Experimental and analytical investigations into the time-dependent performance in post-tensioned timber beam-column joints under sustained loads and varied environment

Abstract

Experiments investigating the time-dependent performance of post-tensioned timber beam-column joints were conducted in an uncontrolled environment. The aim of these experiments is to study the deterioration of joint performance, especially the prestressing force losses and the rotational stiffness degradation. Two types of post-tensioned joint specimens were monitored: one was without external loads, and the other one was subjected to external loads. Environmental temperature and relative humidity were measured in combination with timber moisture content, prestressing force, joint rotation, beam deflection and timber strain. It was shown that the maximum loss percentage of the prestressing force was 11.4% and 19.1% for the unloaded and loaded joints, respectively. The variation of prestressing forces was dominated by the stress level and the relative humidity change. Meanwhile, the joint rotation increased by a factor of 6.56 in the first four months compared to the elastic joint rotation, and the deflection at the end of the beam was 2.55 times bigger compared to the elastic deflection. The stress concentration on the beam-column interface was found as a determinant factor causing the excessive joint rotation. An analytical model was adopted to simulate the prestressing force losses and achieved good agreement with the experimental results.