Research Of Impact Resistant Behavior Of CFRP-spiral Stirrup Composite Confined Concrete

It can effectively improve concrete material properties by imposing constraints on the concrete. Compared to plain concrete, confined concrete has a significant improvement in compressive strength and deformation capacity. Moreover, it can improve the member mechanical properties and seismic capacity. The common methods to confine concrete are FRP constraint, steel tube constraint and spiral stirrup constraint. The members with different constraints have different mechanical characteristics. Therefore, it is very important to analyze different constraint forms and explore more effective ways to confine concrete.This paper firstly discussed the performance of FRP confined concrete and spiral stirrup confined concrete, on the basis of this, a novel form of CFRP-spiral stirrup composite confined concrete were proposed. This form of confinement can take full advantage of FRP and steel. The main works of this paper are as follows:1. Dynamic tensile tests were conducted on the 30 groups of total 240 FRP samples. The stress-strain curves of samples were obtained, and a high-speed camera was used to record the whole process of fracture of specimens. The effects of strain rate and temperature on the tensile strength and toughness of FRPs were analyzed, and the failure morphologies under different conditions were summarized. Besides, Weibull analysis was carried out to quantify the change of tensile strength.2. Based on the results of FRP tests, CFRP was choose to confine the concrete with spiral stirrup. The drop-hammer impact tests were performed on these specimens to investigate its mechanical properties. This paper presents 8 groups of total 24 samples, including 2 groups of CFRP confined concrete, 2 groups of spiral stirrup confined concrete and 4 groups of CFRP-spiral stirrup composite confined concrete. The force-time history curve and strain-time history curve were record, and a high-speed camera was used to capture the failure process of specimens.3. The impact force-time history curve and strain-time history curve of each specimen were analyzed, and the failure morphology of each specimen was summarized. Moreover, the effect of the layer of CFRP, the gap of spiral stirrup, impact energy and hammer mass on the impact properties were investigated.4. ANSYS/LS-DYNA was used to simulate the impact experiment, and the simulation and experimental results agree well. On the basis of this, the changes of energy during impact process were discussed.The results show that, the tensile strength and toughness of FRP increase with the increasing strain rates. However, the strength is not sensitive to temperature, it had no significant decrease until the temperature reach 100 ?. Compared with room temperature, toughness will decrease whether the temperature is lower or higher. CFRP-spiral stirrup composite confined column can effectively take the full advantages of CFRP and spiral stirrup, and this can make the concrete have higher compressive strength and better energy dissipation capacity. The constraint effect on the mechanical properties of concrete is significant, while the impact energy and hammer mass effect on the concrete properties is negligible.