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1.
In the aftermath of an earthquake, data acquired by a monitoring system can be used to identify possible damage that occurred in the structure by using algorithms to estimate proper damage features. In this paper, a new method is proposed for damage localization in beam‐like structures under seismic excitation. The proposed algorithm, named the Interpolation Evolution Method (IEM), is based on the combination of two existing methods: the Interpolation Method and the Curvature Evolution Method. Only responses recorded in story accelerations are required to estimate the damage feature with the combined IEM approach. This method does not require a priori knowledge of a “signature” of the structure because it exploits responses recorded during a single strong motion event. Herein, the IEM is applied to case studies of 2 reinforced concrete frames excited by several different ground motions, simulated using nonlinear finite element models and recorded during experimental tests carried out on a shaking table at the University of California, San Diego (USA) and at the University of Basilicata (Italy).  相似文献   

2.
The seismic behavior of unreinforced masonry buildings is typically characterized by premature brittle collapse mechanisms that can cause serious consequences for the protection of human lives and for the preservation of historical and cultural heritage. Structural health monitoring can be a powerful tool enabling a quick post-earthquake assessment of the structure's performance, but its applications are still scarce as a consequence of the severe limitations affecting off-the-shelf sensing technologies, in terms of local nature of the measurements, costs, as well as long-term behavior, installation, and maintenance. To overcome some of these limitations, the authors have recently proposed a new sensing technology, called “smart brick,” that is a durable clay brick doped with stainless steel microfibers, working as a smart strain sensor for masonry buildings. This paper presents the first full-scale application of smart bricks, used for detecting and localizing progressive earthquake-induced damage in an unreinforced masonry building subjected to shaking table tests. Smart bricks are employed to detect changes in load paths on masonry walls, comparing strain measurements acquired after each step of the seismic sequence with those referring to the undamaged structure. Experimental results are interpreted using a 3D finite element model built to reproduce the shaking table tests. Overall, the results demonstrate that the smart bricks can effectively reveal local permanent changes in structural conditions following a progressive damage, therefore being apt for earthquake-induced damage detection and localization.  相似文献   

3.
The knowledge of fundamental frequency and damping ratio of structures is of uppermost importance in earthquake engineering, especially to estimate the seismic demand. However, elastic and plastic frequency drops and damping variations make their estimation complex. This study quantifies and models the relative frequency drop affecting low‐rise modern masonry buildings and discusses the damping variations based on two experimental data sets: Pseudo‐dynamic tests at ELSA laboratory in the frame of the ESECMaSE project and in situ forced vibration tests by EMPA and EPFL. The relative structural frequency drop is shown to depend mainly on shaking amplitude, whereas the damping ratio variations could not be explained by the shaking amplitude only. Therefore, the absolute frequency value depends mostly on the frequency at low amplitude level, the amplitude of shaking and the construction material. The decrease in shape does not vary significantly with increasing damage. Hence, this study makes a link between structural dynamic properties, either under ambient vibrations or under strong motions, for low‐rise modern masonry buildings. A value of 2/3 of the ambient vibration frequency is found to be relevant for the earthquake engineering assessment for this building type. However, the effect of soil–structure interaction that is shown to also affect these parameters has to be taken into account. Therefore, an analytical methodology is proposed to derive first the fixed‐base frequency before using these results. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

4.
对土石坝振动台模型试验理论和技术进行系统阐述,提出基于原型和模型坝料静、动力特性试验的模型相似设计方法和不同强度地震动递进输入(白噪声微振-设计地震-校核地震-破坏试验)的振动试验方法。基于1g大型振动台和ng超重力离心机振动台设备性能现状,结合高土石坝的结构特点和动力试验相似模拟要求,对土石坝振动台模型试验的优势及局限进行深入讨论。结合已有的工程实践,对土石坝振动台模型试验在工程中的应用进行总结,并以某实际高面板堆石坝为例研究面板坝生命周期内经历多次地震情况下结构动力特性的演化规律。  相似文献   

5.
Damage caused by devastating earthquakes has occurred in many developing countries. In order to mitigate such damage by promoting the study of adequate seismic design strategies, the authors conducted a dynamic collapse test on 3 m × 3 m × 3 m brick masonry house constructed with Pakistani bricks, using a one-direction horizontal large-scale shaking table. In order to analyze and simulate seismic performance of the masonry structures, the authors applied a new numerical simulating method based on the Extended Distinct Element Method (EDEM) and conducted collapse simulations of the brick masonry house behavior during the shaking table tests. In the numerical simulation model, bricks were assumed to be rigid bodies, and mortar was modeled using a mortar spring that consists of a normal spring and a shear spring. The parameters of each mortar spring were defined based on the results of material tests. Simulated results showed various collapsing processes, and the simulated aspects were found to be similar to the results of the shaking table tests.  相似文献   

6.
In this study, signal processing approaches and nonlinear identification are used to measure seismic responses of reinforced concrete (RC) structures using the shaking table test. To analyze structural nonlinearity, an equivalent linear system with time‐varying model parameters, singular spectrum analysis to elucidate residual deformation, and wavelet packet transformation analysis to yield the energy distribution among components are adopted to detect the nonlinearity. Then, damage feature extraction is conducted using both the Holder exponent and the Level‐1 detail of the discrete wavelet component. Finally, the modified Bouc‐Wen hysteretic model and the system identification process are employed to the shaking table test data to evaluate the physical parameters, including the stiffness degradation, the strength deterioration and the pinching hysteresis. Finally, the identified stiffness and strength degradation functions from the test data of RC frames in relation to the degree of ground shaking, damage index and the identified nonlinear features are discussed. Based on the proposed method, both signal‐based and model‐based identifications, the relationship between the damage occurrence and severity of structural damage can be identified. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

7.
This paper proposes a new model for quantifying the damage in structural steel components subjected to randomly applied flexural/shear stress reversals, such those induced by earthquakes. In contrast to existing approaches that consider the damage as a combination of the global amount of dissipated energy and maximum displacement, the proposed model represents the damage by two parameters: (a) the total dissipated energy and (b) the portion of the energy consumed in the skeleton part of the load–displacement curve. These parameters are employed to define a single ‘damage index’, which measures the level between 0 (no damage) and 1 (failure). The proposed model takes into account that the ultimate energy dissipation capacity of the steel component is path‐dependent and can change throughout the entire response duration. The new model is derived from low‐cycle fatigue static tests of round steel rods and steel plates subjected to bending and shear. The accuracy of the model is verified experimentally through dynamic real‐time shaking table tests. From these tests, it is observed that the proposed model measures the level of damage at any stage of the loading process reasonably well and predicts the failure of the structural component accurately. The model can be easily implemented in a computer program to assess the level of seismic damage and the closeness to failure in new structures or to evaluate the safety of existing ones. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

8.
This article extends a signal-based approach formerly proposed by the authors, which utilizes the fractal dimension of time frequency feature(FDTFF) of displacements, for earthquake damage detection of moment resist frame(MRF), and validates the approach with shaking table tests. The time frequency feature(TFF) of the relative displacement at measured story is defined as the real part of the coefficients of the analytical wavelet transform. The fractal dimension(FD) is to quantify the TFF within the fundamental frequency band using box counting method. It is verified that the FDTFFs at all stories of the linear MRF are identical with the help of static condensation method and modal superposition principle, while the FDTFFs at the stories with localized nonlinearities due to damage will be different from those at the stories without nonlinearities using the reverse-path methodology. By comparing the FDTFFs of displacements at measured stories in a structure, the damage-induced nonlinearity of the structure under strong ground motion can be detected and localized. Finally shaking table experiments on a 1:8 scale sixteen-story three-bay steel MRF with added frictional dampers, which generate local nonlinearities, are conducted to validate the approach.  相似文献   

9.
Fragility curves are generally developed using a single parameter to relate the level of shaking to the expected structural damage. The main goal of this work is to use several parameters to characterize the earthquake ground motion. The fragility curves will, therefore, become surfaces when the ground motion is represented by two parameters. To this end, the roles of various strong‐motion parameters on the induced damage in the structure are compared through nonlinear time‐history numerical calculations. A robust structural model that can be used to perform numerous nonlinear dynamic calculations, with an acceptable cost, is adopted. The developed model is based on the use of structural elements with concentrated nonlinear damage mechanics and plasticity‐type behavior. The relations between numerous ground‐motion parameters, characterizing different aspects of the shaking, and the computed damage are analyzed and discussed. Natural and synthetic accelerograms were chosen/computed based on a consideration of the magnitude‐distance ranges of design earthquakes. A complete methodology for building fragility surfaces based on the damage calculation through nonlinear numerical analysis of multi‐degree‐of‐freedom systems is proposed. The fragility surfaces are built to represent the probability that a given damage level is reached (or exceeded) for any given level of ground motion characterized by the two chosen parameters. The results show that an increase from one to two ground‐motion parameters leads to a significant reduction in the scatter in the fragility analysis and allows the uncertainties related to the effect of the second ground‐motion parameter to be accounted for within risk assessments. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

10.
The electromagnetic mass damper （EMD） control system, as an innovative active control system to reduce structural vibration, offers many advantages over traditional active mass driver/damper （AMD） control systems. In this paper, studies of several EMD control strategies and bench-scale shaking table tests of a two-story model structure are described. First, two structural models corresponding to uncontrolled and Zeroed cases are developed, and parameters of these models are validated through sinusoidal sweep tests to provide a basis for establishing an accurate mathematical model for further studies. Then, a simplified control strategy for the EMD system based on the pole assignment control algorithm is proposed. Moreover, ideal pole locations are derived and validated through a series of shaking table tests. Finally, three benchmark earthquake ground motions and sinusoidal sweep waves are imposed onto the structure to investigate the effectiveness and feasibility of using this type of innovative active control system for structural vibration control. In addition, the robustness of the EMD system is examined. The test results show that the EMD system is an effective and robust system for the control of structural vibrations.  相似文献   

11.
In order to evaluate the nonlinear performance and the possible damage to rubber-bearings (RBs) during their normal operation or under strong earthquakes, a simplified Bouc-Wen model is used to describe the nonlinear hysteretic behavior of RBs in this paper, which has the advantages of being smooth-varying and physically motivated. Further, based on the results from experimental tests performed by using a particular type of RB (GZN110) under different excitation scenarios, including white noise and several earthquakes, a new system identification method, referred to as the sequential nonlinear least-square estimation (SNLSE), is introduced to identify the model parameters. It is shown that the proposed simplified Bouc-Wen model is capable of describing the nonlinear hysteretic behavior of RBs, and that the SNLSE approach is very effective in identifying the model parameters of RBs.  相似文献   

12.
Health care facilities may undergo severe and widespread damage that impairs the functionality of the system when it is stricken by an earthquake. Such detrimental response is emphasized either for the hospital buildings designed primarily for gravity loads or without employing base isolation/supplemental damping systems. Moreover, these buildings need to warrant operability especially in the aftermath of moderate‐to‐severe earthquake ground motions. The provisions implemented in the new seismic codes allow obtaining adequate seismic performance for the hospital structural components; nevertheless, they do not provide definite yet reliable rules to design and protect the building contents. To date, very few experimental tests have been carried out on hospital buildings equipped with nonstructural components as well as building contents. The present paper is aimed at establishing the limit states for a typical health care room and deriving empirical fragility curves by considering a systemic approach. Toward this aim, a full scale three‐dimensional model of an examination (out patients consultation) room is constructed and tested dynamically by using the shaking table facility of the University of Naples, Italy. The sample room contains a number of typical medical components, which are either directly connected to the panel boards of the perimeter walls or behave as simple freestanding elements. The outcomes of the comprehensive shaking table tests carried out on the examination room have been utilized to derive fragility curves based on a systemic approach. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

13.
This paper provides a new methodological framework to generate empirical ground shaking scenarios, designed for engineering applications and civil protection planning. The methodology is useful both to reconstruct the ground motion pattern of past events and to generate future shaking scenarios, in regions where strong‐motion datasets from multiple events and multiple stations are available. The proposed methodology combines (1) an ad‐hoc nonergodic ground motion model (GMM) with (2) a spatial correlation model for the source region‐, site‐, and path‐systematic residual terms, and (3) a model of the remaining aleatory error to take into account for directivity effects. The associated variability is a function of the type of scenario generated (bedrock or site, past or future event) and it is minimal for source areas where several events have occurred and for sites where recordings are available. In order to develop the region‐specific fully nonergodic GMM and to compute robust estimation of the residual terms, the approach is calibrated on a highly dense dataset compiled for the area of central Italy. Example tests demonstrate the validity of the approach, which allows to simulate acceleration response spectra at unsampled sites, as well as to capture peculiar physical features of ground motion patterns in the region. The proposed approach could be usefully adopted for data‐driven simulations of ground shaking maps, as alternative or complementary tool to physic‐based and stochastic‐based approaches.  相似文献   

14.
An analytical model for high damping elastomeric isolation bearings is presented in this paper. The model is used to describe mathematically the damping force and restoring force of the rubber material and bearing. Ten parameters to be identified from cyclic loading tests are included in the model. The sensitivity of the ten parameters in affecting the model is examined. These ten parameters are functions of a number of influence factors on the elastomer such as the rubber compound, Mullins effect, scragging effect, frequency, temperature and axial load. In this study, however, only the Mullins effect, scragging effect, frequency and temperature are investigated. Both material tests and shaking table tests were performed to validate the proposed model. Based on the comparison between the experimental and the analytical results, it is found that the proposed analytical model is capable of predicting the shear force–displacement hysteresis very accurately for both rubber material and bearing under cyclic loading reversals. The seismic response time histories of the bearing can also be captured, using the proposed analytical model, with a practically acceptable precision. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

15.
Traditional modal parameter identifi cation methods have many disadvantages,especially when used for processing nonlinear and non-stationary signals.In addition,they are usually not able to accurately identify the damping ratio and damage.In this study,methods based on the Hilbert-Huang transform(HHT) are investigated for structural modal parameter identifi cation and damage diagnosis.First,mirror extension and prediction via a radial basis function(RBF) neural network are used to restrain the troublesome end-effect issue in empirical mode decomposition(EMD),which is a crucial part of HHT.Then,the approaches based on HHT combined with other techniques,such as the random decrement technique(RDT),natural excitation technique(NExT) and stochastic subspace identifi cation(SSI),are proposed to identify modal parameters of structures.Furthermore,a damage diagnosis method based on the HHT is also proposed.Time-varying instantaneous frequency and instantaneous energy are used to identify the damage evolution of the structure.The relative amplitude of the Hilbert marginal spectrum is used to identify the damage location of the structure.Finally,acceleration records at gauge points from shaking table testing of a 12-story reinforced concrete frame model are taken to validate the proposed approaches.The results show that the proposed approaches based on HHT for modal parameter identifi cation and damage diagnosis are reliable and practical.  相似文献   

16.
To help mitigate liquefaction hazards in the Philippines, an inexpensive yet effective approach to liquefaction hazard zonation was developed in this study. The proposed approach is also useful in other areas especially where funds for more rigorous procedures may not be available. The approach utilizes the geomorphology-based criteria to identify liquefaction-prone deposits based on geology and grain characteristics, and generate a preliminary liquefaction susceptibility map. Then, microtremor recordings, popularly used in site effect estimation, are gathered to derive qualitative information on the density and thickness of these deposits and generate a site classification map. This latter map is also essentially a ground shaking hazard map in that it shows those areas where thick, soft deposits likely to amplify and prolong the duration of ground motion can be found. Therefore, it also identifies areas where seismic demand can be high that the possibility of liquefaction being triggered is likewise high. Combining the two maps, an integrated liquefaction hazard zonation map is produced which provides not only an improved characterization of the soils’ capacity to resist liquefaction but also integrates qualitative information on the seismic demand on these deposits as well. With information about the relative thickness of the deposits, the severity of potential damage can likewise be inferred from the map since thicker deposits relate to more serious damage. The proposed approach was applied to Laoag City, Northern Philippines, where it was shown to reliably identify areas that are vulnerable to the hazard.  相似文献   

17.
Although structural mechanical impedance is a direct representation of the structural parameters, its measurement is difficult at high frequencies owing to practical considerations. This paper presents a new method of damage diagnosis by means of changes in the structural mechanical impedance at high frequencies. The mechanical impedance is extracted from the electro‐mechanical admittance signatures of piezoelectric‐ceramic (PZT) patches surface bonded to the structure using the electro‐mechanical impedance (EMI) technique. The main feature of the newly developed approach is that both the real as well as the imaginary component of the admittance signature is used in damage quantification. A complex damage metric is proposed to quantify damage parametrically based on the extracted structural parameters, i.e. the equivalent single degree of freedom (SDOF) stiffness, the mass, and the damping associated with the drive point of the PZT patch. The proposed scheme eliminates the need for any a priori information about the phenomenological nature of the structure or any ‘model’ of the structural system. As proof of concept, the paper reports a damage diagnosis study conducted on a model reinforced concrete (RC) frame subjected to base vibrations on a shaking table. The proposed methodology was found to perform better than the existing damage quantification approaches, i.e. the low‐frequency vibration methods as well as the traditional raw‐signature based damage quantification in the EMI technique. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

18.
Length, maximum width, and residual width of cracks are key indicators of structural damage. However, pattern and propagation of cracks on the affected structural component should be also considered. In addition, damage evaluation based on visual inspection is a subjective and capricious procedure because the damage assessment relies on the expertise and judgment of the inspector engineer. In order to assess a rapid and reliable evaluation approach of seismic damage, pattern and propagation of cracks observed in thin and lightly reinforced concrete walls for low‐rise housing subjected to seismic demands are evaluated in this study by means of fractal dimension of cracking pattern. The proposed parameters are based on the results of an experimental program that comprised 39 low‐rise RC wall specimens having typical variables of this type of housing, such as low compressive strengths of concrete, thin walls, low axial loads, low reinforcement ratios, and web shear reinforcement made of deformed bars and welded‐wire meshes. A statistical analysis is carried out for computing values of fractal dimension associated to cracking patterns at key damage conditions. Recommendations of this study can help the inspector in estimating the current limit state or performance level of the wall and the story‐drift ratio experienced by the wall during shaking. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

19.
This paper proposes a simple conceptual mathematical model for the mechanical components of the NEES‐UCSD large high‐performance outdoor shaking table and focuses on the identification of the parameters of the model by using an extensive set of experimental data. An identification approach based on the measured hysteresis response is used to determine the fundamental model parameters including the effective horizontal mass, effective horizontal stiffness of the table, and the coefficients of the classical Coulomb friction and viscous damping elements representing the various dissipative forces in the system. The effectiveness of the proposed conceptual model is verified through a comparison of analytical predictions with experimental results for various tests conducted on the system. The resulting mathematical model will be used in future studies to model the mechanical components of the shake table in a comprehensive physics‐based model of the entire mechanical, hydraulic, and electronic system. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

20.
All digital seismic recorders of the Crimean seismological network are equipped with sensors inherited from galvanometric recording. Long-term channels are equipped with SKD sensors, and shortterm channels are equipped with SM3, SKM, SKH, and S-5-S sensors. The instruments periodically undergo preventive maintenance due to wear and long operation life. There are no equipment specialists at peripheral stations. All necessary installation, preventive maintenance, adjustment, and calibration work is done by specialists from the Institute of Seismology and Geodynamics’ hardware and software support team during business trips. In this regard, an urgent need arose for the real-time control of velocimeter parameters and the entire end-to-end measuring and recording channel. Experience at peripheral seismic stations and temporary seismic observation points not equipped with shaking tables has demonstrates the convenience of calibrating short-term seismic channels using a reference standard calibrated mobile digital seismic station. This station is assembled based on a Baikal-8 digital seismic recorder and SK1-P three-component sensor. The reference standard is precalibrated on the shaking table located at the Simferopol seismic station. The paper describes the calibration of the reference standard on a shaking table and different approaches to calculating the main parameters of a velocimeter. The relationship is obtained between the main parameters of the velocimeter and the extremum times and zeros of the velocimeter response function to a displacement step. It is possible to control the velocimeter parameters in real time the obtained formulas, even in the field using. Of special note is the idea of calibrating seismometric channels with respect to the reference standard, which can be implemented without forced external actions. A new method for calibrating a digital seismic station using a reference standard is described, based on analysis of the ratio of microseismic background spectra. The parameters of the calibrated station are determined using synchronous recording of the microseismic background and the mathematical optimization package in OriginLab software. The formulas for calculating velocimeter parameters using a standard are given, which make it possible to determine the complex frequency response of the digital station. This is a convenient method because it is real-time and calibration does not require laboratory conditions, the use of microseisms, or the ability to determine all parameters of endto- end measuring and recording channels simultaneously.  相似文献   

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