Suite Of Ground Motions Research Articles

Seismic performance assessment of high arch dams considering the pulse-like and directionality effects of near-fault ground motions

This paper investigates the pulse-like and directionality effects of near-fault horizontal ground-motion records on the seismic performance of high arch dams. A 3-dimensional arch dam-reservoir-foundation finite-element model is built. Two near-fault bidirectional ground-motion suites (i.e. ordinary and pulse-like suite) are collected. The fault-normal and fault-parallel orientations of the horizontal ground-motion records are rotated to reflect the directionality effect. Nonlinear dynamic analyses are further implemented for the high arch dam excited by both near-fault ground motions with different incidence angles. The results show that the pulse-containing ground-motion records can yield more notable dynamic response and damage for high arch dams as compared to the ordinary records. Moreover, with changing the incidence angles, both the dam dynamic response and damage metrics exhibit periodic variation and constant trends for the pulse-containing and ordinary ground-motion cases, respectively. Therefore, the directionality effect has a significant influence on the seismic performance of high arch dams excited by pulse-containing ground-motion records. Compared with the near-fault ordinary ground motions, the pulse-like ground motions will induce a 40 %-increase in the concrete damage volume of high arch dams. In addition, peak ground velocity could be regarded as a preferable intensity measure for assessing the seismic damage of high arch dams.

Ground-motions site and event specificity: Insights from assessing a suite of simulated ground motions in the San Francisco Bay Area

This article presents the results of a research that is part of a larger collaborative effort between the Lawrence Berkeley National Laboratory and the Pacific Earthquake Engineering Research Center, funded by the US Department of Energy Office of Cybersecurity, Energy Security and Emergency Response. The main objective of this study is to assess a suite of near and far-field simulated ground motions obtained from 20 realizations of an M7 Hayward Fault earthquake in the San Francisco Bay Area, California USA, and inform the selection of rupture simulation parameters leading to strong motions. To this aim, comparisons are conducted with NGA-W2 and directivity ground-motion models and a selected population of records. An archetypal steel moment-resisting frame is utilized to assess infrastructure response distributions. The analyses carried out for each simulated event and subdomain with consistent properties in terms of shallow shear-wave velocity proved to be instrumental for better interpreting the differences between simulated motions and empirical models. The main reasons identified for variances between simulations and empirical relationships included (1) directivity effects fully captured by the simulations across the full breadth of rupture models; (2) site vicinity to ruptures that incorporate large-slip patches, particularly if these are in the forward-directivity direction; and (3) presence of geologic structures that can “trap” seismic waves and produce ground motions with large amplitude and long signal duration. The analyses carried out in this work provide a path for interpreting ground-motion site and event specificity obtained from a suite of physics-based simulations, differing only in the rupture model characterization, to inform the selection of simulation scenarios for site-specific engineering analyses under strong excitations. Evidence from this work points to the possibility that current hazard models may underestimate ground-motion intensities in areas where the combined effect of directivity and site conditions results in large ground-motion amplitudes.

Comparative Analysis of Concentrically Braced Frames with FeSMA and Steel BRBs Under Long-Duration Earthquakes

ABSTRACT Owing to high fatigue life, the iron-based shape memory alloy (FeSMA) buckling-restrained braces (BRBs) are emerging as a promising candidate against long-duration earthquakes. However, the corresponding analysis cannot be found. Current emphasis is paid on unveiling the seismic response differences between concentrically braced frames (CBFs) with FeSMA and steel BRBs when they are attacked by long-duration earthquakes. To directly assess the effect of earthquake duration, this paper selects a total of 90 pairs of short- and long-duration earthquake records, which are record-to-record spectrally equivalent over a wide range of fundamental periods, for nonlinear time history analysis. A benchmark six-story CBF is selected for demonstration purposes. In the numerical simulation process, the fatigue-induced damage is particularly considered. A preliminary examination is first conducted in the case study, in which a representative pair of short- and long-duration records is selected. In what followed, the statistical results from the ground motion suites are analyzed. This work not only highlights the higher failure risk of steel BRBs than FeSMA BRBs under long-duration earthquakes associated with maximum considered earthquake hazard level, but also confirms the advantages of FeSMA BRBs over steel BRBs in controlling residual deformations.

Updated Predictive Models for Permanent Seismic Displacement of Slopes for Greece and Their Effect on Probabilistic Landslide Hazard Assessment

Earthquake-triggered landslides have been widely recognized as a catastrophic hazard in mountainous regions. They may lead to direct consequences, such as property losses and casualties, as well as indirect consequences, such as disruption of the operation of lifeline infrastructures and delays in emergency response actions after earthquakes. Regional landslide hazard assessment is a useful tool to identify areas that are vulnerable to earthquake-induced slope instabilities and design prioritization schemes towards more detailed site-specific slope stability analyses. A widely used method to assess the seismic performance of slopes is by calculating the permanent downslope sliding displacement that is expected during ground shaking. Nathan M. Newmark was the first to propose a method to estimate the permanent displacement of a rigid body sliding on an inclined plane in 1965. The expected permanent displacement for a slope using the sliding block method is implemented by either selecting a suite of representative earthquake ground motions and computing the mean and standard deviation of the displacement or by using analytical equations that correlate the permanent displacement with ground motion intensity measures, the slope’s yield acceleration and seismological characteristics. Increased interest has been observed in the development of such empirical models using strong motion databases over the last decades. It has been almost a decade since the development of the latest empirical model for the prediction of permanent ground displacement for Greece. Since then, a significant amount of strong motion data have been collected. In the present study, several nonlinear regression-based empirical models are developed for the prediction of the permanent seismic displacements of slopes, including various ground motion intensity measures. Moreover, single-hidden layer Artificial Neural Network (ANN) models are developed to demonstrate their capability of simplifying the construction of empirical models. Finally, implementation of the produced modes based on Probabilistic Landslide Hazard Assessment is undertaken, and their effect on the resulting hazard curves is demonstrated and discussed.

Uncertainty in Distinct Element Modeling of Freestanding Structures Considering Stiffness Parameters

ABSTRACT Numerical studies on freestanding structures typically leverage the Distinct Element Method where the response is dictated by joints; however, the response carries significant uncertainty due to joint stiffness parameters. This study aims to quantify the influence of joint stiffness parameters on the global response of freestanding structures subjected to seismic excitation in a probabilistic formulation. By using a range of joint stiffness values with rectangular rigid blocks of different aspect ratios, the impact of joint stiffness parameters is evaluated against a large suite of historical ground motions. Results indicate that increasing contact stiffness results in increased stability against overturning.

The importance of hazard-consistency when estimating seismic residual drifts in steel moment frames

Residual drifts are routinely used to assess the post-earthquake safety of buildings. Despite their importance, studies on the probabilistic assessment of residual drifts in multi-storey buildings with Steel Moment Resisting Frames (SMRF) are far less common than those dealing with their transient peak drift counterpart. More seriously, although residual drift prediction models have been developed with a particular broad ground-motion type or soil condition in mind, all models proposed to date remain oblivious to the central issue of hazard consistency. Hence, missing the causal connection between the seismic hazard level and the ground-motion suite used and potentially compromising the meaningfulness of their results. This oversight is expected to introduce a bias in the estimation of residual drifts but its magnitude has not yet been properly evaluated. In this paper, we evaluate and quantify the significance of these effects. To this end, we use the Conditional Scenario Spectra framework, which provides a set of realistic earthquake spectra with assigned rates of occurrences based on their spectral shape and intensity, thus preserving the critical relationship of hazard consistency. Nonlinear Response History Analyses (NRHA) of 24 deteriorating SMRFs under 816 ground-motion records are performed to construct a database of residual drift demands. These NRHA results are used to examine the residual drift trends and to construct benchmark residual drift hazard curves. An extensive feature selection process employing several Machine Learning (ML) algorithms precedes the development of hybrid data-driven predictive models. Finally, we compare our hazard-consistent predictions with currently available models and quantify the massive under- and over-estimations associated with previously proposed non-hazard-consistent assumptions.

A Simplified Approach of Analytical Seismic Fragility Analysis Using the Endurance Time Method

ABSTRACT The endurance time (ET) method is an effective dynamic analysis method for seismic response analysis of structures. It has been recently used for analytical fragility analysis. However, the available ET-based fragility analysis methods have two limitations: 1) the prediction error of the structural median responses estimated by the ET method is ignored; and 2) the record-to-record variability inherent earthquake ground motions is not well considered. To overcome the above limitations, another ET-based fragility analysis method is proposed, where only three times of ET nonlinear analyses are required. To do this, three specific endurance time excitation functions (ETEFs) are generated in correspondence to the mean and 16% and 84% percentile of response spectra of a selected suite of ground motion records (i.e. ETE F m , ETE F v 1 and ETE F v 2 , respectively). The structural response under ETE F m is used to estimate the median response of structures under the selected suite of ground motion. Moreover, the structural responses under ETE F v 1 and ETE F v 2 are used to quantify the record-to-record variability in earthquake ground motions. The fragility relationships are developed by both point and interval estimate methods since another logarithmic standard deviation is introduced to account for the difference between the median responses predicted using ETE F m and those predicted by the dynamic analysis. To validate the proposed method, two RC frame structures with six and nine stories are taken as the study cases. The fragility results based on the proposed ET-based method and those based on the cloud method are compared. It is found that the proposed ET-based fragility analysis method could generate reliable fragility estimation, whereas requiring limited computation cost. The proposed method would provide another simplified way for the rapid fragility assessment of structures.

Performance-based plastic design and seismic fragility assessment for chevron braced steel frames considering aftershock effects

Observations from past earthquakes demonstrated that buildings in high seismic regions might be exposed to several aftershocks following the mainshock which can significantly increase the damage level. Since aftershocks have the potential to increase the vulnerability of buildings damaged under mainshocks, it is crucial to consider aftershock effects in the structural design phase. Performance-based Plastic Design (PBPD) method is an innovative seismic design method in which the building designed by this method shows a desirable performance under severe ground motions. PBPD allows the designer to avoid time-consuming trial and error process of analyses that are usually done in Performance-based Design method to reach a desirable performance. However, this efficient method is only valid for mainshocks only and does not consider aftershock effects in the structural design process. In this study, initially, the seismic performance (interstory drift and plastic hinges distribution) of the three 3-, 6-, and 9- story PBPD designed Chevron-braced Steel frames (CBSF) are compared under mainshocks (MS) and mainshock-aftershock (MS-AS) sequences. Subsequently, a PBPD method is developed for CBSFs considering the aftershock effects in the structural design process. Incremental dynamic analysis (IDA) has been performed using a suite of mainshocks and aftershock ground motions to develop a design base shear modification factor. Using the developed method, the performance of CBSFs under MS and MS-AS sequences is evaluated and compared with the existing PBPD method. Fragility curves are developed to compare the seismic vulnerability of the frames designed based on PBPD and proposed PBPD methods under MS-AS sequences. The outcomes of this study provide a practical design approach for CBSFs under MS-AS sequences and shows that the structures designed using developed PBPD method show more desirable behavior under MS-AS sequences compared with the structures designed using the conventional PBPD method.

Near-fault ground motion effect on self-centering modular bracing panels considering soil-structure interaction

This study investigates the nonlinear seismic response behavior of self-centering modular steel bracing panel (SCMBP) systems subjected to near-fault ground motion records, considering the soil-structure interaction (SSI) effect. Analytical formulas for the load-displacement relationship of an SCMBP were validated through nonlinear 3D continuum finite element analysis while a simplified 2D wireframe model utilizing a constitutive spring model was verified by the 2D refined finite element model and subsequently adopted for time history analysis of the SCMBP structures with SSI effect. Based on the nonlinear time history analysis of a 6-story prototype building subjected to a suite of near-fault ground motions, the prototype structure is found to be able to re-center itself even under near-fault ground motion scaled to the design basis earthquake (DBE) level while frame members remain undamaged, except for fuse devices. Additionally, SSI reduces inter-story drift ratios under both far-field and near-fault ground motions. The findings provide insights into the promising performance of using SCMBP systems as a seismic strengthening system for sites with potential SSI effects and near-fault earthquake impact. The findings of this study can be insightful to other self-centering systems with flag-shaped story shear hysteresis.

Scaling of earthquake ground motions for tri-directional nonlinear response history analyses of reinforced concrete rectangular bridge piers

In performance-based earthquake design (PBED), both the capacity of the structure and the demand from earthquake ground shaking are required to establish the desired performance levels. A range of possible demands can be estimated through nonlinear response history analyses (NRHA), which requires a suite of earthquake ground motions appropriately scaled to the target earthquake intensity for which the structure's performance is to be evaluated. The scaling is usually done for a particular earthquake intensity measure (IM) to get the associated dispersion in the engineering demand parameter (EDP). Several scaling strategies are available for uni-directional (Uni-NRHA) and bi-directional nonlinear response history analyses (Bi-NRHA). However, for tri-directional nonlinear response history analysis (Tri-NRHA), one literature suggests using the same scale factor (SF) for the vertical component, which is estimated for the Bi-NRHA. Therefore, in this study, three well-known scaling strategies, which are usually used for Uni-NRHA, are employed with 16 different methods for application in Tri-NRHA of a reinforced concrete (RC) single-column bridge pier modelled as a single-mass three-degree-of-freedom (3DoF) system. The absolute maximum drift is taken as the EDP, and a total of 1920 Tri-NRHA of the pier are performed using two suites of 20 far-fault and 20 near-fault ground motions, which are scaled to three levels of target earthquake intensity. The sufficiency and efficiency of all the scaling methods are checked statistically under all three target intensities. The study reports the effects of (i) vertical components in calculating the SF, (ii) earthquake intensity and structural nonlinearity, and (iii) far-fault and near-fault ground motion characteristics on the dispersion of the EDP. Out of 16 scaling methods, one is found to be acceptably efficient than the others for application in Tri-NRHA under both far-fault and near-fault ground motions at all target intensities.

Development of seismic fragilities for a base station steel lattice cellular tower

A large portion of the country of Turkey is located in a very high seismic region known as a first-degree earthquake zone where earthquakes occur frequently. Earthquakes result in damage to infrastructure including base station towers and subsequently failure of mobile communication networks. The loss of functionality of mobile communication networks following an earthquake has a direct impact on emergency response and both short and long-term recovery phases. Understanding both these phases requires systematic modeling of infrastructure components, which rely on fragility curves representing the probabilistic relationship between seismic intensity and damage. This study focuses on the development of damage fragility curves (fragilities) for an archetypical mobile cellular tower, namely a 55 m tall steel lattice tower (SLT) used in base station towers in Turkey. Nonlinear time history analysis was performed using a robust suite of far field ground motion records to model the performance of the archetype tower and develop damage fragilities for five specific damage states which were defined in terms of likely performance: damage state 0 (no damage), damage state 1 (uninterrupted communication), damage state 2 (communication interruption), damage state 3 (communication failure), damage state 4 (structural failure). While fragility curve has been developed for lattice towers of different types and sizes in the literature, there is no specific study for 55 m SLT and the novelty of this study is that the resulting SLT archetype fragilities can serve as a benchmark dataset for use in community-level risk and resilience analyses to improve response and recovery planning following earthquakes.

Post-2015 earthquake vulnerability of typical RC buildings in Kathmandu Valley

Continuous assessment of the existing conditions of the buildings and performance expectations for future earthquakes is quite crucial for a high-seismic-risk city like Kathmandu. This study aimed to understand the impact of the 2015 Gorkha earthquake on the reinforced concrete (RC) buildings in Kathmandu Valley. The primary objective of this research is to compare the performance of RC buildings in pre-2015 and post-2015 mainshock-aftershocks-damaged conditions. In a nonlinear model of typical RC representative buildings in Kathmandu, incremental dynamic analysis (IDA) was carried out using a real suite of ground motion records, and the Park-Ang damage index was used to classify the damage. Fragility curves were constructed using the probabilistic seismic demand model (PSDM) from the IDA analysis, and comparisons were made between pre-2015 conditions and post-2015 conditions. The findings indicate that the most recent buildings were not significantly harmed by the Gorkha earthquake, and the performance anticipated for future earthquakes reveals that the code principles for design-level earthquakes do not adequately concur with the performance expected. Additionally, the expected seismic performance of the buildings is shown for several future earthquake scenarios.

Responses of a cantilever retaining wall under multiple earthquake sequences

The seismic behaviors of retaining walls were evaluated considering only a single earthquake. However, aftershock or foreshock ground motions can occasionally be as strong as mainshock ground motions and can aggravate damage to structures. This study investigated the seismic responses of a cantilever retaining wall under earthquake sequences by performing a series of finite-difference-based numerical simulations. We collected a suite of mainshock-aftershock and foreshock-mainshock sequential ground motions, which were used as the input ground motions in the numerical simulations. This study focused on revealing the differences in wall responses under a single earthquake and multiple earthquake sequences, considering a wide range of ground motion intensities. The relative wall movements caused by mainshock-aftershock and foreshock-mainshock sequential ground motions can be much larger than those caused by a single mainshock motion. In addition, the sequence itself had the effect of increasing the relative wall movements under strong sequential ground motions. However, the effects of the aftershock and foreshock motions on the wall responses were insignificant under weak sequential ground motions.

Selection of hazard-consistent ground motions for risk-based analyses of structures

In seismic risk analysis, probabilistic seismic demand analysis (PSDA) is required to determine the probability distribution of structural seismic responses. One of the key steps in PSDA is to select a suite of ground motions that are consistent with seismic hazards at a target site. Current methods for selecting hazard-consistent ground motions only achieve consistency at one or several predefined periods and choose several discrete intensity levels to consider uncertainty of ground motions. To avoid drawbacks of the current methods, this study proposes a novel method for selecting hazard-consistent ground motions. In this method, a scenario earthquake set for ground motion selection is firstly obtained from seismic hazard disaggregation to a hazard level corresponding to a very small value of spectral acceleration at a specific period. Then, a suite of random target response spectra that are consistent with target site seismic hazards are simulated based on the scenario earthquake set. Finally, one suite of hazard-consistent ground motions are selected from a ground motion database. Through a numerical example, this study concludes, a suite of selected ground motions using the proposed method presents very good consistency with the target site seismic hazards. Since hazard-consistent ground motions selected using the proposed method do not depend on the building information, they can be used to accurately perform PSDA of any building and accurately predict structural seismic responses.

Optimal hysteresis of shape memory alloys for eliminating seismic pounding and unseating of movement joint systems

Bridge structures adapt to movement through the addition of joint systems that accommodate anticipated movement due to temperature variations or earthquakes, thereby relieving stress on the bridge structure. Shape memory alloys (SMAs) have been proposed to limit joint displacements because of their ability to dissipate seismic energy and restore their original shape. A parametric study is conducted in this study using computer simulations of some advanced MATLAB programs to show the effects of all hysteretic parameters of SMA retrofit devices on seismic joint openings. The results show that SMA hysteretic parameters have a huge effect on SMA efficiency as a restrainer, which is compatible with energy dissipation philosophy, but there are some reversible impacts of some hysteretic parameters in some cases due to the resonance problem and their dependence on other parameters such as natural time period, period ratio, mass ratio, and seismic records. As a result, some design charts are created in this study after more than 200 million trials, taking into account the variation of all key parameters of the structure and the SMA under a suite of historical ground motion records. Moreover, bridge designers can choose optimal SMA hysteresis for a desired opening width, a desired time period, and desired period/mass ratios between adjacent frames with the help of these charts to overcome the two bridge problems of pounding and unseating of bridge decks.

Incremental Dynamic Analysis and Seismic Fragility Analysis of Reinforced Concrete Frame

Abstract Due to technological developments in last decade, new methods of seismic evaluation are in use like simulation based, algorithm based, probabilistic, software based etc. These developments have enabled researchers to move from linear to non-linear methods of analysis. Incremental dynamic analysis (IDA) is performance evaluation method where a suite of ground motions applied to structure are further scaled to particular levels of seismic intensity. Seismic fragility curves become significant in estimation of structures risk possibility from the point of view of potential earthquakes and helps in predicting the economic consequences for forthcoming earthquakes. The paper reflects IDA and seismic fragility analysis of ground storey + 7 floor (G + 7) reinforced concrete frame subjected to suite of eleven ground motions. Primary objective was to perform equivalent static and linear-dynamic analysis to meet the National and International codal requirements. Then, pushover analysis is carried out by introducing parametric auto hinges as per ASCE 41-13 tables. To carry out pushover analysis, both geometric and material non-linearity was introduced. Strong ground motions were selected as per suitable criteria of seismic intensity. IDA is then carried out as per SeismoStruct 2022 software and using IDA curves, the fragility analysis was carried out. The results of study found useful for researchers to predict the probability of damage of the structure under earthquakes.

EESD special issue: AI and data‐driven methods in earthquake engineering – (Part 1)

EESD special issue: AI and data‐driven methods in earthquake engineering – (Part 1)

Multi-hazard performance evaluation of hillside buildings under earthquakes and landslides

Earthquake-induced landslide, a cascading hazard in hilly regions, can substantially increase the damaging effects of an earthquake. This necessitates performance evaluation of buildings situated in hilly regions under the effects of landslide-only and landslides following earthquakes. In this study, the performance of two commonly observed hillside building configurations is assessed—namely, step-back and split foundation—subjected to the above-mentioned multi-hazard scenarios using an uncoupled approach. The uncertainty in the soil properties that influence the landslide-induced forces is considered based on laboratory tests of soil samples collected from active landslide sites and an existing database of landslide events. Three-dimensional hillside buildings are analysed for uphill-side landslide scenarios by performing force-controlled non-linear static analyses. Further, a suite of earthquake ground motions is scaled to a predefined intensity level, and then non-linear time history analyses are performed to obtain the damaged state of the buildings prior to assessing the landslide response. It is observed that the earthquake loading history and its direction of excitation significantly affect the response of hillside buildings to a landslide following an earthquake. Further, the step-back building is observed to be more vulnerable to landslide damage when compared to its split foundation counterpart for a given uphill-side landslide scenario.

Selection and scaling of 3-component ground motion suite for scenario- and intensity-based assessment of buildings and structures

Selection and scaling of 3-component ground motion suite for scenario- and intensity-based assessment of buildings and structures

Eurocode‐8‐conforming seismic design and behaviour factor of high‐post‐yield stiffness concentrically‐braced steel frames

AbstractA seismic‐resistant steel frame with energy‐dissipating, chevron‐type braces is proposed. The braces are equipped with replaceable hourglass‐shaped pins made of duplex stainless steel. Under design seismic loading, energy is dissipated through inelastic deformations confined in the replaceable pins while the other members remain essentially elastic. As a result, the frame exhibits high post‐yield stiffness due to the inherent properties of the stainless‐steel pins. A Eurocode‐8‐based design methodology is adopted for the frame and assessed following the Eurocode‐8‐compatible INNOSEIS approach. Specifically, the overstrength factor is evaluated through nonlinear pushover analysis while the behaviour factor is assessed through incremental dynamic analysis considering high and medium seismicity site‐specific ground motion suites. The determined behaviour factor satisfies the global collapse prevention and life safety objectives while also keeping the maximum residual inter‐storey drifts below 1/300 to permit an easy substitution of the damaged pins after the design level earthquake.