Study On Tensile Crack Behavior Of A Novel Steel-UHPC Composite Deck Structure

To solve the problems such as high self-weight of concrete deck and steel deck fatigue damage,a novel steel–UHPC(Ultra-High Performance Concrete)lightweight composite deck structure without welding of structural components was proposed in this paper.Compared with the steel deck,the novel deck structure has almost the same self-weight,but the construction cost is only half,and it has excellent fatigue resistance and low operation and maintence cost,which is expected to be the "second" choice of long-span bridge deck system.Since the upper UHPC of the composite bridge deck can be considered as axial tension in a safe approximation under both integral and local load,the crack resistance of the novel structure under axial tension was explored in this paper,and the calculation method was proposed to verify the feasibility of structural application.The following several studies were carried out in this paper:(1)Two steel-UHPC composite deck prefabricated members and two groups of deck transverse joint members(two in each group,including the original plan group and the optimization group)were made to carry out the axial tension test.The results showed that: The rolled section and thin UHPC layer worked cooperatively;During the cracking stage,the stress state of rolled section was eccentric tensile and the distribution of UHPC cracks were fine and dense.Two or three main cracks were localized on the UHPC layer after yielding.The cracks of the joint members appeared at the interface first,and the rest of the cracks were concentrated in the lower step area.The failure of the members were caused by the yielding of the internal anchoring steel bars cut from rolled section.The calculation showed that the cracking performance of the optimized group was better.(2)In order to calculate the crack width of section steel-UHPC composite deck structure,a simplified method for calculating the reinforcement stress at the cracked section of prefabricated member,joint interface and step under joint was proposed.The calculation formula of National addition to Eurocode 2 — Design of concrete structures : specific rules for Ultra-High Performance Fiber-Reinforced Concrete(UHPFRC)and the code for Technical Code for Application of Ultra High Performance Concrete(UHPC)for Highway Bridge and Culverts were used to check the crack width of members,and compared with the test results.(3)The influence of the initial eccentricity caused by load on the cracking behavior of the deck was simulated by ABAQUS and MATLAB.The results showed that with the increase of eccentricity,the initial cracking strain of the structure remains unchanged,but the nominal stress of the initial cracking increases,and the crack width is 9%～72% larger than that of the purely flexural member.The axial tension test results are safely used to control the eccentric tension stress of bridge deck.(4)Combined with the test results,the UHPC tensile performance of Second West River Bridge,which has adopted the novel deck system in this paper,was evaluated,and the feasibility of applying the novel deck system to the extra-large span bridge was further studied by taking a 1408 m extra-large span cable-stayed bridge as the engineering background.The results showed that when the novel deck system was applied to Second West River Bridge,the safety factor of UHPC was more than 2 times.The integral force and stiffness of extra-large span cable-stayed bridge was not affected by the replacement of steel deck system with novel deck system.The tensile performance of bridge deck UHPC met the requirements and effectively improves the economic rationality of the bridge.Therefore,there were no problems in the force and technical economy of the new bridge deck,and it was feasible to be applied to extra-large span bridge.