• Earthquakes and Structures
• /
• 제12권4호
• /
• pp.437-448
• /
• 2017

Soft or extreme soft storeys in multi-storied buildings cause localized damage (and even collapse) during strong earthquake shaking. The presence of such soft or extremely soft storey is identified through provisions of vertical stiffness irregularity in seismic design codes. Identification of the irregularity in a building requires estimation of lateral translational stiffness of each storey. Estimation of lateral translational stiffness can be an arduous task. A simple procedure is presented to estimate storey stiffness using only properties of fundamental lateral translational mode of oscillation (namely natural period and associated mode shape), which are readily available to designers at the end of analysis stage. In addition, simplified analytical expressions are provided towards identifying stiffness irregularity. Results of linear elastic time-history analyses indicate that the proposed procedure captures the irregularity in storey stiffness in both low- and mid-rise buildings.

• Structural Engineering and Mechanics
• /
• 제56권4호
• /
• pp.569-588
• /
• 2015

A comprehensive methodology is proposed for design of metallic dampers in seismic retrofit of earthquake-damaged frame structures. It is assumed that the metallic dampers remain elastic and only provide stiffness during frequent earthquake (i.e., earthquake with a 63% probability of exceedance in 50-year service period), while in precautionary earthquake (i.e., earthquake with a 10% probability of exceedance in 50-year service period), the metallic dampers yield before the main frame and dissipate most of the seismic energy to either prevent or minimize structural damages. Therefore by converting multi-story frame to an equivalent single-degree-of-freedom system, the added stiffness provided by metallic dampers is designed to control elastic story drifts within code-based demand under frequent earthquake, and the added damping with the combination of added stiffness influences is obtained to control structural stress within performance-based target under precautionary earthquake. With the equivalent added damping ratio, the expected damping forces provided by metallic dampers can be calculated to carry out the configuration and design of metallic dampers along with supporting braces. Based on a detailed example for retrofit of an earthquake-damaged reinforced concrete frame by using metallic dampers, the proposed design procedure is demonstrated to be simple and practical, which can not only meet current China's design codes but also be used in retrofit design of earthquake-damaged frame with metallic damper for reaching desirable performance objective.

• Structural Engineering and Mechanics
• /
• 제17권2호
• /
• pp.215-244
• /
• 2004

There is an ever-increasing demand for assessment of earthquake effects on transportation structures, emphasised by the crippling consequences of recent earthquakes hitting developed countries reliant on road transportation. In this work, vulnerability functions for RC bridges are derived analytically using advanced material characterisation, high quality earthquake records and adaptive inelastic dynamic analysis techniques. Four limit states are employed, all based on deformational quantities, in line with recent development of deformation-based seismic assessment. The analytically-derived vulnerability functions are then compared to a data set comprising observational damage data from the Northridge (California 1994) and Hyogo-ken Nanbu (Kobe 1995) earthquakes. The good agreement gives some confidence in the derived formulation that is recommended for use in seismic risk assessment. Furthermore, by varying the dimensions of the prototype bridge used in the study, and the span lengths supported by piers, three more bridges are obtained with different overstrength ratios (ratio of design-to-available base shear). The process of derivation of vulnerability functions is repeated and the ensuing relationships compared. The results point towards the feasibility of deriving scaling factors that may be used to obtain the set of vulnerability functions for a bridge with the knowledge of a 'generic' function and the overstrength ratio. It is demonstrated that this simple procedure gives satisfactory results for the case considered and may be used in the future to facilitate the process of deriving analytical vulnerability functions for classes of bridges once a generic relationship is established.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2002년도 봄 학술발표회 논문집
• /
• pp.53-60
• /
• 2002

It has been recognized that damage control must become a more explicit design consideration. In an effort to develop design methods based on performance it is clear that the evaluation of the inelastic response is required. The methods available to the design engineer today are nonlinear time history analyses, or monotonic static nonlinear analyses, or equivalent static analyses with simulated inelastic influences. Some codes proposed the capacity spectrum method based on the nonlinear static(pushover) analysis to determine earthquake-induced demand given the structure pushover curve. This procedure is conceptually simple but iterative and time consuming with some errors. This paper presents a nonlinear direct spectrum method to evaluate seismic Performance of structure, without iterative computations, given the structural initial elastic period and yield strength from the pushover analysis, especially for multi degree of freedom structures. The purpose of this paper is to investigate accuracy and confidence of this method from a point of view of various earthquakes and unloading stiffness degradation parameters.

• Structural Engineering and Mechanics
• /
• 제78권1호
• /
• pp.53-66
• /
• 2021

The determination of the damage index to reveal the performance level of a structure can constitute the seismic risk generalization approach based on the parametric analysis. This study implemented this concept to one kind of civil engineering structure that is the concrete gravity dam. Different cases of the structure exhibit their individual responses, which constitute different considerations. Therefore, this approach allows the parametric study of concrete as well as soil for evaluating the seismic nature in the generalized case. To ensure that the target algorithm applicable to most of the concrete gravity dams, a very simple procedure has been considered. In order to develop a correlated algorithm (by response surface methodology; RSM) between the ground motion and the structural property, randomized sampling was adopted through a stochastic method called half-fractional central composite design. The responses in the case of fluid-foundation-dam interaction (FFDI) make it more reliable by introducing the foundation as being bounded by infinite elements. To evaluate the seismic generalization of FFDI models, incremental dynamic analysis (IDA) was carried out under the impacts of various earthquake records, which have been selected from the Pacific Earthquake Engineering Research Center data. Here, the displacement-based damage indexed fragility curves have been generated to show the variation in the seismic pattern of the dam. The responses to the sensitivity analysis of the various parameters presented here are the most effective controlling factors for the concrete gravity dam. Finally, to establish the accuracy of the proposed approach, reliable verification was adopted in this study.

• 한국지반공학회논문집
• /
• 제22권4호
• /
• pp.61-71
• /
• 2006

본 논문에서는 유효응력모델을 이용하여 포화된 사면의 동적거동에 관한 연구를 수행하였다. 수치해석에는 저자가 개발한 연성 유효응력모델인 UBSSAND모델을 이용하였으며, 이 모델은 초기전단응력이 수평면에 작용하는 경우와 작용하지 않는 경우를 포함한 반복 직접단순전단시험 자료를 이용하여 검증하였다. 검증된 모델은 느슨한 Fraser River 모래로 성형된 사면을 가진 원심모형모델의 동적거동을 예측하였다. 예측된 과잉간극수압, 가속도 및 변위를 계측치와 서로 비교하였으며, 예측치와 계측치는 비교적 서로 잘 일치하였다. 전단응력도의 응력전환형태는 초기전단응력과 반복전단응력의 크기에 따라 달라지며, 이는 지진시 포화된 사면의 안정해석에 아주 중요한 역할을 하고 있음을 알 수 있었다. 전단응력도의 응력전환이 발생하지 않을 경우에 사면근처의 모래는 낮은 유효응력 구속압과 그에 따른 팽창성으로(부의 과잉간극수압발생) 유효응력이 증가하여, 동적하중 하의 사면의 변위를 저지하였다. 이와 같은 유효응력모델은 액상화를 고려한 지반구조물의 내진해석에 유용하게 사용될 수 있다.

• 대한토목학회논문집
• /
• 제31권2A호
• /
• pp.59-69
• /
• 2011

성능기반 내진 설계방법의 설계철학을 가지고 있는 비선형 정적 해석법(NSPs)은 최근 구조물의 지진해석방법으로서 그 사용성을 인정받고 있다. 비선형 정적 해석법을 통한 지진해석은 기존의 비선형 시간 이력법에 비해서 방법이 간단하며, 직관적으로 구조물의 지진해석을 수행할 수 있는 등의 장점으로 빌딩구조물의 지진해석법으로 널리 사용되고 있다. 하지만, 기본 진동모드에 의해서 구조물의 거동이 지배되지 않는 구조물의 경우에는 그 사용성에 대한 연구가 매우 제한적이다. 이를 개선하기 위한 고차모드의 기여분을 반영할 수 있는 비선형 정적 해석법으로 모드별 비탄성 정적해석법(Modal Pushover Analysis; MPA)이 제시되었고, 또한 이를 개선한 개선된 모드별 비탄성 정적해석법(Improved Modal Pushover Analysis; IMPA) 역시 소개되었다. 본 논문에서는 기존에 소개된 네가지 비선형 정적 해석법을 이용하여 국내에 설계/시공된 두 사장교의 지진해석 가능성을 알아보며, 각 방법의 장/단점을 분석 하여 비선형 정적 해석법의 응용가능성에 대해서 알아보았다.

• Structural Engineering and Mechanics
• /
• 제73권5호
• /
• pp.529-542
• /
• 2020

As limited well-documented experimental data are available for assessing the attributes of different deformation components of flanged walls, few appropriate models have been established for predicting the inelastic responses of flanged walls, especially those of asymmetrical flanged walls. This study presents the experimental results for three large-scale T-shaped reinforced concrete walls and examines the variations in the flexural, shear, and sliding components of deformation with the total deformation over the entire loading process. Based on the observed deformation behavior, a simple model based on moment-curvature analysis is established to estimate flexural deformations, in which the changes in plastic hinge length are considered and the deformations due to strain penetration are modeled individually. Based on the similar gross shapes of the curvature and shear strain distributions over the wall height, a proportional relationship is established between shear displacement and flexural rotation. By integrating the deformations due to flexure, shear, and strain penetration, a new load-deformation analytical model is proposed for flexure-dominant flanged walls. The proposed model provides engineers with a simple, accurate modeling tool appropriate for routine design work that can be applied to flexural walls with arbitrary sections and is capable of determining displacements at any position over the wall height. By further simplifying the analytical model, a simple procedure for estimating the ultimate displacement capacity of flanged walls is proposed, which will be valuable for performance-based seismic designs and seismic capacity evaluations.

• Earthquakes and Structures
• /
• 제14권2호
• /
• pp.155-165
• /
• 2018

Methods based on nonlinear static analysis as simple tools could be used for the seismic analysis and assessment of structures. In the present study, capability of the N2 method as a well-known nonlinear analysis procedure examines for the estimation of the damage index of multi-storey reinforced concrete frames. In the implemented framework, equivalent single-degree-of-freedom (SDOF) models are utilized for the global damage estimation of multi-degree-of-freedom (MDOF) systems. This method does not require high computational analysis and subsequently decreases the required time of seismic design and assessment process. To develop the methodology, RC frames with period range from 0.4 to 2.0 s under 40 records are studied. The effectiveness of proposed technique is evaluated through numerical study under near- and far-field earthquake ground motions. Finally, the results of developed models are compared with two other simplified schemes along with nonlinear time history analysis results of multi-storey frames. To improve the accuracy of damage estimation, a modified relation is presented based on the N2 method results for near- and far-field earthquakes.

• 한국지반환경공학회 논문집
• /
• 제7권6호
• /
• pp.133-143
• /
• 2006

본 논문에서는 저자가 제안한 유효응력모델을 이용하여 지진시 사면의 동적거동에 관한 수치해석을 수행하였다. 항복함수는 동일한 응력비를 가진 무한개의 방사선을 의미하며, 비관련 유동규칙을 가진 탄소성모델인 UBCSAND를 이용하였다. 이 모델은 FLAC내에 내장된 Mohr-Coulomb모델을 변형한 형태이다. UBCSAND모델을 이용하여 RPI에서 수행한 원심모형실험결과를 예측하였다. 먼저, UBCSAND모델을 Nevada모래를 사용한 반복 직접단순전단시험결과를 이용하여 검증하였으며, 액상화전후의 거동을 예측하였다. 이와 같이 검증된 모델을 원심모형실험에서 계측된 가속도, 과잉간극 수압, 변위와 서로 비교하였다. 일반적으로 계측치와 예측치가 일치하였다. 유효응력모델을 이용한 동적 수치해석기법은 서부 캐나다에서 댐, 교량, 터널, 파이프라인과 관련된 액상화 프로젝트에 실제 사용되고 있다.