Multi-storey buildings require provisions to avoid disproportionate consequences after unexpected events, e.g. explosions or human error during design and construction. To prevent failure progression in the structure after an initial damage (loss of load-carrying elements), alternative load paths, like catenary action, should be provided. Catenary action supports the sagging structure after element loss by transferring the loads horizontally to the adjacent elements; this mechanism requires the connections to remain ductile under high load. Conventional dowel-type connectors in timber structures have limited potential to develop catenary action in beams or floors. A previously developed tube connector exhibited desirable behaviour to develop catenary action in cross-laminated timber floors; however, the tube exhibited and undesirable failure mode. In the present study, the behaviour of a newly designed variant of the tube connector was experimentally investigated under catenary action. The new connector design was tested in varying configurations, at both the component level and full-scale floor level, in Canada and Sweden. The results show that a more desirable behaviour of the adapted connector could be achieved compared to the previous design, with respect to catenary action. 

To learn the characteristics of a cross-laminated timber (CLT) panel, it is crucial to perform experimental tests. This study presents two experimental test methods to measure the in-plane shear modulus of CLT panels. This characteristic can be measured by multiple methods such as the picture frame test, the diagonal compression test, and the diaphragm shear test. In this study, the same CLT panels are tested and evaluated in the diaphragm shear test and the diagonal compression test to see if more reliable results can be achieved from the diaphragm shear test. This evaluation is done by experimental tests and finite element simulations. The theoretical pure shear simulation is used as a reference case. Finite element simulations are made for both edge glued and non-edge glued CLT panels. Nine CLT panels are tested in the diaphragm shear test and the diagonal compression test. During ideal conditions (uniform material properties and contact conditions), all three simulated methods result in an almost equal shear modulus. During the experimental testing, the diagonal compression test gives more coherent results with the expected shear modulus based on finite element simulations. Based on the diaphragm shear test results, the CLT panels behave like edge glued, but this situation is dismissed. However, during ideal conditions, the diaphragm shear test is seen as a more reliable method due to the higher proportion of shear in the measured area.

Multi-storey buildings require mitigation of consequences of unexpected or accidental events, to prevent disproportionate collapse after an initial damage. Cross-laminated timber (CLT) in platform-type construction is increasingly used for multi-storey buildings, however, the collapse behaviour and alternative load paths (ALPs) are not fully understood. A 3D non-linear component-based finite element model was developed for a platform-type CLT floor system to study the ALPs after an internal wall loss, in a pushdown analysis. The model, which accounted for connection failure, timber crushing and large displacements, was calibrated to experimental results and then adapted for boundary conditions corresponding to typical residential and office buildings. Subsequently, five parameters (floor span, connection type, vertical location of the floor, tying level, horizontal wall stiffness) were varied, to study their effects on the ALPs in 80 models. The results showed that three ALPs occurred, of which catenary action was the most dominant. Collapse resistance was mainly affected by the floor span, followed by the axial strength, stiffness and ductility of the floor-to-floor connection, the weight of the level above and the floor panel thickness. This study provides an approach to model ALPs in a platform-type CLT floor system to design disproportionate collapse resistant multi-storey CLT buildings.

Tall buildings with a high occupancy need to resist disproportionate collapse caused by unforeseen exposures, e.g. terrorism or accidents. If a damage has occurred in a building, the damage propagation can be halted if the structure is robust, i.e. it provides alternative load paths (ALPs). The ALPs of platform-type cross-laminated timber buildings have not been studied in detail on the component level. The goals of this paper are thus to elicit which ALPs may develop on single storeys in a corner bay of a platform-type cross-laminated timber building, and to study how the various building components contribute to the ALPs. For this purpose, a non-linear quasi-static pushdown analysis was conducted in a finite element model of an 8-storey building after a wall removal. Friction, fastener failure, timber failure and large displacements were accounted for. Four different ALPs were identified at various storeys and their mechanisms were described. The results could be used to improve the capacity of the ALPs and make platform-type cross-laminated timber buildings more robust in the future.

This work was focused on the experimental testing and finite element analysis (FEA) of timber beams with and without flaws (different types of cracks and hole). The aim was analysing the effect of flaws on their load-carrying capacity. This topic is important for designers of timber constructions, since even today there is still a lack of knowledge in the field of fracture mechanics of wood. The results from experimental testing and numerical simulations were discussed in this paper. Two wood products were analysed, namely, sawn and glued laminated beams (glulam beams) and three types of flaws were considered for both products i.e. a vertical crack, an oblique crack and a circular hole. In addition for glulam beams the horizontal crack in the glue line was considered. Four-point bending test was created for experimental testing considering quasi-brittle characteristic of wood. 4 samples for each type of beam, 36 in total. XFEM (Extended Finite Element Method) was used for finite element analysis of beams with considering orthotropic-elastic properties for glulam beams were considered and The results of mechanical tests and FEA gave us an overview on how different types of flaws influence the load-carrying capacity of sawn and glulam beams and with what accuracy we can simulate cracks in wood using computational method.

Multi-storey cross-laminated timber (CLT) buildings are a comparatively recent construction type. Knowledge concerning the performance of CLT buildings regarding the prevention of disproportionate collapse after unforeseeable events (e.g. accidents or acts of terrorism) is not as refined as that for concrete and steel buildings. In particular, alternative load paths (ALPs) after the removal of a wall panel in platform-framed variants have not yet been studied in detail. The goal of this work was therefore to study ALPs in CLT buildings. An eight-storey bay of an existing building was evaluated by conducting a non-linear static pushdown analysis in a finite element analysis on three representative storeys. The analyses accounted for single fastener behaviour, timber crushing, friction, brittle failure and large deformations. The force–deformation behaviours elicited under the pushdown analyses were subsequently inserted in a simplified dynamic model to evaluate the transient response of the entire bay. Four ALPs were identified in this case – shear resistance in the floor panels, arching action of the walls, catenary action in the floor panels and hanging action from the roof. The dynamic analysis did not show a collapse, unless the inter-compartment stiffness was significantly reduced. The resistance mechanisms are described in this paper, which may provide information for improved building design.

The use of cross-laminated timber (CLT) in constructing tall buildings has increased. So, it has become crucial to get a higher in-plane stiffness in CLT panels. One way of increasing the shear modulus, G, for CLT panels can be by alternating the layers to other angles than the traditional 0° and 90°. The diagonal compression test can be used to measure the shear stiffness from which G is calculated. A general equation for calculating the G value for the CLT panels tested in the diagonal compression test was established and verified by tests, finite element simulations and external data. The equation was created from finite element simulations of full-scale CLT walls. By this equation, the influence on the G value was a factor of 2.8 and 2.0 by alternating the main laminate direction of the mid layer from the traditional 90° to 45° and 30°, respectively. From practical tests, these increases were measured to 2.9 and 1.8, respectively. Another influence on the G value was studied by the reduction of the glue area between the layers. It was shown that the pattern of the contact area was more important than the size of the contact area.

Determining the mechanical properties of cross-laminated timber (CLT) panels is an important issue. A property that is particularly important for CLT used as shear walls in buildings is the in-plane shear modulus. In this study, a method to determine the in-plane shear modulus of 3- and 5-layer CLT panels was developed based on picture frame tests and a correction factor evaluated from finite element simulations. The picture frame test is a biaxial test where a panel is simultaneously compressed and tensioned. Two different testing methods are simulated by finite elements: theoretical pure shear models as a reference cases and picture frame models to simulate the picture frame test setup. An equation for calculating the shear modulus from the measured shear stiffnesses in the picture frame tests is developed by comparisons between tests and finite element simulations of the CLT panels. The results show that pure shear conditions are achieved in the central region of the panels. No influence from the size of the tested panels is observed in the finite element simulations.

A shortcoming of the laminated bending process is that the product may become distorted after moulding. This study focused on the influence of fibre orientation deviation for individual veneers on the distortion of a moulded shell. The distortion of 90 cross-laminated shells of the same geometrical shape, consisting of seven peeled birch veneers, were studied under relative humidity variation. All the veneers were straight-grained in the longitudinal-tangential plane, but to simulate a deviation in fibre orientation, some of the individual veneers were oriented at an angle of 7° relative to the main orientation of the other veneers in the laminate. A finite element model (FEM) was applied to study the possibility of predicting the results of a practical experiment. The study confirms the well-known fact that deviation in fibre orientation influences shape stability. The results also show how the placement of the abnormal veneer influences the degree of distortion. From this basic knowledge, some improvements in the industrial production were suggested. However, the FE model significantly underestimated the results, according to the empirical experiment, and it did not show full coherence. The survey shows the complexity of modelling the behaviour of laminated veneer products under changing climate conditions and that there is a great need to improve the material and process data to achieve accurate simulations. Examples of such parameters that may lead to distortion are density, annual ring orientation in the cross section of the veneer, the orientation of the loose and tight sides of the veneer, and parameters related to the design of the moulding tool.

Cross laminated timber (CLT) is a wood panelling building system that is used in construction, e.g. for floors, walls and beams. Because of the increased use of CLT, it is important to have accurate simulation models. CLT systems are simulated with one-dimensional and two-dimensional (2D) methods because they are fast and deliver practical results. However, because non-edge-glued panels cannot be modelled under 2D, these results may differ from more accurate calculations in three dimensions (3D). In this investigation, CLT panels with different width-to-thickness ratios for the boards have been simulated using the finite element method. The size of the CLT-panels was 3.0 m × 3.9 m and they had three and five laminate layers oriented 0°–90°–0° and 0°–90°–0°–90°–0°. The thicknesses of the boards were 33.33, 40.0, and 46.5 mm. The CLT panel deformation was compared by using a distributed out-of-plane load. Results showed that panels with narrow boards were less stiff than wide boards for the four-sided support setup. The results also showed that 2D models underestimate the displacement when compared to 3D models. By adjusting the stiffness factor k88, the 2D model displacement became more comparable to the 3D model.