• Earthquakes and Structures
• /
• 제15권2호
• /
• pp.155-164
• /
• 2018

Design of structures subjected to blast loads are usually carried out through nonlinear inelastic dynamic analysis followed by imposing acceptance criteria specified in design codes. In addition to comprehensive aspects of inelastic dynamic analyses, particularly in analysis and design of structures subjected to transient loads, they inherently suffer from convergence and computational cost problems. In this research, a strategy is proposed for design of steel moment resisting frames under far range blast loads. This strategy is inspired from performance based seismic design concepts, which is here developed to blast design. For this purpose, an algorithm is presented to calculate the capacity modification factors of frame members in order to simplify design of these structures subjected to blast loading. The present method provides a simplified design procedure in which the linear dynamic analysis is preformed, instead of the time-consuming nonlinear dynamic analysis. Nonlinear and linear analyses are accomplished in order to establish this design procedure, and consequently the final design procedure is proposed as a strategy requiring only linear structural analysis, while acceptance criteria of nonlinear analysis is implicitly satisfied.

• Steel and Composite Structures
• /
• 제39권3호
• /
• pp.243-259
• /
• 2021

In the present paper, a Monte Carlo-based framework is developed to investigate the accuracy and reliability of analytical fragility curves of steel moment-resisting frames and simple SDOF systems. It is also studied how the effectiveness of incremental dynamic analysis (IDA) and multiple stripes analysis (MSA) approaches, as two common nonlinear dynamic analysis methods, are influenced by the number of records and analysis stripes in fragility curves producing. Results showed that the simple SDOF systems do not provide accurate and reliable fragility curves compared with realistic steel moment-resisting structures. It is demonstrated that, the effectiveness of nonlinear dynamic analysis approaches is dependent on the fundamental period of structures, where in short-period structures, IDA is found to be more effective approach compared with MSA. This difference between the effectiveness of two analysis approaches decreases as the fundamental period of structures become longer. Using of 2 or 3 analysis stripes in MSA approach leads to significant inaccuracy and unreliability in the estimated fragility curves. Additionally, 15 number of ground motion records is recommended as a threshold of significant unreliability in estimated fragility curves, constructed by MSA.

• Steel and Composite Structures
• /
• 제46권5호
• /
• pp.621-635
• /
• 2023

The combination of replaceable and repairable properties in structures has introduced new approach called "Low Damage Design Structures". These structural systems are designed in such a way that through self-centering, primary members and specific connections neither suffer damage nor experience permanent deformations after being exposed to severe earthquakes. The purpose of this study is the seismic assessment of steel moment resisting frames with the aid of rigid rocking cores. To this end, three steel moment resisting frames of 4-, 8-, and 12-story buildings with and without rocking cores were developed. The nonlinear static analysis and incremental dynamic analysis were performed by considering the effects of the vertical and horizontal components of 16 strong ground motions, including far-fault and near-fault arrays. The results reveal that rocking systems benefit from better seismic performance and energy dissipation compared to moment resisting frames and thus structures experience a lower level of damage under higher intensity measures. The analyses show that the interstory drift in structures equipped with stiff rocking cores is more uniform in static and dynamic analyses. A uniform interstory drift distribution leads to a uniform distribution of the bending moment and a reduction in the structure's total weight and future maintenance costs.

• 한국공간구조학회논문집
• /
• 제7권3호
• /
• pp.87-95
• /
• 2007

The recent completions of free-form spatial structures provide us a very attractive form. To realize such an extraordinary shape, it is absolutely necessary that the connector systems have to be investigated the characteristics of the systems and analyzed with a practicable method. In this context, this research consists of not only literature research but also numerical analysis with selected connector systems, which was adopted in real free-form spatial structures. For numerical analysis, especially, finite element analysis (FEA) is performed with a various test parameter using a commercial program ANSYS. Consequently, the general characteristics of node connectors the moment-rotation-curves are presented by considering a large deformation effect as well as a multi-linear material properties.

• Structural Engineering and Mechanics
• /
• 제23권6호
• /
• pp.599-613
• /
• 2006

A method for the dynamical analysis of FE discretized uncertain linear and nonlinear structures is presented. This method is based on the moment equation approach, for which the differential equations governing the response first and second-order statistical moments must be solved. It is shown that they require the cross-moments between the response and the random variables characterizing the structural uncertainties, whose governing equations determine an infinite hierarchy. As a consequence, a closure scheme must be applied even if the structure is linear. In this sense the proposed approach is approximated even for the linear system. For nonlinear systems the closure schemes are also necessary in order to treat the nonlinearities. The complete set of equations obtained by this procedure is shown to be linear if the structure is linear. The application of this procedure to some simple examples has shown its high level of accuracy, if compared with other classical approaches, such as the perturbation method, even for low levels of closures.

• Structural Engineering and Mechanics
• /
• 제63권2호
• /
• pp.259-268
• /
• 2017

In this paper, the incremental nonlinear dynamic analysis is used to evaluate the seismic performance of steel moment frame structures. To this purpose, three special moment frame structure with 5, 10 and 15 stories are designed according to the Iran's national building code for steel structures and the provisions for design of earthquake resistant buildings (2800 code). Incremental Nonlinear Analysis (IDA) is performed for 15 different ground motions, and responses of the structures are evaluated. For the immediate occupancy and the collapse prevention performance levels, the probability that seismic demand exceeds the seismic capacity of the structures is computed based on FEMA350. Also, fragility curves are plotted for three high-code damage levels using HASUS provisions. Based on the obtained results, it is evident that increase in the height of the frame structures reduces the reliability level. In addition, it is concluded that for the design earthquake the probability of exceeding average collapse prevention level is considerably larger than high and full collapse prevention levels.9.

• 한국전산구조공학회논문집
• /
• 제13권3호
• /
• pp.361-371
• /
• 2000

RC 구조물은 서로 다른 재료적 특성을 지닌 콘크리트와 철근의 복합구조이고, 특히 콘크리트는 복잡한 소성거동을 나타내는 재료이다. 따라서 RC 구조물의 소성해석을 위해서는 콘크리트와 철근 각각의 재료특성과 소성거동을 묘사할 수 있는 세밀한 모델링 기법이 필요하지만, 이때 발생하는 모델링의 어려움, 모델링 규모, 계산용량 및 수렴성 등의 문제점으로 인하여 소성해석 수행에 많은 시간과 노력이 소요되거나 해석자체가 불가능하게 된다. 따라서 본 논문에서는 간편한 RC 구조물의 소성해석을 위해 RC 부재와 동일한 소성거동을 나타내는 균질·등방 재료로의 물성치환 방법을 제시하였다. 물성치환 원리는 RC 부재의 소성거동 특성, 즉 항복모멘트, 항복곡률 및 극한모멘트, 극한곡률로 표현되는 bi-linear 형태의 모멘트-곡률 관계를 이용하여, 이와 동일한 모멘트-곡률 관계(bi-linear 형태의 응력 변형률 관계)를 갖는 균질·등방 재료를 생성하였다. 또한 실제 RC 부재 해석모델과 치환된 균질·등방 재료를 이용한 해석모델에 대한 소성해석 결과를 비교·분석하여 본 연구의 타당성을 검증하였다.

• 한국지진공학회논문집
• /
• 제13권5호
• /
• pp.51-60
• /
• 2009

안전한 내진설계를 위해서는 각 부재에 요구되는 소성변형 요구량을 정확히 예측하여야 한다. 본 연구에서는 등가정적내진설계에 쉽게 활용할 수 있도록, 복잡한 비선형해석 없이 탄성해석을 사용하여 모멘트골조 부재의 소성변형을 평가하는 방법을 개발하였다. 각 부재의 소성변형은 부재 강성과 탄성해석 결과로부터 직접 결정되는 층간변위비 요구량 및 모멘트 재분배 등의 설계 변수로부터 결정된다. 제안된 방법을 8층 2경간의 모멘트골조에 적용하고, 비선형해석을 통하여 제안된 방법의 정확성을 검증하였다. 검증결과, 제안된 방법은 비선형거동에 의한 층간변위비 요구량과 각 부재의 소성변형 요구량을 정확히 평가하였다. 제안된 방법은 부재연성설계와 같은 신축건물의 내진설계에 활용할 수 있을 뿐만 아니라 기존건물의 내진성능평가에도 활용될 수 있을 것으로 기대된다.

• Structural Engineering and Mechanics
• /
• 제52권2호
• /
• pp.291-306
• /
• 2014

In this paper the progressive collapse resisting capacity of steel moment frames with MR dampers is evaluated, and a preliminary design procedure for the dampers to prevent progressive collapse is suggested. Parametric studies are carried out using a beam-column subassemblage with varying natural period, yield strength, and damper force. Then the progressive collapse potentials of 15-story steel moment frames installed with MR dampers are evaluated by nonlinear dynamic analysis. The analysis results of the model structures showed that the MR dampers are effective in preventing progressive collapse of framed structures subjected to sudden loss of a first story column. The effectiveness is more noticeable in the structure with larger vertical deflection subjected to larger inelastic deformation. The maximum responses of the structure installed with the MR dampers designed to meet a given target dynamic response factor generally coincided well with the target value on the conservative side.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 1991년도 봄 학술발표회 논문집
• /
• pp.34-42
• /
• 1991

This study is directed for the development of an efficient system-level Importance Sampling Technique for system reliability analysis of bridge structures Many methods have been proposed for structural reliability assessment purposes, such as the First-order Second-Moment Method, the Advanced Second-Moment Method, Computer Simulation, etc. The Importance Sampling Technique can be employed to obtain accurate estimates of the required probability with reasonable computation effort. Based on the observation and the results of application, it nay be concluded that Importance Sampling Method is a very effective tool for the system reliability analysis.