Experimental Study For The Effect Of Shear Studs On The Confined Shrinkage Cracking Of High Strength Concrete In Steel-concrete Composite Beams

Steel-concrete composite bridge,due to the advantages of both steel and concrete bridge,not only has good mechanical properties,but also inherits the advantages of steel structure and concrete structure in construction performance,durability,economy and so on.It is suitable for the national conditions of China’s basic construction and has strong competitiveness in comprehensive benefits.Therefore it has been developed rapidly in the past 30 years.But at the same time,due to the difference in the properties of the two materials,the free deformation of either material will be constrained by the other material,which leads to the redistribution of stress inside the structure and the additional deformation of the structure.The early shrinkage of concrete is an inherent characteristic of concrete,and the development of constrained shrinkage may cause cracking of bridge deck,which will affect the safety and durability of the structure.In order to solve this problem,a series of experimental analysis of concrete shrinkage under the constraint of shear studs was carried out based on a kind of high strength concrete with small early shrinkage,so as to provide some reference for the control of early cracking risk of steel-concrete composite beams.The main work and conclusions of this thesis are as follows:(1)Based on the concrete specimens with reinforcement in the center of the section,a theoretical model of confined shrinkage of concrete with embedded studs was established,the theoretical relationship between total constrained shrinkage and free shrinkage was deduced,and the theoretical calculation formula was established.The results show that the constrained shrinkage deformation increases with the increase of the free shrinkage of plain concrete.At the same time,the larger the elastic modulus of steel and concrete is,the greater the constraint effect will be,and the smaller the constraint shrinkage will be.Moreover,the higher the height,the larger the diameter and the smaller the spacing of the studs,the greater the limiting effect of the studs on the concrete deformation and the decrease of the constrained shrinkage.Finally,based on the age-adjusted effective modulus method,the shrinkage model of concrete slab with studs was modified.(2)The constrained shrinkage law of concrete slab under the influence of studs related factors was investigated through experiments.The results show that the studs can inhibit the shrinkage and deformation of concrete obviously,and this inhibition effect can’t change the shrinkage law of concrete itself with age.By comparing the restraining degrees of each group of specimens,it can be seen that the restraining effect of studs is usually larger in the early stage and presents a large fluctuation.With the increase of age,the restraining degrees gradually stabilize in a certain range.Through orthogonal analysis,it can be seen that the larger the diameter,the higher the height and the smaller the spacing of the studs,the greater the constraint effect of the studs on the concrete shrinkage.Finally,the calculated results of the established constraint shrinkage formula were compared with the test data.The results show that the calculated results of the formula are in good agreement with the measured data,which can provide some reference for the prediction of the constraint shrinkage of the internal studs.(3)On the basis of the test,finite element simulation of the constrained shrinkage of concrete slab with studs was carried out by ABAQUS.The results show that the error between the shrinkage strain obtained by simulation and the measured value is small,which meets the engineering requirements.It was verified that this simulation method could accurately predict the constrained shrinkage of steel-concrete composite structures.At the same time,by analyzing the internal stress distribution of concrete,the constraint stress of studs for concrete shrinkage is large in local area,and it is easy to produce stress concentration.In addition,the concrete near studs produces big tensile stress,and the cracking trend is obvious,attention should be paid to in the project.