| Because of the large self-weight,traditional ordinary concrete decks cause the limited span capacity of long-span composite girder bridges.Besides,due to the inferior tensile property of ordinary concrete,the traditional ordinary concrete decks have a risk on cracking attributed to the shrinkage and heavy wheel loads.Taking advantage of the excellent mechanical properties and durability of ultra-high performance concrete(UHPC),this paper presents two types of lightweight UHPC bridge deck structures,including steel bar reinforced UHPC flat panels and steel plate reinforced UHPC deck panel with longitudinal ribs.In doing so,the average thickness of concrete decks could be reduced from 28 cm to 13-17 cm.Deck panels as important bridge menbers are always suffering frequent wheel loads directly,thus,the flexural performance of the deck panels becomes the priority control index for design.Several studies were conducted:(1)The static flexural performance of the reinforced UHPC slab structure with an average thickness of 16 cm or 17 cm was studied.First,the effect of adding small coarse aggregates on the basic mechanical properties and self-shrinkage property of conventional UHPC was studied by contrast tests.Then,the UHPC deck specimens with and without small coarse aggregates were fabricated an d tested under a four-point bending pattern.The static flexural test results showed that the nominal cracking strength of the specimens was 13.8-23.2MPa,subsequently,a long-lasting development stage happened to the specimens with the propagation of mult iple cracks and a stable post-cracking stiffness.Finally,the failure mode of the specimens was characterized by the yield of the bottom rebar accompanied by the widening of cracks in UHPC.Based on the test results including the load-deflection behavior,strain response and crack development characteristics,the design and calculation theor ies on the cracking strength,flexural stiffness,flexural bearing capacity and crack width were proposed for the reinforced UHPC slab structure.It was verified that the conventional UHPC deck slabs owned a better static flexural performance than the UHPC deck slabs with small coarse aggregates did.(2)The fatigue flexural performance of the reinforced UHPC slab structure was studied.Several constant-amplitude flexural fatigue tests were conducted based on the design requirements of actual bridge projects.The fatigue flexural test results showed that after experiencing the design fatigue load for 2 or 9 million cycles,the fatigue specimens were not failed by the internal steel bar rupture,instead,they only had some microcracks with a width range of 0.02-0.07 mm.In addition,the crack development,stiffness degeneration,residual flexural capacity and nominal stress S-N curves in the fatigue specimens were studied.Finally,it was verified that the fatigue flexural performance was mainly affected by the cracking in UHPC,and the fatigue damage will not pose a serious threat to the flexural performance of the reinforced UHPC slab structure.(3)A low-profile steel plate reinforced UHPC deck panel only with longitudinal ribs is proposed,and its flexural performance was investigated.The bottoms of the longitudinal ribs were reinforced with 8 mm-thick steel plates as an alternative to traditional flexural reinforcement,and 180 mm-height head studs were welded to the steel plates as shear reinforcement through extending the stud’s head into the top UHPC slab,which could guarantee the composite action between the steel plates and UHPC.The four-point bending test results showed that the nominal cracking strength of the steel plate reinforced UHPC deck specimen was 20.4-23.3MPa,subsequently,a longlasting development stage happened to the specimens with the propagation of multiple cracks.The crack development was concentrated on the ribs.Finally,the failure mode of the specimens was characterized by the yield of the steel plate accompanied by the widening of cracks in the UHPC rib.According to the test results including the loaddeflection behavior,strain response,crack development characteristics,the calculation method of the crack width based on the bond-slip model was studied,and design theory on the flexural bearing capacity was also studied for the steel plate reinforced UHPC deck panel with ribs.It was demonstrated that compared with the above steel bar reinforced UHPC slab structures,this novel steel plate reinforced UHPC deck panels had more superior crack resistance with less self-weights.(4)The steel fiber orientation distribution in the specimens was revealed,and a multiscale finite element(FE)method for predicting the post-cracking flexural behavior in UHPC deck structures is present.By using an X-ray computed tomography(CT)imaging system,the meso-structural characteristics in the UHPC,especially the steel fiber orientation distribution,were observed.The UHPC was modeled as a heterogeneous composite medium made of matrix and steel fibers usin g a reduced order multiscale approach,and the flexural performance of the deck specimens was simulated.By comparison with a single-scale FE method using conventional homogeneous isotropic medium,the multiscale approach has been shown to be considerably more accurate in predicting the post-cracking flexural behavior of the reinforced UHPC deck structures.(5)Applied research was introduced about the first application of the steel plate reinforced UHPC deck panel with ribs to the Qinglong Island Bridge built in 2020.The global and local FE models were established for the above bridge,and the structural performances in the deck under service loads were analyzed theoretically,including the longitudinal and transverse structural performance s as well as the performance of the joint structures.Via a series of full-scale model tests,the several structural performances of the deck specimens were studied experimentally,inclu ding the longitudinal and transverse flexural performance s as well as the shrinkage and flexural performances in the T-shaped joint structure.By comparison between the analysis and experimental results,the technical feasibility of applying the steel plat e reinforced UHPC deck panel on the Qinglong Island Bridge was comprehensively verified. |
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