Ground Motion Selection Methods Research Articles

Empirical correlations between ground motion intensity measures from the NGA‐West2 database and their use in vector generalized conditional intensity measures

AbstractThis paper examines the empirical correlations between 14 intensity measures (IMs) describing the frequency content, amplitude, cumulative effects, and duration aspects of ground motion based on the NGA‐West2 database. The correlation results in this paper are compared with the results of previous models based on the NGA‐West1 database, and the previous correlation coefficient models are updated and extended. The comparison results show that the trend of the correlation coefficients of the model established in this paper is essentially consistent with previous models based on the NGA‐West1 database, with most correlation coefficients observed in this paper being slightly lower than in previous studies. In addition, this paper extends the generalized conditional intensity measure (GCIM) ground motion selection method so that it can consider multiple conditional IMs (VGCIM), and gives full theoretical details. The differences between the theories of VGCIM and GCIM are discussed, and several possible application scenarios of VGCIM are illustrated. An example application of VGCIM is shown, and the results show that there are deviations between the target IMs conditional distribution constructed after considering multiple conditional IMs and considering one IM that is sufficient to make an impact in the ground motion selection. Finally, the effect of the correlation coefficient model on the IMs conditional distributions generated based on GCIM and VGCIM is discussed.

An unsupervised machine learning based ground motion selection method for computationally efficient estimation of seismic fragility

AbstractIn the context of performance‐based earthquake engineering (PBEE), response‐history analysis is currently considered an analytical tool for developing fragility curves. Typically, this involves subjecting a structural system to a large number of ground motion records (GMRs) representing seismic hazards at a site of interest and may be a time‐consuming task. To address this computational challenge, this study proposes a method for selecting a representative subset of GMRs that enables the reproduction of the fragility curve of the general GMR set. In this method, dimension reduction techniques are used to preferentially extract the principal features of earthquake intensity measures, which are applied to construct the feature space. Then, the divisive hierarchical clustering technique is applied to the feature space to obtain a subset of GMRs from the general set until the fragility curve converges. The performance of the proposed method is successfully demonstrated through various numerical examples that include a wide class of single‐degree‐of‐freedom systems and two steel‐frame buildings. The results confirm that the seismic hazard at a given site represented by a general GMR set can be covered in structural fragility estimation using a representative subset of GMRs selected based on the proposed method. The proposed method could contribute to significantly reducing the computational costs for structural fragility estimation without compromising the accuracy.

Spectrum-matched ground motion selection method based on Siamese Convolutional Neural Networks

Selecting spectrum-matched ground motions is one of the critical problems in the seismic analysis and design of structures. The sum of the square errors (SSE) has been commonly used to quantitatively measure the similarity between the response spectrum of a ground motion and a target spectrum. However, it cannot represent the two-dimensional plane feature of the response spectrum because the response spectrum is treated as a one-dimensional vector in the SSE-based approaches. Considering the high-performance feature extraction of images and small-sample learning for the Siamese Convolutional Neural Networks (SCNNs), a new spectrum-matched ground motion selection method is proposed based on the SCNNs. The types of ground A, B, C, and D acceleration design spectra for the Eurocode 8 are selected as the target spectra without loss of generality. The procedures for the sample image generation, network training, testing, and spectrum-matched ground motion selection are elaborated. Analysis results indicate that using 40 samples for each class can achieve satisfactory training results. The mean response spectrum of the ground motions selected by the proposed method is matched with the target spectrum in all periods. Compared to the SSE-based approaches, the results obtained by the proposed method have a minor standard deviation. The proposed method could be used as an alternative in the ground motion selection for the dynamic analysis of structures.

Genetic algorithm‐based ground motion selection method matching target distribution of generalized conditional intensity measures

AbstractThis study developed an approach for selecting sets of ground motion recordings that match a target conditional multivariate distribution of ground motion intensity measures (IMs). This was achieved by applying a genetic algorithm (GA) that treats IMs of interest of each recording as a “chromosome” and the set of the desired number of recordings as a single “individual.” The fitness function was constructed by measuring the mismatch between the target and the individual's means and variances for all IMs. Then, through Roulette wheel natural parent selection, one‐point chromosome crossover, and individual mutation, new generations of ground motion sets were produced and the process was continued until the optimum combination of recordings was obtained. Example application illustrated that the proposed GA method could efficiently search and find a desired number of recordings to represent the target conditional IMs’ distribution, including the mean and variance. The IMs considered included response spectrum (range: 0.05‐10.0 s), amplitude/intensity‐based IMs, cumulative‐based IMs, and duration. Comparison with existing GCIM selection method indicated that the standard deviation of the recordings selected using the proposed GA method was closer to the target and more stable among replications. The results demonstrated that the proposed GA method represents a promising approach for searching pairs of recordings that could simultaneously match the target conditional distribution of various IMs.

The Effect of Ground Motion Selection Methods for Seismic Design of Tall Buildings: A Case Study of Mandalay City

The near-fault earthquakes ground motion usually observed a few kilometers away from the active faults generally contains high energetic velocity pulses as a consequence of directivity effects. Mandalay city is located 8 km away from the Sagaing fault, and the comparative study is conducted to evaluate the structural response of 3 different types of Reinforced Concrete buildings - 4-story, 10-story, and 16-story buildings, respectively. These buildings are subjected to bi-directional ground motions selected from both far-field and pulse-like near-fault earthquakes. The far-field earthquakes produce less seismic demand on the buildings when compared to the near-fault earthquakes, where the ratio of the fundamental period of the building to the pulse period is significant. Comparing 2 ground motion selection and scaling methods of Tall Building Initiative guidelines - TBI (2010) and TBI (2017), the latter approach provides a more meaningful definition of intensity measure and allows reducing some conservatism. The structural response obtained from the design Equivalent Lateral Force (ELF) and Response Spectrum Analysis (RSA) is compared with the code-based linear Response History Analysis (RHA) results.

Ground motion selection for the evaluation of residual inter-story drifts in moment-resisting reinforced concrete frame buildings

An evaluation of some structural parameters affecting the amplitude and height-wise distribution of peak and residual drift demands of reinforced concrete frame buildings modeled as 3D complex MDOF systems is presented. In addition, the influence of different ground motion selection methods on the uncertainty in the estimation of both peak and residual drifts is assessed. For this purpose, buildings with different characteristics were subjected to record sets selected: a) randomly, b) considering the magnitude and epicentral distance, and c) to match an objective spectral shape. Results indicate that parameters like the post-yielding stiffness ratio and the structural overstrength importantly affect the magnitude and height-wise distribution of residual drift demands on buildings. The estimation of residual drifts involves a higher level of uncertainty than that of peak drift demands. Selecting records based on a target spectral shape is very effective in reducing the uncertainty on the estimation of both peak and residual inter-story drift demands. Residual drifts may be underestimated if the design/assessment of buildings is conducted by using seismic records that were selected randomly or according to their magnitude and epicentral distance only.

Effect of Common U.S. Ground Motion Selection Methods on the Structural Response of Steel Moment Frame Buildings

This study quantifies the impact of two common ground motion (GM) selection methods, included in U.S. standards, on the seismic performance evaluation of steel special moment frames. The methods investigated are a “traditional” approach, herein referred to as the target maximum considered earthquake (TMCE) method, and a newer approach known as the conditional mean spectrum (CMS) method. The TMCE method selects GMs using the risk-based maximum considered earthquake (MCER) spectrum as the target spectrum, while the CMS method uses the CMS that anchors the MCER at multiple conditioning periods. Three special steel moment frames of 4, 8, and 16 stories are designed in accordance with ASCE/SEI 7-10, and their seismic performance is assessed with the nonlinear dynamic procedure prescribed in ASCE/SEI 41-13 using GMs selected and scaled in accordance with the aforementioned methods. A comparison of statistical parameters for the reduced beam sections and column hinges is conducted using the normalized demand-to-capacity ratio ( DCR), as the output parameter. The buildings are evaluated at the collapse prevention performance level for a far-field site located in Los Angeles, CA. In general, the CMS method results in lower DCRs of the frame components and smaller output parameter dispersion. In addition to the spectral shape, the demands are largely influenced by the spectral accelerations prescribed for each evaluated method. The consideration of collapse realizations is also documented as well as the existing and proposed statistical methods to account for these realizations. The study shows that the GM selection process can cause significant differences in structural response that may lead to different retrofitting decisions.

Efficient structural seismic performance evaluation method using improved endurance time analysis

Evaluation of structural performance under seismic excitations from low intensity to high intensity is essential to verify the seismic resistant capacity of a structure, and usually carried out by the incremental dynamic analysis (IDA) method or pushover method. The recently developed endurance time (ET) method is another method that uses dynamic pushover excitations, i.e., endurance time acceleration function, to obtain results similar to those obtained by IDA or pushover methods with low computational cost and acceptable accuracy. This study proposes an improvement on the ET method by considering more restrictions for both the elastic and inelastic response spectra in the generation procedure, and by specifying a target duration. Four reinforced concrete frame structures with 4, 8, 12, and 16 stories are adopted to verify the accuracy of the improved method. Comparison of the results obtained by the proposed method, the ET method and the IDA method shows that the improved method has a higher accuracy than the ET method. For evaluation of structural responses under specific ground motion intensity, which is typically required in seismic design codes, the results obtained by the proposed method are compared with five commonly used ground motion selection methods, and shows the proposed method provides acceptable accuracy for engineering applications.

Ground Motion Selection in the Near-Fault Region considering Directivity-Induced Pulse Effects

This paper focuses on the selection of ground motions for seismic response analysis in the near-fault region, where directivity effects are significant. An approach is presented to consider forward directivity velocity pulse effects in seismic hazard analysis without separate hazard calculations for ‘pulse-like’ and ‘non-pulse-like’ ground motions, resulting in a single target hazard (at the site of interest) for ground motion selection. The ability of ground motion selection methods to appropriately select records that exhibit pulse-like ground motions in the near-fault region is then examined. Applications for scenario and probabilistic seismic hazard analysis cases are examined through the computation of conditional seismic demand distributions and the seismic demand hazard. It is shown that ground motion selection based on an appropriate set of intensity measures (IMs) will lead to ground motion ensembles with an appropriate representation of the directivity-included target hazard in terms of IMs, which are themselves affected by directivity pulse effects. This alleviates the need to specify the proportion of pulse-like motions and their pulse periods a priori as strict criteria for ground motion selection.

On the Seismic Fragility Assessment of Concrete Gravity Dams in Eastern Canada

In recent years, probabilistic methods, such as fragility analysis, have emerged as reliable tools for the seismic assessment of dam-type structures. These methods require the selection of a representative suite of ground motion records, resulting in the need for a ground motion selection method that includes all the relevant ground motion parameters in the fragility analysis of this type of structure. This article presents the development of up-to-date fragility curves for the sliding limit states of gravity dams in Eastern Canada using a record selection method based on the generalized conditional intensity measure approach. These fragility functions are then combined with the recently developed regional hazard data to evaluate the annual risk, which is measured in terms of the unconditional probability of limit state exceedance. The proposed methodology is applied to a case study dam in northeastern Canada, whose fragility is assessed through comparison with previous studies and current safety guidelines. It is observed that the more accurate procedure proposed herein produces less conservative fragility estimates for the case study dam.

A Ground Motion Record Selection Approach Based on Multiobjective Optimization

ABSTRACTThe evaluation of the seismic safety and reliability of buildings and building contents within a probabilistic framework often requires response history analyses using site-specific ground motion records. The ground motion selection method proposed in this paper addresses this issue by a stochastic search procedure in which record sets are selected such that first- and second-order statistics (median and dispersion) satisfy predefined ground motion spectrum targets over a wide period range. Once a ground motion record set is selected, it can be used for seismic assessment of a broad class of buildings within the target period range at the given location.

Effect of ground motion selection methods on seismic collapse fragility of RC frame buildings

SummaryVariation in the seismic collapse fragility of reinforced concrete frame buildings predicted using different ground motion (GM) selection methods is investigated in this paper. To simulate the structural collapse, a fiber‐element modelling approach with path‐dependent cyclic nonlinear material models that account for concrete confinement and crushing, reinforcement buckling as well as low cycle fatigue is used. The adopted fiber analysis approach has been found to reliably predict the loss in vertical load carrying capacity of structural components in addition to the sidesway mode of collapse due to destabilizing P–Δ moments at large inelastic deflections. Multiple stripe analysis is performed by conducting response history analyses at various hazard levels to generate the collapse fragility curves. To select GMs at various hazard levels, two alternatives of uniform hazard spectrum (UHS), conditional mean spectrum (CMS) and generalized conditional intensity measure (GCIM) are used. Collapse analyses are repeated based on structural periods corresponding to initial un‐cracked stiffness and cracked stiffness of the frame members. A return period‐based intensity measure is then introduced and applied in estimating collapse fragility of frame buildings. In line with the results of previous research, it is shown that the choice of structural period significantly affects the collapse fragility predictions. Among the GM selection methods used in this study, GCIM and CMS methods predict similar collapse fragilities for the case study building investigated herein, and UHS provides the most conservative prediction of the collapse capacity, with approximately 40% smaller median collapse capacity compared to the CMS method. The results confirm that collapse probability prediction of buildings using UHS offers a higher level of conservatism in comparison to the other selection methods. Copyright © 2017 John Wiley & Sons, Ltd.

Influence of ground motion selection methods on seismic directionality effects

This study investigates the impact of the earthquake incident angle on the structural demand and the influence of ground motion selection and scaling methods on seismic directionality effects. The structural demand produced by Non-Linear Time-History Analyses (NLTHA) varies with the seismic input incidence angle. The seismic directionality effects are evaluated by subjecting four three-dimensional reinforced concrete structures to different scaled and un-scaled records oriented along nine incidence angles, whose values range between 0 and 180 degrees, with an increment of 22.5 degrees. The results show that NLTHAs performed applying the ground motion records along the principal axes underestimate the structural demand prediction, especially when plan-irregular structures are analyzed. The ground motion records generate the highest demand when applied along the lowest strength structural direction and a high energy content of the records increases the structural demand corresponding to this direction. The seismic directionality impact on structural demand is particularly important for irregular buildings subjected to un-scaled accelerograms. However, the orientation effects are much lower if spectrum-compatible combinations of scaled records are used. In both cases, irregular structures should be analyzed first with pushover analyses in order to identify the weaker structural directions and then with NLTHAs for different incidence angles.

Skyline‐based ground motion selection method for nonlinear time history analysis of building structures

SUMMARYThis paper develops a novel ground motion selection procedure for nonlinear time history analysis of critical structures. The skyline query originated from computer science is first introduced, including its concept and related algorithms. Then, the ground motion selection procedure based on skyline query is developed. Meanwhile, a new five‐dimensional vector‐valued intensity measure is defined as a critical ingredient of the selection procedure to measure the damage potential of ground motions. Finally, the process of the selection procedure is illustrated through examples of three shear models, and its efficiency is also validated. Through the examples of three shear models, the ground motion selection procedure based on skyline query proposed in this paper is proven to be capable of selecting a limited set of ground motions with high damage potentials for the nonlinear time history analysis purpose. Copyright © 2012 John Wiley & Sons, Ltd.