Experimental Study On Mechanical Behavior Of Assembled Steel Underpinning Joints Of Concrete Eccentrically Loaded Square

With the development of China’s urbanization process,environmental protection and resource conservation have become the problems that must be considered in the field of building technology.The displacement and transformation of old buildings and the cultural protection of ancient buildings are becoming more and more important.As the key technology of displacement reconstruction project,underpinning technology is becoming more and more important.In the research of building displacement transformation,there are many experimental research and theoretical analysis on underpinning of concrete members under axial compression,and some results have been obtained,but the research on underpinning of concrete members under eccentric compression is relatively less.In recent years,the research group has carried out a lot of research on the assembled steel underpinning joints with axially compressed columns.The experimental results show that the failure of the underpinning joints is the sliding of the contact surface between the underpinning steel beam and the concrete column.In the engineering application,the design value of the friction coefficient of the contact surface is 0.5,and the bearing capacity is 80% of the ultimate bearing capacity.But in the past test and engineering application,the phenomenon of large unilateral slip often appears.It is speculated that the reason is that the column is actually eccentrically loaded.In the actual engineering,there are few concrete columns in the true sense of axial compression,and small eccentric compression is the most common stress form of reinforced concrete columns.Therefore,it is very important to study the influence of eccentricity on the underpinning effect,find out the influence law of eccentricity on the bearing capacity of underpinning joint and the calculation method of bearing capacity,so as to avoid the problems in the process of underpinning due to the large deviation between theoretical calculation and actual stress.In this thesis,on the basis of the former research group’s axial stress test of the assembled steel underpinning joint,the following experimental studies are carried out:1.According to the experimental data of different eccentricities,the adjustment coefficient of friction coefficient of contact surface is obtained,and the calculation formula and parameters of bearing capacity of steel underpinning joints are derived;2.According to the difference between the eccentricity of the joint and the placing direction of the underpinning steel beam,the placing direction of the underpinning steel beam is divided into two types,parallel to the eccentricity direction and vertical to the eccentricity direction.The influence of the eccentricity direction on the underpinning bearing capacity is studied,and the optimal arrangement direction of the underpinning steel beam is given;3.The results show that the failure modes of eccentrically loaded underpinning joints are bilateral failure or bilateral failure when the eccentricity is small,and unilateral failure or unilateral failure when the eccentricity is large.Finally,the thesis summarizes the test,finds out the shortcomings of the test,and causes new thinking,and puts forward some suggestions for the future underpinning project.