The Research Of Long-term Responses Calculate Method Of Steel-fine Recycled Concrete Aggregate Continuous Composite Slabs

The sealed condition of the concrete at the soffit of composite slabs caused by the steel decking forced the moisture of concrete to evaporate only from the top of the slab,which results in a non-uniform shrinkage strain distribution,hence an additional curvature,that significantly increases the long-term deflections of the slabs and the stresses in the steel decking.Furthermore,for continuous composite slabs,the non-uniform shrinkage also increases the bending moment at the negative bending moment region,and further increases the stresses in the reinforcement and the long-term crack width.The inclusion of coarse and fine recycled aggregates(CRA and FRA)increases the drying shrinkage while decreases the autogenous shrinkage strain of concrete,which enlarges the influence of the non-uniform shrinkage.However,the influence of the non-uniform shrinkage is not included in the current Chinese code.In this context,the research group established the equations for the calculation of the long-term deflections and stress in the steel decking through regression analysis based on the results from finite element models(FEM).Meanwhile,available models for the long-term crack width of concrete with CRA are established through pure regression using test data,which makes the application scope of the models limited to the experimental parameters.In addition,no models have been proposed for the long-term crack width of concrete made with FRA.Therefore,this study investigated the influence of the non-uniform shrinkage on the long-term behavior of steel-coarse/fine recycled aggregate concrete continuous slabs using FEM.(1)A non-uniform shrinkage model accounting for both the replacement ratios of CRA and FRA was established based on the previous non-uniform shrinkage test of the research group.Based on the proposed non-uniform shrinkage model and the FEM established by the research group,a new FEM was established accounting for the comprehensive influence of the cracking,creep,and the non-uniform shrinkage of concrete,and was validated using available experimental results.(2)A systematic parametric analysis was conducted on 4500 steel-FRA concrete continuous composite slabs to investigate the influence of the key parameters on the longterm deflections of the slabs,and the long-term stresses of the steel decking and the reinforcement.The considered parameters include the replacement ratios of CRA and FRA,the content of residual mortar of CRA,the water absorption ratios of CRA and FRA,the compressive strength of concrete,if the props are used,the span-depth ratios,the types of steel decking,the depth of steel decking,the reinforcement ratios of the distributed reinforcement,the reinforcement ratios of the negative bending moment reinforcement,the live load levels,and the relative humidity of the environment.The results show that the non-uniform shrinkage and the inclusion of CRA and FRA have significant influence on the long-term behaviors of composite slabs,and a compounding effect exists between the influences of CRA and FRA,which should be considered in the design.(3)Based on the results of the parametric analysis,and taking the influence of the non-uniform shrinkage as a load applied to the slab,the equations for the calculation of the long-term deflections,the long-term stresses in the steel decking and the negative bending moment reinforcement were theoretically derived.Furthermore,based on the analysis of extensive test data collected from literature,the equations were simplified for practical application by using the constant average values of key parameters.The proposed equations have simply form and good prediction accuracy with the average values of the ratio of calculated results to the predicted results using FEM varying between 0.981 and 1.008,and the coefficient of determination R2 of 0.802?0.970.(4)Based on the unified bonding-slip and non-slip theory,the coefficients accounting for the influence of CRA and FRA on the tensile strength,bonding strength,and the amplification factor of the long-term crack width were developed.Using the cross-section analysis method,an equation for the long-term maximum crack width of both reinforce concrete members and the steel-concrete composite slabs was established by calibrating the long-term crack width prediction model in the Chinese concrete code GB50010-2010.The equation has the ability of predicting well the long-term crack width of concrete with the average values of the ratio of calculated results to the tested results being 0.888,and the coefficient of determination R2 of 0.999.