Prefabricated timber modules are increasingly used as load-bearing structures in multi-storey residential buildings. Unlike traditional applications where they serve as non-load-bearing elements within superstructures such as steel frames, these modules must now support not only their own dead weight but also imposed loads, snow loads, wind loads, and more. This means higher need of more accurate predictions of the degree of utilization for both ultimate and serviceability limit states in various structural elements. In this study, an effective structural element based 3D finite element (FE) model initially developed and experimentally validated for small prefabricated modules has been further refined. The paper aims to validate the enhanced FE model, analyze inter-modular connection slip and shear deformations under varying loads, and identify key parameters influencing racking behavior in different module types. The model is experimentally validated against two full-size modules - one designed by platform framing and the other by balloon framing - and used to simulate various load scenarios in parametric studies. The model demonstrated satisfactory prediction of the racking stiffness and strength compared to experimental results. Furthermore, simulations revealed the influence of door opening placement and differences between platform and balloon framing on the non-linear racking behaviors. Balloon framing, in particular, offers advantages for reducing shear deformations within the module. The study also investigates the structural behavior of the inter-modular connections. The observed slip deformations in these connections can significantly affect the global racking behavior of a multi module structure. For a horizontal load F = 63.7 kN, the slip deformation of the inter-modular connections become larger than the shear displacements within the test modules.

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 for predicting the instability of compressed wooden elements, considering the effect of boundary constraints representative of punched metal plates. The general aspects of this research are twofold: (i) proposing an analytical approximate expression for assessing the theoretical buckling load of compressed beams with elastic boundary constraints; (ii) deriving the buckling design curves as a function of the geometric imperfection of the structural element. The authors refer to the constraints exerted by punched metal plates, experimentally characterized to determine the response along the six degrees of freedom. The experimental results were used to generate a high-fidelity finite element (FE) model of the connection, validate it using digital image correlation, and estimate by extrapolation the stiffness properties of a selection of punched metal plates. Additionally, a secondary FE model was developed to simulate the out-of-plane deflection of structural elements with different types of punched metal plates, predict the failure load from static incremental analysis, and estimate the buckling design curves. In conclusion, the research aims to specialize the design method of compressed members according to the Eurocode, taking explicitly into account the boundary constraints representative of punched metal plates. It is found that while the theoretical instability load of beams with elastic constraints closely approximates that of the clamped condition, the instability load under imperfections resembles the pinned condition more closely. This observation leads to systematically higher imperfection coefficients for elastic constraints than pinned conditions.

In the design of multi-dowel timber connections exposed to dominant in-plane moment action under varying environmental conditions, calculation of fastener forces and their directions is not well understood and difficult to perform manually. The problem is that during progressive plasticisation of the dowel group, the dowel force direction of every individual fastener joint varies significantly as loading increases. Since plastic load-carrying capacity values according to Eurocode 5 (EC5) are also direction-dependent, it becomes problematic to find the correct force angles after plasticisation of the first dowel joints. Another disadvantage of the EC5 method is that it does not consider designs of wood connections failing in a brittle manner through cracking of the wood material. This type of failure is quite common in, for example, moment loaded mechanical timber connections. The overall objective of this work is to develop a new effective and flexible finite element model to simulate progressive joint plasticisation and possible crack propagation in mechanically jointed timber structures. The model was used to simulate bending- and moisture-related deformations, elasto-plastic fastener force distribution, and crack growth in glulam beams jointed with slotted-in steel plate connections.

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 development of this type of buildings additional research is needed despite the considerable number of studies previously performed. This study provides an extensive experimental investigation by subjecting three modules to three different load cases. In each load case, the modules were initially loaded with dead -load placed atop of the module. Thereafter the modules were laterally loaded at the top using a servo hydraulic piston in displacement control. The main aim of the study was to assess the structural behavior of these modules under combined lateral and vertical loading, and also to generate experimental data suitable for verification of finite element models. Results from the test series reveal significant variation in racking stiffness and racking strength depending on the module's design. Furthermore, in some cases more stiff and stronger mechanical inter -module connections are needed to enhance their global structural performance. Finally, the experimental results reveal that the modules are relatively ductile in their shear response when subjected to horizontal load.

This study investigates the impact of sheathing panel cracks on the structural performance of light-frame, modular-based timber buildings, focusing on the racking stiffness and strength of the individual timber walls in the modules. Previous research has investigated such walls for decades and lead to practical design methods in the harmonized European design code, Eurocode 5. Such hand calculation methods are effective for simple geometries but for walls with openings or complex forms, a correct prediction of stiffness and strength is considerably harder to achieve and load levels where cracks initiate are almost impossible to predict. The paper presents both experimental and numerical studies to investigate how significant cracking in sheathing panels affects the load-carrying capacity of various light-frame timber walls. Finite element simulations using Abaqus are conducted to model the cracking of sheathing panels with the extended finite element method. Moreover, an orthotropic elasto-plastic connector model is introduced for the nail joints. The results indicate that significant cracking of the sheathing panels influences the stiffness and the load-carrying capacity of the wall elements and that the crack initiation and propagation is strongly affected by factors such as the location of openings, the shape of the sheathing panels and the type and position of sheathing-to-framing connections. The numerical results presented align satisfactory with the experimental data particularly regarding load levels at crack initiation and propagation. Furthermore, a parametric study investigates how cracks, orthotropic connector properties and vertical constraint of bottom rails influence the racking strength of different timber walls.

Structures built with prefabricated timber modules have been recognised as an innovative construction method and have been implemented in several countries and regions. In recent years, there have been considerable research activities directed towards these types of structures. However, most of the studies have focused on modules made of steel and concrete in their load-bearing structures and only a few of them are exploring light-frame timber modules. This study focuses on the racking behaviour of light-frame timber modules through experimental and numerical investigations. Full-size tests were performed to examine the global and local structural behaviours of several test modules. A novel finite element model of the modules is also presented. It is a parameterised structural model with high flexibility concerning the generation of different module geometries, materials, fastener types and assembly methods etc. The numerical model was developed in the commercial finite element software ABAQUS, and the numerical results obtained were validated against results from experimental tests. The validation results indicate that the model is capable of achieving satisfactory accuracy in predicting both the global and local structural behaviour of light-frame timber modules. Furthermore, several parametric studies are conducted and discussed to examine how certain parameters affect the structural response of the modules.

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 hygrothermo- viscoelastic material behavior of these elements and structures as a consequence of the behavior of wood materials. After motivating the need for models of wood, different types of numerical models and their application for determination of mechanical properties and dimensional stability of wooden boards, strand- and veneer-based engineered woodbased products, including glued-laminated and crosslaminated timber, as well as of connections in EWPs are reviewed and application examples are given. Methods and application examples are furthermore provided for moisturerelated stresses and deformations in timber structures, the influence of connections on the structural response, instability of structural systems, and modeling of prefabricated frame structures, before modeling of historical structures of wood is discussed. The chapter ends with discussing bottlenecks in modeling of wood materials and timber structures, which might be a starting point for further improvements and novel modeling strategies. © Springer Nature Switzerland AG 2023.

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 this paper, a parametric Finite Element (FE) model is further developed by introducing elasto-plastic connectors to simulate the mechanical behaviour of the sheathing-to-framing connections. To verify the accuracy of the elasto-plastic model, full-size walls were tested and compared with results from simulations. The numerical results, from a few loading cycles, indicate that the model achieves reasonable accuracy in predicting both the nonlinear elastic and plastic deformations. Both experimental and simulation results demonstrate the importance of opening locations relating to the external racking force. The results also indicate that for a double-layer wall, its racking strength can be achieved by summation of the separate contribution from each layer. Furthermore, the internal layer was observed to contribute significantly less than the external layer since its nail pattern was based on the sheathing pattern of the external layer.

The present work focuses on analysis of deformation and strength behaviour of slotted-in steel plateconnections in glued laminated timber (GLT). In Eurocode 5 (EC5), the design of metal dowel-type timber joints is basedon the yield theory presented by Johansen [1]. It consists of analytical expressions to calculate the lateral load-carryingcapacity of single fastener joints that exhibit different (plastic) failure modes. When designing optimised multiple fastenerconnections that are exposed to dominating moment action, the calculation of fastener forces and their directions duringprogressive plasticization of the dowel group is difficult to perform manually. Therefore, a simple numerical model tosimulate progressive elasto-plastic force development for every individual dowel is needed. This study presents new andsimple models to analyse the bending deformations of glulam beams jointed with mechanical slotted-in steel plateconnections. The proposed models were experimentally verified using results obtained from a joint project with theMaterial Testing Institute (MPA) at University of Stuttgart.

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 veneers were coated with adhesive, inserted in a mould which had the shape of a semicircle, and finally pressed at 20 degrees C to a laminate. Two Teflon-polymer films including sensors for measurement of the contact pressure were placed on both sides of the laminate to measure the local contact pressure (contact stress) between the laminate and the mould. At the beginning of the bending process, the contact stresses were locally distributed over the laminate in a similar pattern as in a three-point bending; after the laminate was further bent, the stress distribution rearranged to be as in four-point bending. In the end of the moulding, the local contact stresses increased over the entire laminate and reached a 'peak-value' over bent area in the middle part of the mould. A finite-element model was created to study the bending process. Regarding the overall development of the contact stress variations, the experimental and the numerical results agreed.