Vertical Peak Ground Acceleration Research Articles

Seismic design and performance analysis of perforated rubber buffer layer in tunnel

Tunnels may be damaged under earthquakes, which has been observed by many earthquake events, and the buffer layer is proposed and widely investigated as a damping measure. The rubber is considered as a qualified buffer layer material because of its small elastic modulus and super elasticity, but its high price makes it difficult to apply in practical engineering. Therefore, four types of rubber buffer layers are proposed in this study, including the common rubber buffer layer and three types of perforated rubber buffer layers (PRBL), which can reduce the seismic damage and cost of tunnels. A pseudo-static method for calculating the seismic response of tunnels under horizontal and vertical earthquake motions is proposed and verified. Based on proposed pseudo-static method, a seismic design method for the buffer layer is present, and the proposed seismic design process is used to study the seismic mitigation performance of buffer layers. The initial design of the buffer layer under earthquake action E1 is carried out by pseudo-static method, and then the seismic mitigation performance is verified through dynamic time history analysis method under earthquake action E2. The earthquake action E1 and earthquake action E2 are the earthquake actions with short and long return periods of the engineering site, respectively. The results show that the common rubber buffer layer has almost no seismic mitigation performance, and the three types of PRBLs have good seismic mitigation performance. The type IV buffer layer is strip-shaped PRBL and the holes are along the longitudinal direction of the tunnel, and it has optimal seismic mitigation performance. The effects of vertical earthquake motion and peak ground acceleration (PGA) on the seismic mitigation performance of the buffer layer are studied. The results show that vertical earthquake motion has little effect on the seismic mitigation performance of different types of buffer layers. For different PGAs, the type IV buffer layer is able to efficiently decrease the peak internal force of secondary lining. The results also prove the validity of design method.

Observed nonlinear site amplification of vertical ground motion in Taiwan

The objective of this study is to evaluate the possible reason for the observed nonlinear site amplification (NSA) of vertical ground motions in Taiwan. First, we observe that NSA generally occurs simultaneously in both the horizontal and vertical components of a ground-motion record and that the NSA levels are similar between these components. We also observe that most vertical peak ground acceleration (PGA) and vertical peak oscillator spectral acceleration (SA) responses for different periods occur during the shear wave (S-wave) window after S-wave arrival. The differences in the source, path, and site effects on PGA and SA responses occurring during the pressure wave (P-wave) and S-wave windows are evaluated individually through a regression analysis. We determine that NSA is observed only when PGA and SA responses occur during the S-wave window. This evidence demonstrates that the observed NSA of vertical ground motions in Taiwan may result from the hysteresis of the soil layer subjected to S-waves. This study provides physical evidence for the observed NSA of vertical ground motions in Taiwan.

Vertical floor acceleration spectra for regular steel frame structures

The scope of this contribution is the assessment of the vertical peak component acceleration of single-degree-of-freedom (SDOF) oscillators attached to elastic moment-resisting steel frames subjected to recorded ground motions. These SDOF oscillators represent nonstructural components (NSCs) flexibly attached to the load-bearing structure whose acceleration demands correlate with their maximum strength demands. The results in terms of floor acceleration spectra show that the interaction between a vertically oscillating NSC and the structure is much more pronounced than for horizontally oscillating NSC of the same mass and natural frequency. This means that even for vertical NSCs with very small mass (in the case of the investigated eight-story frame 0.01% of the frame mass depending on the number of stories) a coupled analysis is required for a realistic prediction of the NSC acceleration demand. In a parametric study of vertical NSCs attached to steel frame structures of different number of stories, a median vertical peak component acceleration was observed up to 5.5 times larger than the vertical peak floor acceleration of the attachment node of the load-bearing structure and up to 20 times larger than the vertical peak ground acceleration. The amplification of the vertical acceleration response is thus of the same order of magnitude as for horizontal NSCs. This means that the vertical dynamic response of flexible NSCs cannot be neglected and should therefore be studied in more detail in the future.

Vertical effects of near-fault ground motions and the optimal IMs for seismic response of continuous girder bridges with FPB isolators

The characteristics of vertical components in the near-fault region were investigated based on 121 pairs of typical near-fault ground motions. A weak positive correlation between the vertical and horizontal peak ground acceleration (PGA) and peak ground velocity (PGV) is shown. Basically, the ratios of vertical to horizontal peak ground acceleration and velocity of the near-fault ground motions comply with the lognormal distribution, and the vertical ground motions are significantly stronger at lower periods. Fifteen scaler horizontal and nine scaler vertical IMs are compared to select the optimal scaler IMs of horizontal and vertical seismic demands of an isolated girder bridge with friction pendulum bearings (FPB isolators). It is found that acceleration-related scalar IMs perform better for vertical seismic demands, while velocity-related scaler IMs perform better for horizontal seismic demands. The optimal vector-valued IM, consisting of scalar horizontal and vertical IMs in the forms of IMh,IMv, for horizontal seismic demands were proposed. The optimal vector-valued IMs show an apparent improvement in efficiency compared with the corresponding scaler IMs when vertical components are considered. Furthermore, the probabilistic seismic demand models (PSDMs) for horizontal seismic demands with optimal vector-valued IM were adopted to assess the seismic demands under a given intensity of vertical and horizontal ground motions. It is identified that the vertical effects significantly influence the shear force of piers while slightly influencing the curvature of piers and bearing displacements.

Orthotropic plates with dynamic vertical seismic load modeled as multi line

Calculation plate floor concrete, using a static load which is a gravity load consisting of a live load and a dead load, with various of boundary conditions, floor slabs are orthotropic plate, and rarely account for dynamic loads due to vertical seismic loads, with other boundary conditions, such as Clamped, simply supported, ES (Elastic Support), ER (Elastic Restraint), and ESR (Elastic Support and Restraint). Analytical solution based on the Modified Bolotin Method to analyze floor slab under Vertical Peak Ground Acceleration (PGAv), the natural frequency solution based on auxiliary Levy’s type problems. Dynamic vertical seismic loads using multiline, first line at 0 < t < 0.5 is linear equation, second line at 0.05 < t < 0.15 is quadratic equation, third line 0.15 > t < 0.6 is sextic equation, last line, t > 0.6 is linear equation, vertical seismic load with two conditions far fault and near fault, multi-line equation are depending on (PGAv/g). A numerical example is given, for various boundary conditions, and far fault, translational stiffness (kx, ky) and rotational stiffness (cx ,cy), from the results of plate calculations due to dynamic vertical seismic loads with 5 types of edge support, ES (elastic support) is the best result.

Inversion of acoustic thunder source spectral model from thunder-induced seismic waves in megacity

SUMMARYThunder-induced seismic waves recorded at dense seismic stations in Seoul, South Korea are analysed for inversion of thunder source spectra. Thunder-induced seismic waves from four local thunder events are analysed. A theory is introduced for the inversion of acoustic source spectra from thunder-induced seismic waves. In the course of source-spectral inversion, the propagation and acoustic-to-seismic coupling effects are counted. The thunder-induced seismic signals were well identified at distances of <∼20 km. Direct acoustic-to-seismic coupled seismic waves present apparent phase velocities of sound speed in atmosphere (340 m s−1). Thunder-induced seismic waves are dominant at high frequencies (>20 Hz). Vertical peak ground accelerations of thunder-induced seismic waves in local regions (0.024–0.110 m s−2 at distances of 2.4–3.7 km) are equivalent to the ground motion levels induced by a moderate-size (∼M5) earthquake at regional distances. The thunder-induced acoustic waves in the atmosphere are obtained by removing the acoustic-to-seismic coupling effect and site-response effect from the observed thunder-induced seismic waves. The quality factors for acoustic wave attenuation in the atmosphere are determined. Urban landscapes and atmospheric effects cause strong acoustic attenuation over atmospheric absorption. Acoustic thunder source spectra are determined by stacking the inverted acoustic spectra at all stations. The peak frequencies of acoustic thunder source spectra are around 34–36 Hz, suggesting the acoustic energy per unit length in lightning strikes to be ∼4 × 106 J m−1. Local seismic records are applicable for the investigation of thunder and lightning properties.

Effect of simulation accuracy of shear keys shear state on seismic response of friction pendulum bearing

In order to study the effect of simulation accuracy of shear keys shear state on seismic response of friction pendulum bearing, a vertical spring-friction system composed of equivalent components is used to simulate the friction pendulum bearing effectively, and two numerical calculation programs are developed. A spring element with life-and-death characteristics is used to realize the simplified simulation of shear keys shear state in the program 1, while shear keys on both sides of the friction pendulum bearing in the same direction are considered independently in the program 2. By comparing the seismic responses of the two programs with different shear key shearing force, vertical spring stiffness and different peak ground acceleration (PGA) conditions, it can be concluded that the precise simulation of shear keys shear state can more accurately calculate the shear key shear time and the maximum acceleration of the structure, which is beneficial to seismic isolation design. When the shear key shearing force is large and the PGA is small, the relative displacement response of bearing will be small if the shear keys are simultaneously sheared off. Increasing the stiffness of the vertical spring can reduce the residual displacement of the friction pendulum bearing. The simulation accuracy of shear key shear state has little influence on the relative displacement response when the equivalent stiffness of friction pendulum bearing is large. In this case, the shear key shear state can be simplified.

Attenuation Relationships for Horizontal and Vertical Peak and Spectral Accelerations for Alborz Zone of Iran

ABSTRACT In the present study, the attenuation relationships of horizontal and vertical peak ground acceleration and 5%-damped spectral acceleration, suitable for the northern region of Iran (Alborz Zone), are presented. The dataset contains 308 three-component records from 104 events with moment magnitudes between 4.5 and 7.6 and hypocentral distances from 10 to 200 km. Site conditions of the stations have been classified into two categories, rock and soil. To determine the unknown constants of the relations, one-step nonlinear regression analysis was used. Finally, it was found that the proposed attenuation relationships show good compatibility with a number of past well-known studies.

An Evaluation of Strong-Motion Parameters at the S-net Ocean-Bottom Seismograph Sites Near the Kanto Basin for Earthquake Early Warning

We analyzed strong-motion records at the ground and borehole in and around the Kanto Basin and the seafloor in the Japan Trench area from three nearby offshore earthquakes of similar magnitudes (Mw 5.8–5.9). The seafloor strong-motion records were obtained from S-net, which was established to enhance tsunami and earthquake early warnings after the 2011 great Tohoku-oki earthquake disaster. The borehole records were obtained from MeSO-net, a dense network of seismometers installed at a depth of 20 m in the Tokyo metropolitan area. The ground records were obtained from the K-NET and KiK-net networks, established after the 1995 great Hanshin-Awaji earthquake disaster. The MeSO-net and S-net stations record the shakings continuously, while the K-NET and KiK-net records are based on triggering thresholds. It is crucial to evaluate the properties of strong motions recorded by the S-net for earthquake early warning (EEW). This paper compared the peak ground accelerations (PGAs) and peak ground velocities (PGVs) between the S-net and K-NET/KiK-net stations. Because the MeSO-net records were from the borehole, we compared the PGAs and significant durations of the low-frequency motions (0.1–0.5 Hz) between the S-net and MeSO-net stations from identical record lengths. We found that the horizontal PGAs and PGVs at the S-net sites were similar to or larger than the K-NET/KiK-net sites for the S wave. In contrast, the vertical PGAs and PGVs at the S-net sites were similar to or smaller than those at the K-NET/KiK-net sites for the S wave. Particularly, the PGAs and PGVs for the P-wave parts on the vertical-component records of S-net were, on average, much smaller than those of K-NET/KiK-net records. The difference was more evident in the PGAs. The average ratios of S-wave horizontal to vertical PGAs were about 2.5 and 5 for the land and S-net sites, respectively. The low-frequency PGAs at the S-net sites were similar to or larger than those of the MeSO-net borehole records. The significant durations between the two-networks low-frequency records were generally comparable. Quantification of the results from a larger dataset may contribute to ground-motion prediction for EEW and the design of the offshore facilities.

Effects of near-fault ground motions on dynamic response of slopes based on shaking table model tests

Slope instability and failure frequently occur in areas near faults. A series of shaking table model tests were conducted to examine dynamic response of slopes to near-fault ground motion in the time and frequency domains. Effects of the intensity and pulse characteristics of near-fault ground motions on slope response were examined. Test results show that peak ground acceleration (PGA) induced by near-fault ground motion is amplified by elevation. When the amplitude of seismic loading exceeds a critical value (which is between 0.2 g and 0.5 g), intensity of near-fault ground motion increases, amplification of PGA by elevation weakens, and the high-frequency filtering effect of the slope is enhanced. Amplification of PGA by elevation and interfacial reflections are more prominent under pulse-like than non-pulse-like waves. The PGA amplification factor of the slope crest under pulse-like wave is 1.2 times of that triggered by non-pulse-like wave. Due to the interfacial reflections, vertical accelerations can be monitored simultaneously in cases which have only horizontal seismic loadings. The vertical PGA is 72.4% of horizontal PGA when the intensity of pulse-like waves is 1.1 g. These findings can provide a basis for designing earthquake-resistant of slopes near faults.

Peak ground acceleration prediction by fuzzy logic modeling for Iranian plateau

In this study, fuzzy logic modeling is applied to a complex and nonlinear set of data to predict both horizontal and vertical peak ground accelerations in Iranian plateau. The data used for the model include an up-to-date seismic catalogue from earthquakes in Iran for prediction of both horizontal and vertical acceleration of a probable earthquake. Fuzzy logic toolbox on MATLAB program was used for modeling. Earthquake magnitude ranging from 4 to 7.4, source-to-site distance from 7 to 80 km and three different site conditions were considered: rock, stiff soil and soft soil. Results are compared with those from worldwide and regional attenuation relationships, which show the higher capability of the model in comparison with the other models. After training the model, testing of the fuzzy model with the remaining data set was performed to confirm the accuracy of the model. Changes in the peak ground accelerations in connection with changes in input parameters are studied which are in agreement with basic characteristics of earthquake input motions.

Peak ground motions and characteristics of nonlinear site response during the 2018 Mw 6.6 Hokkaido eastern Iburi earthquake

The observed peak ground accelerations and peak ground velocities (PGVs) of the 2018 Mw 6.6 Hokkaido eastern Iburi earthquake generally followed the median values from ground motion prediction equations with reasonable errors at fault distances ≥ 50 km. However, at smaller distances, the equations significantly underestimated the peak ground motions, and it was eminent for PGVs. A comparison of surface-to-borehole spectral ratios of S-waves during the mainshock and other events revealed that the sites at smaller distances experienced various degrees of nonlinear site response. The two most widely known characteristics of nonlinear site response are the weakening of higher-frequency components and shifting of predominant frequencies to lower ones in comparison with the linear site response. At one of the sites that recorded the largest intensity of 7 in JMA scale of 0–7, the latter nonlinear effect was so dominant that the ground motions around the new predominant frequency got intensified by one order of magnitude in comparison with that during the weak-motions. Two sites, which were closely located, recorded vertical peak ground accelerations exceeding 1 g for the up-going motions. The recordings showed asymmetric waveforms and amplitudes characteristics of the nonlinear site response in extreme vertical ground motions recorded during a few earthquakes in the past. Few sites having lower vertical peak ground accelerations were also suspected of being experienced nonlinear site response on vertical motions. These findings suggest taking a cautious approach to enumerate the reduction in amplification at higher frequencies using the single-station horizontal-to-vertical (H-to-V) spectral ratio technique. However, we found that the H-to-V technique was still useful to detect nonlinearity. Finally, an ad hoc equation was derived to correct the nonlinear site amplification in predicting horizontal PGVs with respect to one of the most widely used attenuation models in Japan. The results indicated that the effect was much stronger for a larger input motion than that for a proportional change in the Vs30 values.

Vertical peak floor accelerations of elastic moment-resisting steel frames

The scope of this study is the quantification of vertical peak floor acceleration demands at column lines and along the length of beams of elastic moment-resisting steel frames subjected to recorded ground motions. These demands correlate with the maximum strength demands on rigid nonstructural components attached to a frame structure. Since it is commonly assumed that buildings behave flexibly in the horizontal direction and rigidly in the vertical direction, the assessment of vertical acceleration demands is typically not considered in most cases. The results of this study show that vertical peak floor accelerations can be up to five times larger than the vertical peak ground acceleration, in contrast to horizontal peak floor accelerations that are only up to two times larger than the horizontal peak ground acceleration for the numerical models used in this study. The most significant amplifications estimated in the vertical direction are found at the center of the girders. Further investigations of modified steel frames indicate that the story-wise mass distribution has an influence not only on the vertical acceleration demand, but also on the horizontal component of the response, though to a lesser degree. In contrast, the response in the vertical and horizontal direction is only slightly affected by an increase in the flexural stiffness of the beams. The results of this study strongly indicate that in steel frames it can be considered highly questionable to ignore the amplification of the vertical acceleration component along the height of the structure.

Vertical Seismic Effect on the Seismic Fragility of Large‐Space Underground Structures

The measured vertical peak ground acceleration was larger than the horizontal peak ground acceleration. It is essential to consider the vertical seismic effect in seismic fragility evaluation of large‐space underground structures. In this research, an approach is presented to construct fragility curves of large‐space underground structures considering the vertical seismic effect. In seismic capacity, the soil‐underground structure pushover analysis method which considers the vertical seismic loading is used to obtain the capacity curve of central columns. The thresholds of performance levels are quantified through a load‐drift backbone curve model. In seismic demand, it is evaluated through incremental dynamic analysis (IDA) method under the excitation of horizontal and vertical acceleration, and the soil‐structure‐interaction and ground motion characteristics are also considered. The IDA results are compared in terms of peak ground acceleration and peak ground velocity. To construct the fragility curves, the evolutions of performance index versus the increasing earthquake intensity are performed, considering related uncertainties. The result indicates that if we ignore the vertical seismic effect to the fragility assessment of large‐space underground structures, the exceedance probabilities of damage of large‐space underground structures will be underestimated, which will result in an unfavorable assessment result.

Erratum to: A model for predicting vertical component peak ground acceleration (PGA), peak ground velocity (PGV) and 5% damped pseudospectral acceleration (PSA) for Europe and the Middle East

In this study, we present a ground-motion model for the vertical component of peak ground acceleration, peak ground velocity, and 5% damped pseudo acceleration response spectra at periods ranging from 0.01 to 4 s. The vertical model is based on the ground-motion models previously developed for the horizontal component and vertical-to-horizontal ratio of ground motion by Akkar et al. (Bull Earthq Eng 12:359–387, 2014a; 517–547, 2014b) rather than on an independent regression analysis of strong-motion data available for Europe and the Middle East. The proposed ground-motion model includes formulations for the median values as well as for the aleatory within-event, between-event, and total standard deviation values of the vertical ground motion. We validate the proposed model by comparing it against the strong-motion database of Europe and the Middle East. Our vertical ground-motion model is applicable for moment magnitudes ranging from 4.0 to 8.0, for source-to-site distances ranging from 0 to 200 km, average shear-velocity down to 30 m (Vs30) values ranging from 150 to 1200 m/s and for reverse, normal and strike-slip styles of faulting as is the case for the underlying horizontal component and vertical-to-horizontal ratio ground-motion models of Akkar et al. (2014a, b). Within the scope of this study, a method to develop a vertical spectrum that is fully consistent with the corresponding horizontal uniform hazard spectrum is also proposed.

Performance of road bridges during the 14 November 2016 Kaikōura Earthquake

The transport infrastructure was majorly affected by the 14th November 2016 Kaikōura Earthquake. Severe vertical and horizontal peak ground accelerations generated high inertial forces, land-slides, and liquefaction. Most of the bridges in the Hurunui, Malborough and Kaikōura districts were critical nodes to the railway and road networks. In total, 904 road bridges across those districts were affected. Two reached the life safety limit state, suffering severe damage, however, most of the affected bridges experienced only minor to moderate damage. This paper describes the structural performance of the most severely damaged bridges based on observations made from site inspections. In addition to this, several performance issues have arisen from this event and are posed in this paper, hopefully to be addressed in the near future.

Nonlinear dynamic behavior of base-isolated buildings with the friction pendulum system subjected to near-fault earthquakes

ABSTRACTIn spite of the fact that avant-garde sliding bearings have been proposed, the application of the single friction pendulum (FP) bearing is increasing due to its conceptual simplicity; yet there are still important aspects of its behaviour that need further attention. More specifically, the FP system presents spatial variation of friction coefficient, depending on the sliding velocity of the FP bearings. Moreover, the frictional force and restoring stiffness during the sliding phase are proportional to the axial load. Long duration intense velocity pulses in the horizontal direction and high values of the ratio between vertical and horizontal peak ground acceleration are expected for near-fault earthquakes. Torsion with residual displacement and uplift of the FP system need to be better understood for base-isolated structures located in near-fault areas. To this end, a numerical investigation is carried out with reference to a six-storey reinforced concrete (r.c.) framed building, characterized by an L-shaped plan with wings of different length and setbacks at different heights along the main in-plan directions. Twelve base-isolated test structures are designed in line with the Italian seismic code, considering (besides the gravity loads) the horizontal seismic loads acting alone or in combination with the vertical ones. Three design values of the radius of curvature for the FP system and two in-plan distributions of dynamic-fast friction coefficient for the FP bearings, ranging from a constant value for all isolators to a different value for each, are assumed. A nonlinear force-displacement law of the FP bearings in the horizontal direction, depending on sliding velocity and axial load, is considered, while a gap model takes into account the vertical uplift of the FP bearings. The nonlinear seismic analysis is performed on two sets of seven near-fault earthquakes, both sets with significant horizontal or vertical components selected and normalized on the basis of the design hypotheses adopted for the test structure.

A model for predicting vertical component peak ground acceleration (PGA), peak ground velocity (PGV), and 5% damped pseudospectral acceleration (PSA) for Europe and the Middle East

A model for predicting vertical component peak ground acceleration (PGA), peak ground velocity (PGV), and 5% damped pseudospectral acceleration (PSA) for Europe and the Middle East

The Effect of the Vertical Acceleration on Stability Assessment of Seismically Loaded Earth Dams

Abstract In the assessment of slope stability, the vertical component of acceleration is commonly neglected. However, signal analyses performed on a large number of acceleration time histories have revealed that the vertical peak ground acceleration can be as high as the horizontal one. In this paper, a method of slope stability analysis regarding the vertical component of acceleration is proposed. It considers a rigid body system affected by the acceleration time histories in both horizontal and vertical directions. In a general case, the strength of the contact between acceleration components is time dependent. Parametric analysis was performed on the basis of cyclic harmonic loading, assuming a safety criterion in the form of permanent displacement. The results, for both harmonic and real acceleration time histories, were compared with the results of the commonly used Newmark’s sliding block approach, which revealed significant differences in permanent displacements calculated by the two methods.

Nonlinear seismic analysis of irregular r.c. framed buildings base-isolated with friction pendulum system under near-fault excitations

The application of the friction pendulum (FP) system is increasing due to its conceptual simplicity; yet there are still aspects of its behaviour that need further attention. Long duration intense velocity pulses in the horizontal direction and high values of the ratio between vertical and horizontal peak ground acceleration are expected in the near-fault areas. Base-isolated structures subjected to near-fault earthquakes present variation of friction force and lateral stiffness of the FP system during the sliding phase which can induce torsion with residual displacement and uplift. To investigate these effects, a nonlinear dynamic analysis is carried out considering a six-storey reinforced concrete (r.c.) framed building, characterized by an L-shaped plan with wings of different length and setbacks at different heights along the in-plan principal directions. Twelve base-isolated test structures are designed in line with the Italian seismic code, considering (besides the gravity loads) the horizontal seismic loads acting alone or in combination with the vertical ones. Three design values of the radius of curvature and two in-plan distributions of dynamic-fast friction coefficient are assumed for the FP bearings, ranging from a constant value for all isolators to a different value for each. A nonlinear force-displacement law of the FP bearings is considered in the horizontal direction, depending on sliding velocity and axial load, while a gap model takes into account the vertical uplift of the FP bearings. The nonlinear seismic analysis is performed on near-fault ground motions with significant horizontal or vertical components, selected and normalized on the basis of the design hypotheses adopted for the test structure.