Experimental Study On The Bidirectional Mechanical Behavior Of UHPC Box-girder Bridge Deck With Dense Diaphragms

A new super-long-span UHPC(Ultra High Performance Concrete, UHPC) continuous box-girder bridge, with longitudinal one-way prestress, has an organic combination of ultra-high-performance concrete, thin-walled box girder with dense diaphragms and external prestressed force. The girder bridge of this structure system has outstanding performance, which is expected to solve the concrete crack and excess deflection on traditional prestressed concrete box girder bridges. Moreover it will realize the exceeding of the economy span of prestressed concrete continuous girder bridges to 400 m.The setting of compact diaphragms helps to solve the problems thin-walled UHPC box girder facing such as the overall stability, cross section distortion and the problem of web plate shear. At the same time, compared with traditional concrete box girder bridges, it changes the local mechanical property of the box girder bridge panel under automobile loads. In traditional concrete box girder bridges, transverse diaphragm is usually set at the top of the pier and the middle of the span, which leads to the bridge deck wheel loads only being transfered to the web by deck; however, in UHPC box girder bridges, the compact longitudinal transverse diaphragms together with the box girder web plates support the bridge decks under wheel loads, so the wheel loads on bridge deck are transferred along vertical and horizontal direction, which leads to its mechanical properties and force transmission mechanism being changed when compared with traditional concrete box girder bridge panel structure.This research is conducted in such two aspects,the mechanical properties of UHPC box girder bridge panel with a dense transverse diaphragm structure and its force transmission mechanism:(1) In order to get the change rule of the UHPC box girder bridge decking improvement, the qualitative analysis on the performance and characteristics of internal force distribution of UHPC box girder bridge panel is made, through the static model test and finite element numerical simulation;at the same time, the two-way bearing load effective distribution width is studied, to form a reference for further theoretical analysis. The results show that UHPC box-girder bridge deck is still in the linear elastic stage when it is under 5.5 times of the design local wheel loads under test conditions; and the UHPC box-girder bridge deck with dense diaphragms behaves as a bidirectional load transferring component, with a main transferring orientation of longitudinal direction; diaphragm plate has certain constraints to the load effective distribution width of strip at transverse the bridge.(2) The load distribution and internal forces are calculated at the bridge deck bidirectional transmission mode of power through theoretical deduction and calculation as the principle of equivalent simply supported span based on the test and finite element analysis. Results show that during linear elastic stage and subjected to the most unfavorable load, the bridge’s part with sparse diaphragms has a load aspect ratio of 1: 0.64, and the part with dense diaphragms has a value of 1: 0.53, proving that the load distribution on the bridge deck tends to be uniform and the load-carrying efficiency of bridge deck is improved; in addition, the moment in the top of the diaphragm is specified as the control value of negative moment, and the calculation method in the current specifications is not suitable to be used in this research for its theoretical source.