Experimental Investigation On Seismic Performance Of Unreinforced Masonry Walls Strengthened By Pre-stressed Steel Strips

In the early stage,brick mansory structures were widely used in our country because of the advantages of extensive materials and low cost.With the gradual development of social economy,most of the existing brick mansory buildings have some problems,such as shortage of seismic measures and low strength of materials.If the current seismic appraisal criteria are used,they would fail to meet the requirements.Therefore,it is particularly important to adopt effective reinforcement methods.Common reinforcement methods of brick masonry walls generally have the problems of harsh reinforcement conditions,wet operation and stress lag.This paper proposed the new reinforcement method of using pre-stressed steel strips.This method is to arrange orthogonal rectangular steel strips on both sides of the existing brick masonry walls and fix the steel strips to the wall by pulling bolts,which belongs to the pure dry connection.The application of prestressing force in transverse steel strips reduces the stress lag effect of newly added strenthening materials,which is an active reinforcement mode.In order to study the seismic behavior of unreinforced brick masonry walls strengthened by pre-stressed steel strips,one unreinforced brick masonry wall and four reinforced brick masonry walls strengthened with pre-stressed steel strips were tested under quasi-static loading.And main seismic characteristics of reinforced brick mansory walls was analyzed through the comparisons of peak load,ductility coefficient,hysteretic curve,skeleton curve,stiffness degradation curve and hysteretic energy dissipation.The test results showed that: Compared with the unreinforced brick masonry wall,the cracking load of reinforced brick masonry walls strengthened with pre-stressed steel strips were increased by 27.33% on average and the increase range of peak load was 45.91%~94.66%.The ductility coefficient of reinforced brick masonry walls were increased by at least 2.5 times,and the hysteretic curves were fuller than unreinforced one.In terms of the reinforced brick masonry walls strengthened with pre-stressed steel strips,the speed of stiffness degradation would be slower in the later stage and would achieve greater energy consumption.Because of the prestress,the stress lag effect of steel trips could be reduced,and the utilization efficiency of transverse steel strip could reach 53.9%~85.5%.Reinforced brick masonry walls strengthened with pre-stressed steel strips could effectively improve the seismic shear capacity of brick masonry walls,increase the deformation capacity,and significantly improve the hysteretic energy dissipation and other important seismic indicators,showing good seismic performance.On the basis of experiments,ABAQUS finite element analysis software was used to analyze the specific effects of parameters including the effective prestress eigenvalue ? of transverse steel strips,compressive stress,the aspect ratio and the masonry strength.The results showed that: The shear capacity of composited walls would increase first and then decrease with the effective prestress eigenvalue ? of transverse steel strips getting higher.When ? is 0.219,the composited wall could obtain relatively high shear capacity.The shear capacity of reinforced brick masonry walls would also increase first and then decrease with the increase of the compressive stress.When the vertical load level exceeds 0.3,the bearing capacity would decrease,but it is still higher than the unreinforced brick masonry wall.The shear capacity of the reinforced brick masonry walls would decrease with the increse of the aspect ratio of the walls.This reinforced methed of strenthening brick mansory walls with pre-stressed steel strips could greatly improve the shear capacity and deformation capacity of brick masonry walls with low to high strength grades,and get the best reinforcement effect when masonry walls with low strength.In addition,a three-fold linear restoring force model for the brick masonry walls strenthened with pre-stressed steel strips were established in this paper by means of experimental fitting;And the calculation methods of yield point and shear capacity of composited walls were further proposed;Finally,on this basis,the suggestions of principled structural measures were put forward to guide the design of such projects.