Research On Shear Resistance Behavoir Of Masonry Walls Retrofitted By Prestressed Steel Strips

In the existing masonry-concrete buildings,the vertical bearing components are basically brick masonry walls,whose materials are brittle and some functions will degrade after a certain service life.Reinforcement and renovation of these buildings can not only improve seismic performance,but also meet the needs of functional renovation of buildings.In view of the problems of stress lag,involving wet work and high requirement of material strength which common reinforcement technology of brick masonry walls have at present,a new method that using prestressed steel strips is proposed in this paper.The reinforcement method is to arrange orthogonal rectangular steel strip grids on both sides of existing brick masonry wall,and apply pre-tensile stress in transverse steel strips.The steel strips and wall are connected by tension bolts,which belongs to dry connection.In order to study the shear behavior of brick masonry walls strengthened with prestressed steel strips,Experimental study and corresponding theoretical analysis were carried out in this paper.Firstly,the monotonic horizontal load tests of one unreinforced brick masonry wall and four reinforced brick masonry wall with prestressed steel strips were conducted,taking the spacing of transverse steel strip,the level of pretension stress in transverse steel strips and the strength of mortar as the research parameters.The failure characteristics of brick masonry walls,the peak load,displacement and the development of strain of steel strips were all obtained through the experimental study.The test results show that the shear capacity of brick masonry walls strengthened with prestressed steel strips increases by 30%~36%,the ductility of the wall is improved and the deformation capacity is enhanced.Increasing the level of horizontal pretension stress can enhance the restrictive effect on wall deformation and crack development,but excessive prestress level will lead to early wall failure.Increasing the mortar strength of brick masonry wall can improve the ductility of the wall,increase the shear capacity of composite wall and enhance the deformation capacity.On the basis of experimental study and results,this paper carried out the finite element analysis of brick masonry walls strengthened with prestressed steel strips by Abaqus,established integral finite element models that were verified based on the experimental results.After that,through analysis of the variation factors such as spacing of transverse steel strips,level of pretension stress in transverse steel strips,strength grades of masonry and steel strips,the discipline of the peak load of brick masonry walls reinforced by prestressed steel strips were obtained.The analysis results show that reducing spacing of transverse steel strips can improve the lateral stiffness,shear capacity and deformation capacity of composite walls;The shear capacity of the composite wall increases firstly and then decreases with the increase of the level of horizontal pretension stress,and reaches the maximum When the effective prestressing eigenvalue of transverse steel strip is 0.235.the higher the strength of masonry wall,the higher the peak load of the composite wall,and reducing the strength of masonry can enhance the reinforcement effect.Increasing the strength grade of steel strip can increase the peak load of composite wall.The material performance can be brought into play more fully when the strength of steel strip is lower.Finally,based on the results of test and analysis of finite element,the formula of shear bearing capacity of brick masonry walls reinforced by pretressed steel strips is put forward,and compared with the results of experiment to verify the accuracy of the formula,which provides reliable reference for the design of this reinforcement technology.