ZHANG Rui, MENG Qing-li, HE Wei, NIWA Junichiro
China Journal of Highway and Transport. 2017, 30(12): 234-241,249.
To investigate the shear reinforcing effect of stirrups in the steel reinforced engineered cementitious composite (ECC, R/ECC) beams, in allusion to the steel reinforced concrete (RC) structural member with shear failure, four-point loading tests were conducted on both RC and ECC beams by considering the effect of stirrup ratios. The tensile mechanical properties of polypropylene fiber reinforced engineered cementitious composites (PP-ECC) were firstly investigated by conducting uniaxial tensile tests. Based on the results, a total of 7 beams, classifying into 2 categories, namely, 5 steel reinforced PP-ECC and 2 RC beams, were designed and constructed. All beams were tested by four-point loading tests. In addition, the shear cracking behavior of 5 PP-ECC beams were carefully observed and measured during the loading, and the effect of stirrup ratio on the shear cracking behavior was analyzed. Through the modified truss model, the shear capacities of 5 PP-ECC beams were investigated by considering the effect of stirrup ratio. The experimental results show that PP-ECC exhibiting pseudo strain-hardening behavior and multiple fine cracking has tensile yield and tensile strength which is no less than 2 MPa and 3 MPa, respectively, and its tensile strain capacity is greater than 2.5%. ECC beams are with good ductility, whose shear capacity gradually increases with the increase of stirrup ratio. Under the same stirrup ratio, the shear capacity of R/ECC beam is larger than that of RC, and the R/ECC beam without stirrups shows twice shear capacity of RC beam. In addition, the shear carried by PP-ECC decreases with the increase of the stirrup ratio. The reason is that the higher stirrup ratio restricts the development of shear cracks, and the sliding in the critical shear cracks increases, thus decreasing the bridging effect of fibers. However, the current design and specification does not take the effect of shear sliding into considerations, which may result in overestimation on shear capacity of R/ECC beams.