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.

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. 

The properties of sheathing-to-framing joints considerably affect the load carrying capacity of a light-frame timber shear wall. A fastener with isotropic or kinematic hardening properties is modelled for the sheathing-to-framing joints with a zero-length element, with coupled properties in two perpendicular (orthogonal translational) directions to avoid the overestimation achieved with an uncoupled alternative. A single fastener experiment is performed to determine the elastic and plastic properties. For both fastener level and wall level modelling, monotonic as well as cyclic loading scheme is analysed. A concept of modelling the elasto-plastic coupled behaviour with hardening of the connector model for the fasteners is suggested. A damage response of the fastener is also studied to estimate the failure in load capacity of the connector model and decrease in the wall capacity after the maximum loading.

The use of structural timber in residential buildings has increased considerably in Sweden during the last decade. Concomitantly, there has been an emphasis on augmenting the level of prefabrication for such structures. A simultaneous need for education imparted in universities exists, and this paper contributes to this need by outlining a design example of a residential timber building with simple geometry using prefabricated volumetric elements. The serviceability limit state as well as the ultimate limit state have been defined and studied for some critical design situations. The results indicate, for example, that the degree of utilisation in the studied building system for compression perpendicular to the bottom rail in the first storey and buckling of the studs are in the same range - 91 % to 97 % - for the walls separating apartments.  

From an environmental sustainability point of view, modern construction practices increasingly favorcarbon neutral buildings including those made from timber. Prefabricated timber modules havebecome popular due to their efficient in-house production followed by systematic and rapid on-siteinstallation. Construction companies often use these lightweight modules for residential buildings upto six story when feasible. While several studies are available that simulate stiffness and strength ofshear walls, a major component of the module responsible for transferring shear load and acting asa load bearing wall for vertical loads, e.g [1] and [2] for the EC5 design principles, relatively little workhas been done to analyze the structural performance of entire modules. This is likely due to limitedtime span the construction type has been common practice, practical challenges associated withexperimental tests and numerically demanding simulations of large structures. However, there aresome exceptions, e.g [3].This study introduces the concept of “super elements”, which are developed by condensing theinternal degrees of freedom (DOF:s) of a whole timber module to specified parts of its boundary. Theaim of this study is to reduce the number of DOF:s by using substructuring so that an entire structurecan be analyzed while subjected to external loading. Substructuring is a method of dividing a wholemodel into user defined parts (super elements) and coupling these together to create a global model[4]. The internal DOF:s of the super elements are “condensed” using static condensation, and thesuper elements are then connected to the rest of the model along selected restrained DOF:s [5].Figure 1(a) shows an example of a building with timber modules, while Figure 1(b) illustrates partsof a full-size timber module. Figure 1(c) represents a super element of the module. A simple, linearFE super element is developed for analyzing a part of a whole timber structure and it is coupled tothe rest of the structure only at designated pre-selected nodes. The model is then used to analyzethe response during various load cases applied to the whole structure.

Over the last decade timber residential buildings with a prefabricated load bearing structure intimber have become increasingly common. Occasionally prefabricated timber modules up tosix stories are built and this accentuate among other issues that of large relative verticaldisplacements due to elastic and time-dependent displacements and displacements byshrinkage. In the current study vertical displacements were measured on three modules loadedvertically by a total of 151 kN over the time period of 90 hours. In average the verticaldisplacements measured by the displacement gauges of the modules were 3.17 mm includingdeformation in both a rail and an elastomer isolating block for sound and vibration isolation.