• Earthquakes and Structures
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• v.12 no.4
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• pp.397-407
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• 2017

To estimate the structural seismic demand, some methods are based on an equivalent linear system such as the Capacity Spectrum Method, the N2 method and the Equivalent Linearization method. Another category, widely investigated, is based on displacement correction such as the Displacement Coefficient Method and the Coefficient Method. Its basic concept consists in converting the elastic linear displacement of an equivalent Single Degree of Freedom system (SDOF) into a corresponding inelastic displacement. It relies on adequate modifying or reduction coefficient such as the inelastic deformation ratio which is usually developed for systems with known ductility factors ($C_{\mu}$) and ($C_R$) for known yield-strength reduction factor. The present paper proposes a rational approach which estimates this inelastic deformation ratio for SDOF bilinear systems by rigorous nonlinear analysis. It proposes a new inelastic deformation ratio which unifies and combines both $C_{\mu}$ and $C_R$ effects. It is defined by the ratio between the inelastic and elastic maximum lateral displacement demands. Three options are investigated in order to express the inelastic response spectra in terms of: ductility demand, yield strength reduction factor, and inelastic deformation ratio which depends on the period, the post-to-preyield stiffness ratio, the yield strength and the peak ground acceleration. This new inelastic deformation ratio ($C_{\eta}$) is describes the response spectra and is related to the capacity curve (pushover curve): normalized yield strength coefficient (${\eta}$), post-to-preyield stiffness ratio (${\alpha}$), natural period (T), peak ductility factor (${\mu}$), and the yield strength reduction factor ($R_y$). For illustrative purposes, instantaneous ductility demand and yield strength reduction factor for a SDOF system subject to various recorded motions (El-Centro 1940 (N/S), Boumerdes: Algeria 2003). The method accuracy is investigated and compared to classical formulations, for various hysteretic models and values of the normalized yield strength coefficient (${\eta}$), post-to-preyield stiffness ratio (${\alpha}$), and natural period (T). Though the ductility demand and yield strength reduction factor differ greatly for some given T and ${\eta}$ ranges, they remain take close when ${\eta}>1$, whereas they are equal to 1 for periods $T{\geq}1s$.

• Earthquakes and Structures
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• v.10 no.1
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• pp.105-123
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• 2016

In this paper, using the probabilistic methods, the seismic demand of buckling restrained braced frames subjected to earthquake was evaluated. In this regards, 4, 6, 8, 10, 12 and 14-storybuildings with different buckling restrained brace configuration (including diagonal, split X, chevron V and Inverted V bracings) were designed. Because of the inherent uncertainties in the earthquake records, incremental dynamical analysis was used to evaluate seismic performance of the structures. Using the results of incremental dynamical analysis, the "capacity of a structure in terms of first mode spectral acceleration", "fragility curve" and "mean annual frequency of exceeding a limit state" was determined. "Mean annual frequency of exceeding a limit state" has been estimated for immediate occupancy (IO) and collapse prevention (CP) limit states using both Probabilistic Seismic Demand Analysis (PSDA) and solution "based on displacement" in the Demand and Capacity Factor Design (DCFD) form. Based on analysis results, the inverted chevron (${\Lambda}$) buckling restrained braced frame has the largest capacity among the considered buckling restrained braces. Moreover, it has the best performance among the considered buckling restrained braces. Also, from fragility curves, it was observed that the fragility probability has increased with the height.

• Earthquakes and Structures
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• v.19 no.2
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• pp.129-144
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• 2020

In this study, the idea of damping force linearly proportional to horizontal isolation displacement is implemented into sloped rolling-type bearings in order to meet different seismic performance goals. In addition to experimentally demonstrating its practical feasibility, the previously developed analytical model is further modified to be capable of accurately predicting its hysteretic behavior. The numerical predictions by using the modified analytical model present a good match of the shaking table test results. Afterward, several sloped rolling-type bearings designed with linearly variable damping force are numerically compared with a bearing designed with conventional constant damping force. The initial friction damping force adopted in the former is designed to be smaller than the constant one adopted in the latter. The numerical comparison results indicate that when the horizontal isolation displacement does not exceed the designed turning point (or practically when subjected to minor or frequent earthquakes that seldom have a great displacement demand for seismic isolation), the linearly variable damping force design can exhibit a better acceleration control performance than the constant damping force design. In addition, the former, in general, advantages the re-centering performance over the latter. However, the maximum horizontal displacement response of the linearly variable damping force design, in general, is larger than that of the constant damping force design. It is particularly true when undergoing a horizontal isolation displacement response smaller than the designed turning point and designing a smaller value of initial friction damping force.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.54 no.12
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• pp.527-531
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• 2005

Because of increasing demand for safety of the power transformer, the seismic qualification process in accordance with the standard of IEEE Std 693-1997 is essentially required by customer. Dynamic analysis method and static analysis method were used to qualify the seismic withstanding of the power transformer at high seismic level. Maximum stress was detected at the connection between the main structure and appendages, and maximum displacement was detected at the point of appendage's end tip. Load path and substructure system can be considered as important elements to prevent over stress and over displacement.

• Earthquakes and Structures
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• v.22 no.6
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• pp.585-595
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• 2022

Using the nonlinear static procedures has become very common in seismic codes to achieve the nonlinear response of the structure during an earthquake. The capacity spectrum method (CSM) adopted in ATC-40 is considered as one of the most known and useful procedures. For this procedure the seismic demand can be approximated from the maximum deformation of an equivalent linear elastic Single-Degree-of-Freedom system (SDOF) that has an equivalent damping ratio and period by using an iterative procedure. Data from the results of this procedure are plotted in acceleration- displacement response spectrum (ADRS) format. Different improvements have been made in order to have more accurate results compared to the Non Linear Time History Analysis (NL-THA). A new procedure is presented in this paper where the iteration process shall not be required. This will be done by estimation the ductility demand response spectrum (DDRS) and the corresponding effective damping of the bilinear system based on a new parameter of control, called normalized yield strength coefficient (η), while retaining the attraction of graphical implementation of the improved procedure of the FEMA-440. The proposed procedure accuracy should be verified with the NL-THA analysis results as a first implementation. The comparison shows that the new procedure provided a good estimation of the nonlinear response of the structure compared with those obtained when using the NL-THA analysis.

• Earthquakes and Structures
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• v.22 no.1
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• pp.15-23
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• 2022

One of the key tools in assessing the seismic vulnerability of the structures is the use of fragile functions, which is the possibility of damage from a particular damage surface for several levels of risk from the seismic movements of the earth. The aim of this study is to investigate the effect of two categories of earthquake events on the fragile curve (FRC) of the steel construction system. In this study, the relative lateral displacement of the structures is considered as a damage criterion. The limits set for modifying the relative lateral position in the HAZUS instruction are used to determine the failure modes, which include: slight, moderate, extensive and complete. The results show, as time strong-motion increases, the probability of exceeding (PoE) increases (for Peak ground acceleration (PGA) less than 0.5). The increase in seismic demand increases the probability of exceeding. In other words, it increases the probability of exceeding, if the maximum earthquake acceleration increases. Also, 7-storey model in extensive mode has 20 and 26.5% PoE larger than 5- and 3-storey models, respectively.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1998.10a
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• pp.3-11
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• 1998

Response of tall buildings to near-field ground motions with distinct low-frequency pulses can differ dramatically from, for example, the response to the 1940 El Centro ground motion. For the same peak ground acceleration (PGA) and duration of shaking, ground motions with a pulse-like characteristic can generate much higher base shear, inter-story drifts and roof displacement in a high-rise building as compared to ground motions without the characteristic pulse. Also, the ductility demand is much higher and the effectiveness of supplemental damping is lower for pulse-like ground motions. This paper presents a simple interpretation of the response characteristics for two recorded and one synthetic near-field pulse-like ground motions.

• Journal of the Earthquake Engineering Society of Korea
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• v.15 no.5
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• pp.35-44
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• 2011

PGA (Peak Ground Acceleration) is the parameter which indicates the peak value for strong ground motion and is mainly due to the intensity of the seismic wave. Usually, seismic waves can consist of different characteristics and can have different effects on structures. Therefore, it may be undesirable that the effects of a seismic wave are evaluated only based on the PGA. In this study, time history analysis was executed with a single degree of freedom model for inelastic seismic analysis. The numerical model was assumed to be a perfect elasto-plastic model. Input accelerations were made with El Centro NS (1940), other earthquake records and artificial earthquakes. The displacement ductility demand and cumulative dissipated energy, which were calculated from other artificial earthquakes, were compared. As a result, different responses from other seismic waves which have the same PGA were identified. Therefore, an index which could reflect both seismic and structural characteristics is needed. The SI (Spectrum Intensity) scale which could be obtained from integration by parts of the velocity response spectrum could be an index reflecting the inelastic seismic response of structures. It can be possible to identify from correlation analysis among the SI scale, displacement ductility demand and cumulative dissipated energy that the SI scale is sufficient to be an index for the inelastic response of structures under seismic conditions.

• Earthquakes and Structures
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• v.3 no.2
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• pp.141-168
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• 2012

The Retrofit Yield Spectrum (RYS) is a new spectrum-based device that relates seismic demand of a retrofitted structure with the fundamental design parameters of the retrofit. This is obtained from superposition of Yield Point Spectra with design charts that summarize in pertinent spectrum-compatible coordinates the attributes of a number of alternative retrofit scenarios. Therefore, once the requirements for upgrading a given structure have been determined, the RYS enable direct insight of the sensitivity of the seismic response of the upgraded structure to the preliminary design decisions made while establishing the retrofit plan. By virtue of their spectrum-based origin, RYS are derived with reference to a single mode of structural vibration; a primary objective is to control the contribution of this mode in the retrofit design so as to produce a desirable distribution of damage at the ultimate limit state by removing soft storey formations and engaging the maximum number of structural members in deformation, in response to the input motion. Calculations are performed with reference to the yield-point, where secant stiffness is proportional to the flexural strength of reinforced concrete members. Derivation and use of the Retrofit Yield Spectra (RYS) refers to the seismic demand expressed either in terms of spectral acceleration, spectral displacement or interstory drift, at yield of the first storey. A reinforced concrete building that has been tested in full scale to a sequence of simulated earthquake excitations is used in the paper as a demonstration case study to examine the effectiveness of the proposed methodology.

• Geomechanics and Engineering
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• v.34 no.4
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• pp.341-380
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• 2023

This study evaluates the seismic fragilities in fill slopes in South Korea through parametric finite element analyses that have been barely investigated thus far. We consider three slope geometries for a slope of height 10 m and three slope angles, and two soil types, namely frictional and frictionless, associated with two soil states, loose and dense for frictional soils and soft and stiff for frictionless soils. The input ground motions accounting for four site conditions in South Korea are obtained from one-dimensional site response analyses. By comparing the numerical modeling of slopes using PLAXIS^2D against the previous studies, we compiled suites of the maximum permanent slope displacement (D_max) against two ground motion parameters, namely, peak ground acceleration (PGA) and Arias Intensity (I_A). A probabilistic seismic demand model is adopted to compute the probabilities of exceeding three limit states (minor, moderate, and extensive). We propose multiple seismic fragility curves as functions of a single ground motion parameter and numerous seismic fragility surfaces as functions of two ground motion parameters. The results show that soil type, slope angle, and input ground motion influence these probabilities, and are expected to help regional authorities and engineers assess the seismic fragility of fill slopes in the road systems in South Korea.