Research On Seismic Performance Of Frame Filled Unreinforced Brick Masonry Wall Strengthened By Pre-stressed Steel Strips

For the existing frame structure buildings,due to the use of functional changes,storey expansion,design standards and other reasons,it will not meet the current seismic appraisal standards,so reinforcement measures are urgently needed.Traditional reinforcement methods only focus on the frame itself,ignoring the interaction between brick masonry wall and frame,which will lead to wider range of beams,columns and joints that need reinforcement,and low reinforcement efficiency.Therefore,this paper intends to take the brick masonry infilled wall as the direct reinforcement object,so as to improve the cooperative working ability of the infilled wall and the frame,and ultimately to improve the overall performance of the structure.Brick masonry walls are strengthened by orthogonal steel strips,and the end of the strip is anchored on the frame beams and columns.In order to reduce the stress lag of the strip,prestressing force is applied to the vertical and transverse steel strips respectively.In this paper,experimental research,numerical simulation and theoretical analysis are used as the main methods to study the reinforcement effect,seismic performance and its influencing factors,hysteretic model and peak bearing capacity of frame filled unreinforced brick masonry wall strengthened by pre-stressed steel strips.The main work of this paper is as follows:(1)The experimental investigation and analysis on seismic performance of frame filled unreinforced brick masonry wall strengthened by pre-stressed steel strips are performed in the article.The specimens are scaled at 1/2 scale.Including pure frame,frame filled unreinforced brick masonry wall and frame filled unreinforced brick masonry wall strengthened by pre-stressed steel strips with different mortar strengths.Through tests,the failure process and characteristics,bearing capacity,hysteretic curve and skeleton characteristics,ductility index,stiffness degradation characteristics and energy dissipation capacity of the structure under low cyclic repeated loads are compared and analyzed.The test results show that the frame filled unreinforced brick masonry wall strengthened by pre-stressed steel strips can further improve the integrity of the original structure on the basis of fully utilizing the filled wall,thus greatly improving the seismic performance of the structure.Mortar strength will affect the failure mode of infilled wall.When mortar strength is high,the failure mode of wall is diagonal compression shear failure;when mortar strength is low,the wall is shear slip failure.This failure mode will cause relatively large lateral displacement of the wall and reduce the structural bearing capacity.(2)The finite element model of frame filled unreinforced brick masonry wall strengthened by pre-stressed steel strips is established by using finite element software ABAQUS.The results of finite element analysis are compared with the test results to verify the accuracy of the model.On this basis,the relevant parameters affecting the seismic performance of the structure are further analyzed.The results show that with the increase of the vertical prestress level(stress/yield strength),the bearing capacity of the reinforced structure decreases slightly.Therefore,the prestress can not be applied in the vertical steel strip for the structure with the vertical bearing capacity meeting the requirements.Increasing the prestressing level in the transverse steel strip can improve the bearing capacity and ductility of the structure,but the lifting efficiency decreases with the increase of the prestressing level.When the prestressing level is greater than 0.2,the effect of further improving the prestressing force is not significant.Therefore,the recommended prestressing level is 0.2 when strengthening.The increase of masonry strength grade can significantly improve the peak bearing capacity and initial stiffness of reinforced structures.The increase of vertical load level of frame columns can improve the bearing capacity of the structure,but it has little effect on the initial stiffness of the structure.(3)A four-fold linear hysteretic model for frame filled unreinforced brick masonry wall strengthened by pre-stressed steel strips is proposed by means of experimental fitting.(4)Based on the mechanical characteristics of the structure and the traditional mechanics theory,the calculation method of the peak bearing capacity and the peak displacement of the reinforced structure is proposed.