Static Load Tests and Ultimate Load Bearing Capacity Calculation of Local External Joints of Concrete Box Girders with Steel Truss Webs
This study investigates the load bearing behaviors of the external joints of concrete box girders with steel truss webs(concrete top and bottom slabs and steel webs)under horizontal loads.Based on a design alternative of a double-track railway bridge,a 1∶3 scale model of the external joints with maximum axle forces was designed and prepared for static tests,which consisted of the concrete chords,square steel webs and gusset plates,and the original concrete slabs were simplified to be concrete chords.Multiple issues were analyzed,including the phenomena in the static test,failure mode,load-displacement curve as well as the stress distribution in the concrete chords,gusset plates and steel webs.Based on the effective width method,tearing surface method and the maximum strength criterion,the method to calculate the ultimate load bearing capacity of the external joint was proposed.It is shown that the fracture of gusset plates is the failure mode of the external joint specimen,the ultimate load bearing capacity is 5.71 times of the design loads,indicating that the load bearing capacity met the requirements.The stresses in the concrete chord gradually decreased along the loading direction,but increased downwards along the vertical direction.The stresses in the gusset plates changed from increase to decrease along the loading direction,and the exposed gusset plates are the key load bearing components.The weaker one,no matter it is the gusset plate or the steel web,dominates the ultimate load bearing capacity of the node.There is a 6%difference between the ultimate load bearing capacities calculated by the presented method and the test results.
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