Long-Term Experimental Study on Prestressed Steel-Concrete Composite Continuous Box Beams

A long-term load test of 420days was performed on three prestressed steel-concrete composite continuous box beams (non-prestressed, partly prestressed, and fully prestressed) to investigate the combined effects of sustained load, shrinkage, creep, and prestressing. Several time-varying parameters, such as deflection, concrete strain, prestressing force, support reaction, and relative slippage between the concrete slab and the steel box beam, were monitored in the test. The long-term performance of the prestressed beams that was developed using a special law increased and decreased the support reactions at the middle and end piers over time, respectively, due to the distinct configuration of prestressed strands (i.e., installation was only at the negative moment area). The growth rate of the deflection of the prestressed beams was slightly greater than that of the deflection of the non-prestressed beam. Moreover, cracking at the negative moment region significantly accelerated the development of the relative slippage of the non-prestressed beam. A calculation model of long-term deflection based on classical theories was proposed to theoretically analyze the measured data and provide valuable insights for future research.