Application Study Of Cast-in-situ Concrete Hollow Floor

Cast-in-situ hollow floor is a new type of long-span structure system, which can reduce the self-weight of the structure by embedding permanent cavities in thick plank. It is applicable to buildings with greater loads and span. It can economize the storey height; reduce the total cost of the project. So it is a type of floor with good application function and economy benefit. Cast-in-situ hollow floor has been applied to build great multiple-bay structures which are continuously cast without construction joints. The pilot projects indicate that the structure has good crack resistance.The key problem of hollow floor is the law of stress distribution under loads action. Presently, most researches on cast-in-situ hollow floor are fewness experiments and simple numerical simulation. People can know the mechanics capability of the hollow floor to a certain extent through these researches, but it is not very clear yet. The paper utilizes FEM software to analyze the hollow floor accurately basing the conclusions of other research departments; it reveals the laws of stress distribution, shear stress distribution in the section and laws of deformation of the cast-in-situ hollow floor.The key problem of super-long concrete structure is how to control the crack under non-load factors. The main non-load factors are: thermal stress caused by temperature rise due to hydration heat, shrinkage of concrete and the thermal stress due to variation of ambient temperature. The paper studied the hydration at early ages, shrinkage and the strain of steel bar through experiments. It utilized FEM software to simulate the temperature field of cast-in-situ hollow floor and compared the computation results with the experiment results. It indicated that it was feasible to analyze the temperature field through FEM. At last, the paper summarized the laws of distribution of the temperature field and the main factors influencing the temperature rise due to hydration and put forward some measures to control the temperature field of concrete hollow floor and minimize the inside and outside temperature difference; summarized the law of concrete shrinkage and put forward some advice on material, design and construction aiming at the key problem, which is how to minimize the shrinkage of concrete and prevent the structure from cracking.