| After the “911” event,a great deal of researches on the performance of steel structure under fire and blast impact sprang up.However,the present research at home and abroad mainly focuses on the individual effect of fire and explosion load.In the condition of the construction damage caused by secondary impact of the upper floors or other dead weight in fire,it is not only necessary to consider the effect of temperature on material strain rate effect under combine action of the fire and impact load,but also the contact problem between impactor and building construction in impacting process.There are basically no related studies in these two aspects at present.Therefore,it is necessary to study the performance of the steel structure under the joint action of elevated temperature and impact load.Experimental test and numerical simulation analysis on the impact resistance of different connection types of steel frame under elevated temperature environment are investigated.This paper has carried out mainly the following aspects of work:(1)Experimental research on the impact resistance of welded connection,bolt-welding connection and extended endplate connection steel frames under elevated temperature is carried out.The deflection in the midspan of steel beam and failure modes of beam-column joints of steel frames with different connection forms are analyzed.The experimental conclusions are obtained as follows: The impact resistance of three types of steel frames are all decrease with the increase of temperature.And a certain degree of bending deformation occurred in the midspan of the steel beams.There is slight bending deformation in the beam-column joint of welded steel frame.There are weld cracks in the beam-column joint of bolt-welding steel frame because of the defects in the weld bead.The endplate of the extended steel frame is broken down by dropping hammer at elevated temperature.(2)The finite element analysis model of steel frames subjected to drop hammer at elevated temperature is established.The influence of temperature on the material strain rate effect is considered in the model.The numerical simulation results are compared with the experimental results.And the numerical analysis results of the welded steel frame agrees well with the impact test results.For bolt-welding steel frame and extended steel frame,the defects of weld and material failure are neglected in the simulation analysis.Therefore,there are some differences between the numerical analysis and the test results.(3)Based on the material constitutive model corresponding to the test,several factors affecting the impact resistance of steel frames under elevated temperature are analyzed in detail through finite element simulation analysis.After analysis,the results of simulation analysis are in agreement with the experiment.The higher is the temperature,the weaker is the impact resistance of the steel frames.Under the condition of neglecting the weld defects and material failure,the impact resistance performance of bolt-welding steel frame at elevated temperature is the best.(4)By changing the mass and the impact velocity of the drop hammer,the influence of impact speed and mass on the impact resistance of steel frames are analyzed.The results show that the influence of impact by low-mass hammer at high velocity,on the steel frame is larger than the impact by high-mass hammer at low velocity and when the momentum is fixed.(5)Without considering the material failure case,the impact resistance performances of welded connection,flush endplate connection,extended endplate connection steel frames at elevated temperature are discussed.Combined with the experimental conclusions above,constraint function of bolt-welding connection is better than that of the other three connection types under the combined action of elevated temperature and drop hammer.That is to say,the impact resistance of bolt-welding connection frame is the best at elevated temperature. |
PDF Full Text Request