Abstract

     The performance of structural timber connections is of utmost importance since they control the global response of the building. A ductile failure mechanism on the global scale is desirable, especially in the design of structures in seismic areas, where dissipative components in which ductile failure modes need to be ensured are considered. Therefore, the knowledge of possible brittle failure modes of connections is crucial. The paper investigates the brittle failures of laterally loaded dowel-type connections in cross-laminated timber subjected to tensile load in a lap joint configuration through experimental investigations and analytical estimations. A set of 13 different test series has been performed with fully threaded self-tapping screws of 8 mm diameter and different lengths (40 to 100 mm) in cross-laminated timber composed of 3 or 5 layers (layer thickness range from 20 to 40 mm), giving rise to the activation of different brittle failure modes at different depths. Plug shear was among the most typically observed failure modes. A previously proposed model for the brittle capacity was applied to the tested connections at the characteristic level. As shown by the performed statistical analysis, the existing model is not reliable and mainly unconservative.

Introduction

     Nowadays, one of the best solutions for decarbonisation of the construction sector is to introduce more wood into building practices, which means that this material should not be used only for single-family housing, as was common practice in the 20th century. Consequently, there is a high demand for wood to be used in various types of structures, especially mid-rise (up to 10 storeys) and high-rise buildings (more than 10 storeys) that are the predominant type of buildings in dense urban environments. With the development of high-performance engineered wood products (EWPs) such as cross-laminated timber (CLT), building with wood has enabled larger and taller buildings to be erected. However, due to the relatively short period since emerging and implementation of advanced EWPs and their new structural systems have been present on the market, the knowledge and experience using these materials for high-rise buildings is still limited.

Conclusions

     The paper analyses the possibility of brittle failure modes for tensile loaded CLT with laterally-loaded screw connections, considering loading orientations both parallel and perpendicular to the direction of the laminations in the outer CLT layer. High-load bearing connections in CLT structures as analysed in this work would mainly be needed for hold-downs, where in most cases the connection is oriented parallel to the grain of the outer layer (α = ۰°), and mainly designed for tensile loads.

     The experimental results suggest that the load-bearing capacity of the connection increases with the width of the CLT specimen; e.g. a 45% increase was found between series CD2 (w = 250 mm) and series CD4 (w = 750 mm). However, increasing specimen width does not appear to affect the resulting elastic stiffness. The length of the screws was found to have a large impact on the elastic stiffness; e.g. an increase of more than 70% was found between 40 mm (series CD1) and 100 mm (series EF1) fastener lengths. The CLT layup does not seem to influence the elastic stiffness notably, while it influences the resulting load-bearing capacity, mainly concerning the penetration of the fastener into the different layers.