Experimental Study On Flange Connectors Of Double-tees In Precast Parking Structures

Parking structures adopt scissor layout which allow parking lots arranged along the sides of ramps and it drive smoothly two-way in the middle of ramps.Precast prestressed double-tees are the main components of floors and ramps in parking structures.Precast double-tee diaphragm is a kind of totally precast assembly PC floor system,with simple construction,fast erection speed and desirable technical economy benefit.But the special mechanical characters of double-tees make it unpractical to design double-tee diaphragm with current design codes,which pose a great challenge to the application of this new-type floor system,and traditional flange-to-flange connectors have some disadvantages,such as poor deformation capacity and anchor failure,which pose a great challenge to the application of this precast double-tee floor system.In the present study,the in-plane mechanical property of new-type flange-to-flange connectors was studied through experimental and theoretical analysis method,and shear capacity design methods of these connectors were proposed on the basis of aforementioned research.In this paper,A total of nine specimens,including three types of connectors,were designed and fabricated by considering three parameters:(1)different flange-type connectors;(2)the depth of the double-tee flanges hf,and(3)the loading pattern.The combination of test and simulation methods was used to study the connectors' shear capacity under a variety of loading conditions with both monotonic and cyclic reversing in-plane shear,and the failure modes,load-deformation relationship,skeleton curve,stiffness,ductility,bearing capacity and strain of the three types of mechanical connectors were obtained,the advantages of the new connectors compared with the traditional ones are compared and analyzed.The results show that new connectors exhibited better deformation characteristics and full hysteresis loops with large energy dissipation compared with traditional ones,stiffness or ductility could also get improved in some cases.The stress level of all connectors is generally low,so the traditional calculation model may overestimate the shear capacity of the connectors.The pretopped slabs can effectively improve the strength and deformation capacity of the connectors,as well as providing each leg of the connector with additional anchorage beyond that provided through bond,thus preventing pullout of the legs.The data also shows that the ultimate strength and deformability of the connectors are barely influenced by the presence of an out-of-plane load.The mechanical property of three types of connectors were also studied by finite element analysis.The results of finite element analysis are in good agreement with thoseof experiment,the embedded steel plate,section steel,anchor bar and welded cover plate are not yielding,in addition,the stress level in the concrete compression zone is low,which will not be damaged before the anchor bar,becoming an important part of the shear capacity of the connectors.Based on the test and simulation results,the mechanism of connectors are analyzed.The truss model and shear-friction model commonly used in the analysis of connectors are modified,and the bearing capacity calculation formulas suitable for six kinds of connectors are proposed.The results show that the calculation results of the formula are in good agreement with the test results.