Acceleration Response Spectra Research Articles

Comparison of Various Input Energy Spectra for the February 6th, 2023, Kahramanmaraş Earthquake Sequence

ABSTRACT This study aims to evaluate the success of various seismic input energy spectra equations in capturing the energy content of the ground motion records of the Türkiye earthquakes since the acceleration response spectra of some records exceeded the design spectra. Although most existing spectra had limited success, especially near the corner period, some recent equations yielded accurate results. Based on the obtained results, it is envisaged that the energy-based seismic design concept will have the maturity to be included in the next-generation seismic design codes as a reliable alternative to the current approaches.

Thermo-seismic performance of the novel thermal anchor pipe frame (TAPF) structure for supporting slope in earthquake-prone permafrost regions

The thermal anchor pipe frame (TAPF) structure is a new type of permafrost slope support technology, but its thermo-seismic characteristics are still unclear. In this paper, the coupled hydro-thermal-dynamic model of the thermal anchor pipe frame permafrost slope system is established. The cooling performance of the TAPF structure is investigated and the seismic responses are comparatively analyzed for different freeze-thaw periods. Results show that the presence of “elliptical” freezing cores with lower temperatures (which ranged from −3.94 to −5.36 °C) near the active layer at the end of the thawing period, which raised the permafrost table. The strip-shaped unfrozen moisture accumulation layer appears near the upper part of the thawing front at the highest temperature in the warm season. The peak acceleration response is the largest on October 15, 52.3% greater than the peak acceleration on April 15. The peak axial force of the thermal anchor pipe during the freezing period was 119 kN, which was 32.2% greater than that during the thawing period, and the peak total axial force after the earthquake appeared at the location of the freeze-thaw interface, and the axial force of the heat-transfer free section is greater than that of the anchored section. The frame structure is sensitive to earthquakes during the freezing period, and plastic bending damage may occur, especially at connection locations with thermal anchor pipes. Seasonal effects also have a strong influence on the shape of the acceleration response spectrum. The results can provide useful references for the maintenance and safe operation of permafrost slopes along the Qinghai-Tibet Project as well as for the seismic design of the new structure.

Design and Performance Assessment of Base Isolated Structures Supplemented with Vibration Control Systems

This paper investigates the implementation of supplemental vibration control systems (VCS) in base isolated (BI) structures, to improve their dynamic performance. More specifically, the aim of the VCS is to reduce the base displacement demand of BI structures, and at the same time mitigate the superstructure seismic responses. The purpose of the examined VCS is dual, and for this reason a multi-objective optimization methodology is formulated for the design of the VCS. The examined vibration absorbers include modifications of the KDamper concept. The KDamper is an extension of the traditional Tuned Mass Damper (TMD), and introduces a negative stiffness (NS) element to the additional oscillating mass of the TMD. The generated NS force is exactly in phase with the inertia force of the added mass, thus, artificially amplifying it. This way, lighter configurations are possible with an enhanced damping behavior. These VCS are designed based on engineering criteria and manufacturing constraints, while the excitation input used in the multi-objective optimization procedure is selected from a dataset of artificial accelerograms, designed to be spectrum-compatible with the EC8 design acceleration response spectrum. The effectiveness of the examined VCS is also assess with real near-fault earthquake records, and a comparison is performed with TMD-based VCS having 50 times larger additional masses. The numerical results demonstrate the superiority of the KDamper-based VCS in improving the dynamic behavior of BI structures over other mass-related systems (TMD).

Are the Italian microzonation level 2 abacuses applicable in the Friuli Venezia Giulia (Italy) plain? Comparison between the national abacuses and the numerically simulated amplification factors and between the derived elastic response spectra

Seismic shaking of an area is strongly affected by the local geology. The so-called local site effects must be considered for the estimation of seismic effects on structures and urban planning. Thus, the seismic microzonation is the process aimed at identifying and mapping the subsoil local response in a given area, usually at urban/municipality scale and in terms of ground shaking parameters and susceptibility to ground instabilities. In Italy, for areas that can be schematised as a 1D subsoil model (e.g. alluvial plain), a simplified approach is proposed to quantify the seismic amplification (amplification factor, AF). This approach consists of tables of correspondences, called seismic abacuses, available for the whole national area as well as for some regional territories, and derived for simplified subsoil models. In this work, the results of the comparison between the AF values retrieved from national abacuses applied in the Friuli Venezia Giulia (Italy) plain municipalities and those from 1D numerical simulations are presented. In general, the abacuses underestimate the local seismic site effects a part for sites with a shallow bedrock. No correlations/trends were identified between the AF derived from abacuses and those from numerical simulations. Moreover, considering the elastic acceleration response spectra, it emerges that in the 49.5% of the FVG analysed sites the abacuses approach, even though it underestimates the real seismic response, is a more suitable approximation compared to the soil class simplified approach proposed by the Italian regulation. Finally, what emerges is that the limit of 30 m, as indicated in the Italian regulation, to consider a deep or shallow bedrock seams underestimated, and the AFs are not correlated with the seismic bedrock depth when it is higher than 100 m.

Vertical Elastic Acceleration Response Spectra for Vrancea Intermediate-Depth Earthquakes

This study is focused on the evaluation of vertical elastic acceleration response spectra for Vrancea intermediate-depth earthquakes in Romania in the context of the ongoing update of the national seismic design code. The ground motion database employed in this research consists of about 500 ground motions recorded during moderate and large Vrancea intermediate-depth earthquakes with moment magnitudes MW ≥ 5.2. The analysis of the dataset showed that a single ground motion recording had a peak ground acceleration larger than 0.20 g. The results of the analyses showed that no significant differences between the control periods of the vertical elastic response spectra as a function of the site class could be inferred. It was also observed that the mean value of the amplification factor computed for the entire ground motion database was about 2.5, irrespective of the earthquake magnitude, site class, or level of horizontal peak ground acceleration. However, larger-magnitude earthquakes generate larger spectral amplifications in the medium- and long-period ranges. The analysis of the ground motions recorded in Bucharest area revealed a magnitude dependency of the control period for the vertical ground motion TC,v. Finally, a single spectral shape for vertical acceleration response spectra characterized by a maximum dynamic amplification factor of 2.5 and control periods TBv and TCv of 0.05 s and 0.60 s is proposed for design purposes. This aspect allows for a major update from the current version of the national seismic design code which proposes control periods of the elastic vertical response spectrum dependent on the horizontal ones. The short-period (at T = 0.2 s) and long-period (at T = 1.0 s) ratios of the vertical acceleration response spectrum to the corresponding horizontal ones are 0.50 and 0.40.

Nonlinear seismic response of seabed with terrain variation and seawater-seabed coupling

Understanding the seismic characteristics of submarine sites and conducting seismic response analysis for such locations are crucial for the safety of marine engineering. However, due to a shortage of strong motion records, the ground motion of offshore earthquakes has not yet been fully characterized. The actual seabed conditions are highly intricate, necessitating consideration of factors such as the dynamic coupling effect between seawater and seabed, the strong nonlinearity of seafloor soft sediments, and the diverse nature of natural submarine terrain. In this study, the modified Davidenkov dynamic constitutive model is used to simulate the nonlinear behavior of the soil. The Coupled Acoustic-Structure method is utilized to simulate the interaction between seawater and seabed. Three typical and simplified terrains, namely flat terrain, valley terrain, and hilly terrain, are individually modeled. The measured seafloor ground motions with different frequency components are used as bidirectional seismic excitations input from the bedrock. The amplification factor in terms of CAV is introduced to evaluate the amplification of seismic ground motion characteristics at seabed surface with respect to those at the bedrock surface. The acceleration response spectra in both horizontal and vertical directions, as well as the corresponding vertical-to-horizontal response spectral ratios, at the representative points are obtained, respectively. Several key findings are consistent with the features of the observed offshore and onshore earthquake ground motions. Numerical examples are presented to illustrate the different influence rules of terrain condition, overlying water depth, and seismic intensity on the nonlinear seismic response characteristics.

Dynamic Failure Experimental Study of a Gravity Dam Model on a Shaking Table and Analysis of Its Structural Dynamic Characteristics.

Investigating the dynamic response patterns and failure modes of concrete gravity dams subjected to strong earthquakes is a pivotal area of research for addressing seismic safety concerns associated with gravity dam structures. Dynamic shaking table testing has proven to be a robust methodology for exploring the dynamic characteristics and failure modes of gravity dams. This paper details the dynamic test conducted on a gravity dam model on a shaking table. The emulation concrete material, featuring high density, low dynamic elastic modulus, and appropriate strength, was meticulously designed and fabricated. Integrating the shaking table conditions with the model material, a comprehensive gravity dam shaking table model test was devised to capture the dynamic response of the model under various dynamic loads. Multiple operational conditions were carefully selected for in-depth analysis. Leveraging the dynamic strain responses, the progression of damage in the gravity dam model under these diverse conditions was thoroughly examined. Subsequently, the recorded acceleration responses were utilized for identifying dynamic characteristic parameters, including the acceleration amplification factor in the time domain, acceleration response spectrum characteristics in the frequency domain, and modal parameters reflecting the inherent characteristics of the structure. To gain a comprehensive understanding, a comparative analysis was performed by aligning the observed damage development with the identified dynamic characteristic parameters, and the sensitivity of these identified parameters to different levels of damage was discussed. The findings of this study not only offer valuable insights for conducting and scrutinizing shaking table experiments on gravity dams but also serve as crucial supporting material for identifying structural dynamic characteristic parameters and validating damage diagnosis methods for gravity dam structures.

Earthquake response evaluation of cylindrical latticed roofs supported by BRBs: Comparison of responses based on Chinese codes and Japanese regulations

The present study investigates the effectiveness of design strategies that induce yielding in the substructure of a single-layer latticed roof. The roof has a span of 28.9 m and a half-open angle of 30°. It is supported by a ductile substructure consisting of buckling-restrained braces (BRBs), and the substructure is designed to initiate yielding under a base shear coefficient of 0.40. The responses are analyzed using artificial earthquake motions corresponding to Chinese and Japanese design acceleration response spectra. The responses demonstrated that the dynamic amplification within the roof is considerably suppressed in comparison with a roof supported by elastic substructures. The negligible variance in the roof responses to the Japanese and Chinese spectra is also illustrated, suggesting the potential for reciprocal applicability of research results.

Dynamic Analysis of the Almagrera Tailings Dam with Dry Closure Condition

In light of growing concerns over sustainability, particularly in the wake of environmental disasters like the Aznalcollar dam break, the Spanish authorities have heightened their awareness of issues surrounding ore tailings management. The main aim of this paper is to study the dynamic behavior for the dry closure of the Almagrera dam under the action of an earthquake. This study was carried out with the Plaxis 2D v9.02 program, which uses the finite element (FE) method. The dynamic analysis of the dam was interpreted in terms of deformations, displacements and principal stresses. The construction of the Uniform Seismic Hazard Acceleration Response Spectrum (USHARS) and the selection of real accelerograms for the time-history dynamic calculations is a noted feature of this research. Numerical analyses show that the dam is safe enough because a failure surface has not been formed, although several plastic zones may appear in the dam. The FE study of deformations display that the tailings may attain large deformations, displacements and failure, although this does not jeopardize the safety of the dam where the displacements are smaller than 3 mm. Neither the tailings nor the dam are expected to suffer liquefaction. It was determined that the 0.09 g threshold value is not exceeded in the acceleration-time graphs on the old reservoir field surface, which is the most critical situation.

Estimation of structural dynamic response induced by individual sit-to-stand loading using acceleration response spectrum approach

Crowd sit-to-stand (STS) loading are always featured with pulse-like action, high crowd density and high synchronization rate among individuals, which may cause severe vibration comfort or even safety issues of supporting structures. However, related work in structural dynamics remains limited. As an early attempt, this study focuses on the individual STS loading and tries to develop an efficient tool to evaluate the potential dynamic response of the supporting structure when subjected to an individual STS action. Firstly, a comprehensive test campaign involving twenty participants was conducted by simultaneously footfall force measurement and 3D motion tracking of the human body. Secondly, the mathematical model of the individual STS loading was developed. Then a response spectrum framework that can give quick estimation of structural dynamic response induced by individual STS loading was proposed. The design response spectrum was formulated based on the measured force data. The effect of seat height, with or without armrests and the types of vibration assessment index on response spectrum was further discussed. The effectiveness of the method was finally verified on four full-scale structures having fundamental frequency from 2 Hz to 10 Hz subjected to individual STS actions.

Accessing Near-Field Strong Ground Motions Using a Multi-Scheme Method in the Kalawenguquan Fault, Xinjiang, China

The middle segment of the Kalawenguquan fault has been active since the Holocene, with a maximum credible earthquake magnitude of MS 7.5. We established two source models based on empirical relationships, as well as geological, geomorphological, and seismic characteristics. Taking into account the uncertainties of simulation parameters, we adopted the stochastic finite-fault method to calculate all combinations of a multi-scheme simulation. The effects of different source models, initial rupture points, and site locations on the prediction of ground motion parameters were analyzed. The results indicate that when a site is located on a smaller asperity and is a certain distance from the largest asperity, the simulation results are higher. For different sites, when the initial rupture point is located near the smaller rather than the larger asperity, the acceleration response spectra are higher. Our results show that the relationships between the initial rupture points, asperities, and sites have a significant impact on the simulation results. Therefore, our study highlights the relevance of determining the initial rupture point and source model to obtain a reasonable evaluation for near-field strong ground motion simulations at major infrastructures.

Response Characteristics of Irregular Continuous Rigid Frame Bridges with Long-Span and High-Rise Piers under Ground Motion Excitations with Different Fault Distances

An innovative seismic performance evaluation strategy for irregular rigid frame bridges with a long-span and high-rise piers under the action of ground motions with different fault distances is presented in this paper. A total of 129 mainshock records taken during the Wenchuan earthquake, from national seismic stations with different fault distances, were analyzed using statistical methods, to determine the attenuation characteristics of the intensity index of the Wenchuan earthquake records from the perspective of aseismic engineering, and the attenuation of the acceleration response spectrum is discussed. The Miaoziping Bridge on the Dujiangyan–Wenchuan Expressway, which was damaged in the Wenchuan earthquake, is taken as the analysis background; two sets of samples for long-span continuous rigid frame bridges with different pier heights are constructed, to discuss the seismic response characteristics of continuous long-span rigid frame bridges; and representative values for the natural periods of these two bridge structural groups are subsequently compared and analyzed. After the peak responses for various bridges with various pier heights are determined through a response spectrum analysis under the action of ground motions with different fault distances, and the surfaces for the obtained peak responses are fitted and the response characteristics for different fault distances are discussed. It is shown in the results that the seismic response characteristics of the continuous rigid frame bridges with long-span and high-rise piers were significantly different under the action of the ground motions with different fault distances, and the seismic responses of these two bridge groups were distinctly larger under the action of near-fault ground motions. Furthermore, based on the above research, suggestions for the pier arrangement and bridge site selection for continuous rigid frame bridges with long-span and high-rise piers are also discussed. The results of this paper also provide some theoretical guidance for the sustainable development of bridges with long-span and high-rise piers, from the perspective of bridge seismic response characteristics.

Dynamic soil-structure interaction analysis for base-isolated nuclear island building based on the method of external source wave motion

Soil-structure interaction (SSI) is crucial to the dynamic response of nuclear power plants (NPPs), and should be properly considered when analysing the seismic isolation performance of base-isolated NPPs. In this study, a three-dimensional numerical simulation program is developed for the time-domain dynamic analysis of base-isolated NPPs considering SSI effects. The seismic input is realised using the method of external source wave motion, and the nonlinear behavior of isolators is fully considered. Using this program, the SSI effects of the base-isolated nuclear island building under different sites are analysed and compared, including the acceleration, displacement, and floor response spectra. The numerical results show that the SSI effects change the spectral characteristics of the actual seismic input. When the shear wave velocity of the site is relatively large, the SSI effects can increase the dynamic response of base-isolated NPPs. Additionally, the isolation performance of the base-isolated NPPs is weakened when SSI effects are considered, and with a decrease in the shear wave velocity of the site, the isolation capacity is further reduced. The influence of the SSI effects should be fully considered in the base isolation design of NPPs.

Influence of near-fault velocity pulse on the seismic response of subway station structure

This research aims to explore the influence of near-fault velocity pulse on the seismic response of subway station under the condition of acceleration response spectra being consistent. Two suites of seismic motions are utilized, one suite is twelve as-recorded seismic motions with velocity pulses, and the other one suite is the corresponding artificial seismic motions synthesized with the response spectra of seismic motions in the first suite as target spectra. For each seismic motion with velocity pulse, the corresponding synthetic seismic motion without velocity pulse is generated by using the method of superimposing narrow-band time histories. Numerical model of soil-subway station interaction is developed by using the commercial software ABAQUS with a practical 3-span, 3-story subway station as the prototype. Numerical results indicate that with the engineering sites change from hard to soft and the burial depths change from shallow to deep, the adverse effect of velocity pulse is more significant, and the maximum inter-story drift ratio of subway station with a burial depth of 20 m embedded in site classes I, II and III has increased by 16.5%, 20.1% and 21.7%, respectively. However, the influence of velocity pulse on the concrete compression damage of subway station is not obvious.

Study on the dynamic characteristics of pile wharves subjected to underwater explosion

A test was conducted to investigate the dynamic response characteristics and damage modes of pile wharves subjected to underwater explosions. To simulate the explosion process, a fluid-solid coupling finite element model of the pile wharf was constructed. The structural damage process, response characteristics, and failure modes of the pile wharf were analyzed based on the experimental and numerical simulation results. The results showed that the main damaged components of the pile wharf were the piles, with damage modes of cracks, spalling, and brittle shear. The probability of moderate or more significant damage to the inclined piles was 25% higher than that of the vertical piles. The inclined piles with low deformation ability were more prone to local concrete brittle failure, significantly increasing the possibility of instability and failure of the pile wharf structure. The acceleration response spectrum indicated that although the structure of the pile wharf was severely damaged, the personnel on its surface slab still had a high probability of survival. The study indicates that replacing inclined piles with alternative optimized structures benefits the blast resistance of pile wharves.

Stochastic simulation of earthquake ground motions based on improved finite-fault model

In the seismic reliability analysis of engineering structures, it is often necessary to adopt stochastic ground motions as inputs. However, the current methods used to generate stochastic samples, such as the spectral representation method, the spectral transfer method, the dynamic source method, the physical source method, and the comprehensive method, etc., are not very convincing since they do not contain the complete information of seismic occurrence and propagation. In this study, an improved finite-fault model for stochastic simulation of ground motions is proposed. Compared to existing stochastic finite-fault model, the improved model considers the propagation law of phase spectrum, local site effect, and the impact of wave velocity on the arrival time of seismic waves. Besides, identification and statistics of model parameters are carried out based on ground motion records. Reasonable samples of stochastic ground motions are then obtained. In addition, parameter sensitivity analysis is conducted to determine critical random variables, which reduces the complexity of stochastic simulation. Simulation results are compared with recorded accelerograms from the 1999 Chi-Chi earthquake. It is shown that the improved stochastic finite-fault model is reliable, and the acceleration response spectra of simulated samples are consistent with those of station records collected at various site classes and the design spectra.

Dynamic Response of Pile-Raft Systems with Various Forms of Connection under Cyclic Condition

This study aimed to examine the aseismic performance of the pile-raft systems with various connection forms. The related shaking table test and numerical simulation were performed for in-depth investigation. The acceleration response spectra on the top of the soil layer and raft were obtained and plotted for contrastive analysis based on the model test at a reduced scale of 1 : 30 and finite element numerical simulation. Accordingly, the working mechanisms of the pile-raft systems in conventional connections with the embedment of the compressible blocks and cushion layers under cyclic loading were explored. The results showed that the embedment of the cushion layer on the pile top could most significantly mobilize the potential of the foundation soil, effectively reduce the bending moment peak of the pile, and reduce the acceleration amplification effect on the top of the soil layer and raft. The embedment of the compressible block on the pile top most markedly reduced the bending moment peak of the pile and effectively mobilized the potential of the foundation soil, which was most favorable for lowering the amplification effect of acceleration on the top of the soil layer and raft.

An ameliorative duration of pulse-like ground motion records for nonlinear structural analysis

The near-field pulse-like ground motion contains obvious long-period and large pulse characteristic, which makes the nonlinear response of the structure exceed the general prediction of seismic response results. In order to reserve the obvious pulse component while selecting the strong ground motion duration part of the near-field pulse-like ground motion record without causing a large loss of spectral characteristics, the paper proposes an ameliorative truncated strong ground motion duration—useful duration. It is proposed based on the elastic acceleration response spectrum. Its principle is to make the acceleration response spectrum corresponding to useful duration and that corresponding to the original ground motion record as close and consistent as possible. The research results show that from the perspective of elastic response spectrum matching, the response spectrum matching error corresponding to useful duration is smaller than that of significant duration. In addition, the five types of periods corresponding to useful duration are closer to the period of original ground motion. Ulteriorly, from the displacement ratio spectrum of the elasto-plastic single-degree-of-freedom system, it is found that the average value of the elasto-plastic displacement ratio spectrum of useful duration and the original ground motion record is 0.98, which is very close to 1.00. It shows that the truncated ground motion can be used to replace the original ground motion to fully predict the nonlinear response of typical structures. Additionally, the effectiveness is further verified in the nonlinear response of three reinforced concrete frame structures, and the nonlinear response results of the structures are calculated using the time-history of useful duration, with less discreteness.

The prediction of seismic amplification effect in three-dimensional sedimentary basins and its application

Numerous studies have shown that the basin amplification effect is influenced by characteristic parameters such as basin geometry and media impedance contrast, but quantitative analysis of the effect for three-dimensional (3D) basins is still rare. In this paper, the basin amplification effect is quantified through an aggravation factor (AGF ), which is defined as the ratio between 3D and 1D acceleration response spectra along the basin surface. Considering the 3D geometry of the actual basin, we investigate the sensitivity of aggravation factors to inclination angles, shape ratios, and impedance contrasts by establishing 78 3D trapezoidal sedimentary basin models with different characteristic parameters. Furthermore, we perform a statistical analysis of the aggravation factors and propose their prediction formulas, which are applied to the Euroseistest basin and the Shidian basin. The above analysis reveals that: (1) The effects of inclination angle and shape ratio on the aggravation factor are concentrated in the edge part and central part of the basin, respectively, while the impedance contrast has less influence on the aggravation factor along the basin surface; (2) From the prediction results for the Euroseistest basin, the aggravation factor of the 3D model is higher than that of the 2D model with a maximum error of 22%, while the distribution pattern of the aggravation factor along the surface is similar; and (3) The predicted results for the Shidian basin show that the basin with a small inclination angle has a larger aggravation factor in the edge part and even exceeds the central part; for example, the highest aggravation factor is 2.155 in the edge part of the basin with an inclination angle of 6°.

Comparison of a tailings material and a natural sand in seismic site response analyses

This article investigates the seismic response of a tailings sand material in the context of site response analysis. The computed response is contrasted with that obtained for an equivalent deposit consisting of a well-characterised natural sand. Initially, the fundamental properties of both materials are used to interpret and compare their behaviour in the framework of Critical State Soil Mechanics (CSSM). Subsequently, both materials' monotonic and cyclic responses are calibrated for an advanced bounding surface plasticity model. Finally, the impact of different calibration approaches is examined through site response analyses under a strong motion. This process identifies fundamental differences between the two geo-materials, impacting the single elements simulations, especially the accuracy of undrained cyclic triaxial tests. The site response analyses examined herein show the impact of the calibrations adopted for both materials in terms of acceleration response spectra, displacements, and excess of pore water pressures (PWP). Although a relatively deep phreatic surface is adopted, the cyclic resistance and permeability of both materials plays a dominant role in the site response characteristics, controlling the excess PWP generation and hence the non-linear behaviour in the soil deposit. Finally, parametric studies are also conducted to explore the impact of permeability of the sands in the site response.