A Bayesian probabilistic approach for structure damage detection

A Bayesian probabilistic approach is presented for the damage detection of multistorey frame structures. In this paper, a Bayesian probabilistic approach is applied to identify multiple damage locations using estimated modal parameters when (1) the measurement data are potentially corrupted with noise, (2) only a small number of degrees of freedom are measured, and (3) a few fundamental modes are estimated. To reduce the potentially intensive computational cost of the proposed method, a branch-and-bound search scheme is proposed and a simplified approach for the modelling of multistorey frame structures is employed. A six-storey shear frame example and two multistorey frame examples, with multiple damage locations, are presented to illustrate the applicability of the proposed approach. © 1997 John Wiley & Sons, Ltd.     

Cyclic tests of four two‐story narrow steel plate shear walls. Part 2: experimental results and design implications

This paper is the second part of a two‐part paper presenting the cyclic tests of four two‐story narrow steel plate shear walls (SPSWs). The first paper introduces the analytical studies and the specimen designs. This paper describes the test results. Some design implications including the capacity design for the first story column and the width‐to‐thickness ratio check for the beam web are discussed based on key observations from the tests. Test results confirm that the simplified strip model can accurately predict the inelastic responses of the specimens. Test results also confirm that the proposed capacity design method is effective in ensuring the plastic hinge formation at the bottom end of the first story column for SPSW with or without restrainers. Test results also show that the horizontal restrainers are effective in reducing the member forces in the boundary beam and column elements. Comparing the test results of the typical SPSW with those of the restrained SPSW (R‐SPSW) specimens, it is found that the R‐SPSW possesses an improved cyclic performance and reduced material weight. Analytical results predict the compressed column moments at the onset of the column plastic hinge formation well. The analytical hysteretic energy distribution in the first story column agrees very well with the observed inelastic actions developed in the four specimens. The detailed frame response analyses and the test results confirm that the assumptions made in developing the proposed column capacity design method are reasonable. Copyright © 2009 John Wiley & Sons, Ltd.     

基于纤维梁柱单元的桥梁墩柱地震反应模拟方法研究

为讨论利用纤维梁柱单元进行钢筋混凝土桥墩地震反应分析的建模方法,分别以4个悬臂式单柱墩和1个双柱墩拟静力加载试验,以及1个悬臂式单柱墩的振动台试验结果为依据,基于OpenSees数值分析平台建立了桥墩的地震反应分析模型。通过改变单元数量,分析了基于力的纤维梁柱单元和基于位移的纤维梁柱单元对桥墩地震反应的模拟精度。结果表明:对悬臂式单柱墩的拟静力和振动台试验,可沿墩高仅建立1个基于力的纤维梁柱单元,并在墩底串联1个考虑纵筋塑性渗透和粘结滑移的转动弹簧单元,即可获得很好的模拟结果。当采用基于位移的纤维梁柱单元时,应沿墩高至少建立2个单元,且塑性铰区至少有1个,才能保证获得较高的模拟精度。对双柱墩拟静力试验,采用基于力的纤维梁柱单元建模,沿每个墩高建立2个单元即可;以基于位移的纤维梁柱单元建模,建议沿每个墩高建立3个单元,且其中2个单元布置在塑性铰区。当数值模型可对静力滞回曲线取得很好的模拟结果后,该模型一般可对动力作用下墩顶最大位移和墩底最大剪力进行较为准确的模拟,但对墩顶残余位移的模拟精度无法保证。     

装配式人工消能塑性铰框架-摇摆墙抗震性能研究

为提高装配式钢筋混凝土(RC)框架结构的抗震性能,并针对震后梁、柱构件损伤严重等问题,提出一种基于人工塑性消能铰的装配式混凝土框架-摇摆墙结构.人工消能塑性铰即梁、柱构件在梁端采用机械铰及附加耗能钢板连接的构造,基于该构造的框架结合底部铰接的剪力墙,形成人工消能塑性铰框架-摇摆墙结构.使用OpenSEES软件建立了人工...     

Analytical prediction of seismic behaviour for concentrically-braced steel systems

This paper presents an analytical model for the inelastic response analysis of braced steel structures. A model is first presented for the behaviour of steel struts subjected to cyclic axial load, which combines the analytical formulation of plastic hinge behaviour with empirical formulas developed on the basis of experimental data. The brace is modelled as a pin-ended member, with a plastic hinge located at the midspan. Braces, with other end conditions, are handled using the effective length concept. Step-wise regression analysis is employed, to approximate the plastic conditions for the steel UC section. Verification of the brace model is performed on the basis of quasi-static analyses of individual struts and a one-bay one-storey X-braced steel frame. The comparison of analytical and experimental data has confirmed that the proposed brace model is able to accurately simulate the cyclic inelastic behaviour of steel braces and braced systems. A series of dynamic analyses has been performed on two-storey V- and X-braced frames to study the influence of brace slenderness ratio on the inelastic response, and to look at the redistribution of forces in the post-buckling range of behaviour of CBFs. Recommendations have been made as to the estimation of maximum storey drifts for concentrically-braced steel frames in major seismic event. © 1997 John Wiley & Sons, Ltd.     

基于钢筋混凝土足尺柱拟静力试验的离线模型更新混合试验方法

离线模型更新混合试验对构件拟静力数据进行恢复力模型参数识别,并更新数值子结构中相应构件的模型参数来提高混合试验精度,但该方法尚缺少真实试验的验证。本文基于课题组开展的足尺RC柱拟静力试验,取恢复力模型为集中塑性铰Ibarra-Medina-Krawinkler（IMK）模型,进行框架结构离线模型更新混合试验研究。结果表明,当物理子结构取为RC足尺柱时,离线模型更新混合试验能获得接近于真实试验情况下结构的地震响应,从而对该方法的有效性进行了试验验证。利用IMK经验公式,将真实试验模型参数识别值按轴压比进行对照修正,应用于不同层数的框架结构地震响应模拟,实现了试验数据的重复利用。     

Cyclic test of a coupled steel plate shear wall substructure

Coupled steel plate shear wall (C‐SPSW) consists of two or more steel plate shear walls interconnected by coupling beams at the floor levels. In this study, a six‐story C‐SPSW prototype building was designed. A 40% scale C‐SPSW specimen, which is representative of the bottom two‐and‐half‐story substructure of the prototype, was cyclically tested using Multi‐Axial Testing System at the National Center for Research on Earthquake Engineering in 2009. In addition to a constant vertical force representing the gravity load effects, cyclic increasing displacements and the corresponding overturning moments transmitted from the upper stories were computed online and simultaneously applied on the substructural specimen. This paper firstly introduces the designs of the prototype C‐SPSW and the test specimen. Then, the test results and the numerical simulation are discussed in detail. Test results confirm the effectiveness of the proposed column capacity design method, which aims at limiting the plastic hinge formation within the bottom quarter height of the bottom column. Test and analytical results suggest that the coupling beam rotational demands can be estimated as the design story drifts when the formation of desirable plastic mechanism of the C‐SPSW is expected. Copyright © 2011 John Wiley & Sons, Ltd.     

基于主组分分析的概率神经网络损伤定位研究

概率神经网络(PNN)以贝叶斯概率的方法描述测量数据,因而PNN在有噪声条件下的结构损伤检测方面具有巨大潜力。与此同时,PNN的网络规模随着训练样本的增加而增大,这极大地降低了网络运行速度。基于此,本文提出了基于主组分分析(PCA)的PNN损伤定位方法,分别用传统PNN(TPNN)、主组分分析PNN(PCAPNN)和自适应PNN(APNN)三种模型进行了悬索桥的损伤定位研究。研究发现,APNN的识别精度最好,PCAPNN次之,TPNN最差。但APNN需要很长的训练时间,网络规模较大;其他两个网络几乎不需要训练时间,且PCAPNN网络规模较其他两个网络减少了1／3～1／4。在低噪声情况下,PCAPNN的识别效果基本上等同于APNN。     

Controlled rocking pile foundation system with replaceable bar fuses for seismic resilience

Bridges designed following a conventional approach minimize the risk of collapse, but often require challenging, costly, and time-consuming restoration after an earthquake occurs. The new seismic design philosophy requires bridges to maintain functionality even after severe earthquakes. In this context, this paper proposes a controlled rocking pile foundation(CRPF) system and numerically evaluates bridges′ degree of seismic resilience. The CRPF system allows a pile cap to rock on a pile foundati...     

Bridge health monitoring system based on vibration measurements

A bridge health monitoring system is presented based on vibration measurements collected from a network of acceleration sensors. Sophisticated structural identification methods, combining information from the sensor network with the theoretical information built into a finite element model for simulating bridge behavior, are incorporated into the system in order to monitor structural condition, track structural changes and identify the location, type and extent of damage. This work starts with a brief overview of the modal and model identification algorithms and software incorporated into the monitoring system and then presents details on a Bayesian inference framework for the identification of the location and the severity of damage using measured modal characteristics. The methodology for damage detection combines the information contained in a set of measurement modal data with the information provided by a family of competitive, parameterized, finite element model classes simulating plausible damage scenarios in the structure. The effectiveness of the damage detection algorithm is demonstrated and validated using simulated modal data from an instrumented R/C bridge of the Egnatia Odos motorway, as well as using experimental vibration data from a laboratory small-scaled bridge section.     

Seismic performance and design of bridge column-to-pile shaft pipe-pin connections in precast and cast-in-place bridges

Hinge or “pin” connections may be used in integral bridges to connect columns to pile shafts to reduce the foundation force demand. Used in combination with prefabricated columns, pins facilitate accelerated bridge construction (ABC). These innovative methods could improve the quality and economy of project compared with conventional construction in seismic regions. This study developed pipe pins that reduce moment transfer between the column and pile shaft under seismic excitations. The pipe pins consist of two steel pipes and a rod that transfer shear and tension while allowing rotation between the column and shaft. The primary objective of this research was to investigate the seismic performance and develop design guidelines of column-to-pile shaft pipe pins for cast-in-place and precast constructions. This research was composed of experimental and analytical studies. The experimental portion of the study consisted of testing of a large-scale bent model subjected to seismic loadings. The test results confirmed that the proposed design method meets the safety and performance requirements of the codes under seismic loadings. The pins maintained structural integrity with minimal damage, while the columns reached the full plastic hinge capacity. The analytical studies consisted of (a) a simple stick model to be used as a design tool, (b) a finite element model (FEM) for global analysis of bridges, and (c) an elaborate FEM to investigate the microscopic performance and interaction of the components. The analytical models were subsequently used in parametric studies.     

Damage identification method using harmonic excitation force considering both modelling and measurement errors

A method of structural damage identification using harmonic excitation force is presented. It considers the effects of both measurement and modelling errors in the baseline finite element model. Damage that accompanies changes in structural parameters can be estimated for a damaged structure from the change between measured vibration responses and ones calculated from the analytical model of the intact structure. In practice, modelling errors exist in the analytical model due to material and geometric uncertainties and a reduction in the degrees of freedom as well as measurement errors, making identification difficult. To surmount these problems, bootstrap hypothesis testing, which enables statistical judgment without information about these errors, was introduced. The method was validated by numerical simulation using a three‐dimensional frame structure and real vibration data for a three‐storey steel frame structure. Copyright © 2005 John Wiley & Sons, Ltd.     

Residual structural capacity evaluation of steel moment‐resisting frames with dynamic‐strain‐based model updating method

This paper presents a method for evaluating the residual structural capacity of earthquake‐affected steel structures. The method first quantifies the damage severity of a beam by computing the dynamic‐strain‐based damage index. Next, the model used to analyze the structure is updated based on the damage index, to reflect the observed damage conditions. The residual structural capacity is then estimated in terms of changes in stiffness and strength, which can be applied by structural engineers, via a nonlinear static analysis of the updated model. The main contributions of this paper are in performance evaluation of the dynamic‐strain‐based damage index for seismically induced damage using a newly developed substructure testing environment, consideration of various damage patterns in composite beams, and extension of a local damage evaluation technique to a residual capacity estimation procedure by incorporating the model‐updating technique. In laboratory testing, the specimens were damaged quasi‐statically, and vibration tests were conducted as the damage proceeded. First, a bare steel beam–column connection was tested, and then a similar one with a floor slab was used for a more realistic case. The estimated residual structural capacities for these specimens were compared with the static test results. The results verified that the proposed method can provide fine estimates of the stiffness and strength deteriorations within 10% for the specimen without the floor slab and within 30% for that with the floor slab. Copyright © 2017 John Wiley & Sons, Ltd.     

Numerical study of characteristics of underground blast induced surface ground motion and their effect on above-ground structures. Part II. Effects on structural responses

Studies of structural responses and damage to high-frequency blast motion are very limited. Current practice uses some empirical allowable ground vibration limits in assessing structural performance. These empirical limits overlook the physical parameters that govern structural response and damage, such as the ground motion characteristics and inherent structural properties. This paper studies the response of RC frame structures to numerically simulated underground blast-induced ground motions. The structural response and damage characteristics of frame structures to ground motions of different frequencies are investigated first. The effects of blast ground motion spatial variations and soil–structure interaction on structural responses are also studied. A suitable discrete model that gives accurate response prediction is determined. A damage index defined based on the accumulated plastic hinge rotation is used to predict structural damage level. Numerical results indicated that both the low structural vibration modes (global modes) and the first elemental vibration mode (local) might govern the dynamic structural responses depending on the ground motion frequency and structural response parameters under consideration. Both ground motion spatial variations and soil–structure interaction effects are prominent. Neglecting them might yield inaccurate structural response prediction. The overall structural response and damage are highly ground motion frequency dependent. Numerical results of structural damage are also compared with some test results obtained in a previous study and with code specifications. Discussions on the adequacy of the code allowable ground vibration limits on RC frame structures are also made.     

Stiffness and cyclic deformation capacity of circular RC columns with or without lap-splices and FRP wrapping

Mechanics-based models are developed for the moment, the curvature and the chord rotation at yielding of circular concrete columns or piers, their secant stiffness to the yield point and the ultimate curvature and flexure-controlled ultimate chord rotation in cyclic loading. The strain criteria for yielding or ultimate are calibrated on the basis of over four hundred test results. Besides the model for the secant-to-yield-point stiffness which is in terms of the yield moment and chord rotation, an empirical one, independent of the vertical reinforcement, is fitted to the data. The ultimate chord rotation is obtained from a plastic hinge model employing a plastic hinge length, the yield and the ultimate curvatures of the end section and the fixed-end rotation due to slippage of bars from their anchorage zone beyond the column length. All models are extended to columns the vertical bars of which are lap-spliced within the plastic hinge and to columns with FRP wrapping and continuous or lap-spliced vertical bars. The comprehensive portfolio of expressions proposed for the deformation properties of circular columns is fully consistent across the various situations of continuous or lap-spliced bars, with or without FRP wrapping, and with models developed by the authors from much larger databases of rectangular columns in similar situations; the aspects specific to circular sections are limited to the mechanics-based section analysis for moment and curvature, a purely empirical coefficient for the secant-to-yield-point stiffness and the empirical plastic hinge length.     

Joint PP‐ and PSV‐wave amplitudes versus offset and azimuth inversion for fracture compliances in horizontal transversely isotropic media

We propose a robust approach for the joint inversion of PP‐ and PSV‐wave angle gathers along different azimuths for the elastic properties of the homogeneous isotropic host rock and excess compliances due to the presence of fractures. Motivated by the expression of fluid content indicator in fractured reservoirs and the sensitivity of Lamé impedances to fluid type, we derive PP‐ and PSV‐wave reflection coefficients in terms of Lamé impedances, density, and fracture compliances for an interface separating two horizontal transversely isotropic media. Following a Bayesian framework, we construct an objective function that includes initial models. We employ the iteratively reweighted least‐squares algorithm to solve the inversion problem to estimate unknown parameters (i.e., Lamé impedances, density, and fracture compliances) from PP‐ and PSV‐wave angle gathers along different azimuths. Synthetic tests reveal that the unknown parameters estimated using the joint inversion approach match true values better than those estimated using a PP‐wave amplitude inversion only. A real data test indicates that reasonable results for subsurface fracture detection are obtained from the joint inversion approach.     

Damage evolution in reinforced concrete columns subjected to biaxial loading

An analysis of the damage observed in 24 reinforced concrete (RC) columns tested under uniaxial and biaxial horizontal loading is presented. The test results show that for biaxial loading conditions specific damage occurs for lower drift demands when compared with the corresponding uniaxial demand (a reduction of 50–75 % was found). The damage distribution observed in each column is also analysed. No significant differences are found in the plastic hinge length for uniaxial and biaxial loading. The drift demands associated with each damage state are compared with reference values proposed in international guidelines. Finally, and based on the philosophy of the Park and Ang uniaxial damage index, two new expressions are proposed for the evaluation of damage in RC elements under biaxial loading. The results of the application of these expressions to the experimental results are discussed.     

Collapse of a nonductile concrete frame: Evaluation of analytical models

The current paper presents nonlinear dynamic analyses that simulate shaking table tests performed on a four‐column reinforced concrete frame described in a companion paper. The frame consists of two ductile and two nonductile columns interconnected by a stiff beam. In order to validate existing analytical models for nonductile concrete columns, a blind comparison of the test data and results of the analysis is performed. The analysis adequately captures the drift response and correctly detects collapse of the structure; however, strength degradation due to cover spalling is exaggerated in the analytical model. Refinement of the analysis by changing the concrete cover model results in an excellent agreement between the test data and analysis results at the initiation of shear failure and collapse of the frame. The experimental data are further compared with lumped‐plasticity nonlinear models used in engineering practice. The results suggest that the sudden strength degradation used in ASCE/SEI 41‐06 results in an exaggerated estimate of the displacement demands. It is also observed that ignoring the strength degradation, using an elastic‐perfectly‐plastic model, provides a good estimate of the displacement demands when strength degradation is not severe. Copyright © 2008 John Wiley & Sons, Ltd.     

岩溶区砌体建筑环境振动特性分析

当前地震动速度时程时域特性分析方法,仅能分析岩溶区地震动速度时程的振动周期、强弱程度与时间变动的问题,但未能准确计算岩溶区砌体建筑物自振频率,导致砌体建筑环境振动特性分析结果存在误差。深入研究岩溶区砌体建筑环境振动特性分析方法,构建混凝土损伤塑性模型,分析岩溶区砌体建筑材料的屈服(受压)应力-非弹性应变关系、开裂(受拉)应力-非弹性应变关系和损伤因子;采用贝叶斯方法检测岩溶区砌体建筑受压受拉时的自振频率,通过L-M神经网络法消除自振频率后,使用振动特性分析方法准确分析岩溶区砌体建筑环境振动特性。实验结果表明,所提方法分析准确率高达0.99,分析16栋岩溶区砌体建筑环境振动特性耗时仅有5 ms,具有较高的分析精度和效率。