Vertical Ground Motion Research Articles

Horizontal and Vertical Ground-Motion Duration Prediction Models from Interplate and Intermediate-Depth Intraslab Earthquakes in Mexico City

ABSTRACT In this study, we present predictive models for significant ground-motion duration from interplate and intermediate-depth intraslab earthquakes at Mexico City for the horizontal components, the vertical component, and the vertical-to-horizontal ratio case. The considered sites are located over several zones in Mexico City, from rock to soft-soil sites. For the ground-motion duration models, the significant durations for ranges between 5% and 75%, 5% and 95%, and 2.5% and 97.5% of Arias intensity are considered for the analyses. The equations were developed as functions of magnitude, distance of the earthquake, and site period using 16 and 23 event recordings from interplate and intermediate-depth intraslab earthquakes at the hill, transition, and lakebed zones of the city using mixed-effect regression analyses. For the intraslab events, in particular, the new database includes recordings from two significant normal-faulting events that occurred in 2017. The models lead to differences with respect to the previous models. Therefore, predictive models for both considered focal mechanisms are proposed. The model is valid for interplate events at distances from 280 to 500 km and magnitude Mw from 6 to 8.1, for intraslab events at distances of 100 km up to about 650 km, magnitude Mw from 5 to 8.2, and focal depths from 40 km to over 120 km.

Influence of South-to-North Water Diversion on Land Subsidence in North China Plain Revealed by Using Geodetic Measurements

As a major grain-producing region in China, the North China Plain (NCP) faces serious challenges such as water shortage and land subsidence. In late 2014, the Central Route of the South-to-North Water Diversion Project (SNWD-C) began to provide NCP with water resources. However, the effectiveness of this supply in mitigating land subsidence remains a pivotal and yet unassessed aspect. In this paper, we utilized various geodetic datasets, including the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow On (GRACE-FO), Global Navigation Satellite System (GNSS) and leveling data, to conduct a spatial-temporal analysis of the equivalent water height (EWH) and vertical ground movement in the NCP. The results reveal a noteworthy decline in EWH from 2011 to 2015, followed by a slight increase with minor fluctuations from 2015 to 2020, demonstrating a strong correlation with the water resources supplied by the SNWD-C. The GRACE-derived surface deformation rate induced by hydrological loading is estimated to be <1 mm/yr. In comparison, GNSS-derived vertical ground movements exhibit considerable regional differences during the 2011–2020 period. Substantial surface subsidence is evident in the central and eastern NCP, contrasting with a gradual uplift in the front plain of the Taihang Mountains. Three-stage leveling results indicate that the rate of subsidence in the central and eastern plains is gradually increasing with the depression area expanding from 1960 to 2010. Based on these geodetic results, it can be inferred that the SNWD-C’s operation since 2014 has effectively mitigated the reduction in terrestrial water storage in the NCP. However, land subsidence in the NCP persists, as the subsidence rate does not turn around in sync with the change in EWH following the operation of SNWD-C. Consequently, it’s necessary to maintain and enforce existing policies, including controlling groundwater exploitation and water resources supply (e.g., SNWD-C) to curtail the exacerbation of land subsidence in the NCP. Additionally, continuous monitoring of land subsidence by GRACE, GNSS, leveling and other geodetic techniques is crucial to enable timely policy adjustments based on monitoring results.

The effect of errors in structural system design on the structure damaged in 2023 Turkey earthquakes: A case study

On 6 February 2023, two large earthquakes of Mw 7.7 and 7.6 occurred in the Pazarcik and Elbistan districts of Kahramanmaras province in Turkey, causing extensive structural damage, collapsed buildings and casualties. This study examines a damaged building and presents the relevant repair and strengthening procedures. The importance of design flaws in the structural system, particularly when subjected to horizontal and vertical ground motions, on the performance of the structure is highlighted in this case study. The effects of the interrupted frames and components with unsuitable cross-sectional properties for load transfer within the structure were comprehensively assessed using 3D modelling and on-site investigations. Following repair and strengthening works to improve load transfer, the analysis carried out on the model showed a reduction in LS of approximately 33 % for beams and 45 % for columns.

Seismic resilient performance of code-designed, base-isolated slender steel buildings in firm soils

The seismic response of slender base-isolated structures can be significantly compromised during strong earthquakes, as significant tensional forces or uplifts can be demanded to exterior and corner base isolators. Nevertheless, there are few studies published in the literature where the expected seismic response of fully-designed base-isolated buildings according to a given base-isolation code or standard is shown and discussed when subjected to ground motions records related to the design earthquake scenario. In this paper, the authors present the results obtained from the cases of study of four code-designed base-isolated buildings, from 8 to 24 stories in height, with different global slenderness ratios H/L: 2.0, 2.5, 4.0 and 6.0. Subject buildings were assumed to be located at the city of Puebla, Mexico, in firm soil sites. Buildings were designed according to current base-isolation guidelines for the Manual of Civil Works (MOC) using the modal response spectrum analysis method while neglecting the vertical component in the design process. The base isolation system was composed of high-damping rubber bearings (HDRB). The considered structural system above the isolation system was a dual system composed of special concentrically steel braced frames (SCBFs) and special moment steel frames (SMFs). The resulting base-isolated (TI) to fixed-base (Tfb) natural periods ratio for the designed buildings was within the range 2.55 ≤ TI/Tfb ≤ 3.02. Nonlinear dynamic analyses were conducted for the designed buildings when subjected to five strongest pairs of orthogonal ground motions recorded during the September 19, 2017 Puebla-Morelos earthquake, which correspond to the design earthquake scenarios considered in MOC. In addition, the impact of the vertical ground motion component was evaluated for the most critical station. From the obtained results, it can be concluded that for the studied buildings, the modal response spectrum design method was safe enough to achieve resilient seismic designs. Nevertheless, net tensile forces and uplifts were triggered in corner base isolators, particularly for ground motion records which corresponding displacement spectra was close to the code displacement spectra for the target design base-isolated period TI. Tensile forces and uplifts in base isolators were slightly increased when considering the action of the vertical ground motion component of the critical station. In addition, peak accelerations at the floor levels were moderately increased when considering the vertical component, which may have detrimental effects in acceleration-sensitive non-structural components and the shear capacity of floor systems.

Effect of variable axial load with different amplitude, frequency and phase on seismic behavior of RC columns: Experimental study and numerical simulation

The aim of this study is to investigate the effects of variable axial loads caused by horizontal and vertical ground motions on the seismic performance of reinforced concrete columns. First, three groups of cyclic loading tests were conducted. Further, the effects of constant axial load, axial load amplitude variation and frequency variation on the seismic performance indicators of the specimens, such as the failure mode, hysteresis curve, skeleton curve, stiffness degradation, ductility and energy dissipation, were studied. Subsequently, numerical analysis models were established using fiber finite elements, and verified their accuracies using experimental data. Finally, parametric analyses were conducted based on the verified numerical models to examine the effects of variable axial loads with different amplitudes, frequencies and phases on the columns. The results indicate that the axial load ratio of the columns changes constantly under the variable axial load, which results in readily apparent asymmetry in the hysteresis curve, ductility, and ultimate load. The hysteresis behavior of columns under variable axial load mainly depends on the axial load ratio corresponding to the positive and negative peak lateral drifts of each cycle. An equivalent axial load ratio method is proposed to determine the hysteresis model of columns under variable axial loads accurately.

Equivalent Near-Field Corner Frequency Analysis of 3D Dynamic Rupture Simulations Reveals Dynamic Source Effects

Abstract Dynamic rupture simulations generate synthetic waveforms that account for nonlinear source and path complexity. Here, we analyze millions of spatially dense waveforms from 3D dynamic rupture simulations in a novel way to illuminate the spectral fingerprints of earthquake physics. We define a Brune-type equivalent near-field corner frequency (fc) to analyze the spatial variability of ground-motion spectra and unravel their link to source complexity. We first investigate a simple 3D strike-slip setup, including an asperity and a barrier, and illustrate basic relations between source properties and fc variations. Next, we analyze >13,000,000 synthetic near-field strong-motion waveforms generated in three high-resolution dynamic rupture simulations of real earthquakes, the 2019 Mw 7.1 Ridgecrest mainshock, the Mw 6.4 Searles Valley foreshock, and the 1992 Mw 7.3 Landers earthquake. All scenarios consider 3D fault geometries, topography, off-fault plasticity, viscoelastic attenuation, and 3D velocity structure and resolve frequencies up to 1–2 Hz. Our analysis reveals pronounced and localized patterns of elevated fc, specifically in the vertical components. We validate such fc variability with observed near-fault spectra. Using isochrone analysis, we identify the complex dynamic mechanisms that explain rays of elevated fc and cause unexpectedly impulsive, localized, vertical ground motions. Although the high vertical frequencies are also associated with path effects, rupture directivity, and coalescence of multiple rupture fronts, we show that they are dominantly caused by rake-rotated surface-breaking rupture fronts that decelerate due to fault heterogeneities or geometric complexity. Our findings highlight the potential of spatially dense ground-motion observations to further our understanding of earthquake physics directly from near-field data. Observed near-field fc variability may inform on directivity, surface rupture, and slip segmentation. Physics-based models can identify “what to look for,” for example, in the potentially vast amount of near-field large array or distributed acoustic sensing data.

The Influence of Vertical Seismic Acceleration on the Triggering of Landslides Constrained by Bedding Faults under an Inertial Frame Reference: The Case of the Daguangbao (DGB) Landslide

The Daguangbao (DGB) landslide was the largest landslide that was triggered by the 2008 Wenchuan earthquake with a magnitude of Ms8.0. The sliding surface of this landslide was constrained on a bedding fault 400 m below the ground surface. Seismic records show that the landslide suffered not only from strong horizontal but also vertical ground shaking that was almost equal to the horizontal component. In this study, to reveal the landslide triggering mechanism of the DGB landslide, this study ignores the steep dipping tension fracture section and the leading edge-locking section of the trailing edge of the DGB landslide, and the geological model of the large optical package landslide is generalized into a block model with the bottom controlled slip soft zone as the interface. Based on the improved Newmark method that considers vertical ground motion, the three-way seismic acceleration data and the shear strength parameter of the sliding surface being taken as a variable are used to calculate the cumulative permanent displacement of the slider. Then, by considering the cumulative permanent displacement ratio of vertical seismic acceleration or not and the cumulative permanent displacement ratio value considering the inertial force as the index, the response characteristics of the cumulative permanent displacement of the block-to-vertical ground motion and inertial forces were analyzed. The results show that both the horizontal inertial force and the vertical acceleration significantly increased the permanent displacement. The permanent displacement is 4.9 cm when considering the vertical acceleration, whereas it is only 2.0 cm without taking this into account. The contribution of vertical acceleration is significantly enlarged (87.8–90.7%) by the decreasing of the internal friction angle of the slide surface, while it is less influenced (5–27.4%) by the cohesion. Compared with the lower shear strength parameter of the sliding surface, the contributions of vertical acceleration and inertial force to the permanent displacement are more obvious when the shear strength parameter of the sliding surface is higher. When ϕ > 18°, the D/D* is greater than 1, and the maximum D/D* reaches 7. The fast accumulation event of permanent displacement is triggered in the concentration stage of the seismic energy release. In the DGB landslide area, 50% of the energy is released within 30–50 s, as indicated by the acceleration peaks recorded at the nearest seismic station, Qingping station. It is assumed that the DGB landslide may be triggered at 30–50 s due to half of the seismic energy being released during that time span.

Nonlinear dynamic response analysis of a hybrid concrete‐filled steel tubular truss lightweight bridge under strong earthquakes

AbstractConcrete‐filled steel tubular (CFST) trusses have seen recent development and application in bridges found in mountainous regions with deep valleys, and especially in seismic zones. In this study, a hybrid CFST truss lightweight bridge was selected as the research object. This bridge is composited of CFST composite truss girders (superstructure) and CFST lattice piers (substructure). Two different finite element models (FEM) for nonlinear seismic response analysis, one is detailed model and the other is simplified model, were established. By comparing with the detailed model, the results of the shaking table test as well as the real bridge test, the simplified model was found to be accurate. Considering the CFST columns' edge strain, the most unfavorable input direction of horizontal ground motion was perpendicular to the connection line of the bearings at both ends of the main girder. Also, the simultaneous influence of vertical ground motion and horizontal ground motion needs to be taken into consideration. By increasing the intensity of input ground motion, the yielding order of CFST lattice piers and its effect on the seismic response were also discussed. Results indicated that the bridge was in the elastic stage for the designed seismic ground motion. After the CFST lattice piers reached the plastic stage, the displacement and in‐plane bending moment had larger amplification coefficients compared to the increase coefficient of the input ground motion, while had a much smaller axial force amplification coefficient. Moreover, the in‐plane bending moment had a larger amplification coefficient in high piers compared to short piers.

Historical vertical ground movements in the Campi Flegrei volcano: A new transect across the caldera rim

This research focuses on a geoarchaeological study of the coastal sector extending from Fusaro coastal lake to Punta Pennata Islet, located in the western peripheral area of Campi Flegrei Caldera (Gulf of Pozzuoli, Italy), to reconstruct relative sea-level (RSL) oscillations and related vertical ground movements which have occurred since the Roman period. Campi Flegrei Caldera is characterized by sudden vertical ground movements of volcano-tectonic origin (i.e. bradyseismic crisis) which strongly modified the coastal landscape during the Holocene. Despite this, the area has been densely inhabited since the Greek-Roman times, preserving numerous traces of its ancient splendor. Part of these findings can be interpreted as high- or low- precision sea-level markers, helping in the reconstruction of the RSL change history. By using a multi-technique approach made of both direct and indirect surveys, the latter performed at the key-site of Punta Pennata through the use of an unmanned surface vessel prototype (ARGO), we investigated different archaeological sites with a twofold purpose. We reconstructed the RSL change of the study area during the last 2.1 ka and, by comparing the RSL data with site-specific geophysical models, we demonstrated that during the considered period the area went through five different evolutive phases characterized by an alternation of prevailing uplift, stability, and subsidence of volcano-tectonic origin, bringing the RSL from −4 and +5 m MSL, up to its current elevation. Moreover, by comparing the RSL data with the present-day sea level, we observed a differential overall subsidence of almost 1-m between the inner and outer sectors of the caldera at Miseno Cape. This validated the presence of a fault, crossing the promontory in an NNW-SSE direction, previously mentioned by other authors. Moreover, the integration of our data and historic sources enabled reconstructing the palaeo-environmental scenario of this area during the 1st century BC.

Evaluation of isolation performance of, reticulated shell structures with curvature-consistent frictional pendulum isolation system through shaking table tests

In this study, we investigated the isolation effect of a curvature-consistent frictional pendulum bearing isolation system (CC-FPB-IS) on a long-span spatial structure. Considering a typical spherical reticulated shell in a long-span spatial structure as the research object, we conducted shaking table tests on a scaled reticulated shell structure equipped with fixed hinge bearings and CC-FPBs. In addition, a refined finite element simulation method was established to analyze to the seismic impact on an actual reticulated shell structure with isolation layers under different isolation conditions. The variations in the isolation effect on the dynamic responses under horizontal unidirectional, vertical, and three-dimensional ground motions were compared. The results indicated that the isolation layer comprising the CC-FPB can notably reduce the horizontal dynamic response of a reticulated shell structure under horizontal seismic action while retaining its elastic state during rare earthquakes. With increasing loading amplitude, the isolation rate of the long-span spatial structure increased and gradually reached the optimal value. However, the proposed CC-FPB-IS did not effectively reduce the dynamic response of the vertical component, and the isolation rate was relatively small. When subjected to a three-dimensional earthquake, the structure exhibited an isolation effect because of the coupling of earthquake components in different directions. Thus, the CC-FPB-IS has notable effects on the dynamic response of the overall structure.

Sensitivity Study of Seismic Amplification Effect of Large-Scale Sichuan Basin on Key Parameters During the Great Wenchuan Earthquake

The effect of soil parameters on basin amplification effect has been widely investigated, especially for the small and medium-sized basins under plane wave incidence or point source ruptures. However, the sensitivities of seismic amplification effect of large-scale basins with respect to soil parameters during great earthquakes with tremendous rupture faults have obtained relatively less attention. In this paper, based on the established three-dimensional Sichuan basin model, the effects of four material parameters of the basin sediments, including the shear wave velocity, Poisson’s ratio, and the shear quality factor of the Quaternary sediment, as well as the velocity of the rock above the basin crystalline basement (which will be referred as SVQS, PRQS, QFQS, and VCBR, respectively), on the long-period wave amplification patterns of the Sichuan basin during the great Wenchuan earthquake are investigated by using the spectral element method and parallel computing technique. The results show the following: (1) SVQS has the greatest influence on the basin horizontal component ground motions, while the vertical component is comparably insensitive to it. (2) PRQS demonstrates comparable effects on the horizontal and vertical basin ground motions. With the increase of PRQS, the amplitudes and regions of the strong shakings both become smaller. However, the influence of PRQS is less significant compared with SVQS and VCBR. (3) QFQS mainly affects the relatively high-frequency motions inside the basin, and the low-frequency motions are generally insensitive to it. With the reduction of QFQS, the amplitudes and regions of the basin strong ground motions turn a little smaller, but the distribution features are generally unchanged. (4) Effects of VCBR on the horizontal and vertical component basin ground motions are opposite. With the growth of VCBR, the amplitudes and areas of strong horizontal motions increase consequently, but they decrease for the vertical component.

The Effect of Vertical Ground Motion in Dynamic Analysis for Near Fault Area in Yogyakarta

Indonesia is surrounded by three major tectonic plates which are Indian-Australian, Eurasian and Pacific tectonic plates. Consequently, Indonesia is prone to seismic hazard. Horizontal ground motion has taken a major role in conducting nonlinear time histories analysis or in assessing liquefaction potential. However, for site near fault area, vertical ground motion can be quite significant and cannot be neglected. This paper aims to evaluate the effect of vertical ground motion in the near fault area by conducting dynamic analysis using MIDAS GTS NX. UBC Sand model is employed to model liquifiable material. Standard penetration test, laboratory test and downhole seismic tests are conducted at the site in order to characterize the shear wave velocities and properties of the soil at the area and to determine the thickness of the liquifiable layer. For this paper, two dynamic analyses will be conducted. For first analysis, only horizontal ground motion is applied to the model while in the second analysis, both horizontal and vertical ground motion will be applied. Based on dynamic analysis result, the horizontal surface motion and horizontal surface response spectrum that is propagated using bi-directional time histories will have bigger acceleration if being compared by only using horizontal time histories.

Seismic performance of underground structures improved by using PET FRP retrofitting central columns

The seismic failure mechanism of underground structures presents that the insufficient lateral deformation capacity of central columns will result in the collapse of the overall structure. Therefore, this study proposed applying Polyethylene Terephthalate Fiber-reinforced Polymer (PET FRP) to enhance the lateral deformation capacity of the central columns of underground structures and then improve the seismic capacity of the overall structures. The numerical models of PET FRP retrofitting reinforced concrete (RC) columns subjected to high axial loads and increasing cyclic deformations were verified by experimental results. With the calibrated models, the inter-story deformation capacity of the underground structures with and without PET FRP retrofitting was contrastively analyzed, and the seismic response of the two underground structures subjected to both horizontal and vertical ground motions was simulated and discussed. It was found that the PET FRP retrofitting structure experienced smaller earthquake threats due to the larger lateral deformation capacity. Furthermore, the repairability of the PET FRP retrofitting underground structures after earthquakes was also investigated. Numerical results presented that applying PET FRP retrofitting central columns of underground structures could improve the seismic performance of overall underground structures.

Driving Source of Change for Ionosphere before Large Earthquake -Vertical Ground Motion-

This paper discusses the relationship between the vertical ground motion and ionospheric disturbances before the Kumamoto earthquake on 16 April 2016, in Kyushu, Japan, using the vertical ground motion measured by slant gauges widely distributed in Kyushu, and the NmF2 observed by ionosondes in Japan and another region. We provide evidence that vertical ground motion excites internal gravity waves (IGWs) that disturb changes in the ionospheric plasma density. From the spectral analysis results of the vertical ground motion data, the summation of various period (frequency) components analyzed from the original data of the slant gauge shows a possible correlation with the change of NmF2 before the earthquake. On the other hand, the influence of the geomagnetic disturbance on vertical ground motion seems to exist. However, we cannot confirm that vertical ground motion is influenced by the geomagnetic disturbance (Kp index) and that the earthquake is triggered by the geomagnetic disturbance. There are two conditions for the vertical ground motion to disturb variations in the ionospheric plasma density: (1) The effective vertical ground motion period should be shorter than 5 h. In addition, (2) vertical ground motion should continue to exist so that wave energy can be continuously injected into the atmosphere. A possible mechanism with which to modify the ionosphere is discussed. The results of this study can provide a basis for the future ionospheric precursors of earthquakes by using the vertical ground motion.

Numerical investigation on the characteristics of dynamic response and damage of a RC tall chimney considering vertical ground motions

Although seismic risk assessment models for structures have become more sophisticated, they have typically disregarded the effects of vertical ground motions (VGMs). Nevertheless, this trend is gradually shifting due to recent recordings and field observations that have demonstrated the potentially destructive effects of high VGMs.In this paper, a nonlinear finite element (FE) model of a 234 m reinforced concrete (RC) chimney is developed, with a focus on investigating its dynamic response and damage characteristics under the effect of VGMs. The results are compared with the case of a combination of horizontal and vertical ground motions (HVGMs). First, a time history analysis (THA) is performed under various VGMs input conditions. The findings reveal that the vertical seismic force increases with the intensity of ground motion. However, the distribution of the seismic force remains unchanged, with the maximum vertical seismic force occurring at 85% of the chimney height. Then, the seismic response of the chimney under HVGMs input conditions is examine, revealing that the maximum vertical seismic force increased by 4%–6%, but its distribution does not change significantly. Furthermore, the effect of the additional mass of the flue is considered, resulting in a significant increase in the vertical seismic force at the suspension points, leading to a change in its distribution. An abrupt increase of about 40% at 1/3 height and an increase of about 45% in the horizontal displacement at the top are observed. The paper also highlights the potential stress concentration and resultants cracks or damage caused by the opening of the chimney barrel.

Key technologies research on of soil-structure interaction base story isolated structure response in 3D seismic zone

The development of karst in Karst area leads to poor stability of stratum. If earthquake occurs, the area will produce destructive disaster. In order to improve the stability capacity of the grassroots in the region, this study investigates the seismic response of inter-story isolation structures considering soil-structure interaction (SSI) in three-dimensional earthquakes. A model of the inter-story isolation structure incorporating SSI was developed, and one-dimensional, two-dimensional, and three-dimensional ground motions were applied to compare the seismic response under different input conditions. A three-dimensional isolation system was introduced and compared with traditional horizontal isolation structures to address excessive tensile and compressive stresses on the isolation structure during three-dimensional ground motion. The results demonstrate that the seismic response to three-dimensional earthquakes surpasses one-dimensional and two-dimensional inputs. Furthermore, adding a three-dimensional isolation structure effectively isolates vertical ground motion and reduces structural seismic response. Moreover, it minimizes soil stresses on the foundation compared to traditional horizontal isolation structure, enhancing foundation stability. This study will provide theoretical value and practical guidance for the research on key technology of SSI base story isolation structure response in Karst Plateau 3D Seismic zone.

Correlation and Joint Distribution of Spectral Accelerations of Vertical Ground Motions

ABSTRACT This paper estimates a correlation model and joint distribution model of spectral accelerations of vertical ground motions based on the NGA-West2 ground motion database. The correlation model calculated via BC16 vertical GMPE in this study is compared with those published models via other vertical NGA-West2 GMPEs. It is verified that the calculated residuals of vertical ground motions at multiple periods follow the multivariate normal distributions via both a qualitative validation method and a set of quantitative validation methods. The correlation model and the joint distribution model of vertical spectral accelerations are the theoretical basis for research on the joint occurrence of spectral accelerations of vertical ground motions, and an example of applied research on joint occurrence of spectral accelerations of vertical ground motions is studied: the conditional mean spectrum of vertical ground motions. Finally, the effects of different vertical correlation models and ground motion prediction equations on vertical conditional spectra are investigated for wide application of the correlation model and the joint distribution model of spectral accelerations of vertical ground motions.

Quantifying Site Effects and Their Influence on Earthquake Source Parameter Estimations Using a Dense Array in Oklahoma

AbstractWe investigate the effects of site response on source parameter estimates using earthquakes recorded by the LArge‐n Seismic Survey in Oklahoma (LASSO). While it is well known that near‐surface unconsolidated sediments can cause an apparent breakdown of earthquake self‐similarity, the influence of laterally varying site conditions remains unclear. We analyze site conditions across the 1825‐station array on a river plain within an area of 40 km by 23 km using vertical ground motions from 14 regional earthquakes. While the source radiation pattern controls P‐wave ground motions below 8 Hz, the surface geology correlates with P‐wave ground motions above 8 Hz and S‐wave ground motions at 2–21 Hz. Stations installed in alluvial sediments have vertical ground motions that can exceed three times the array median. We use the variation of ground motion of regional earthquakes across the array as a proxy for site effects. The corner frequencies and stress drops of local earthquakes (ML = 0.01–3) estimated using a standard single‐spectra approach show negative correlations with the site‐effect proxy, while the seismic moments show positive correlations. In contrast, the spectral‐ratio approach effectively shows no correlation. The overall bias is small as expected for this relatively homogeneous structure; accurate estimation of site‐related biases requires at least 30 stations. Correcting for site‐related biases reduces the standard deviations of the source parameters by less than 13% of the total variations. Remaining variations are partially associated with source directivity and model misfits— as small earthquakes can have complex ruptures.

Shaking table test on seismic behavior of posttensioned precast segmental Concrete-Filled double skin steel tubular piers

Posttensioned precast segmental bridge piers have proven to be an attractive solution for accelerated bridge construction and seismic resilience. Although extensive research efforts have been made to understand the seismic performance of such piers under quasi-static loading and unidirectional/bidirectional ground motions, there is limited information available regarding to their dynamic behavior when subjected to tri-directional ground motions. Therefore, this study performed shaking table tests on an innovative posttensioned precast segmental concrete-filled double skin steel tubular (CFDST) pier to explore its seismic behavior under a set of tridirectionally applied far-field ground motions. A total of six 1/5 scaled piers were investigated with different design details, including one monolithic pier as reference, two posttensioned precast segmental piers without internal energy-dissipating (ED) bars but different amounts of prestressing tendons, and three posttensioned precast segmental piers with different amounts of ED bars. It has found that the relative displacement responses decreased with increase in amounts of prestressing tendons or ED bars. The segmental piers without ED bars twisted obviously when PGA reached 0.3 g under tri-directional ground motion excitations, while the segmental piers with ED bars did not due to additional shear resistance across joints provided by ED bars. Moreover, the dynamic responses of segmental piers with and without vertical ground motion excitation were compared in details to investigate the effect of vertical ground motion on their seismic behavior. It has found that the change in vertical acceleration response due to vertical ground motion excitation was a significant importance compared to the change in lateral accelerations, relative displacements and tendon force increment. In consequence, the axial compressive force as well as shear resistance across joint provided by dead load reduced by almost 33% due to appearance of vertical ground motion at the PGA of 0.7 g.

Contribution of vertical ground motion on seismic response of multi-span simply-supported T-girder RC bridges in the presence of corrosion-fatigue degradation

Highway bridges, located in heavy traffic and corrosive environments, are prone to corrosion-fatigue degradation, due to which material properties of steel and concrete in bridge girders get altered and effective area of rebars reduces resulting in reduced flexural stiffness of girders. Consequently, exposed bridges become weaker to resist earthquake loads, particularly for the ones having three significant translational components. It is, therefore, important to evaluate life-long performance of bridges that suffer from corrosion-fatigue degradation and are subjected to seismic events having substantial vertical ground motions (VGMs). Such a threatening scenario for seismic safety of bridges has not been explored yet. The current study demonstrates the confronting role of corrosion-fatigue degradation and VGM on bridge seismic response through a representative multi-span RC bridge in Gujarat, India, and required information on corrosion, traffic, and seismic activities is acquired from appropriate sources. The degradation mechanism is modeled as a coupled phenomenon of pitting corrosion of rebar and traffic-induced fatigue stresses that give rise to fatigue cracks at deep pit locations of rebars in girders. Developed numerical model of the bridge composes of all essential features to accurately capture the gradual degradation along life-span and fluctuations in response of key vulnerable bridge components under horizontal and vertical excitations. Results suggest that ignoring the impact of this degradation mechanism and VGM can lead to higher seismic vulnerability of bridges and endanger their safety under future earthquakes.