Modeling of CLT creep behavior and real-time hybrid simulation of a CLT-LiFS building

Abstract

CLT-LiFS is an innovative hybrid structural system. This type of structure has emerged as a promising structural system for mid-rise to tall wood buildings in the seismic areas. CLT-LiFS is made by integrating post-tensioned Cross Laminated Timber (CLT) panels with Light Frame Wood Systems (LiFS). The post-tensioned CLT panels can provide excellent load bearing and self-centering capacity. And the LiFS can dissipate a large amount of energy through the slip of fasteners when it deforms. The behaviors of CLT-LiFS have been studied through a series of experimental tests under cyclic loading protocols and earthquake motions at different hazard levels using real-time hybrid simulations. Results from the experimental tests showed that the CLT-LiFS performed well under MCE (Maximum Considered Earthquake) hazard level with the maximum drift less than 1%. To obtain a good self-centering performance, the post-tensioned tendon force in CLT panels needs to be maintained at a desired level in long-term until the earthquake hits. Under the creep behavior, the post-tensioned force in the tendon will reduce as a function of time and moisture content in CLT panels. In this dissertation, a moisture content diffusion model was introduced by applying Fick’s law to estimate the moisture content migration in CLT panels under the variation of environmental relative humidity. A numerical model combined with data from a series of moisture content experiments were used to obtain the moisture content diffusion coefficients for CLT material. The four-element creep model was also proposed. This creep model could predict the creep deformation of CLT panels versus time under variations of ambient environmental conditions. A 3D finite element model (FEM) was developed with an integration of the creep and moisture content diffusion model to predict the tendon force of post-tensioned CLT panels versus time. This FEM model was used to predict the loss of tendon force in CLT panels. This tendon force loss did not include the instant loss at the beginning due to anchor slip or other factors.