Study On Shear Compression Performance Of Clay-mixed Mortar Masonry Strengthened By Cement Mortar Replacement

Historical buildings have important historical and cultural values.Therefore,to strengthen the masonry structure of historical buildings,we must not only adhere to the principle of minimal intervention to achieve the purpose of preserving or restoring as much as possible,but also ensure that the safety of the structure can be improved to meet the requirements.However,the current common reinforcement technologies are difficult to guarantee these two requirements at the same time,and often cause too much disturbance to the existing buildings.Therefore,this paper proposes a method of replacing the mortar to strengthen the masonry structure.Under the condition of minimizing the change of the facade,the specific part of the low-strength mortar in the masonry structure is replaced with high-performance mortar to form a masonry structure composed of old and new mortars,thereby achieving the purpose of strengthening the masonry structure.In this paper,the effects of shear strength on masonry structure strengthened by mortar replacement method are investigated through diagonal loading shear test.The test considered 9 factors including before and after the mortar replacement,whether to replace the vertical joint mortar,the replacement mortar strength,the replacement depth,the replacement form,the masonry method,the wall thickness,the mortar thickness,and the shear pressure ratio,etc.,and 18 specimens are designed.The test results show that the replacement of mortar can effectively improve the shear performance of masonry structures.When the specimen thickness is 225mm,the specimen of double-sided X-shaped 40mm depth cement mortar replacement has a better effect of improving the diagonal shear strength,which is 127.31%higher than that of the specimen with non-replaced mortar.The shear strength of masonry structure strengthened by replacement mortar is significantly affected by vertical joint mortar,and the diagonal shear strength of masonry structure strengthened with joint mortar replacement is 97.06%higher than that of masonry structure without joint mortar replacement.According to the tests of different masonry methods,the shear strength of different masonry methods is different,and more horizontal bricks or more vertical joints are conducive to the improvement of shear strength.According to the shear strength,they can be arranged as follows:English garden wall bond>Header bond>English bond>Flemish bond.For walls of different thicknesses,the replacement area ratio and wall thickness are mainly considered.The higher the replacement area ratio and the thicker the wall thickness,the greater the increase in shear strength.According to the test results,the shear strength of the specimen of 105mm thickness is the highest,the specimen of 340mm thickness is next,and the specimen of 225mm thickness is the smallest.The shear strength of wall varies depending on the thickness of the joints.The effect of improving the shear strength is the best when the joint thickness is 10mm.The specimens with different shear pressure ratios have different proportions of shear forces and different failure modes.The influence of the above factors should be fully considered in actual engineering.The failure process of the test specimens with different factors under the diagonal shear test has a certain similarity.The first crack of most test specimens appears in the middle of the test specimen.As the load increases,the cracks begin to develop,and finally a through crack is formed inside the test piece.Through the description and analysis of the test failure process,the influence of shear strength of masonry structure strengthened by mortar replacement method under various factors is obtained.Through summarizing the existing calculation methods of shear strength and failure criteria of masonry structure under the shear compression composite action,it is found that the average shear strength formula of masonry structure under shear compression composite action in the masonry structure design code is also applicable to the test piece of low strength clay composite mortar masonry,and the calculation value is partial to safety,8.4%higher than the test value.Therefore,the average value formula of masonry gauge is proposed for the test specimens of low-strength clay mixed mortar,and for the test specimens reinforced with replacement mortar,it is proposed to calculate the shear strength of masonry according to separate clay mixed mortar and replacement cement mortar respectively,and then stack them according to the proportion.The ANSYS finite element analysis was performed on the specimens before and after the mortar replacement.It was found that after the mortar replacement,the performance of the specimen replacement area was significantly changed,and the strength and stiffness were improved to a certain extent.At this time,the stress state of the mortars and bricks in the non-replacement area were changed,and the stress in the replacement area was significantly greater than that in the non-replacement area,so the stress transfer path of the specimens was significantly changed,which completely coincided with the test phenomenon before and after mortar replacement.The finite element analysis further provides a theoretical basis for strengthening the masonry structure with mortar replacement.