【作者】 张凡榛；

【导师】 易伟建；

【作者基本信息】 湖南大学 ， 结构工程， 2012， 博士

【摘要】 从历史上看,在偶然荷载下建筑物发生倒塌事故的例子并不鲜见。特别是近年美国俄亥俄州Alfred P.Murrah大楼和纽约世贸双塔遭遇恐怖袭击,建筑发生部分和整体倒塌,更是把对建筑结构安全性能的研究,推到结构工程领域的前沿。国内外研究人员对钢筋混凝土框架结构连续倒塌性能进行了较为广泛的研究,主要针对的是钢结构或混凝土框架等梁柱结构,但对钢筋混凝土板柱结构抗连续倒塌破坏的研究却很少见。混凝土板柱结构是一种常用的结构形式,具有多种优点,但其发生连续倒塌破坏的潜在危险因素,却较梁柱结构复杂,对于结构工程师而言,避免板柱结构遭受意外荷载发生连续倒塌这方面,仍缺少相关的概念和试验依据。1.本文采用拟静力的试验方法,对板柱结构进行了中柱破坏(位移达到板厚1倍)、边柱破坏(位移达到板厚2倍)和角柱破坏(位移达到板厚2倍)的抗连续倒塌试验。所谓柱破坏就是正常工作状态下,板柱结构进行抽柱或移柱,来模拟框架柱失效后的结构倒塌。基于试验结果研究了板柱结构在连续倒塌过程中的破坏过程和受力状态,探讨了板柱结构在下层柱破坏后,形成的新荷载路径和传力转换机制,板的压-拉力薄膜作用可以在板柱结构柱破坏后提供高于屈服线承载力的抗倒塌能力。试验以持续施加均布荷载的方式估计结构倒塌极限承载力。试验板柱结构的设计和一些构造措施,在抵抗倒塌冲击的过程发挥了重要作用。2.基于板屈服线形式,按屈服线理论计算板承载力。依据板柱结构试验参数,建立有限元分析模型,分别对三种位置柱破坏后的倒塌过程进行模拟分析,将计算结果与试验结果进行对比分析,讨论倒塌破坏形态,最大承载力等等方面的计算结果,比较完整和准确的模拟了板柱结构试验过程,揭示了板柱结构受力特性,可以用来模拟和计算板柱结构的抗连续倒塌能力,为板柱结构进行抗连续倒塌设计提供了参考。3.基于板柱结构中间区格、边区格和角区格倒塌试验获得的板面转角临界值,建立板柱结构抗倒塌设计的临界判定标准。在静力抗倒塌设计荷载作用下,依据试验获得板柱结构倒塌判定值,指导板柱结构抗倒塌设计。另外通过有限元模型参数分析,讨论了板柱结构配筋率,混凝土强度和层数对结构倒塌的影响。4.对中间区格试验板柱结构进行了集中荷载试验。中间区格板在自身均布荷载作用下,仍能提供一定程度集中荷载承载力,说明板柱结构在其柱破坏后不仅具有均布荷载承载能力,还可以分担上层柱传轴力,可以为解决多层板柱结构柱传轴力的问题提供路径。本文建模分析与集中力试验结果吻合较好,并对边区格和角区格也进行集中力加载的模拟分析。通过静载试验来模拟固支板结构承担集中力作用能力。板的压力薄膜作用使得其集中力承载能力比屈服线理论计算值提高40%左右。根据试验结果,研究了承受集中荷载板的倒塌过程的静力特性,破坏过程和受力特点,并指出依靠板压-拉力薄膜作用实现板结构抵抗集中荷载的途径,建立了对应有限元模型,进行过程分析。5.完成了在实验室刚性地基上的板柱结构模态试验。结果表明了随混凝土龄期增长,结构各阶频率也得到增加,而试验期间温度变化对各阶频率的影响较小。本文依据试验结果和有限元模拟分析对该板柱结构进行了参数识别和损伤诊断,识别出该板柱结构“中柱”(浇注框架时用千斤顶替代该中柱)无法传递节点弯矩和提供向下的支持力,为板柱结构的损伤诊断提供了参考。6.基于试验和分析结果,提出了板柱结构抗倒塌设计流程,充分发挥板柱结构抗倒塌性能。分析板柱结构柱破坏后相邻柱轴压比变化以及相邻板柱节点不对称冲切,提出改善结构体系,保证连续性、赘余度的构造措施以及充分利用板的压-拉力薄膜悬索作用效应以增加结构的抗倒塌性能。更多还原

【Abstract】 Progressive collapse of structures caused by earthquakes, blasts, and other accidents results in catastrophic loss of life and money. Many practicing engineers and academic researchers have been engaged in the prevention of progressive collapse since the partial collapse of the22-storey Ronan Point apartment building in1968. Especially after the terror attack on the Alfred P. Murrah Federal building in1995and World Trade Center in2001, several changes to the philosophy and practice of design for important buildings have been made in the last decade. Resistance of building structures to progressive collapse has been an important task for the development of structural design codes. The RC flat plate construction systems are being widely used in residential and industrial buildings in many parts of the world. This system is highly advantageous because of the formwork costs reduction, fast execution and easy installation. The reduced storey height and increased architectural freedom in design result in lower overall construction and maintenance costs. However, because of brittle punching failure occurred at the slab-column connections, the flat plate construction is vulnerable under gravity or earthquake load.The study on the collapse-resistant experiment of RC flat slab-column structures has not been found in the literature. It is important to explore the alternative load path in a flat slab-column structure when the structure subject to a load-carrying member loss. As the vulnerable behavior of the flat slab-column structures after punching failure of the slab-column connections, it should be interesting to know the collapse-resistant performance after a column loss in the structure. However, the complete design concept is not explicit duo to the lack of relevant experimental investigation on the flat plate structures.1. This paper presents a collapse experimental research on two single-stories2×2-bay reinforced concrete flat slab-column structure in order to find the alternative load path in the flat slab-column structures when an interior/side/corner column was removed. The research described in this paper demonstrates the feasibility of using a static unloading approach to simulate column loss and to study the collapse-resistant behavior of flat slab-column structures. The data generated from this experiment will contribute to the much-needed database on collapse behavior of RC flat plate structures. The results of experiments and the analyses reported in this paper will contribute to the future development of collapse resistant design methods.2. The experiments utilize a quasi-static method to simulate the failure of a flat plate structure subjected to a sudden column loss, which reveal the plate load transmission mechanism change process and mechanical characteristics. During the collapse process of the flat plate structure, it has experienced elastic stage and plastic stage accompanied by membrane action. The experiment indicates that the compressive membrane action and tensile membrane action could be considered as an alternative load path, compressive membrane action or compressive-tensile composite membrane action is the main characteristics of new alternative load path when the flat plate structure subject to a column loss.3. Based on the experimental results, it can be judged that the conventional designed flat plate frame will not collapse after the interior column sudden removed, because the column-losing frame carried2times uniform design load characteristic value finally, the progressive collapse did not happen (dynamic impact factor<2),1.7time design load characteristic value with side column loss,1.17time design load characteristic value with corner column loss.4. The experimental results of flat plate structure show that the load-carried capacity is larger than the value predicted by yield-line theory. For flat plate, its plane stiffness is mainly provided by exterior cantilevered plate and surrounding column. Limited compressive membrane could play a certain action with limited plane stiffness, which makes the load-carrying capacity greater than plastic hinge line value.The compressive-tensile membrane action should have important effect on the load transfer mechanism when the flat plate structure with an interior column loss. However, the analytic value is hard to be obtained. A finite element model was established and verified by comparing the experimental results, the same loading procedures and constraints as in the testing were used. Finite element method was conducted to simulate the test and it shows a good agreement with the interior span test. The flat plate frame collapse-resistant assessment criterion obtained by the Finite element method is useful for the large deformation/strain analysis of the RC structure collapse, and it could be a preparation for the next parameter analysis.5. The collapse failure of the RC flat plate frame is ultimately controlled by the longitudinal reinforcement breaking. The reinforcements were almost all broken, and punching failure occurred when concentrated force113kN (uniform load unload to1time characteristic load stage) was applied downward on the interior column stub. It also shows good performance of deformation which conducive to collapse-resistant capacity of flat plate structure. The collapse-resistant capacity would be further enhanced by the reinforcement ratio which goes through the column.6. Damage identification and health monitoring is an important aspect in the evaluation of structural safety recently. This paper also presents a modal experiment and analysis for the RC flat plate frame structure. The displacement mode experiments were carried out by hammer-hitting excitation method in the age of frame concrete. The varieties of the modal parameters of the flat plate were obtained by dynamic testing along with the growth of elastic modulus of concrete and change of the environment temperature. It can be used to identify the location of the damage. Base on the missing of some specific structure modal shapes and reduction of the frame horizontal stiffness, it can be revealed that the interior slab-column connection cannot transfer the unbalance moment well. A3-D solid finite element models with the interior column fixed/hinged were constructed, they were validated to match the frame natural frequencies and mode shapes. The results demonstrate the effectiveness of modal parameters identification method in estimate the damage of column in RC flat plate frame.7. The design recommendations for the flat plate structure collapse-resistantant are proposed, the variety of the column axis compression ratio and the increment of the uneven punching shear force of the adjacent slab-column connection are analyzed, two. The structure system integrity, continuity, reducndancy, well-anchored structure and compressive-tensile membrane action would play important roles in the flat plate collapse-resistant performance.更多还原