the HD. Under cyclic loading, no strength or stiffness degradation was observed, even after multiple loading cycles. When designing CLT shear walls with the proposed hyperelastic HD, both the CLT panel as well as the steel parts must be capacity protected to prevent the brittle failure of the CLT or premature yielding of the steel.
... Similar R d and R o seismic force modification factors were proposed by Pei et al. (2013a). Development of the R factor for CLT platform buildings in ASCE-7 in the United States (van de Lindt et al. 2020;Amini et al. 2018;Pei et al. 2013b) and q factor for implementation in Eurocode 8 (e.g., Lukacs et al. 2019;Izzi et al. 2018;Pozza and Trutalli 2017;Pozza et al. 2016) is ongoing. Alternate design procedures, such as displacement-based design and energy-based design, were proposed by several authors (Hummel and Seim 2019;Tesfamariam et al. 2019b;Goertz et al. 2018;Loss et al. 2018). ...
Article
Full-text available
In this work, a 10-story uncoupled (10S-U) hybrid seismic force resisting system, consisting of cross-laminated timber (CLT) walls and reinforced concrete (RC) beams, is considered. Required design ductility factor Rd, in congruence with the National Building Code of Canada, was developed using FEMA P695 collapse risk procedure. Two trial Rd factors, Rd=2 and Rd=3, were first used to design the hybrid building for seismicity of Vancouver, BC, and 3D numerical models were developed in Open System for Earthquake Engineering Simulation (OpenSees) finite element framework. The energy dissipation of the structural system was enhanced using buckling restraining brace hold-downs and energy dissipator connection between the panels. The rocking response mechanism governed and, as a result, the cyclic pushover results show recentering capability. A suitable set of 30 ground motion records that reflect the seismic hazard of Vancouver, British Columbia, was selected in congruence with the 2015 National Building Code of Canada (NBC). Using incremental dynamic analysis, the collapse risk and collapse margin ratios were obtained to check the suitability of the two proposed Rd factors. The Rd=2 factor was shown to be acceptable for the 10S-U structural system.
... Recent studies in New Zealand have focused on CLT rocking walls that incorporate novel energy-dissipating devices in the panel (Hashemi et al. 2018;Hashemi and Quenneville 2020). A recent comprehensive review of the seismic behavior of CLT can be found in Izzi et al. (2018a). ...
Article
Full-text available
Cross-laminated timber (CLT) is a mass timber product that has recently garnered considerable attention for lateral-force resisting system (LFRS) applications. The main objectives of this study were to investigate the rocking behavior of a high-aspect-ratio (height/width) CLT shear wall without post-tensioning, and to validate a finite-element (FE) model based on the cyclic and dynamic response of the wall. To this point, high-aspect-ratio walls in the literature have primarily been post-tensioned. The testing component of this study included connector tests, quasistatic cyclic shear wall tests, and shake-table tests under four different ground motions scaled to design earthquake (DE)- and maximum considered earthquake (MCE)-level intensities. A generic shear connector was used for this study to allow for proprietary and other systems to demonstrate equivalence. The connectors were tested under shear and uplift, and shear-wall tests were performed using the Consortium of Universities for Research in Earthquake Engineering (CUREE) displacement protocol, which has been widely used for light-frame wood structures. Interstory drift (ISD) ratios in the shake-table tests ranged from 0.97% to 2.02%, and the tests demonstrated the system's ability to resist seismic loading. An FE model of the CLT wall was developed that showed good agreement with the cyclic and shake-table tests. The difference between the ISD ratios in the numerical model and the shake-table tests ranged from 5.4% to 31.3%, with an average of 17.9%, which was in good accordance with the accuracy of the existing CLT models. This system can be utilized as a retrofit option, in conjunction with light-frame wood shear walls, where lack of space may be a challenge.
... CLT provides high tensile strength parallel to the grain and high compressive strength perpendicular to the grain of timber. CLT is a sustainable solid-wood based construction material characterized by low mass, high stiffness, good seismic behaviour, and good thermal properties [1]. A wide range of different timber species for CLT production has been investigated as reported in the literature review [2]. ...
Article
Full-text available
In recent years, hybrid steel-timber structures are seeing an increasing use in modern building construction at a competitive price. Cross-laminated timber (CLT) is a prefabricated multi-layer engineered panel wood product, manufactured by gluing layers of solid-sawn lumber at perpendicular angles. Their orientation results in excellent structural rigidity in both orthogonal directions. CLT construction materials are used not only for flooring systems and roof assemblies, but CLT infill shear walls are also gaining a lot of interest as a promising alternative for sustainable primary lateral load resistance systems. This paper extends the current research background on hybrid steel-timber structures. To achieve that, this work is conducted in such way as to explore the potentiality of incorporating CLT infill shear walls within steel framed structures with semi-rigid connections (STSW). In particular, a three-dimensional finite element model using the general-purpose finite ele-ment program ANSYS is generated herein to study the mechanical behaviour of a single-bay, two storey STSW system with semi-rigid connections. Analytical results show that the presence of CLT infill shear walls can significantly improve the performance of moment-resisting frame systems, for multi-storey buildings. Moreover, it is observed from the extended parametrical study that the STSW systems show better performance when an appropriate plastic moment ratio index is defined.
... CLT panels perform in high stiffness, resistance to shear, tension and compression in-plane, and act in low ductility and dissipation of energy [1]. The connections between the CLT elements play a key role in ductility and energy dissipation of timber structures in addition to providing sufficient stiffness and strength between the structural elements and, thus, require special attention [2]. Therefore, the behaviour of CLT buildings during earthquakes depends mainly on the performance of connections between adjacent panels and other structural elements [3]. ...
Article
Full-text available
This study investigates timber connections with flexible polyurethane adhesives, which prove to have the potential for timber-adhesive composite structures without mechanical connections for seismic regions. Results of conducted cyclic double lap-shear adhesive timber joints tests were compared with available experimental results on timber connections with standard mechanical dowel-type fasteners and with results of numerical finite element analysis. The study found that the shear strength, elastic stiffness and strength degradation capacity of the flexible adhesive connections were significantly higher compared to mechanical fasteners commonly used in seismic-resistant timber connections. The latter, however, manifested larger ultimate displacements but also yielded at lower displacements.
... The majority of the research studies conducted on CLT shearwalls have been focused on the role of the mechanical anchors [12][13][14][15][16] and CLT shearwalls with no opening [17][18][19][20][21][22]. The outcomes from these studies have made it clear that the wooden panels behave mostly like rigid bodies, whereas the main deformation contributions and energy dissipation of the shearwall are chiefly related to the non-linear behaviour of mechanical anchors (i.e. ...
Article
The current study presents the results of an extensive numerical analysis using a validated Finite Element model and aims at investigating the influence of the geometrical and mechanical properties of lintel beams and parapets on the stiffness and strength of multi-storey cross laminated timber (CLT) symmetric shearwalls with either door or window openings. The influence of construction techniques, where the opening is cut out of the panel or constructed using separate elements is investigated. The results of the analysis show that in general, monolithic models resulted in significantly higher strength and stiffness values compared to those obtained from models assuming segmented shearwalls. The assumptions associated with the connectivity between the various structural components in the wall may have a very significant effect on the internal forces and efficiency of the design. The study also particularly highlights the importance of the parapet on the overall behaviour and failure mechanism, even though no structural function is typically associated with it. The lintel height seemed to only play a significant role when no parapet is present, i.e. in the case of door openings, where height of the lintel was observed to directly influence the failure mechanism, with intermediate lintel heights leading to failure in the wood elements, while for relatively small or large values, the failure occurred in the mechanical anchors.
... These characteristics has made timber very popular in the last years. The interest in timber structures has risen, especially in the last 2 decades, due to the advent of new engineering wood products, like cross-laminated timber (Ceccotti et al. 2013;Brandner et al. 2016;Izzi et al. 2018;Aloisio et al. 2021b). The low weight of timber, however, is a double-edged sword to the dynamic performance. ...
Article
Timber floors are prone to exhibit vibration levels, which can cause discomfort to the occupants. In the last 20 years, ambient vibration tests have become very popular due to the many advantages they have over traditional forced vibration tests when dealing with civil engineering structures. Furthermore, sensitivity analyses and black-box" optimization algorithms can support the development of refined finite-element models that accurately predict the structures' responses based on the experimental modal parameters. However, applications of these methods and techniques to timber structures are scarce compared with traditional materials. This paper presents and discusses the findings of an experimental testing campaign on a lightweight timber floor. At first, each component of the assembly was tested separately under different boundary conditions. Then, the authors evaluated the behavior of the whole floor assembly. In a second step, the authors carried out a covariance-based sensitivity analysis of finite element (FE) models representative of the tested structures by varying the different members' mechanical properties. The results of the sensitivity analysis highlighted the most influential parameters and supported the comparison among diverse FE models. As expected, the longitudinal modulus of elasticity is the most critical parameter, although the results are very dependent on the boundary conditions. Then automatic modal updating algorithms tuned the numerical model to test results. As a concluding remark, the experimental and numerical results were compared with the outcomes of a simplified analytical approach for the floor's first natural frequency estimate based on current European standards.
... In addition to other structural applications such as floors and vertical load resisting walls, CLT panels are being used for the lateral load resisting system in multi storey buildings around the world (e.g. as shear walls), and "designing and building CLT structures, also in earthquake-prone regions", is becoming a part of regular timber engineering practice . The consensus from research on the seismic behaviour of CLT buildings (Ceccotti and Follesa 2006;Ceccotti et al. 2013;Shahnewaz et al. 2019Shahnewaz et al. , 2020Izzi et al. 2018) was that the structural performance is governed by the energy dissipative connections, while CLT panels behave as almost rigid bodies. This assumption is adopted in the CSA O86 provisions (CSA 2019) for the design of CLT shear walls and diaphragms in platform-type buildings. ...
Article
Full-text available
Novel solutions with large-diameter connectors for cross-laminated timber (CLT) assemblies require wood brittle failure to be avoided through capacity-design-based provisions to protect the CLT panels. Current design standards, such as the Canadian Standard for Engineering Design in Wood (CSA-O86), do not cover the block tear-out resistance of CLT panels associated with large-diameter connectors. The primary objective of the research presented herein was to assess the block tear-out and net-section tension resistances of CLT panels loaded in plane and to provide guidance for the required end distances of single large-diameter connectors such as internal-bearing hold-downs. A total of 117 full-scale CLT specimens were tested to determine their in-plane tear-out resistance. 3-ply and 5-ply CLT panels with different loaded end and the edge distances and varying the grain direction of the outer layers were tested under quasi-static monotonic loading. The results demonstrate that brittle block tear-out or net-section tension failure can occur in CLT panels. These failure modes have to be accounted for in design. A simple stress-based strength criterion considering the rolling shear strength of wood delivers conservative and reasonably accurate predictions of the CLT brittle resistance.
... Refs. [18][19][20][21][22][23][24]) (see Izzi et al. [25] for a recent review on the seismic behaviour of CLT structures). An emerging trend for timber structures to control the effects of seismic loads is the use of seismic protection technologies that have been proven to operate for conventional reinforced concrete and steel buildings. ...
Article
Based on a six-storey cross-laminated timber building equipped with a base isolation system, this article proposes predictive models for the fundamental period of vibration, a parameter that needs to be selected in early stages of a seismically isolated building's design process, in relation to economic losses, such as repair costs and repair time, and environmental losses, such as repair-related carbon footprint and embodied energy. The predictive models were calibrated using a dataset of 114 bidirectional accelerograms recorded in Chile between 1985 and 2020, with event magnitudes ranging from Mw 7 to Mw 8.8. A single functional form was selected for the four resilience parameters used, having an average coefficient of determination of R² = 0.62. Results suggest that the selection of the fundamental period of vibration of a mid-rise seismically isolated CLT building can have a significant impact on the potential economic and environmental losses likely to occur when subjected to severe seismic events, and therefore, its selection should be based not only on technical aspects but also resilience and sustainability parameters.
... Recently, the bending properties of CLT under the in-plane loading form were also attracted more attention, which was investigated by Sikora et al. [19], Shahnewaz et al. [20], and Vessby et al. [21]. For the CLT members under the in-plane loading form, scholars are more interested in shear performance and seismic response [22,23], which are the important basis for the design of CLT wall members. In addition, for CLT under the out-of-plane and in-plane loading forms, much attention also has been paid to the vibration control [24][25][26] (e.g., non-destructive assessment and human-induced vibration performance) and other static mechanical properties [27][28][29] (e.g., rolling shear properties, compressive behavior, and dowel-type fasteners and connections performance). ...
Article
In mass timber construction, cross-laminated timber (CLT) and glued-laminated timber (GLT) usually build a load-bearing system together. Exploring the mechanical properties of CLT and GLT can provide a better understanding and inspiration for designing their members. This study presents a comparative study on the bending and shear characteristics of CLT and GLT beams under the out-of-plane and in-plane loading forms. A series of mechanical properties parameters in the major strength direction were obtained through the tests, and the bending properties were compared with theoretical results. A single-strength direction contribution rate model was developed to quantify the effects of the bending modulus relationship between adjacent layers. Under the same loading forms, the CLT presented lower bending and shear properties in the major strength direction than the GLT, mainly due to the orthogonal structure inside the CLT. The shear analogy theory showed higher accuracy in the out-of-plane bending results, and the calculation theory that considered all layers could better predict the in-plane bending results. Furthermore, the proposed contribution rate model was consistent with the test results and intuitively revealed the effect of the layer stiffness on the overall stiffness for bending specimens under two loading forms.
... With respect to seismic events, mass timber structures have performed well under simulations (as high as 7.2 on a Richter scale) and are often standing after most tests (Laguarda-Mallo & Espinoza 2015). Izzi et al. (2018) specifically reported that mass timber structures display acceptable performance under seismic conditions versus comparable steel and concrete structures. Unfortunately, like other wood products that are not treated with preservatives, CLT can be susceptible to termite infestations and fungal damage; however, there is limited research in this area (Franca et al. 2018). ...
Article
Full-text available
Cross Laminated Timber (CLT) is an engineered wood product for the construction industry offering multiple structural, environmental and supply chain benefits. CLT can be used for an entire building, as both the lateral and vertical load resisting system, or for select elements such as the roof, floors or walls. CLT products were developed in the early 1990’s and have been widely adopted throughout Europe, and more recently, in Canada. However, use of CLT products is still relatively rare in the US. We present the results of a nationwide phone survey in the US conducted with architects and structural engineers to gauge their awareness, rate of adoption and assimilation of CLT products. Although adoption of CLT amongst architects and structural engineers is still at a nascent level within the construction sector, awareness is high, with 100% of our sample respondents cognizant of CLT. Architects and structural engineers perceive relative advantages of using CLT as well as compatibility with traditional construction. However, the adoption process is impeded by issues associated with complexity, trialability and observability. Key barriers to adoption of CLT as perceived by these two stakeholders are lack of experience from construction stakeholders, lack of training and tools for construction management stakeholders, lack of client requests and CLT inventory.
... Over the last decade, North America, Europe and other countries have begun to study the new system of building multi-storey and high-rise timber hybrid structures with other materials, for example, the concrete or the steel (He et al., 2016;Zhang et al., 2017;Zhang et al., 2018). Several feasibility studies for innovative tall timberbased hybrid structural systems were carried out, and many prototype buildings were tested (Kuilen et al., 2011;Hristovski et al., 2013;Zhang et al., 2016;Izzi et al., 2018). Meanwhile, several tall timber and timber-hybrid buildings, e.g., the 18story Brock Commons in Canada (Tannert and Moudgil, 2017) and the 18-story Mjøstårnet in Norway (Abrahamsen, 2017), have been successfully built and are operating well, which demonstrates great competitiveness in the aspects of structural performance, environmental friendliness, and construction speed. ...
Article
Full-text available
The benefits of using wood in tall and commercial construction are undisputed, namely reducing the carbon footprint, shortening construction times, and enhancing seismic and building physics performance. The international market for wood as a structural material in tall and non-residential construction, however, is still relatively untapped. China is home to the world’s largest population and the largest construction sector worldwide, yet wood products are only used in a small fraction of buildings. The main reasons for this situation are the fire regulations and lack of guidelines for novel wood-based structural systems. This paper describes the design of a 10-storey timber-concrete business hotel which will be erected in the Guizhou province of China. The foundation design, gravity system design, lateral load resisting system design, seismic analysis and the fire resistance design were conducted, and the procedure provided appropriate information to the technological feasibility to promote the development of timber-based hybrid high-rise construction systems in China.
... For multipanel shear walls, two distinct lateral behaviors can be attained, namely coupled-panel (CP) behavior, in which each panel acts as an independent segment with an individual center of rotation, or single-wall (SW) behavior, in which the wall acts like a single segment with one global center of rotation . Experimental studies have demonstrated the high in-plane rigidity of CLT panels, and found that the individual panels may be assumed to act as rigid bodies, whereas the connections predominantly determine the lateral resistance, stiffness, and energy dissipation (e.g., Ceccotti et al. 2013;Yasumura et al. 2016;Popovski and Gavric 2016;Histovski et al. 2017;Izzi et al. 2018;Reynolds et al. 2017;Sun et al. 2018). Due to their importance, connections have been investigated to establish their behaviors and evaluate 1 Ph.D. Candidate, Dept. of Civil Engineering, Univ. of Ottawa, Ottawa, ON, Canada K1N 6N5 (corresponding author). ...
Article
The applicability of the capacity-based design approach to buildings consisting of cross-laminated timber (CLT) shear walls has lacked analytical expressions that depend on the structural type and failure mechanisms. This project developed such expressions for multipanel CLT shear walls used in multistory buildings with emphasis on including the bidirectional contribution of the angle brackets. The proposed method addresses the hierarchy of yielding among different groups of dissipative zones. New categories with dissipative and limited energy dissipative capabilities were introduced, and expressions for overstrength factors were defined. The proposed procedure was verified using numerical models, and insignificant differences were obtained between the proposed method and the numerical models. It can be concluded that when the proposed conditions are met, the desired coupled-panel behavior can be achieved and the angle brackets can be assured to remain elastic. It was shown that when the applied shear force is calculated based on the proposed methodology, it correctly coincides with the yielding of the hold-down obtained from the numerical models. Additionally, a case study was presented for a two-story building composed of multipanel CLT shear walls to demonstrate the suitability of procedure beyond a single story.
... A CLT wall has several structural advantages over a traditional light-frame wood-joisted wall, including bidirectional strength and stiffness, fire resistance, and dimensional stability (Frangi et al. 2008(Frangi et al. , 2009Klippel et al. 2014;Brandner et al. 2015;Wang et al. 2015;Sikora et al. 2016). In addition, in seismically active regions, CLT structures have shown good seismic resistance (Gavrić et al. 2012;Hristovski et al. 2013;Izzi et al. 2018;Hashemi and Quenneville 2020). Cross-laminated timber constructions also reduce carbon emissions. ...
Article
Cross-laminated timber is a wood product with excellent fire resistance and mechanical performance that is often used in tiny houses. Using the ASTM standard E564, the shear performance of cross-laminated timber wall panels, with and without openings, were investigated in this study. The specimens were made of spruce-pine-fir IIc lumber and installed on a test platform using high-strength bolts passing through them. This connection mode limited the displacements obtained in the test, primarily the shear displacements and rocking displacements. By comparing the static load test data of the three specimens with openings and the one without an opening, it was found that openings reduced the shear strength and shear stiffness. For the same sized rectangular opening, the shear stiffness of the cross-laminated timber panel was less when the wider side was horizontal (normal to the direction of the applied force). The shear stiffness of the cross-laminated timber wall panels can be effectively improved by reinforcing the areas near the openings with metal sheets. With reinforcement, the shear strength did not change drastically, but the damage to the cross-laminated timber wall panels was significantly reduced.
... These two effects have a negative impact on the capacity design. On one hand, the low ductility limits the value of the behaviour coefficient q and on the other hand the high overstrength values [7,8,9,10] inevitably leads to high overstrength factors γ Rd . What is gained through the behaviour factor q is almost immediately lost through the over-strength factor γ Rd to be applied for the capacity design of the non-dissipative zones. ...
Article
Full-text available
A R T I C L E I N F O Keywords: Doweled connections Capacity design Displacement ductility Fully confined timber member Notch effect restraining measures Post-elastic steel properties Constriction of dowels A B S T R A C T According to Eurocode 8 moderate to high dissipative behaviour of timber structures requires sufficient ductility of the critical regions. Earlier experiments on timber connections with slotted-in steel plates and laterally loaded common steel dowels rarely achieved high ductility values. Connections consisting of LVL-C members, dowel-type fasteners with different post-elastic steel properties, full confinement of the timber member and measures to restrain the notch effect were investigated by means of monotonic and cyclic tests with regards to the displacement ductility. The measures taken proved to be effective in enhancing the plastic deformation capacity of the steel dowels to a large extent. However, a new aspect was observed: the constriction of the dowels in the contact area with the plate. The research results provided a better understanding of the factors influencing the behaviour of slotted-in steel plate connection.
... Timber structure is a sustainable and prefabricated structure with mechanical advantages such as light weight and good seismic behavior (Izzi et al., 2018;Van de Lindt et al., 2011a, 2011b, and with ecological advantages such as low carbon dioxide emission and low energy consumption (Green and Karsh, 2012;Gustavsson and Sathre, 2006;Gustavsson et al., 2010). Nonetheless, the low elastic modulus and large mechanical diversity of the timber material inhibit its application to large-span structures. ...
Article
Full-text available
The lateral torsional buckling (LTB) of steel-timber composite (STC) beam with partial interaction was investigated in this paper. The composite beam is constructed by connecting the timber to both flanges of the H-shaped steel with bolts or screws. Twelve push-out specimens were designed to evaluate the shear performance of bolt or screw connectors. It was shown that the slip stiffness and the shear bearing capacity of the connectors increased with the thickness of timber increasing. Then, eight full-scale composite beams with lengths of 6000 mm were studied through bending tests and compared to a bare steel beam. The experimental behaviors of the specimens were identified, including the failure mode, load-deflection relationship and load-strain response. The LTB phenomenon and composite action were discussed by analyzing the strain distribution, stiffness and strength. The results demonstrated that the STC beams fastened with bolts or screws displayed partial composite action. Although the stiffness of the composite beam showed little augmentation, the maximum strength of the composite beam substantially increased by suppressing the LTB phenomenon. A finite element analysis was conducted to reveal the failure mechanism of the specimens with different geometric and physical parameters, including the number of timber layers, the interface shear stiffness and the initial imperfection. It was found that increasing the number of timber layers in the upper flange suppressed the lateral torsional buckling, and the interface shear stiffness was the key factor to control the stiffness and failure modes of STC beams.
... Since the in-plane shear test cannot be conducted without including the effect of steel connections [21], an alternative method for testing CLT panels under in-plane loads to assess their strength and stiffness could be done by performing a component diagonal compression test. By using this test configuration, the in-plane loads can be induced in the CLT walls without the need for base-to-wall connections. ...
Article
The high in-plane shear strengths of cross-laminated timber (CLT) make it a good candidate for use as shear walls in buildings in areas of high seismicity such as Japan. One important aspect of CLT walls, and one that is presently poorly understood, is the influence of openings on the in-plane shear carrying capacity. The main purpose of this paper is to experimentally evaluate the effect of openings on the in-plane strength and stiffness of CLT panels with openings. In this study, 24 CLT panels were tested using a diagonal compression test configuration. In particular, they were three identical replicates of eight CLT panels. One of these eight panels was a solid panel, while the other seven panels had openings with different sizes and aspect ratios. The results showed that the panels with openings with the same area but different aspect ratios had different failure directions and reduction factors for panel shear strength and stiffness. Panels with rectangular openings with different orientations relative to the panel’s major and minor shear direction had different failure direction and reduction factors. In addition, the effect of openings on the reduction of initial stiffness for CLT panels was found to be greater than their effect on the reduction of shear strength. This paper's findings will help clarify the reduction in strength and stiffness of CLT panels with openings, which is an important aspect of the seismic design of buildings.
Article
Cross Laminated Timber (CLT) is an engineered wood product for the construction industry offering multiple structural, environmental and supply chain benefits. CLT can be used for an entire building, as both the lateral and vertical load resisting system, or for select elements such as the roof, floors or walls. CLT products were developed in the early 1990’s and have been widely adopted throughout Europe, and more recently, in Canada. However, use of CLT products is still relatively rare in the US. We present the results of a nationwide phone survey in the US conducted with architects and structural engineers to gauge their awareness, rate of adoption and assimilation of CLT products. Although adoption of CLT amongst architects and structural engineers is still at a nascent level within the construction sector, awareness is high, with 100% of our sample respondents cognizant of CLT. Architects and structural engineers perceive relative advantages of using CLT as well as compatibility with traditional construction. However, the adoption process is impeded by issues associated with complexity, trialability and observability. Key barriers to adoption of CLT as perceived by these two stakeholders are lack of experience from construction stakeholders, lack of training and tools for construction management stakeholders, lack of client requests and CLT inventory.
Article
The interest in multi-storey CLT buildings in seismic areas is leading to the development of new strategies to increase the lateral stiffness of shear walls and to resist high tensile forces due to rocking. Both these purposes can be achieved with vertical steel ties placed at each shear-wall end, to transfer directly tensile forces from each storey to foundation. Three technologies are proposed for transferring forces from the CLT panels to the ties: the use of nailed plates, of screwed connectors, or directly by contact with a thick plate at the top of each storey wall. The dynamic behaviour of CLT shear walls, representing the bracing system of a building, anchored with the aforementioned technologies has been investigated by means of dynamic analyses and a comparison with the use of common nailed plates or screwed connections without ties is presented. Results, varying the number of storeys and the seismic mass, show that the proposed technology is an effective strategy to increase the feasibility of multi-storey CLT buildings. Complementary non-linear static analyses have been performed to evaluate the actual displacement capacity and ductility of the systems.
Article
A strain-based criterion is presented in this paper to investigate mixed-mode I/II fracture behavior in orthotropic materials. The maximum principal strain component, in the vicinity of a crack existing in an orthotropic medium, is formulated considering the T-stress effect as well as the singular terms. The criterion predicts the onset of mixed-mode I/II fracture when the maximum principal strain reaches its critical value. The role of T-stress, calculated for an orthotropic domain, in the mixed-mode I/II fracture toughness assessment is explored theoretically. Along with other criteria, the accuracy of the proposed criterion is evaluated by predicting the fracture test data in the literature for wood species and laminated composites. The developed criterion is shown to be superior to other criteria in predicting the onset of mixed-mode I/II fracture in orthotropic materials.
Article
An investigation of the mechanical behaviour of CLT shearwalls, where either door or window openings are cut out of the panel, is undertaken. The main aim of the study is to investigate failure modes related to either mechanical anchor or CLT panel, based on the geometrical dimensions and mechanical properties of shearwall. The results of six full-scale monolithic CLT shearwalls with window or door openings are presented and discussed. The results obtained from the full-scale shearwall tests are used to validate a proposed numerical model, where input parameters, such as the mechanical properties of the CLT panels and mechanical anchors, are obtained from component level tests on beams and connections in isolation. The study shows that differently from single-panel shearwalls with no openings, brittle failure in the CLT panels is a possible mode of failure, which needs to be considered in design. The failure mode in the CLT panels is observed to occur either in bending or net shear in the lintel beams. The proposed numerical procedure is found capable of estimating the maximum load with reasonable accuracy, and the model predictions of the failure mode, number of centre of rotations, and the overall deformation of the CLT panel are accurate for all the studied specimens.
Chapter
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Determination of structural resistance to seismic loads is a complex problem. To overcome the complexity, simple but efficient methods have been developed for engineers. In that process for the sake of simplicity and practicality, certain assumptions are made in defining seismic demand. One of the them is energy dissipation by structural members during seismic actions. However, energy dissipation is directly related to damage occurrence and propagation in the member. Calculation of plastic energy to be dissipated by structural member requires definition of energy demand on the structural system. This study aims to assess plastic energy spectrum approach on frame type reinforced concrete structures. Plastic energy demand values on three frame systems representing low- to mid-rise buildings are obtained from plastic energy spectrum and also nonlinear time history analysis (NLTH). Plastic energy spectrum is taken from the previous study of the authors. Comprehensive NLTH analyses on selected frame systems are conducted on the pre-designed systems which consists of concentrated plastic hinges. Moment and rotation response time histories of the structural members are used in calculation of energy dissipation. Comparisons between spectra- and NLTH-based results are made on three systems. For low-rise system, both plastic energy dissipation values are found approximate whereas for mid-rise systems, plastic energy spectrum is found conservative. The numerical examples reveal that plastic energy spectrum is a robust concept for energy-based design methodologies.
Article
Cross-laminated timber (CLT) modular construction possesses the advantages of wood, such as excellent carbon storage and thermal insulation, and of modular construction, such as considerably reduced construction period and cost as well as high productivity. This study evaluates the hygrothermal performance of CLT walls considering modular construction in future climatic conditions. Firstly, CLT walls with plywood applied to a core layer were manufactured. A mock-up of a CLT building was produced and its construction process was analyzed. Hygrothermal behavior of the CLT walls was simulated using WUFI simulation program, and the predicted results were verified against measurements obtained from the mock-up experiment. Finally, the hygrothermal performance of the CLT wall was evaluated for four types of insulation and future climate in eight cities of USA. The coefficient of variation—root mean square error (CV(RMSE))—of the temperature and relative humidity inside the ply-lam CLT wall from mock-up experiments and simulation evaluation were 6.43% and 7.02%, respectively, which met the validation criteria. Based on the hygrothermal performance, the ply-lam CLT wall with extruded polystyrene insulation was evaluated as safe from moisture problems in all the eight cities considered in this study. However, the risk of mold growth in all regions and insulation types increased under climate change with a rise of average annual temperature.
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The comprehensive experimental study examining the general load–displacement behavior, stress distributions and shear stress–shear-displacement behaviors in the connection area when wood structural elements are combined with adhesive or adhesive with mechanical anchorages have been found in very limited number of studies in the literature. Therefore, an experimental study was planned. In this study, the general load–displacement behavior of the timber connection regions which are connected by adhesive and mechanical anchorages together with adhesive, with varying lengths of 180, 240 and 350 mm are investigated experimentally. Besides, the effect of changing the number and location of mechanical anchorages used in the connection area on the general load–displacement behavior and shear stress–shear-displacement behavior was also investigated. Using the load–displacement graphs obtained as a result of the experimental study, a generalized material model is proposed for the shear stress–shear-displacement interfacial adhesion surface for wood–wood junction points. This material model, which is proposed for wood–wood connection points with mechanical anchors, is a model that can be useful and can be used in the analysis of structural systems containing such connections using finite element software. It is thought that the overall capacity and load–displacement behavior of structural systems containing such connection points can be calculated more realistically using the proposed interfacial material model.
Article
Rolling shear is one of the major concerns that significantly impact the performance of CLT walls if they are subjected to combined out-of-plane bending and compression loads. Because the effects of rolling shear and out-of-plane bending are coupled to each other, prediction of the load-carrying capacity of CLT wall is always a challenge for the design of CLT structures. Current design codes employ an Ayrton-Perry type interaction equation as the failure criterion to check the safety of a CLT panel loaded with combined bending and compression. Nevertheless, there is no model available to predict their load-carrying capacity. The presented work aims at developing an analytical model to predict the load-carrying capacity of CLT wall loaded with combined out-of-plane bending and compression. In total 12 five-layer CLT panels loaded with different initial load eccentricities were tested to investigate the failure modes. Observed during the test were two ultimate failure modes, i.e., compression crush on the concave side and tension rupture in convex side. Based on these failure modes and deeming the test member as a beam-column, an analytical model which takes rolling shear effects into account to predict the load-carry capacity of CLT compression-bending members was developed. An explicit formula based on compression failure mode was proposed. The model is capable of determining the distribution of rolling shear stress along longitudinal direction, rolling shear-induced axial force and moments in CLT beam-columns. By calculating the load-carrying capacities of the specimens tested in this study as well as the additional three- and seven-layer specimens tested by another studies, it was found that the compression failure mode-based formula can provide good agreements with the test results.
Article
Timber-concrete composite (TCC) connections are crucial elements for transferring loads and dissipating energy for a timber-concrete hybrid system under seismic load. This work investigates the mechanical characteristic of TCC bolted connections and simulates the hysteretic behavior using the simplified models. Specifically, a total of 12 TCC bolted connections were tested subjected to cyclic loading. The variables of bolt diameter, timber thickness and steel pad are investigated. The tested results showed that the connections without steel pads failed with one hinge, whereas those with steel pads failed with two hinges. The steel pad can effectively improve the load-carrying capacity and energy-dissipating capacity. The tested hysteretic curves exhibited strength and stiffness degradation, as well as pinching effect. According to the tested data, the simplified models assigned to two different hysteretic models of Saws and Pinching4 are analyzed and compared. The simulated hysteretic curves from both the Saws and Pinching4 models are consistent with the tested data. The obtained model associated with calibrated parameters is quite useful when such TCC connections are embedded into the analysis of the whole structure.
Article
Composite timber-concrete connections transfer shear forces between the timber component and the concrete through bolts, which improves the effectiveness of the composite action. This paper investigates the influencing factors of timber-concrete connections under shear tests on the loading-carrying capacity, with a specific focus on the effect of steel pads. A series of connections considering the variables of bolt diameters, glulam timber thickness, and the presence or lack of steel pads was tested under monotonic loading. The failure modes of different components are presented and discussed. The mechanical properties extracted from the tested force–displacement curves, including the initial stiffness, yield force, and maximum load-carrying capacity, are analysed and compared. An analytical model considering the effect of steel pads is derived based on the yield theory. The predicted load-carrying capacity of connections using the deriving formulas is consistent with the tested results, which demonstrates that the proposed method is reliable and accurate. The analysis results will provide insight into the mechanical behaviour of timber-concrete connections and guidance for the composite connection design.
Article
The paper presents a simple yet robust frame model to be used as an alternative to continuous 2D or 3D finite element models for the purpose of analyzing multi-storey cross-laminated timber (CLT) shearwalls with openings when subjected to lateral loads. The proposed model is applicable to monolithic CLT walls and takes into account the mechanical interaction between wall segments and lintel/parapet elements as well as the non-linear behaviour of the mechanical anchors, while the contribution of the vertical load is omitted. Pushover numerical analyses were conducted on the proposed equivalent frame model (EFM) and 2-D finite element model, and the results showed good agreement between the two models along the entire force-displacement curves. The failure conditions were found to be consistent in all cases, and the distribution of the internal forces were found to be reasonable. The proposed EFM was also compared with published test results on CLT shearwalls and the fit was deemed reasonable, with a slight tendency to underestimating the ultimate capacity of the shearwalls.
Article
The availability of a reliable estimate of the dispersion relation of plates is of great importance for acoustic modelling. Several experimental methods for the extraction of wavenumber and wave velocity information are discussed in the literature. They differ, among other factors, by the sensitivity to noise and multiple reflections, frequency range of application and implementation of the processing algorithm. While for homogeneous thick or thin plates well-established analytical solutions are available, non homogeneous materials would benefit from experimental characterisation. In this framework, our attention is focused on cross-laminated timber (CLT) elements, load-bearing orthotropic layered wood plates that revolutionised the sector of timber construction. The anisotropic and non homogeneous nature of wood suggested testing methods that, though converging for homogeneous materials, could bring different results in their application to CLT elements. The aim of this paper is therefore to benchmark methods for the extraction of wavenumber information on CLT plates, from which the effective elastic properties to model CLT structures as an equivalent homogeneous plate can be derived. This is achieved through a numerical and experimental benchmark of well-established methods for the evaluation of the real component of the propagating wavenumber in CLT elements. Five relevant methods were selected through a literature review, implemented and analyzed: three in the time domain, namely maximum peak, cross-correlation and kurtosis, and two in the frequency domain: phase difference and wave correlation. First, the five methods were benchmarked by numerical simulation on a homogeneous material. In this ideal case, results showed to be consistent for all methods. Then, wavenumber measurements were performed on a cross-laminated timber plate. The results show that the maximum peak, cross-correlation and the wave correlation method provide the lowest dispersion of the data. Considering the time required by the installation of the setup, the wave correlation method seems to be the best alternative among the proposed ones.
Conference Paper
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In this paper, a new capacity design approach for designing X-Lam structures was presented. Based on the results of an extended experimental test program on typical X-Lam connections, X-Lam wall panels and full-scale X-Lam buildings, analytical and numerical studies were performed and behaviour properties of X-Lam structures subjected to horizontal loads were determined. Different classifications of the global behaviour of X-Lam wall systems were introduced. Typical failure mechanisms of connections and wall systems used in X-Lam system were presented and provisions for a proper X-Lam seismic design were given. Also, the influences of different types of X-Lam walls behaviour on mechanical properties and energy dissipation of the X-Lam wall systems were introduced and critically discussed. The axial stiffness and resistance of angle brackets are important and should not be neglected in the equilibrium of the wall under lateral forces. Rocking behaviour of wall systems should precede sliding behaviour to achieve higher ductility, energy dissipation capacity and easier repair after seismic events. Special attention should be given to the design of vertical joints between adjacent wall panels, as the global behaviour of wall panels can change dramatically and, consequently, the wall performance in terms of mechanical properties, energy dissipation capacity and displacement capacity can significantly differ. Overstrength values and capacity design principles were investigated and proposed. For metal connectors an overstrength factor 1.3 proved to be sufficient for both directions (tension and shear). For screwed connections, the scatter of strength was higher, thus also the overstrength factors resulted in higher values (1.6). Both, overstrength factors and capacity-based design principles, could be implemented in the new generation of the Section 8 (Timber structures) of Eurocode 8 as currently there is no value suggested for the overstrength factors for timber structures, although the need for capacity based design is clearly stated.
Article
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Cross-laminated timber (CLT) wall systems are composed of massive timber panels that are fastened together and to the horizontal elements (foundations or intermediate floors) with step joints and mechanical connections. Due to the high in-plane stiffness of CLT, the shear response of such systems depends strongly on the connections used. This paper proposes a numerical model capable of predicting the mechanical behavior and failure mechanisms of CLT wall systems. The wall and the element to which it is anchored are simulated using three-dimensional (3D) solid bodies, while the connections are modeled as nonlinear hysteretic springs. Typical racking tests of wall systems are reproduced by varying the assumptions used to schematize the behavior of the connections. Results are compared with test data published in the literature, and the differences are discussed. The influence of the boundary conditions (vertical load applied on top of the wall and friction at its base) and aspect ratio of the panel are investigated via a parametric numerical study. Finally, the performance of a wall system assembled with two CLT panels is analyzed, highlighting how the properties of the anchoring connections and vertical step joints affect the load-displacement response and energy dissipation.
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Cross-laminated timber has recently gained great popularity in earthquake-prone areas for construction of residential, administrative, and other types of buildings. At the Laboratory of the Institute of Earthquake Engineering and Engineering Seismology in Skopje, comparative full-scale shaking-table tests of cross-laminated timber panel systems have been carried out as a part of the full research program on the seismic behavior of these types of wooden systems, realized by Institute of Earthquake Engineering and Engineering Seismology, Skopje, and the Faculty of Civil and Geodetic Engineering (UL FCG), University of Ljubljana. Two different specimens built of cross-laminated timber panels have been tested: specimen containing a pair of single-unit principal wall elements (Specimen 1) and specimen containing a pair of two-unit principal wall elements (Specimen 2). In this article, the results from the shaking-table tests obtained for Specimen 2 and numerically verified by using appropriate finite element method–based computational model are discussed. Reference is also made to the comparative analysis of the test results obtained for both specimens. One of the most important aspects of the research has been the estimation of the seismic energy-dissipation ability of Specimen 1 and 2, via calculation of the equivalent viscous damping using the performed experimental tests. It is generally concluded that Specimen 2 exhibits a similar rocking behavior as Specimen 1, with similar energy-dissipation ability. Both specimens have manifested slightly different dynamic properties, mostly because Specimen 2 has been designed with one anchor more compared to Specimen 1. Forced vibration tests have been used for identification of the effective stiffness on the contacts for Specimen 2. This research is expected to be a contribution toward clarification of the behavior and practical design of cross-laminated timber panel systems subjected to earthquake loading.
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Cross-laminated timber shear wall systems are used as a lateral load resisting system in multistory timber buildings. Walls at each level typically bear directly on the floor panels below and are connected by nailed steel brackets. Design guidance for the lateral-load resistance of such systems is not well established and design approaches vary among practitioners. Two cross-laminated two-story timber shear wall systems are tested under vertical and lateral load, along with pullout tests on individual steel connectors. Comprehensive kinematic behavior is obtained from a combination of discrete transducers and continuous field displacements along the base of the walls, obtained by digital image correlation, giving a measure of the length of wall in contact with the floor below. Existing design approaches are evaluated. A new offset-yield criterion based on acceptable permanent deformations is proposed. A lower bound plastic distribution of stresses, reflecting yielding of all connectors in tension and cross-grain crushing of the floor panel, is found to most accurately reflect the observed behavior.
Article
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This paper presents an evaluation of overstrength based on an experimental study on dowelled connections in Cross Laminated Timber (CLT). Connection overstrength needs to be well understood in order to ensure that ductile system behaviour and energy dissipation can be achieved under seismic loading. Overstrength is defined as the difference between the code-based strength, using characteristic material strengths, and the 95th percentile of the true strength distribution. Many aspects contribute to total connection overstrength, which makes its definition challenging. In this study, half-hole embedment tests were performed on CLT to establish embedment strength properties and three point bending tests were performed to determine the fastener yield moment. Different connection layouts, making use of mild steel dowels and an internal steel plate, were tested under monotonic and cyclic loading to evaluate theoretically determined overstrength values and study the influence of cyclic loading on overstrength. Experimental results were compared with strength predictions from code provisions and analytical models for ductile response under monotonic loading. It was found that cyclic loading does not significantly influence overstrength for connections that respond in a mixed-mode ductile way indicating that in future more expedient monotonic test campaigns could be used. This work also provides further experimental data and theoretical considerations necessary for the estimation of a generally applicable overstrength factor for dowelled CLT connections.
Article
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The effects of irregularity in elevation of cross-laminated timber buildings have not been fully analysed in literature to provide useful information for the design. In this work, a number of building configurations, regular or irregular in elevation, characterized by a different arrangement per storey of the floor–wall joints have been analysed by means of non-linear dynamic analyses. Comparative results in terms of ratio between the behaviour q-factor of the investigated irregular configurations and that of reference regular ones, show that less dissipative capacity can be expected if the building is irregular due to a disequilibrium among storeys between the actual and the required strength provided by the floor–wall joints. A correlation method to estimate the behaviour q-factor for perfectly regular cross-laminated timber buildings is here presented and extended to in-elevation irregular ones. A new empirical formulation to assess the reliable corrective factor accounting for the irregularity in elevation of cross-laminated timber buildings, according to Eurocode 8 provisions, is also proposed. A final discussion about the implications of in-elevation irregularity on the building design is reported.
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Frame - shear wall buildings are common for high rise multi-storied RC buildings. When these walls are situated in advantageous positions in a building, they perform as an efficient lateral-force resisting system, and also fulfilling other functional requirements. In conventional analysis, shear wall is modeled as wide column, which does not always provide the realistic behavior of a shear wall. In this present work, buildings have been modeled and designed, and a detailed analysis is carried out on structural walls. The building frame and length of shear wall design has been carried out by Unified Performance Based Design (UPBD) with takes both elastic and plastic rotation into consideration along with performance level. In this study shear walls are modeled as multi layered shell element which is an advanced addition in SAP2000 software. A few challenges in interpreting the performances of shear wall as per UPBD method were faced while using shell element. Non-linear analysis with shell element is carried out and attempts to interpret its performance in terms of stresses in different layers and hinge rotation have been carried out.
Article
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The seismic response of cross-laminated timber buildings is analysed with the aim of assessing the correlation between the dissipative capacity (i.e., q-factor) and the assembling methodologies and geometrical properties. A parametric study was performed by means of incremental dynamic analyses on various building configurations with varying constructive features such as density of panel-to-panel joints and building slenderness. The results are firstly used to define parameters representative of the building geometry and assembling methodology and then to develop an analytical relationship to compute their most suitable q-factor starting from such parameters. The proposed method is finally validated referring to significant case studies available in literature.
Conference Paper
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This paper presents the results of experimental studies on the behaviour of CLT walls under cyclic loading carried out at the University of Kassel and TU Graz with focus on the influence of different configurations of anchorage and connection. Results of a case study – performed to identify realistic loading conditions of wall elements for testing – are presented first. A brief introduction on data processing is given to evaluate parameters like ductility and hysteretic damping. The influence of vertical load, support conditions and loading protocol is also discussed.
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This paper describes the main outcomes of a shake table test on a full-scale light-timber framed building carried out within the framework of the SERIES project at National Laboratory of Civil Engineering (Lisbon, Portugal) in coordination with the University of Trento (Trento, Italy). The specimen was a single family house with a 7 × 5 m2 footprint and a maximum height of 7.65 m. The walls were sheathed only with gypsum-fibre boards (GFB). The seismic tests were performed by scaling a natural earthquake from 0.07 g up to 0.66 g in two different stages. In the first stage, the building was characterized by its design geometry, whereas in the latter stage, the sheathing panels of five external walls at ground level were removed in order to reduce the racking capacity of the building. Precious and interesting data were found from the experimental results to investigate the seismic capacity of light-frame buildings sheathed with GFB. A comparison between the un-weakened and weakened specimen was also performed.
Article
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Cross laminated timber (CLT) has become a well-known engineered timber product of global interest. The orthogonal, laminar structure allows its application as a full-size wall and floor element as well as a linear timber member, able to bear loads in- and out-of-plane. This article provides a state-of-the-art report on some selected topics related to CLT, in particular production and technology, characteristic material properties, design and connections. Making use of general information concerning the product’s development and global market, the state of knowledge is briefly outlined, including the newest findings and related references for background information. In view of ongoing global activities, a significant rise in production volume within the next decade is expected. Prerequisites for the establishment of a solid timber construction system using CLT are (1) standards comprising the product, testing and design, (2) harmonized load-bearing models for calculating CLT properties based on the properties of the base material board, enabling relatively fast use of local timber species and qualities, and (3) the development of CLT adequate connection systems for economic assembling and an increasing degree of utilization regarding the load-bearing potential of CLT elements in the joints. The establishment of a worldwide harmonized package of standards is recommended as this would broaden the fields of application for timber engineering and strengthen CLT in competition with solid-mineral based building materials.
Article
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This paper presents a new alternative energy dissipation solution to be used with cross-laminated timber (CLT) self-centering walls. CLT is a relatively new building product in North America and could potentially be used for high-rise construction. The development of high-performance seismic design solutions is necessary to encourage innovative structures and the design of these structures to new heights. The objective of this paper is to propose a wall-to-floor connection system that is easy to install and replace (structural fuse) after the occurrence of a large damaging event. The proposed energy dissipators are fabricated following concepts used in developing steel buckling restrained steel braces (BRB), having a milled portion, which is designed to yield and is enclosed within a grouted steel pipe. The connection system is investigated experimentally through a test sequence of displacement-controlled cycles based on a modified version of the test method developed by the American Concrete Institute (ACI) to facilitate development of special precast systems (ACI T1.1-01 Acceptance Criteria for Moment Frames Based on Structural Testing). Digital Image Correlation (DIC) was used to analyze strain behavior of the milled portion, as well as track movement of the panels during quasi-static uniaxial and cyclic testing. The results show the yield behavior and energy dissipation properties of the connection system. Damage was focused primarily in the energy dissipators, with negligible deformation and damage to the CLT panels and connections.
Article
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Investigations on in-plane loaded wooden wall elements are part of a comprehensive research program performed in recent years at University of Ljubl-jana to enable better understanding of response of wooden buildings exposed to earthquake action. Recently, Division of Timber Construction of MPA University of Stuttgart joined the research program. This paper reports on some results emerging from the research cooperation. Eurocode 5 contains two methods for determination of the racking strength of cantilever-type wall diaphragms: an analytical approach and an experimental approach using the test protocol according to EN 594. Both approaches are related only to timber frame walls having sheathing plates. The test procedure according to EN 594 predefines the partially anchored wall which does not necessarily represent the actual anchorage and loading conditions in the building and does not apply for cyclic horizontal loads to simulate earthquake loadings. It is reported on experimentally obtained responses of wall elements with different build-ups exposed both to the EN 594 protocol and to cycling loading. In detail three different cases of boundary conditions that may occur in real structures and the influence of additional vertical loads is regarded.
Conference Paper
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Cross-laminated timber (CLT) as a structural system is not introduced in European or North American building codes, and there is limited information available on the seismic factors for design of such structures. The objective of the study was to derive suitable ductility-based force modification factors (R d-factors) for seismic design of CLT buildings in the National Building Code of Canada (NBCC). For that purpose, the well-known six-storey NEESWood Capstone wood-frame building was redesigned as a CLT structure. Non-linear analytical models of the building designed with different R d-factors were developed using the SAPWood program. CLT walls were modeled using the output from mechanics models developed in Matlab that were verified against CLT wall tests conducted at FPInnovations. Each of the 48 building models was subjected to a series of 22 bi-axial input earthquake motions suggested in the FEMA P-695 procedure. Results showed that an R d-factor of 2.0 is appropriate for the building studied.
Article
By means of a graphical procedure, the capacity spectrum method compares the capacity of a structure with the demands of earthquake ground motion on it. In the present version of the method, highly damped elastic spectra have been used to determine seismic demand. A more straightforward approach for the determination of seismic demand is based on the use of the inelastic strength and displacement spectra which can be obtained directly by time‐history analyses of inelastic SDOF systems, or indirectly from elastic spectra. The advantages of the two approaches (i.e. the visual representation of the capacity spectrum method and the superior physical basis of inelastic demand spectra) can be combined. In this paper, the idea of using inelastic demand spectra within the capacity spectrum method has been elaborated and is presented in an easy to use format. The approach represents the so‐called N2 method formulated in the format of the capacity spectrum method. By reversing the procedure, a direct displacement‐based design can be performed. The application of the modified capacity spectrum method is illustrated by means of two examples. Copyright © 1999 John Wiley & Sons, Ltd.
Article
This paper presents the results of the ongoing work on the revision of the provisions for the seismic design of timber buildings in Europe included within Chapter 8 of Eurocode 8. The most recent research results and technical developments regarding both wood-based materials and structural systems have been implemented into the proposed new version together with the application of the capacity design to each structural system. The main objectives are to update the few and incomplete provisions included in the current version to the current state-of-the-art and to correct some misleading rules. This manuscript represents the authors’ point of view on the basis of a scientific research background and the design common practice regarding different key aspects in the seismic design of timber structures.
Article
Nowadays, the design of CLT wall connections is based on the hypothesis that hold-down connections are subjected only to tension and angle-brackets only to shear. Nevertheless, experimental investigations on CLT walls under seismic action highlighted that hold-downs may be subjected also to significant lateral displacement, and then to a tension-shear coupled action. The aim of this work is to experimentally investigate the axial-shear interaction in typical hold-down connections. To this purpose, an extensive experimental campaign was conducted with a specific setup allowing to impose prescribed levels of lateral displacement and varying the axial displacement in a monotonic or cyclic way. The test results on 15 specimens are presented here and critically discussed in terms of load–displacement curves, strength, stiffness, energy dissipation, strength degradation and ductility. Moreover, two different approaches for the definition of the connection’s yielding limit are used, according to a tri-linear approximation of the experimental load–displacement curve. Forces and stiffnesses provided by these methods are compared with those predicted by code provisions.
Article
With the increasing demand for multi-storey timber buildings in areas with high wind loads and high seismic activity, stiff lateral load resisting systems are becoming a crucial design component. Post-tensioned Pres-Lam mass timber lift shafts and stairwell core walls not only provide a strong and very stiff lateral load resisting system, but also damage limiting response in the case of a large seismic event. This paper describes the results of experimental tests on Cross-Laminated Timber (CLT) Pres-Lam core walls tested under bi-directional quasi-static seismic loading. In the first configuration the CLT wall panels were connected in the corners with screws, while in the second configuration, steel pivotal columns were introduced at the corners and the CLT wall panels were connected to the steel columns with dissipative U-shaped Flexural Plates (UFPs). Overall the testing showed that the Pres-Lam system, when used for structural timber core walls subjected to bidirectional loading regimes, sustains nominal damage after large drift demands. By adding ductile screw-connections or steel columns with UFPs at the corners additional strength and dissipation capacity is obtained. Friction between the CLT panels improved the seismic performance of the structure, which in Serviceability Limit State (SLS) conditions led to rigid behaviour of the splices between the panels. Displacement incompatibilities between the floor diaphragm and the core walls were accommodated by locating the connections at the centre of the walls, or by pinned connections in the corner pivotal columns. Relative displacements between orthogonally running connector beams were accommodated by using flexible connections out-of-plane. Under low axial forces there was horizontal sliding of the walls at the foundation level, but this was not observed when larger post-tensioning forces were applied.
Article
Structures assembled with cross-laminated timber (CLT) panels, and designed to resist gravity and lateral loads, are being considered as viable options for low-rise to mid-rise buildings. In this paper, an analytical approach based on the minimum total potential energy principle has been developed in order to determine the mechanical behavior of 1-story multipanel CLT walls. Expressions for determination of the elastic stiffness and capacity are proposed that take into account the geometry of the panels and stiffness of hold-down and vertical joint connections. Kinematic models demonstrated in the case of relatively stiff hold-down connections that each panel has an absolute center of rotation, whereas for relatively flexible hold-down connections panels can exhibit progressively increasing uplift. An analytical expression to evaluate the elastic strength of an entire wall is presented for different kinematic cases. Results are verified by comparing them with predictions made using detailed numerical models.
Article
This paper focuses on the point-to-point X-RAD connection system for the construction of cross laminated timber buildings in earthquake prone areas. Tests on X-RAD connectors subjected to "shear-tension" and "shear-compression" loading configurations are presented as supplement to the experimental data provided in previously published research. Tests aimed at characterizing the behavior of timber walls assembled with the system and loaded by lateral force are also reported. A capacity domain that allows for quick safety checks for any given load combination on the connector was derived from the experimental outcomes and is presented herein. An extremely simplified, yet effective numerical approach (the connector behavior is reproduced by 3-link elements) is proposed and compared with the experimental evidence. The 3-link model was able to reproduce with sufficient accuracy both, the elastic and post-elastic response of the walls. In the discussion section, particular attention is given to the system capability of dissipating energy and exhibiting ductile behavior.
Article
The paper presents a new connection system for cross-laminated timber (CLT) structures, named X-RAD. This innovative connection system is characterised by the use of a single connector type that is positioned at the corners of the CLT panels. X-RAD is formed by a metal part surrounding a hardwood insert that is fixed to the panels by means of all-threaded screws introduced with double inclination. The peculiar geometry of the connector and the combination of different materials allow the full exploitation of the capacity of the CLT panels while ensuring a ductile response of the connection. Construction modularity, fast assembly/disassembly speed and prefabrication are some of the aspects that can be associated with X-RAD development. The outcomes of an extensive testing campaign on the new connector are also presented in the paper.
Article
This paper reports on a shaking table test conducted on a timber-framed building sheathed with oriented strand board within the framework of the European Series project at the National Laboratory of Civil Engineering in Lisbon, Portugal. The test structure was a full-scale, three-storey, 7m×5m plan building. The aim of the tests was to assess the integrity of the structural members and the non-structural components during a seismic event. The structural design was carried out in accordance with European standards. The input signals comprised ‘accelerograms’, which were scaled versions of those recorded during the Montenegro (1979) and Tohoku (2011) earthquakes. The outcome of the tests showed excellent seismic behaviour, as demonstrated by the fact that the structure frequency did not change until the last step of the procedure. Moreover, after 17 simulations, no visible damage was detected.
Article
In this paper, a non-linear procedure for the seismic design of metal connections in cross-laminated timber (CLT) walls subjected to bending and axial force is presented. Timber is conservatively modelled as an elasto-brittle material, whereas metal connections (hold-downs and angle brackets) are modelled with an elasto-plastic behavior. The reaction force in each connection is iteratively calculated by varying the position of the neutral axis at the base of the wall using a simple algorithm that was implemented first in a purposely developed spreadsheet, and then into a purposely developed software. This method is based on the evaluation of five different failure mechanisms at ultimate limit state, starting from the fully tensioned wall to the fully compressed one, similarly to reinforced concrete (RC) section design. By setting the mechanical properties of timber and metal connections and the geometry of the CLT panel, the algorithm calculates, for every axial load value, the ultimate resisting moment of the entire wall and the position of the neutral axis. The procedure mainly applies to platform-type structures with hold-downs and angle brackets connections at the base of the wall and rocking mechanism as the prevalent way of dissipation. This method allows the designer to have information on the rocking capacity of the system and on the failure mechanism for a given distribution of external loads. The proposed method was validated on the results of FE analyses using SAP2000 and ABAQUS showing acceptable accuracy.