Study On Dynamic Response Of RC Beams Under Drop Hammer Impact

The impact load itself is a disaster to structure, terrorist attacks?vehicles and vessels impact make all kinds of structure faced with the immediate threat of impact. The secondary disasters of traffic accident and earthquake include the impact on the structure too. Thus, the threat of impact on the structure is increasing. Once the impact load occurres, it may cause serious or even fatal damage to structure. In most existing specifications in China, there are no special terms that take impact load into consideration. So the study on the response of the impact on component or structure is of great significance, it will help us understanding the impact load better and better, and getting ready to add relevant provisions into the specification. Using element software LS-DYNA as tool, dynamic response of RC beam under the drop hammer impact has been studied as the following three aspects.(1) The finite element model of RC beam under the drop hammer impact has been set up. On the one hand, this paper focus on study the important details of setting up the finite element model,like the size of the finite element, the way to control hourglass energy and the bonding modes of steel and concrete etc.One the other hand, compare the results in this paper with the authoritative conclusion to prove the correctness of modeling, there are two comparation in this paper, the first one is to compare the dynamic response of the elastic rod impact, it proves that LS-DYNA is a reliable software to solve the problem of impact. The second one is to compare the dynamic response of RC beam under drop hammer impact,it proves that the modeling of the drop impact is correct.(2) Sensitivity analysis of the HJC constitutive model parameter of concrete. 22 parameters constitute the HJC conctitutive model, and the mechanical properties of concrete relates to 18 of them, for these 18 parameters, Sensitivity analysis has been conducted, finally we find 6 sensitive parameters in HJC constitutive model, they are A? B? G? lP ?l? andcf. After that, detailed analysis to these sensitive parameters has been done to find the way how they affect the impact response.(3) Study on the related influence factors of impact response. Select the deflection and the impact force of RC beam as the response index, take concrete strength, longitudinal reinforcement ratio, beam span, impact location, quality and speed of the hammer as assumed influence factors. The study found that the factors significantly influence the deflection response are longitudinal reinforcement ratio, beam span, impact location, quality and speed of drop hammer. The factors significantly influence the impact force are longitudinal reinforcement ratio, beam span, impact position and speed of drop hammer.