• Steel and Composite Structures
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• 제42권1호
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• pp.59-74
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• 2022

This study introduces a general reliability-based, performance-based design framework to design frames regarding their uncertainties and user-defined design goals. The Iterative-R method extracted from the main framework can designate a proper R (i.e., response modification factor) satisfying the design goal regarding target reliability index and pre-defined probability of collapse. The proposed methodology is based on FEMA P-695 and can be used for all systems that FEMA P-695 applies. To exemplify the method, multiple three-dimensional, four-story steel special moment-resisting frames are considered. Closed-form relationships are fitted between frames' responses and the modeling parameters. Those fits are used to construct limit state functions to apply reliability analysis methods for design safety assessment and the selection of proper R. The frameworks' unique feature is to consider arbitrarily defined probability density functions of frames' modeling parameters with an insignificant analysis burden. This characteristic enables the alteration in those parameters' distributions to meet the design goal. Furthermore, with sensitivity analysis, the most impactful parameters are identifiable for possible improvements to meet the design goal. In the studied examples, it is revealed that a proper R for frames with different levels of uncertainties could be significantly different from suggested values in design codes, alarming the importance of considering the stochastic behavior of elements' nonlinear behavior.

• 한국환경복원기술학회지
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• 제9권1호
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• pp.100-111
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• 2006

This study was carried out to increase the efficiency of site investigation through the evaluation of the applicable methods of investigation for cutting slope design. In an effort to find out the applicability of the method employed during the slope investigation, some tests were carried out on 6 subjects i.e location of weak zones, characteristics of discontinuities, distribution of strata, in situ tests for geo-technical properties, laboratory test and estimation of weathering. The method was highly applicable and produced expected results during the test of weak zones, discontinuities and distribution of strata. In order to apply the method to in- situ test for geo-technical properties and laboratory test on soil and rock slope, a statistic analysis of the existing data were required in advance. However its design applicability on rock slope was good although actual cases of application were not many due to limitation of the cases for investigation. The method was frequently referenced but not actually applied for anti seismic design test and estimation of weathering.

• Structural Engineering and Mechanics
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• 제65권4호
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• pp.401-408
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• 2018

Concentric braced frames are commonly used in steel structures to withstand lateral forces. One of the drawbacks of these systems is the possibility that the braces are buckled under compressive loads, which leads to sudden reduction of the bearing capacity of the structure. To overcome this deficiency, the idea of the Buckling Restrained Brace (BRB) has been proposed in recent years. The length of a BRB steel core can have a significant effect on its overall behavior, since it directly influences the energy dissipation capability of the member. In this study, numerical methods have been utilized for investigation of the optimum length of BRB steel cores. For this purpose, BRBs with different lengths placed into several two-dimensional framing systems with various heights were considered. Then, the Response History Analysis (RHA) was performed, and finally, the optimum steel core length of BRBs and its effect on the responses of the overall system were investigated. The results show that the shortest length where failure does not occur is the best length that can be proposed as the optimum steel core length of BRBs. This length can be obtained through a formula which has been derived and verified in this study by both analytical and numerical methods.

• Geomechanics and Engineering
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• 제31권3호
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• pp.291-304
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• 2022

Maximum shear modulus (G_max or G₀) is an important soil property useful for many engineering applications, such as the analysis of soil-structure interactions, soil stability, liquefaction evaluation, ground deformation and performance of seismic design. In the current study, bender element (BE) tests are used to evaluate the effect of the void ratio, effective confining pressure, grading characteristics (D₅₀, C_u and C_c), anisotropic consolidation and initial fabric anisotropy produced during specimen preparation on the G_max of sand-gravel mixtures. Based on the tests results, an empirical equation is proposed to predict G_max in granular soils, evaluated by the experimental data. The artificial neural network (ANN) and Adaptive Neuro Fuzzy Inference System (ANFIS) models were also applied. Coefficient of determination (R²) and Root Mean Square Error (RMSE) between predicted and measured values of G_max were calculated for the empirical equation, ANN and ANFIS. The results indicate that all methods accuracy is high; however, ANFIS achieves the highest accuracy amongst the presented methods.

• Earthquakes and Structures
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• 제22권2호
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• pp.169-184
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• 2022

The importance of seismicity in developing countries and the strengthening of buildings is a topic of major importance. Therefore, the study of several solutions with the development of new technologies is of great importance to investigate the damage on retrofitted structures by using probabilistic methods. The Federal Emergency Management Agency considers three types of performance levels by considering different scenarios, intensity and duration. The selection and scaling of ground motions mainly depends on the aim of the study. Intensity-based assessments are the most common and compute the response of buildings for a specified seismic intensity. Assessments based on scenarios estimate the response of buildings to different earthquake scenarios. A risk-based assessment is considered as one of the most effective. This research represents a practical method for developing countries where exists many active faults, tall buildings and lack of good implementable approaches. Therefore, to achieve the main goal, two high-rise steel buildings have been modeled and assessed. The contribution of buckling-restrained braces in the elastic design of both buildings is firstly verified. In the nonlinear static range, both buildings presented repairable damage at the central top part and some life safety hinges at the bottom. The nonlinear incremental dynamic analysis was applied by 15 representative/scaled accelerograms to obtain levels of performance and fragility curves. The results shown that by using probabilistic methods, it is possible to estimate the probability of collapse of retrofitted buildings by buckling-restrained braces and tuned mass dampers, which are practical retrofitting options to protect existing structures against earthquakes.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2000년도 춘계 학술발표회 논문집 Proceedings of EESK Conference-Spring
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• pp.18-20
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• 2000

At 1:47 a.m, local time on September 21, 1999, a strong earthquake measured 7.3 on the Richter scale struck central Taiwan evoking another two earthquakes a few seconds late to wake up unprepared people of this small island. It caused 2,465 people killed 11,305 injured about 10,000 buildings collapsed and around 41,000 severely damaged, The major concerns after the earthquake are how to have learned from this natural disaster and how to rebuild earthquake-proof buildings without rendering up safety within reasonable costs. Inevitable actions for redrafting the building codes have been taken to re-strengthen the existing and new structures. Structural analysis tools and computer programs adopted by most practicing engineers have been re-examined to take into account the effects of the vertical component of ground shakings on structural responses. Most private structures were repaired by traditional methods without considering upgrading seismic resistibility because of economical reasons. Buildings open to the public are under consideration possibly enforced by making regulations to be upgraded to satisfy revised building codes. In addition new rehabilitation technologies such as structural control have been moving much faster than before and have become accepted by the public due to frequent reports by media and specialists. Building codes related to base isolators and energy absorption systems are still under legislation and expected to be published soon. Most of the new structures under construction designed by the building codes promulgated before the earthquake have been reconsidered to comply with the new codes even though it is not compulsory. Efforts have been made by the government engineering and research communities and universities in an attempt to reduce structural damage for future earthquakes and to construct if possible Taiwan as an earthquake-proof island.

• 콘크리트학회논문집
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• 제26권2호
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• pp.135-142
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• 2014

이 논문에서는 한국인근에서 강한 지진이 발생된 후 조사한 국내의 학교건물의 경우 86%가 지진에 취약한 것으로 나타났으며 내진설계가 된 학교건축물은 14%에 불과한 것으로 파악되고 있다. 이에 국내에서는 교육부가 주도하는 학교건축물의 내진보강프로젝트가 수행되고 있으나, 일본 등의 다양한 시스템내진보강에 대해서는 기술과 공법 등이 도입되어 국내의 실정에 맞는지 검토 및 검증 절차 없이 적용되고 있으나 부재내진보강에 대해서는 시스템내진보강에 밀려 실무적용 및 연구가 미비한 실정이다. 그러므로 최근에 부착 및 래핑형 복합재료를 이용한 기둥전단보강방법에 관한 실험 및 이론적인 연구를 진행하였다. 이 연구에서는 기존의 연구실적을 바탕으로 기존학교건물의 비선형해석을 통한 내진성능평가를 하고 기둥내진보강방법을 제시하여 그 효과를 실험적으로 입증한 후 실제 학교구조물을 설계 예로 들어 내진보강설계에 적용하고자한다.

• Structural Engineering and Mechanics
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• 제74권6호
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• pp.821-832
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• 2020

The fundamental period is an important parameter for seismic design and seismic risk assessment of building structures. In this paper, a simplified theoretical method to predict the fundamental period of masonry infilled reinforced concrete (RC) frame is developed based on the basic theory of engineering mechanics. The different configurations of the RC frame as well as masonry walls were taken into account in the developed method. The fundamental period of the infilled structure is calculated according to the integration of the lateral stiffness of the RC frame and masonry walls along the height. A correction coefficient is considered to control the error for the period estimation, and it is determined according to the multiple linear regression analysis. The corrected formula is verified by shaking table tests on two masonry infilled RC frame models, and the errors between the estimated and test period are 2.3% and 23.2%. Finally, a probability-based method is proposed for the corrected formula, and it allows the structural engineers to select an appropriate fundamental period with a certain safety redundancy. The proposed method can be quickly and flexibly used for prediction, and it can be hand-calculated and easily understood. Thus it would be a good choice in determining the fundamental period of RC frames infilled with masonry wall structures in engineering practice instead of the existing methods.

• 한국지진공학회논문집
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• 제22권4호
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• pp.253-259
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• 2018

Structure behaviors resulting from an earthquake are experimentally simulated mainly through a shaking table test. As for large-scale structures, however, size effects over a miniature may make it difficult to assess actual behaviors properly. To address this problem, research on the hybrid simulation is being conducted actively. This method is to implement numerical analysis on framework members that affect the general behavior of the structure dominantly through an actual scale experiment and on the rest parts by applying the substructuring technique. However, existing studies on hybrid simulation focus mainly on Slow experimental methods, which are disadvantageous in that it is unable to assess behaviors close to the actual level if material properties change depending on the speed or the influence of inertial force is significant. The present study aims to establish a Real-time hybrid simulation system capable of excitation based on the actual time history and to verify its performance and applicability. The hybrid simulation system built up in this study utilizes the ATS Compensator system, CR integrator, etc. in order to make the target displacement the same with the measured displacement on the basis of MATLAB/Simulink. The target structure was a 2-span bridge and an RC pier to support it was produced as an experimental model in order for the shaking table test and Slow and Real-time hybrid simulations. Behaviors that result from the earthquake of El Centro were examined, and the results were analyzed comparatively. In comparison with the results of the shaking table test, the Real-time hybrid simulation produced more similar maximum displacement and vibration behaviors than the Slow hybrid simulation. Hence, it is thought that the Real-time hybrid simulation proposed in this study can be utilized usefully in seismic capacity assessment of structural systems such as RC pier that are highly non-linear and time-dependent.

• 터널과지하공간
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• 제21권5호
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• pp.341-348
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• 2011

터널설계를 위해 상세지반조사를 실시한 결과 터널 주요통과구간에 지질이상대로서 암종경계부 및 단층대 구간이 예측되었다. 특히 지질이상대에서 황철석이 분포하는 것을 확인하였으며 대심도 구간 시추조사과정에서 단층파쇄대(F3)에서 피압에 의한 지하수 용출현상이 나타났다. 이에 따라 지질이상대 구간에서의 보강대책을 수립하기 위해 황철석 함유구간에 대한 시설물 보강대책을 검토하였으며, 피압수 다량 구간에서는 침투류 해석 및 차수대책 등 별도의 지보패턴을 계획하였다. 또한 한반도 인근 대지진이 주로 단층대에서 발생하고 있기 때문에 단층대 통과구간에 대해 지반-구조물 상호작호(SSI) 내진해석과 구조물 보강대책을 수립하였다.