Damage identification of a 3D full scale steel–concrete composite structure with partial‐strength joints at different pseudo‐dynamic load levels

Partial‐strength composite steel–concrete moment‐resisting (MR) frame structures represent an open research field in seismic design from both a theoretical and an experimental standpoint. Among experimental techniques, vibration testing is a well‐known and powerful technique for damage detection, localization and quantification, where actual modal parameters of a structure at different states can be determined from test data by using system identification methods. However, the identification of semi‐rigid connections in framed structures is limited, and hence this paper focuses on a series of vibration experiments that were carried out on a realistic MR frame structure, following the application of pseudo‐dynamic and quasi‐static cyclic loadings at the European laboratory for structural assessment of the Joint Research Centre at Ispra, Italy, with the scope of understanding the structural behaviour and identifying changes in the dynamic response. From the forced vibration response, natural frequencies, damping ratios, modal displacements and rotations were extracted using the circle fitting technique. These modal parameters were used for local and global damage identification by updating a 3D finite element model of the intact structure. The identified results were then correlated with observations performed on the structure to understand further the underlying damage mechanisms. Finally, the latin hypercube sampling technique, a variant of the Monte Carlo method, was employed in order to study the sensitivity of the updated parameters of the 3D model to noise on the modal inputs. Copyright © 2009 John Wiley & Sons, Ltd.     

Parameter identification of framed structures using an improved finite element model‐updating method—Part I: formulation and verification

In this study, we formulate an improved finite element model‐updating method to address the numerical difficulties associated with ill conditioning and rank deficiency. These complications are frequently encountered model‐updating problems, and occur when the identification of a larger number of physical parameters is attempted than that warranted by the information content of the experimental data. Based on the standard bounded variables least‐squares (BVLS) method, which incorporates the usual upper/lower‐bound constraints, the proposed method (henceforth referred to as BVLSrc) is equipped with novel sensitivity‐based relative constraints. The relative constraints are automatically constructed using the correlation coefficients between the sensitivity vectors of updating parameters. The veracity and effectiveness of BVLSrc is investigated through the simulated, yet realistic, forced‐vibration testing of a simple framed structure using its frequency response function as input data. By comparing the results of BVLSrc with those obtained via (the competing) pure BVLS and regularization methods, we show that BVLSrc and regularization methods yield approximate solutions with similar and sufficiently high accuracy, while pure BVLS method yields physically inadmissible solutions. We further demonstrate that BVLSrc is computationally more efficient, because, unlike regularization methods, it does not require the laborious a priori calculations to determine an optimal penalty parameter, and its results are far less sensitive to the initial estimates of the updating parameters. Copyright © 2006 John Wiley & Sons, Ltd.     

基于响应面的预应力混凝土桥动力有限元模型研究

建立了基于正交实验的响应面模型和精细有限元模型,并将其用于中华大桥的有限元模型修正,通过实测动力数据对修正后的有限元模型计算结果进行了验证。基于修正后的有限元模型,分析了预应力对预应力钢筋混凝土桥梁模态信息（频率和振型）的影响,以及单元类型对桥梁模态频率的影响。结果表明,修正后的有限元模型能够比较准确地反映桥梁实际结构的动力特性,基于响应面模型和遗传算法的修正方法可有效地用于大桥的健康监测和状态评估;预应力对预应力钢筋混凝土桥梁模态信息的影响较小,建模时可不予精确考虑;对于由多根预应力混凝土梁组成的桥梁体系,采用实体单元分析较好。     

Ambient vibration based seismic evaluation of isolated Gülburnu highway bridge

This paper describes ambient vibration based seismic evaluation procedure of an isolated highway bridge. The procedure includes finite element modeling, ambient vibration testing, finite element model updating and time history analysis. Gülburnu Highway Bridge located on the Giresun–Espiye state highway is selected as a case study. Three dimensional finite element model of the bridge is created by SAP2000 software to determine the dynamic characteristics analytically. Since input force is not measured, Operational Modal Analysis is applied to identify dynamic characteristics. Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification methods are used to obtain experimental dynamic characteristics. Analytical and experimental dynamic characteristic are compared with each other and finite element model of the bridge is updated by changing of material properties to reduce the differences between the results. Analytical model of the bridge after model updating is analyzed using 1992 Erzincan earthquake record to determine the seismic behavior. EW, NS and UP components of the ground motion are applied to the bridge at the longitudinal, transverse and vertical directions, respectively. It is demonstrated that the ambient vibration measurements are enough to identify the most significant modes of highway bridges. Maximum differences between the natural frequencies are reduced averagely from 9% to 2% by model updating. It is seen from the earthquake analyses that friction pendulum isolators are very effective in reducing the displacements and internal forces.     

Damage identification of structures with uncertain frequency and mode shape data

A statistical method with combined uncertain frequency and mode shape data for structural damage identification is proposed. By comparing the measured vibration data before damage or analytical finite element model of the intact structure with those measured after damage, the finite element model is updated so that its vibration characteristic changes are equal to the changes in the measured data as closely as possible. The effects of uncertainties in both the measured vibration data and finite element model are considered as random variables in model updating. The statistical variations of the updated finite element model are derived with perturbation method and Monte Carlo technique. The probabilities of damage existence in the structural members are then defined. The proposed method is applied to a laboratory tested steel cantilever beam and frame structure. The results show that all the damages are identified correctly with high probabilities of damage existence. Discussions are also made on the applicability of the method when no measurement data of intact structure are available. Copyright © 2002 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.     

Dynamic model updating using a combined genetic‐eigensensitivity algorithm and application in seismic response prediction

A reliable computational model is necessary for evaluating the state and predicting the future performance of existing structures, especially after exposure to damaging effects such as an earthquake. A major problem with the existing iterative‐based model updating methods is that the search might be trapped in local optima. The genetic algorithms (GAs) offer a desirable alternative because of their ability in performing a robust search for the global optimal solution. This paper presents a GA‐based model updating approach using a real‐coding scheme for global model updating based on dynamic measurement data. An eigensensitivity method is employed to further fine‐tune the GA updated results in case the sensitivity problem arises due to restricted measurement information. The application on shear‐type frames reveals that with a limited amount of modal data, namely the lowest three natural frequencies and the first mode shape, it is possible to achieve satisfactory updating by the GA alone for cases involving a limited number of parameters (storey stiffness herein). With the incorporation of the eigensensitivity algorithm, the updating capability is extended to a sufficiently large number of parameters. In case the modal data contain errors, the GA is also shown to be able to update the model to a satisfactory accuracy, provided the required amount of modal data is available. An example is given in which a 6‐DOF stick model for an actual six‐storey RC frame is updated using the measured dynamic properties. The effectiveness of the updating is evaluated by comparing the measured and predicted seismic response using the updated model. Copyright © 2005 John Wiley & Sons, Ltd.     

Correlating measured and simulated dynamic responses of a tall building to long‐distance earthquakes

For almost a decade, a 66‐storey, 280m tall building in Singapore has been instrumented to monitor its dynamic responses to wind and seismic excitations. The dynamic characteristics of the tall building have been investigated via both the finite element method and the experimental modal analysis. The properties of the finite element model have been shown to correlate well with those derived from the data recorded during the ambient vibration tests. During the study period, 21 sets of earthquake ground motions have been recorded at the building site. The basement motions may be divided into three categories based on their predominant frequency components with respect to the building's fundamental frequency. The calibrated three‐dimensional finite element model is employed to simulate the seismic response of the tall building. Correlation analysis of the time histories between the recorded data and the simulated results has been carried out. The correlation analysis results show that the simulated dynamic response time histories match well with those of the recorded dynamic responses at the roof level. The results also show that the simulated maximum response at the roof level is close to the peak response recorded during the earthquakes. Copyright © 2004 John Wiley & Sons, Ltd.     

Effects of infill walls and floor diaphragms on the dynamic characteristics of a narrow‐rectangle building

Most buildings in Singapore are lightly reinforced concrete structures, which are mainly designed for gravity loading only, because Singapore is an island country located in a low‐to‐moderate seismic region. The dynamic properties of a typical high‐rise residential building with a long, narrow rectangular floor plan are studied using both experimental and numerical methods. The effects of the brick infill walls and the flexible diaphragms on the dynamic characteristics of the building are discussed in detail. The results from the ambient vibration tests are correlated with the numerical results of three different finite element models with different levels of sophistication. They include a bare frame model, a frame model with brick infill walls, and a frame model with both brick infill walls and flexible diaphragms. The dynamic properties of the third model match very well with the measured results in terms of both the natural frequencies and the mode shapes. The correlation results demonstrate the respective effects of the brick infill walls and the flexible diaphragms on the dynamic characteristics of the narrow‐rectangle building structure. Copyright © 2006 John Wiley & Sons, Ltd.     

Two‐stage damage detection algorithms of structure using modal parameters identified from recursive subspace identification

Structural damage assessment under external loading, such as earthquake excitation, is an important issue in structural safety evaluation. In this regard, appropriate data analysis and feature extraction techniques are required to interpret the measured data and to identify the state of the structure and, if possible, to detect the damage. In this study, the recursive subspace identification with Bona‐fide LQ renewing algorithm (RSI‐BonaFide‐Oblique) incorporated with moving window technique is utilized to identify modal parameters such as natural frequencies, damping ratios, and mode shapes at each instant of time during the strong earthquake excitation. From which the least square stiffness method (LSSM) combined with the model updating technique, called efficient model correction method (EMCM), is used to estimate the first‐stage system stiffness matrix using the simplified model from the previously identified modal parameters (nominal model). In the second stage, 2 different damage assessment algorithms related to the nominal system stiffness matrix were derived. First, the model updating technique, called EMCM, is applied to correct the nominal model by the newly identified modal parameters during the strong motion. Second, the element damage index can be calculated using element damage index method (EDIM) to quantify the damage extent in each element. Verification of the proposed methods through the shaking table test data of 2 different types of structures and a building earthquake response data is demonstrated to specify its corresponding damage location, the time of occurrence during the excitation, and the percentage of stiffness reduction.     

Nonlinear finite element analysis of three‐dimensional free and harmonically forced vibrations of stranded conductor cables

The 3D finite deformation beam model originally developed by Simo is appropriately modified to derive a finite element formulation for the static and dynamic analysis of flexible electrical conductors. In contrast to what is currently carried out in the literature, a linear viscoelastic constitutive equation and an additional mass proportional damping mechanism are introduced to account for energy dissipation in a physically consistent way. The model is used for simulation of free and forced vibration tests performed on an actual electrical conductor. Energy balance calculations illustrate the reliability of the computations. The experiments reveal amplitude dependence of both stiffness and damping, pointing out the presence of material nonlinearity in the cable. The development of numerical models that can account for the amplitude dependence of bending stiffness and energy dissipation capacity is subject of current computational and experimental work. Copyright © 2014 John Wiley & Sons, Ltd.     

地铁列车曲线运行引起学校建筑物振动响应分析

地铁以其快捷、准时、运量大等优点,已成为重要的轨道交通形式,但由此引起的环境振动问题日益突出。针对杭州市地铁3号线曲线地段的某中学建设工程,利用有限元软件ABAQUS,对车辆-普通整体道床轨道系统的竖向耦合模型进行振动响应分析,得到考虑轨道高低不平顺影响的轨道振动源强。应用有限元软件MIDAS GTS/NX,建立双孔平行曲线盾构隧道-土-桩-建筑物系统的三维有限元模型。以轨道支点力作为激励对地铁列车运行时的隧道-土-桩-建筑物系统的振动响应进行计算,研究地铁振动波在地层中的传播规律和建筑物的动力响应特性。根据相关环境振动控制标准对建筑物的振动舒适性进行评价。结果表明：轨道加速度和扣件动支点力的最大值分别约为40 m/s²和30 kN;地层和建筑物的振动以竖向为主,水平Y向振动略大于水平X向振动;地面加速度随着距隧道中心线距离的增加而逐渐衰减;各建筑物楼层的振动主频位于16~40 Hz;部分建筑物楼层的振动响应水平已超出了规范的限值要求,建议对地铁轨道或建筑物采取适当的减振措施。     

System identification of a concrete arch dam and calibration of its finite element model

A magnitude 4.3 earthquake occurred near Pacoima Dam on 13 January 2001. An accelerometer array that had been upgraded after the Northridge earthquake recorded the motion with 17 channels on the dam and the dam–foundation interface. Using this data, properties of the first two modes are found from a system identification study. Modal properties are also determined from a forced vibration experiment performed in 2002 and indicate a significantly stiffer system than is estimated from the 2001 earthquake records. The 2001 earthquake, although small, must have induced temporary nonlinearity. This has implications for structural health monitoring. The source of the nonlinear behaviour is believed to be loss of stiffness in the foundation rock. A finite element model of Pacoima Dam is constructed and calibrated to match modal properties determined from the system identification study. A dynamic simulation of the 2001 earthquake response produces computed motions that agree fairly well with the recorded ones. Copyright © 2006 John Wiley & Sons, Ltd.     

System identification and modeling of a dynamically tested and gradually damaged 10‐story reinforced concrete building

This paper discusses the dynamic tests, system identification, and modeling of a 10‐story reinforced concrete building. Six infill walls were demolished in 3 stages during the tests to introduce damage. In each damage stage, dynamic tests were conducted by using an eccentric‐mass shaker. Accelerometers were installed to record the torsional and translational responses of the building to the induced excitation, as well as its ambient vibration. The modal properties in all damage states are identified using 2 operational modal analysis methods that can capture the effect of the wall demolition. The modal identification is facilitated by a finite element model of the building. In turn, the model is validated through the comparison of the numerically and experimentally obtained modal parameters. The validated model is used in a parametric study to estimate the influence of structural and nonstructural elements on the dynamic properties of the building and to assess the validity of commonly used empirical formulas found in building codes. Issues related to the applicability and feasibility of system identification on complex structures, as well as considerations for the development of accurate, yet efficient, finite element models are also discussed.     

Comparison of eigensensitivity and ANN based methods in model updating of an eight-story building

Analytical models prepared from field drawings do not generally provide results that match with experimental results.The error may be due to uncertainties in the property of materials,size of members and errors in the modelling process.It is important to improve analytical models using experimentally obtained data.For the past several years,data obtained from ambient vibration testing have been successfully used in many cases to update and match dynamic behaviors of analytical models with real structures.This paper presents a comparison between artificial neural network(ANN) and eigensensitivity based model updating of an existing multi-story building.A simple spring-mass analytical model,developed from the structural drawings of the building,is considered and the corresponding spring stiffness and lumped mass of all floors are chosen as updating parameters.The advantages and disadvantages of these updating methods are discussed.The advantage is that both methods ensure a physically meaningful model which canbe further employed in determining structural response and health monitoring.     

The vibrational characteristics of a twelve-storey steel frame building

The Ralph M. Parsons World Headquarters building, a twelve-storey steel frame structure, was subjected to a series of forced vibration tests. The natural frequencies, three-dimensional mode shapes and damping coefficients of nine modes of vibration were determined. Other features of this investigation included the study of non-linearities associated with increasing levels of response, detailed measurements of the deformation of the first floor and the ground surrounding the structure, and measurements of strain in one of the columns of the structure during forced excitation. The dynamic characteristics of the building determined by these tests are compared to those predicted by a finite element model of the structure. The properties of primarily translational modes are predicted reasonably well, but adequate prediction of torsional motions is not obtained. The comparison between measured and predicted strains suggests that estimates of stress determined from finite element analyses of buildings might be within 25 per cent of those experienced by the structure for a known excitation.     

Dynamic investigation of a hybrid suspension and cable‐stayed bridge

Ambient and forced vibration tests were carried out on the Beauharnois bridge, a unique, 177‐m combined suspension and cable‐stayed structure near Montreal, Canada. A rehabilitation program was completed on the bridge during which the deck was completely rebuilt with an orthotropic slab on two steel trusses. The rehabilitation program also included the addition of two pairs of stay cables on both towers, creating a hybrid suspension system. The paper presents a series of dynamic tests performed to evaluate the dynamic properties and the dynamic amplification factor (DAF) for the rehabilitated bridge. The experimental program involved the measurement of vertical, transverse, and longitudinal acceleration responses of the deck and tower under ambient and controlled traffic loads. Displacement, strain, and integrated acceleration DAFs were computed under different loading conditions. Modal properties were evaluated and used to correlate a three‐dimensional finite element model for the bridge, including non‐linear cable behaviour. The paper discusses the experimental setup as well as the techniques used to evaluate vibration frequencies, mode shapes, and the DAF. Correlation of numerical dynamic properties and experimental results is also presented. Copyright © 2000 John Wiley & Sons, Ltd.     

Influence of masonry infill panels on the vibration and stiffness characteristics of R/C frame buildings

Vibration measurements were performed on two adjacent, three-storey reinforced concrete frame buildings with hollow clay brick infill panels. The first building was a bare frame and the second one was a similar frame infilled with brick panels. The fundamental period for the infilled frame building was much smaller than that of the bare frame building. Using shear beam lumped mass models and the vibration data the actual lateral stiffness of both buildings was identified. The lateral stiffness of the infilled frame building was found to be seven times that of the bare frame building. Four numerical models of the infilled frame building were constructed. The frame and floors were represented using an experimentally validated model and the infill panels by one of three commonly used ‘equivalent diagonal truss’ models or by plane stress finite elements. Only the plane stress finite element model produced a reasonable agreement with the experimental results. Copyright © 1999 John Wiley & Sons, Ltd.     

Implementation of a second‐order paraxial boundary condition for a water‐saturated layered half‐space in plane strain

A half‐space finite element and a transmitting boundary are developed for a water‐saturated layered half‐space using a paraxial boundary condition. The exact dynamic stiffness of a half‐space in plane strain is derived and a second‐order paraxial approximation of the stiffness is obtained. A half‐space finite element and a transmitting boundary are then formulated. The development is verified by comparison of the dynamic stiffness of impermeable and permeable rigid strip foundations with other published results. The advantage of using the paraxial boundary condition in comparison with the rigid boundary condition is examined. It is shown that the paraxial boundary condition offers significant gain and the resulting half‐space finite element and transmitting boundary can represent the effects of a water‐saturated layered half‐space with good accuracy and efficiency. In addition, the numerical method described herein maintains the strengths and advantages of the finite element method and can be easily applied to demanding problems of soil–structure interaction in a water‐saturated layered half‐space. Copyright © 2010 John Wiley & Sons, Ltd.     

Design,simulation, and large‐scale testing of an innovative vibration mitigation device employing essentially nonlinear elastomeric springs

This study proposes an innovative passive vibration mitigation device employing essentially nonlinear elastomeric springs as its most critical component. Essential nonlinearity denotes the absence (or near absence) of a linear component in the stiffness characteristics of these elastomeric springs. These devices were implemented and tested on a large‐scale nine‐story model building structure. The main focus of these devices is to mitigate structural response under impulse‐like and seismic loading when the structure remains elastic. During the design process of the device, numerical simulations, optimizations, and parametric studies of the structure‐device system were performed to obtain stiffness parameters for the devices so that they can maximize the apparent damping of the fundamental mode of the structure. Pyramidal elastomeric springs were employed to physically realize the optimized essentially nonlinear spring components. Component‐level finite element analyses and experiments were conducted to design the nonlinear springs. Finally, shake table tests using impulse‐like and seismic excitation with different loading levels were performed to experimentally evaluate the performance of the device. Experimental results demonstrate that the properly designed devices can mitigate structural vibration responses, including floor acceleration, displacement, and column strain in an effective, rapid, and robust fashion. Comparison between numerical and experimental results verified the computational model of the nonlinear system and provided a comprehensive verification for the proposed device. Copyright © 2014 John Wiley & Sons, Ltd.