Research On Early-age Cracks Of High-strength Mass Concrete In Steel Plate-Concrete Composite Shear Wall

The issue of cracks on the early-age mass concrete has been concerned by the engineering.In steel plate-concrete composite shear walls with mass concrete,the stress is generated by thermal deformation and shrinkage,and the differential of steel and concrete thermal dilation coefficient(TDC),the stress state is more complex than mass concrete.In this paper,experiments were performed on a high-rise building with concrete-steel plate shear wall for research,the temperature distribution and thermal stress were analyzed combining with theoretical method.Autogenous shrinkage,drying shrinkage and TDC were measured by monitoring the length of testing blocks.The concrete early-age temperature is mainly affecting by initial temperature,hydration temperature rise and environmental temperature.The actual early-time temperature distribution was calculated as the sum of concrete temperature under each factor,and compared with the measured temperature value,the accuracy of this calculation method.The WEIBULL statistics principle was applied for concrete damage analysis,combining with real-time concrete strain at each point,the damage coefficient of each point was calculated.Internal stress measured by shear principle represented the effective stress,the accuracy of the damage coefficient based on WEIBULL statistics theory was verified by comparing the measured stress with calculated stress.On this basis,the method was used for surface concrete stress analysis.Results show that internal concrete stress of composite shear wall does not reach the tensile strength,whereas surface concrete stress reaches the tensile strength and cracks occur,the result is fitted with the practical situation.Each reason leads to the concrete stress was analyzed,the rules of each factor was described.The internal concrete stress is mainly composed of self-restraint thermal stress,TDC differential stress and autogenous shrinkage stress,it can be concluded that the TDC differential stress and self-restraint thermal stress account for a high proportion of total stress;The surface concrete stress is composed of self-restraint thermal stress and total shrinkage stress,it can be concluded that the self-restraint stress always account for a high proportion,whereas shrinkage stress values are small but keep growing,tensile stress is improved by shrinkage stress.Some measures were proposed to reduce early-age concrete stress for each factor.