Research On Mechanical Performance And Crack Width Calculation Theory Of Steel-uhpc Lightweight Composite Deck Structures

The steel-UHPC lightweight composite deck which composed of orthotropic steel deck(OSD)and a thin reinforced UHPC layer through short studs is a novel bridge deck.The composite deck provides a new solution to alleviate the fatigue cracking issue in OSDs and the frequently reported damage issue of asphalt overlays.The steelUHPC lightweight composite deck is a novel structure with thin UHPC layer,dense arrangement of studs and reinforcement bars,small cover thickness,and thus the structural force characteristics become complicated.While the influences of key design parameters(i.e.,fiber types,cover thickness,stud spacing,reinforcement ratio,thickness of UHPC layer)on the transverse bending and longitudinal bending behavior of steel-UHPC lightweight composite deck structures are less studied,and the research on transverse bending fatigue performance is limited.At the same time,the crack width calculation theory of steel-UHPC lightweight composite deck structure considering the structural characteristics of steel-UHPC lightweight composite deck and the influence of main design parameters is lacking.Therefore,this dissertation focuses on the following five contents:(1)The effects of fiber contents and types on the properties of UHPC materials and the bending performance of steel-UHPC composite plates were investigated.Eight groups of material property tests including two fiber types(straight fiber,hybrid fiber)and four fiber contents(2%,2.5%,3%,3.5%)were carried out,and the influence of fiber types and fiber contents on basic material properties such as compressive strength,elastic modulus and flexural strength were obtained.On this basis,eight negative bending moment tests of steel-UHPC composite plates with different fiber types(straight hybrid fiber and end-hook hybrid fiber)were carried out.The influence of different hybrid fiber types on the bending behavior of steel-UHPC lightweight composite deck was revealed from the structural level.(2)The transversal bending behavior and longitudinal bending behavior of steelUHPC lightweight composite deck structure were revealed.In order to clarify the influences of key design parameters(i.e.,cover thickness,stud spacing,reinforcement ratio,thickness of UHPC layer)on the transversal bending behavior and longitudinal bending behavior of steel-UHPC lightweight composite deck structure,40 steel-UHPC composite plates and 8 steel-UHPC composite beams were investigated by negative bending tests,respectively.The failure modes,load-deflection curves,strain response,the characteristics of crack generation,propagation and distribution,slip between steel plate and UHPC layer,stress characteristics of reinforcement bars were obtained.According to the experimental phenomenon,the calculation method of cracking stress of steel-UHPC lightweight composite deck structure was proposed by linear elastic analysis instead of complex nonlinear analysis.The influences of key design parameters on cracking stress,ultimate bearing capacity and average crack spacing were discussed,and the sensitivity ranking of main design parameters to their influence was obtained.The calculation theory of ultimate bearing capacity of steel-UHPC composite structure was proposed.The calculated ultimate bearing capacity is in good agreement with the experimental measured values.It can be used in the design of steelUHPC lightweight composite deck structure.(3)Considering the characteristics of steel-UHPC lightweight composite deck structure and the influence of main design parameters,the stress calculation theory of steel-UHPC lightweight composite deck was proposed.In addition,the calculated values are compared with the experimental results of forty reinforced steel-UHPC composite plates and eight reinforced steel-UHPC composite beams and the results are in good agreement.It can be used to calculate the reinforcement stress of steel-UHPC lightweight composite deck structure.(4)The calculation theory of crack width of steel-UHPC lightweight composite deck structure considering the influence of main design parameters was proposed.Firstly,based on crack width calculation methods of code for design of concrete structures in China(GB50010-2010),technical specification for fiber reinforced concrete structures(CECS38:2004),model code for concrete structures(MC2010)and crack width calculation methods of reinforced UHPC,the applicability of these crack width calculation methods for steel-UHPC lightweight composite deck was verified.The results show that the calculated values obtained by these crack width calculation methods and experimental values are quite different,and the reasons are analyzed.According to the test results and the characteristics of steel-UHPC composite structure crack generation and development,based on the code(GB50010-2010),the formulas for calculating average crack spacing and non-uniform coefficient of steel strain were revised.A calculation model for crack width of steel-UHPC lightweight composite deck structure considering the influences of main design parameters was proposed and its applicability was verified.The results show that the crack width calculation method of steel-UHPC light composite bridge deck structure can accurately predict crack width.Moreover,the guarantee rate is more than 95%,thus,the crack width calculation theory can be used for the design of steel-UHPC lightweight composite deck structure.(5)The transverse bending fatigue behavior of steel-UHPC lightweight composite deck structure was tested and the feasibility of the steel-UHPC lightweight composite deck was evaluated.Firstly,based on the actual project-Humen Bridge,a local finite element analysis(FEA)model was established,and the maximum tensile stress of the UHPC layer and the stress reduction of the typical fatigue details of the orthotropic steel deck under the design load were obtained.Then the transverse bending fatigue test of steel-UHPC lightweight composite deck structure was carried out to study the transverse bending fatigue performance.Finally,the feasibility of the steel-UHPC lightweight composite deck was evaluated from the aspects of static performance and fatigue behavior.The results show that increasing the 60 mm UHPC layer can significantly reduce the stress amplitude of the typical fatigue details of the orthotropic steel deck,with a reduction of 44.8%-90%,and the risk of fatigue cracking of orthotropic steel deck is greatly reduced.Under the design stress amplitude,a crack appear with a crack width of 0.05 mm on the surface of UHPC af ter 66.12 million fatigue cycles,which far exceeding 10 million cycles of infinite fatigue life requirements,in addition,the stiffness of the specimens is basically not reduced.This indicates that the steel-UHPC lightweight composite deck has good transversal bending fatigue performance.According to the static test results of 48 steel-UHPC composite plates and 8 steel-UHPC composite beams and fatigue test results,the mechanical performances of the steel-UHPC lightweight composite deck structure with 45-60 mm UHPC layer can fully meet the design requirements,and the scheme is feasible.