Flexural behavior of concrete-filled rectangular steel tubular composite truss beams in the negative moment region

Abstract

Two concrete-filled rectangular steel tubular (CFRST) composite truss beams were tested to investigate the flexural behaviors in the negative bending moment region. The specimens were designed with different forms of concrete slab and shear connection as follows: one truss with slip-releasing shear studs and prestressed concrete slab and the other one with conventional shear studs and reinforced concrete slab. In the test, the load–deflection response, cracking development, ultimate bearing capacity, relative slip between concrete slab and steel truss, and strain distributions on steel truss, concrete slabs and reinforcement were measured. The test results indicated that the difference in concrete slabs and shear studs had negligible influences on the ultimate bearing capacity, but significant effects on failure modes and stresses redistributions. Using the prestressed concrete slab and slip-releasing shear studs can improve the degree of prestressing applied to the concrete slab, thus effectively delaying the cracking development. For the purpose of the practical design, the formulae were derived to predict the cracking moment, concrete crack width under the serviceability limit state and the flexural bearing capacity under the ultimate limit state. The validation against test results showed that the proposed formulae were reliable.