| With the rapid development of modern social economy,more and more construction and transportation industries at home and abroad are also growing fast.However,the frequency of fire occurrence in the construction industry has also gradually increased in recent years.As it is we known,the high temperatures induced by fire conditions will not only pose a serious threat to our lives and property.Also,the high temperatures of fires will cause concrete cracking in reinforced concrete(RC)building structures.Considering the significant expansion of water vapor in the concrete matrix,the damage caused by concrete spalling is far greater than that of a simple fire,so it is necessary to investigate the impact of concrete fragments generated by concrete spalling especially on the lower floors.In this dissertation,the commercial finite element analysis software ABAQUS is used to establish the entire floor model(including internal reinforcement,stirrups,longitudinal reinforcement,etc.)and concrete fragment model.The following conclusions are obtained:(1)By using the finite element analysis software ABAQUS,a drop impact model is established to simulate the deformation and damage behaviour of RC floor under the fragment impact after concrete spalling.Considering the temperature-related damage of the concrete constitutive,by applying different temperature fields to the entire structure to simulate and investigate the trend of the stress and time of the concrete floor under actual fire conditions.It can be clearly seen that the higher the temperature,the greater the induced stress.The concrete material itself has thermal expansion,and the damage effect of the concrete material at high temperature is considered.When the temperature is changed,the Young’s modulus of the material will change with increasing temperature.Therefore,the stress value increases and the temperature increases and becomes larger.(2)By analyzing the dynamic response of RC floors under different impact load conditions,the influential factors and the corresponding changing trends of stress,equivalent plastic strain,displacement and other factors after impacting concrete floor slabs were obtained and studied.The induced consequences of different impact conditions on the floor slabs were compared and analyzed.According to the boundary conditions adopted in this dissertation,the corresponding empirical formulas were proposed for each working condition.(3)In this dissertation,the influential factors of the concrete fragment impact on the RC floor were studied through the comparative simulation of the control variable method.From the aspects of drop impact position,drop impact height,impact force,initial impact velocity,etc.,four of the most influential factors were compared and found on the concrete floor slab.The maximum stress induced by impact is concentrated at the connection position of the floor and the column,indicating that this position is the most vulnerable position under actual working conditions if the impact occurs.The stress on the location near the drop impact location is greater than other locations on the RC floor,and the equivalent plastic strain accumulated over time also shows the same pattern.The higher the impact position of the fragment drop,the greater the impact on the floor impact.This is also the same trend of the stress value,displacement,and equivalent plastic strain.The greater the impact force,the greater the impact on the RC floor.When the impact load is large enough,the concrete floor slab deforms plastically,and the corresponding displacement of the entire floor no longer undergoes elastic recovery.As the initial impact velocity increases,the impact response of the RC floor becomes more significant,and the stress and displacement become greater as well.(4)The combined subassembly structure of an RC floor and columns is proposed,and the deformation and damage of the combined structure on the impact prevention effect is simulated.The results show that the combined structure of concrete floor slabs and columns owns advantages in terms of stress or displacement caused by impact compared with the individual concrete floor slabs.According to the relevant factors analyzed in this paper,some protective measures are proposed for the concrete spalling and impact of concrete. |
