单层球面网壳火灾爆炸动力响应

以K8型单层球面网壳为研究对象,考虑几何非线性和温度对材料性能的影响,完整模拟了单层球面网壳在发生火灾的不同阶段受到爆炸冲击作用时的动力性状。据B-R准则,通过爆炸峰值超压与结构动力特征响应之间的关系,可判定K8型单层球面网壳在不同火灾阶段,爆炸冲击作用下的动力稳定性临界峰值超压。分析了单层球面网壳的矢跨比、屋面荷载、约束布置等参数对其在不同火灾阶段的爆炸冲击动力稳定性的影响。研究表明:火灾对网壳结构在爆炸冲击作用下的动力稳定性有较大影响,当网壳杆件最高温度达500℃以上时,结构的抗爆能力明显降低。矢跨比、屋面质量、约束布置对网壳在火灾不同阶段的抗爆能力均有不同程度的影响。     

单层球面网壳的弹塑性稳定性

为了解和掌握单层球面网壳在静力荷载作用下的弹塑性稳定性能,采用有限元软件ANSYS及自编的前后处理程序对典型单层球面网壳结构稳定性能进行对比分析,初步了解了球面网壳弹性与弹塑性稳定性能的主要差异。在此基础上进行了1000余例K8型单层球面网壳弹性、弹塑性全过程分析,同时考虑竖向均布荷载的不对称分布、初始几何缺陷等因素对球面网壳稳定性能的影响,掌握了以上因素变化对球面网壳弹塑性稳定性能的影响规律,并将其定量化。最后,通过对弹性、弹塑性稳定极限承载力的统计分析,提出适用于K8、K6型球面网壳的塑性折减系数,用以表示材料非线性对极限承载力的影响。这些成果的获得为进一步开展网壳结构的弹塑性稳定性能研究以及工程实践提供了理论依据和技术参考。     

单层网壳结构动力稳定性分析方法

本文系统分析了单层网壳结构动力稳定性的研究方法。论证了对于在复杂荷载作用下非线性、多自由度复杂结构的动力稳定性问题,基于严格数学定义的Lyapunov运动稳定性理论目前尚不能提供有效的判别准则。通过理论分析和计算指出“刚度矩阵的正定与负定”不足以判定结构是否动力失稳。提出了动力响应全过程曲线的概念,并以此曲线为基础结合结构的时程响应曲线来判定网壳结构的动力稳定性。通过对不同类型荷载、不同计算条件下的网壳结构的弹性和弹塑性动力稳定性的分析,验证了本文所提判别方法的合理性。     

阶跃荷载作用下单层球面网壳动力破坏研究

针对K 8型单层球面网壳在阶跃荷载下的响应进行了系统分析,综合多项特征响应指标分析了结构响应特点并给出结构破坏定义.在大量参数分析的基础上,讨论了屋面重量、矢跨比、跨度和初始缺陷对结构破坏临界荷载、结构塑性发展、位移延性系数的关系,为网壳动力破坏机理研究提供了大量基础性材料.     

Cost-effectiveness of protective measures for single-layer reticulated domes subject to impact loading

Many spatial structures, including some public buildings, were built in the last thirty years, but considerable uncertainty remains with respect to their structural performance under impact loading. This paper focuses on single-layer reticulated domes because they encounter significant safety hazards when subject to terrorist attack. Three kinds of protective measures are proposed for mitigating the probability of global structural collapse under impact loads. The risk reduction measures include Lighter Roofs, Whole Member Strengthening and Strengthening of Key Members. These measures are compared and evaluated with respect to risk reduction. A technique is then used for assessing the cost-effectiveness of these measures. An example of a single-layer reticulated dome subject to airplane impact is used to illustrate when the protective measures are cost-effective, with quantifying costs being useful in the decision-making process.     

Effect of substructures upon failure behavior of steel reticulated domes subjected to the severe earthquake

This paper presents the study on the influence of substructures on the failure behavior of steel reticulated domes subjected to the severe earthquake. The full-range dynamic response analysis method is applied to investigate the failure characteristics of single-layer steel reticulated domes with substructures subjected to the severe earthquake. The natural vibration properties are studied. Two typical failure modes of steel reticulated domes with substructures are illustrated according to the stiffness of substructures. Failure criterion is proposed to estimate the ultimate load strength for single-layer steel reticulated domes. It is observed that the substructure has great influence on the failure characteristics and the ultimate load strength of steel reticulated domes subjected to the severe earthquake. It is necessary to take substructure into consideration in analysis and design stage.     

基于三向敏感频率的单层球面网壳结构地震动强度参数分析

选择合适的地震动强度参数可减小其与结构响应相关分析结果的离散性。以Kiewitt-8型单层球面网壳结构为研究对象,对算例结构进行谐响应分析,确定结构三个方向的敏感频率;提出基于三向敏感频率的地震动强度参数加速度谱Sa,3d。采用有限元软件ABAQUS对算例结构进行三向地震动作用下的增量动力分析,并对分析结果进行统计分析,从相关性和有效性两个方面对Sa,3d进行评价。结果表明：Sa,3d与单层球面网壳结构的地震响应具有更好的相关性,且具有较好的有效性,建议对单层球面网壳结构,采用Sa,3d 作为地震动强度参数进行增量动力分析。     

Wind loading and its effects on single-layer reticulated cylindrical shells

In this paper, the wind load distribution as well as its effects on single-layer reticulated cylindrical shells, which are widely used in practice, is investigated. At first, wind pressure distributions on three rigid cylindrical shell models considering different shape ratios are measured simultaneously in a wind tunnel. Some special characteristics of the measured wind pressure, especially its fluctuating component, are discussed. Then, considering the special structural mechanical behaviors, the effects of wind load, especially the fluctuating component, on the limit load-carrying capacity and the stability of the shells are investigated by both equivalent static analysis and dynamic analysis. Suitable methods to get a reasonable estimation of wind load effects in estimating the equivalent static wind load distribution for such shells are investigated. Finally, with comparison analyses using different methods mentioned in this paper, the efficiency of the method in estimating the effective wind load distribution presented by the authors previously for single-layer reticulated spherical shells is demonstrated, and some advices for estimating the wind load distribution on single-layer reticulated cylindrical shells is given for wind-resistant design in practice.     

Failure modes of reticulated domes subjected to impact and the judgment

FE models of both the single-layer Kiewitt-8 reticulated domes with a span of 60 m and the cylindrical impactor were developed incorporating ANSYS/LS-DYNA. Numerical simulations of the dynamic behaviours of domes subjected to impact on the apex were conducted, and the four failure modes were indentified according to the dynamic responses. It was found that correlation between the initial impact conditions, mass and velocity of impactor, and dynamic responses, and correlation between the initial impact conditions and the failure modes are both poor. However, close correlation between the response velocity v_IJ of the impacted joint, i.e. the velocity of the impacted joint when the first impact is just over, and the dynamic responses of dome was revealed. v_IJ was used to judge the failure modes. Furthermore, theoretical solution of v_IJ was achieved by means of the defined impact zone and the equivalent mass of the zone. By so doing, the response velocity v_IJ and the judgment of the failure modes of dome can be solved by the simplified theoretical approach, without resorting to the sophisticated FE modelling.     

基于IDA的网壳结构动力失稳分析

地震作用下网壳结构的倒塌本质上属于动力失稳问题,如何确定网壳结构倒塌的极限状态点,是网壳结构倒塌分析中一个非常重要的问题。采用近年来发展起来的一种用于评价结构抗震性能的动力参数分析方法,即增量动力分析(IDA)方法,作为分析结构整体倒塌能力的新方法,为网壳结构的动力失稳分析和倒塌分析提供了一个新的分析途径,并据此可以找到网壳结构倒塌的极限状态点。最后,指出该方法的优点和有待改进之处。     

Research on stability of single-layer inverted catenary cylindrical reticulated shells

The structural configuration and method of analysis of the single-layer inverted catenary cylindrical reticulated shell are introduced in this paper, and the elastic as well as elastic–plastic stability of this kind of reticulated shell is then investigated. The stability of the structures with different types of grid patterns is compared, and the reasonable grid pattern is hence recommended. The structural buckling mode and ultimate load-carrying capacity are studied in detail by parametric analysis. Influence of various factors on structural ultimate load is investigated, and the fitting formula of ultimate load is thus presented. Comparison analysis between the inverted catenary and circular cylindrical reticulated shells is also carried out. The work will provide guidance in theory for practical applications of this kind of structure.     

节点刚度对三向单层球面网壳稳定承载力的影响

为了评估节点刚度对网壳极限承载能力的影响,建立了一种能同时考虑节点刚度(弯曲刚度、轴向刚度、扭转刚度与剪切刚度)和节点大小的力学模型.借鉴节点正则化弯曲刚度指标κb的概念,建议采用正则化轴向刚度κa、正则化扭转刚度κt与正则化剪切刚度κs来衡量节点的轴向、扭转及剪切刚度.经过数值计算,主要得出如下结论:节点弯曲刚度对网...     

Dynamic response and reliability analysis of tall buildings subject to wind loading

This paper explores the wind stochastic field from a new viewpoint of stochastic Fourier spectrum (SFS). The basic random parameters of the wind stochastic field, the roughness length z₀ and the mean wind velocity at 10 m height U₁₀, as well as their probability density functions (PDF), are obtained. It provides opportunities to use probability density evolution method (PDEM), which had been proved to be of high accuracy and efficiency, in computing the dynamic response and reliability of tall buildings subject to the wind loading. Principals and corresponding numerical solving algorithm of the PDEM are first presented. Then, the adopted model of the wind stochastic field is described briefly. The simulation method of the fluctuating wind velocity based on the SFS is introduced. Finally, as an example of the application of the PDEM, a 20-storey frame subject to wind loading is investigated in detail. The responses, including the mean value and the standard deviation, and the reliabilities of the frame are evaluated by the PDEM. The results demonstrate that the PDEM is applicable and efficient in the dynamic response and reliability analysis of wind-excited tall building.     

钢管混凝土柱抗爆性能试验研究

为研究钢管混凝土柱（CSTC）的抗爆性能,通过12个钢管混凝土柱试件的现场爆炸试验,得到柱上迎爆面与背爆面的冲击波压力时程曲线及其压力分布形式,分析柱的位移和应变变化等,并研究不同炸药当量、炸药安置距离、试件轴压比、混凝土强度等级、含钢率等对钢管混凝土柱抗爆性能的影响。结果表明：柱背爆面上冲击波压力值很小,可忽略不计;柱以弯曲变形为主,且随着轴压比及炸药当量的增加,试件最大和残余变形都相应增大;随着炸药安置距离、含钢率和混凝土强度等级的增大,试件残余变形相应减小。塑性变形在最大变形中所占比例均随变形的增大而增加,柱以整体变形为主。     

Seismic performance and collapse prevention of concrete-filled thin-walled steel tubular arches

The primary objective of this paper is to investigate the seismic behaviour of concrete-filled steel tubular (CFST) arches using incremental dynamic analysis (IDA). A nonlinear elastic–plastic finite element model is developed using OpenSees software and is verified with a shaking table test. Single-record IDA studies indicate that a CFST arch undergoes global dynamic instability when subjected to ground motions of increasing intensity levels. During this process, either dynamic elastic buckling or dynamic elastic–plastic buckling may occur. Dynamic strength, which is defined as the capacity for preventing global dynamic instabilities of CFST arches, is determined with a series of multi-record IDA calculations. A lower bound equation that takes into account the effect of slenderness ratio, axial compression ratio, and included angle is proposed for the prediction of the dynamic strength of CFST arches.     

Fatigue properties of intact sandstone samples subjected to dynamic uniaxial cyclical loading

In this paper, the fatigue behaviour of intact sandstone samples obtained from a rockburst prone coal mine and studied under dynamic uniaxial cyclic loading in the laboratory is presented. Tests were conducted on dry and saturated samples with loading frequencies ranging from 0.1, 1 and 10 Hz and amplitudes of 0.05, 0.1 and 0.15 mm. From the laboratory investigations, it was found that the loading frequency, as well as the amplitude, was of great significance and influenced the rock behaviour in dynamic cyclic loading conditions. The dynamic fatigue strength and the dynamic axial stiffness of the rock reduced with loading frequencies and amplitude. The dynamic modulus was found to increase with the loading frequency but decrease with the amplitude. In the case of the saturated samples, it was found that the dynamic fatigue strength reduced by approximately 30 per cent, while the dynamic Young's modulus reduced by about 20 per cent. From the presented study, the dynamic energy was found to be independent of the testing conditions while other rock properties were found to be dependent on these. Finally, it was concluded that rock would more readily succumb at low frequencies and amplitude than at high frequencies and amplitude for a given energy availability.     

CFRP加固钢筋混凝土梁抗爆性能试验研究

通过对三组15根CFRP加固钢筋混凝土梁进行抗爆性能试验,研究了CFRP粘贴层数、配筋率、爆炸荷载大小等因素对裂缝开展、破坏形式、应变和挠度的影响。试验结果表明,加固梁的裂缝数量明显增多,但裂缝宽度减小了43%～71%,裂缝间距减小了79%～89%,U形锚固有效阻止了CFRP剥离,使加固梁呈CFRP拉断破坏。随着CFRP粘贴层数的增加,梁的抗爆能力平均提高量为13%～42%。对应于配筋率为0.84%、1.30%、1.88%的加固梁在第1、2、3次爆炸加载时的抗爆能力平均提高量分别为14%、16%和29%,但随着配筋率增加,加固梁的抗爆能力提高幅度有所减小。当爆炸荷载较大时,CFRP与受拉纵筋之间开始出现应变差,CFRP的存在使得钢筋的应变发展滞后于未加固梁中钢筋的应变发展,这种现象随爆炸荷载增大而趋于明显。CFRP可以有效提高钢筋混凝土梁的刚度,但加固梁的变形能力减小。     

Response of stiffened and unstiffened plates subjected to blast loading

This paper describes the results of dynamic analyses carried out on both stiffened and unstiffened panels using both simplified and advanced analytical techniques. For unstiffened panels with inplane restraint along their edges, the dynamic response of an imperfect panel was predicted using a large displacement elastic analysis based on Lagrange's equation, with the panel being treated as a shallow shell. For stiffened panels, the finite element (FE) technique was used to establish the validity of using the simplified technique to predict the inter-stiffener panel displacements for a simply supported panel. A parametric study has been carried out to analyse the effects of in-plane boundary conditions, local stiffener buckling and initial imperfections on the overall response. The significant effect of boundary conditions is demonstrated by including the actual boundary conditions of a test frame in the finite element modelling of a large-scale stiffened floorplate panel used in an experimental test series.     

Proposal of a probabilistic assessment of structural collapse concomitantly subject to earthquake and gas explosion

In recent decades, many public buildings, located in seismic-prone residential areas, had to grapple with abnormal loads against which the structures were unguarded. In this piece of research, an ordinary three dimensional reinforced concrete building is selected as case study. The building is located in an earthquake-prone region; however, it is designed according to seismic building codes. Yet, it is not shielded against abnormal loads, such as blasts. It is assumed that the building suffers a blast load, due to mechanical/thermal installation failure during or after intense seismic oscillations. These two critical incidents are regarded codependent and compatible. So the researchers developed scenarios and tried to assess different probabilities for each scenario and carried out an analysis to ensure if progressive collapse had set in or not. In the first step, two analysis models were used for each scenario; a non-linear dynamic time history analysis and a blast local dynamic analysis. In the second step, having the structural destructions of the first step in view, a pushdown analysis was carried out to determine the severity of progressive collapse and assess building robustness. Finally, the annual probability of structural collapse under simultaneous earthquake and blast loads was estimated and offered.     

Beam-column element for non-linear dynamic analysis of steel members subjected to blast loading

This paper addresses an innovative semi-analytical non-discretisation numerical methodology for the non-linear dynamic analysis of steel beam-column elements subjected to loading produced by an explosion. For the mechanical-based formulation, the steel beam-column member is modelled as being restrained at its ends by translational and counterpart rotational springs which simulate semi-rigid joints in a frame. The modelling of the cross-section as comprising of elastic and inelastic domains allows for the spread of yielding to be modelled accurately, whilst the effects of large displacements and the rate-dependent effect of steel material due to rapid dynamic loading is taken into account. The generic steel beam-column element that is developed is shown to agree well with solutions given by finite element modelling using ABAQUS, while providing a computationally superior formulation to that of commercial finite element packages. In addition, it provides a more efficacious formulation to those of conventional plastic zone and plastic hinge methods, while it has the potential to be used as a platform for structural analysis and design in which scenarios of progressive collapse are important.