Research On L-shaped RC Columns With Unequal Legs Considering Second-order Effect

Special-shaped columns are usually referred to as columns with sections L,T,十and Z.RC structure with Special-shaped columns,the leg length is in the same thickness with the fill-up wall,no oblique columns,good for use and the high rate of getting houses,have gained wide popularity among its customers and developers.It also gained special attention from the government for its newly-adopted materials and its environment-friendly and energy-saving characteristics.This kind of structure is more suitable to the multiple or high-level residential houses.As a newly-structured form,the framework of special-shaped columns have got wide recognition for its favorable properties.The second-order effect of the slender concrete columns especially the second-order effect in eccentricity compressed column remains unsolved in China.Construction Administry issued the〝Technical Procedure of Concrete Special-shaped columns〞in March 9,2006.To the Special-shaped columns with equal legs,l0/ra>17.5,deflection should be taken.When l0/ra≤17.5,Do not take it into consideration.There is no clear definition for the special-shaped columns with unequal legs.Based on the previous researches and the behavior of R.C. columns subjected to biaxially eccentric loading,Using general-purpose software ABAQUS,a method for L-shaped R.C. columns with unequal legs subjected to biaxially eccentric loading is simulation analysis.Researched on Concrete Damaged Plasticity and failure code, constitutive relation of concrete,reinforced bar and stirrup,element type,mesh partition, boundary condition,loading mode and the finite element analysis.Then,adopting a slenderness ratios,eccentricity ratios and 4 kinds of loading angle,on the basis of the nonlinear analysis of complete response process for long column calculated by the program,the behavior formula for eccentrocoty magnified factor is proposed,and the boundary for the classification of short columns and slender columns is given.When slenderness ratios is not bigger than 17.5,then p-δadditional moment effect is smaller than first order moment of area in the sections of components,The influence of second-order effect can be ignored,calculated as short column.Discussed the relationship between the slenderness ratio,eccentricity ratio and eccenentricity magnified factor with unequal legs column considering second-order effect.A parabola relationship existe between eccentricity magnified factor and slenderness ratios,the relation between eccentricity magnified factor and eccentricity ratios is characterized by a hyperbolic curve.Curve of axial deformation when x-axis and y-axis approximate equal sinusoidal graph.The relationship between mid-span under lateral deflection and loading angle is close to unequal legs column considering second-order effect,when loading angle is 0°and180°, mid-span deflection when long pier varies comparatively great,where loading angle is 90°and270°,mid-span deflection when shot pier varies comparatively great.