Experimental Investigation On Performance Of Double-tees And Connectors In Precast Parking Structures

Precast parking structures use scissor structural layout which allows parking lots arranged along the sides of ramps and cars to drive smoothly two-way in the middle of ramps.Based on first fabricated parking sturcture in China,mechanical behavior and design methods about double-tees utilized for parking structures were carried out.The investigation may provide theoretical support for precast prestressed concrete public building.Based on the requirement of parking or driving load for floors and ramps in parking structures,double-tees as horizontal compontent,composed of 15.2mm seven wire prestressing stands and steel mesh of HRB400 rebars,were designed and conducted by means of static experiments and FEM simulation to analyze the feasibility.Due to diaphragm holes weakening horizontal stifness,the diaphragm is controlled by horizontal connectors between double-tees.Connectors were designed and conducted by means of both monotonic and cylic reversing in-plane shear experiments and FEM simulation was used to analyze the feasibility.Firstly,Double-Tee beams with the span of 18 m or 24 m which were divided into untopped and pretopped were designed,conducted under statically three-point loads.Tests provide the process of crack and deflection propagating and flexural capacity.Tests results show that double-tees failed because of flexural deflection growing more quickly than the speed of load.Main cracks extended below the flange but no crushing of concrete was observed.Flexural capacity,cracks control,stiffness and ductility are improved as a result of pretopped deck.Through nonlinear analysis of double-tees based on discrete models,load-deflection relation was obtained which showed results similar to those of experiments.Meanwhile,flexural performance under uniform load and local load was simulated.Results show that double-tees designed meet the requirement of safety,cracks and deflection control for parking structures.Secondly,large-size precast members,for example,double-tees have obvious size effect on shear capacity.Calculation of double-tees obtained from current method derived from small-size member tests may be greater than test results,causing shear failure prior to flexural failure.Focused on the shear behavior of pretensioned double-tees,especially pretopped deck and size effect on crack,load-point deflection curve and shear capacity,full-size 18 m and 24 m double-tees were conducted to fail in two different groups which were respectively shear tension failure and breakdown of bond between strands and concrete.Cross-sectional size and presressing have significant effect on crack development and shear capacity.Shear behavior with the shear aspect ratio ranging from 1 to 9 was analyzed.Combined with experimental results,it was found that shear capacity met the requirement of possible concentrated load near the end of double-tees.Thirdly,based on the requirement of horizontal connection for untopped and pretopped double-tees in parking structures,two new types of connectors which are named post channel and bolt respectively were designed.And the connector named post plate and bar were also ameliorated.Five types of connectors were manufactured and loaded with monotonic in-plane shear.According to experiments,shear capacity was obtained and the relation between load and deformation was analyzed.Meanwhile,stiffness calculation was definited.Failure mode of five types of connectors was weld fracture,anchor pullout,bolt cut,plate pullout and concrete spalling respectively.FEM analysis was used to simulate connectors,and the optimization suggestions were proposed.Lastly,five types of connectors were conducted under cylic reversing in-plane shear.Also one connector was selected for loading under cylic shear with out-plane load to simulate the effect of driving or parking on the behavior of the connector.According to test results,shear capacity,hysteretic curve,and full process of loading,splitting and failing were obtained.Failure mode was consistent under different loading conditions.Out-plane force has significant effect on shear capacity,stiffness and deformation.Mechanism of different types of connectors was analyzed,on the basis of experimental test and FEM simulation.