Sigurdur Ormarsson

• Professor at Linnaeus University

This study addresses the instability of wooden trusses assembled with punched metal plates. The instability of compressed wooden elements is a complex problem due to the specific boundary conditions, the timber orthotropy, and the difficult quantification of the defects. This research presents an analytical framework based on the Eurocode approach...

Prefabricated timber modules are being increasingly used in the load-bearing structure of entire residential buildings reaching heights up to six stories. The development is driven by the demand of high-quality housing that remains affordable while fulfilling tough environmental requirements imposed on modern construction. To enable further develop...

This chapter aims at highlighting the benefit of numerical methods and their broad application in the field of wood, engineered wood-based products (EWPs), structural elements including glued-laminated and cross-laminated timber, and engineered timber structures. It focuses on the hygro-thermo-viscoelastic material behavior of these elements and st...

Light-frame timber shear walls have been used as load-bearing elements in buildings for several decades. To predict the performance of such structural elements under loading, numerous analytical and numerical models have been developed. However, little focus has been on the prediction of the plastic damage behaviour and unloading of the walls. In t...

Laminated veneer products (LVPs) are veneers glued together into a predetermined shape. Experimental and numerical investigations were performed under lamination and simultaneously bending of veneer laminate to study the stress distribution in the laminate. Laminates of different thicknesses were made of peeled veneers of European beech. The veneer...

In recent decades, there is a trend in Scandinavian countries to build multi-storey residential houses using prefabricated timber modules. It is a highly efficient construction process with less environmental impact and less material waste. A significant building element in the timber modules is the light-frame timber wall, which has to be carefull...

A three-dimensional numerical model was employed in simulating nonlinear transient moisture flow in wood and the wood’s hygro-mechanical and visco-elastic behaviour under such conditions. The model was developed using the finite element software Abaqus FEA ® , while taking account of the fibre orientation of the wood. The purpose of the study was t...

This paper introduces, with the development of user-subroutines in the finite-element software Abaqus FEA®, a new practical analysis tool to simulate transient nonlinear moisture transport in wood. The tool is used to revisit the calibration of moisture simulations prior to the simulation of mechanical behaviour in bending subjected to climate chan...

In timber exposed to moisture variations such as in wood drying, shape distortions are often a serious problem since it can make the wood products obtained unsuitable for construction purposes. Two characteristics of wood are that its behaviour is strongly orthotropic and that it is very sensitive to variation in moisture. In addition, wood is char...

According to the harmonized European design code for timber structures, Eurocode 5, all pitched timber trusses are designed as an in-plane structure, meaning that the bracing systems used are assumed to prevent the out-of-plane failure of the truss if sufficient strength and stiffness are provided. The present paper studies how the stiffness of a w...

Building with prefabricated light-frame volume modules is a prevalent and innovative construction method for low and mid-rise timber buildings. Compared to traditionally site-built constructions this method is very advantageous due to its high prefabrication level and the fast on-site assembly of the modules. The focus of this project is to study a...

Timber boards manufactured with a traditional sawing pattern often contain both heartwood and sapwood. In such boards, internal constraints can occur during drying because of a radial variation in green-state (GS) MC between the heartwood (30-60%) and sapwood region (120-200%). Despite such knowledge, the initial MC is seldom considered when evalua...

This study was conducted to increase the knowledge of moisture-related distortion and damage in the field of wood-based lightweight panels. By increasing the possibilities of predicting moisture-related distortion and damage, the possibilities of using lightweight wood materials could increase. The study was performed through experiments and modell...

Wood is a hygroscopic and moisture-sensitive material that seeks to achieve equilibrium moisture content (EMC) with its surrounding environment. For softwood timber structures exposed to variations in climate throughout their service life, this behaviour results in variable moisture-content gradients that cause moisture-induced stresses in the dire...

The impact of cold temperatures on the shear strength of Scots pine (Pinus sylvestris) joints glued with seven commercially available adhesives was studied in this work. The cold temperatures investigated were: 20, -20, -30, -40, and -50 °C. Generally, within the temperature test range, the shear strength of Scots pine solid wood and wood joints we...

The design of spatial connections in load bearing timber structures with steel angle brackets has insufficient support in the existing design standards. Therefore, research has been necessary to improve this state of the art. In the current paper an experimental study on two designs of angle brackets is presented and the results from full-scale exp...

Tensile wood creep has not been measured previously in the temperature region 135°C–150°C for a range of moisture content (MC) up to fiber saturation point due to equipment and measurement challenges. Yet this is the region where the most dramatic softening effects can be observed. The aim of this study was to develop specialized equipment to measu...

As wood construction increasingly uses engineered wood products worldwide, concerns arise about the integrity of the wood and adhesives used. Bondline strength is a crucial issue for engineered wood applications, especially in cold climates. In this study, Norway spruce (Picea abies) joints (150 mm × 20 mm × 10 mm) were bonded with seven commercia...

Timber is normally dried by kiln drying, in the course of which moisture-induced stresses and fractures can occur. Cracks occur primarily in the radial direction due to tangential tensile strength (TSt) that exceeds the strength of the material. The present article reports on experiments and numerical simulations by finite element modeling (FEM) co...

There is a need of more advanced analysis for studying how the long-term behaviour of glued laminated timber structures is affected by creep and by cyclic variations in climate. A beam theory is presented able to simulate the overall hygro-mechanical and visco-elastic behaviour of (inhomogeneous) glulam structures. Two frame structures subjected to...

When solid wood dries from a green condition to a moisture content used for further processing, moisture-induced fracture and stresses can occur. The drying stresses arise because of internal deformation constraints that are strongly affected by the cross-sectional moisture gradient differential shrinkage and the inhomogeneity of the material. To o...

Wood is a hygro-mechanical, non-isotropic and inhomogeneous material concerning both modulus of elasticity (MOE) and shrinkage properties. In stress calculations associated with ordinary timber design, these matters are often not dealt with properly. The main reason for this is that stress distributions in inhomogeneous glued laminated members (glu...

Relatively few studies have been performed on the equilibrium moisture content (EMC) of wood under conditions of elevated temperature and pressure. Eight studies indicated that EMC near saturation decreased between 100 and 150 °C, whilst five studies indicated that EMC increased. The aim of this study was to identify the likely source of the disagr...

The aim of this study was to obtain tensile elastic modulus (EM) information for radiata pine (Pinus radiata D. Don) sapwood in tangential grain direction, over a temperature range of 70°C to 150°C for a wide range of moisture contents. Such information is scarce, probably because of difficulties with research equipment design and process control s...

Numerical and experimental investigations were carried out on well defined log-disc samples of Norway spruce consisting of both heartwood and sapwood, with the aim of gaining more adequate knowledge of stress and fracture generation during the drying process. Use of thin discs of a log enabled a well-controlled and simplified drying history of the...

An improved method tor calculating force distributions in moment-stiff metal dowel-type timber connections is presented, a method based on use of three-dimensional finite element simulations of timber connections subjected to moment action. The study that was carried out aimed at determining how the slip modulus varies with the angle between the di...

Moisture-induced fractures in solid timber create considerable problems for both building industries and sawmills. Cracks caused by kiln-drying of solid timber are extremely difficult to predict. This paper reports on experiments concerned with methods of reducing cracks in wood and with the cracking behaviour of Norway spruce discs. The spruce was...

It is not fully understood how much growth stresses affect the final quality of solid timber products in terms of, e.g. shape stability. It is, for example, difficult to predict the internal growth stress field within the tree stem. Growth stresses are progressively generated during the tree growth and they are highly influenced by climate, biologi...

This paper describes experiments made to find methods to reduce cracks in wood. Experiments were performed with Norway spruce by drying the wood from green moisture content down to equilibrium moisture content (EMC). The moisture related strains and crack development on solid wood discs were measured with Aramis [1] during drying at 23°C and RH of...

Numerical simulations of stress distribution within a moment stiff timber frame corner have been performed. The frame corner is a multi-dowel connection with two slotted-in steel plates. The interaction between the fasteners and the wood material is modelled as a full contact interaction based on penalty formulation. The wood material is assumed to...

• The board distortion that occurs during the sawing and the drying process causes major problems in the utilisation of sawn timber. The distortion is highly influenced by parameters such as spiral grain angle, modulus of elasticity, shrinkage, growth stresses and sawing pattern. • In this study a finite element simulation of log sawing and timber...

Lack of straightness in timber is the most frequent complaint regarding solid (and laminated) timber products worldwide. Nowadays, customers demand higher quality in the shape stability of wood products than they did earlier. The final distortion of timber boards is mostly caused by moisture-related stresses in wood (drying distortions) and growth-...

Customers demand a very a high quality of veneered furniture products with regard to surface appearance, shape stability and rigidity. To meet these requirements, it is important to improve the manufacturing process by a better understanding of the thermohydromechanical behaviour of the individual veneers. During the manufacture of strongly curved...

A nonlinear model for analysing heat and moisture flow in wood during drying below the fiber saturation point is presented. The model used considers wood at a macro level without taking the various moisture transports mechanisms at the microscopic level into account. Based on the finite-element method, a coupled system of equations resulting from t...

Matching timber quality with end-user requirements is a major research issue and lack of straightness in timber is the most frequent complaint worldwide. The final distortion of timber boards is caused mostly by moisture-related deformations and growth stresses that develop during growth of the tree, but how much the growth rate and growth stresses...

The study concerns the question of how the shape stability features of laminated columns of Norway spruce can be improved in terms of twist through optimal orientation of the individual laminates. Both experimental testing and numerical simulations were employed for evaluating twist stability. In all the columns studied, deformations were measured...

Based on material data obtained by several researchers at Forest Research in New Zealand, with respect to variations in the main material properties from pith to bark, the distortion model developed earlier for Norway spruce has been further modified for radiata pine. Numerical simulations were performed for both pine and spruce to investigate how...

An experimental study of shape stability in wooden glued boards was performed to verify certain results of particular interest obtained earlier in numerical simulations. Possibilities for achieving products of good shape stability by gluing boards together in an optimal way are discussed. Since twist is often the most serious form of distortion def...

Numerical simulations were performed to investigate how the annual ring orientation affects the shape stability of sawn timber. The influence of radial variations in the basic properties and the spiral grain is also studied. The knowledge obtained can contribute to more effective use of the raw material through allowing boards having properties tha...

Stiffness, strength and shape stability analysis of sawn timber should be based on how the material properties vary in the stem due to different growth conditions. As part of an EU study, results from investigations of the modulus of elasticity, shrinkage coefficient and spiral grain angle of spruce are presented. The variation in properties with t...

A theory for analysing the shape stability of sawn timber was implemented in a finite element program. To illustrate the types of results that can be obtained, the behaviour of a board during drying was simulated. The simulation yields information about unfavourable deformations and stresses during the drying process. To investigate factors that in...

A 3D theory for the numerical simulation of deformations and stresses in wood during moisture variation is described. The constitutive model employed assumes the total strain rate to be the sum of the elastic strain rate, the moisture-induced strain rate, the mechano-sorption strain rate and the creep strain rate. The 3D theory used for analyzing t...

A three-dimensional theory for the numerical simulation of deformations and stresses in wood during moisture variation is described. The constitutive model employed, assumes the total strain rate to be the sum of the elastic strain rate, the moisture-induced strain rate and the mechano-sorption strain rate. Wood is assumed to be an orthotropic mate...

A method for defining effective schedules for kiln drying of wood is presented. The method is designed in such a way that it proposes an optimized variation of temperature and humidity which yields the minimum total drying time, with the condition that the moisture content and the deformation not exceed specified limits after the drying and that th...

Deformation processes in wood exposed to drying and other types of environmental loading are simulated by use of the finite element method. In the material model applied, the orthotropic structure of the wood material is considered. The differences of properties in the longitudinal, radial and tangential directions for stiffness parameters as well...

The sawmills and the building industry have a serious problem with warping of timber products during drying or after drying when the products are exposed to moisture variations. The customers require better shape stability of the products today than they did earlier. The twist deformations are said to be the most serious case of distortion. To solv...

The drying quality is defined from the end-users' (building industry) viewpoint. The most significant problems related to timber quality were identified (Johansson et al. 1994; Kliger et al. 2001) and are 1) to minimise/prevent distortion of timber as a result of drying and in service conditions and 2) to achieve the target moisture content (MC) an...