Experimental Study On The Seismic Performance Of Masonry Structure Building With Irregular Lengthwise Walls

China is a country with severe earthquake disaster.Although the concrete structure and steel structure buildings has been widely applied in China,but in residential buildings multi-storey masonry structure is still a considerable proportion,especially in the medium and small towns,multi-storey residential made of masonry structure are agreed by almost all the developers.With the increasing number of vehicles,the phenomenon of parking disorder and hard is becoming more and more serious in residential areas.At the same time,the problems of poor privacy,big noise,poor lighting and poor security exist in the underlying buildings,so more and more first storey are designed to garage,in order to solve the problem of poor living of the first storey and parking hard.In the design of the ground storey garage,in order to meet the requirements of the use of garage function,it is necessary to open a big hole on the vertical wall outside the bottom.Article 7.1.7 in the China's " code for seismic design of buildings " stipulates that the opening rate of vertical wall mustn't be too big,6 or 7 degrees should not exceed 55%,8 or 9 degrees should not be greater than 50%.The large opening at the bottom of the longitudinal wall will lead to uneven vertical rigidity of the structure and asymmetry of the plane rigidity,which belongs to the irregular building with plane layout.From the technical point of view,if the problem of uneven stiffness can be solved technically,it will be able to overcome the adverse effects of the opening of the longitudinal wall on the seismic performance of the structure.In this paper,a new method for seismic strengthening of masonry structures with irregular openings at the bottom of longitudinal walls is proposed.The equivalent stiffness method is based on the upper and lower wall lateral stiffness of the principle of equality,the reinforced concrete columns are arranged at the bottom of the outer wall on both sides of the big hole,and the cross-sectional dimensions of the columns are determined according to the equivalent lateral displacement stiffness requirements.In this paper,an experimental model is used to study the seismic performance of the irregular framestructure with the longitudinal wall arrangement of the equivalent frame column.The prototype test model of six storey residential building common masonry structure,from which a unit test analysis,design and production of large openings,designed 1: 4 outside the vertical wall of large openings,asymmetrical vertical wall layout irregular masonry structure housing model.Through the cyclic loading test of the scale model,get the longitudinal wall irregular arrangement of masonry structure damage morphology,structural stress distribution,structure under horizontal load,the horizontal displacement of each layer,and analyzes the longitudinal wall layout setting equivalent column irregular masonry structure stress mechanism,hysteretic curve,skeleton curve,ductility and energy dissipation performance,and put forward design suggestions on the design of concrete frame column and beam.The main conclusions are as follows:1.For the bottom of the vertical wall of the vertical wall of the vertical arrangement of irregular masonry structure of housing,by setting the equivalent frame and beam,to solve the vertical wall of the masonry structure on the adverse effects of seismic performance.2.The cross-sectional dimension of the concrete frame column can be calculated from the lateral stiffness of the upper wall according to the equal stiffness method.For the middle frame column,the lateral stiffness can be calculated by the upper and lower fixed connection;for the equivalent frame at the ends of the gable can be calculated by the upper hinge and the lower fixed connection.3.Equivalent frame column to bear the level of seismic force,according to their respective equivalent stiffness distribution of the total shear at the bottom of the earthquake.4.The masonry structure building with irregular lengthwise walls with equivalent frame column and the beam,by the level of seismic action,in the elastic phase before cracking,the layers of displacement is basically the same,the house does not exist to reverse the problem.When the horizontal load is relatively large,the walls of the second storey of serious damage,reduced stiffness,increased inter-layer displacement,a layer of frame column damaged,and a layer of wall damage than the two relatively light and just under the soft.With the increase of the load,due to the different degree of damage to the wall,the stiffness changes,the house will have a certain twist effect,but the test results not obvious.5.The longitudinal cracks in the longitudinal axis are mostly horizontal bending cracks and shear diagonal cracks.The horizontal bending cracks are mainly distributed on both sides of the structural column,the bottom of the window wall and the window wall and the window under the wall junction,the damage in the form of bend the stretch.Shear diagonal cracks are mainly distributed in the walls of the wall and the lower part of the window wall,the cracks for the presentation of "X" or "inverted character" of the diagonal cracks,the destruction of the form of shear damage.When the window wall width is relatively small,the window wall mostly horizontal cracks,when the window wall is relatively wide,mostly inclined cracks.The walls of the second storey damage is relatively heavy,the walls of the first storey is light,and frame column no failure.6.The cracks on both sides of the wall(on the gable)are mostly horizontal bending cracks,the horizontal bending cracks are mainly distributed in the bottom of each layer of the wall,the damage in the form of bending tension damage,it is shown that the model is subjected to horizontal seismic action and the masonry structure building will be subjected to the spatial structure.7.Under repeated loads,there is little difference between the upper and lower bending moment of the middle frame column,the reason is that both the slab and the upper wall have obvious restraint on the bottom column.When analyzing its internal force,it can be calculated according to the diagram of the the upper and lower fixed connection;For the side span frame column(the equivalent frame column at the gable),the bending moment at the lower part and the bending moment at the upper part are very small,which can be simplified as the calculation sketch of the bottom joint at the upper end of the column,and the internal forces are analyzed.8.The stress variation of four longitudinal bars in each structural column is basically the same(all force or compression),indicating that the constructional column acts as a part of the wall.9.Under horizontal load,the two storey wall has both shear and moment.When the wall produces horizontal or oblique cracks,the path of the upper load will change,the vertical load each wall to be directly transferred to the upper part of the frame column on the lintel,at the same time,the moment is not effect of wall node in horizontal loads and equivalent concreteframe column in the lintel,it will make the constructional column wall tension,local compression,equivalent concrete frame column side of the lintel by pressure produced by the bending moments,at this moment,the positive bending moment will be produced in the span of the beam,resulting stress lintel completely different with the general frame beam.Therefore,in the design of longitudinal reinforcement should be appropriate to increase the lintel.10.the hysteretic curve of the model accords with the main feature of the inverse S shape,In the end of the equivalent concrete frame column and frame beam(or ring beam)method of component framework can significantly improve the lateral stiffness of a layer.The asymmetric cracks produced under repeated loads can be found in the test model,and the cracks in the two layers are more serious and the damage is serious according to the asymmetry of the hysteretic curves.In each layer of wall,with the increase of horizontal displacement,the energy consumption of each layer wall increases,among which the two layer wall energy consumption increases the most,the energy consumption is the largest,and the two layer energy dissipation capacity is effectively played.Moreover,the ductility of the masonry structure houses is similar to that of the ordinary multistory masonry structures.