Performance degradation of glued-laminated timber beams under multi-factor environmental aging and sustained load

Structural performance of timber buildings can be adversely affected by exposed harsh environment and sustained load. This study investigates bending performance degradation of glued laminated timber (GLT) beams (50 mm x 50 mm x 950 mm) that are exposed to unfavorable environmental conditions. The experiments consider eight scenarios, including various climate cycling periods, duration, and stress levels. Eight groups of GLT beams were exposed to the different scenarios for four stages, then loaded by short-term bending to obtain the MOR and MOE. The results showed that coupling effects of sustained loading and the environmental factors such as UV-light and mist spraying aggravated the pronounced damage on the laminates and gluelines and caused the degradation of strength and stiffness. The highest degradation rate occurred in the first stage. In the relatively mild environments, some performance recovery was observed in the later stages, most specimens exhibited ductile failure accompanied by the significant increase of the ultimate deflection with the exposure time. While in the harsh environments, the MOR and MOE degradation was evident and continuous, more specimens experienced brittle failure, and the increase of the ultimate deflection slowed down greatly with the exposure time. Additionally, the effects of sustained loading period were significantly exacerbated under the harsh environmental conditions, the specimens loaded by less than 50% stress level exhibited the distinguished degradation in 24 days.