Effects Of Ground Motions Research Articles

Seismic response and collapse analysis of a transmission tower-line system considering uncertainty factors

People's cognitive limitations and the unpredictability of structures introduce uncertainties into seismic performance analyses of structures in which transmission tower-line systems are essential components that may exhibit highly uncertain behavior. Nevertheless, it is important to have a clear understanding of the procedure required to manage the uncertainties surrounding structural seismic demand estimations. A practical method used to solve uncertainty problems is sensitivity and uncertainty analysis based on randomness and probability. To propagate all pertinent sources in aleatory uncertainty (input loading) in conjunction with epistemic randomness (modeling assumption errors) to actual structural seismic response and failure quantitative analysis, an uncertainty analysis method developed especially for transmission tower-line systems under seismic excitation is constructed based on sensitivity analysis and the Latin hypercube sampling method combined with incremental dynamic analysis. Sensitivity analysis reveals the relative importance of each parameter independently, while uncertainty analysis indicates the variation in the structural seismic performance under the combined actions of different uncertainty parameters. The final results demonstrate the need to consider the effects of both ground motion and structural modeling parameter uncertainties in seismic performance analyses of transmission tower-line systems.

Post-Earthquake Damage Assessments of Historic Mosques and Effects of Near-Fault and Far-Fault Ground Motions on Seismic Responses

ABSTRACT This paper is based on the the post-earthquake evaluation of two heavily damaged historic masonry mosques and the investigation of the effects of near-fault and far-fault ground motions on their seismic behaviors. The Hüsrev Pasha and Kaya Çelebi mosques, located in Van province, Turkey, were exposed to two devastating earthquakes (on October 23, 2011 and November 9, 2011) and their aftershocks. The minaret, the dome covering the main structure and porch of Kaya Çelebi mosque and the porch of Hüsrev Pasha mosque collapsed after earthquakes. This paper consists of two main sections. In the first, the post-earthquake performances of the mosques, and the damage to them, is evaluated by using the linear time-history analyses. In the other, the structural responses of the mosques are compared in order to evaluate the near-fault and far-fault ground motion effects on seismic behaviors. Results indicate that the vertical components of the 2011 Van earthquakes lead to structural responses for the mosques which are as crucial as their horizontal components. This is due to the vibration modes in the vertical direction, with and without high modal participating mass ratios, corresponding to high spectral acceleration values. It has been found that this situation significantly affects the structural behavior of mosques and especially domes. However, the analyses show that both near-fault and far-fault ground motions may have substantial effects on such historic structures, depending on the earthquake characteristics.

The effect of vertical near-field ground motions on the collapse risk of high-rise reinforced concrete frame-core wall structures

According to the observations of past earthquakes, the vertical ground motions have had a striking influence on the engineering structures, especially reinforced concrete ones. Nevertheless, the number of studies on their aftermath is insufficient, and despite some endeavors done by researchers, there is still a shortage of knowledge about the inclusion of vertical excitation on the seismic performance and the collapse probability of RC buildings. Hence, the variation in the collapse risk of three high-rise RC frame-core wall structures when they undergo bi-directional ground motions is discussed. In this paper, incremental dynamic analyses are carried out under two circumstances, including the horizontal (H) and the combined horizontal and vertical (H+V) earthquakes, and the seismic fragility curves are derived. The inter-story drift ratio corresponding to the onset of collapse has also been defined. The buildings collapse risk under the two circumstances is obtained from the risk integral. Results indicate that in the H+V state, structures meet the collapse criteria for lower intensity measures. Thus, the collapse risk increases as the structures are subjected to bi-directional seismic loads, and the consideration of this effect leads to a more accurate evaluation of buildings seismic performance.

Improved arithmetic optimization algorithm for design optimization of fuzzy controllers in steel building structures with nonlinear behavior considering near fault ground motion effects

Improved arithmetic optimization algorithm for design optimization of fuzzy controllers in steel building structures with nonlinear behavior considering near fault ground motion effects

Effects of Strong Ground Motion with Identical Response Spectra and Different Duration on Pile Support Mechanism and Seismic Resistance of Spherical Gas Holders on Soft Ground

Safety measures are required for spherical gas holders to prevent them from malfunctioning even after a large earthquake. In this study, considering the strong nonlinearity of the ground and damage to the pile during an earthquake, a three-dimensional seismic response analysis of the holder–pile–ground interaction system was conducted for an actual gas holder on the soft ground consisting of alternating layers of sand and clay. In the analysis, the seismic response of the structure to strong ground motions of different durations with the same acceleration response spectrum was verified. The results show that the piles were relatively effective in controlling the settlement when the duration of the earthquake motion was long. This is because the axial force acting on the pile increased due to the redistribution of the holder load caused by the lowering of the effective confining pressure of the sand and clay layers during the earthquake, which increased the bearing capacity of the pile. In contrast, when the duration of the seismic motion was short, the piles had little effect on the reduction in the settlement because the maximum acceleration was higher than that in the former case, and the piles immediately lost their support function.

Loss assessment of rigid-frame bridges under horizontal and vertical ground motions

Previous investigations have attributed some reinforced concrete (RC) bridge piers suffered significant damages during large earthquakes due to vertical ground motion effects. This has motivated this study to investigate the use of concrete-filled steel tube (CFST) columns as a more resilient and sustainable alternative to resist combined horizontal and vertical ground motions. The classic performance-based earthquake engineering (PBEE) framework is used to examine the seismic performance of a rigid-frame bridge with construction options of circular RC, circular CFST, and square CFST columns. The hysteretic response of each column is calibrated to the results of hybrid testing of columns under combined horizontal and vertical ground motions. The incremental dynamic analysis (IDA) is conducted using a suite of 50 near-fault records. The results are used to compare the observed damage states and quantify the repair sustainability metrics including repair cost (economic), repair downtime (social), and repair carbon emissions (environmental), as well as the loss of resilience. The losses are integrated with the hazard curves to compute the expected annual losses, all defined as a set of decision variables in the PBEE framework. The results confirm the outstanding seismic performance of CFST columns and highlight their benefits in improving the resilience and sustainability of critical and post-disaster bridges that are prone to strong multi-directional ground motions.

Fragility and risk assessment for sliding artifacts in artifact-showcase-museum systems subjected to three-component ground motions

Vertical ground motions may increase irregularity of sliding response, while the subsequent impact on the sliding fragility of building contents is not clear. Moreover, seismic risk of structural collapse contributes to the total sliding risk of building contents, while it is usually ignored. This paper first introduces a seismic fragility and risk assessment method for the sliding artifact in the artifact-showcase-museum (ASM) system subjected to three-component ground motions. In this method, the square roots of the sums of the squares of peak ground accelerations and peak sliding displacements in two orthogonal horizontal directions are implemented as the intensity measurement and the engineering demand parameter, respectively. Incremental dynamic analysis using the nonlinear three-dimensional finite element model of the ASM system is performed to generate seismic fragility curves of sliding artifacts. The total sliding risk of the artifact is estimated as the sum of the sliding risk of the artifact on the premise of no structural collapse and the structural collapse risk. Then, the seismic fragility and risk of the sliding artifacts within a four-story frame structure and an existing museum is assessed when the systems are subjected to three-component ground motions, respectively. Effects of vertical ground motions, freestanding and restrained showcases, floor levels, sliding thresholds, structural collapse and different structures on the sliding fragility and risk of the artifact are investigated. Results show that the influence of vertical ground motions on the sliding fragility of artifacts in different structures may be significant or marginal depending on the ratios of peak vertical to horizontal floor acceleration. Moreover, the artifact in the freestanding showcase is less fragile than that in the restrained showcase regarding sliding failure. Furthermore, neglecting the structural collapse risk and estimating the sliding risk of the artifact by not removing the structural collapse data would underestimate the total sliding risk of the artifact.

Effects of vertical ground motions on the dynamic response of URM structures: Comparative shake‐table tests

AbstractThis paper discusses the results of an experimental study aimed at evaluating the influence of the vertical ground motion component on the seismic performance of unreinforced brick‐masonry buildings. The research was motivated by post‐earthquake observations of significant structural damage in the vicinity of the fault, where horizontal and vertical ground motions are often strong and synchronized. Vertical accelerations can fluctuate gravity loads, which control the in‐plane lateral load capacity of masonry piers and affect the out‐of‐plane overturning stability of thin walls. Such phenomena seem not to be sufficiently explained in existing literature, while experimental evidence is undoubtedly missing. Here, the damage potential of vertical accelerations was investigated through a series of multidirectional shake‐table tests on full‐scale structures under simulated near‐source ground motions of increasing intensity. The experiments comprised three nominally identical building specimens subjected to the principal horizontal component alone, the horizontal component combined with the vertical one, and the full three‐component ground motion. The buildings included structural/nonstructural elements (e.g., gables, chimneys, and parapets) sensitive to gravity load variations due to their low axial loads. Two different sets of three‐component earthquake records were employed to assess the effects of both tectonic and induced seismicity scenarios. Overall, the vertical earthquake motion did not cause appreciable differences in the behavior of the buildings. Any influence on the strength and peak response of structural/nonstructural walls was marginal and non‐systematic. Data and observations from these experiments add substantially to our understanding of the vertical acceleration effects on masonry structures.

The antenna phase center motion effect in high-accuracy spacecraft tracking experiments

We present an improved model for the antenna phase center motion effect for high-gain mechanically steerable ground-based and spacecraft-mounted antennas that takes into account non-perfect antenna pointing. Using tracking data of the RadioAstron spacecraft we show that our model can result in a correction of the computed value of the effect of up to $2\times10^{-14}$ in terms of the fractional frequency shift, which is significant for high-accuracy spacecraft tracking experiments. The total fractional frequency shift due to the phase center motion effect can exceed $1\times10^{-11}$ both for the ground and space antennas depending on the spacecraft orbit and antenna parameters. We also analyze the error in the computed value of the effect and find that it can be as large as $4\times10^{-14}$ due to uncertainties in the spacecraft antenna axis position, ground antenna axis offset and misalignment, and others. Finally, we present a way to reduce both the ground and space antenna phase center motion effects by several orders of magnitude, e.g. for RadioAstron to below $1\times10^{-16}$, by tracking the spacecraft simultaneously in the one-way downlink and two-way phase-locked loop modes, i.e. using the Gravity Probe A configuration of the communications links.

Amplification Effect of Ground Motion in Offshore Meandering Sedimentary Valley

A sedimentary valley has a visible amplification effect on a seismic response, and the current 2D topographies cannot truthfully reflect the twists and turns of a large-scale river valley. Taking a sinusoidal curved valley site as a model, the dynamic finite element analysis method and the introduction of a viscoelastic artificial boundary were developed to study the 3D seismic response of the dimensional topographies in the homogeneous curved valley to vertical incident P, SV, and SH waves. The results showed that the bending sedimentary valley site earthquake presented significant features simultaneously, depending on the number of valley bends, the frequency of the excitations, the shear wave velocity of sedimentary soil, and the depth of the river valley. The surface displacement amplitudes of three-dimensional meandering sedimentary valleys are significantly different from those of sedimentary basins. The amplification area of the meandering valley is related to the angle between the valley axis and wave vibration direction, and the amplification effect is significant when the angle is small. The movement in the main direction showed a center focus, and the secondary y-direction displacement showed both a central focus and an edge effect. When the frequency of the incident wave was close to the natural vibration frequency in a specific direction, the movement in this direction significantly increased because of the resonance effect. The displacement amplitude of the surface was proportional to the depth of the river valley, and the surface displacement was presented in different forms based on the frequency of the excitations. The results provided some guidance for the earthquake resistance of the curved valley site.

Probabilistic seismic assessment of steel gabled frames with web-tapered members under near-fault ground motions along strike-normal and strike-parallel components

The seismic assessment of steel gabled frames (SGFs) is of great importance and a key problem in any high-seismicity region, given the enormous costs of industrial equipment and the remarkable number of individuals working in such structures. Near-fault ground motions, especially their strike-normal component that usually contain a long-period pulse in the velocity time-history, can lead to a significant demand in these structures in comparison to the far-fault ground motions. Although numerous studies have confirmed the destructive effects of near-fault ground motions on concrete and steel structures, no research has been devoted to the impact of this ground motions on steel gabled structures yet. Hence, the findings of this research can unveil novel dimensions of such structures. In this regard, in the present paper, an incremental dynamic analysis (IDA) was conducted for the first time on four SGFs with the spans of 20 m and 60 m and heights of 6 m and 12 m using far-fault ground motions (OR set), as well as near-fault ground motions along the strike-normal and strike-parallel components (SN and SP sets, respectively). The results were presented in the form of multi-record IDA curves, summarized IDA curves, probabilistic seismic demand models (PSDMs) and probabilistic seismic demand analysis (PSDA) curves. The outcomes indicated that compared to far-fault ground motions, near-fault ground motions (especially pulse-like ones) produced significant changes on the seismic behavior of long-period SGFs, resulting in raises the changes of stiffness and demand sensitivity, reduces the dynamic capacity, enhances the data dispersion and uncertainty, and increases the mean annual frequencies (MAFs) in such structures. However, the results of PSDA analysis showed that under any type of ground motion (OR, SN and SP), short-period SGFs are more vulnerable than long-period SGFs and should be prioritized for retrofitting. Finally, the importance of combining the hazard curve of the study region with the results of IDA analysis of the structure in evaluating the seismic behavior of SGFs is highlighted.

Empirical models of bridge seismic fragility surface considering the vertical effect of near-fault ground motions

Near-fault vertical ground motions (VGMs) caused great damage to bridge structures, but investigations of the effect on probabilistic seismic performance and structural vulnerability are insufficient. For this purpose, a novel model of bridge seismic fragility surface conditioned on the horizontal peak ground velocity (Vx) and the αVH (ratio of vertical to horizontal ground motion) is proposed. The quantitative formulation for probabilistic seismic demand model (PSDM) and probabilistic seismic capacity model (PSCM) of bridge piers considering the effect of VGM are established, and then the empirical model of fragility surface with the parameters of Vx and αVH is obtained by convolution. A simply supported bridge model is simulated in OpenSees as an illustrated example to establish the seismic fragility surface under the combined actions of horizontal ground motion and VGM. Furthermore, the damage probability (Fr) influenced by VGM is analyzed compared with the damage probability (Fr0) without VGM, and the sensitivity intervals of the difference between Fr and Fr0 for varying damage states are identified. The mechanism of fragility variation under VGM is explored, indicating that the variation of seismic demand caused by VGM is the main reason. Finally, the seismic fragility surface model considering VGM is applied to a set of variable piers, and the sensitivity interval associated with the fundamental period is investigated under different Vx.

An approach for estimating the response of steel moment resisting frames to pulse-like ground motions

Given the limitations of equivalent pulses in investigating the effects of pulse-like ground motions, the present study is mainly aimed at providing an approach to capture the maximum response characteristics of steel moment resisting frames using the simulated pulses. Accordingly, the behavior of three moment resisting frames of 3, 9, and 20-story buildings from the SAC project prior to the Northridge earthquake in the Seattle are investigated under pulse-like ground motions. Twenty-six pulse-like records from Imperial Valley and Northridge earthquakes in 1979 and 1994 are selected from the Next Generation Attenuation (NGA) Project database. The pulse-like records are developed in selected seismic regions by combining of high frequency content of records and artificial pulses. The inter-story drift, critical story, and base shear are evaluated as structural demand parameters using over 54000 nonlinear time history analyses. Then response contours are provided to determine the critical story, the largest normalized base shear, and estimate the structural damage. The results indicate the contribution of high frequency content to the response. The response contours are often conservative or offer acceptable estimates of the largest maximum inter-story drift and the largest normalized base shear.

Effects of Vertical Ground Motion on Flat Slab Structure

Effects of Vertical Ground Motion on Flat Slab Structure

The effect of pulse-like ground motion on the performance-based confidence level of setback special steel moment-resisting frames

This paper addresses the effects of near-fault (NF) earthquake records containing forward directivity pulses and the pulse-to-structure period ratio (TP/T1) on the performance-based confidence levels of regular and setback frames. For this purpose, ten steel moment-resisting frames, including a regular structure and nine setback frames, were subjected to 55 near-fault pulse-like records as well as their low- and high-frequency components called the “pulse” and “residual” portions, respectively. To study the effect of the TP/T1 ratio, the records were classified into four groups representing average values of TP/T1 ∼ 0.5, 1, 2, and >2. In addition to NF motions, 32 far-fault records were imposed on the studied structures. The results from incremental dynamic analyses revealed the higher confidence level of meeting performance levels under NF records compared to far-fault ones for both regular and setback frames (the case of TP/T1≥1 for the regular frame and the cases of TP/T1 ∼ 1 and 2 for the irregular ones). The importance of considering the TP/T1 ratio was shown by comparing the performance-based confidence levels under FF and NF ground motions as well as those under original NF records and their frequency components. It was found that ignoring such classification can lead to reversed results for both regular and irregular structures. Furthermore, directivity pulses with TP/T1>1 can represent original NF records when evaluating the confidence levels of the regular structures, especially as LS and CP limit states. However, it is highly recommended to impose original NF records on irregular structures to assess their performance-based confidence levels.

A lateral load distribution for the static analysis of base-isolated building frames under the effect of far-fault and near-fault ground motions

This paper attempts to examine the effect of the scaling of ground motion records on the seismic responses of base-isolated buildings by using the three scaling methods including the ASCE 7–10, acceleration spectrum intensity, SIa, and the spectral acceleration corresponding to the effective period of the base-isolated structure at the design displacement, Sa(TD). The buildings had steel moment-resisting and X-braced systems and were isolated with lead rubber bearings (LRBs) at the base. Near-fault ground motions with Forward Directivity (FD), Fling-Step (FS) and No Pulse (No P.) characteristics as well as far-fault ground motion records were studied in this paper. The discrepancy in the seismic responses as well as the effect of the pulse period in the case of pulse-like ground motions was scrutinized for the three scaling methods. Also, the response spectrum analysis (RSA) and static method with the equivalent lateral force distribution prescribed in ASCE 7–10 were carried out. The results indicate that the RSA as well as the static analysis, prescribed in ASCE 7–10, underestimates the story shears of the base-isolated buildings. The underestimation increases in the case of the FF and No P. ground motions having a large amount of spectral acceleration in the higher modes region. Also, the underestimation increases with the increase in the height of the base-isolated buildings as well as in the case of the moment-resisting frames compared to the X-braced ones. Finally, by means of the results derived from the time history analyses, a formula was proposed to determine the lateral force distribution along the height of the base-isolated buildings with LRBs considering the characteristics of the isolator and the structure for different types of the ground motions.

Experimental investigation of pulse‐type ground motion effects on a steel building with nonlinear viscous dampers

AbstractNear‐fault pulse‐type ground motions have characteristics that are substantially different from ordinary far‐field ground motions. It is essential to understand the unique effects of pulse‐type ground motions on structures and include the effects in seismic design. This paper investigates the effects of near‐fault pulse‐type ground motions on the structural response of a 3‐story steel structure with nonlinear viscous dampers using the real‐time hybrid simulation (RTHS) testing method. The structure is designed for 75% of the code‐specified design base shear strength. In the RTHS, the loop of action and reaction between the experimental and numerical partitions are executed in real time, accurately capturing the velocity pulse effects of pulse‐type ground motions. A set of 10 unscaled pulse‐type ground motions at the design basis earthquake (DBE) level is used for the RTHS. The test results validated that RTHS is a viable method for experimentally investigating the complicated structural behavior of structures with rate‐dependent damping devices, and showed that the dampers are essentially effective in earthquake hazard mitigation effects involving pulse‐type ground motions. The average peak story drift ratio under the set of pulse‐type ground motions is 1.08% radians with a COV value less than 0.3, which indicated that structural system would achieve the ASCE 7–10 seismic performance objective for Occupancy Category III structures under the DBE level pulse‐type ground motions. Additionally, a nonlinear Maxwell model for the nonlinear viscous dampers is validated for future structural reliability numerical studies involving pulse‐type ground motions.

Mesoscale seismic hazard zonation in the Central Seismic Gap of the Himalaya by GIS-based analysis of ground motion, site and earthquake-induced effects

Mesoscale seismic hazard zonation in the Central Seismic Gap of the Himalaya by GIS-based analysis of ground motion, site and earthquake-induced effects

Indirect boundary element method solution to the seismic ground motion of near-fault sedimentary valley

In this paper, the indirect boundary element method (IBEM) is developed to solve the ground motion effect of the near-fault complex site. By establishing a two-dimensional kinematic finite fault model, the amplification effect of seismic response of sedimentary valley under the continuous dislocation of reverse faults is quantitatively analyzed. Meanwhile, the influence of the parameters such as the buried depth of the fault top, the fault dip-angle, the fault distance of sedimentary valley, the fault-plane shape, and the rupture velocity of fault on the seismic response are studied. The results show that the sedimentary valley has a pronounced amplification effect on the seismic response induced by near-fault, and the peak value of the acceleration response spectrum of the analyzed model can be amplified by 99.3%. In the sedimentary valley, the duration of earthquake motion is significantly prolonged, and the long-period velocity pulse appears, and the first velocity pulse can be amplified by 68.7%. The near-fault ground motion damages have typical concentration-effect and hanging wall effect. This study provides a new and effective method, which is of great significance for seismic zoning of complex sites near-fault. It will be of guiding significance for regional planning and seismic fortification of near-fault sites.

Exceedance of design actions in epicentral areas: insights from the ShakeMap envelopes for the 2016\u20132017 central Italy sequence

ShakeMap is the tool to evaluate the ground motion effect of earthquakes in vast areas. It is useful to delimit the zones where the shaking is expected to have been most significant, for civil defense rapid response. From the earthquake engineering point of view, it can be used to infer the seismic actions on the built environment to calibrate vulnerability models or to define the reconstruction policies based on observed damage vs shaking. In the case of long-lasting seismic sequences, it can be useful to develop ShakeMap envelopes, that is, maps of the largest ground intensity among those from the ShakeMap of (selected) events of a seismic sequence, to delimit areas where the effects of the whole sequence have been of structural engineering relevance. This study introduces ShakeMap envelopes and discusses them for the central Italy 2016–2017 seismic sequence. The specific goals of the study are: (i) to compare the envelopes and the ShakeMap of the main events of the sequence to make the case for sequence-based maps; (ii) to quantify the exceedance of design seismic actions based on the envelopes; (iii) to make envelopes available for further studies and the reconstruction planning; (iv) to gather insights on the (repeated) exceedance of design seismic actions at some sites. Results, which include considerations of uncertainty in ShakeMap, show that the sequence caused exceedance of design hazard in thousands of square kilometers. The most relevant effects of the sequence are, as expected, due to the mainshock, yet seismic actions larger than those enforced by the code for structural design are found also around the epicenters of the smaller magnitude events. At some locations, the succession of ground-shaking that has excited structures, provides insights on structural damage accumulation that has likely taken place; something that is not accounted for explicitly in modern seismic design. The envelopes developed are available as supplemental material.