Design And Calculation Methods For Steel-Concrete Composite Bridge Deck Slabs

The steel-concrete composite（SCC）deck slab has gained quite an increasing popularity recently because it can achieve enough capacity with reduced thickness and enable cost-competitive and time-efficient construction.Existing studies paid little attention to the fatigue performance of SCC deck slabs,resulting in insufficient knowledge of the fatigue mechanism and related calculation methods.Besides,for low shear span-depth ratios or when the flexure and longitudinal shear capacities are greatly enhanced,the design of the SCC deck slab is likely governed by vertical shear,highlighting the need for a calculation method of vertical shear capacity.Furthermore,SCC deck slabs are mainly applied on steel-concrete composite bridges,in which the sectional moments of SCC deck slabs depend on the constraints of the steel girders.However,no specific calculation method has been proposed.Consequently,by employing experiments,finite element analysis,and theoretical analysis,this paper investigates the fatigue mechanism,calculation method of vertical shear capacity,and sectional moments of SCC deck slabs when applied in composite bridges,as well as the design method.Specifically,the following attempts have been made:（1）Two full-scale specimens were tested under fatigue-induced sagging moments.The failure process is discussed,as well as the deformation performance,steel-concrete relative slips,strain results,and effects of the load amplitude and loading sequence.Further,a finite element model is established and verified,through which the multiaxial stress state of the welding part between the steel plate and perforated rib is revealed.Following that,the critical plane approach is used to estimate the crack initiation position based on the SWT parameter,and the effects of geometric parameters and the shear-span ratio are clarified using a parametric analysis.The influence lines of stresses in the welding part under moving vehicle loads are then numerically calculated and the crack initiation position is evaluated.Finally,by employing section analysis,the calculation methods of nominal stress and shear stress of the welding part are proposed and validated,and the relations between the equivalent stress amplitude and fatigue life are established.（2）Two full-size slab specimens reinforced by different steel fibers（i.e.mill-cut steel fibers（MF）and corrugated steel fibers（CF））were tested under fatigue-induced hogging moments.The failure mode,steel-concrete composite action,and crack behavior are measured and discussed.Both finite element and theoretical analysis are employed,through which the influence mechanisms of SFRC’s strength parameters and slab’s structural parameters on the stress amplitude of rebar in tension are clarified.Later,several simplifications are introduced to the section analysis of SFRC section and the practical calculation method of stress amplitude of rebar is developed and validated.（3）The vertical shear capacity of SCC deck slab V_u is computed as the summation of the contributions of concrete layer(V_c,u)and steel members(V_s,u).V_c,u is treated as the product of the shear capacity of an equivalent reinforced concrete member without web reinforcement and a coefficient that reflects the effects of steel ribs.The formula of V_s,u is developed based on the force equilibrium conditions between the concrete layer and steel members and the section analysis considering the steel-concrete slips.Later,an iterative calculation method is proposed and verified against experiments and finite element（FE）models established via validated simulation techniques.Lastly,an extensive parametric analysis is implemented using the iterative method,from which a simplified calculation method is proposed and proved.（4）By establishing and analyzing the FE models,the distribution law of sectional moments of SCC deck slabs applied in twin-girder steel-concrete composite bridges is investigated.Then,for predicting the sectional-moment distribution coefficients,a simplified method is proposed based on a frame model.A parametric analysis is performed to investigate the effects of geometric parameters and the cracking of concrete slabs on the transverse moment distribution coefficients.The difference between the sectional-moment distributions of SCC deck slabs and concrete deck slabs is discussed,and the superiority of the calculation method over existing codes is demonstrated.（5）On the basis of the above works and related codes,a comprehensive design method for SCC deck slabs are summarized,which covers structural analysis,and the check of important design indices（such as capacity,stress,deflection）under the ultimate stage,serviceability stage,and construction period.Besides,the requirements and suggestions for the dimension,material,design of the steel-concrete interface,construction,and durability are also provided.