Axial Compression Behavior Of Reinforced Concrete Column Retrofitted By Steel Jacket

Reinforcement and reconstruction of existing buildings has become a very important topic in the civil industry at home and abroad.At the same time,steel sheet materials are more and more applied to the reinforcement of building structures.Therefore,this paper chooses casing made of steel sheet to reinforce.This reinforcement method has excellent mechanical properties,and the construction is fast and convenient,and has high popularization value.However,after the analysis of previous studies,it is found that the research on reinforced concrete columns retrofitted by steel-jacket mainly focuses on the reinforcement of circular steel-jacket;the reinforcement of steel-jacket is always confused with concrete filled steel tubular columns in mechanical analysis;and the number of relevant literatures is also small.In order to study the axial compressive behavior of square reinforced concrete short columns retrofitted with square steel tube,four steel tube retrofitted columns and one ordinary reinforced concrete column were tested on the basis of the existing research.The influence of the thickness of steel-jacket and whether the inner wall of the steel-jacket is notched on the bearing capacity of the reinforced column under axial compression is mainly studied.The finite element software is used to carry out numerical analysis.In the numerical analysis,the influence of changing the size of the reinforced column and increasing the strength of the filling concrete on the axial compressive bearing capacity of the reinforced column is considered.The results and conclusions are as follows:(1)According to the test results,the influence of the thickness of steel-jacket on the axial failure load of reinforced concrete columns retrofitted by steel-jacket is very obvious.The axial failure load is increased by 50%~81%,and the effect is obvious.It can be seen that the thickness of steel-jacket is the main factor affecting the bearing capacity of reinforced columns under axial compression.(2)According to the test results,the increase of the axial failure load of reinforced concrete column retrofitted by steel-jacket with notched inner wall is not obvious.The axial failure load of the member with notched inner wall of steel-jacket is about 7% higher than that of the component without notched inner wall.This may be due to the small bonding effect of notched surface of steel-jacket on the filling concrete.If there is no effective bond between the filling concrete and the steel sleeve,the steel sleeve can not play a good role,resulting in unsatisfactory reinforcement effect.(3)From the numerical analysis,it is found that under the condition that the thickness of steel-jacket is constant,the reinforcement effect decreases gradually with the increase of the size of core concrete.This may be because the increase of the size of core concrete weakens the restraint effect of filling concrete and steel-jacket on core concrete,so the reinforcement effect of reinforced columns decreases.The failure load of reinforced concrete short columns retrofitted by steel sleeve is not significantly increased with the increase of strength grade of filling concrete.The axial failure load is increased by 0.93%~1.77%.This may be because the joint filling concrete mainly plays the role of sticky core concrete and steel-jacket,as well as transferring shear stress,so the influence on the axial bearing capacity is not obvious.The numerical analysis shows that when the secondary stress is considered,the bearing capacity of the retrofitted column decreases gradually with the increase of the initial load.When the top load of the retrofitted column is 0.1 ? 0.9 of the primary stress member,the axial bearing capacity of the retrofitted column is 26.83% ? 91.77% of the primary force.Therefore,in practical engineering,we should try our best to remove the load on the top of the column and then carry on the reinforcement treatment.(4)According to the stress mechanism of reinforced columns and the test results of axial compressive behavior of reinforced concrete retrofitted with steel-jacket,the formula of ultimate axial failure load of square reinforced concrete columns retrofitted with steel-jacket is presented in this paper.