Influence Of Floor Opening On Seismic Performance Of Reinforced Concrete Frame Structures

Reinforced concrete frame structure can satisfy the needs of people for large utilization space,and the space layout is flexible,so it is one of the most widely used structural forms in China.With the continuous development of social science and technology,economy and culture,people began to pursue buildings with fashionable appearance and various internal functions.In order to meet the use function or appearance requirements of buildings,it is often necessary to make openings in the floor.Floor slab plays a very important role in the seismic performance of cast-in-place reinforced concrete frame structure.It is not only a significant load-bearing component but also a significant force transmitting component.Its role is to bear and transfer the vertical load.At the same time,the floor slab should have enough stiffness in its own plane,and transmit the horizontal load to the connected lateral force resisting component,so that all components can cooperate with each other and the structure can act as a whole.The partial opening of the floor slab will cause the deviation of the stiffness center and the mass center,which will cause the obvious torsion effect;it will also cause the weakening of stiffness of the floor slab in the plane,and the horizontal load cannot be evenly transmitted to all the vertical members in the whole plane,which will cause the stress concentration of the vertical members,and inevitably have a negative impact on the overall seismic performance of the structure.Therefore,it is necessary to study the seismic performance of the structure with floor openings.In this paper,the research status of floor stiffness is summarized,and the influence of various floor forms on the seismic performance of the structure is summarized.Based on a cast-in-place reinforced concrete frame structure of 6 floors in Taiyuan City,Shanxi Province,three groups of models are established.The first group of models all have openings in the second floor slab,with opening rates of 0,8.33%,16.67%,25% and 33.33% respectively.Using the finite element analysis software ETABS,the modal analysis,response spectrum analysis,static elastic-plastic pushover analysis and elastic-plastic time history analysis of the five models are carried out;In the second group of models,16.67% of openings are opened in the second floor slab,and the openings are located in the middle,side and corner respectively.Modal analysis,response spectrum analysis and static elastic-plastic pushover analysis are carried out for the four models with ETABS program;In the third group,the openings are opened in the top floor slab in the same form as the first group,and modal analysis and response spectrum analysis are carried out for the five models.The data are sorted,analyzed and compared.Combined with previous studies,the following conclusions are drawn:(1)opening on the second floor will weaken the lateral stiffness of structure.The larger the opening area is,the larger the weakening effect is.When the opening ratio is less than 16%,the elastic and elastic-plastic seismic performance of the structure is not significantly affected.The influence of top floor opening on lateral stiffness is not obvious.(2)The unsymmetrical floor opening will weaken the torsional stiffness of structure and cause the torsional effect.The most unfavorable position of the opening is at the corner,followed by the edge.When the opening position is unsymmetrical and the opening rate is more than 16%,the elastic-plastic seismic performance of structure will be greatly affected.It is necessary to comprehensively evaluate the rationality of the structure,strengthen the weak parts and improve the overall seismic performance.(3)The stress around the opening increases with the increase of the opening area,especially around the frame columns,and the larger the opening area is,the more the stress increases.The floor around the opening should be properly strengthened.(4)When the opening position is at the edge or the corner,independent beams will appear at the edge and corner which are not connected with floor slab.Such beams are the weak points of the structure and are easy to be damaged too early under earthquake,so they need to be strengthened.