Areas Of High Seismic Hazard Research Articles

Evaluating the response modification factor (R) for reinforced concrete and steel structures equipped with TADAS devices designed for high seismic hazard in Colombia

Colombia is a country with high seismic activity due to its location at the convergence of the Nazca and South American tectonic plates, making structural safety a key priority in the design, construction, and retrofit of buildings. Currently, one of the most used seismic resistance systems are moment-resisting frames, due to their easy construction and good behavior under vertical loads, however, they are susceptible to structural damage when subjected to moderate to high-intensity earthquakes, which makes the use of seismic protection systems an adequate alternative to prevent damage during seismic events. The Colombian seismic design code NSR-10 proposes a design methodology using a linear structure that represents a non-linear behavior of the building when the expected design earthquake occurs through the response modification factor R. However, the NSR-10 seismic design code does not contemplate the response modification factor for structures with seismic protection systems. Therefore, in this research, a design procedure was configured for buildings with moment-resisting frames of reinforced concrete and steel equipped with TADAS (triangular-plate added damping and stiffness) dampers. The procedure evaluated the developed response modification factor of structures located in high seismic hazard areas in Colombia and considered regular buildings with varying numbers of stories and special energy dissipation capacity. The capacity of the structures was evaluated through nonlinear static analysis using the Pushover method in SAP2000 software. Finally, the response modification factors were calculated for regular buildings with moment-resisting frames and different numbers of stories.

Shaking table test of a timber building equipped with a novel cost-effective, impact-resilient seismic isolation system

In most cases, construction of Light Frame Timber Buildings (LFTBs) in areas of high seismic hazard requires strong wood frame shear walls and continuous rod systems, which increases the cost of LFTBs. Frictional seismic isolation might be applied to protect LFTBs against extreme ground motions and mitigate the cost of continuous rod systems. However, there are no experimental studies on the response of LFTBs equipped with frictional isolation and subjected to extreme seismic ground motions that might cause impacts between the slider and the perimetral ring or between the isolated base and the perimetral moat wall.This study explores the potential of using impact-resilient frictional isolators as a feasible solution to alleviate stiffening and overturning costs of LFTBs while making them resilient to impacts in case of extreme events. This issue has been researched by evaluating the response of a 1:2 scaled 3-story LFTB isolated with a novel Impact Resilient Double Concave Frictional Pendulum recently developed by the authors. The specimen was subjected to a suite of shaking table tests (white noise, harmonics signals, and seismic records), including strong ground motions such as the Concepcion record (2010 Maule, Chile earthquake, Mw = 8.8) scaled to 130 %. Results indicate that despite being subjected to extreme excitations, peak acceleration ratios (i.e., the ratio of peak floor acceleration to peak ground acceleration) did not exceed 0.75, and story drift ratios were smaller than 0.52 % in most cases. Thus, the superstructure remained in the elastic range without damage. The study demonstrates the potential of achieving effective seismic protection of LFTBs using Impact Resilient devices. In addition, this paper presents a numerical model developed with experimental data, which provides insight into modeling issues such as, for instance, damping properties.

CONSTRUCTION SYSTEM SELECTION IN LOW-BED CAPACITY HEALTH BUILDINGS WITH FUZZY AHP IN EARTHQUAKE ZONES

Purpose: Reconstruction of health buildings that were heavily damaged after the earthquake has become an important issue in Turkey. The negative performance of the construction systems of health buildings after major earthquakes necessitates the evaluation of the building system (CS) options, which can create an alternative to the market, according to various criteria. The main purpose of the study is to develop a systematic basis for the CS of 1816 health institutions to be rebuilt within the scope of the UDSEP 2023 project and to decide between alternatives in Turkey. In this study, the example of a hospital with a low bed capacity (20 beds) was discussed. Method: In the application of the Methodology-Fuzzy Analytical Hierarchy Process (FAHP) method of the research, 40 expert opinions were taken at the stages of planning, construction and inspection of health buildings. Findings: Experts in various fields of the construction industry have determined that CS performance is the primary criterion and cost is the secondary criterion for healthcare buildings in high seismic hazard areas. Conclusion: Among the CS alternatives, Structural Steel Frame (SSF) was determined as the most suitable structural system for earthquake zones.

Performance of prototype seismic isolators reinforced with fiber and a recycled rubber tire matrix

Seismic isolators are passive control devices that reduce the energy transferred from an earthquake to the superstructure, this avoiding damage to building elements. Seismic isolators are classified according to their connection to the structure; for example, unbonded isolators lack mechanical connections with the building. Unbonded fiber-reinforced elastomeric isolators (U-FREIs) are formed of intercalated layers of bidirectional polyester mesh used as reinforcement and agglomerated ground rubber from end-of-life tires (ELTs) as an elastomeric matrix. This paper presents the mechanical behavior of U-FREIs built at a reduced scale to provide an affordable alternative for the mitigation of seismic forces that affect low-rise buildings. The isolators were designed for a low-rise residential frame structure located in an area of high seismic hazard and were subjected to shear and compression tests to characterize their mechanical behavior. The experimental results show good behavior of the prototypes with respect to standards and design requirements.

Generalized response spectrum analysis based computational morphogenesis for metal gridshells with buckling-restrained braces subjected to seismic loading

Structural morphogenesis is widely used as a parametric tool to find an optimal structural shape of shell structures for a prescribed objective function and a given design load. However, the current optimization methods are limited to finding a geometry under only a specific static load like the dead load or an equivalent static seismic load for predefined geometrical shapes, and so can not be applied to free-form gridshells. This poses a challenge to achieving an efficient free-form shell structure in high seismic hazard areas. This paper aims to resolve this by presenting a computational morphogenesis method to obtain form-found shell structures by considering the dynamic seismic loads and the response reduction effects of seismic energy-dissipating devices using generalized response spectrum analysis. The method was applied to optimize the buckling-restrained brace layouts on target spherical metal gridshell structures with different diameter-to-height ratios. The resulting form-found structures had an efficient roof geometry, along with an efficient damper layout (to prevent member buckling and the dropout of finishing materials). Dampers were found to be more efficient if placed in the (relatively heavy) supporting structure instead of the roof, and a flattened but locally bulged roof shape proved to be the most efficient in mitigating the seismic response. The generalized response spectrum analysis significantly reduced the computation time while evaluating the displacement response with sufficient practical accuracy, although it slightly underestimates the acceleration response if compared to the conventional nonlinear response history analysis results.

Seismic performance of prefabricated steel tube-confined concrete circular pier

In this study, a prefabricated steel tube-confined concrete (PSTC) circular pier with a bottom grouted sleeve connection was developed to correct some limitations in typical precast concrete (PC) piers, such as over-dense grouting sleeves and insufficient energy dissipation capacity, thus promoting their use in high seismic hazard zones. To validate the performance of the proposed design, four scale models of an actual circular bridge pier, including two PSTC, one PC, and one cast-in-place (CIP) specimens, were fabricated and their seismic response under cyclic loading was investigated via quasi-static experimental and numerical tests. The seismic performance indices, hysteretic energy dissipation characteristics, skeleton curve, flexural strength, stiffness degradation, residual displacement, and ductility of the different specimens were compared. The experimental and numerical results indicated that, compared with the CIP and PC circular piers, the flexural strength and energy dissipation capacity of the PSTC piers were significantly improved owing to the confinement provided by the steel tube to the concrete core, their ductility and initial stiffness effectively increased, and the pier body stiffness (pier body curvature) was more uniformly distributed. Moreover, parametric finite element analyses of the PSTC pier under low-cycle reciprocating load were used to determine the influence of the steel tube thickness and strength on the seismic performance of the pier. It was found that an increase in the thickness and strength of the steel tube also increases the flexural strength, yield load, yield displacement and initial tangent stiffness of the PSTC circular pier. Consequently, this study demonstrates that PSTC piers are reliable and suitable for prefabricated bridge construction in high seismic hazard areas.

Numerical evaluation of the seismic performance of thin reinforced concrete wall buildings representative of the industrialized building system

The industrialized building system has specific characteristics that set it apart from the conventional concrete wall system, namely, a reduced wall thickness, the use of electro-welded wire mesh, and a lack of boundary element confinement. These conditions have attracted the interest of researchers, who have developed various experimental programs to evaluate the behavior of these walls. However, evidence on the seismic performance of buildings remains scarce. In this study, the performance of 5-, 8- and 12-story buildings was evaluated by nonlinear chronological analysis. Numerical models were constructed using the Shell Layered element of the ETABS software and adjusted based on the results from tests of isolated walls and the periods of one of the buildings identified in an ambient vibration test. The findings suggest that these buildings may fail to meet the life safety performance level in high seismic hazard areas.

Accounting for horizontal torsional vibrations of foundations when calculating seismic load

The article presents a method for calculating in-plane vibrations of building structures under seismic load taking into account the possibility of foundation displacement, which is similar to horizontal torsional vibrations when calculating earthquake forces. The method is illustrated by the structural design of a seven-storey tower-like building with a massive foundation. We develop transfer functions for a massive rigid body, which are subsequently used for calculating the response of the foundation subject to base shears and moments applied to the outer plane of the foundation under seismic forces. The structural calculations conducted for ductile structures with the first frequency of ~2.4 Hz and for more rigid structures with the first frequency of 7.1 Hz showed that, depending on the building stiffness, reduced seismic forces increase by 1.5–2 times. According to the results obtained, when designing structures in areas of high seismic hazard, account should be taken of possible foundation flexibility effects depending on different types of soil and structural solutions of particular buildings.

Intervention Strategies for the Seismic Improvement of Masonry Buildings Based on FME Validation: The Case of a Terraced Building Struck by the 2016 Central Italy Earthquake

Residential masonry buildings represent a large stock among highly vulnerable structures in medium–high seismic hazard areas, often built without any anti-seismic provisions. Their rehabilitation and/or strengthening according to optimised intervention strategies is topical and may contribute to revaluating zones characterized by depopulation phenomena. In this paper, a terraced building struck by the 2016 Central Italy earthquake is analysed through a frame by macro element (FME) model. The building is composed of six two-storey units made of stone and clay block masonry walls and semi-rigid diaphragms. The numerical model was calibrated based on the damage pattern caused by the earthquake and then used to carry out parametric analyses on the strengthened conditions by simulating both one unit and the entire terrace. The effects of interventions applied to either vertical or horizontal components, both singularly and in combination, were analysed in terms of nonlinear static analyses, and quantified by a performance factor, according to the upgraded seismic code in Italy. Kinematic analyses also completed the assessment of the building. Results compared the capacity of interventions in attaining the targets defined for improvement at both local and overall levels.

Early assessment of seismic hazard in terms of Voronezh massif-Moscow Depression contact

Purpose is to develop a system approach for early assessment of areas being of high seismic hazard and characterizing by low stability of rock mass relative to external loads. Methods. Well cores have been assessed down to 30 depth and seismic observations have been accumulated. Complexes of field geophysics methods have been applied for the research as well as remote sensing materials, digital model of surface relief, and techniques of qualitative and quantitative interpretation. Findings. Seismic hazard map has been formed in terms of seismic intensification and ground displacement units. The abovementioned is quite reliable but a cost-based result involving early assessments of high seismic hazard areas to infill network of geophysical measurements in the neighbourhood of the areas for their further quantitative characterization. It has been identified that rare well network and definite geophysical lines, run under conditions of a complex terrain, cannot localize the areas of high seismic hazard to focus builders on the enforcement of certain components of the erected structures. It has been defined that end result of the prognostic developments takes a shape of mapping of local areas with the decreased stability of upper share of the geological section supported by further measurements by means of a common depth point method (CDP). Comparison of potential secondary earthquake sources with high permeability zones makes it possible to predict highly reliable areas of the increased seismic magnitude. Originality.For the first time, interpretation techniques have been adapted to describe parametrically nonpotential geofields (i.e. optical density of remote basis; and relative elevation), accepted during the steps of potential field processing, with the use of wave analogies. Practical implications.The methods have been developed helping optimize field geological and geophysical operations in terms of area and well number as well as measuring stakes under the conditions of the limited prior data amount.

Out-of-plane mechanism in the seismic risk of masonry façades

A framework for evaluating the risk of the out-of-plane mechanism of masonry facades subjected to earthquake excitations is presented. The effect of seismic events on masonry facades is investigated and results are presented in terms of fragility curves and seismic risk for several masonry supporting restrictions. The restrictions considered are (1) masonry facade unrestricted to rock on a firm base, (2) masonry facade restricted to rock in one direction, and (3) restrained rocking masonry facade in one-sided motion. Because the available empirical information is insufficient to obtain fragility functions for masonry facades, the study is based on numerical analysis and recent studies on seismic risk. The conceptual framework is illustrated with information from masonry facades characteristic of Mexican religious structures and within the seismic hazard areas of Mexico. Since the frequency characteristics of ground motions strongly depend on the distance from the epicenter to the site, which is of cardinal importance to the vulnerability of these structures, the impact of this distance for hard-soil sites is thoroughly investigated. The probability of failure for the three types of masonry facades was calculated. It was found that the probability of failure decreases with an increased width-to-height relation; conversely, the probability of failure (reported in terms of the reliability index) increases with increased block size dimensions. Results in this study show that restraining conditions of the facades inconsequentially affect the probability of failure. Although the reliability of freestanding masonry facades are marginally greater, this finding holds true regardless of whether or not one considers far-field ground motions. The results in this study can be useful for evaluation and reinforcement tasks of masonry facades located in areas of high seismic hazard.

Refuerzo de un edificio mediante la incorporación de un sistema de disipación de energía

En zonas de alta peligrosidad sísmica existen estructuras que pueden requerir un refuerzo estructural para mejorar su desempeño. Una alternativa para realizar estos refuerzos es la incorporación de sistemas pasivos de energía. Este trabajo tiene por objeto aplicar una metodología de diseño propuesta por el autor a un caso de estudio. Se diseñan los dispositivos y posteriormente se contrasta el método propuesto con análisis dinámico no lineal según requerimientos de la norma americana ASCE/SEI 7-16. Para la excitación sísmica se eligen dos grupos de siete registros representativos de la zona de emplazamiento escalados por ajuste espectral. En base a la consideración de varios parámetros de respuesta se muestra la eficiencia del procedimiento de diseño propuesto.

Cumulative absolute velocity (CAV) seismic hazard assessment for Taiwan

ABSTRACT Cumulative absolute velocity (CAV) is a ground motion intensity measure that is considered more indicative of structure damage than other intensity measures (e.g., PGA). Nevertheless, most seismic hazard assessments are PGA-based rather than CAV-based. In this paper, the first CAV seismic hazard assessment for Taiwan was presented. According to this CAV seismic hazard assessment, central-western and central-eastern Taiwan is of higher CAV seismic hazards than other areas. At the 475-year return period, the CAV of exceedance in those high seismic hazard areas is around 0.6–0.7 g-sec.

Numerical analysis, design and behavior of rockfill dams with reinforced concrete faces during seismic actions

Introduction. Over the last 10–20 years many rockfill dams with reinforced concrete faces that are 140–200 m high (Mohale in Lesotho, Tian Sheng Yao, Zipingpu in China, etc.) have experienced serious problems, including face slab cracking and perimeter joint opening. Most of these dams were built in high seismic hazard areas, and their seismic resistance to the maximal earthquake exposure, having the magnitude equal to 8–9, raises doubts. The goal of this research is to employ numerical methods to verify the seismic resistance of dams, to project their behavior in case of the seismic exposure that may damage the dam face, cause the face joints to open and the dam face to detach from its toe, etc. Materials and methods. The author offers his analysis of reliability and applicability of numerical methods to the seismic resistance of dams. Incidents have demonstrated the need for a thorough assessment and analysis of each aspect of a new project whenever it is extrapolated from the precedent. Results. The analysis of the dam behavior in the course of the first reservoir filling has demonstrated face top cracking that causes its damage. Deeper in the water, face joints may be exposed to localized damages due to compression and shear; one should expect vertical face joints to open; excessive compressibility of the downstream rockfill zone may cause the water to leak through the dam face. The author offers recommendations for the performance of the dynamic analysis of dams in respect of the boundaries of the computational domain, given that seismic waves are transmitted or absorbed at the interface between the dam face and the transition zone, on the one hand, and between dam slabs, on the other hand. In furtherance of his recommendations, real and synthetic accelerograms are applied to the bottom boundary of the computational domain; the choice of an explicit or implicit computational method should be made; the author’s method pre-sets the intermediate solution which is to comply with the accelerogram digitization pattern. Conclusions. In addition to internationally established measures for improving the static and seismic safety of dams, the author proposes a new effective dam safety improvement method to be used in the course of designing high dams to be con-structed in high seismic hazard areas. This method improves dam safety by drastically reducing face deflections with the help of a support zone made of roller compacted concrete instead of the gravel transition zone, as exemplified by the 275 m high Kambaratinskaya-1 dam in Kyrgyzstan and the 192 m high Sogamoso dam in Colombia (both dams are located in highly seismic regions). The information on China's successful track record in designing and building similar dams, which are 220–250 m high, is also provided.

Peligro Sísmico por Efecto de Sitio en el Recinto Universitario Rubén Darío de la UNAN-Managua. Nicaragua

La presente investigación tiene como objetivo caracterizar el peligro sísmico por efecto de sitio en el área de la UNAN-Managua y está orientada a conocer las características y respuesta sísmica de los suelos en sus modos de vibrar ante un evento sísmico. El área de la UNAN-Managua corresponde a una zona de alta peligrosidad sísmica por localizarse al oeste una falla geológica activa, conocida como la Falla Zogaib, la cual tiene una longitud de 2.7 km y orientación norte-sur, y representa un peligro sísmico para la Ciudad Capital, que históricamente ha sido devastada por terremotos de magnitud moderada (Ms 6-6.2) originados por fallas geológicas, dejando daños en las infraestructuras provocando el colapso total de viviendas y edificaciones y la pérdida de vidas humanas en el país. La investigación es un aporte valioso para la UNAN-Managua y es de base para la planificación de fututos proyectos de construcción en el recinto universitario para la prevención de desastres por terremotos y aporta información para la reducción del riesgo sísmico en área. El estudio se llevó a cabo como un proyecto de investigación titulado “Estudio de efecto de sitio en la UNAN-Managua”, que se realizó con el apoyo económico de los Fondos para proyectos de investigación (FPI) de la UNAN-Managua.

Seismic fragility analysis of retrofitted steel tanks considering corrosion

Several types of steel tank are used in industrial plants to store hazardous chemical products. Most of these are unanchored tanks that are not designed to withstand seismic loads. Many of the old process industries in high seismic hazard areas have launched retrofitting programmes for their components, especially cylindrical tanks. Providing mechanical anchors is a common strategy for the seismic retrofitting of cylindrical tanks and there are thus several existing pre-code tanks that have been retrofitted by the provision of anchor bolts. In this work, fragility analyses of pre-code and retrofitted tanks were conducted for existing broad tanks. The effects of steel corrosion were considered in the fragility analyses and 250 tank–earthquake non-linear analysis cases were considered. The results of the study revealed that shell corrosion is an important source of uncertainty in the seismic fragility analysis of tanks. Moreover, it was found that providing mechanical anchors is a suitable technique for preventing moderate to major damage states in broad tanks, but is not efficient at preventing minor damage, especially for small peak ground accelerations.

Trends of Global Seismic Noise Properties in Connection to Irregularity of Earth’s Rotation

The properties of continuous records of low-frequency seismic noise on a global network consisting of 229 broadband seismic stations located around the world are considered. Changes in the properties of seismic noise, estimated daily for the time interval from the beginning of 1997 to the end of February 2019, are investigated. We consider the generalized Hurst exponent, the singularity spectrum support width, the entropy of the wavelet coefficients, and wavelet-based Donoho–Johnstone index. For the centers of 50 clusters of seismic stations, the average values of these 4 statistics from the 5 nearest operational stations are calculated daily. As a result, 4 multidimensional time series with a dimension of 50 are obtained with a time step of 1 day for more than 22 years of measurements. Average daily values of the noise properties studied, calculated over all cluster centers, have piecewise linear trends, the break point of which is estimated by the principal component method as mid-2003. After the break point, the average values of generalized Hurst exponent, singularity spectrum support width and Donoho–Johnstone index the parameters decrease whereas the entropy increases. This is interpreted as a simplification of the noise structure which is typical for areas of high seismic hazard. Trends in average noise properties after 2003 are accompanied by a linear increase with imposed 3-years quasi-periodic fluctuations in the average value of pairwise correlation coefficients between the values in cluster centers when evaluated in a sliding time window with a length of 1 year. It is hypothesized that the simultaneous simplification of the structure of global seismic noise, an increase in its spatial correlation and an increase in the intensity of the strongest earthquakes in the world after the end of 2004 is a single process associated with the irregularity of the Earth’s rotation. To confirm this hypothesis, a change in the coherence spectrum between the first principal component of the seismic noise properties and the time series of the length of day is estimated.

Connections in mixed structures with steel columns with threaded rods and normal strength concrete beams: Numerical analysis with incremental load

ABSTRACTThis research proposes to evaluate the suitability of a new type of hybrid or mixed joint for framed structures that are composed of H shape vertical elements made of structural steel and reinforced concrete with rectangular section horizontal elements. Researchers of Spanish origin have made the first experimental campaigns of these mixed joints using stud connectors welded to the flanges of the structural steel, which implies a follow‐up to the welding procedure. These researchers have concluded that these joints offer good resistance to static loading and that the contribution of strength by adherence and friction between the steel column and the concrete beam is important. In the framework of this research, relevant laboratory tests (cyclic load tests) will be carried out to evaluate and characterize the behavior of the joint in the event of seismic events, for areas of high seismic hazard, in addition, the modeling of the joint using the Finite Elements Method and the theory of mixtures of composite materials that anticipates their mechanism of failure. The innovative components of this research are the implementation of threaded rods, which will cross the flanges of the steel column and the evaluation of this joint under cyclic loading. This article will present and analyze the results of the first stage of this investigation, in which two partial models of the mixed joint with static load were made, which was applied at the end of each of the beams until producing its mechanism of failure. The results show an early failure mechanism on the outside contact surface between the two materials and deformations in the column outside the area embedded by the concrete.

Natural hazards and mineral commodity supply: Quantifying risk of earthquake disruption to South American copper supply

Mineral resources, and their mining and enrichment operations, are not equally distributed across Earth. The concentration of mineral supply in certain regions, owing to the geology or geography of the mineral resource, raises the level of risk related to supply disruption. Where mineral production coincides with areas prone to natural hazards, supply may be especially at risk. However, the level of risk that natural hazards pose to mineral supply has yet to be quantified on a global or regional scale. Using copper in South America as a case study, this paper offers methods for quantifying (i) the coincidence of mineral production and seismic hazards, and (ii) the Expected Annual Disruption (EAD) of the mineral supply from earthquakes. The first of these methods indicates that, of the 101 copper producing facilities in South America considered, 76 are located within an area of high seismic hazard, taken here as the area with >85% chance of exceeding Modified Mercalli Intensity VI earthquake shaking in 50 years. Collectively, the 76 facilities comprise 82%, 87%, and 91% of the 2015 South American mine production, smelter capacity, and refinery capacity, respectively. For each of the 101 facilities, the second method calculates the EAD using a full earthquake shaking hazard forecast at the location, the annualized copper production of the facility, and models of the vulnerability of that production to shaking. The EADs are summed by country, here within South America, as a demonstration of how supply risk could eventually be quantified globally. Consideration of two illustrative vulnerability models shows that future work is needed to determine percentages of disruption to mineral production for different levels of earthquake shaking. Ultimately, the methods presented herein could be applied to other mineral commodities and/or adapted for other natural hazards, and the resulting EADs could be summed. Results from these methods could be used to focus more detailed risk assessments where the risk is highest.

Traditional techniques for the rehabilitation and protection of historic earthen structures: The seismic retrofitting project

ABSTRACT Historic earthen structures are a significant portion of the built heritage worldwide and are associated with intangible building techniques, wide material availability and low-cost construction. Nonetheless, dueto their low mechanical properties and, often poor connections, historic earthen structures are susceptible to early structural damage, and even collapse in areas of high seismic hazard. Inaddition, the lack of maintenance can further reduce structural performance and durability. The Getty Conservation Institute (GCI)’s Seismic Retrofitting Project (SRP) aims to research, designand test low-tech retrofitting techniques, as well as to implement maintenance programs, enhancing the performance of historicearthen buildings in seismic areas where the most advanced equipment, structural skills and materials are not easily available. Results: Accounting for recommendations from national building codes, conservation principles and local practices, the complete design, assessment and implementation of strengthening for twoprototype buildings in Peru, involved in the SRP, are discussed; the Church of Kuño Tambo and Ica Cathedral. Conclusions: Theretrofitted structures, complied with performance criteria and seismic local demands, with sufficient safety and acceptable levels of repairable damage.