Erik Serrano

Lund University | LU · Division of Structural Mechanics

A short stakeholder article presenting the experimental work performed under the framework of a ForestValue project InnoCrossLam. Additionally, computational modelling of wood and CLT as a powerful mean of closer investigation of CLT and its components is also presented.

Cross-laminated timber (CLT) as a prime example of an innovative product within the field of civil engineering has over the recent years attracted attention of the construction industry and engineers around the world. As a natural composite with different orientation of layers in addition to anisotropic properties of wood, CLT can be a challenging...

The paper describes some of the findings of the European project InnoCrossLam - Innovative Solutions for Cross Laminated Timber (CLT) structures. The project aims at increasing even further the competitiveness of CLT as a versatile engineered product, by increasing its predictability in demanding design situations not covered by the guidelines of t...

Experimental strength tests are performed on two series of nominally equal plate specimens of annealed soda-lime glass subjected to either ring-on-ring or ball-on-ring bending. The Weibull effective area which represents a fictitious surface area exposed to uniform tension is calculated using closed-form solutions. Finite-size weakest-link systems...

Numerical modeling is an efficient tool for experimental validation and for gaining a deeper understanding of complex material phenomena, especially when causal relationships are overlaid by material variability. Wood is such a highly orthotropic and complex material, which in engineering problems however is considered as macro-homogeneous. The aim...

The use of cross-laminated timber (CLT) in multi-story buildings is increasing due to the potential of wood to reduce green house gas emissions and the high load-bearing capacity of CLT. Compression perpendicular to the grain (CPG) in CLT is an important design aspect, especially in multi-storied platform-type CLT buildings, where CPG stress develo...

Wall-to-floor-to-wall connections are important for the performance of multi-storey, platform-type cross- laminated timber (CLT) structures. Their stiffness properties are studied by means of a numerical model, which was previously validated with experimental data from material testing and CLT connections loaded perpendicular to the grain. In this...

Theoretical investigations of Cross Laminated Timber (CLT) at in-plane shear loading conditions are presented with focus on shear failure mode III, relating to shear stresses acting in the crossing areas between orthogonally bonded laminations of different layers. Failure criteria for structural design, test configurations and material parameters a...

The density and modulus of elasticity (MOE) distribution can provide information on the effectiveness of parametric and non-parametric methods in calculating the characteristic value of MOE. In this study, we aim to determine the optimal distribution model of the actual measured data of the lumber. We also estimate the lumber’s MOE characteristic v...

Glued-in rods are important connecting and reinforcing elements in modern timber engineering used in new and existing timber structures. The complex stress distribution along the bondline between rod and wood depends on the type and properties of the adhesive and the type of load application. In this chapter, different models for the determination...

The moisture-dependency of the fracture energy for unmodified and acetylated Scots pine (Pinus sylvestris L.) and birch (Betula pendula Roth) has been investigated. Specimens were conditioned at relative humidity levels of 20, 75, and 97%, as well as dry and water-saturated. At moisture contents below 15%, the fracture energy increased with increas...

This chapter deals with the application of adhesives in timber engineering, including wood-based products. This work is aiming to describe the general subjects in wood gluing technology, which are characteristic to wood substrates. Firstly, an overview of the basic needs and prerequisites is given, followed by a brief overview of the characteristic...

In this study, static coefficients of friction for laminated veneer lumber on steel surfaces were determined experimentally. The focus was on the frictional behaviors at different pressure levels, which were studied in combination with other influencing parameters: fiber orientation, moisture content, and surface roughness. Coefficients of friction...

A study on the fracture characteristics of unmodified and chemically modified Scots pine (Pinus sylvestris) is presented. The investigated material consisted of small-dimension sawn timber originating from young logs (thinnings), aged 30–40 years. The modified samples were acetylated with acetic anhydride in an industrial scale process without the...

InnoCrossLam is a ForestValue project aimed at increasing the competitiveness of cross laminated timber (CLT) as a versatile engineered product. The project will have impact on: •new, demanding and innovative design situations in CLT structures (beams, openings, point supports, joints, moisture risks, seismic resistance) •proofs of concepts (ther...

The shear plate dowel joint (SPDJ) is a novel connection design for heavy timber structures. The connection uses a single large diameter dowel and glued-on steel plates to transfer loads between members. Consequently, the design of the dowel is of great influence for the global performance of the connection. This paper presents an experimental and...

An experimental study on the duration of load effects in a glued shear plate dowel joint was conducted. The joint design features a single large diameter dowel for load transfers between members, via external steel plates, which are bonded to the timber with a low stiffness bond line. Due to the low bond line stiffness, the timber element is subjec...

Cross laminated timber (CLT) at in-plane beam loading conditions presents a complex stress state wherefore several failure modes and geometry parameters need to be considered in design. The work presented here includes experimental investigations of CLT beams for comparison and validation of an analytical model and design proposals previously sugge...

Treated bamboo can be made into large, durable structural elements which have the potential to become a transformative large-scale building material, but the fracture behaviour which determines their ultimate strength in various loading scenarios has not been studied. Laminated bamboo is a promising structural engineered bamboo material, and is gen...

The article Experimental investigation of the axial strength of glued-in rods in cross laminated timber, written by Boris Azinović, Erik Serrano, Miha Kramar, Tomaž Pazlar, was originally published online without Open Access.

Numerical simulations and parametric studies of glued-in rods in cross-laminated timber have been performed. The simulations were based on 3D finite element analysis, using a cohesive surface model for the bond-lines between the laminations and the bond-line along the rod. The parametric studies investigated the influence of the glued-in length, th...

Cross laminated timber (CLT) at in-plane beam loading conditions presents a complex stress state wherefore several failure modes and geometry parameters need to be considered in design. The work presented here includes experimental investigations of CLT beams for comparison and validation of an analytical model and design proposals previously sugge...

Vlepljene palice predstavljajo zanimivo rešitev stikovanja nosilnih lesenih elementov, s številnimi ugodnimi lastnostmi kot so visoka nosilnost, dobra požarna odpornost, prilagodljivost z arhitekturnega vidika, idr. Kljub številnim prednostim, je uporaba vlepljenih palic v praksi relativno omejena. Uporablja se le v posebnih primerih za stikovanje...

The work presented concerns validation of a specific analytical model for Cross Laminated Timber (CLT) at in-plane beam loading conditions. The original model (model A) has previously been presented in the literature and is also suggested to be used as a basis for design equations for the next version of Eurocode 5. An improved version (model B) of...

This paper presents results from an experimental assessment of glued-in rods in cross laminated timber (CLT). For the purposes of the study more than 60 pull-pull tests were performed, where the specimens varied in terms of bonded-in length (from 80 to 400 mm), rod diameter (16 to 24 mm) and rod-to-grain angle (parallel and perpendicular). Several...

The COST Action FP1402 is a research network established under the aegis of the COST domain "Forests, their Products and Services". The aim of the Action was to overcome the gap between broadly available scientific results and the specific information needed by designers, industry, authorities and code committees, providing transfer for practical a...

Cross Laminated Timber (CLT) at in-plane beam loading conditions present a very complex stress state and many failure modes need to be considered in design. The work presented here aims at finding improvements of a specific analytical model for stress analysis and strength verification that has been suggested in literature and which is also suggest...

This report concerns element strength and stiffness of cross laminated timber (CLT) at in-plane beam loading and includes presentation of experimental investigations and a review of some analytical models for structural analysis. A total of 20 individual tests were carried out, divided into five different test series which each comprise four nomina...

Fracture propagating along the grain of timber is one of the most relevant failure mechanisms due to the wood’s low strength and its brittle failure behaviour when subjected to excessive shear and tensile stresses perpendicular to the grain. According to the current procedures, the fracture energy of wood is determined on small clear specimens. How...

The competitiveness of timber as structural material in large structures is often governed by the cost of structural joints. Tests indicate that the new joint concept presented herein using glued wood-to-steel plate joints can possibly reduce the cost by matching joint strength to member strength. The design is inspired by two previously proposed d...

This paper deals with theoretical and experimental investigations of nailed steel plate connections. For the experimental part, a total of 43 laboratory tests on connections loaded in tension parallel to the grain are reported. The paper deals also with finite element analysis of the connection, presenting a study on the 3D stress distributions wit...

Since the 80’s, Johanssen’s Yield Theory has been adapted to fit new design practices: fastening of timber elements with a layer of insulation (or gap) between the elements or fastening with inclined fasteners. However no rules exist for connections with large gaps (up to 500 mm) and inclined fasteners. The behaviour of screwed connections (timber/...

Förord Avsikten med Limträhandbok Del 2 är att hjälpa konstruktören att dimensionera limträkonstruktioner. I synnerhet betonas förståelsen av: • Bakgrunden för dimensionering av konstruktionssystem utförda med limträ, särskilt konstruktioner med lång spännvidd. • Bakgrunden för dimensionering av förband i konstruktionssystem utförda med limträ. Den...

In order to be able to realistically and consistently elucidate and subsequently simulate the load–displacement behavior of single-dowel connections, the material behavior of the individual components, namely steel dowels and wood, needs to be investigated. The behavior of slotted-in, single-dowel steel-to-laminated veneer lumber (LVL) connections...

The structural behaviour and failure mechanisms of unreinforced and reinforced notched glulam beams were studied in a test series. It could be shown that shear failure of the reinforced notched beam is an important failure mechanism and that adequate reinforcement in tension perpendicular to grain and shear is required in order to regain the load-c...

The impact of knots and grain deviations on the perpendicular to grain strength of wood was studied by computational models and test results from literature. It was found that knots in general seem to have a positive influence on the perpendicular to grain fracture strength. A strongest link model for strength analysis relating to failure due crack...

The aim of the experimental study presented herein is the assessment and quantification of the behavior of individual dowels in multi-dowel connections loaded by a bending moment. For this purpose, double-shear, steel-to-timber connections with nine steel dowels arranged in different patterns and with different dowel diameters were tested in four-p...

The mechanical properties of structural timber—particularly in terms of stiffness and strength—are subject to high variability, which also affects the properties of timber products made from structural timber, e.g., glued laminated timber (GLT). In this paper, the influence of the longitudinal stiffness variability of wooden lamellas on the effecti...

The thorough experimental characterization of a dowel-type connection under various combinations of bending moments and normal forces is presented in this study. Double-shear steel-to-timber connections with 12 and 20 mm steel dowels were tested in a 4-point bending test set-up. The load, between the connected steel and wood beams, was transferred...

The paper presents results from the experimental testing of load-bearing timber–glass composite shear walls and beams. Shear wall specimens measuring 1200 × 2400 mm² manufactured with three adhesives of varying stiffness were tested. Twelve specimens with a single 10 mm thick glass pane and one specimen with an additional insulating glass unit were...

The research and development of connecting and strengthening timber structural elements with glued-in rods (GiR) has been ongoing since the 1980s. Despite many successful applications in practice, agreement regarding design criteria has not been reached. This state-of-the-art review summarises results from both research and practical applications r...

Glued-in rods (GiR) have been successfully used for both constructing new and strengthening existing timber structures. The research and development of connecting and strengthening timber structural elements with GiR has been going on since the 1980s. However, agreement regarding design criteria for these applications has not been reached. Today, s...

Beyond its transparency, glass offers a large potential to fulfill load-bearing functions. Timber-glass composite elements take advantage of the high stiffness and strength of glass. At the same time, their post-breakage behavior increases significantly compared to the brittle failure of a pure glass. This study relates especially to timber-glass c...

Timber-glass composite I-beams were manufactured and tested in bending to failure. The glass web of the I-beam was adhesively bonded to the timber flanges using three different adhesives: Epoxy, Acrylate and Silicone. For the webs two types of 8 mm thick glass were used: annealed float and heat heat-strengthened glass. Before testing the beams with...

Finger jointing of unseasoned Norway Spruce was studied with respect to tensile strength, adhesive penetration and durability. Finger joints were manufactured with 1) unseasoned wood and one component polyurethane (PUR) adhesive, 2) dried wood and PUR adhesive and 3) dried wood and phenol resorcinol formaldehyde (PRF) adhesive. Two levels of wood d...

The results from bending tests on 107 laminated, green-glued, beams manufactured from Norway spruce side boards are presented. The beams were made by face gluing 21-25 mm thick boards using a commercial one-component moisture curing polyurethane adhesive. In addition to the bending test results, results from shape stability measurements after clima...

Models for estimation of structural properties of glued laminated timber (glulam) are generally based on the relationship between properties of the individual laminations and properties of the glulam. In this investigation, a recently presented machine strength grading method based on laser scanning of fibre direction fields was applied for determi...

Although cross-laminated timber (CLT) plates are increasingly used in high-performance building structures, a tailored composition of them or, at least, a performance-based classification scheme is not available. Especially, the influence of the quality of the ‘raw’ material (wooden boards) on the load carrying capacity of CLT elements is hardly in...

Glued-in rods are often considered as “new, innovative and highly efficient” way to connect timber elements. However, they have been used for at least 30 years. Glued-in rods represent a versatile joint system with advantages such as high load transition, appropriate behaviour in case of fire, easy application combined with a high level of prefabri...

Machine strength grading of structural timber is based upon relationships between so called indicating properties (IPs) and bending strength. However, such relationships applied on the market today are rather poor. In this paper, new IPs and a new grading method resulting in more precise strength predictions are presented. The local fibre orientati...

This study relates to the topic of anchorage of shear walls. At times, eccentric forces between the sheathing and the anchoring devices may be introduced in the sill plate. In severe cases, such forces may cause the sill plate to split and to fail in a brittle manner. In this study, fracture mechanics are applied to develop a simple closed-form han...

A study of three different adhesives, silicone, acrylate and polyurethane, intended for adhesive joints in structural timber/glass applications is presented in this paper. Intentionally, adhesives with a wide range of properties were chosen. The adhesive bonds between timber and glass were tested both in tension and in shear with a bond area of 800...

Unseasoned (green) spruce timber side boards of size 25 × 120 × 600 mm were flatwise-glued with a one-component PUR adhesive. Glued pairs of boards were then kiln-dried to 12 % moisture content. A special small-scale specimen for testing the fracture properties of the adhesive bond in Mode I was developed in order to evaluate the adhesive bond prop...

Strength grading of Norway spruce [Picea abies (L.) Karst.] side boards in the wet state was investigated. For a sample of 58 boards, density and dynamic modulus of elasticity in the axial direction (MOE dyn) were determined in the wet state. The boards were then split into two parts and the procedure of determining MOE dyn was repeated both before...

Adhesive joints have been known and applied for timber structures for decades. Hybrid joints with glued-in rods are nowadays successfully used for both constructing new and strengthening existing timber structures. Since the 1980s the research and development of timber joints with bonded-in rods have been going on, however agreement regarding desig...

The indoor climate in buildings has changed in the last decade due to more efficient climatic systems, floor heating systems and larger open floor areas with more natural light. All these factors have induced increasing ranges of relative humidity between different seasons. Also with decreasing relative humidity (in the winter 30-50% RH, in the sum...

Four different elastic models for sheathing-to-framing connections are presented and evaluated on a single connection level and on a shear wall level. Since the models are elastic in their nature they are suitable mainly for cases where the sheathing-to-framing connections are subjected to monotonically increasing displacements. Of the four models...

Wood specimens to each of which a laminate of carbon fibre reinforcement polymers (FRP) was glued (creating a lap joint in each case) were loaded to failure. A total of 15 specimens of three types differing in the glued length (anchorage length) of the FRP laminate (50, 150 and 250mm respectively) were tested, their strength, stiffness and strain d...

The work presented in this paper deals with the use of green gluing (also known as wet gluing) as a mean to overcome the difficulties in making use of side boards for structural applications. By manufacturing laminated beams from unseasoned side boards several advantages are obtained. Beams were manufactured from side boards of approximately 25 mm...

The work presented involved testing of the compression strength of square specimens made from three-layer CLT. In one of the test set-ups a uniform compression over the complete square face of the specimen was used -similar to what is defined in the current European test standard for glued-laminated timber. In addition, several other test set-ups i...