Analysis Of Pre-Stressed Concrete T Beam’s Mechanical Properties Under Low Velocity Impact

This thesis mainly focuses on pre-stressed simple T beam’s mechanical properties. It includes two parts-pre-stressed concrete simple T beam’s mode analysis and analysis of pre-stressed concrete simple T beam’s mechanical properties under low velocity impact. To make sure that parameters of the HJC constitutive model used in this thesis are reliable and reasonable, the author analyzed the influence of HJC’s four important parameter’s variation on Stress-Strain curve derived from HJC constitutive model. Here are the works that has been done by the author through this thesis:1. The author took LS-DYNA, the mass implicit dynamic calculation program, to stimulate Hopkinson split bar test. Through the stimulation, the author observed the variation of four important parameters’-normal cohesion strength A, normal pressure enhance coefficient B, pressure exponent N and strain rate sensitive coefficient C-effect on Stress-Strain curve derived from HJC constitutive model.The results indicate that HJC constitutive model’s yield strength is sensitive to the four parameters although in different ways. Unlike the other parameters, the normal pressure enhance coefficient B and pressure exponent N’s variation lead to change of not only yield strength but also stress-strain curve’s shape. The analysis implied that revised parameters published by ZhangRuoqi are reasonable. The revised parameters would be used in the following parts to make sure that the parameters’set about HJC constitutive model are both reliable and reasonable.2. Formulas of pre-stressed beam’s natural frequencies were derived respecively through the force equivalent principle and the energy principle. A finite element model of pre-stressed concrete simple T beam was established through node coupling method. The mass finite element program ANSYS was taken to analyze the models’mode properties. The results of numerical stimulation are in accordance with the one derived from theoretical analysis. Besides, in different cases, pre-stressed concrete beam’s natural frequencies were analyzed. The results indicate that tension variation in pre-stressed gird causes so insignigicant change of pre-stressed beam’s natural frequencies that it is negligible. Different pre-stressed gird distribution in concrete causes different natural frequencies.3. The Plastic Rigid Analyzing Method was taken to analyze a beam’s mechanical properties under impact. The beam’s dynamic response and way of yield were analyzed. In addition, finite element models of a pre-stressed concrete simple T beam and an impact rigid bar were established. LS-DYNA, the mass explicit dynamics calculation program, was taken to stimulate the process of impact. The results indicate that the numerical stimulation successfully stimulates damage and destroy of concrete simple T beam under impact. The stimulation also proves that the assumed three stages of Plastic Rigid Analyzing Method are reasonable.4. Impacts with different low velocities were stimulated through LS-DYNA. The results imply that both density and length of cracks increase when impact velocity rises. In addition, penetrating cracks on webs appear at 45 degree angle. Impacts were stimulated when tension in pre-stressed gird were different. The results indicate that pre-stressed gird is able to improve beams’impact resistant capacity. Under impact with different velocities, there are critical values of tension in pre-stressed gird minimizing the beam’s transverse displacement.