| In recent years,steel structures have been widely used in industrial and civil buildings.However,many steel are under construction or have been in service for many years.And due to natural disasters,use function changes,aging and other reasons,many steel structures need to be reinforced.With the increasing number of steel structures,the reinforcement of steel structures has become a new field in the construction industry.The method of welding reinforcement under load is widely used in the actual reinforcement project,and the welding heat input is the main factor affecting the reinforcement effect of the method.However,the influence of welding heat input on the mechanical properties of reinforced components has not been systematically studied and concluded.In addition,the existing research mainly focuses on the H-section members and the members whose initial stress ratio is less than 75%,and there are great differences in the provisions of the strength reduction coefficient of the members after welding reinforcement in different literatures.In view of the above problems,this paper studies the mechanical properties of welded square steel tubular columns under different initial loads.The main research contents and results are as follows:(1)The static tests of welded steel columns with initial stress ratios of 0,40%,60%,80% and 90% are completed.The test results show that the ultimate bearing capacity improvement coefficient of the strengthened column is between 1.21 and 1.35,which is similar to the section stiffness improvement coefficient of the square tube steel column after the reinforcement.It shows that the reinforcement method of the square tube steel column strengthened by the four corner sticking welded angle steel is reasonable and efficient,and the stress performance of the reinforcement can be fully exerted.(2)The initial stress ratio has little effect on the ultimate bearing capacity of short columns,which can be ignored.The results show that when the initial stress ratio is more than 60%,the larger the initial stress ratio is,the larger the welding residual deformation is,and the larger the initial stress ratio is,the larger the increment of welding residual deformation Δ u is.The stress-strain redistribution of the strengthened column is affected by the heat input of welding,the initial stress ratio and the welding sequence.(3)The finite element analysis method which does not consider the welding heat effect and the welding heat effect is established.The error between the numerical simulation results and the test results obtained by the two methods is less than 10%,which verifies the accuracy and reliability of the finite element model and analysis method in this paper,and provides the method and basis for the subsequent parametric research.(4)Using the verified finite element model and analysis method,the parametric analysis is carried out,and the effects of the initial stress ratio,slenderness ratio and the cross-sectional area ratio of the reinforcement and the original component on the mechanical properties of the welded reinforced square steel columns are studied.Based on the test results and numerical simulation results,the calculation formula of ultimate bearing capacity and prediction formula of welding residual deformation of steel columns after welding reinforcement are proposed.It is proved that the calculation formula presented in this paper can provide some theoretical support for the application of welding reinforcement method under load in practical engineering. |
