Numerical Investigation On Dynamic Response Of Reinforced Concrete T-sectional Beams Under Impact Loading

With the frequent occurrence of traffic accidents,terrorist attacks or other accidents worldwide,reinforced concrete structures are faced with the threat of extreme impact loads during their service.Various impact loads put forward higher requirements for the bearing capacity and safety of concrete structures.Reinforced concrete T-sectional beams are widely applied in building structures such as bridges and underground civil air defense projects because of their light weight and equivalent flexural strength with rectangular beams.However,at present,scholars at home and abroad mainly focus on the static field of reinforced concrete T-sectional beams,but relatively few on their dynamic mechanical response under impact loads.Based on above analysis,dynamic responses of reinforced concrete T-sectional beams under impact loading are investigated via the FEM code LS-DYNA in this thesis.Besides,the effects of different design parameters(reinforcement ratios,stirrup ratios,span lengths,boundary conditions,etc.)and different impact conditions(impact qualities,cushion plate materials,impact point locations,etc.)on the impact resistance of reinforced concrete T-beams are comprehensively analyzed.Furthermore,the impact dynamic behavior of reinforced concrete T-beams strengthened with carbon fiber reinforced polymer(CFRP)and pre-stressed concrete T-beams are further studied.The main research works are as follows:(1)Based on the experimental results in the literature,three-dimensional finite element numerical analysis models of reinforced concrete T-beams without web reinforcement under impact loads are established.The dynamic responses of the beams,such as impact force,reaction force,midspan displacement,crack development process and failure mode,cross-sectional damage assessment and energy transformation,are analyzed comprehensively and compared with the experimental results.The simulation results show that when reinforced concrete T-beams without web reinforcement are subjected to impact load,shear inclined cracks develop downward from the impact point of 45 degrees rapidly in the web shear span region,showing a typical shear failure mode.The failure state of T-beams are basically consistent with the test results.The calculational error between the simulated and experimental values of the maximum midspan displacement of the beam is about 3.2%.On this basis,the effects of different design parameters such as reinforcement ratios,stirrup ratios,span lengths,boundary conditions,and different impact conditions such as impact qualities,cushion plate materials and impact point locations on the impact resistance of reinforced concrete T-beams are analyzed.(2)Three-dimensional finite element numerical analysis models of T-beams strengthened with CFRP under impact load are established and compared with that of T-beams not strengthened.The numerical simulation results indicate that the overall stiffness of T-beams and the plastic deformation of the structure are obviously improved due to external CFRP strip reinforcement.For example,compared with unstrengthened beams,the maximum mid-span displacement and residual displacement of CFRP-strengthened beams are reduced by about 7.9% and 23.3% respectively.The sectional damage factors of the whole span of the CFRP strengthened beams are reduced to less than 0.3 so that the impact bearing capacity of the beams are effectively enhanced.In addition,the effects of CFRP strengthening mode,CFRP strengthening sizes,CFRP layers and FRP material types on the impact resistance of T-beams strengthened with FRP are further studied.(3)Three-dimensional finite element numerical analysis models of the pre-stressed T-beams under impact load are established.The dynamic responses of the pre-stressed T-beams under different prestressing levels are reported,such as impact force,reaction force,mid-span displacement,failure mode and sectional damage factor.The results show that with the increase of prestressing force,the mid-span displacement of the beam decreases,but the reduction of mid-span displacement increases.Besides,the number of cracks decreases significantly,and the cracking degree of main inclined cracks is reduced as well when the prestressing force is increasing.Additionally,the effects of different concrete strength classes,reinforcement ratios and impact velocities on the impact resistance of prestressed T-beams are investigated as well.