Study On Explosion Resistance Design And Reliability Of I-Shaped Steel Beam Considering Local Deformation

In today’s world,terrorist bombings are increasing,and accidental explosions caused by old equipment and negligence of personnel have also occurred from time to time,which has sounded the alarm for the safety of people ’s lives.As an important load-bearing member of building structure,I-shaped steel beam is prone to produce large local deformation under blast load.However,most of the current anti-explosion analysis methods only consider the overall deformation of the structure,ignoring the influence of local deformation on the overall displacement of the structure,so it is impossible to fully describe its response characteristics,and the calculation results usually have large errors.Therefore,it is necessary to propose a simplified anti-explosion analysis method of I-shaped steel beam considering local distortion.Affected by air humidity,temperature,explosive type,shape,urban layout and other factors,the blast load acting on the building structure has a strong discreteness.Therefore,in order to accurately reflect the response characteristics of I-shaped steel beams under blast load,it is necessary to carry out the reliability research of I-shaped steel beams under the uncertainty of blast load.As follows :(1)The characteristics of explosion and explosion overpressure time history curve are summarized.The prediction formulas and charts of blast load by scholars at home and abroad are collected and summarized.It is proved that the blast load has strong volatility,that is,the randomness of blast load can not be ignored in the study of structural explosion resistance.A large number of blast load test data was collected at home and abroad.Combined with the empirical formula summarized by predecessors,the best fitting formulas and charts of the mean value μ,standard deviation σ and coefficient of variation δ of each parameter of blast load was obtained by probability and statistics method.(2)The response characteristics and failure modes of I-shaped steel beams under blast load were analyzed by finite element software.The rationality of material model selection and finite element model modeling of I-shaped steel beam in this paper is verified by the steel plate antiexplosion test of Yuen et al.and the anti-explosion test of I-shaped steel beam of Nassr et al.According to the displacement nephogram of I-shaped steel beam at different times of explosion and the displacement and velocity time history curves of key nodes in the mid-span section of I-shaped steel beam,it is found that the displacement response of the flange of I-shaped steel beam is earlier than that of the whole steel beam under blast load.According to the stress nephogram of I-shaped steel beam under three explosion conditions and the displacement time history curves of the whole steel beam and the local flange,three typical failure modes of Ishaped steel beam are analyzed.(3)Based on the above research results and the theory of single degree of freedom,by analyzing the influence of local deformation of the flange on the overall displacement of the steel beam,the improved single degree of freedom method and the equivalent double degree of freedom method for the anti-explosion analysis of I-shaped steel beams are proposed,the model calculation results are compared with the finite element simulation results.The results show that compared with the equivalent SDOF model,the ISDOF model can more accurately reflect the maximum vertical displacement of the mid-span of the steel beam considering the local deformation of the flange.The equivalent DDOF model can accurately reflect the maximum vertical displacement of the mid-span of the steel beam and the local displacement of the flange.It can more fully reflect the actual dynamic response of the I-shaped steel beam,simplify the anti-explosion analysis of the I-shaped steel beam,and guide the anti-explosion design of the project.(4)By analyzing the basic theory of structural reliability and the reliability application of Monte Carlo method,the calculation process of failure probability of I-shaped steel beam is established.Considering the uncertainty of blast load,based on the proposed equivalent DDOF model,the reliability of I-shaped steel beam is analyzed by Monte Carlo method.In the study,the possible overall damage and local damage of the flange of the I-shaped steel beam,as well as the influence of different section sizes and explosive mass on the failure probability of the Ishaped steel beam were fully considered.The results show that the equivalent DDOF model proposed in this paper can accurately judge the failure probability of I-shaped steel beam components after explosion,and the equivalent DDOF model can be used to analyze the reliability of I-shaped steel beams.