The mechanism and calculation method of bilateral shear strength of rectangular frame columns ( RFC) under low-cyclic oblique horizontal loads were investigated based on an experiment including 5 rectangular frame columns without stirrup and 7 rectangular frame columns with stirrup. The results indicate unilateral shear theory can not be used to calculate bilateral shear strength of RFC. The main reason is that the diagonal crack of column develops rapidly under bilateral shear force,and the the concrete strength increased by axial force is limited. Secondly,the bilateral shear strength offered by concrete of RFC is calculated iteratively by unilateral shear theory. Based on the above analysis,the correlation property of bilateral shear strength of RFC without stirrup is analyzed. The results show the correlation relationship can be described as ellipse equation. And then an amendatory theory was put forward , Which reduced the shear strength offered by concrete and axial force together on two principal axes. The comparison between the calculation and experimental results shows the formula is feasible and safe. At last,a formula to calculate bilateral shear strength of RFC under qrthquake was presented,in which RE is considered.
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