Research On Trial Design Of Invertible T-shaped Voided Slab Bridge

Assembly voided slab bridge is a popular bridge type in China,precast voided slab is connected by the hinge joint or welded steel plate.In a practical application,hinge joint is became the weakest part of prefabricated voided slab bridges.Crack load of hinge joint is lower than that of voided slab,and once hinge joint cracks,straight crack of the interface appears immediately and then single slab bearing phenomenon appears.In order to avoid the diseases of hinge joint of hinged voided slab bridge,this study analyzed mechanical behavior of a new kind of voided slab bridge,which called invertible T-shaped voided slab bridge.With the aim of providing the basis for popularization and application of the new type bridge,conducted the full-scale model experiment and finite element analysis for analyzing the mechanical behavior and fail mode,and discussed the design calculation methods.Main work and main conclusions are listed as follows:Firstly,based on the hinged voided slab bridge with similar span of highway bridge standard drawing that issued by the Ministry of Communication,the cross section structure was conducted.It adopted respectively transverse load distribution of assembly beam bridge and the load distribution width of integral cast in-situ slab bridge to calculate the structural internal force.Conducted a trial design of an invertible T-shaped voided with the span of 8m,which structural type is simply-supported reinforced concrete beam bridge,and provided the detail design drawing.Secondly,on the basis of the trial design of invertible T-shaped voided slab bridge,L-shaped steel plate and ?-shaped steel plate was added.Selected three middle slabs to design and make the full-scale experimental model,the full-scale experiment was loaded under the simulated vehicle load.It shows that:when the external load reached 55kN,the bottom part of mid-span section of three slabs appeared transverse cracks;when the external load reached 70kN(1 times of vehicle load of highway class I),the maximal crack width of the bottom part of mid-span section is 0.13mm,which is lower than the specification limit of 0.2mm;when the external load reached 370kN,the deflection of three slabs grew rapidly,and the tensile reinforcement and steel plate reached yield strength;During the load test,the transverse distribution of deflection of three slabs was similar,the transmission capacity of transverse load didn't decrease,it showed the bridge had good integrity.Thirdly,ABAQUS was used to establish finite element model(FEM)of invertible T-shaped voided slab bridge.The deflection,the strain and the cracks results from finite element analysis,the results were compared to the experiment results and verified.The failure mode of the weak part of invertible T-shaped voided slab bridge was analyzed.The results show that when the external load reached 90kN,the cracks extend to the interface,and extend upward with the increasing load;However,as the interfaces occur cracks,the bonding stress of the interfaces don't over than the limit,it shows the interfaces don't occur failure.The weak part is the concrete of tensile area above ?-shaped steel plate;When the external load reaches 90kN,it appears cracks earlier than the other concrete area of the same height and extends vertical upward with the load increasing;When the external load reaches 165kN,the cracks extend to the neutral axis.Fourthly,the experiment and FEM were used to analyze and obtain the transverse load distribution factor,which compared to the results of the shear key deck method,the method with transversely rigid joint between beams and G-M method.It shows that G-M method applies to calculate the transverse load distribution factor of invertible T-shaped voided slab bridge;Meanwhile,suggested using "beam grid method" to establish the bar system FEM for the design calculation of invertible T-shaped voided slab bridge;And given the design proposals of stress checking of construction stage,the setting of camber and the checking of the weak part.