Relevant Parameters Of An Equivalent SDOF Structural System For One-way Components Under Chemical Blast Loading

Explosive accidents often occur in explosive places,which caused structural damage,massive casualties and economic losses due to improper production and transportation of explosive materials.This paper studies the motion law and dynamic response characteristics of one-way components under chemical blast loading,which provides a theoretical basis for the dynamic analysis of protective structures.This paper considers the span of one-way members.This study investigates the definition of the equivalent load transformation factor K_L.The cosine function related to the mode shape in the expression of equivalent load transformation factor is expanded through a finite series,and the equivalent load expression is integrated.Then the load transformation factor expression considering the structural span is obtained.In addition,this paper studies the effects of the dynamic resistance factor K_h for one-way components under chemical blast loading.The final response state of one-way components under blast loading is considered.Combined with differential equations of an equivalent single-degree-of-freedom（SDOF）system in elastic and plastic response stages.Substituting the equivalent mass-load transformation factor K_m-l in the plastic stage into the formula.The ratio of the elastoplastic mass-load transformation factor that affects the dynamic resistance factor has been evaluated more accurately.Finally,the existing literature experiments verify the validity and rationality of the idea of solving the equivalent SDOF load transformation factor in this paper.In addition,the validity of the theory for solving the dynamic resistance factor has also been verified.The specific contents and results are as follows:（1）The equivalent SDOF load transformation factors expressions of the simply supported,fixed end and simply-fixed one-way members subjected to air blast loading are derived by finite series expansion method or finite point fitting method.It is concluded that for the blast-resistant structural design,if the error of 3%in the elastic stage and 5%in the plastic stage can be allowed,γ=1.0 is the demarcation point between near field blast and far field blast,and if the error of0.5%can be allowed,γ=2.0 is the demarcation point between near field blast and far field blast.This paper provides a clear numerical definition for the distinction between near field and far field explosions.（2）According to the final plastic deformation state of the structure,the dynamic increase factors under different ratios of equivalent mass-load transformation factors in the elastic stage and elastoplastic stage were analyzed.Using simply supported beams,simply supported and fixed beams,and fixed-end beams as the types of analysis beams,nine calculation conditions of the dynamic increase factor were completed.The calculation results were compared with the Chinese code formula.The results show that for a one-way member with a large ductility ratioβ（β>2）,the ratio of the mass-load transformation factors in the elastic and plastic stages larger than 1 would increase the engineering cost.Compared with simply supported one-way members and simply fixed one-way members,the relative error caused by the different ratios for the equivalent mass-load transformation factors is smaller for fixed-end beams.（3）The calculation accuracy of the load transformation factor K_L expression for simply supported one-way members in this paper has been verified by the near-field blast experiments.It is obtained that the calculation results of the overpressure parameters proposed by various representative scholars in this paper are very close to the calculation results based on the experiment by M.Nagata et al.,which can well predict the variation trend of K_L under different stand-off distances.In addition,the theoretical method of calculating the dynamic factor is compared with the experimental data of the existing literatures.The results show that the ductility ratio based on the theory is consistent with the test report,which verifies the accuracy of the theoretical method for calculating the dynamic resistance factor K_h.