Researches Of Performance-Based Open Floor Areas Overturn Issues For Multilayered Frame Structure

The article 3.4.6 of “Technical specification for concrete structures of tall buidling”(JGJ3-2010)makes the following rules: When the floor is relatively narrow,and there is a large concave and hole,the design should be considered in its adverse effects on the structure.The width of the effective floor should not be less than 50% of the floor width;the total area of opening in floor should not exceed 30% of the floor area;after the deduction of recess or hole,the minimum net width of the floor in any direction should not be less than 5m and the net width of the floor on each side should not be less than 2 m.While in the actual project,open floor areas overturn issues abound.The floor opening area and sizeis often beyond the norms of the provisions of the open floor.What is more,with the improvement of living standards,people’s requirements for the building’s form and function are higher and higher,so the phenomenon of open floor areas overrun is increasing.If the floor overruns,it may have an adverse impact on the structure and weaken the seismic performance of the structure.Frame structures of open floor overrun are rarely researched by domestic and foreign scholars,and elastic calculation analysis of floor is studied mainly.In this paper,performance-based seismic design method was adopted to research this issue,then simulate and analyze the structure of the floor with openings in various forms.PMCAD,SATWE,PMSAP and EPDA belonged to PKPM were used to model,elastic computational analysis under small earthquake,analysis on floor stress,elasto-plastic calculate and analysis respectively.At last,the calculation results are analyzed to find out the weak parts of the structure,and the seismic strengthening measures are taken to provide reference for the construction design of the floor with openings.The main processes of the study and the drawn conclusions are presented as follows:(1)Considering the different opening areas of the floor,five analytical models were established.Under the other conditions same,the effect of opening ratio on the aseismic behavior of the structure is studied by controlling the opening size of the first layer and increasing the opening area of the first layer.The results show that the bigger opening area of the slab is,the more disadvantageous the structure is.When the opening area is greater than 30%,the whole rigidity of the structure will be weakened.What is more,there will be some plastic hinges on the beams and columns and stress concentration will appear around the opening.But after taking the strengthening measures,the structure design can reach the expected performance objective.(2)When the opening areas and the other conditions are same,the analysis models were established respectively for the hole in the middle,the edge and the corner of the floor to study the influence of the opening location on the seismic performance of the structure.Studies show that the stiffness of the structure is weakened when the corner is opened.The researche results indicate: if the hole is opened in the corner of the floor,the structural rigidity will be weakened seriously and the plastic hinges will appear more on the beams and columns,but after taking the strengthening measures,the s tructure design can reach the expected performance objective;if the hole is opened in the middle of the floor,there will be a significant stress concentration on the floor.(3)When the opening areas and the other conditions are same,the analysis models were established respectively for the openings in the middle of the floor,two on the opposite side and the opposite corners of the floor,and the irregular L-shaped opening to research the influence of the opening form on the seismic performance of the structure.Studies show that the rigidity of the structure is weakened when the floor hasirregular L-shaped opening.The torsion effect of the structure whose two opposite corners of the floor were with openings was greatest.If two holes are opened in the middle of the floor,there will be a significant stress concentration on the floor.(4)When the floor opening area is same,the analysis models were established respectively for t he holes in the first layer,the middle layer,the top layer and the whole layers of the construction to study the influence of the opening in different floors on the seismic performance of the structure.The results show that openings are made on the whole layers,the rigidity in the short direction of the structure weaken greatly,and whole stress level of the floor is larger under medium earthquake.(5)Considering the size of the connection plate between the slabs,the analysis models were established respectively to research the influence of the connection plate size on the seismic performance of the structure.And the distance between the two holes was set respectively so that the connection plates between the two openings are formed in different sizes.Studies show that different sizes of connection plates have little influence on whole rigidity of structure,while stress concentration would happen on the floor when size of connection plates overrun.