Cracking Mechanism And Anti-Crack Design Of Large-Span Heavy Duty Urban Transportation Hub Slab

With the rapid development of social economy,China's cities are facing increasing traffic pressure.The new urban public transport hub has the characteristics of large capacity,fast transfer and small floor space,which can effectively alleviate the traffic pressure of large cities.However,due to the limitations of existing design methods and the lack of understanding,the cracking of the large-span bus hub slab occurred under the load of heavy-duty vehicles.In this paper,the cracking problem of the large-span heavy-duty public transportation hub is carried out,and the dynamic amplification factor of the slab is measured,the crack resistance and bearing capacity test of the slab,the equivalent uniform live load value method of the large-span heavy-duty floor slab,the slab anti-crack design and other research are carried out.The main research work and conclusions are as follows:(1)The research on the dynamic amplification factor of the large-span heavy-duty public transport hub structure is carried out.The analysis shows that under the action of heavy-duty public transport vehicles,the dynamic effects of the response and displacement of the hub structure are more significant;With increase of speed of bus,the dynamic response and the dynamic amplification factor increases first and then become smaller.Based on the results of the measured data,it is recommended to use strain as the calculation index of the dynamic amplification factor,and the dynamic amplification factor is greater than 2.5;the dynamic amplification factor calculated according to domestic and foreign specifications is too small to accurately reflect the dynamic effects of the vehicle response of this type of structural system.(2)Based on the prototype structure,the slab specimens with scales were designed,and the modal test,crack resistance and bearing capacity test and numerical simulation of the slab were carried out.The results show that the vibration frequency of the layered floor is higher than the overall slab frequency,and the damping ratio is nearly same.After cracking,the stiffness of the slab becomes smaller,the integrity is worse,the natural frequency is reduced,the damping ratio is increased by more than 60%,and the energy consumption is enhanced.Under the linear loading,The cracking load and the ultimate bearing capacity of the layered load and the overall slab are not much different,but the failure mode of the layered slab is the separation fracture failure of the layer,and the failure mode of the integral slab is the ultimate compressive strain failure of the concrete compression zone;under the cyclic incremental loading The damage pattern of the floor is the same as the linear loading.The bearing capacity,stiffness degradation and mechanical performance of the integral slab are better than the stratified floor slab.The solid model can effectively simulate the cracking load,initialstiffness and bearing capacity of the slab.At the same time,the contact iterative algorithm can be used to simulate the performance of the stratified floor.(3)Based on the standard method of slab live load,the revised equivalent uniform live load value method is proposed for the large-span heavy-duty urban transportation hub load,and the engineering verification is carried out.The analysis results show that the equivalent uniform load obtained by considering the revised equation of the aspect ratio of the slab is basically consistent with the structural response under the actual vehicle load and is safe.On this basis,through the verification analysis of actual engineering,it shows that the revised equation can be applied to the calculation of equivalent uniform live load in different areas of the floor.(4)Using numerical simulation analysis,the key problems of the design method of the slab are discussed,the existing theoretical equation are verified,and the anti-crack design method and engineering measures of the floor slab are proposed.The analysis shows that with the increase of the thickness of the slab,the cracking load and bearing capacity of the slab are greatly improved;the strength of the surface concrete is increased,and the bearing capacity of the floor slab is slightly increased;the ratio of the surface layer to the cracking load and bearing capacity of the slab is relatively small.The existing cracking load and ultimate bearing capacity theoretical equation can accurately calculate the cracking load and bearing capacity of the layered and integral slab.On this basis,the anti-crack measures and design methods for the large-span heavy-duty public transportation hub are proposed,which provide the basis for the design of the large-span heavy-duty public transportation hub.