Effect Of Vertical Ground Motion Research Articles

Bidirectional seismic response of assembled monolithic subway station-aboveground structure system under artificial bedrock ground motions

Assembled monolithic subway station partly synthesizes the advantages of cast-in-place and precast subway stations. However, the related seismic response analysis considering the influences of vertical ground motion and aboveground structure is still scant. In this study, we firstly performed the statistical analysis on bidirectional bedrock ground motion parameters (response spectrum, duration and envelope function) using KiK-net data, and obtained some suggested values of the above parameters. Then, four sets of artificial bedrock ground motions with statistical meanings were generated and a three-dimensional finite element analysis of the seismic response of an existing two-story three-span subway station was conducted. The main results are summarized below. (1) The significant damage to assembled monolithic station under far-field strong motion firstly occurred at side middle slab; middle slab, upper column and related grouting sleeve joints were more damage-prone. (2) When horizontal peak ground acceleration stayed constant, overall the damage of far-field motion was stronger than that of near-fault motion. (3) Vertical ground motion obviously accelerated the damage progresses of various structural members at various positions, then aboveground structure further enhanced the damages and vertical displacement responses of parts of top slab. (4) For the axial force time-history of upper column during far-field strong motion, aboveground structure uplifted the baseline, and vertical ground motion increased the amplitude and advanced the obvious drop of the baseline, among which the latter effect of vertical ground motion on assembled monolithic station was stronger than that on cast-in-place station. (5) Vertical ground motion enhanced inter-story displacement during far-field strong motion, among which the influence on the upper story of assembled monolithic station could be obviously amplified by aboveground structure, and the amplification effect lagged behind the influence of vertical ground motion. Based on the results of this study, some suggestions for the seismic design of subway station are also provided.

A data-driven approach for structural integrity assessment of prestressed concrete containment vessel considering the effect of vertical ground motions

As a final barrier against the release of radioactive material, the prestressed concrete containment vessel (PCCV) plays an important role in the nuclear power plant (NPP). When subjected to seismic loads, its structural performance requires high structural integrity. During an earthquake, the PCCV experiences ground motions (GMs) consisting of horizontal and vertical components in a global coordinate system, and its structural integrity is probably overestimated if only the horizontal component is considered in numerical analyses. In this study, a novel cumulative damage index is first employed to quantitatively assess the structural integrity of PCCVs. Accordingly, the failure probability of structural integrity of the PCCV is investigated by incremental dynamic analysis (IDA) and further seismic fragility analysis considering the effect of vertical ground motions (VGMs). The results show that the effect of VGMs on structural integrity of PCCVs is gradually non-negligible with the increase of vertical intensity. Moreover, an accurate cumulative damage prediction model for the PCCV is established based on eight mainstream machine learning (ML) algorithms, and the necessity of incorporating vertical intensity measures (IMs) in ML models is investigated. The results show that the ML model considering the vertical IMs is superior in capturing the cumulative damage of the PCCVs. The best estimates are obtained by GB with R2 of 0.912, MAE of 1.301, MSE of 6.186, and RMSE value of 2.487. Finally, the SHapley Additive exPlanation (SHAP) method is adopted for interpreting the prediction results of the optimal ML model to assess the effect of each IM and its interactions on the generalization performance of the model. The proposed ML-based cumulative damage prediction model for PCCVs considering the effect of VGMs enables an accurate quantitative assessment on structural integrity of PCCVs. This provides an important reference for evaluating the potential environmental hazard due to the leaking of radioactive materials.

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.

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.

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.

The effect of vertical motions on damage accumulation on concrete gravity dams

AbstractThe effect of vertical ground motions on the seismic response of dams has long been a concern in the seismic design and evaluation of concrete gravity dams. The guidelines regarding the use of vertical motions in time history analysis (THA) are not clear due to the complexity of the effect as well as the large uncertainty in the motion selection process. The goal of this study is to assess the significance of vertical motions’ effects on concrete gravity dams considering the relevant variability due to ground motion, system frequency response as well as the shaking level. To this end, a carefully selected ground motion set providing realistic vertical(V)/horizontal(H) loading was used in nonlinear THAs of three different systems with different modal properties. In order to evaluate the intensity of shaking on the vertical motions’ effect, the responses were calculated at different seismic levels corresponding to operation, design, and maximum shaking levels. Along with traditional demand parameters commonly employed in assessing seismic response, cracking on the base and at the upstream face of the monolith was adopted as demand measures using a model capable of yielding discrete cracking on the system. The effect of vertical motions was quantified by comparing the response of H + V to H only shaking. The results show the vertical shaking can significantly affect upstream cracking for the operation or design level earthquakes, the effect increasing for larger dams.

Synthetic experimental and numerical investigation on the vertical seismic effect on underground structures

Seismic damage patterns of underground structures indicate unignorable effects of vertical seismic actions. To deal with this, this study distinguished the impact of the vertical seismic effect on the seismic safety of underground structures experimentally and theoretically and provides important shaking table test results for this topic. A typical shallow buried subway station-tunnel junction structure was designed by following the Buckingham similarity law, based on which the shaking table test was performed to investigate the vertical seismic effect on underground structures. The vertical wave propagation laws of the free field, the model structure, and the soil–structure interaction (SSI) system were comparatively analyzed. Numerical simulations considering the soil’s nonlinear behaviors under vertical loads were performed using the equivalent linear analysis method and were verified by the test records. By combining both the experimental and numerical results, it was found that the surrounding soils have very weak constraints on the structural vertical movements. By distinguishing lateral soil pressures from horizontal actions, the vertical seismic action is found to be mainly an inertia force that can stimulate high-frequency vibration modes of the system and cause considerable vertical relative deformations within the underground structure. Consistent with the observed structural damage at the Daikai station, the participation of high-frequency vibration modes is a rational approach that can explain the amplification effect of vertical ground motions on structural seismic responses. In addition, the equivalent linear method is generally satisfactory for simulating the soil compressional nonlinearity.

Effects of Vertical Ground Motion on Pedestrian-Induced Vibrations of Footbridges: Numerical Analysis and Machine Learning-Based Prediction

Current codes and guidelines for the dynamic design of footbridges often only specify the pedestrian-induced excitations. However, earthquakes may occur during the passing stage of pedestrians in earthquake-prone regions. In addition, modern footbridges tend to be slender and are sensitive to vertical ground motions. Therefore, we investigate the effects of vertical ground motion on pedestrian-induced vibrations of footbridges. A total of 138 footbridges with different materials, dimensions, and structural types are considered as the target structures. The classical social force model combined with the pedestrian-induced load is used to simulate crowd loads for the scenarios with six typical pedestrian densities. Furthermore, 59 vertical ground motions with four seismic intensities are taken as the seismic inputs. An amplification factor is introduced to quantify the amplification effects of vertical ground motion on human-induced vibrations of footbridges. Four machine learning (ML) algorithms are used to predict the amplification factor. The feature importance indicates that the scaled peak ground acceleration, the pedestrian density, and the bridge span are the three most important parameters influencing the amplification factor. Finally, the vibration serviceability of the footbridge subjected to both crowd load and vertical ground motion is assessed.

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.

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.

Effects of Vertical Ground Motion on Flat Slab Structure

Effects of Vertical Ground Motion on Flat Slab Structure

A state-of-the-art review of vertical ground motion (VGM) characteristics, effects and provisions

Previous earthquake events have shown that the vertical component of strong ground motion has been proved to damage or totally destroy the structures. But in seismic resistant design of structures, effects of horizontal ground motions are mainly considered and effects of vertical ground motions (VGMs) are ignored. However, the field evidence of damaged structures indicates that the VGM was more significant particularly for near-fault earthquakes. Therefore, the addition of vertical component in seismic design has been recognized in the literature. In seismic resistant design of structures, horizontal ground motions are extensively studied and used for designing of structures. However, VGMs are not considered of more importance as horizontal one. But with the past near-fault earthquakes and their damage evidence effects have increased the awareness of VGMs. In this paper, the critical reviews of the literature associated with VGM are explained and reviewed. The important characteristics like vertical response spectra, near-fault influence, frequency influence and time lag between peak vertical and peak horizontal ground motion, vertical response period influence and local site conditions are explained. The provisions in latest national and international standards and the field evidence of damaging effects caused by VGM are also explained. Considering all the above parameters associated with VGM, the past studies on different types of structures are reviewed. Finally, a methodology for identification of critical parameters and future scope on VGM is proposed. This study leads to some important conclusions that VGM needs to be included in analysis and design.

Parametric study for long-span roof truss subjected to vertical ground motion

Generally in the seismic resistant design of structures, effects of horizontal ground motions are mainly considered and effects of vertical ground motions (VGMs) are ignored. However, considering the field evidences of damage of structures due to vertical component of ground motion for near-fault earthquakes, the importance of inclusion of effect of vertical component of earthquake in seismic design has been recognized. Therefore in this paper, a parametric study has been carried out on 25 m long-span industrial steel roof truss with the help of 12 near-fault ground motions without pulse. The parameters related to roof truss as well as an earthquake data are studied to get the response of long-span roof truss under vertical ground motion (VGM) with nonlinear time history analysis using SAP2000V19.2.1 software. From the parametric study, it has been realized that for a chosen long-span industrial roof truss, the parameters such as vertical to horizontal peak ground acceleration ratio, axial force, vertical displacement and base bending moment are identified as critical. From the time history analysis results, it is also found that response of truss under vertical ground motion is critical for ground motions having V/H ratio more than 1 and therefore the long-span structure in near-fault zone should be considered separately in design rather than taken as 2/3 of horizontal acceleration as per given in IS1893:2016 (Part-1).

Effects of Vertical Ground Motion on Seismic Performance of Reinforced Concrete Flat-Plate Buildings

AbstractNonlinear time-history analyses are conducted on a flat-plate building to explore the damaging effects of vertical ground acceleration on punching shear failure of slab–column connections, ...

수직 지진파 성분을 고려한 강재 물탱크의 유체 압력 응답 거동

본 연구는 강재 물탱크가 수평방향과 수직방향 성분을 포함한 지진하중에 종속될 때, 전산 유체 역학을 이용하여 강재 물탱크 내부 벽면에 작용하는 유체 압력 응답 거동을 분석한다. 이를 위해 본 연구에는 우선 문헌에서 이용 가능한 진동대 실험 데이터와 수치해석 결과를 비교함으로써 해석 모델링 기법을 제안한다. 또한 수직 지진파 성분에 의해 발생되는 슬로싱 유체 압력의 변화를 분석하기 위해 실제 강재 물탱크를 선택한 후 제안된 모델링 기법을 이용해 해석 모델을 생성한다. 생성된 모델에 대해 수직 성분 지진파의 고려에 따라 두 가지 경우의 지진하중 시나리오를 사용하여 수치해석 결과를 분석한다. 비교 결과, 수직 지진파 성분을 고려하면, 강재 탱크 내부의 최대 압력, 탱크 높이에 따른 압력 분포도 및 최대 압력 발생 위치를 변화시킴을 알 수 있다.

Earthquake Response Analysis of Tall Reinforced Concrete Chimneys considering Eccentricity

A numerical algorithm is presented to analyze earthquake response of tall reinforced concrete (RC) chimneys based on stick multidegree-of-freedom models. The algorithm considers the eccentricity phenomena between spatial discrete nodes and corresponding centroids of investigated lumps. The spatial discrete segments of the chimney are used to construct the investigated lumps. The equations of dynamic equilibrium of the investigated lumps are derived, and the numerical calculation procedure is implemented. Phenomena of eccentricity are studied for 150 m and 210 m RC chimneys. Seismic stresses and effects of vertical ground motion for the two chimneys are also studied. Numerical results show that the tensile and compressive stresses of the seismic control cross sections of the chimneys may increase under the actions of several specific earthquake waves by considering existing eccentricities. The effect of eccentricity on the earthquake responses of tall RC chimney should be considered, and stresses caused by vertical ground motion should not be neglected to obtain accurate earthquake response of chimneys.

Near-fault vertical ground motion effects on the response of balanced cantilever bridges

Post-tensioned balanced cantilever reinforced concrete (RC) bridges allow the economic spanning of wide spans using fewer columns than in more traditional bridges. More and more post-tensioned balanced cantilever bridges are constructed every year all round the world. The aim of this study was to investigate numerically the effects of near-fault vertical ground motions (VGMs) on the seismic behaviour of segmentally constructed, balanced cantilever RC bridges. Two long bridges constructed in Artvin, Turkey – the three-span Budan Bridge and the two-span Sengan Bridge – were selected for the application. Three-dimensional finite-element models (FEMs) of the bridges were created to obtain their dynamic characteristics such as natural frequencies and mode shapes numerically. The frequencies calculated from the FEMs of the bridges were then verified using experimental frequencies measured from ambient vibration tests. Acceleration records of near-fault earthquakes (1992 Erzincan (M = 6·69), 1999 Kocaeli (M = 7·51), 1999 Düzce (M = 7·14) and 1989 Loma Prieta (M = 6·93)) were selected for the seismic analyses. The seismic behaviours of the verified FEMs of the bridges with two and three spans were determined by considering horizontal, vertical and combined horizontal and vertical components of the earthquakes. It was found that near-fault VGM significantly affects the seismic response of segmentally constructed, balanced cantilever bridges.

Effect of vertical ground motions and overburden depth on the seismic responses of large underground structures

Underground structures such as subway stations, which are operated at a high capacity and frequency, are prone to damage by large earthquakes. To study the seismic performance of underground structures, this paper presents a three-dimensional nonlinear finite element simulation of the seismic behavior of subway stations, considering the influence of vertical ground motions and structural overburden depth. The results show that the consideration of vertical seismic motions increases the structural seismic responses; the influence extent depends greatly on the characteristics of the vertical seismic excitation. The station′s overburden depth influences the structural response significantly and alters the structural resonant frequency; the influence of the structural burial depth is a complex problem. Besides, it is deduced that the influence of structural burial depth tends to vanish with an increase in the induced frequency, particularly for deeper stations; more attention should be paid to deeper structures built on soft sites or deeper structures that suffer from long-period seismic shaking; the stiffer tunnel experiences less deformation, and the lateral earth pressure applied on the stiffer tunnel is higher. A few results in this paper are consistent with a damage survey of the Daikai subway station damaged in the 1995 Kobe Earthquake.