EFFECTS OF VARIABLE CLIMATE CONDITIONS ON THE BEHAVIOR OF POST-TENSIONED MASS TIMBER WALL PANELS

Abstract

Post-tensioned (PT) mass timber rocking walls are innovative lateral force-resisting systems used in resilient seismic design. The system relies on an initial tensioning of wall panels using high-strength steel rods. However, tension losses are known to occur in PT systems over time, especially when these systems are exposed to variable climate conditions. In mass timber rocking wall designs, existing creep models do not allow for reliable prediction of long-term PT losses. Thus, the purpose of this research is to characterize the long-term behaviour of PT mass-timber wall panels exposed to variable climate conditions and to develop a model for reliable prediction of the effects of such exposures. The mass timber panels consist of ANSI PRG 320 approved cross-laminated timber (CLT) and mass ply panels (MPP). The components of the complex effect of long-term variable climate exposure are isolated by comparing data collected on similar panel specimens exposed to controlled humidity cycles in post-tensioned and unloaded conditions with those collected on loaded specimens exposed to a constant environment. Panel in-plane deformations, loads, and moisture content in the tested systems are continuously monitored. These tests provide data for the development of an in-plane creep model for mass timber panels that will be validated on two monitored full-scale 9.1 m tall post-tensioned rocking walls, exposed to naturally varying indoor conditions in a large-scale structural testing laboratory for 12 months. This paper summarizes the experimental data collected from specimens in the environment with controlled humidity cycles and the constant environment and some lessons learned. The data shows the following trends: (1) it appears that, during the test time frame and under the imposed changing environmental conditions, the PT system’s response is dominated by the in-plane shrinkage and swelling of the specimens, (2) the MC profiles of the PT panels have a significant effect on the panel’s strain behaviour, and (3) under constant environmental conditions, the CLT panels experienced more viscoelastic creep compared to the MPP panels.