A system identification approach to the detection of changes in both linear and non-linear structural parameters

This paper explores the potential of a new time domain identification procedure to detect changes in structural dynamic characteristics on the basis of measurements. This procedure is verified using mathematical models simulated on the computer. The experiments involve two eight-storey steel structures with and without energy devices, and a 47-storey building at San Francisco during the Loma Prieta earthquake. The recursive instrumental variable method and extended Kalman filter algorithm are used as identification algorithms. An exploratory investigation is made of the usefulness of various indices, such as mode shape and storey drift, that can be extracted accurately from identification to quantify changes in the characteristics of the physical system. It is concluded that the change of storey drift is the key information to the detection of changes in structural parameters, from which the proposed system identification algorithm can be applied with an appropriate inelastic model to simulate the dynamic behaviour of real structures undergoing strong ground motion excitations.     

Identification of yield drift deformations and evaluation of the degree of damage through the direct sensing of drift displacements

Inter‐story drift displacement data can provide useful information for story damage assessment. The authors' research group has developed photonic‐based sensors for the direct measurement of inter‐story drift displacements. This paper proposes a scheme for evaluating the degree of damage in a building structure based on drift displacement sensing. The scheme requires only measured inter‐story drift displacements without any additional finite element analysis. A method for estimating yield drift deformation is proposed, and then, the degree of beam end damage is evaluated based on the plastic deformation ratios derived with the yield drift deformation values estimated by the proposed method. The validity and effectiveness of the presented scheme are demonstrated via experimental data from a large‐scale shaking table test of a one‐third‐scale model of an 18‐story steel building structure conducted at E‐Defense. Copyright © 2016 John Wiley & Sons, Ltd.     

高层钢结构建筑横向支撑地震动力响应分析

为测试高层钢结构建筑抗震性能,在有限元模型中以某高层钢框架结构办公大厦作为研究对象,测试其横向支撑地震动力响应状况。选取地震峰值加速度为200 cm/s^2的El-Centro波作为地震波输入,采用瞬态动力方法分析不同楼板厚度下建筑地震模拟响应,得到建筑顶层位移时程曲线;在SAP2000结构软件中分析建筑工程添加横向支撑前后的反应谱,记录各楼层垂直与水平方向位移与层间位移角。得到如下结果:高层钢结构建筑在地震响应下产生的位移不随楼板厚度的增加而增大,楼板厚度为100 mm、170 mm时位移波动显著;添加横向支撑后,建筑水平刚度显著提升,同理,添加横向支撑后横向层间位移角的最大值变化较大,且低于1/250,符合相关建筑标准。     

Seismic behavior of asymmetric RC wall buildings: principles and new deformation‐based design method

The seismic design of multi‐story buildings asymmetric in plan yet regular in elevation and stiffened with ductile RC structural walls is addressed. A realistic modeling of the non‐linear ductile behavior of the RC walls is considered in combination with the characteristics of the dynamic torsional response of asymmetric buildings. Design criteria such as the determination of the system ductility, taking into account the location and ductility demand of the RC walls, the story‐drift demand at the softer (most displaced) edge of the building under the design earthquake, the allowable ductility (ultimate limit state) and the allowable story‐drift (performance goals) are discussed. The definition of an eccentricity of the earthquake‐equivalent lateral force is proposed and used to determine the effective displacement profile of the building yet not the strength distribution under the design earthquake. Furthermore, an appropriate procedure is proposed to calculate the fundamental frequency and the earthquake‐equivalent lateral force. A new deformation‐based seismic design method taking into account the characteristics of the dynamic torsional response, the ductility of the RC walls, the system ductility and the story‐drift at the softer (most displaced) edge of the building is presented and illustrated with an example of seismic design of a multi‐story asymmetric RC wall building. Copyright © 2005 John Wiley & Sons, Ltd.     

Structural pounding between adjacent buildings subjected to strong ground motions. Part I: The effect of different structures arrangement

The effect of different structures configurations on the collision between adjacent planar RC building frames subjected to strong earthquakes is examined in this paper. Two 5‐storey and two 8‐storey frames, regular or with setbacks, are combined together to produce nine different pairs of adjacent RC structures. These pairs of buildings are subjected to six strong ground motions that are absolutely compatible with the design process. Various parameters are investigated such as maximum displacements, permanent displacements, members' ductility and internal forces and interstorey drift ratios. It is concluded that the effect of collision of adjacent frames seems to be unfavourable for most of the cases and, therefore, the structural pounding phenomenon is rather detrimental than beneficial. Copyright © 2013 John Wiley & Sons, Ltd.     

Investigation of effect of near-fault motions on substandard bridge structures

The objective of this study was to investigate the effects of near-fault ground motions on substandard bridge columns and piers. To accomplish these goals, several large scale reinforced concrete models were constructed and tested on a shake table using near- and far-field ground motion records. Because the input earthquakes for the test models had different characteristics, three different measures were used to evaluate the effect of the input earthquake. These measures are peak shake table acceleration, spectral acceleration at the fundamental period of the test specimens, and the specimen drift ratios. For each measure, force-displacement relationships, strains, curvatures, drift ratios, and visual damage were evaluated. Results showed that regardless of the measure of input or response, the near-fault record generally led to larger strains, curvatures, and drift ratios. Furthermore, residual displacements were small compared to those for columns meeting current seismic code requirements.     

Strong motion displacement waveforms using 10‐Hz precise point positioning GPS: an assessment based on free oscillation experiments

The recently developed precise point positioning (PPP) technique permits to compute instantaneous coordinates of a GPS station relatively to distant reference stations and waveforms of ground displacements during strong motions at the 1 Hz level. This is another application of GPS, different from the computation of static coseismic movements or of accurate monitoring of dynamic displacements of structures using a static receiver and a nearby moving receiver (DGPS). Recently, earthquake ground displacement waveforms using 10‐Hz GPS data have also been calculated, but no independent evidence to assess their quality exists. To overcome this problem, we evaluated the output of 10‐Hz PPP results on the basis of supervised learning experiments. Semistatic and dynamic displacements (damped harmonic oscillations) of known characteristics of the order of a few centimeter were produced and were recorded by GPS, an accelerometer, and a robotic total station. Time series of instantaneous displacements were analyzed using different PPP techniques and were compared with reference (true) values derived from DGPS and the other sensors. Our analysis revealed that the PPP‐derived coordinates are contaminated by long‐period noise but they can display the details of semistatic displacements, while their short‐period component describes well the pattern of waveforms and spectra (at least up to 4 Hz) of dynamic displacements, with up to 20 mm accuracy for isolated points. These results indicate that 10‐Hz PPP‐GPS is useful for earthquake engineering and can safely be used to reconstruct waveforms of deflections of the ground and of various points on structures during strong motions. Copyright © 2014 John Wiley & Sons, Ltd.     

Evaluation of blast effects on reinforced concrete buildings considering Operational Modal Analysis results

Seismic protection of buildings under risk can be achieved by increasing the knowledge about the behaviour of existing structures. Operational Modal Analysis is a powerful tool used for this purpose all over the world. It provides the dynamic characteristics of structures under operational conditions or some particular environmental issues such as blasts and earthquakes. The main objective of this study is to evaluate blast effects on a reinforced concrete (RC) building considering experimentally determined dynamic characteristics. The study consists of three phases: the measurement of vibration characteristics of blasting, the theoretical modal analysis of the inspected building, and experimental verification of dynamic characteristics using modal testing. The vibration characteristics of blasting are measured around the inspected building on hard soil using a geophone set. The initial analytical model of the building is constructed according to the in-situ investigation on building. The theoretical modal analysis results are verified by carrying out modal testing on the RC building. The Operational Modal Analysis method is used for the extraction of the dynamic characteristics of the building, and blast vibrations are taken into account as environmental vibrations. The effects of blasting on the reinforced concrete building are introduced by assessing the vibration of blasting with the dynamic characteristics of the building.     

Multidimensional performance limit state for probabilistic seismic demand analysis

Based on a framework of Probabilistic Seismic Demand Analysis, a nonlinear dynamic model of a reinforced concrete (RC) building was established to obtain a demand hazard curve that considers multidimensional performance limit states (MPLSs), including combinations of peak floor acceleration and interstory drift. A definition of the two limit states is expressed using a generalized MPLSs equation. The peak floor acceleration and the interstory drift were considered to be dependent and were assumed to follow a bidimensional lognormal distribution. The maximum interstory drift and the maximum peak floor acceleration were calculated using Increment Dynamic Analysis and nonlinear time history analysis. The numerical formula for a demand hazard curve of the modelled building was then derived by coupling the bidimensional lognormal distribution with the ground motion hazard curve. The uncertainties involved in MPLSs and structural parameters, as well as the different threshold values for peak floor acceleration, were further considered to determine the sensitivity of demand hazard curves. The analysis results showed that the proposed method can be used to describe the damage performance of various building structures, which are sensitive to multiple response parameters including drift and acceleration. Moreover, it was demonstrated in this study that the demand hazard curves were relatively conservative if the coefficient of variation, the peak floor acceleration threshold, the interaction factor N _IDR and added stiffness, were appropriately selected.     

Engineering vibration monitoring by GPS： long duration records

Monitoring the performance of any structure requires real-time measurements of the change of position of critical points.Different techniques can be used for this purpose,each one offering advantages and disadvantages.The technique based on satellite positioning systems(GPS,GLONASS and the future GALILEO)seems to be very promising at least for long period structures.The GPS in particular provides sampling rates that are able to track dynamic displacements with high accuracy.Its service ability is indepen...     

Hybrid platform for vibration control of high‐tech equipment in buildings subject to ground motion. Part 2: analysis

The experimental results of using a hybrid platform to mitigate vibration of a batch of high‐tech equipment installed in a building subject to nearby traffic‐induced ground motion have been presented and discussed in the companion paper. Based on the identified dynamic properties of both the building and the platform, this paper first establishes an analytical model for hybrid control of the building‐platform system subject to ground motion in terms of the absolute co‐ordinate to facilitate the absolute velocity feedback control strategy used in the experiment. The traffic‐induced ground motion used in the experiment is then employed as input to the analytical model to compute the dynamic response of the building‐platform system. The computed results are compared with the measured results, and the comparison is found to be satisfactory. Based on the verified analytical model, coupling effects between the building and platform are then investigated. A parametric study is finally conducted to further assess the performance of both passive and hybrid platforms at microvibration level. The analytical study shows that the dynamic interaction between the building and platform should be taken into consideration. The hybrid control is effective in reducing both velocity response and drift of the platform/high‐tech equipment at microvibration level with reasonable control force. Copyright © 2003 John Wiley & Sons, Ltd.     

Full-scale dynamic testing of the Alamillo cable-stayed bridge in Sevilla (Spain)

Accelerations and displacements due to dynamic excitation by simulated traffic consisting of two trucks, were measured on the deck and tower of the Alamillo cable-stayed bridge. Also the dynamic testing program included the measurement with accelerometers of the free-damped vibration of the 26 cables achieved by means of quick-releasing force. From these measurements it was possible to obtain the dynamic parameters of the bridge (natural frequencies and damping ratios) and the real forces in the cables. In the paper, only the tests, results and conclusions related to dynamic parameters of the bridge are presented. The objective of the dynamic tests herein described was to validate the mathematical modelling and the wind-tunnel models used in the dynamic analysis of the bridge in front of traffic and wind-forces. As the agreement between dynamic parameters of the real bridge and theoretical and scaled models was very satisfactory, the correct dynamic behaviour of the bridge in response to traffic and wind (vortex shedding, flutter, etc.) can be deduced jointly with the correct alignment and expected internal forces in the permanent state in tower and deck.     

Direct displacement-based seismic design of steel eccentrically braced frame structures

This paper details a direct displacement-based design procedure for steel eccentrically braced frame (EBF) structures and gauges its performance by examining the non-linear dynamic response of a series of case study EBF structures designed using the procedure. Analytical expressions are developed for the storey drift at yield and for the storey drift capacity of EBFs, recognising that in addition to link beam deformations, the brace and column axial deformations can provide important contributions to storey drift components. Case study design results indicate that the ductility capacity of EBF systems will tend to be relatively low, despite the large local ductility capacity offered by well detailed links. In addition, it is found that while the ductility capacity of EBF systems will tend to reduce with height, this is not necessarily negative for seismic performance since the displacement capacity for taller EBF systems will tend to be large. To gauge the performance of the proposed DBD methodology, analytical models of the case study design solutions are subject to non-linear time-history analyses with a set of spectrum-compatible accelerograms. The average displacements and drifts obtained from the NLTH analyses are shown to align well with design values, confirming that the new methodology could provide an effective tool for the seismic design of EBF systems.     

双防线可恢复性能斜交网格结构耗能机制和抗震性能研究

为提高斜交网格结构的抗震性能,提出一种双防线可恢复性能斜交网格结构。双防线可恢复性能斜交网格结构采用剪切耗能段和特定梁端塑形铰进行集中耗能,使主体结构构件保持弹性。剪切耗能段不承受和传递重力荷载,易在震后修复或更换,使建筑可迅速恢复功能。为实现目标耗能机制,对等效能量塑形设计法进行改进以适用于可恢复性能斜交网格结构,并进行结构设计举例。采用OpenSees软件对所设计结构建立详细的有限元计算模型,进行非线性动力时程分析,以验证双防线耗能机制并评估抗震性能。分析结果表明:（1）小震、中震和大震下的结构顶部位移角分别为0.28%、0.8%和1.7%,与性能设计目标基本相同;（2）中震时剪切耗能段屈服,特定梁端未出现塑性铰;（3）大震时,特定梁端出现塑性铰以增加结构耗能能力,剪切耗能段屈服且处于延性范围内。因此新型可恢复性能斜交网格结构具有有效的双防线耗能机制,在中震后可迅速修复,在大震中可保持延性,实现"中震可修,大震不倒"的性能目标。     

Modified three‐dimensional seismic assessment method for buildings based on ambient vibration tests: extrapolation to higher shaking levels and measuring the dynamic amplification portion of natural torsion

This paper presents applications of the modified 3D‐SAM approach, a three‐dimensional seismic assessment methodology for buildings directly based on in situ experimental modal tests to calculate global seismic demands and the dynamic amplification portion of natural torsion. Considering that the building modal properties change from weak to strong motion levels, appropriate modification factors are proposed to extend the application of the method to stronger earthquakes. The proposed approach is consistent with the performance‐based seismic assessment approach, which entails the prediction of seismic displacements and drift ratios that are related to the damage condition and therefore the functionality of the building. The modified 3D‐SAM is especially practical for structures that are expected to experience slight to moderate damage levels and in particular for post‐disaster buildings that are expected to remain functional after an earthquake. In the last section of this paper, 16 low to mid‐rise irregular buildings located in Montreal, Canada, and that have been tested under ambient vibrations are analyzed with the method, and the dynamic amplification portion of natural torsion of the dataset is reported and discussed. The proposed methodology is appropriate for large‐scale assessments of existing buildings and is applicable to any seismic region of the world. Copyright © 2016 John Wiley & Sons, Ltd.     

Shake table tests on standard and innovative temporary partition walls

Shake table tests are performed on temporary internal partitions for office buildings. Four different specimens are tested. A steel frame is designed to exhibit relative displacements which typically occur at a given story of ordinary buildings. Four different partition walls are tested simultaneously for each specimen typology. This allows investigating the influence of an innovative device on the seismic performance of the tested components. The innovative device avoids the unhooking of the panels from the supporting studs. Several shake table tests are performed subjecting the specimens to interstory drift ratios up to 1.57%. Both the hysteretic curves and the natural frequency trend highlight that the partitions do not contribute to the lateral stiffness of the test setup. The damping ratio increases after the partition walls are installed within the test frame, causing a beneficial effect in the dynamic response. Minor damage state occurs for interstory drift ratio (IDR) in the range 0.41–0.65% in standard specimens, whereas moderate and major damage states are attained for IDR in the range 0.51–0.95%. Significant increase of collapse IDR is recorded with the introduction of the innovative device, up to IDR larger than 1.45%. It can be therefore concluded that a simple innovative device is defined, which significantly improves the seismic performance of the tested specimen. Copyright © 2017 John Wiley & Sons, Ltd.     

Evaluating the inelastic displacement ratios of moment-resisting steel frames designed according to the Egyptian code

Seismic codes estimate the maximum displacements of building structures under the design-basis earthquakes by amplifying the elastic displacements under the reduced seismic design forces with a deflection amplification factor(DAF). The value of DAF is often estimated as ρ× R, where R is the force reduction factor and ρ is the inelastic displacement ratio that accounts for the inelastic action of the structure according to the definition presented by FEMA P695. The purpose of this study is to estimate the ρ-ratio of moment resisting steel frames(MRSFs) designed according to the Egyptian code. This is achieved by conducting a series of elastic and inelastic time-history analyses by two sets of earthquakes on four MRSFs designed according to the Egyptian code and having 2, 4, 8 and 12 stories. The earthquakes are scaled to produce maximum story drift ratios(MSDRs) of 1.0%, 1.5%, 2.0% and 2.5%. The mean values of the ρ-ratio are calculated based on the displacement responses of the investigated frames. The results obtained in this study indicate that the consideration of ρ for both the roof drift ratios(RDRs) and the MSDRs equal to 1.0 is a reasonable estimation for MRSFs designed according to the Egyptian code.     

Collapse risk and residual drift performance of steel buildings using post-tensioned MRFs and viscous dampers in near-fault regions

The potential of post-tensioned self-centering moment-resisting frames (SC-MRFs) and viscous dampers to reduce the collapse risk and improve the residual drift performance of steel buildings in near-fault regions is evaluated. For this purpose, a prototype steel building is designed using different seismic-resistant frames, i.e.: moment-resisting frames (MRFs); MRFs with viscous dampers; SC-MRFs; and SC-MRFs with viscous dampers. The frames are modeled in OpenSees where material and geometrical nonlinearities are taken into account as well as stiffness and strength deterioration. A database of 91 near-fault, pulse-like ground motions with varying pulse periods is used to conduct incremental dynamic analysis (IDA), in which each ground motion is scaled until collapse occurs. The probability of collapse and the probability of exceeding different residual story drift threshold values are calculated as a function of the ground motion intensity and the period of the velocity pulse. The results of IDA are then combined with probabilistic seismic hazard analysis models that account for near-fault directivity to assess and compare the collapse risk and the residual drift performance of the frames. The paper highlights the benefit of combining the post-tensioning and supplemental viscous damping technologies in the near-source. In particular, the SC-MRF with viscous dampers is found to achieve significant reductions in collapse risk and probability of exceedance of residual story drift threshold values compared to the MRF.     

Performance‐based earthquake engineering assessment of a self‐centering,post‐tensioned concrete bridge system

Highway bridges in highly seismic regions can sustain considerable residual displacements in their columns following large earthquakes. These residual displacements are an important measure of post‐earthquake functionality, and often determine whether or not a bridge remains usable following an earthquake. In this study, a self‐centering system is considered that makes use of unbonded, post‐tensioned steel tendons to provide a restoring force to bridge columns to mitigate the problem of residual displacements. To evaluate the proposed system, a code‐conforming, case‐study bridge structure is analyzed both with conventional reinforced concrete columns and with self‐centering, post‐tensioned columns using a formalized performance‐based earthquake engineering (PBEE) framework. The PBEE analysis allows for a quantitative comparison of the relative performance of the two systems in terms of engineering parameters such as peak drift ratio as well as more readily understood metrics such as expected repair costs and downtime. The self‐centering column system is found to undergo similar peak displacements to the conventional system, but sustains lower residual displacements under large earthquakes, resulting in similar expected repair costs but significantly lower expected downtimes. Copyright © 2010 John Wiley & Sons, Ltd.     

Seismic vulnerability evaluation of RC moment frame buildings in moderate seismic zones

A multi‐level seismic vulnerability assessment of reinforced concrete moment frame buildings located in moderate seismic zones (0.25g) is performed on a set of ductile versions of low‐ to mid‐rise two‐dimensional moment frames. The study is illustrated through application to comparative trial designs of two (4‐ and 8‐story) buildings adopting both space‐ and perimeter‐framed approaches. All frames are dimensioned as per the emerging version of the seismic design code in Egypt. These new seismic provisions are in line with current European norms for seismic design of buildings. Code‐compliant designs (CCD), as well as a proposed modified code design relaxing design drift demands for the investigated buildings, are examined to test their effectiveness and reliability. Applying nonlinear inelastic incremental dynamic analyses, fragility curves (FC) for the frames are developed corresponding to various code‐specified performance levels. Code preset lower and upper bounds on design acceleration and drift, respectively, are also addressed along with their implications, if imposed, on the frames seismic performance and vulnerability. Annual spectral acceleration hazard curves for the case study frames are also generated. Estimates for mean annual frequency (MAF) of exceeding various performance levels are then computed through an integration process of the data resulting from the FC with the site hazard curves. The study demonstrates that the proposed design procedure relaxing design drift demands delivers more economic building designs relative to CCDs, yet without risking the global safety of the structure. The relaxed design technique suggested herein, even though scoring higher, as expected by intuition, MAF of exceeding various code‐limiting performance levels expressed in terms of interstory drift ratios, still guarantees a reasonably acceptable actual margin against violating code limits for such levels. Copyright © 2010 John Wiley & Sons, Ltd.