Performance Research Of Pre-stressed Steel Reinforced Concrete Beams During Construction Period In Building Structure

Nowadays, the height and span of building construction expands increasingly, and high-rising building develops rapidly in our country. With the gradual development of high-rise building, Steel Reinforced Concrete(short for "SRC") spreads extensively as a special combination, for it can satisfy people's requirement for ability to use of the building house space. As a new kind of combinations, the SRC can give play to the shear capacity, the tensile strengths and the compressive strength of shaped steel.Combining pre-stressed technique with SRC can fully improve the weight and crack problems of SRC, promote the structure's shear capacity and itself durability, and improve load conditions of the concrete structure, thus it forms Pre-stressed Steel Reinforced Concrete(short for “PSRC”). In recent years, PSRC has been developed rapidly and applied in many high rise structures.PSRC beam has the characteristics of complicated construction procedure, which is mainly due to the diversity of its components. Therefore, if we consider the installation of shaped steel and the pre-stressed tension, the construction procedure will be increased and the schedule will be delayed to some degree. For these reasons, many project managers who blindly catch up with schedule cause the concrete in early age to bear the construction load, which may also have an impact on structures in the late performance. Accordingly, this paper has systematically conducted the research on this problem, analyzed the load condition of PSRC beam component in early age, and summarized the force of pre-stress. The main work is as follows:(1)By analyzing the change regulation of the structural force performance in the early age, we can acquire the limit table of construction load stress from comprehensive simulation results. When considering PSRC in the early age under the construction load, we can use the date in the limit table of construction load stress to limit the construction load.(2)By analyzing the influence of different stress on the force performance of structure, we can acquire the regulation of pre-stressed tension and its technique control table of PSRC component in early age under construction. According to the data of the control table, we can master the value of pre-stressed tension in the early age.(3)Under construction, the concrete strength will increase as the age increases, and the concrete strength in the early age changes faster. Under construction, we just make sure that the value of concrete stress in the early age is not more than 70% of the concrete strength at the same time, and the maintenance conditions will satisfy the standardized requirements in the late maintenance, therefore, we can ignore the influence of stress in the early age.(4)According to the stimulate research, if the maintenance time reaches 3 days, the components' strength will increase to 46% of standardized strength and the ultimate load will increase to 70% of standardized conditions. At this time, the components have certain strength, and the simulation results show that the failure modes of components have a certain plastic deformation capacity. So in 3 days, the components can carry on the pre-stressed tension and a certain construction load(5)Even though the pre-stress can improve the crack of components, it may not always do good to components. The increase of pre-stress can reduce the yield deflection and the ultimate deflection, making against the components' deformation. In addition, the pre-stress in the early age will leave great impact on components. Accordingly, if the pre-stress is imposed more, it will reduce the ultimate load capacity.(6)From the research on the force of PSRC beam in the early age, we can draw a conclusion: Under the age stimulation, the crack load, the yield load and the ultimate load capacity increase as the age increases, and they increase faster in the early age. Among them, the pre-stressed tension influences greatly on the crack load and the yield load. If the pre-stress increases, the crack load and the yield load of beams will increase too. But the pre-stressed tension has less influence on the ultimate load capacity. After load cracking,the load capacity of beams does not change obviously as the pre-stressed tension changes. The increase of the age is not good for the components' deformation before yielding, but the components' deformation after yielding. In the early age, the increase of the effective pre-stress is not good for the components' deformation before cracking, but the components' deformation after cracking. When the age of concrete is beyond 7 days, the increase of pre-stress begins to do harm to the components' deformation after yielding.