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"Seismic Analysis"
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Elements of rock physics and their application to inversion and AVO studies
\"This book deals with a series of topics in rock physics, including elasticity, pore pressure, incompressibility of rocks and the Gassmann equation, fluid substitution, forward modeling and empirical equations, rock physics applications to AVO studies and inversion studies, and the Differential Effective Medium (DEM) method\"-- Provided by publisher.
Book
Seismic performance of deep excavation restrained by guardian truss structures system using quasi-static approach
The control of deformation and stability of the deep excavation walls under seismic and static loads is one of the most important issues in geotechnical engineering. Therefore, in the present study, using the finite element method and taking into account Hardening soil's behavioural model, the effect of different parameters affecting the performance of the deep excavation walls with the guardian truss structures using quasi-static analysis and its comparison with static analysis has been performed. According to the most important results, increasing in the geotechnical parameters of soil such as cohesion, friction angle and elastic modulus will reduce the maximum horizontal displacement in the vertical trench wall. Besides, the maximum settling in the adjacent ground and the maximum swelling in the bottom of the excavation will be reduced. In this way, the improvement in soil resistance parameters will increase the safety factor. Conversely, by increasing the horizontal distance between the trusses, the maximum horizontal displacement and the maximum settling in the adjacent ground and the maximum swelling in the bottom of the excavation will increase and the safety factor will be reduced. Also, the findings from this research show that by increasing the horizontal seismic acceleration coefficient (
K
h
) and as the construction stages progress, the maximum horizontal displacement of the wall, the maximum settling of the adjacent ground of the wall and the maximum swelling on the bottom of the trench increase and the safety factor will decrease. As well as, the results obtained from the quasi-static seismic analysis of the vertical trench restrained by the guardian truss structure such as the maximum horizontal displacement of the vertical trench wall and the maximum settling in the adjacent ground and the maximum swelling of the bottom of the excavation are much more than the static analysis.
Journal Article
Seismic sources for southern Pakistan and seismic hazard assessment of Karachi
Karachi is Pakistan’s largest city with population exceeding 18 million and is amongst the top five most congested cities in the world. Karachi has experienced no earthquake related damage in the recorded history of past ~ 175 years. Yet, Karachi is located in a seismically active tectonic setting often compared to Los Angeles with active plate boundary faults and triple junctions within a radius of ~ 150 km. This discrepancy in earthquake history and seismotectonic setting has led to diverse seismic hazard assessments for Karachi ranging from assignment of seismic hazard zones I (least severe) to IV (most severe). Recent assessment adopted in Building Code of Pakistan (2007) assigns an intermediate seismic hazard value of 0.16–0.24 g (Zone IIB) to Karachi, which is broadly accepted but sometimes criticized to be an underestimation (e.g. Bilham et al. Seismol Res Lett 78(6):601–631, 2007). The present study based on a new active faults compilation and seismic sources definition together with incorporation of maximum possible information on historical earthquakes (up to 893AD) has led to a re-assessment of seismic hazard for Karachi using probabilistic and deterministic seismic hazard assessment approaches. According to this study, Karachi is assessed to be prone to ground motions ~ 0.25 g with metropolitan areas having hazard values between 0.21 and 0.25 g for 10% probability of exceedance in 50 years (475-year return period). The deterministic seismic hazard analysis suggest maximum that peak ground acceleration (PGA) varies from 0.19 to 0.99 g in Karachi and its higher values are concentrated around the Nagar Parker fault that is controlling and hazardous for Karachi.
Journal Article
Probabilistic seismic demand and fragility analysis of a novel mid-rise large-span cassette structure
This paper presents the probabilistic seismic demand and fragility analyses of a novel mid-rise large-span cassette structure. A newly designed nine-storey office building in Hunan, China, is selected, and its two different design schemes, namely, a traditional frame structure and a novel cassette structure, are examined using numerical models established on the basis of a shake table test. Based on probabilistic seismic theory, the appropriate intensity measures are firstly studied based on a set of 110 seismic records; and PGV and GeoSaavg, which consider the 3D characteristics of the structure, are selected. In addition, the uncertainty of earthquakes, including spectral characteristics, fault distance and input direction, are considered, and 25 seismic records recommended by the Federal Emergency Management Agency are selected. An incident angle interval of 22.5° is selected to consider the uncertainty in the input directions of real earthquakes. Incremental dynamic analyses are conducted, and the structural responses in every individual input direction as well as in all the directions are studied. Finally, probabilistic seismic fragility analysis is conducted, and the probabilities of exceeding different limit states of the frame and cassette structures is presented. Amongst the studies, the novel cassette design can not only achieve much larger span, but also shows a better, more stable seismic performance. Therefore, the cassette structure may be a better alternative in seismic design.
Journal Article
SeismicV: A Mobile Tool for Assessing the Seismic Vulnerability of Buildings
Rapid visual screening has been used worldwide as the first approach to evaluate the seismic vulnerability of civil structures in a specific area, in order to prioritize buildings based on the need for upgrading or retrofitting. In this work, a novel mobile application tool for the rapid visual screening of reinforced concrete buildings is presented and discussed. The herein suggested “SeismicV” tool performs a pre-seismic visual screening based on the Japanese guidelines for the seismic evaluation of existing RC buildings. A preliminary seismic vulnerability assessment of a complex modern building situated in the capital of Brazil, Brasilia, was carried out using this mobile app. The data were collected from in situ and based on some data from plants and documents. The SeismicV tool consists of an effective, user-friendly, and straightforward mobile application. Since the methodology is based on a performance score that is compared to the seismic demand, this application design allows for the knowledge of intermediate indices at each step of the evaluation, including dominant variables such as structural irregularity, building age, ground index, and usage index. Although the application was conceived and applied to heritage buildings in the early stages, it can be employed for other complex structures. The findings highlight that utilizing SeismicV to assess the seismic vulnerability of complex buildings through the rapid visual screening method offers significant benefits, including faster evaluations, increased accuracy, and improved accessibility for field assessments.
Journal Article
Optimal intensity measure for seismic performance assessment of shield tunnels in liquefiable and non-liquefiable soils
Relating the ground motion intensity measure (IM) and the structural engineering demand parameter is a crucial step in the performance-based earthquake engineering framework. This study investigates the selection of IM for development of probabilistic seismic demand model of urban shield tunnels subjected to earthquake ground motions in liquefiable and non-liquefiable soils. Nonlinear dynamic effective stress analyses are conducted to develop a database of the intensity measures and structural seismic responses exposed to ground shaking and soil liquefaction. Two advanced soil constitutive models (i.e., Pressure DependMultiYield03 and PressureIndependMultiYield for liquefiable and non-liquefiable soils, respectively) are employed to capture the nonlinear behavior. A suite of 23 ground motion intensity measures is selected and assessed based on the evaluation criteria of correlation, efficiency, practicality and proficiency. Eventually, the multi-level fuzzy comprehensive evaluation method is employed to comprehensively consider the four evaluation criteria and establish the optimal ground motion IM suitable for probabilistic seismic demand analysis of shield tunnel structures. The obtained results show that the sustained maximum acceleration is the optimal IM for evaluating the structural seismic response, followed by the peak ground acceleration in both liquefiable and non-liquefiable soils. Peak pseudo velocity spectrum, displacement square integral and Housner spectral intensity are found to be not suitable for the probabilistic seismic demand analysis of shield tunnel structures.
Journal Article
REASSESS V2.0: software for single- and multi-site probabilistic seismic hazard analysis
Probabilistic seismic hazard analysis (PSHA) is generally recognized as the rational method to quantify the seismic threat. Classical formulation of PSHA goes back to the second half of the twentieth century, but its implementation can still be demanding for engineers dealing with practical applications. Moreover, in the last years, a number of developments of PSHA have been introduced; e.g., vector-valued and advanced ground motion intensity measure (IM) hazard, the inclusion of the effect of aftershocks in single-site hazard assessment, and multi-site analysis requiring the characterization of random fields of cross-correlated IMs. Although software to carry out PSHA has been available since quite some time, generally, it does not feature a user-friendly interface and does not embed most of the recent methodologies relevant from the earthquake engineering perspective. These are the main motivations behind the development of the practice-oriented software presented herein, namely REgionAl, Single-SitE and Scenario-based Seismic hazard analysis (REASSESS V2.0). In the paper, the seismic hazard assessments REASSESS enables are discussed, along with the implemented algorithms and the models/databases embedded in this version of the software. Illustrative applications exploit the potential of the tool, which is available at http://wpage.unina.it/iuniervo/doc_en/REASSESS.htm.
Journal Article
Seismic source modeling and probabilistic seismic hazard analysis for Bangladesh
The probabilistic seismic hazard analysis (PSHA) has been performed for Bangladesh using background seismicity, crustal fault, and subduction zone source models. The latest ground motion prediction equations (GMPEs) that are developed using global data sets have been used to estimate ground motion. The uncertainties in seismic sources and GMPEs to estimate ground motion are accounted using the logic tree approach. The activity rates of the background and regional seismicity sources are estimated using a declustered and complete catalog of the study regions. The activity rates of the crustal fault and subduction zone sources are estimated from the geodetic strain rates using the well-accepted relationships. The peak ground acceleration (PGA) and spectral acceleration (SA) at spectral periods of 0.2, 0.5, 1.0, 2.0, 5.0, and 10.0 s have been estimated at a grid size of 0.250 at the bedrock ground condition. The PGA and SA maps of various spectral periods have been prepared for Bangladesh for both 10% and 2% probability of exceedance in 50 years. These seismic hazard maps can be used for seismic risk management of Bangladesh.
Journal Article
Magnetic damped links to reduce internal seismic pounding in base-isolated buildings
A limited gap between closely spaced structural parts may induce internal pounding in seismically isolated structures, because of notable displacement at the level of the isolation system under severe earthquakes. A gap between a fixed-base elevator shaft and the surrounding building is presented here with reference to a reinforced concrete building located in the Sicilian town of Augusta. The building, comprising a basement and three storeys above the ground level, is seismically isolated at the top of rigid columns in the basement with a hybrid isolation system including elastomeric and sliding bearings, while a steel framed elevator shaft crosses the isolation level. Despite the gap, internal pounding may occur at all levels of the superstructure when the elevator with maximum load stops at the upper floors. To reduce structural pounding effects, a magnetic damped link (MDL) between adjacent corners of the elevator and the surrounding building is proposed. This is obtained as an in parallel combination of an eddy current damped link (ECDL) and an elastic helicoidal spring, and occupies less space than traditional passive dampers and transmits considerably less forces compared to a rigid link configuration. Specifically, an ECDL consists of an outer cylindrical copper tube, as conductor, and an inner tube, equipped with an array of axially magnetized and ring-shaped permanent magnets separated by iron pole pieces, as mover. The relative motion between conductor and magnets, during seismic loading, induces an eddy current producing electromagnetic damping. Given that viscoelastic linear behaviour can be hypothesized for the MDL, a simplified iterative design procedure of the ECDL is proposed, with optimization of the thickness and radius of the magnets, thereby enhancing magnetic flux and energy dissipation. The directionality of the near-fault ground motions is investigated through nonlinear seismic analysis, comparing no connection with four configurations of the interconnection: i.e., flexible and rigid elastic links, viscous and magnetic damped links.
Journal Article
Regularity classification and corresponding analysis method requirements of horizontally curved bridges with unequal pier heights
The seismic behavior of horizontally curved bridges, particularly with unequal height piers, is more complicated than that of straight bridges due to their geometric properties. In this study, the seismic responses of several horizontally curved single-column-bent viaducts with various degrees of curvature and different pier heights have been investigated, employing three different analysis approaches: namely, modal pushover analysis, uniform load method, and nonlinear time history analysis. Considering the investigated bridge configurations and utilizing the most common regularity indices, the results indicate that viaducts with 45-degree and 90-degree deck subtended angles can be categorized as regular and moderately irregular, respectively, while the bridges with 180-degree deck subtended angle are found to be highly irregular. Furthermore, the viaducts whose pier heights are asymmetric may be considered as irregular for almost all ranges of the deck subtended angles. The effects of higher transverse and longitudinal modes are discussed and the minimum analysis requirements are identified to assess the seismic response of such bridge configurations for design purposes. Although the Regularity Indices used here are useful tools to distinguish between regular and irregular bridges, further studies are needed to improve their reliability.
Journal Article