Experimental Study On Mechanical Behavior Of Recycled Brick Aggregate Concrete-filled Cross Shaped Steel Tubular Long Columns Under Eccentric Compression Loading

At present,the construction industry in our country is developing rapidly,many old buildings have been demolished which results in a large amount of construction waste.The waste bricks account for 30%～40%of the total.Using recycled concrete technology,it can be turned into treasure.The cross-shaped columns are used as central columns in the building to prevent the comers from being exposed.In the meantime,the cross-shaped column with the same area has greater stiffness than the(square)rectangular column,and its limb length is longer than the side length of the rectangular column,so the beam span between columns can be shortened,thus increasing the building height.However,the common reinforced concrete cross column has some shortcomings such as low vertical bearing capacity and poor aseismic performance,which can be overcome by using the concrete-filled steel tube composite column.In this paper,seven recycled concrete long columns made of cross-shaped steel tubular brick aggregate are studied to investigate their mechanical properties under compression.The basic mechanical parameters of concrete with 0%,50%and 100%replacement rate of reclaimed brick aggregate were measured by experiments;Renewable brick aggregate replacement ratio,slenderness ratio and eccentricity,three factors as variables to study its effects on deformation and ultimate bearing capacity;The numerical simulation method was used to simulate the test process,and it was found that the simulation results were in good agreement with the test results,so two variables of steel tube wall thickness(steel ratio)and steel strength were added to study the influence of them on the bearing capacity of members;The calculation formula of the bearing capacity of the member short column is obtained.Combining CECS28-2012 specification,through experiment and numerical simulation data,fitting the slenderness ratio and eccentricity of the bearing capacity of reduction factor and,get the formula to calculate capacity.The main conclusions of this paper are as follows:(1)When the aggregate replacement rate of recycled brick increases from 0%to 50%to 100%,the cube compressive strength,axial compressive strength and elastic modulus of recycled brick decrease by 11.8%and 33.9%,22.3%and 41.8%,18.4%and 41.8%respectively,and the Poisson’s ratio does not change significantly.(2)The axial load-axial displacement curves,axial load-column lateral deflection curves and axial load-column strain curves of members with different replacement rates are obtained.When the replacement rates increase from 0%to 50%to 100%,the ultimate bearing capacity of members decreases by 3.9%and 8.8%,and the vertical displacements increase by 18.1%and 40.7%.(3)When the slenderness ratio increases from 37.4 to 40.3 to 43.2 under axial compression,the ultimate strength decreases by 7.0%and 15.7%,and the vertical displacement increases by 64.4%and 81%.(4)When the eccentricity increases from 0mm to 25mm to 50mm,the ultimate bearing capacity decreases by 5.7%and 11.5%,and the vertical displacement increases by 30.2%and 127.9%.(5)The calculation formula of axial compression and bias bearing capacity of recycled concrete long column with cross shaped steel tube brick aggregate is fitted.