Long-term performance of timber-concrete composite systems with notch-screw connections

Abstract

This paper presents the experimental results of long-term tests performed on six push-out specimens, one timber-concrete composite (TCC) beam with notch-screw connections, and one timber beam. The interface slip of shear connections was evaluated in a constant temperature and humidity environment, and two loading cases (15% and 30% of the ultimate bearing capacity of push-out specimens) were considered. After 342 days of loading, the long-term slip for the push-out specimens with 0.15 and 0.30 loading levels were 0.221 mm and 0.338 mm, respectively. The beam specimens were tested in an uncontrolled indoor environment. The long-term loads sustained by the beam specimens were approximately 18.8% of the short-term flexural capacity. After more than 400 days of loading, the maximum mid-span deflection of the timber beam and TCC were 4.25 and 4.20 mm, respectively. The timber strain and the interface slips of the TCC specimen showed more obvious environmental sensitivity than the mid-span deflection. Three existing creep models and a modified model were adopted to fit the long-term slip curves of the push-out specimens. The modified model showed the best fitting accuracy with the recorded data, and the most reasonable prediction tendency for the whole service life. The final mid-span deflections of beam specimens were predicted by the modified model for the 50-year service life, and the predicted results for the timber beam and TCC were 12.7 mm and 10.1 mm, respectively. These results are in good agreement with the calculation results according to Eurocode 5 and NDS-2018.