Experimental Study On Seismic Behavior Of Specially Shaped RC Columns With Different Limb Lengths

Frame structure with specially shaped RC columns has been increasing used in multi-storey dwelling buildings over recent decades in China.The thickness of specially shaped column leg is the same as a wall,so the edges of columns are invisible and the structure with specially shaped columns is beautiful in architecture.But the section of specially shaped column is irregular and its behavior is different from that of rectangular column.Sometimes,the specially shaped columns with different limb lengths may be adopted in actual engineering and the effect of limb length on mechanic behavior needed to be studied further.In this paper,the following work has been done.1.Based on the test results of 13 specially shaped columns under low reversed cyclic loading,the effects of several parameters(such as axial load ratio,limb length,stirrup ratio and arrangement of longitudinal bars,etc.) on seismic behavior are analyzed.It can be concluded that axial load ratio is one of the major factors that affect the seismic behavior.The specimen with low axial load ratio has better ductility and energy dissipation capacity for the hysteretic curve is fat.The ductility of column increases with the stirrup ratio for that the transverse reinforcements can confine the core concrete.The bearing capacity of column increases with the increase of limb length,but the deformation capacity was reduced. Increasing the longitudinal bars inthe web has little influence on seismic behavior.2.The force-displacement relationship of specially shaped column under axial compression and lateral force is calculated by numerical integral method.And a computer program is presented to simulate the skeleton curves of L,T-shaped columns.The model is proved valid by comparing the test results and calculating values,so the effects of concrete strength,axial load ratio and limb length on bearing capacity are analyzed by the computer program.Moreover,axial load ratio is calculated by numerical method for L,T-shaped columns with different limb lengths.It can be concluded that the value of axial load ratio is the minimum for L-shaped columns when the neutral axis is parallel to section edge and the shorter limb is compressed.While for T-shaped columns regardless of flange or web is larger, it is the minimum when the neutral axis is parallel to flange edge and the web limb is compressed.And some values of axial load ratio for L,T-shaped columns with different limb lengths are suggested.Also,the transverse reinforcements have effect on axial load ratio,and the values are given for reference. 3.Based on the experimental results of 12 specially shaped RC columns with different limb lengths subjected to combined action of shear and moment,a broad range of parameters that influence the shear capacity of columns were investigated.The parameters include limb length,axial load ratio,horizontal force direction and stirrup ratio.It can be concluded that the limb length can enhance the shear resistance of columns.The shear resistance of L-shaped column subjected to two directions is not always larger than that under frame direction.4.The truss-arch model is used to analyze the shear resistance of specially shaped columns.The calculated values are compared with test results and they agree well with each other.It can be concluded that the shear resistance is compressed of two parts contributed by truss model and arch model.Combining with test data of others,the formulas for shear resistance of specially shaped columns are presented by considering the flange.5.Four exterior joints with specially shaped columns which have different limb lengths are tested under low reversed cyclic loading.The ductility,energy dissipation capacity and stiffness degenerating of joints are studied systematically.Test results indicate that crack pattern,failure mode and shear resistance of joints are influenced by limb length.The joint occurring beam flexural failure has better seismic behavior.6.The nonlinear finite element models were used to analyze crack development and stress distribution of joints with specially shaped columns.The parameters include axial load ratio,limb length and section shape.And the analysis results indicate that the nonlinear finite element method is valid if the model and parameters are chosen suitably.The section shape and size have effect on crack pattern or stress distribution.On the basis of joint core's mechanical properties,the formula of anti-crack capacity of joint with specially shaped column is proposed.The calculating results agree well with test data.According to the test and theory analysis,the specification formula is reversed to calculate the shear resistance of joint with different limb lengths.