Bending Behaviors Of Composite Bridge Deck System Composed Of OSD And Reinforced UHPC Layer

Orthotropic Steel Deck(OSD)bridges are inevitably plagued by two inherent issures,which are a costly wearing surface with short service lifetime and frequently observed fatigue cracks threatening structural safety in steel elements.To address those formidable challenges in the conventional OSDs,a simple and effective solution is to increase the stiffness of steel deck plate.By virtue of outstanding mechanical properties and durability of Ultra High Performance Concrete(UHPC),an innovative composite bridge deck system composed of OSD and reinforced UHPC layer is proposed for stiffening the flexible deck plate of OSD.The present studies focus on the proposed steelreindorecd UHPC composite bridge deck structure,and gradual deepening of theoretical and experimental analysis is developed in direct tensile properties and constitutive relationships of UHPC material,flexural behaviors of UHPC material and Twice Inverse Analysis Method(TIAM),direct tensile behaviors of reinforced UHPC members,structural responses of reinforced UHPC beams and bending behaviors of steel-reinforced UHPC composite bridge deck elements.The major contributions are provided as follows.(1)Tensile characteristics of strain hardening and multiple cracking are developed for UHPC material,and a two-stage tensile constitutive relationship is proposed to characterize the strain-hardening UHPC.Based on the state-ofart review for UHPC in tension,essential characteristics of UHPC material in direct tension are firstly described.The dissertation reviews and categorizes a variety of tensile test methods used by other researchers,and compares and analyzes the specimen shapes and test setups of direct tension tests available in published literature.A revised tensile test setup tailored to obtain reliable results with minimal special preparation effort is presented.For purpose of obtaining tensile properties of UHPCs,the experimental investigation considers two types of steel fibers,each in various volume fractions,and the respective influence on the tensile behaviors particularly for observedcracking stress and strain are discussed.Based on the test results,the tensile constitutive model consisting of a stress verus strain relationsip and a stress verus crack opening relationship is proposed for representing the tensile response of the material.(2)A point-by-point TIAM is proposed with intent to acquire the stressstrain relationship of UHPC material easily and accuately.For bending properties of UHPC material,simple determination of stress-strain curve with indirect tensile test method is intentionally analyized for strain-hardening UHPCs.On the base of virtual work principle,the present study comprehensively explores the effects of shear deformation and the nonlinear longitudinal distribution of curvature on the mid-span deflection of simple beam with four-point loading.The TIAM considering the influence of shear deformation and nonlinear distribution of curvature is then presented.Based on the measured force verus mid-span deflection responses of UHPC specimens with different casting directions,the corresponding tensile stressstrain curves are derived by TIAM.Finally,the effectiveness of determining stress-strain relationship through TIAM is evaluated by comparison with the direct tensile results.(3)Direct tensile behaviors of reinforced UHPC with steel fibers and reinforcing bars are investigated.First,based on the mechanics of fiber reinforced cementitious composites,objective advantages of reinforced UHPC with combined reinforcements are qualitatively analyzed for strengthening and toughening UHPC matrix.Considering the relatively high stress of UHPC layer in composite bridge decks in some cases of complicated mechanical and environmental situations,the requirement of strengthening UHPC material is targeted.Direct tension tests of reinforced UHPCs are orthogonally designed with fiber content and reinforcement ratio of steel bar,and then their effects on tensile behaviors of reinforced UHPCs are analyzed.The feasibility of partially substituting reinforcing bars for steel fibers in UHPC to achieve superior tensile behaviors is assessed by the tensile behaviors of UHPCs with combined reinforcements.Based on crack characteristics of reinforced UHPC specimens in tension,the formula of calculating crack width for reinforced UHPC is eventually proposed.(4)The structural behaviors of reinforced UHPC elements in bending are explored.According to the proposed constitutive model of strain-hardening UHPC,structural responses of plain UHPC beam and then reinforced UHPC element are analyzed and compared.Futher,a bending test of reinforced UHPC specimen is conducted by using simply-supported beam with four-point loading.Based on the test results,tensile behaviors of reinforced UHPC elements in bending are investigated.Last,the cracking characteristics of reinforced UHPC beam are discussed,and a revised formula for calculating crack width of reinforced UHPC in bending is presented.(5)The bending behaviors of composite bridge deck system composed of OSD and UHPC layer are investigated.Based on the differential equation and analytical solution of an idealized orthotropic plate when loaded normally to the plane of plate,the techniques to reduce the internal forces and local deformation for OSD are firstly analyzed.Then,the orthotropic steel-UHPC composite bridge deck is presented to stiffen traditional OSDs.According to the configuration of composite bridge deck,important factors that influence the global stiffness are discussed.The reinforcement ratio of steel bars in UHPC layer and geometrical height of steel beam are selected as the design parameters of composite deck specimens,and static bending tests are conducted to model the composite bridge decks loaded in longitudinal and lateral direction respectively.Based on the test results,the bending behaviors of composite bridge deck are analyzed.Finally,a formula applicable to calculating maximium crack width of UHPC layer in composite bridge deck is proposed,and it is verified by the measured results of static bending tests.