Terms Of Acceleration Research Articles

Operational Modal Analysis, Model Update and Fragility Curves Estimation, through Truncated Incremental Dynamic Analysis, of a Masonry Belfry

Masonry towers, located in seismic zones, are vulnerable and prone to damages up to compromise their stability. The scatter of data on the mechanical properties of masonry, geometry and boundary conditions determine a lack of building knowledge on their expected behaviour. Therefore the assessment of the seismic capacity represents a critical task. This paper contributes to the issue of seismic analysis of masonry towers, focusing a meaningful case study: the St.Silvestro belfry in L’Aquila, Italy. The tower, severely damaged by the 2009 earthquake sequence, underwent extensive restoration works, endeavoured to mitigate its vulnerability. The observed seismic damage, the performed no-destructive testing campaign and the accomplished rehabilitation measures are described in the paper. The authors appraised the actual seismic performances of the St.Silvestro belfry, reinforced by the last restoration works. At first, the Operational Modal Analysis (OMA) is carried out to enhance building knowledge. In a second step, a refined finite element model is calibrated on the results from OMA to seize the actual dynamic response. Ultimately, by using the updated finite element model, the authors estimate the fragility curves in terms of peak ground acceleration using truncated incremental dynamic analyses.

Probabilistic seismic hazard mapping of National Capital Region of India using a modified gridded seismicity model

This is the first comprehensive study for a seismic macro-zonation of the National Capital Region of India by using the probabilistic seismic hazard analysis approach. A modified gridded seismicity model is used for this purpose, in which the earthquake occurrence rates obtained using the Gutenberg-Richter's (G-R) relationships for conventional area type seismic sources are distributed non-uniformly among a grid of cells. This provides a more robust approach than the commonly used weighted sum of area sources of homogeneous seismicity and the zone-free smoothed gridded seismicity. Other distinguishing features of the present analysis include: detailed seismotectonic evaluation of the region to identify seven area type seismic sources, compilation of a comprehensive earthquake catalogue for the estimation of seismicity recurrence parameters, selection of the most appropriate ground motion prediction equation by using a database of 71 strong motion accelerograms recorded in the region, and estimation of the compatible distance parameters by associating a fictitious fault rupture plane to each grid cell with appropriate strike and dip angles. Hazards maps are prepared for the hard rock site condition in terms of the peak ground acceleration and the 5%-damping acceleration response spectrum amplitudes for several combinations of natural periods and return periods. A simple empirical approach is also developed to obtain amplification factors for modifying the uniform hazard response spectra for the rock sites to those for the soil sites with a given VS30 value. The hazard estimates from this study are found to be somewhat higher with greater site-to-site variations as compared to those from the earlier studies.

On the influence of earthquakes and soil characteristics on seismic response and performance of isolated bridges

Seismic isolation technology is an effective means of reducing seismic risk and enhancing the structural seismic performance. However, some parameters, such as earthquake inputs and soil characteristics, affect and mitigate the efficiency of this technology. The main purpose of this study is to investigate the simultaneous effects of different records and flexible soils on isolated bridges. To this end, an isolated bridge is assumed to be at different distances from the ruptured fault (Rrup) in order to represent near-fault (NF) and far-field (FF) situations. These records are extracted on different soils, which are categorized based on their shear velocity, to represent different soil behaviours and characteristics. Nonlinear time history analysis (NTHA) is carried out on a typical isolated bridge model using the SAP2000 software. Responses in terms of deck acceleration, base shear, displacement of the isolation system, and the performance of the isolation units are studied. Results demonstrate that for NF zones, the soil effects must absolutely be taken into account. In soft soils, all seismic responses are amplified, leading to higher forces and displacement demands. In such zones, failing to consider this fact during the design process results in largely underestimated seismic displacement and force demands for the isolated bridge system, seriously harming its seismic performance. Likewise, the amplification of responses in soft soils is observed for FF records and it should be considered for these prone areas. However, despite their importance, these records are not as destructive as NF records for isolated bridges on soft soils.

A Novel Shock Absorber with the Preload and Global Negative Stiffness for Effective Shock Isolation

A novel shock absorber with the preload structure and global negative stiffness is proposed for the shock isolation of sensitive systems. The novel shock absorber is composed of a linear spring and permanent magnet sets. The preload force and negative stiffness region are related to the attractive force between permanent magnet sets. The aim of this paper is to investigate the shock isolation performance of the novel shock absorber. Firstly, a static analysis of the novel shock absorber is carried out. Secondly, the motion stability of the NSA is analyzed by the Jacobian Matrix and the shock response is calculated numerically compared with the conventional preload structures. Finally, the shock test of the novel shock absorber is completed to verify the above results. It is found that the novel shock absorber could be advantageous in improving shock isolation in terms of relative displacement and absolute acceleration compared with conventional preload structures.

Seismic Response of Flat Ground and Slope Models through 1 g Shaking Table Tests and Numerical Analysis

In order to verify the reliability of numerical analysis, a series of 1 g shaking table tests for flat ground and slope were conducted using a laminar shear box subjected to different seismic waves. Firstly, numerical analyses, using the DEEPSOIL and ABAQUS software, were done to compare the results of flat ground experiments. After that, finite element analyses with ABAQUS were conducted to compare the results of slope experiments. For numerical analyses, considering the influence of the boundary, the concept of adjusted elastic modulus was proposed to improve the simulation results. Based on the analyses, it is found that in terms of acceleration-time history and spectral acceleration, the numerical analysis results are in good agreement with the experiment results. This implies that numerical analysis can capture the dynamic behavior of soil under 1 g shaking table test conditions.

Dynamic response of asphalt pavement under vibration rolling load: Theory and calibration

Vibrating compaction is a critical procedure to guarantee the quality of asphalt pavement, and the dynamic response of asphalt pavement is a complicate problem in the process of vibration rolling. This paper aims to theoretically investigate the dynamic response regulation and influencing factors of pavement under the moving vibration load. Firstly, based on the viscoelastic theory of multi-layer system, the dynamic response governing equation of asphalt pavement is established under the vibration load, the governing equation was then simplified by the two-dimensional Fourier transform method. Further, the stiffness matrices of the single-layer and multi-layer pavement structures are obtained by using the dynamic stiffness method. Consequently, the exact solution is obtained for the plane strain problem by programming and validated with the finite element results, which is proved to be more efficient in the calculation. Moreover, the model is calibrated by the field test to determine the wave number and dynamic modulus during the vibration rolling process. Subsequently, the effects of material and load frequency are investigated on the dynamic response in terms of acceleration and displacement. The results show that both of the acceleration and displacement of pavement surface vibrate periodically with the vibrating load, and the changing regulations of the acceleration and displacement with loading time can be divided into three stages corresponding to the engineering practice such as rapid decline, slow decline and stable stages. Finally, the influencing factors are analyzed in terms of the modulus of materials (i.e., surface course and base course) and the frequency of load. It shows that the peak values of acceleration and displacement of the pavement surface change significantly and nonlinearly with the material modulus in the form of power function. Meanwhile, the influence of vibrating frequency is also significant and a quadratic relationship between the acceleration/displacement and frequency. This paper provides an insight into understanding the dynamic response of pavement under vibration rolling condition to some extent, and potentially provides theoretical and technical support for accurately determining and modifying some indexes that characterize the compaction degree of asphalt pavement.

Probabilistic seismic hazard assessment studies for Mumbai region

The present study attempts to understand and assess the seismic hazard of Mumbai using probabilistic seismic hazard analysis (PSHA) with an updated catalogue of earthquake clubbed with recent knowledge on seismotectonics of the region. An updated catalogue of instrumental and pre-instrumental earthquake data within 300 km radius around the city has been compiled from different sources. The PSHA has been computed using two different seismic source models, viz., a fault (linear) and zone model (areal). A hybrid of five suitable ground motion prediction models (GMPM) consisting of widely accepted and latest GMPMs is used to compute the PSHA of Mumbai. The results obtained from different methodologies are integrated with logic tree approach to minimize the epistemic uncertainties in hazard calculation. Probabilistic seismic hazard maps in terms of peak ground accelerations (PGA) at bedrock levels for 2% and 10% probability of exceedance in 50 years are developed for Mumbai. Uniform hazard response spectrum (UHRS) on bedrock at eight different sites within Mumbai for spectral periods of 0.01—2 s is also computed. The low seismic hazard is observed and reasonably compared with the previous PSHA studies done for Mumbai region.

Dynamic response of dry cask storage systems for spent nuclear fuel to near field blast loading

Dry storage casks are the most common form of spent nuclear fuel (SNF) storage in the United States. An explosion near a spent nuclear storage facility poses a serious public risk due to the potential of radioactive leakage. In this study, for the first time, the structural performance of vertical steel–concrete-steel sandwich (SCSS) and reinforced concrete (RC) casks under blast loading scenarios is studied using explicit finite element simulations considering material and geometric nonlinearity and strain rate effects. The response of the cask is investigated in terms of stress levels, deformations, and peak accelerations. The conventional weapons (CONWEP) model was used to induce a blast load on the structure at varying blast charges. The accelerations experienced by the canister and the fuel assemblies, which are critical for design are estimated. The inherent vibration damping characteristics of the cask are evaluated, and a novel damper configuration is proposed to improve the energy dissipation capacity of the system. The results showed that the general integrity of the cask could be preserved in the presence of a thick reinforced concrete layer. However, due to the lack of a damping mechanism, the blast wave can propagate through the system and result in very large accelerations in the canister and the fuel assemblies. Results also revealed that the SCSS configuration has a more ductile response compared to the RC design. The results of this study could be used for the safety evaluation and design optimization of current casks in service and other cylindrical composite containment structures.

Integration of automated vehicles in mixed traffic: Evaluating changes in performance of following human-driven vehicles

The introduction of Automated Vehicles (AVs) into the transportation network is expected to improve system performance, but the impacts of AVs in mixed traffic streams have not been clearly studied. As AV’s market penetration increases, the interactions between conventional vehicles and AVs are inevitable but by no means clear. This study aims to create new knowledge by quantifying the behavioral changes caused when conventional human-driven vehicles follow AVs and investigating the impact of these changes (if any) on safety and the environment. This study analyzes data obtained from a field experiment by Texas A&M University to evaluate the effects of AVs on the behavior of a following human-driver. The dataset is comprised of nine drivers that attempted to follow 5 speed-profiles, with two scenarios per profile. In scenario one, a human-driven vehicle follows an AV that implements a human driver speed profile (base). In scenario two, the human-driven vehicle follows an AV that executes an AV speed profile. In order to evaluate safety, these scenarios are compared using time-to-collision (TTC) and several other driving volatility measures. Likewise, fuel consumption and emissions are used to investigate environmental impacts. Overall, the results show that AVs in mixed traffic streams can induce behavioral changes in conventional vehicle drivers, with some beneficial effects on safety and the environment. On average, a driver that follows an AV exhibits lower driving volatility in terms of speed and acceleration, which represents more stable traffic flow behavior and lower crash risk. The analysis showed a remarkable improvement in TTC as a result of the notably better speed adjustments of the following vehicle (i.e., lower differences in speeds between the lead and following vehicles) in the second scenario. Furthermore, human-driven vehicles were found to consume less fuel and produce fewer emissions on average when following an AV.

Effect of Long-Distance Earthquake from Philippines and Sulawesi to Sabah Region

Sabah is known for its active earthquake activities, especially in Ranau, Kudat and Lahad Datu areas. The effects of local earthquake can reach M W 6.0. Furthermore, Sabah was also hit by earthquakes from neighbouring countries such as Sulawesi and Philippines. These countries produce highly active earthquakes that can reach as high as M W 8.6. The increase in the frequency of earthquakes is one of the concerns of the Sabah government for the safety of its people because most people live in concentrated areas near the coast. This study shows the effects of major earthquakes from the Philippines and Sulawesi which have been recorded between 1900 to 2020 and analyzed in terms of peak ground acceleration (PGA). The eastern region of Sabah is adopted in the analysis for the effect of long-distance earthquakes, as these areas are close to both countries. The analysis uses standard seismic hazard assessment procedure with compilation magnitudes greater than M W 5.0. In the final analysis, it is shown that the effects of large earthquakes from both countries are relatively small compared to the effects of local earthquakes.

Shaking table test of a 1:10 scale thermal power plant building equipped with passive control systems

The seismic performance of electric power system is of paramount importance to maintain functionality of the served urban communities after earthquakes. Passive control techniques are widely accepted as effective measures to improve the seismic resilience of structural buildings. In this study, an actual thermal power plant building characterized by mass and vertical irregularities was studied. For a comparison purpose, two different design schemes in which one adopted the conventional steel braced frame scheme and the other retrofit one endowed with heavy equipment isolation and metallic dampers were considered. Shaking table tests were conducted to investigate the seismic performance of the two cases. The test models were designed and constructed based on the similitude law with a length scale factor of 1/10. Extensive test scenarios were performed with three ground motion pairs taken as inputs. The seismic responses between the conventional model and the retrofit model are compared in terms of tier drift, floor acceleration, base shear and damage observations. The experimental results indicated the effectiveness of employed passive control strategies in mitigating tier drift and base shear responses. The detrimental effects induced by heavy coal bunkers were addressed by using isolation technique. The results validated the metallic dampers have limited control effect in floor acceleration response and the effect is dependent on the seismic input. Discussions were made at the end regarding the scaling effect on the test results and cost-benefit of using passive control devices for the thermal power plant building.

The use of Stick‐IT model for the prediction of direct economic losses

AbstractThe Stick‐IT model (Stick for Infilled frames Typologies), that is a MDOF system consisting of a series of lumped masses connected by nonlinear shear link elements, was introduced to predict the response, in terms of interstory drift ratio (IDR) and peak floor acceleration (PFA), for infilled RC building typologies. Stick model parameters can be defined starting from low level building geometrical features, easily retrievable at the large scale, such as in plan dimensions, number of stories or the percentage of infills openings and considering the infills consistency. This paper investigates the applicability of Stick‐IT to predict the performance and direct economic losses for existing RC infilled frame type buildings. In the framework of a performance‐based assessment, the comparison of seismic‐loss outcomes provided by using either a detailed finite element model (FEM) (L1) or simplified Stick‐IT structural models (L2) are illustrated and discussed. The potential of Stick‐IT model is investigated referring to a real building damaged and repaired after the 2009 L'Aquila earthquake and adopting as earthquake input records registered in the proximity of the building. Story‐level building damage simulated by L1 and L2 models is compared to real damage, showing satisfactory prediction. The comparison of the real repair costs with those evaluated using L1 and L2 models provides encouraging validation. The application suggests that simplified models such as Stick‐IT, despite the low level of information required for its application, can be usefully applied to perform damage and loss scenarios at the large scale. Matlab code to generate the Stick‐IT, as well as the example code for the present study, are openly shared through the repository https://github.com/marcogaetanidaragona/Stick-IT.

"Efficiency Comparison of Algorithms for Finding Determinants Via Permutations "

"Determiners have been used extensively in a selection of applications throughout history. It also biased many areas of mathematics such as linear algebra. There are algorithms commonly used for computing a matrix determinant such as: Laplace expansion, LDU decomposition, Cofactor algorithm, and permutation algorithms. The determinants of a quadratic matrix can be found using a diversity of these methods, including the well-known methods of the Leibniz formula and the Laplace expansion and permutation algorithms that computes the determinant of any n×n matrix in O(n!). In this paper, we first discuss three algorithms for finding determinants using permutations. Then we make out the algorithms in pseudo code and finally, we analyze the complexity and nature of the algorithms and compare them with each other. We present permutations algorithms and then analyze and compare them in terms of runtime, acceleration and competence, as the presented algorithms presented different results.

Evaluation of seismicity of Karachi city in the context of modern building codes

Spectral acceleration is representative of seismic hazard in modern building codes as well as an important parameter used in seismic design these days. Karachi, an economic artery of Pakistan, is located in the vicinity of an active tectonic setting, i.e., triple junction, with uncertain seismicity. Keeping in view the modern seismic design practices, efforts are required to evaluate the seismic hazard of Karachi city in terms of spectral acceleration. This study is focused on the estimation of seismic hazard for the metropolitan city of Karachi in the context of modern building codes. The seismic potential of around 800–900-km circle was considered a threat for the city, and 13 seismic zones (A-1 to A-13) were identified as seismic sources. A seismicity model based on Gutenberg-Richter law was developed, identifying A-1 and A-11 as zones of high seismicity. The ground attenuation model recommended for the Middle East region proposed by Akkar and Bommer was utilized for the computation of different ground motion scenarios. Short-period, SS, and 1-s, S1, spectral acceleration values for considered region were calculated as 1.37 m/s2 and 0.41 m/s2, respectively. In addition, peak ground acceleration (PGA) values for Karachi city were observed to be in a range of 0.7–0.77 m/s2. The results of this study provide bases for the preparation of seismic risk maps, the estimation of earthquake insurance premiums, seismic zonation for region lying on Arabian and Indian plates, and the preliminary site evaluation of critical facilities.

Accidental Injuries Caused by Automotive Frontal Collision

ABSTRACT This study aimed to use a simulated vehicle to asses quantitatively the head and neck injuries of the occupants, in a frontal car crash, when the driver has only one hand on the steering wheel, such as while using a cell phone when driving. First, we conducted a survey of NHTSA reports on real laboratory tests of frontal collisions involving sedans. The effects of these collisions on the neck of a Hybrid III 50th percentile male crash test dummy were measured in terms of average head acceleration and force along the X, Z, and Y-axes. These acceleration, force and torque values obtained from the NHTSA database were used to validate the simulated model. The results obtained were compared with case E, the standard dummy position used in frontal collision tests. The results obtained in the simulation of the four cases of driving with only one hand demonstrate a probability of more than 67% that the driver will sustain AIS+2 injuries during a frontal crash. In all the cases, the skull fracture percentage was the most representative, occurring between 89 and 94% of cases where the driver had only one hand on the steering wheel.

Enhanced Seismic Structural Reliability on Reinforced Concrete Buildings by Using Buckling Restrained Braces

The control of vibrations and damage in traditional reinforced concrete (RC) buildings under earthquakes is a difficult task. It requires the use of innovative devices to enhance the seismic behavior of concrete buildings. In this paper, we design RC buildings with buckling restrained braces (BRBs) to achieve this objective. For this aim, three traditional RC framed structures with 3, 6, and 9 story levels are designed by using the well‐known technique nondominated sorting genetic algorithm (NSGA‐II) in order to reduce the cost and maximize the seismic performance. Then, equivalent RC buildings are designed but including buckling restrained braces. Both structural systems are subjected to several narrow‐band ground motions recorded at soft soil sites of Mexico City scaled at different levels of intensities in terms of the spectral acceleration at first mode of vibration of the structure Sa(T1). Then, incremental dynamic analysis, seismic fragility, and structural reliability in terms of the maximum interstory drift are computed for all the buildings. For the three selected structures and the equivalent models with BRBs, it is concluded that the annual rate of exceedance is considerably reduced when BRBs are incorporated. For this reason, the structural reliability of the RC buildings with BRBs has a better behavior in comparison with the traditional reinforced concrete buildings. The use of BRBs is a good option to improve strength and seismic behavior and hence the structural reliability of RC buildings subjected to strong earthquake ground motions.

Seismic Acceleration and Displacement Demand Profiles of Non-Structural Elements in Hospital Buildings

The importance of non-structural elements in performance-based seismic design of buildings is presently widely recognized. These elements may significantly affect the functionality of buildings even for low seismic intensities, in particular for the case of critical facilities, such as hospital buildings. One of the most important issues to deal with in the seismic performance assessment of non-structural elements is the definition of the seismic demand. This paper investigates the seismic demand to which the non-structural elements of a case-study hospital building located in a medium–high seismicity region in Italy, are prone. The seismic demand is evaluated for two seismic intensities that correspond to the definition of serviceability limit states, according to Italian and European design and assessment guidelines. Peak floor accelerations, interstorey drifts, absolute acceleration, and relative displacement floor response spectra are estimated through nonlinear time–history analyses. The absolute acceleration floor response spectra are then compared with those obtained from simplified code formulations, highlighting the main shortcomings surrounding the practical application of performance-based seismic design of non-structural elements. The absolute acceleration floor response spectra are then compared with those obtained from simplified code formulations. The results, both in terms of absolute acceleration and relative displacement floor response spectra, highlighted the influence of the higher modes of the structure and the inaccuracy of the code provisions, pointing out the need for more accurate simplified methodologies for the practical application of performance-based seismic design of non-structural elements.

Compilation of the seismic hazard maps in Bosnia and Herzegovina

Bosnia and Herzegovina is located in the center of the Western Balkans. Until 2018 Bosnia and Herzegovina used the hazard maps based on the macroseismic intensity. The first generation of probabilistic seismic hazard maps of Bosnia and Herzegovina is compiled and presented. Two seismotectonic models were created, the areal and linear (fault) together with the earthquake catalogue filtered out from foreshock and aftershock events. Hazard maps were constructed in terms of the peak ground acceleration, and presented in two maps, with an exceedance on average once in 95 or 475 years. The hazard map used for the design of earthquake-resistant buildings (return period of 475 years with a probability of exceedance of 10% in 50 years) is created for the ground type A with the velocity of the seismic wave propagations of vs,30 = 800 m/s. These maps have been accepted as a part of the National Annex in BAS EN 1998–1:2018.

Numerical Modelling of Structures Adjacent to Retaining Walls Subjected to Earthquake Loading

In an urban environment, it is often necessary to locate structures close to existing retaining walls due to congestion in space. When such structures are in seismically active zones, the dynamic loading attracted by the retaining wall can increase. In a novel approach taken in this paper, finite element-based numerical analyses are presented for the case of a flexible, cantilever sheet pile wall with and without a structure on the backfill side. This enables a direct comparison of the influence exerted by the structure on the dynamic behaviour of the retaining wall. In this paper, the initial static bending moments and horizontal stresses prior to application of any earthquake loading are compared to Coulomb’s theory. The dynamic behaviour of the retaining wall is compared in terms of wall-top accelerations and bending moments for different earthquake loadings. The dynamic structural rotation induced by the differential settlements of the foundations is presented. The accelerations generated in the soil body are considered in three zones, i.e., the free field, the active and the passive zones. The differences caused by the presence of the structure are highlighted. Finally, the distribution of horizontal soil pressures generated by the earthquake loading behind the wall, and in front of the wall is compared to the traditional Mononobe-Okabe type analytical solutions.

Multihazard framework for investigating high‐rise base‐isolated buildings under earthquakes and long‐duration winds

AbstractJapan experiences a considerable number of low to medium earthquake shocks and long‐duration winds throughout the year, which is relatively more as compared to other different regions of the world. Considering this multihazard scenario, structures designed using the existing guidelines may have significant chances to underestimate the induced distress level in the structure as well as in the energy dissipation devices, which are designed based on traditional peak variables neglecting accumulation of damage. To overcome the shortcoming of the existing assessment technique, a multihazard framework is formulated that deals in estimating probable number of earthquakes and long‐duration winds likely to occur in the design life of a structure. The sequence of design earthquakes and long‐duration winds obtained through the proposed methodology is subsequently implemented in base‐isolated high‐rise buildings of two different heights, which are designed based on Japanese standard. Responses are addressed in terms of displacement and acceleration at isolation and top floor level, force‐deformation and fatigue damage induced in the isolation devices under individual and multihazard scenarios. Results show that a particular range of building exists that is governed by both earthquake and wind events, and it is recommended that design of such building types should include the effects of both hazards. Moreover, the series of events likely to occur in design life of the buildings induce significant damage in the isolators as compared to the individual hazard event, thereby emphasizing a strong need to develop multihazard framework, where the occurrence rate of such extreme events is relatively higher.