• Steel and Composite Structures
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• 제16권2호
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• pp.135-156
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• 2014

In this research the effect of seismic design level as a practical approach for progressive collapse mitigation and reaching desired structural safety against it in seismically designed concentric braced frame buildings was investigated. It was achieved by performing preliminary and advanced progressive collapse analysis of several split-X braced frame buildings, designed for each seismic zone according to UBC 97 and by applying various Seismic Load Factors (SLFs). The outer frames of such structures were studied for collapse progression while losing one column and connected brace in the first story. Preliminary analysis results showed the necessity of performing advanced element loss analysis, consisting of Vertical Incremental Dynamic Analysis (VIDA) and Performance-Based Analysis (PBA), in order to compute the progressive collapse safety of the structures while increasing SLF for each seismic zone. In addition, by sensitivity analysis it became possible to introduce the equation of structural safety against progressive collapse for concentrically braced frames as a function of SLF for each seismic zone. Finally, the equation of progressive collapse safety as a function of bracing member capacity was presented.

• 한국구조물진단유지관리공학회 논문집
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• 제18권2호
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• pp.9-20
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• 2014

철골 중간모멘트골조는 강한 지반운동에 대하여 적합한 저항능력을 확보하기 위한 지진력저항시스템으로서 일반적으로 사용되고 있다. 하지만 국내의 대다수 중 저층 철골건축물은 내진설계가 도입되기 이전에 건설되었거나 현재의 내진설계기준의 요구조건을 준수하지 않은 것들로, 이러한 건물들이 가지는 내진성능에는 의문점이 존재한다. 이와 같은 문제점의 인식에 기반하여 본 연구에서는 국내 철골 중간 모멘트골조의 내진성능에 대한 정량적 제시를 목표로 우선 층수 종류, 지진에 대한 보유내력, 부재 연성도, 제진장치의 유무를 변수로 하여 표본 건물을 설계하였다. 표본 건물의 내진 성능과 붕괴 매커니즘은 비선형 정적해석과 증분동적해석으로부터 획득한 붕괴여유비와 붕괴확률을 이용하여 분석하였다. 해석결과를 통하여 현행 국내기준에 따라 내진설계된 신축건물은 설계지진에 대해 충분한 내진성능을 가졌으며, 이에 반해 구조부재의 연성저감이 발생하거나 낮은 설계 밑면전단력에 대한 저항력을 가진 기존건물의 경우에는 높은 붕괴확률을 가지며 목표로 한 내진성능을 만족시키지 못하는 것으로 나타났다. 이와 같은 내진성능을 충족시키지 못하는 내진설계 도입 이전의 건물에 대해서 에너지 소산장치를 통해 보강하게 되면 장치의 에너지 소산능력뿐만 아니라 소성힌지의 재분배를 통해 붕괴확률 및 내진성능이 신축건물 수준으로 향상되었다.

• Steel and Composite Structures
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• 제21권3호
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• pp.479-500
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• 2016

Seismic design criteria allow enhancing the structural ductility and controlling the damage distribution. Therefore, detailing rules and design requirements given by current seismic codes might be also beneficial to improve the structural robustness. In this paper a comprehensive parametric study devoted to quantifying the effectiveness of seismic detailing for steel Moment Resisting Frames (MRF) in limiting the progressive collapse under column loss scenarios is presented and discussed. The overall structural performance was analysed through nonlinear static and dynamic analyses. With this regard the following cases were examined: (i) MRF structures designed for wind actions according to Eurocode 1; (ii) MRF structures designed for seismic actions according to Eurocode 8. The investigated parameters were (i) the number of storeys; (ii) the interstorey height; (iii) the span length; (iv) the building plan layout; and (v) the column loss scenario. Results show that structures designed according to capacity design principles are less robust than wind designed ones, provided that the connections have the same capacity threshold in both cases. In addition, the numerical outcomes show that both the number of elements above the removed column and stiffness of beams are the key parameters in arresting progressive collapse.

• 한국지진공학회논문집
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• 제28권1호
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• pp.11-20
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• 2024

The ductility of the system based on the capacity of each structural member constituting the seismic force-resisting system is a significant factor determining the structure's seismic performance. This study aims to provide a procedure to supplement the current seismic design criteria to secure the system's ductility and improve the seismic performance of the steel ordinary moment frames. For the study, a nonlinear analysis was performed on the 9- and 15-story model buildings, and the formation of collapse mechanisms and damage distribution for dynamic loads were analyzed. As a result of analyzing the nonlinear response and damage distribution of the steel ordinary moment frame, local collapse due to the concentration of structural damage was observed in the case where the influence of the higher mode was dominant. In this study, a procedure to improve the seismic performance and avoid inferior dynamic response was proposed by limiting the strength ratio of the column. The proposed procedure effectively improved the seismic performance of steel ordinary moment frames by reducing the probability of local collapse.

• Earthquakes and Structures
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• 제11권3호
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• pp.445-459
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• 2016

Quantitative estimation of seismic response of various structural systems at the collapse limit state is one of the most significant objectives in Performance-Based Earthquake Engineering (PBEE). Assessing the effects of uncertainties, due to variability in ground motion characteristics and random nature of earthquakes, on nonlinear structural response is a pivotal issue regarding collapse safety prediction. Incremental Dynamic Analysis (IDA) and fragility curves are utilized to estimate demand parameters and seismic performance levels of structures. Since producing these curves based on a large number of nonlinear dynamic analyses would be time-consuming, selection of appropriate earthquake ground motion records resulting in reliable responses with sufficient accuracy seems to be quite essential. The aim of this research study is to propose a methodology to assess the seismic behavior of reinforced concrete frames at collapse limit state via accurate estimation of seismic fragility curves for different Engineering Demand Parameters (EDPs) by using a limited number of ground motion records. Research results demonstrate that accurate estimating of structural collapse capacity is feasible through applying the proposed method offering an appropriate suite of limited ground motion records.

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

• Structural Engineering and Mechanics
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• 제71권3호
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• pp.305-315
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• 2019

Extremely long-span transmission tower-line system is an indispensable portion of an electricity transmission system, and its failures or collapse can impact on the entire electricity grid, affect the modern life, and cause great economic losses. It is therefore imperative to investigate the failure and safety of the transmission tower subjected to ground motions. In the present study, a detailed finite element (FE) model of a representative extremely long-span transmission tower-line system is established. A segmental damage indicator (SDI) is proposed to quantitatively assess the damage level of each segment of the transmission tower under earthquakes. Additionally, parametric studies are conducted to investigate the influence of different ground motions and incident angles on the ultimate capacity and weakest segment of the transmission tower. Finally, the collapse fragility curve in terms of the maximum SDI value and PGA is plotted for the exampled transmission tower. The results show that the proposed SDI can quantitatively assess the damage level of the segments, and thus determine the ultimate capacity and weakest segment of the transmission tower. Moreover, the different ground motions and incident angles have a significant influence on the SDI values of the transmission tower, and the collapse fragility curve is utilized to evaluate the collapse resistant capacity of the transmission tower subjected to ground motions.

• Earthquakes and Structures
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• 제15권5호
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• pp.541-553
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• 2018

In this paper a limit analysis based procedure for the rapid evaluation of the in-plane seismic capacity of masonry arch bridges is carried out. Attention has been paid to the effect of the backfill on the collapse load. A parametric investigation has been performed by varying the rise/span ratio and the results have been compared with those obtained by finite element modelling. The comparison highlights the conservative feature of the proposed model in terms of ultimate loads and a good agreement in terms of collapse mechanisms.

• Earthquakes and Structures
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• 제19권6호
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• pp.445-457
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• 2020

An ultra-high voltage (UHV) transmission system has the advantages of low circuitry loss, high bulk capacity and long-distance transmission capabilities over conventional transmission systems, but it is easier for this system to cross fault rupture zones and become damaged during earthquakes. This paper experimentally and numerically investigates the seismic responses and collapse failure of a UHV transmission tower-line system crossing a fault. A 1:25 reduced-scale model is constructed and tested by using shaking tables to evaluate the influence of the forward-directivity and fling-step effects on the responses of suspension-type towers. Furthermore, the collapse failure tests of the system under specific cross-fault scenarios are carried out. The corresponding finite element (FE) model is established in ABAQUS software and verified based on the Tian-Ma-Qu material model. The results reveal that the seismic responses of the transmission system under the cross-fault scenario are larger than those under the near-fault scenario, and the permanent ground displacements in the fling-step ground motions tend to magnify the seismic responses of the fault-crossing transmission system. The critical collapse peak ground acceleration (PGA), failure mode and weak position determined by the model experiment and numerical simulation are in relatively good agreement. The sequential failure of the members in Segments 4 and 5 leads to the collapse of the entire model, whereas other segments basically remain in the intact state.

• Steel and Composite Structures
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• 제13권6호
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• pp.561-570
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• 2012

Seismic collapse analysis requires efficient and automated method to perform thousands of time history analyses. The paper introduced the advantages of speed and convergence property of explicit method, provided a few techniques to accelerate speed of calculation and developed an automated procedure for collapse assessment, which combines the strong capacity of commercial explicit finite element software and the flexible, intelligent specialties of control program written in FORTRAN language aiming at collapse analysis, so that tedious and heavy work of collapse analysis based on FEMAP695 can be easily implemented and resource of calculation can be made the best use of. All the key commands of control program are provided to help analyzers and engineers to cope with collapse assessment conveniently.