【作者】 李杨；

【导师】 胡志坚；

【作者基本信息】 武汉理工大学 ， 桥梁与隧道工程， 2019， 硕士

【摘要】 爆炸荷载作为一种极限荷载,在一些重要的结构如斜拉桥的设计中必须被考虑到。目前国内外桥梁设计过程中,较少考虑抗爆设计,但近年来桥梁在车载炸弹以及恐怖袭击所造成的爆炸事故中所表现出的脆弱性问题越来越突出,爆炸荷载会对桥梁的关键部位构件造成损坏甚至整体垮塌,进而造成交通瘫痪,带来巨大的人身以及财产的损失。因此,有必要针对桥梁的整体和局部构件在爆炸荷载作用下的动力响应进行分析,相关结论可用来评估现有桥梁的抗爆性能,同时可为有效的桥梁抗爆方法研究提供参考。本文基于LS-DYNA,建立斜拉桥整体模型,斜拉索局部模型以及钢箱梁节段模型,分析斜拉桥整体和构件在爆炸荷载作用下的响应,主要结论如下:首先,为研究斜拉桥整体的抗爆性能,建立斜拉桥实体模型,基于LBE方法施加爆炸荷载,开展了不同桥面爆炸位置时斜拉桥的抗爆分析,结果表明:等效TNT当量为1814kg的车载爆炸作用下,斜拉桥表现为局部破坏,不会出现整体倒塌;爆炸荷载作用下,桥梁上部结构的振动由爆炸冲击波作用方向的第一阶振型来控制;爆炸荷载作用下索塔表现向爆点纵飘,且主跨跨中爆炸时,索塔的纵飘程度大于边跨跨中爆炸;与其他斜拉索相比,靠近爆点和索塔处的斜拉索更容易失效,偏载爆炸引起的斜拉索锚固区破坏值得重视。其次,为研究斜拉索的抗爆性能,基于ALE多物质流固耦合理论,开展近场爆炸作用下斜拉索的抗爆分析,根据钢板爆炸试验验证了模拟方法的准确性,开展了斜拉索应力和挠度分析,进一步就不同比例距离展开参数化分析。研究结果表明:近场爆炸作用下,斜拉索不会出现脆性断裂,其破坏形式表现为应力超过名义屈服应力带来的失效;斜拉索最薄弱的位置是索梁锚固区,该区域斜拉索的应力由于爆炸冲击波的反射大于靠近爆点的斜拉索;给出了保持斜拉索不失效的安全比例距离为0.287kg/m~3,可认为大于该临界比例距离时,斜拉索不会发生失效。最后,为研究钢箱梁的抗爆性能,基于ALE多物质流固耦合理论,开展近场爆炸作用下钢箱梁的数值模拟,针对钢箱梁损伤及压力场分析,在此基础上就不同炸药当量、不同钢板厚度及不同加劲肋布置展开参数化分析。研究结果表明:爆炸荷载作用下钢箱梁的破坏形式主要可分为塑性变形和破裂开口两种;爆炸冲击波破坏顶板后在翼板处狭小的空间内,封闭效应显著,箱梁内部超压峰值最大发生在顶板最靠近爆点的加劲肋处;结合抗爆性能、经济性和桥面铺装推荐2cm为钢箱梁顶板最优厚度;加劲肋与顶板可看作一个“熔断”体系,利用加劲肋和顶板相对刚度的差别,可以将破损区域限制在两加劲肋之间。更多还原

【Abstract】 Blast loads have been recognized as one of the extreme events that must be considered in the design of important structures such as cable-stayed bridges.Currently the blast loading has not been considered as an extreme limit state in bridge design codes both in China and abroad.However,the vulnerability of the bridges that is exhibited in car bomb and terrorist attacks has attracted more and more attentions of the bridge engineers and transportation authorities in recent years.The damages of the key bridge components or even collapse of the bridges caused by blast loadings will lead to serious traffic congestion and tremendous personnel and property losses.Therefore,it is necessary to analyze the dynamic response of the blast loaded bridges to characterize the structural performance globally and locally.The conclusions can be used to evaluate the performance of existing bridges and provide the effective methods for new structural design.Based on LS-DYNA,this paper establishes the global model of a cable-stayed bridge,the local model of the stay cable,and the segmental model of the steel box girder.For each model the detail dynamic analyses that consider different blast load cases,are conducted,and the conclusions are made as follows:Firstly,in order to investigate the dynamic response of the blast loaded cable-stayed bridge,based on load blast enhanced(LBE)method,the finite element model of a cable-stayed bridge was established,and the blast resistance analyses for different detonation locations on the bridge deck were performed.It is found that the damages of the bridge exhibit the localized property and the risk of the progressive collapse is low.The vibration of the superstructure is governed by the first mode shape in the direction of the explosion shock wave propagation.The pylon bends toward to the detonation center.When the explosive is detonated in the middle of main span,the tower deflection is greater than those the explosive detonated in the middle side spans.The results show that the standoff has significant effect on the blast resistant performance of the stay cables.The cables closed to the detonation center and tower show more vulnerable than those that have larger standoff distance.It is suggested the more attentions should be paid to those cables separated with superstructure due to the eccentric blast loading.Secondly,in order to investigate blast resistance of stay cables,and near field explosion effects on the stay cable dynamic behavior,based on arbitrary Lagrange-Euler method,the finite element model of stay cable was established and the accuracy of the numerical method was verified according to the steel plate explosion experiment,the stresses and the deflections of cables were analyzed,and the parametric study was carried out for the different proportional distances.The results show that for a near filed event,the cable’s failure mode is governed by yield and no brittle fracture was found in this case.The most vulnerable position of the cable is the anchorage zone.The stress of the cable of in area was larger than that of the cable near the detonation center due to the reflection of the explosion shock wave.The minimum safe proportional distance is 0.287 kg/m~3,which is the critical survival proportional distance in a near filed event.Finally,in order to investigate the blast resistance of steel box girder,based on arbitrary Lagrange-Euler method,the finite element model of steel box girder was established,the steel box girder damage and pressure were analyzed,and then parametric analysis was carried out for different charge sizes,different plate thickness and different stiffener arrangements.The results show that there are two main failure modes of steel box girders:plastic deformation and local rupture.In the narrow space of the wing plate,the explosion shock wave will be reflected multiple times,and the sealing effect is significant.The peak value of the maximum overpressure inside the box girder occurs at the stiffening ribs of the top plate where is closed to the explosion point.Taking into account of the blast resistance,economy,and deck pavement,an optimal thickness,2cm,of steel box girders is recommended.Stiffeners and top plates can be designed as a fuse system,and the damage zone can be limited between two stiffeners by using the stiffness difference between the stiffeners and the top plate.更多还原