The Static Experimental Study Of The HRB500 Reinforced Concrete Frames

The crack behavior of concrete members reinforced with HRB500 steel in varying moment region is experimental studied in this paper. HRB500 bar is a new hot-rolled ribbed bar with yield strength of 500MPa, which can enhance the bearing capacity of concrete member and reduce the amount of steel. But it always reaches high stress and the crack width may exceed the limit of the code, as a result the crack width may become primary instead of the bearing capacity in the design, which makes the high strength of HRB500 bar cannot exert. The calculation formula of crack width in Chinese code is based on the experimental results of constant moment region and the theory of bond stress and bond slip, but the corresponding formula in varying moment region is not suggested. Especially on the support of the frame beam, the moment and the shear both reach the largest, so the influence of the shear on the crack width must be considered.The static test of two HRB500 reinforced concrete frames and one HRB400 reinforced frame is studied. In the initial stage the concentrated symmetric loads are applied and in the failure stage the deflection of the frame beam is controlled. During the experimental process, the strain in the key sections, the rotation angle in the beam-column end and the deflection are recorded, meanwhile the crack width and distribution are also recorded. By use of the strain in the section of column base, the reaction force can be calculated, so the shear force and the bending moment on the arbitrary section of the frame beam can also be computed, which can be checked by the strain of the key sections of the frame beam.Using the measured data, the nonlinearity, the deformation performance, the internal force redistribution and the rotation capacity of the plastic hinge are further studied. The test shows, owing to good ductility of HRB500 bar and enough rotation capacity of the plastic hinge, the frame can implement the plastic internal force redistribution, so this can be taken into account in the design.By use of the reaction force, the shear force and the bending moment on the dominating crack section of the frame beam can be calculated. By comparing the measured crack width with that computed according to the code, the coefficient of the shear is given on the formula of the crack width.