Time-dependent capacity of large scale deep beams under sustained loads

Abstract

The aim of this study is to investigate the effect of sustained loads on the capacity of large-scale deep beams as a part of underground reinforced concrete, and to conduct parametric studies by numerical methods. The reduced shear capacity under long-term sustained loads is investigated to be associated with the mode of failure, and the higher timedependency is numerically suggested for deep-beams irrespective of their gain in the short-term static capacity. The main source of the possible decay of shear capacity is analyzed to originate from the creep damage of diagonal compression strut over the web concrete, and a simple expression of the strut-tie analogy is extended to the creep shear rupture of deep beams. Finally, it is concluded that the design safety factor of 1.2∼1.3 for shear is appropriate for avoiding the risk of creep failure against long-term sustained loads of about 100 years.