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Single and multi degree of freedom analysis of steel beams under blast loading

机译:爆炸荷载作用下钢梁的单自由度和多自由度分析

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This paper presents detailed analysis of the results of field tests on 13 full scale wide flange steel beams subjected to blast loads generated by the detonation of up to 250 kg of ANFO explosive. The experimental results are analyzed using an equivalent Single-Degree-of-Freedom (SDOF) model of a beam, which includes material nonlinearity and strain rate effects. To account for strain rate effect on beam stiffness and strength, its full moment-curvature response is determined by dividing its cross-section into a number of layers and a strain rate-dependent stress-strain relationship, based on the Cowper-Symonds strain rate model, is used to capture the nonlinear stress distribution over the section. To determine the effects of higher modes of vibration and the variation of beam mechanical properties along its length on its dynamic response, the test beams are also analyzed using a Multi-Degree-of-Freedom (MD0F) model involving beam finite elements. Each element has two nodes and three degrees of freedom and is again divided into a number of layers to capture the strain rate effect and nonlinear stress distribution over its depth. The predicted displacements and strains by the two models are compared with the corresponding experimental data and the results show that for the given beams, the time-dependant deformations, internal forces, and moments can be adequately predicted by either model because the first mode of vibration is found to dominate their response; however, the use of a constant strain rate through the so-called Dynamic Increase Factor (DIF) can lead to highly conservative estimate of the actual strength of such members.
机译:本文详细分析了13种全尺寸宽翼缘钢梁的现场测试结果,这些钢梁承受了由250公斤ANFO炸药的爆炸产生的爆炸载荷。使用等效的光束单度(SDOF)模型分析了实验结果,该模型包括材料非线性和应变率效应。为了考虑应变率对梁刚度和强度的影响,通过将其横截面分成多个层并根据Cowper-Symonds应变率确定应变率相关的应力-应变关系,来确定其完整的弯矩曲率响应。模型,用于捕获截面上的非线性应力分布。为了确定更高振动模式以及梁力学特性沿其长度变化对其动态响应的影响,还使用涉及梁有限元的多自由度(MD0F)模型对测试梁进行了分析。每个元素都有两个节点和三个自由度,并再次分为多个层以捕获应变速率效应和其深度上的非线性应力分布。将两个模型预测的位移和应变与相应的实验数据进行比较,结果表明,对于给定的梁,这两种模型都可以充分预测时变,内力和力矩,因为第一种振动模式被发现主导他们的反应;但是,通过所谓的动态增加因子(DIF)使用恒定的应变率会导致对此类构件的实际强度进行高度保守的估计。

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