砌体结构长脉宽爆炸荷载损伤等级评估方法

随着百千吨级当量爆炸工业事故的频繁发生,建筑结构的损伤评估和抗爆安全性更受到关注。目前,构件级的评估方法相对成熟,而大当量冲击波作用下的建筑结构整体毁伤评估依旧是个开放性问题。本文中,面向结构级的毁伤评估,提出了一种新的评估方法?构件损伤加权。该方法以承重构件损伤程度为基础,通过基于应变能的构件权系数加权,进而评估结构级损伤破坏程度。为了验证评估方法的有效性,以典型砌体结构为例,利用自主研发的冲击波结构毁伤模拟有限元程序,开展了百毫秒脉宽爆炸冲击波荷载下结构动力学响应数值模拟。根据数值模拟结果,结合构件损伤加权的评估方法,获取砌体结构损伤等级与冲击波超压的关系。预测的超压值的相对误差为?16.9%～26.2%,验证了评估方法的有效性。该评估方法为获取砌体结构的超压-冲量曲线提供了可行的途径,可为结构的抗爆安全设计提供参考。     

桥梁结构抗爆安全评估研究进展

随着恐怖袭击和偶发爆炸事故造成的桥梁爆炸事故不断增多,桥梁结构抗爆安全问题越来越受到关注。本文中系统总结了桥梁结构抗爆安全评估的研究进展,分析桥墩、桥面、桥索和桥塔爆炸载荷作用下桥梁的理论简化方法和结构的动力响应,和桥梁的连续性、冗余性和鲁棒性对结构连续性倒塌的影响,通过对建筑和桥梁抗连续倒塌的研究现状及相关规范的归纳,明确了桥梁连续倒塌的特性及现行桥梁设计方法的缺陷。而后,就承载能力评估、耐久性评估和适用性评估等桥梁安全评估问题的研究进展进行了梳理,并对桥梁爆破拆除技术和近地下爆炸对桥梁产生的响应和破坏作用进行分析,并针对当前研究的现状,分别提出建议。     

结构元件安全评估与监控的风险预测方法

提出了一种评估结构疲劳可靠性的方法－风险预测方法。该方法利用结构在服股过役过程中的信息,在考虑了工程结构承采载荷的各态历经性的基础上,结合了结构元件寿命机分布形式和Ｍｉｎｅｒ线性累积损伤理论,以风险值来评价并监控结构元件在不同时间失效的危险性,并用算例和试验结果进行对比分析。     

爆炸荷载作用下UHPC板的弯曲损伤评估

为构建爆炸荷载作用下超高性能混凝土（UHPC）板弯曲损伤等级评估的p-I（压力-冲量）曲线：采用条带法进行截面分析,建立了考虑UHPC材料拉/压软化和塑性铰影响的UHPC简支单向板的非线性抗力方程和等效单自由度（ESDOF）理论模型;通过与六炮次爆炸实验中UHPC板的挠度时程,以及UFC 3-340-02和FHWA规范推荐方法的计算结果对比,验证了本文理论模型的可靠性;基于验证的ESDOF模型,构建了评估UHPC板的不同弯曲损伤等级的p-I曲线并开展了参数影响分析,提出并验证了UHPC板弯曲损伤评估的p-I曲线经验公式。结果表明：提高混凝土强度等级和钢筋屈服强度、增加受拉钢筋配筋率和板厚,以及减小净跨均可提升UHPC板的抗爆性能。     

瓦斯爆炸载荷作用下矿用柱壳救生舱抗爆性分析及结构优化

矿用救生舱是矿井安全生产中必备的救生装备,其稳定性和抗爆性能决定着逃生人员的生存概率。本文中设计了一种圆柱壳结构救生舱,优化了该救生舱在瓦斯爆炸载荷作用下的抗爆性能:首先,采用ANSYS/LS DYNA软件模拟并验证了爆炸流场载荷;其次,采用ALE流固耦合算法揭示了真实环境下爆炸流场与救生舱的耦合作用;然后,对其进行抗爆性模拟分析及结构设计优化;最后,对比分析了原模型和优化模型的动力响应、强度及能量变化特征,结果表明优化后的救生舱抗爆性满足国家规范要求。     

爆炸荷载作用下多排钢管结构的大变形响应

采用八塑性铰变形模态,对爆炸荷载作用下多排钢管的压扁运动场进行了描述。基于虚速度原理,建立了多排钢管动力压扁模态解方程。由拉格朗日第二类方程确立初始条件,用差分法求解出各层钢管结构的传递荷载和压扁量大变形响应。计及应变率效应和材料硬化效应,计算值与试验结果相符。结果表明,采用模态法求解多排钢管的大变形动响应是可行的。     

基于小波分析的建(构)筑物爆破振动安全评估

基于现场实测爆破振动数据,采用小波分析技术对爆破振动信号的能量特征进行分析,得到了信号不同频带上的能量分布,根据受控结构体对爆破振动动态响应特征,探索建立了能考虑爆破振动的强度、频率和持续时间以及受控建(构)筑物本身的动态响应特性(固有频率和阻尼比)等因素的综合安全判据响应能量判据,并用工程实例验证了该判据的可行性和可靠性。响应能量判据能准确地描述爆破振动对受控建(构)筑物的影响程度,较现行的速度-频率安全判据,更能全面地反映爆破振动对建(构)筑物危害的本质。     

城市地下浅埋管沟可燃气体爆炸的灾害效应(Ⅱ):影响因素分析及后果评估

为系统地评估城市地下浅埋管沟可燃气体爆炸的灾害后果,利用FLACS软件模拟得到了可燃气体的爆炸荷载,并分析了该灾害对建筑物破坏和人员伤害的危险距离及影响因素。结果表明:当点火位置靠近管沟中间位置时,超压峰值和危险距离较大;泄爆口的大小对危险距离的影响不大,而对离泄爆口较近处的超压峰值影响较大;气云长度越长,超压峰值和危险距离也越大,但增幅逐渐减小直至不变;管沟的横截面面积越大,超压峰值和危险距离也越大;为避免造成严重的灾害后果,高耸建筑物和密集人群应远离泄爆口。     

钢筋混凝土桥墩弯剪数值分析模型

基于修正的压力场理论MCFT(The Modified Compression Field Theory)和纤维单元模型建立了钢筋混凝土桥墩的弯剪数值分析模型,以MCFT理论确定桥墩的剪切力-剪切位移关系,并与考虑桥墩弯曲变形的纤维单元模型组合,共同考虑桥墩的弯-剪-轴力耦合作用.通过与六个弯剪破坏控制的圆形截面钢筋混凝土桥墩拟静力试验结果的对比,对分析模型进行了验证.主要认识结论为基于MCFT理论可准确地计算弯剪破坏桥墩的屈服荷载、极限荷载和弹性阶段剪切刚度,剪切开裂是引起钢筋混凝土构件剪切力-剪切位移关系刚度突变的主要因素,而弯曲开裂与纵筋屈服对刚度的影响较小;分析模型对弯剪破坏桥墩的滞回曲线、弯曲与剪切变形成分均进行了较为准确的模拟分析.     

Variational eigenstrain analysis of residual stresses in a welded plate

We present the formulation for finding the distribution of eigenstrains, i.e. the sources of residual stress, from a set of measurements of residual elastic strain (e.g. by diffraction), or residual stress, or stress redistribution, or distortion. The variational formulation employed seeks to achieve the best agreement between the model prediction and some measured parameters in the sense of a minimum of a functional given by a sum over the entire set of measurements. The advantage of this approach lies in its flexibility: different sets of measurements and information about different components of the stress-strain state can be incorporated. We demonstrate the power of the technique by analysing experimental data for welds in thin sheet of a nickel superalloy aerospace material. Very good agreement can be achieved between the prediction and the measurement results without the necessity of using iterative solution. In practice, complete characterisation of residual stress states is often very difficult, due to limitations of facility access, measurement time or specimen dimensions. Implications of the new technique for experimental analysis are all the more significant, since it allows the reconstruction of the entire stress state from incomplete sets of data.     

钢筋混凝土剪力墙受火性能非线性分析

为了研究钢筋混凝土剪力墙的抗火性能,本文基于纤维元模型,提出了一种非线性分析方法。该方法无需计算截面的弯矩-曲率曲线族,计算过程中采用了高温下耦合的混凝土本构关系,其中考虑了混凝土高温热膨胀应变、瞬态热应变和徐变。编制了相应的非线性计算分析程序,程序考虑了轴力二阶效应的影响,计算得到了剪力墙跨中平面外挠度以及火灾下其跨...     

A smeared / layered reinforced concrete model for finite element analysis

A new reinforced concrete model, in which the reinforcement steel is assumed as smeared / layered in concrete, is established and installed into a currently used finite element code for nonlinear analysis. It performs the nonlinear behaviors of both concrete and the reinforcement steel. The results of examples are in good agreement with the experimental data.     

Nonlinear damage model for seismic damage assessment of reinforced concrete frame members and structures

A nonlinear damage model based on the combination of deformation and hysteretic energy and its validation with experiments are presented. Also, a combination parameter is defined to consider the mutual effect of deformation and hysteretic energy for different types of components in different loading stages. Four reinforced concrete (RC) columns are simulated and analyzed using the nonlinear damage model. The results indicate that the damage evolution evaluated by the model agrees well with the experimental phenomenon. Furthermore, the seismic damage evolution of a six-story RC frame was analyzed, revealing four typical failure modes according to the interstory drift distribution of the structure; the damage values calculated using the nonlinear damage model agree well with the four typical failure modes.     

火灾下钢筋混凝土板的非线性有限元分析

根据大挠度板单元理论,对常温钢筋混凝土简支板的力学性能进行数值分析,验证了模型及程序的可靠性。在此基础上,提出双轴受压瞬态热应变模型和瞬态模量的概念,利用温度场模拟结果,对钢筋混凝土简支板火灾行为进行了数值模拟,并研究了不同准则下板的耐火极限。结果表明,数值计算结果与试验曲线吻合较好,验证了瞬态热应变模型的有效性;与其他准则相比,基于温度准则所得的耐火极限值相对保守。     

On structural safety assessment by load factor maximization in piecewise linear plasticity

The safety assessment of structures by the maximization of a load factor up to a critical threshold is considered in this paper and a procedure is developed which generalizes limit analysis by the static approach. The following issues are dealt with: (a) piecewise linear approximation of material models is adopted as a unifying framework; (b) a procedure is developed apt to reduce the computing effort by means of yield mode selection or “sifting”; (c) a method which combines limit and deformation analysis is presented, based on mathematical optimization under linear and complementarity constraints and apt to compute, also in the presence of nonassociativity and softening, the safety factor with respect to either plastic collapse or local fracture or unserviceability because of excessive deformations, alternatively. Classical limit analysis rooted in associative perfect plasticity has well-known limitations, which are substantially mitigated in its generalization represented by method (c) proposed herein.     

High resolution COD image analysis for health monitoring of reinforced concrete structures through inverse analysis

Direct and inverse problems of a fracture mechanics based RC beam model are solved. Solution of the direct problem that maps crack bridging stresses into crack opening displacements (COD) is straightforward, but the inverse problem is ill-posed, and better solved by the theory of inverse problems. This paper exploits the Tikhonov regularization method to solve the inverse problem, and estimates the force and location of rebar in buried concrete from CODs. Bending tests are carried out on model RC beams in the laboratory to demonstrate the applicability of the method. During the tests, a microscopic camera snaps high resolution digital pictures of cracked concrete surface. The images are analyzed by a software to measure surface CODs that are input into the inverse problem. The practical CODs inevitably include noise due to experimental error, which makes the inverse problem ill-posed, and necessitates regularization. In the current inverse analysis by the Tikhonov regularization method, bridging stress profiles, i.e. variation of the crack bridging stress along the crack length, has been figured out. Results are compared with those from other theoretical methods of analysis as well as with the readings from strain gauges. The method is a suitable non-destructive means for existing structures in cases where the section information is inadequate, or damages/repairs have altered the designed cross-section.