Set Of Earthquake Ground Motions Research Articles

Constant-strength inelastic displacement ratio spectra for assessment of superstructures in seismically isolated buildings

A reliable estimation of maximum displacement demands of seismically isolated inelastic superstructures is crucial for assessment of base-isolated buildings under beyond-design earthquakes. Constant-strength inelastic displacement ratio, CR, spectra, as applied in the performance-based seismic assessment procedure, can be used to estimate the inelastic displacement demands of structures. Currently, a suitable analytical expression of CR is lacking for base-isolated structures considering the influencing parameters comprehensively. This paper seeks to fill this gap. The constant-strength spectra are computed from nonlinear dynamic analyses of simplified two-degree-of-freedom models considering the inelastic behavior of the superstructure and isolator system, using a set of earthquake ground motions recorded on stiff soil sites. The effects of strength reduction factor of superstructure, superstructure elastic period, secondary stiffness ratio of superstructure, mass ratio, isolation period, normalized strength of isolation system and superstructure viscous damping on the mean and dispersion of CR are investigated. In particular, the effects of variations in earthquake intensity and isolator strength on CR are taken into account by the normalized strength of isolation system. Besides, limiting values of CR as the superstructure elastic period tends to zero or infinity are discussed and verified using the statistical values of CR. Finally, based on the trends of CR with respect to the design parameters of the superstructure and isolation system, and the boundary conditions to the CR formula, an analytical estimating equation with reasonable accuracy is developed to approximate the mean constant-strength inelastic displacement ratios during seismic assessment of base-isolated building structures built on stiff soil sites.

Dissipative exoskeletons for seismic rehabilitation of RC buildings

Relevant buildings like schools, public offices, assembly halls, and so on, should retain their structural integrity since their collapse could cause major human losses and significant economic impact. Moreover, such buildings should remain operational even during seismic retrofit work. This has stimulated the development of seismic retrofit solutions based on rapid, low-impact, and reversible interventions that can be done while the building is in use, removed and rapidly replaced if damaged due to earthquake, and integrated with energy efficiency measures. This situation has encouraged the use of external additive structures, commonly called exoskeletons, as a feasible solution for seismic retrofit. Typically, the research and applications deal with non-dissipative steel exoskeletons based on diagrids or external braces. This paper outlines the design and evaluation of dissipative exoskeletons. It focuses on a real school building case study, where both parallel and orthogonal exoskeleton configurations are employed. The dissipative exoskeletons are designed using a displacement-based design procedure. The effectiveness of the retrofit strategy for ductile failure modes is finally demonstrated by nonlinear time-history analyses under different sets of earthquake-ground motions.

Influence of uncertainties on the seismic performance of steel moment resisting frames

The present paper investigates the probabilistic assessment of the seismic performance of steel MRFs designed according to Eurocodes. The considered MRFs are three- and five-storey high and are analysed by the multiple stripe method of analysis by means of sets of earthquake ground motions that depend in frequency content, energy and duration on the value of the selected seismic intensity measure. Additional uncertainties are related to the mechanical properties of steel, dead and live loads and equivalent viscous damping ratio. Different criteria are defined to assess the performance at the achievement of different limit states, in terms of interstorey drifts and damage indexes. To reach a synthetic evaluation of the seismic performances, the mean annual frequency of exceedance of the assigned limit state condition is also reported. Based on a Monte Carlo simulation the paper evaluates the effects of the single uncertainties on the seismic performances and suggests proper modifications to the simplified approach included in FEMA documents to mime the results of a full probabilistic approach.

EVALUATION OF SEISMIC PERFORMANCE ENHANCEMENT TECHNIQUES FOR SHEAR WALL BUILDINGS USING ADVANCED MATERIALS AND SYSTEMS

There has been constant deliberation regarding promising seismic performance enhancement techniques for the reinforced concrete (RC) high-rise structures built before adopting existing seismic design codes. The research reported in this paper focuses on advanced approaches for improving the seismic performance of the shear wall structural system using high-performance reinforced concrete jackets and an outrigger-bracing system consisting of braces with improved hysteresis response. Following the case study region’s seismicity and design criteria, inelastic analyses are conducted to evaluate the demand-to-capacity ratios of primary vertical structural members of a pre-code twenty-six-story building. With the application of the proposed retrofit approaches and their various configurations, the design inadequacy of several structural members is eradicated. After validating the adopted fiber-based discretizations of the retrofit techniques with recent experimental studies, detailed three-dimensional numerical models are developed for the high-rise structures. Inelastic pushover analyses and dynamic response simulations under a diverse set of earthquake ground motions with increasing intensity levels are conducted to capture the buildings’ seismic performance until failure. The probabilistic seismic performance assessment enabled selecting the most effective technique for enhancing the seismic performance of shear wall buildings while minimizing disruption to the building.

EVALUATION OF SEISMIC PERFORMANCE ENHANCEMENT TECHNIQUES FOR SHEAR WALL BUILDINGS USING ADVANCED MATERIALS AND SYSTEMS

There has been constant deliberation regarding promising seismic performance enhancement techniques for the reinforced concrete (RC) high-rise structures built before adopting existing seismic design codes. The research reported in this paper focuses on advanced approaches for improving the seismic performance of the shear wall structural system using high-performance reinforced concrete jackets and an outrigger-bracing system consisting of braces with improved hysteresis response. Following the case study region’s seismicity and design criteria, inelastic analyses are conducted to evaluate the demand-to-capacity ratios of primary vertical structural members of a pre-code twenty-six-story building. With the application of the proposed retrofit approaches and their various configurations, the design inadequacy of several structural members is eradicated. After validating the adopted fiber-based discretizations of the retrofit techniques with recent experimental studies, detailed three-dimensional numerical models are developed for the high-rise structures. Inelastic pushover analyses and dynamic response simulations under a diverse set of earthquake ground motions with increasing intensity levels are conducted to capture the buildings’ seismic performance until failure. The probabilistic seismic performance assessment enabled selecting the most effective technique for enhancing the seismic performance of shear wall buildings while minimizing disruption to the building.

Seismic Retrofit of an Existing Reinforced Concrete Building with Buckling-restrained Braces

Background: The seismic retrofitting of frame structures using hysteretic dampers is a very effective strategy to mitigate earthquake-induced risks. However, its application in current practice is rather limited since simple and efficient design methods are still lacking, and the more accurate time-history analysis is time-consuming and computationally demanding. Aims: This paper develops and applies a seismic retrofit design method to a complex real case study: An eight-story reinforced concrete residential building equipped with buckling-restrained braces. Methods: The design method permits the peak seismic response to be predicted, as well as the dampers to be added in the structure to obtain a uniform distribution of the ductility demand. For that purpose, a pushover analysis with the first mode load pattern is carried out. The corresponding story pushover curves are first idealized using a degrading trilinear model and then used to define the SDOF (Single Degree-of-Freedom) system equivalent to the RC frame. The SDOF system, equivalent to the damped braces, is designed to meet performance criteria based on a target drift angle. An optimal damper distribution rule is used to distribute the damped braces along the elevation to maximize the use of all dampers and obtain a uniform distribution of the ductility demand. Results: The effectiveness of the seismic retrofit is finally demonstrated by non-linear time-history analysis using a set of earthquake ground motions with various hazard levels. Conclusion: The results proved the design procedure is feasible and effective since it achieves the performance objectives of damage control in structural members and uniform ductility demand in dampers.

Seismic performance assessment of weak first-storey RC buildings designed with old and new seismic provisions for Mexico City

This paper presents the main results of an investigation focused on evaluating the new seismic design requirements for weak first-story reinforced concrete (RC) buildings prescribed in the 2017 edition of the Technical Norms for Seismic Design (NTCS-2017) for Mexico City. To provide a context, the seismic response of a family of low-to-medium height buildings designed with the updated NTCS-2017 was compared with that of counterpart’s buildings designed with the 1976 old edition of the NTCS (NTCS-1976). All building models where subjected to a set of earthquake ground motions recorded at the transition and soft soil sites during the recent strong intermediate-depth intraslab September 19, 2017 (Mw = 7.1) Puebla-Morelos earthquake, which caused significant structural damage to this type of buildings. Results from this investigation revealed that the requirements for weak first-storey RC buildings change the distribution of peak interstorey drift, IDR, along height, which avoids a concentration of IDR at the first-story. In addition, they delay the formation of a weak first-storey mechanism. This study also exhibited that weak first-storey RC buildings designed with old seismic provisions are susceptible to experience moderate-to-severe structural damage under strong normal-faulting intraslab earthquakes, which is consistent with field reconnaissance of damaged buildings after the September 19, 2017 (Mw = 7.1) Puebla-Morelos earthquake.

Correlation of Ground Motion Intensity Measures and Seismic Damage Indices of Masonry-Infilled Steel Frames

The main aim of this study was to analyze the response of structures with masonry infill walls to the intensity measure (IMs) parameters. Hence, two sets of earthquake ground motions, ordinary seismic records (OSR) and pulse-like seismic records (PLSR), were used for the nonlinear dynamic analysis of multi-story steel structures with masonry infill walls. Seismic performance was evaluated using the general indicators of damage (modified Park–Ang index), maximum inter-story drift ratio (MIDR) and roof drift ratio (RDR). The correlation between the multiple IM parameters with and without pulse-like ground motion and the damage indices of steel moment frames with and without masonry-infilled walls was determined using the Spearman correlation coefficient. Moreover, the correlation between the damage criteria and IMs was investigated. The results revealed that the spectral acceleration and velocity at the primary period of the structure and seismic parameters which are related to velocity have a strong relationship with MIDR and RDR. However, the correlations for PLSR and OSR were differed. The results indicated that the analysis of IMs with ground motion could help predict the parameters for building failure in various systems. The presence of masonry-infilled walls has changed the correlation coefficient for a fully infilled frame when compared with a bare frame.

Damage Index for Different Structural Systems Subjected to Recorded Earthquake Ground Motions

This study quantifies the damage index previously proposed by the writer ( Rodriguez 2015 ) for different structural systems subjected to a set of earthquake ground motions recorded during 12 strong earthquakes in different countries. Damage spectra were also computed using this seismic damage index. This study revisits the previously proposed index and shows that this index can also be interpreted as a ratio of velocities in the structural system responding to the earthquake demand. In addition, this study gives a more general damage analysis interpretation than that of the previous study since damage spectra were computed to assess the damage potential of a given recorded earthquake ground motion for different types of earthquake-resisting systems. The results from the damage analysis are consistent with the findings from previous research: most structural wall buildings show satisfactory earthquake performance, whereas frame buildings frequently show severe damage and collapse.

Influence of frequency‐dependent soil–structure interaction on the fragility of R/C bridges

SummaryBridge performance under earthquake loading can be significantly influenced by the interaction between the structure and the supporting soil. Even though the frequency dependence of the interaction mentioned in this study has long been documented, the simplifying assumption that the dynamic stiffness is dominated by the mean or predominant excitation frequency is still commonly made, primarily as a result of the associated numerical difficulties when the analysis has to be performed in the time domain. This study makes use of the advanced lumped parameter models recently developed in order to quantify the impact of the assumption on the predicted fragility of bridges mentioned in this study. This is achieved by comparing the predicted vulnerability for the case of a reference, well studied, actual bridge using both conventional, frequency‐independent, Kelvin–Voigt models and the aforementioned lumped parameter formulation. Analysis results demonstrate that the more refined consideration of frequency dependence of soil–structure interaction at the piers and the abutments of a bridge not only leads to different probabilities of failure for given intensity measures but also leads to different hierarchy and distribution of damage within the structure for the same set of earthquake ground motions even if the overall probability of exceeding a given damage state is the same. The paper concludes with the comparative assessment of the effect for different soil conditions, foundation configurations, and ground motion characteristics mentioned in this study along with the relevant analysis and design recommendations. Copyright © 2016 John Wiley & Sons, Ltd.

Evaluation of approximate methods to estimate residual drift demands in steel framed buildings

SummaryThis paper presents the evaluation of two approximate methods recently proposed in the literature to estimate residual (permanent) drift demands at the end of earthquake excitation for seismic assessment of buildings. Both methods require an estimate of the peak (maximum) interstory drift demand and the corresponding drift demand at significant yielding of the building. Additionally, an approximate method is proposed as part of this study. The introduced method follows a coefficient‐based approach similar to the Coefficient Method included in several US documents. For evaluating the approximate methods, five moment‐resisting steel framed buildings having different number of stories were analyzed under four sets of earthquake ground motions. Quantification of the accuracy of the approximate methods to estimate residual drift demands with respect to results from nonlinear time‐history analyses was performed through error measures computed for each building and each set of earthquake ground motions. Results show that the mean standard error tends to increase as the seismic hazard level increases. Between the two methods, the method introduced by Erochko et al. seems more effective in predicting residual drift demands than that proposed in the FEMA P‐58 recommendations in the USA. It is demonstrated that including additional sources of stiffness and strength in the modeling approach constrains the amplitude of residual drift demands. As a beneficial consequence, the accuracy of both approximate methods in predicting residual drift demands is significantly improved (i.e., mean standard error decreases). The introduced method also provides similar accuracy than the approximate methods available in the literature. Copyright © 2015 John Wiley & Sons, Ltd.

Extended Kalman filter for material parameter estimation in nonlinear structural finite element models using direct differentiation method

SummaryThis paper presents a novel nonlinear finite element (FE) model updating framework, in which advanced nonlinear structural FE modeling and analysis techniques are used jointly with the extended Kalman filter (EKF) to estimate time‐invariant parameters associated to the nonlinear material constitutive models used in the FE model of the structural system of interest. The EKF as a parameter estimation tool requires the computation of structural FE response sensitivities (total partial derivatives) with respect to the material parameters to be estimated. Employing the direct differentiation method, which is a well‐established procedure for FE response sensitivity analysis, facilitates the application of the EKF in the parameter estimation problem. To verify the proposed nonlinear FE model updating framework, two proof‐of‐concept examples are presented. For each example, the FE‐simulated response of a realistic prototype structure to a set of earthquake ground motions of varying intensity is polluted with artificial measurement noise and used as structural response measurement to estimate the assumed unknown material parameters using the proposed nonlinear FE model updating framework. The first example consists of a cantilever steel bridge column with three unknown material parameters, while a three‐story three‐bay moment resisting steel frame with six unknown material parameters is used as second example. Both examples demonstrate the excellent performance of the proposed parameter estimation framework even in the presence of high measurement noise. Copyright © 2015 John Wiley & Sons, Ltd.

Prediction of inelastic response periods of buildings based on intensity measures and analytical model parameters

This paper investigates the elongation of the fundamental period of reinforced concrete buildings that occurs during earthquake loading and its correlation with various intensity measures and engineering demand parameters. For this purpose, five buildings designed according to modern seismic codes are studied through equivalent single degree of freedom nonlinear systems with hysteretic laws that represent various levels of stiffness degradation, strength deterioration and pinching. By means of an extensive parametric analysis using a large set of earthquake ground motions and a rigorous validation procedure, the period elongation is quantitatively assessed as a function of building configuration and design (structural system and ductility class), ground motion characteristics (peak ground acceleration, spectral acceleration, frequency content) and demand parameters (displacement ductility). The results indicate that structures, designed according to modern seismic codes, are expected to exhibit low-to-moderate period elongation even for twice the intensity of the design earthquake. Given that the fundamental period of buildings is a key parameter in most seismic code procedures for ground motion selection, design and assessment, the implications of the predicted period lengthening are also discussed. The results are of interest to designers and analysts, as well as code-development committees.

Effect of ground motion characteristics on the pure friction isolation system

The performance of pure friction isolation system with respect to the frequency bandwidth of excitation and the predominant frequency is investigated. A set of earthquake ground motions (artificial as well as recorded [with different combinations of magnitude-distance and local site geology]) is considered for investigating effectiveness of pure friction isolators. The results indicate the performance of pure friction base isolated system does not only depend upon coefficient of friction and mass ratio but the stick-slip behaviour depends upon the frequency content of the excitation as well. Slippage prevails if the excitation frequency lies in a suitable frequency range. This range widens with increasing mass ratio. For larger mass ratios, the sliding effect is more pronounced and the maximum acceleration response is further reduced in the neighbourhood of frequency ratio (w/wn) of unity. The pure friction isolation system is effective in the case of broadband excitations only and that too, in the acceleration sensitive range of periods. The pure friction system is not effective for protection against narrow band motions for which the system response is quasi-periodic.

Seismic Performance Evaluation of a Steel-Concrete Hybrid Frame-Tube High-Rise Building Structure

Due to its unique advantages, the steel-concrete hybrid structure has been widely used in tall buildings around the world. In Mainland China it has been utilized as one of the most popular structural types for super tall buildings. In this study the seismic performance of a code-exceeding tall building with the hybrid frame-tube structure to be constructed in Beijing is evaluated by numerical analysis. The analytic model of the structure is established with the aid of PERFORM-3D program, and the nonlinear time history analysis is performed by inputting four sets of earthquake ground motions. The elastic dynamic characteristics, the global displacement responses, the performance levels and the deformation demand-to-capacity ratios of structural components under different levels of earthquakes are presented. Numerical analysis results indicate that the hybrid structure has good seismic performance.

매설가스배관의 지진 취약도 해석

본 연구에서는 국내에서 널리 사용되고 있는 매설가스배관인 API X65에 대해 지진 취약도 해석을 수행하였다. 이를 위해, 15가지 경우의 배관 해석모델에 대해 12본 세트의 다양한 지진파를 0.1g 등간격으로 스케일링하여 비선형 시간이력해석을 수행한 후, 비선형 시간이력해석으로 얻어진 매설가스배관의 최대 변형률을 이용하여 지진취약도 해석을 수행하였다. 지진 취약도 해석을 위해 본 연구에서는 또한, 지반조건, 단부지점조건, 매립깊이 및 배관형태 등을 변수로 고려하여 지진 취약도 해석을 수행하였다. 지진 취약도 해석결과, 지반조건, 단부지점조건 및 매립깊이는 매설가스배관의 취약도 곡선에 영향을 끼치는 것으로 판단되었고, 특히 지반조건이 미치는 영향은 다른 두 변수에 비해 다소 큰 것을 확인할 수 있었다. 반면에, 배관형태가 취약도 곡선에 미치는 영향은 미미한 것을 알 수 있었다. 종합적으로, 매설가스배관의 지진 취약도 해석과 관련된 연구가 많지 않은 현실을 감안할 때, 본 연구결과는 매설가스배관의 지진 취약성 평가해석에 초석으로 고려되어질 수 있고, 추후 관련분야 연구에 좋은 참고자료가 될 것으로 사료된다. In this paper, earthquake fragility analysis has been comparatively performed with regard to a buried gas pipeline of API X65 which has been widely used in Korea. For this purpose, a nonlinear time-history analyses has been carried out for 15 different analytical models of a buried gas pipeline in terms of the selected 12 sets of earthquake ground motions with 0.1g of scaling interval. Following that, earthquake fragility analyses have been conducted using the maximum axial strain of the pipeline obtained from the nonlinear time-history analyses. Parameters under consideration for subsequent earthquake fragility analyses are soil conditions, end-restraint conditions, burial depth and the type of pipeline. Comparative analyses reveal that whereas the first three parameters influence the fragility curves, particularly soil conditions amongst the three parameters, the last parameter has a little effect on the curves. In all, the present study can be considered as a benchmark fragility analysis of a buried gas pipeline in the absence of an earthquake fragility analysis of the pipeline and thus is expected to be a useful source regarding earthquake fragility analyses of a buried gas pipelines.

Seismic parameters characterization at Texcoco lake, Mexico

Texcoco lake area, in the Valley of Mexico, presents particularly difficult geotechnical conditions due to the presence of thick deposits of soft, highly compressible lacustrine clay, randomly interbeded with sand lenses. In contrast to other sites in the valley, there is a lack of information regarding the geotechnical subsoil conditions, dynamic properties, and earthquake recordings at rock sites. Thus, the seismic environment is not completely identified. This paper describes field and laboratory investigations as well as analytical studies, aimed at characterizing the ground response of a particular site located in this region, where is planed to be built an strategic power station, which will be the driving force for the urban and industrial development of Mexico City northeast side. In situ measurements of shear wave velocity, using suspension PS logging, along with cone penetration, CPT, and standard penetration, SPT, resistance values, and results from series of resonant column and cyclic triaxial tests were used to obtain a 3-D representation of the subsoil characteristics found at the site, and the variation of dynamic properties with strain level. Predicted shear wave velocity profiles derived through empirical correlations compared well with measured values. Ground motion definition was achieved indirectly through empirically derived response spectra obtained from sets of earthquake ground motions recorded at a nearby station located in soft soil. Acceleration time histories representative of the design earthquake were obtained using time-domain spectral matching. 1-D shear wave deconvolution was used to obtain the corresponding ground motions in rock.

Variability of seismic demands according to different sets of earthquake ground motions

AbstractIt is a challenging task to predict seismic demands for earthquake resistant design, particularly for tall buildings. In current seismic design provisions, seismic demands are expressed as a design base shear of which the key components are linear elastic design response spectra, force reduction factor (‘R factor’), and building weight. For tall buildings, response spectrum analysis or response history analysis is recommended in current design provisions. In recent years, new methods for predicting seismic demands have been developed, such as the capacity spectrum method (CSM) and displacement coefficient method. This study investigates the effect of different earthquake ground motion (EQGM) sets on seismic demands. Key components of the base shear and performance points in the CSM are considered as the seismic demands to be tested. For this purpose three EQGM sets are collected independently at rock sites. This study found that seismic demands can vary significantly according to different EQGM sets even though those sets were obtained at sites with similar soil conditions. This study also attempts to provide a criterion for reducing the variability in seismic demands according to different EQGM sets. Copyright © 2007 John Wiley & Sons, Ltd.

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

AbstractFor 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.

Inelastic deformation response of SDOF systems subjected to earthquakes

AbstractPerformance‐based seismic design requires reliable methods to predict earthquake demands on structures, and particularly inelastic deformations, to ensure that specific damage‐based criteria are met. Several methods based on the response of equivalent linear single‐degree‐of‐freedom (SDOF) systems have been proposed to estimate the response of multi‐degree‐of‐freedom structures. These methods do not offer advantages over the traditional Veletsos–Newmark–Hall (VNH) procedure, indeed, they have been shown to be inaccurate. In this study, the VNH method is revised, considering the inelastic response of elastoplastic, bilinear, and stiffness‐degrading systems with 5% damping subjected to two sets of earthquake ground motions. One is an ensemble of 51 earthquake records in the Circumpacific Belt, and the other is a group of 44 records in California. A statistical analysis of the response data provides factors for constructing VNH inelastic spectra. Such factors show that the ‘equal‐displacement’ and ‘equal‐energy’ rules to relate elastic and inelastic responses are unconservative for high ductilities in the acceleration‐ and velocity‐sensitive regions of the spectrum. It is also shown that, on average, the effect of the type of force–deformation relationship of non‐linear systems is not significant, and responses can be conservatively predicted using the simple elastoplastic model. Copyright © 2001 John Wiley & Sons, Ltd.