• Earthquakes and Structures
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• v.19 no.4
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• pp.261-272
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• 2020

Recent severe earthquakes in and around the vital public places worldwide indicate the severe vulnerability of ground excitation to be assailed. Reducing the effect of seismic lateral load in structural design is an important conception. Essentially, seismic isolation is required to shield the superstructure in such a way that the building superstructure would not move when the ground is shaking. This study explores the effectiveness, design, and practical feasibility of base isolation systems to reduce seismic demands on buildings of varying elevations. Thus, static and dynamic analyses were conducted based on site-specific bi-directional earthquakes for base-isolated as well as fixed-based buildings. Remarkably, it was discovered that isolators used in low-rise to high-rise structures tend to significantly decrease the structural responses of seismic prone buildings. The higher allowable horizontal displacement induces structural flexibility and ensure good structural health of the building stories. Reinforcement from vertical and horizontal members can be reduced in significant amounts for BI buildings. Thus, although incorporating base isolators increases the initial outlay, it considerably diminishes the total structural cost.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.1 s.53
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• pp.89-97
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• 2007

Parameters including the seismic sources and the elastic wave propagation characteristics were analysed using the observed ground motions from 12 Fukuoka region earthquakes. The Levenberg-Marquardt algorithm was applied to invert all the variables non-linearly and simultaneously with S wave energy in fiequency domain. Average stress drop of 12 events and local attenuation parameter $\kappa$ under seismic stations were estimated to about 79.2-bar and 0.043 respectively. Regional attenuation parameter, Qo and ${\eta}$, were also estimated to be about 248.1 and 0.558 respectively. Low value of Qo seems to caused by inhomogeneous tectonic characteristics between Japan island and southern Korean peninsula. $\kappa$ values are much higher than that characterizing EUS (Eastern United States) region, and nearly similar to that of WUS (Western Waited States) region. If the informations on site specific amplification of all the seismic stations are known, $\kappa$ values can be estimated more precisely. All the values including the seismic sources and the site and crustal scale propagation characteristics can be used as seismic design parameters.

• Earthquakes and Structures
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• v.11 no.3
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• pp.517-538
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• 2016

This paper presents a probabilistic fragility analysis for two groups of bridges: simply supported and integral bridges. Comparisons are based on the seismic fragility of the bridges subjected to accelerograms of two seismic sources. Three-dimensional finite-element models of the bridges were created for each set of bridge samples, considering the nonlinear behaviour of critical bridge components. When the seismic hazard in the site is controlled by a few seismic sources, it is important to quantify separately the contribution of each fault to the structure vulnerability. In this study, seismic records come from earthquakes that originated in strike-slip and reverse faulting mechanisms. The influence of the earthquake mechanism on the seismic vulnerability of the bridges was analysed by considering the displacement ductility of the piers. An in-depth parametric study was conducted to evaluate the sensitivity of the bridges' seismic responses to variations of structural parameters. The analysis showed that uncertainties related to the presence of lap splices in columns and superstructure type in terms of integral or simply supported spans should be considered in the fragility analysis of the bridge system. Finally, the fragility curves determine the conditional probabilities that a specific structural demand will reach or exceed the structural capacity by considering peak ground acceleration (PGA) and acceleration spectrum intensity (ASI). The results also show that the simply supported bridges perform consistently better from a seismic perspective than integral bridges and focal mechanism of the earthquakes plays an important role in the seismic fragility analysis of highway bridges.

• Earthquakes and Structures
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• v.9 no.3
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• pp.603-623
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• 2015

The scale and nature of the recent earthquakes in the world and the related earthquake disaster index coerce the concerned community to become anxious about it. Therefore, it is crucial that seismic lateral load effect will be appropriately considered in structural design. Application of seismic isolation system stands as a consistent alternative against this hazard. The objective of the study is to evaluate the structural and economic feasibility of reinforced concrete (RC) buildings with base isolation located in medium risk seismic region. Linear and nonlinear dynamic analyses as well as linear static analysis under site-specific bi-directional seismic excitation have been carried out for both fixed based (FB) and base isolated (BI) buildings in the present study. The superstructure and base of buildings are modeled in a 3D finite element model by consistent mass approach having six degrees of freedom at each node. The floor slabs are simulated as rigid diaphragms. Lead rubber bearing (LRB) and High damping rubber bearing (HDRB) are used as isolation device. Change of structural behaviors and savings in construction costing are evaluated. The study shows that for low to medium rise buildings, isolators can reduce muscular amount of base shears, base moments and floor accelerations for building at soft to medium stiff soil. Allowable higher horizontal displacement induces structural flexibility. Though incorporating isolator increases the outlay, overall structural cost may be reduced. The application of base isolation system confirms a potential to be used as a viable solution in economic building design.

• Structural Engineering and Mechanics
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• v.71 no.1
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• pp.1-12
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• 2019

This study investigates optimum designs of steel space truss towers under seismic loading by using Jaya optimization algorithm. Turkish Earthquake Code (2007) specifications are applied on optimum designs of steel space truss towers under the seismic loading for different local site classes depending on different soil groups. The proposed novel algorithm does not have any algorithm-specific control parameters and depends only a simple revision equation. Therefore, it provides a practical solution for structural optimization problems. Optimum solutions of the different steel truss examples are carried out by selecting suitable W sections taken from American Institute of Steel Construction (AISC). In order to obtain optimum solutions, a computer program is coded in MATLAB in corporated with SAP2000-OAPI (Open Application Programming Interface). The stress and displacement constraints are applied on the design problems according to AISC-ASD (Allowable Stress Design) specifications. Firstly, a benchmark truss problem is examined to see the efficiency of Jaya optimization algorithm. Then, two different multi-element truss towers previously solved with other methods without seismic loading in literature are designed by the proposed algorithm. The first space tower is a 582-member space truss with the height of 80 m and the second space tower is a 942-member space truss of about 95 m height. The minimum optimum designs obtained with this novel algorithm for the case without seismic loading are lighter than the ones previously attained in the literature studies. The results obtained in the study show that Jaya algorithm is a practical and robust optimization method for structural optimization problems. Moreover, incorporation of the seismic loading causes significant increase in the minimum design weight.

• Geotechnical Engineering
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• v.11 no.2
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• pp.139-156
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• 1995

A set of field investigations was performed to estimate accurately the predominant periods of seismic 8round motions and the attenuation characteristics of the seismic ground vibration. Predominant periods of ground motions were estimated from the measurement of the continuous microseismic vibratins of certain periods, inherent in the ground and in the buildings, utilizing the high sensitivity digital velocity seismometer consisting of 3-component geophones and a digital seismograph. Estimated predominant periods of microseismic vibraion of the ground(measured on'the ground surface) and the building (measured on the second floor) were in the range of 0.18~0.235 sec. and 0.26~0.31 sec. respectively. The subsurface structure of the site ground was surveyed by the seismic refraction method utilizing the digital seismicwave probing system. The ground structure was found to be a two-layered system : an upper top soil layer of 7m in thickness with the P-wave velocity of 662m1sec and a lower layer of silty-clayey soils with the P -wave velocity of 2210m1 sec. The attenuation characteristics of the seismic ground vibrations were determined by the amplitude decay measurement method us;ng the Seisgun, which produces strong artificial seismic energy. Measured spatial attenuation coefficients of the ground vibration in vertical(Z) longitudinal(X), transverse(Y) direction were 0.1137, 0.0025, and 0.0290 respectively. Estimated Spartial QP's (inverse of the specific dissipation constant w.r.t. shear waved of X, Y, and Z directions were in the range of 5.913~7.575, 32.371~41.452, 2.794~3.579 re spectively. This indicates that aseimic design of the structures on the site should take stronger consideration regarding the earthquake resistance characteristics of the structures against longitudinal ground motion.