Shear strength of concrete composite beams with shear reinforcements

Currently, the hybrid construction of precast concrete (PC) and cast-in-place concrete (CIPC) with different concrete strengths is frequently used for precast concrete structures. However, in ACI 318-14, the shear strength of PC-CIPC composite beams is defined as the sum of the respective shear strengths or the lower concrete strength of the two concretes, without clear evidence. In the present study, the shear strengths of simply supported composite beams with shear reinforcement were investigated. The test variables included the cross-sectional area ratio of the precast concrete and cast-in-place concrete, the spacing of the stirrups, and the shear span-depth ratio. The test results showed that the use of high-strength concrete (HSC) in the compression increased the contribution of shear reinforcement by increasing the depth of the tension zone. Thus, the use of HSC in the compression zone significantly increased the shear strength of the composite beams. The shear design equation of ACI 318 safely predicted the shear strengths of the specimens by using the sum of the individual strengths of the two concretes or by using the average concrete strength.