Increase In Peak Ground Acceleration Research Articles

Running Safety Assessment of a High-Speed Train on Bridges During Braking Under Near-Fault Ground Motions

This study aims to investigate the adverse effects of near-fault ground motions on the long-term development of high-speed railways. In this paper, the ground motions are analyzed based on the Train–Track–Bridge Coupling Braking System (TTBCBS) which has been validated during earthquakes. The effects of earthquakes on the whole system are discussed in depth, focusing on the random nature of earthquakes, the impulsive character of near-fault earthquakes and the effects of different initial speeds on the system behavior. The results show that under random earthquakes, the probability of train derailment gradually increases with the increase of peak ground acceleration (PGA) of earthquakes. When the PGA exceeds 0.2[Formula: see text]g, the train is highly susceptible to derailment and the bridge itself may incur damage. When analyzing the nature of pulses of near-fault ground motions, it was found that the responses induced by class B and class C pulses are significantly similar. Meanwhile, the calculated values of derailment coefficients are basically the same when the PGA of class A pulse wave is at 0[Formula: see text]g and 0.1[Formula: see text]g. This suggests that train braking somewhat mitigates the response induced by near-fault ground motions. Furthermore, the value of improved spectral intensity (SI) for the running safety during earthquakes indicates that the increase in seismic intensity is detrimental to the system. In terms of the effect of train initial speeds on the system during earthquakes, it is observed that the system response reaches the lowest point when the train speed is 250[Formula: see text]km/h, which is more favorable to the smooth deceleration of the train. When the train speed is 400[Formula: see text]km/h, the system response reaches its maximum value. These research findings provide crucial insights and guidance for seismic safety design and management of high-speed railways.

Safety speed threshold of high-speed train running on bridges under seismic excitation of different soil types

This study investigates the safety speed threshold of high-speed train running on bridges under seismic excitation of different soil types. In this paper, a train-track-bridge shaking table scale model test was conducted, and the train-track-bridge spatial coupling dynamics model was established. The reliability of the numerical model was verified by the tests. Afterward, the effects of transverse seismic excitation of different soil types on the train’s running safety were investigated, and the train’s safety speed thresholds were obtained. The results indicated that the dynamic response of the train-track-bridge system and the train’s running safety indices have an obvious increasing trend with the increase of peak ground acceleration and train’s running speed, and there are significant differences in the impact of different soil types. For the train-track-bridge system and the selected seismic records in this paper, the speed thresholds under different seismic fortification intensities were obtained based on the evaluation indices for the running safety of train. Among the four soil types, the safety speed threshold of soil type IV is lowest. The main frequency of soil type IV record is closer to that of the CRH380A train, resulting in severe rolling vibration of the train, and the offload factor has exceeded the limit when the speed is 50 km/h under the Loma seismic records with 8-degree seismic precautionary intensity.

Shake table tests on timber frame structure infilled with dry bond masonry

This study presents the results of a series of half-scale shake table experiments conducted on a single-room; single-story timber frame filled with dry-bonded brick masonry. Two half-scale models, one without infill and one infilled with dry bond brick masonry, were fabricated and tested on a shaking table to examine the seismic performance of timber-framed masonry structural systems. For dynamic characterization, both models were subjected to white noise base excitation, and to investigate the seismic behaviour, the models were subjected to incrementally increasing ground motion in accordance with single ground motion record incremental dynamic analysis. The dynamic characteristics, such as natural frequencies, damping, mode shapes, and stiffness degradation, were evaluated. The stiffness degraded to 43% in the model infilled with bricks and 62% in the model without infill. The peak acceleration and displacement responses and the global hysteresis response were assessed and evaluated. While determining the acceleration profiles of the model, the maximum out-of-plane acceleration recorded was of the order of 1.1 g for the model without infill and 1.6 g for the model with infill. The acceleration response was more amplified for models with brick infill, while a lower value was observed in models without infill. Based on the fact that the structure was linear even at maximum acceleration amplification during the test, it can be inferred that the timber-framed structure possesses a high degree of flexibility and deformability, and also that the energy dissipation capacity of the structure increased with the increase in peak ground acceleration of the input ground motion.

Seismic Vulnerability Analysis of Masonry Structures Built with Disassembled Brick Wall Sections

Disassembling brick wall pieces into brick wall sections and constructing masonry buildings with disassembled brick wall sections (DBWSs) can reduce construction waste production at source and help achieve carbon peak and carbon neutrality. A finite element model (FEM) for typical MSBD is established based on the calibrated finite element analysis method to evaluate the seismic performance of masonry structures built with disassembled brick wall sections (MSBD). Subsequently, the peak ground acceleration is selected as the ground motion intensity index, and the maximum inter-story displacement angle is chosen as the structural damage index. The 20 ground motion records are selected and scaled by peak acceleration in 0.2 g steps to form 120 structure-ground vibration samples for incremental dynamic analysis (IDA) and seismic vulnerability analysis. The IDA results indicated that with the gradual increase in peak ground acceleration, the maximum inter-story displacement angle increases and the model transits from the elastic stage to the elastoplastic stage. Because the characteristics of ground motion records are different, the order of structural plasticity development will be different and the number of ground motion records needs to be considered in the seismic performance assessment. The calculation model will not collapse under the 7 and 8 degree design-based earthquake and the probability of moderate and severe damage of the structure under the rare earthquake is minimal, according to the seismic vulnerability curves. The seismic vulnerability analysis results indicate that MSBD has good seismic performance under earthquakes and meets the requirements of “perfect subjected to frequent earthquake, reparable subjected to design based earthquake, no collapse subjected to rare earthquake.” The seismic vulnerability analysis based on probability statistics can provide a reference for seismic design and evaluation of earthquake damage.

Shake-table study on the effect of masonry infill on the seismic response of reinforced concrete frames

This paper presents results of an experimental shake-table study that examines the effects of position and stiffness of masonry infill in two-story single-bay concrete frame on its behavior under an earthquake. Six small-scale frame types were tested: bare frame (without infill) and five frames with different infill configuration. Herein, an identical reinforced concrete structure (columns, beams) was adopted for all frames. Besides self-weight load, frames were additionally loaded with the dead load at the floor levels. Afterwards, all frames were exposed to horizontal acceleration of an artificial accelerogram, with successive increase of peak ground acceleration (PGA) up to 0.8g. Characteristic displacements and accelerations of the frame, concrete and steel strains in characteristic points, as well as crack states in frame and infill were measured. The effect of the infill type on the obtained results was discussed. Finally, main conclusions of this research are given.

Shaking table test study on seismic performance of UHPC rectangular hollow bridge pier

To study the seismic failure mode and dynamic response characteristics of ultra-high performance concrete (UHPC) rectangular hollow bridge pier under dynamic loads, the El Centro wave, Taft wave, and Northridge wave were selected as seismic excitation for the shaking table test. The responses such as natural frequency, damping ratio, acceleration-time and displacement–time curves were investigated and the results were compared with the finite element simulation results. At the same time, 8 finite element models (FEMs) of UHPC rectangular hollow bridge pier were established to explore the influence of longitudinal reinforcement ratio and stirrup ratio on the seismic performance of bridge piers. The results indicated that with the increase of peak ground acceleration (PGA), the damping ratio, acceleration, displacement and UHPC strain of the specimen increased, while the natural frequency and the dynamic amplification factor of the pier decreased gradually due to the accumulation of damage. The increase of longitudinal reinforcement ratio improves the ductility, and the increase of stirrup ratio enhances the constraint effect of core UHPC and ductility to a great extent, which leads to different acceleration, displacement and equivalent plastic strain response of bridge piers. On the whole, the stiffness of UHPC rectangular hollow bridge pier was degraded after the input of seismic wave, but the ultimate bearing capacity was not deteriorated. The overall seismic performance is superior. In areas with low seismic fortification intensity, the reinforcement ratio of UHPC rectangular hollow bridge piers can be appropriately reduced.

Seismic characteristics of isolated plate-shell integrated concrete LSS

Plate-shell integrated concrete liquid-storage structure (PSICLSS) has been widely applied with the development of water treatment technology. However, there are few anti-seismic performance and base-isolation design researches on it. The seismic performance of PSICLSS was studied, and the accuracy of finite element analysis was verified by experimental study. A calculation method of damping coefficient is proposed and used in a PSICLSS study. Based on 5 natural accelerations and 2 artificial accelerations, the dynamic responses of the isolation liquid storage structure under different peak ground acceleration are analyzed. The analysis results show that, non-isolated PSICLSS is easy to damage when subject to earthquake. The principal stress of the structure is maximum at the upper beam, and the maximum liquid hydrodynamic pressure appears at the connection position of the upper and lower conical shell. When the base isolation measure is used, the stress of the structure can be effectively reduced, but the liquid sloshing response will be magnified. With the increase of peak ground acceleration, the structural dynamic response and liquid sloshing response will increase.

On Setting the Level of Seismic Effect in Seismic Intensity Scales and Design Standards

It is noted in the article that the increase in peak ground acceleration (PGA) by a factor of about 1.4 proposed by seismologists in a project of seismic intensity scale clearly reflects the lessons learned from earthquakes of the past. However, the use of suggested PGA values in the design codes and standards requires modification of the codes and standards themselves, as well as differentiated approach to defining the design level of PGA. Engineers should consider the dependence of the design PGA on the oscillation periods of structures, whereas seismologists should differentiate the PGA value depending on the prevailing period of the seismic effect. Transition to the new seismic scale affects the design and maximum design earthquakes differently. The intensity of a design earthquake for objects of massive structure does not exceed VII on the MSK scale, and in this aspect the new seismic scale does not differ considerably from the existing one. For maximum design earthquakes, PGA increases significantly, but the criterion of seismic resistance changes from acceleration of the structure to the work of plastic deformation forces. In this case, possible destruction depends little on PGA, but rather on such energy seismic effect characteristics as the Arias intensity, absolute cumulative velocity, and seismic energy density. A correct approach to calculation when carrying out the performance-based design and transition to the new intensity scale would not lead to higher costs for most buildings and structures. Moreover, if one does not use the new scale, transition to modern methods of performance-based design will be impossible.

Wave propagation modelling of induced earthquakes at the Groningen gas production site

Gas extraction from the Groningen natural gas field, situated in the Netherlands, frequently induces earthquakes in the reservoir that cause damage to buildings, and pose a safety hazard and a nuisance to the local population. Due to the dependence of the national heating infrastructure on Groningen gas, the short-term mitigation measures are mostly limited to a combination of spatiotemporal redistribution of gas production and strengthening measures for buildings. All options become more effective with a better understanding of both source processes and seismic wave propagation. Detailed wave propagation simulations improve both the inference of source processes from observed ground motions and the forecast of ground motions as input for hazard studies and seismic network design. The velocity structure at the Groningen site is relatively complex, including both deep high-velocity and shallow low-velocity deposits showing significant thickness variations over relatively small spatial extents. We performed a detailed 3-D wave propagation modelling study for an induced earthquake in the Groningen natural gas field using the spectral-element method. We considered an earthquake that nucleated along a normal fault with local magnitude of ML = 3. We created a dense mesh with element size varying from 12 to 96 m, such that with a dominant source frequency of 7 Hz, waveforms with a frequency content up to 10 Hz could be accurately modelled. The velocity/ density model is constructed using a 3-D geological model of the area, including both deep high-velocity salt deposits overlying the source region and shallow low-velocity sediments present in a deep and narrow tunnel valley. The results show that the 3-D density/velocity model in the Groningen area clearly plays a large role in the wave propagation and resulting surface ground motions, and causes significant lateral variations in site response. The highvelocity salt deposits have a dispersive effect on the radiated wavefield, reducing the seismic energy reaching the surface near the epicentre. In turn, the presence of low-velocity tunnel valley deposits can locally cause a significant increase in peak ground acceleration. Here we study induced seismicity on a local scale and use SPECFEM3D to conduct full waveform simulations and show how local velocity variations can affect seismic records. © The Author(s) 2018.

Numerical Study on the Seismic Performance of a Steel–Concrete Hybrid Supporting Structure in Thermal Power Plants

This paper presents the numerical investigation on the seismic performance of a steel–concrete hybrid structure consisting of reinforced concrete (RC) tubular columns and steel braced truss with A-shaped steel frames, which is a novel supporting structural system to house air-cooled condensers (ACC) in large-capacity thermal power plants (TPPs). First, the finite element (FE) modeling approach for this hybrid structure using the software ABAQUS was validated by a range of pseudo-dynamic tests (PDTs) performed on a 1/8-scaled sub-structure. The failure process, lateral displacement responses, changing rules of dynamic characteristic parameters and lateral stiffness with increase of peak ground acceleration (PGA) were presented here. Then, nonlinear time-history analysis of the prototype structure was carried out. The dynamic characteristics, base shear force, lateral deformation capacity, stiffness deterioration and damage characteristics were investigated. Despite the structural complexity and irregularity, both experimental and numerical results indicate that the overall seismic performance of this steel–concrete hybrid supporting structure meets the seismic design requirements with respect to the high-intensity earthquakes.

COMPARISON OF DISTRIBUTION OF LANDSLIDES TRIGGERED BY WENCHUAN, LUSHAN, AND LUDIAN EARTHQUAKES

All of the MS8.0 Wenchuan, MS7.0 Lushan, and MS6.5 Ludian earthquakes have triggered a large number of landslides. Due to differences in magnitude, geology, and topographical conditions, the distribution of seismic landslides vary widely. In this study, existing research results are combined to perform a contrastive analysis of seismic landslide distribution patterns based on three aspects:earthquake characteristics, geology, and topography. The following results are obtained. (1) The number and density of landslides due to the three earthquakes increase with the increase of peak ground acceleration(PGA) and magnitude. The number of landslides shows an increasing trend following an increase of intensity during the Wenchuan and Ludian earthquakes. However, the area affected by the relatively low-intensity Lushan earthquake also develops numerous landslides. (2) The maximum distance of influence of a geological fault on landslide distribution increases with the increase of magnitude. Within the range of 0.2 times of the maximum distance of influence, the Wenchuan earthquake has an 80% landslide distribution, whereas the other two earthquakes have only 30%. Moreover, the number of landslides decreases exponentially with distance of the Wenchuan earthquake from geological faults. (3) The distribution of seismic landslides is strongly influenced by topography. In the Ⅶ or higher intensity regions, the relief depth increases and earthquake-triggered landslides in high concentration areas have relatively higher relief. Furthermore, the slopes gradient with concentrated landslides can subsequently increase. Seismic landslides occur more frequently along mountain ridges and deep slopes in areas of higher relief, which may be related to the topographic amplification effect.

Seismic response of non-structural components attached to reinforced concrete structures with different eccentricity ratios

This paper presents average numerical results of 2128 nonlinear dynamic finite element (FE) analyses of lightweight acceleration-sensitive non-structural components (NSCs) attached to the floors of one-bay three-storey reinforced concrete (RC) primary structures (P-structures) with different eccentricity ratios. The investigated parameters include the NSC to P-structure vibration period ratio, peak ground acceleration, P-structure eccentricity ratio, and NSC damping ratio. Appropriate constitutive relationships were used to model the behaviour of the RC P-structures. The NSCs were modelled as vertical cantilevers fixed at their bases with masses on the free ends and varying lengths so as to match the vibration periods of the P-structures. Full dynamic interaction was considered between the NSCs and P-structures. A set of seven natural bi-directional ground motions were used to evaluate the seismic response of the NSCs. The numerical results show that the acceleration response of the NSCs depends on the investigated parameters. The accelerations of the NSCs attached to the flexible sides of the P-structures increased with the increase in peak ground acceleration and P-structure eccentricity ratio but decreased with the increase in NSC damping ratio. Comparison between the FE results and Eurocode 8 (EC8) predictions suggests that, under tuned conditions, EC8 provisions underestimate the seismic response of the NSCs mounted on the flexible sides of the plan-irregular RC P-structures.

A spatio-temporal model for probabilistic seismic hazard zonation of Tehran

A precondition for all disaster management steps, building damage prediction, and construction code developments is a hazard assessment that shows the exceedance probabilities of different ground motion levels at a site considering different near- and far-field earthquake sources. The seismic sources are usually categorized as time-independent area sources and time-dependent fault sources. While the earlier incorporates the small and medium events, the later takes into account only the large characteristic earthquakes. In this article, a probabilistic approach is proposed to aggregate the effects of time-dependent and time-independent sources on seismic hazard. The methodology is then applied to generate three probabilistic seismic hazard maps of Tehran for 10%, 5%, and 2% exceedance probabilities in 50 years. The results indicate an increase in peak ground acceleration (PGA) values toward the southeastern part of the study area and the PGA variations are mostly controlled by the shear wave velocities across the city. In addition, the implementation of the methodology takes advantage of GIS capabilities especially raster-based analyses and representations. During the estimation of the PGA exceedance rates, the emphasis has been placed on incorporating the effects of different attenuation relationships and seismic source models by using a logic tree.

Active seismic and passive microtremor HVSR for assessing site effects in Jammu city, NW Himalaya, India—A case study

Abstract 1-D shear wave velocity structure is important for site effect studies and geotechnical engineering, but it is quite difficult and expensive to derive from the conventional geophysical techniques. Active (MASW) and passive (microtremors, HVSR) methods were conducted at 30 sites in the frontal part of the Himalaya which is characterized by soft sediments and strong seismological effects. Shear wave velocity (Vs) in the range of ~ 238 m/s to ~ 450 m/s has been obtained from 30 m thick layer of quaternary sediments overlying Lower Miocene bed rock (Upper Siwalik Conglomerate) in Jammu city, NW Himalaya. The shear wave velocity (Vs) along with seismic input motion of Chamoli earthquake (mb 6.8) has been used to obtain site response spectrum. The response spectrum suggests five to seven times increase in peak ground acceleration for single or two storey buildings and by eight to twelve times increase in amplification ratio with respect to input ground motion. The amplification spectrum shows peak amplification of ~ 2 Hz–~ 3 Hz in the central part and ~ 1.75 Hz–2 Hz in the northern, southwestern and southeastern parts of the city. The advantage of microtremor HVSR is that it yields direct estimate of the fundamental frequency which is found to vary from ~ 1 Hz to ~ 3 Hz for same sites. Further, the 1-D velocity models obtained from ModelHVSR Matlab routine have been compared with the soil models prepared by derived using MASW. The comparison shows correlation between soil models for sites having high shallow impedance contrast between the overlying sediments and very stiff material (bedrock) underneath as than sites having less impedance contrast.

Directivity effects for moderate-magnitude earthquakes (Mw 5.6–6.0) during the 1997 Umbria–Marche sequence, central Italy

The Colfiorito Mw 6.0 (September 26, 1997, 09:40 UTC) and the Sellano Mw 5.6 (October 14, 1997) normal-faulting earthquakes are the two strongest events of the 1997–1998 Umbria–Marche seismic sequence (central Italy). They provided accelerograms recorded at epicentral distances within nearly two fault lengths. Previous studies on these events revealed clear evidence of unilateral rupture propagation and directivity effects on the source time functions. We developed an approximate procedure to correct the observed peak ground motion for the site effects, and we found a systematic increase of peak ground acceleration (PGA) and peak ground velocity (PGV) at sites located in the direction of the rupture propagation respect to the stations located to the backward. In particular we showed that, for the Colfiorito earthquake, the average PGV at the north-west sites is 2.8 times larger than the PGV at south-east sites (2.1 for PGA); an opposite behaviour is found during the Sellano earthquake, with an amplification factor of about 1.9 for PGV (1.5 for PGA) recorded at south-east sites respect to the north-west stations. We explained these behaviours in terms of directivity effect, by comparing recorded ground accelerations with synthetics simulated by a deterministic–stochastic technique. This method computes high-frequency ground motions ( f > 0.5 Hz) from extended faults, generalizing the point-source stochastic method to capture the essence of near-source effects. The synthetic PGAs decrease with distance in agreement with the ground-motion empirical predictive model available for the area and describe the azimuthal variation of recorded data in terms of source effects.

Strong Ground Motion in the Taipei Basin from the 1999 Chi-Chi, Taiwan, Earthquake

The Taipei basin, located in northwest Taiwan about 160 km from the epicenter of the Chi-Chi earthquake, is a shallow, triangular-shaped basin filled with low-velocity fluvial deposits. There is a strong velocity contrast across the basement interface of about 600 m/sec at a depth of about 600–700 m in the deeper section of the basin, suggesting that ground motion should be amplified at sites in the basin. In this article, the ground-motion recordings are analyzed to determine the effect of the basin both in terms of amplifications expected from a 1D model of the sediments in the basin and in terms of the 3D structure of the basin. Residuals determined for peak acceleration from attenuation curves are more positive (amplified) in the basin (average of 5.3 cm/sec 2 compared to −24.2 cm/sec 2 for those stations outside the basin and between 75 and 110 km from the surface projection of the faulted area, a 40% increase in peak ground acceleration). Residuals for peak velocity are also significantly more positive at stations in the basin (31.8 cm/sec compared to 20.0 cm/sec out). The correlation of peak motion with depth to basement, while minor in peak acceleration, is stronger in the peak velocities. Record sections of ground motion from stations in and around the Taipei basin show that the largest long-period arrival, which is coherent across the region, is strongest on the vertical component and has a period of about 10–12 sec. This phase appears to be a Rayleigh wave, probably associated with rupture at the north end of the Chelungpu fault. Records of strong motion from stations in and near the basin have an additional, higher frequency signal: nearest the deepest point in the basin, the signal is characterized by frequencies of about 0.3 – 0.4 Hz. These frequencies are close to simple predictions using horizontal layers and the velocity structure of the basin. Polarizations of the S wave are mostly coherent across the array, although there are significant differences along the northwest edge that may indicate large strains across that edge of the basin. The length of each record after the main S wave are all longer at basin stations compared to those outside. This increase in duration of ground shaking is probably caused by amplification of ground motion at basin stations, although coda Q (0.67 – 1.30 Hz) is slightly larger inside the basin compared to those at local stations outside the basin. Durations correlate with depth to basement. These motions are in the range that can induce damage in buildings and may have contributed to the structural collapse of multistory buildings in the Taipei basin.