• Structural Engineering and Mechanics
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• 제32권6호
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• pp.771-786
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• 2009

In the past few decades, effects of natural hazards, such as earthquakes and wind, on existing structures have attracted the attention of researchers and designers. More recently, however, the phenomenon of progressive collapse is becoming more recognized in the field of structural engineering. In practice, the phenomenon can result from a number of abnormal loading events, such as bomb explosions, car bombs, accidental fires, accidental blast loadings, natural hazards, faulty design and construction practices, and premeditated terrorist acts. Progressive collapse can result not only in disproportionate structural failure, but also disproportionate loss of life and injuries. This paper provides an up-to-date comprehensive review of this phenomenon and its momentousness in structural engineering communities. The literature reveals that although the phenomenon of progressive collapse of buildings is receiving considerable attention in the professional engineering community, more research work is still needed in this field to develop a new methodology for efficient and inexpensive design to better protect buildings against progressive collapse.

• 국제초고층학회논문집
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• 제9권2호
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• pp.127-154
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• 2020

Disproportionate collapse triggered by local structural failure may cause huge casualties and economic losses, being one of the most critical civil engineering incidents. It is generally recognized that ensuring robustness of a structure, defined as its insensitivity to local failure, is the most acceptable and effective method to arrest disproportionate collapse. To date, the concept of robustness in its definition and quantification is still an issue of controversy. This paper presents a detailed review on about 50 quantitative measures of robustness for building structures, being classified into structural attribute-based and structural performance-based measures (deterministic and probabilistic). The definition of robustness is first described and distinguished from that of collapse resistance, vulnerability and redundancy. The review shows that deterministic measures predominate in quantifying structural robustness by comparing the structural responses of an intact and damaged structure. The attribute-based measures based on structural topology and stiffness are only applicable to elastic state of simple structural forms while the probabilistic measures receive growing interest by accounting for uncertainties in abnormal events, local failure, structural system and failure-induced consequences, which can be used for decision-making tools. There is still a lack of generalized quantifications of robustness, which should be derived based on the definition and design objectives and on the response of a structure to local damage as well as the associated consequences of collapse. Critical issues and recommendations for future design and research on quantification of robustness are provided from the views of column removal scenarios, types of structures, regularity of structural layouts, collapse modes, numerical methods, multiple hazards, degrees of robustness, partial damage of components, acceptable design criteria.

• 국제초고층학회논문집
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• 제10권4호
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• pp.311-321
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• 2021

Perception of the public to structural fires is very important because there are only a number of tall timber buildings constructed in the world. People are hesitating to accept tall timber buildings, so it is essential to ensure the first generation of tall timber buildings to a very high standard, especially fire safety. Right now, there are no specific design standards or regulations for fire design of tall timber buildings in Europe. Even though heavy timber members have better fire resistance than steel components, many conditions still need to be verified before considering the use of timber materials, e.g. fire spread, post-fire collapse, etc. This research numerically explores the structural behaviours of a tall Glulam building when one of its internal Glulam (Glued laminated timber) columns fails after sustaining a full 120-min standard fire and is removed from the established finite element building model created in SAP2000. The numerical results demonstrate that the failure and removal of the selected internal Glulam column may lead to the local failure of the adjacent CLT (Cross laminated timber) floor slabs, but will not lead to large disproportionate damage and collapse of the whole building. Here, the building is assumed to be located in Glasgow, Scotland, UK.

• Structural Engineering and Mechanics
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• 제76권2호
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• pp.193-205
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• 2020

The growing need for assuring efficient and sustainable investments in civil engineering structures has determined a renovated interest in the rational design of such structures from designers, clients and authorities. As a result, risk-informed decision-making methodologies are increasingly being used as a direct decision tool or as an upper-level layer from which performance-based approaches are then calibrated against. One of the most important and challenging aspects of today's structural design is to adequately handle the system-level effects, the known unknowns and the unknown unknowns. These aspects revolve around assessing and evaluating relevant damage scenarios, namely those involving unacceptable/intolerable damage levels. Hence, the importance of risk analysis of disproportionate collapse, and along with it of robustness. However, the way robustness has been used in modern design codes varies substantially, from simple provisions of prescriptive rules to complex risk analysis of the disproportionate collapse. As a result, implementing design for robustness is still very much a grey area and more so when it comes to defining means to quantify robustness. This paper revisits the most common robustness frameworks, highlighting their merits and limitations, and identifies one among them which is very promising as a way forward to solve the still open challenges.

• Steel and Composite Structures
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• 제14권4호
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• pp.379-395
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• 2013

Aim of this paper is to apply to a steel truss bridge a methodology that takes into account the consequences of extreme loads on structures, focusing on the influence that the loss of primary elements has on the structural load bearing capacity. In this context, the topic of structural robustness, intended as the capacity of a structure to withstand damages without suffering disproportionate response to the triggering causes while maintaining an assigned level of performance, becomes relevant. In the first part of this study, a brief literature review of the topics of structural robustness, collapse resistance and progressive collapse takes place, focusing on steel structures. In the second part, a procedure for the evaluation of the structural response and robustness of skeletal structures under impact loads is presented and tested in simple structures. Following that, an application focuses on a case study bridge, the extensively studied I-35W Minneapolis steel truss bridge. The bridge, which had a structural design particularly sensitive to extreme loads, recently collapsed for a series of other reasons, in part still under investigation. The applied method aims, in addition to the robustness assessment, at increasing the collapse resistance of the structure by testing alternative designs.

• 대한기계학회논문집A
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• 제37권1호
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• pp.83-88
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• 2013

연쇄붕괴는 충격이나 폭발 등의 비정상 하중에 의하여 구조물의 하중 전달요소가 제거됨으로써 구조물의 일부 또는 전체가 연쇄적으로 붕괴되는 형상을 말한다. 예상외의 하중이 기둥부재에 작용할 경우, 좌굴이 발생하며 내력저하가 급격히 진행되어 붕괴에까지 이르게 된다. 하지만 좌굴 후 에너지를 흡수할 수 있는 잔존내력이 충분하면 붕괴를 막을 수 있다. 따라서, 구조물이 최종 붕괴상태에 도달되는 전 과정에 대한 기둥부재의 하중-변형관계를 명확히 파악할 필요가 있다. 본 논문에서는 비선형유한요소해석을 실시하여 H 형 강재기둥의 단부 구속조건이 고정일 경우 잔존내력의 변화추이를 파악하였다. 또한, 처짐이론을 기반으로 이론식을 도출하여 해석값과의 적합성을 검토하였다.

• 국제초고층학회논문집
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• 제9권3호
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• pp.245-253
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• 2020

With the ever-increasing height of timber buildings, the complexity of timber as a structural material gives rise to behaviors not previously studied by engineers. An urgent call is needed regarding their performance in damage scenarios: activating alternative load paths in tall timber buildings is not the same as in tall buildings made with steel and concrete. In this paper we propose a robustness framework covering all building materials, whose application in timber may lead to new conceptual designs for the next generation of tall timber buildings. Qualitatively, the importance of building scale and the distinction between localized and systematic exposures are discussed, and how existing supertall structures can be an example for future generations of tall timber buildings. Quantitatively, the robustness index is introduced alongside a method to calculate the performance of a given building regarding robustness, in order to find the most cost-effective structural solutions for improved robustness. A three-level application recommendation is made, depending on the importance of the building in question. Primarily, the paper highlights the importance of conceptual design to achieve structural robustness and encourages the practicing engineering community to use the proposed framework to quantitatively come up with the new generation of tall timber buildings.

• 대한조선학회지
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• 제24권2호
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• pp.29-35
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• 1987

As offshore activities move into deeper ocean, conventional fixed-base platforms drastically increase in size and cost, One of alternatives available is a guyed tower, in which environmental loads are supported by guylines instead of structural members. The guying system of the guyed tower is designed on one hand to be stiff enough to limit the structural displacement in normal operations, but on the other hand to be soft enough to permit large slow sways during the presence of design-level storms. This compliancy provides an efficient means of withstanding harsh environment so that the disproportionate increase in size of deep water platforms can be kept to a rational limit. Novel configurations contain always some degrees of potential risks mainly due to the lack of experience. The most critical hazard inherent to a guyed tower may be the pullout of anchor piles. Once it happens, the guyline fails to function and it may eventually lead to the total collapse of the system. It is the aim of this paper to discuss and quantify the anchor-pullout risk of a guyed tower. A stochastic analysis is made for evaluating the first-upcrossing probability of the tension acting on anchor piles over the uplift capacity. Nonlinearities involved in the mooring stiffness and hydrodynamics are taken into account by using time-domain analysis. A simplified two dimensional dynamic model is developed to exemplify the underlying concept. Real hurricane data in the Gulf of Mexico spanning over 70 years are incorporated in a numerical example of which result clearly indicates highly potential risk of anchor pullout.

• Earthquakes and Structures
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• 제15권5호
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• pp.453-462
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• 2018

Damages to buildings affected by a near-fault strong ground motion are largely attributed to the vertical component of the earthquake resulting in column failures, which could lead to disproportionate building catastrophic collapse in a progressive fashion. Recently, considerable interests are awakening to study effects of earthquake vertical components on structural responses. In this study, detailed modeling and time-history analyses of a 12-story code-conforming reinforced concrete moment frame building carrying the gravity loads, and exposed to once only the horizontal component of, and second time simultaneously the horizontal and vertical components of an ensemble of far-field and near-field earthquakes are conducted. Structural responses inclusive of tension, compression and its fluctuations in columns, the ratio of shear demand to capacity in columns and peak mid-span moment demand in beams are compared with and without the presence of the vertical component of earthquake records. The influences of the existence of earthquake vertical component in both exterior and interior spans are separately studied. Thereafter, the correlation between the increase of demands induced by the vertical component of the earthquake and the ratio of a set of earthquake record characteristic parameters is investigated. It is shown that uplift initiation and the magnitude of tensile forces developed in corner columns are relatively more critical. Presence of vertical component of earthquake leads to a drop in minimum compressive force and initiation of tension in columns. The magnitude of this reduction in the most critical case is recorded on average 84% under near-fault ground motions. Besides, the presence of earthquake vertical components increases the shear capacity required in columns, which is at most 31%. In the best case, a direct correlation of 95% between the increase of the maximum compressive force and the ratio of vertical to horizontal 'effective peak acceleration (EPA)' is observed.