爆炸荷载下泡沫混凝土分配层最小厚度的计算方法

A calculation method for the minimum thickness of a foam concrete distribution layer under blast load

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。

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.