Theoretical And Experimental Investigation On Mechanical Performance Of Top Slabs In Concrete Box Girder

Reactive powder concrete with excellent performance was applied to concrete box girder structure,not only can reduce weight,increase spanning capacity,at the same time also can improve the durability of the structure,thus get the wide attention of scholars both at home and abroad.When making the design of RPC box girder,because of its high qualities,the thickness of top slabs can be designed very thin.Then under the partial wheel load,the possibility of punching shear of top slabs in the box girder will increase,so it is a problem worth further study for the punching shear of RPC slabs.For the transverse force of top slabs on ordinary concrete box girder,the present study mainly focused on elastic analysis and nonlinear numerical simulation analysis,and the plastic analysis is relatively small,especially lack of corresponding experimental study.Based on this,the punching shear behavior of RPC box girder slabs and the transverse force of top slabs on ordinary concrete box girder in the plastic stage are studied in this paper.Main points are listed as follows:(1)The influences of thickness,loading area,loading location,RPC strength and reinforcement ratio on the punching shear capacity of RPC slabs were considered,then 11 simply supported slabs were made for the punching shear failure test.And detailed test results of each RPC slab were given,including the ultimate load,displacement,strain and fracture morphology,etc.Except specimen S10,the failure modes of all the rest RPC slabs were punching shear failure.Finally on the basis of experimental results,the influence of each parameter on punching shear capacity of RPC slabs was discussed in detail.(2)The calculation formula of punching shear capacity in the related structure design specification of America,Europe and China has been sorted out.The punching shear capacities of 10 RPC slabs with punching failure were calculated,and then the calculation results and the test results were compared in this paper.Results show that the there is a certain degree of deviation between the calculated value of all national standard with the test value.Recommended calculation formula of punching shear capacity was proposed on the basis of relevant structural design codes in China.The calculated results by the recommended formula agree well with the test value.(3)Two reinforced concrete box girder models were fabricated and then tested under a local load that applied on the top slabs,and then the test results were monitored,which include the ultimate load,the load-displacement curve,the fracture distribution and the transverse effective width at plastic stage.A plastic analysis model for a top slab in a box girder was then developed by the results of two slabs.Based on the limit analysis using plastic yield line theory,a formula for predicting the ultimate resistant-capacity and evaluating the plastic transverse effective width of a top slab was proposed.Finally the test results were compared with the value of those bridge codes in China and America.The research results indicated that the limit equilibrium method can predict the ultimate resistant-capacity and the plastic transverse effective width of a top slab accurately.The transverse mechanical characteristics of the top slab in reinforced concrete box girders could be carved by the simplified failure mode at plastic stage.