强震和冲击荷载下球面网壳的动力失效分析与试验研究

发布时间：2018-08-13 18:04

【摘要】：近年来由于各种人为因素或地质灾害的影响,建筑物严重破坏的事故频繁发生。重要的大跨度网壳结构,例如地区标志性建筑,如果遭受特大地震、撞击等意外危害时发生破坏,不仅会造成生命财产的重大损失,甚至还会有深远的政治影响。结构设计的根本任务是保证结构安全而防止结构倒塌则是保证结构安全的底线。对有大量人群聚集的大跨度建筑结构进行倒塌分析,采取防止动力倒塌的措施,将逐步成为结构设计的一项重要内容。造成建筑物失效破坏的突发事故既可是自然界中的突发地震,也可是意外的冲击。本文以球面网壳为研究对象,具体包括单层网壳、双层网壳两种形式,以数值模拟和试验研究相结合的方法,分析了强震和冲击荷载下网壳结构的动力响应、失效模式,模拟了动力倒塌的过程,并揭示了倒塌机理,主要内容如下： (1)以结构倒塌的数值模拟为基础,选用显式动力非线性程序LS-DYNA作为数值模拟平台。对数值模拟的相关技术及其难点进行了分析,自编制前处理子程序,采用了钢材的弹塑性损伤本构模型。建立了基于IDA方法的球面网壳的动力倒塌的计算流程,提出了基于能量守恒的倒塌判断准则。 (2)通过对单层球面网壳结构的动力分析,定义了强震下网壳结构的失效模式。研究了单层网壳结构在强震下的动力响应和失效特征,重点模拟了结构倒塌的全过程,从凹陷产生、扩展的角度揭示了倒塌机理。对影响网壳结构极限承载力的影响因素,如：矢跨比、屋面荷载、有无下部支承结构进行了分析。对荷载分布不对称下的网壳结构进行了动力倒塌分析。对空腹双层网壳进行了动力全过程分析。 (3)提出了在网壳中增设开孔的双钢管约束屈曲支撑作为减震装置,对其耗能能力进行了分析。提出了在单层网壳、双层网壳中,约束屈曲支撑布置的方式,对其减震效果进行了分析。并对无约束屈曲支撑和有约束屈曲支撑的网壳的极限承载力进行了对比分析。结果表明,约束屈曲支撑具有较好的减震效果,并能提高网壳的极限承载力 (4)通过缩尺模型振动台试验,对网壳结构在不对称荷载作用下的动力失效模式进行了验证。结果表明：荷载不均匀分布会降低强震下网壳结构的极限承载力。在设计过程中,应充分考虑不对称荷载对网壳动力稳定性的影响。 (5)研究了如落石等这种质量较大、速度较小的冲击荷载,对冲击荷载进行了分析。建立了网壳结构冲击响应的计算模型,定义了网壳结构在这种荷载作用下的失效模式,分析了各失效模式对应的动力响应特点,对失效机理进行了研究。分析了当网壳同时遭受两点冲击、三点冲击的动力响应,对三点冲击下的网壳结构的整体倒塌机理进行了研究。结果表明：对于单点冲击,对应的失效模式为轻度损伤、局部凹陷、局部冲切破坏。当冲击质量和速度均较小时,冲击能量较小,冲击点处的杆件有轻微的损伤；当速度较大时,一般发生的是局部冲切破坏,当质量较大,速度适中时,才会发生局部凹陷。网壳结构在最不利两点冲击和三点冲击下的失效机理为；由于局部凹陷形成、扩展、联通,导致结构最后动力倒塌。 (6)进行了缩尺模型的网壳结构的冲击试验,采用不同质量的冲击物对网壳结构的不同节点进行了冲击测试,分析了整体结构的动应力、动位移及加速度,和有限元结果进行了对比分析,研究了网壳结构的动力响应特点,验证了网壳结构在低速冲击下局部凹陷的失效模式。结果表明：冲击区域测点的响应明显大于非冲击区域的测点,主肋节点测点的响应大于其他测点的响应,说明冲击荷载产生的应力波主要沿冲击方向传播,沿环形传播的能量衰减的较快。不同冲击点产生的结构响应也不同,主肋靠近顶点的节点、中间部位的节点为不利加载点。
[Abstract]:In recent years, due to various man-made factors or geological disasters, serious building damage accidents occur frequently. Important large-span reticulated shell structures, such as regional landmark buildings, will not only cause significant loss of life and property, but also have far-reaching political shadow if they are damaged by major earthquake, impact and other accidental hazards. The basic task of structural design is to ensure structural safety and prevent structural collapse is the bottom line of structural safety. Collapse analysis of large-span building structures with large crowds and measures to prevent dynamic collapse will gradually become an important part of structural design.
In this paper, the dynamic response of reticulated shells under strong earthquakes and impact loads is analyzed by means of numerical simulation and experimental study, which includes single-layer reticulated shells and double-layer reticulated shells. The failure mode is simulated, and the collapse mechanism is revealed. The main contents are as follows:
(1) Based on the numerical simulation of structural collapse, the explicit dynamic nonlinear program LS-DYNA is selected as the numerical simulation platform. The related techniques and difficulties of numerical simulation are analyzed. The pretreatment subroutine is compiled and the elastic-plastic damage constitutive model of steel is adopted. The dynamic collapse of spherical reticulated shell based on IDA method is established. Based on the calculation process, a collapse criterion based on energy conservation is proposed.
(2) Based on the dynamic analysis of single-layer reticulated spherical shells, the failure modes of reticulated shells under strong earthquakes are defined. The dynamic response and failure characteristics of single-layer reticulated shells under strong earthquakes are studied. The whole collapse process is simulated with emphasis. The collapse mechanism is revealed from the angle of depression and expansion. Influencing factors, such as rise-span ratio, roof load, and whether or not the lower supporting structure is analyzed. The dynamic collapse of reticulated shell under asymmetric load distribution is analyzed.
(3) The double steel tube restrained buckling braces with openings in reticulated shells are proposed as shock absorbers, and their energy dissipation capacity is analyzed. The results show that the restrained buckling braces have better damping effect and can improve the ultimate bearing capacity of reticulated shells.
(4) The dynamic failure modes of reticulated shells subjected to asymmetric loads are validated by scale model shaking table test. The results show that the ultimate bearing capacity of reticulated shells under strong earthquakes can be reduced by non-uniform load distribution.
(5) The impact loads with large mass and small velocity, such as rockfall, are studied, and the impact loads are analyzed. The calculation model of impact response of reticulated shells is established, the failure modes of reticulated shells under such loads are defined, the corresponding dynamic response characteristics of each failure mode are analyzed, and the failure mechanism is studied. The overall collapse mechanism of reticulated shells subjected to two-point impact and three-point impact is studied. The results show that the failure modes of reticulated shells subjected to single-point impact are slight damage, local depression and local punching failure. There is a slight damage to the bar at the impact point; when the velocity is high, the local punching failure usually occurs. When the mass is large and the velocity is moderate, the local depression will occur.
(6) The impact tests of reticulated shells with different mass impactors were carried out. The dynamic stress, displacement and acceleration of the whole structure were analyzed and compared with the results of finite element method. The dynamic response characteristics of reticulated shells were studied and the reticulated shells were verified. The results show that the response of the measured points in the impact area is obviously greater than that in the non-impact area, and the response of the main rib node is greater than that of the other measuring points. It shows that the stress wave produced by the impact load mainly propagates along the impact direction, and the energy attenuates rapidly along the ring. The structural response is also different. The nodes near the top of the main rib and the middle part are the unfavorable loading points.
【学位授予单位】：兰州理工大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU399;TU311.3

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