A calculation method for the minimum thickness of a foam concrete distribution layer under blast load
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摘要: 为了研究爆炸荷载下泡沫混凝土分配层的设计厚度，采用LS-DYNA软件建立了一维爆炸波在泡沫混凝土杆中传播衰减的数值模型并经过了实验验证，分析了半无限长和有限长泡沫混凝土杆中爆炸波的传播衰减规律及荷载增强效应产生机理。数值模拟结果表明：三角形爆炸荷载经过足够长的泡沫混凝土杆会衰减为幅值与其平台应力相当的梯形荷载，而当泡沫混凝土杆长度较小时，固定端在更强的反射波作用下将产生荷载增强效应。基于泡沫混凝土杆中的压实情况，将杆分为5个区域，即密实区1、平台区1、弹性区、平台区2和密实区2，其中弹性区的范围随着杆长减小而逐渐缩短；为避免荷载增强效应产生且最大程度降低作用于主体结构上的荷载，定义了平台区1、弹性区和平台区2范围为零时对应的杆长为泡沫混凝土分配层的最小厚度。对爆炸荷载和泡沫混凝土密度的参数敏感性分析表明，最小厚度随爆炸荷载峰值的增大和作用时间的延长而增大，而同一爆炸荷载下低密度泡沫混凝土的最小厚度大于高密度泡沫混凝土的最小厚度。基于数值模拟结果，进一步提出了最小厚度的计算公式。Abstract: In order to study the design thickness of the foam concrete distribution layer under blast load, the numerical model of one-dimensional blast wave propagation in foam concrete was established based on the LS-DYNA software, which was verified by comparing it with the corresponding experimental data, and then the propagation and attenuation of the blast wave in the foam concrete bars with semi-infinite and finite thicknesses were analyzed in detail based on the simplified stress-strain curve of foam concrete. The numerical results demonstrate that the triangular-shaped blast load will be attenuated into a trapezoidal-shaped load with the same amplitude as the yield strength of foam concrete when its thickness is enough, while the so-called load enhancement effect will occur at the fixed end due to the action of the stronger reflected wave when its thickness is small. Based on the compaction of foam concrete, the foam concrete with sufficient length can be divided into five regions, i.e., the compaction zone 1, the plateau zone 1, the elastic zone, the plateau zone 2, and the compaction zone 2, where the range of the elastic zone is gradually shortened as the pole length decreases. To avoid the load enhancement effect and minimize the load on the protected structures, the minimum thickness of the distribution layer of foam concrete was defined corresponding to that when the elastic area and two plateau areas disappeared. The sensitivity analysis of blast load and density of foam concrete on the minimum thickness of foam concrete shows that for the blast load concerned, the minimum thickness increases with the peak and duration time of blast load, but is less affected by the rise time of blast load. Furthermore, the minimum thickness of low-density foam concrete is larger than that of high-density foam concrete under the same blast load. Based on the numerical results, a formula for minimum thickness was proposed.
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Key words:
- foam concrete /
- distribution layer /
- one-dimensional blast wave /
- minimum thickness
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图 3 一维波在泡沫混凝土中传播的有限元模型
Figure 3. The finite element model of one-dimensional wave propagation in a foam concrete bar
图 6 经过3种不同长度泡沫混凝土试件作用于结构上的荷载随时间的变化
Figure 6. Variation of stress exerted by three foam concrete specimens with different lengths on structure with time
图 8 简化的应力-应变曲线与实验数据对比
Figure 8. Comparison of the simplified stress-strain curve with the experimental one
图 9 基于简化应力-应变曲线模拟得到的荷载与实验数据的对比
Figure 9. Comparison of the simulated load-time curves based on the simplified stress-strain curve with the experimental ones
图 10 一维爆炸波在半无限长泡沫混凝土杆中的传播衰减
Figure 10. Propagation of one-dimensional blast wave in a foam concrete bar with semi-infinite length
图 11 半无限长泡沫混凝土杆的应力和应变峰值分布
Figure 11. Distribution of stress and strain peaks in a foam concrete bar with semi-infinite length
图 12 一维爆炸波在500 mm长泡沫混凝土杆中的传播衰减
Figure 12. Propagation of one-dimensional blast wave in a foam concrete bar with the length of 500 mm
图 13 300 mm长泡沫混凝土杆的应力和应变峰值分布
Figure 13. Stress and strain peak distribution in a foam concrete bar with the length of 300 mm
图 14 不同长度泡沫混凝土杆的应力和应变峰值分布
Figure 14. Stress and strain peak distribution in foam concrete bars with different lengths
图 15 一维爆炸波在100 mm长泡沫混凝土杆中的传播衰减
Figure 15. Propagation of one-dimensional blast wave in a foam concrete bar with the length of 100 mm
图 16 泡沫混凝土层最小厚度设计准则
Figure 16. Design criteria for the minimum thickness of a foam concrete layer
图 18 泡沫混凝土不同密度等级对应的平台应力区间
Figure 18. Plateau stress ranges of foam concretewith different densities
图 19 4种典型密度泡沫混凝土的应力-应变简化曲线
Figure 19. Simplified stress-strain curves of foam concretewith four typical densities
图 20 爆炸荷载升压时间对泡沫混凝土层最小厚度的影响
Figure 20. Influence of rise time of blast load on the minimum thickness of a foam concrete layer
图 21 爆炸荷载特征系数对泡沫混凝土层最小厚度的影响
Figure 21. Influences of blast load characteristic coefficients on the minimum thickness of a foam concrete layer
图 22 泡沫混凝土密度对最小厚度的影响
Figure 22. Influence of density of foam concrete on the minimum thickness
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