Work reported in this study was carried out with the key objective of evaluating and providing recommendations on potential improvement of connection systems typically used in prefabricated wood wall panels. Several visits were made to major prefabricated wall panels and modular houses in Quebec to provide a better understanding of the typical connection systems being used in the prefabricated wall assemblies and to identify issues of concern.
Results of eighteen (18) racking tests and nine (9) bending tests on full-size 2.44 by 2.44 m walls composed of two segments (1.22 by 2.44 m) attached with three (3) different types of connection configurations are presented. Several wall-to-foundation attachments were also investigated; including bolted, nailed, and fully anchored walls. Monotonic and cyclic racking tests were performed according to relevant ASTM standards. Bending wall tests were carried out according to a proposed protocol based on the calculation of the wind pressure corresponding to five hurricane categories from 112 to 257 km/h. Bending wall tests were carried out using an airbag system to simulate the inward wind-pressure with three (3) types of attachments to the foundation.
Results reveal that the racking load carrying capacity of wall assemblies subjected to either monotonic or cyclic loading was not strongly affected by the type of central connection configuration used to joint the two wall segments. In addition, for all types of inter-segment connections tested under monotonic or cyclic loading, wall assemblies with hold-down anchors were nearly three times stronger than those nailed to the base. They showed 80% higher stiffness and dissipated five to seven times more energy before failure. Moreover, the type of loading seems to have some influence on the maximum load carrying capacity and to a less extent on stiffness of prefabricated wall assemblies, regardless of the type of inter-segment and wall-to-foundation attachments. As for out-of-plane loads, the tested wall assemblies resisted wind-pressure beyond 4.3 kPa corresponding to 232 km/h sustained wind speed equivalent to Category 4 hurricane. Their strength was controlled by the strength of the studs rather than the type of the connections used.
In addition, results on static and monotonic tests carried out on small size connections used in full-size racking and bending tests are also given. Such information is necessary for the finite element model being developed to predict the performance of prefabricated wall panels subjected to bending and racking forces, with special focus on the interface and anchorage behaviour for performance optimization.
Recommendations are given on how to improve the connection systems used in the assembly of wall panels. The information generated in this study provides data for comparative quantitative analysis of conventional and engineered wall assemblies and is expected to serve the development of design methodology for lateral load resisting systems of prefabricated houses.