Study On Mechanical Behavior Of UHPC Bridge Deck Slab Reinforced With FRP Bars

With the increasing demand of the construction of bridge engineering,in order to extend the longevity of bridge decks,accelerate the construction of bridge decks and reduce the self-weight of bridge deck,it is necessary to develop bridge decks with high durability and low self-weight.Fiber Reinforced Polymer(FRP)and Ultra-high Performance Concrete(UHPC)possess excellent properties and durability.In this study,the bridge deck slabs by using FRP bars and UHPC was adopted as the research object,and the tests of UHPC slabs reinforced with FRP bars(FRP-UHPC slabs)under concentrated load and flexural load were carried out respectively.The failure modes,stiffness,loading capacity,crack development and strain characteristics of FRP-UHPC slabs were investigated.In addition,the flexural ductility of FRP-UHPC members was analyzed emphatically,and a modified Newhook model in ductility calculation was proposed.The main research and results in this study is as follows:(1)An innovative FRP-UHPC short-ribbed bridge deck slab,with low self-weight and high structural performance,was proposed in this study.With the aim to simplify the specimen design and the test setup,finite element analysis with ABAQUS software was conducted first,to determine the deformation,stress and strain state of the deck under concentrated load.According to the finite element simulation results,four test slabs were designed with the parameters of loading area,plate thickness and reinforcement type(steel/FRP).The test of one-way UHPC slab under concentrated load was performed to analyze the crack development,failure modes,stiffness,strain characteristics and ductility.The punching calculation method in the existing normal concrete(NC)slab reinforced with FRP bars(FRP-NC slabs)was adopted to evaluate the loading capacity of the one-way FRP-UHPC slabs under concentrated load.(2)Seven GFRP-UHPC slabs with different GFRP bars diameter(spacing),the reinforcement ratios,the slab thickness and the UHPC cover were fabricated and tested.The flexural behavior,failure modes,stiffness,crack development and strain characteristics of GFRP-UHPC slabs are analyzed.To predict the deformability behavior and flexural capacity of GFRP-UHPC slabs,the section analysis model was established by using MATLAB program on the basis of considering the compression and tension properties of UHPC and the linear elastic characteristics of FRP bars.The moment-curvature relationship of the whole loading process up to failure for GFRP-UHPC slabs was analyzed.(3)Using the moment-curvature curves obtained from the cross section analysis,a MATLAB program was established based on the conjugate beam method to calculate the load-deflection curves of the GFRP-UHPC slabs.According to the characteristic points on the moment-curvature and the load-deflection curves,the ductility factors of FRP-UHPC members were calculated.Due to the lack of ductility model for FRP-UHPC members,the applicability of existing ductility models for FRP-NC members was discussed at first,and modification of these models was then proposed by considering the outstanding mechanical properties of UHPC.Then,this model was adopted to analyze the influence of key material parameters,including the compressive strength of UHPC,peak compressive strain of UHPC,initial crack strength of UHPC and the type of FRP bars,on the flexural ductility of FRP-UHPC members.