• Steel and Composite Structures
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• 제8권1호
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• pp.85-98
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• 2008

In this study the progressive collapse potential of three- and nine-story special steel moment frames designed in accordance with current design code was evaluated by nonlinear static and dynamic analyses. It was observed that the model structures had high potential for progressive collapse when a first story column was suddenly removed. Then the size of beams required to satisfy the failure criteria for progressive collapse was obtained by the virtual work method; i.e., using the equilibrium of the external work done by gravity load due to loss of a column and the internal work done by plastic rotation of beams. According to the nonlinear dynamic analysis results, the model structures designed only for normal load turned out to have strong potential for progressive collapse whereas the structures designed by plastic design concept for progressive collapse satisfied the failure criterion recommended by the GSA guideline.

• Steel and Composite Structures
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• 제20권2호
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• pp.357-378
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• 2016

The progressive collapse phenomenon in structures has been interested by civil engineers and the building standards organizations. This is particularly true for the tall and special buildings ever since local collapse of the Ronan Point tower in UK in 1968. When initial or secondary defects of main load carrying elements, overloads or unpredicted loads occur in the structure, a local collapse may be arise that could be distributed through entire structure and cause global collapse. One is not able to prevent the reason of failure as well as the prevention of propagation of the collapse. Also, one is not able to predict the start point of collapse. Therefore we should generalize design guides to whole or the part of structure based on the risk analysis and use of load carrying elements removal scenario. There are some new guides and criteria for elements and connections to be designed to resist progressive collapse. In this paper, codes and recommendations by various researchers are presented, classified and compared for steel structures. Two current design methods are described in this paper and some retrofitting methods are summarized. Finally a steel building with special moment resistant frame is analyzed as a case study based on two standards guidelines. This includes consideration of codes recommendations. It is shown that progressive collapse potential of the building depends on the removal scenario selection and type of analysis. Different results are obtained based on two guidelines.

• Steel and Composite Structures
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• 제31권6호
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• pp.617-628
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• 2019

As an extremely destructive accident, progressive collapse is defined as the spread of an initial local failure from element to element, resulting eventually in the collapse of an entire structure or disproportionately large of it. To prevent the occurrence of it and evaluate the ability of structure resisting progressive collapse, the nonlinear static procedure is usually adopted in the whole structure design process, which considered dynamic effect by utilizing Dynamic Increase Factor (DIF). In current researches, the determining of DIF is performed in full-rigid frame, however, the performance of beam-column connection in the majority of existing frame structures is not full-rigid. In this study, based on the component method proposed by EC3 guideline, the expression of extended endplate connection performance is further derived, and the connection performance is taken into consideration when evaluated the performance of structure resisting progressive collapse by applying the revised plastic P-M hinge. The DIF for structures with extended endplate beam-column connection have been determined and compared with the DIF permitted in current GSA guideline, the necessity of considering connection stiffness in determining the DIF have been proved.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2008년도 정기 학술대회
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• pp.307-312
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• 2008

Local damage may cause sequential collapse of structure, which is called progressive collapse. Current progressive collapse analysis is based on the mean value of design variables. This deterministic approach has a low reliability as it doesn't consider uncertainty of variables. In this study the sensitivity of design variables for progressive collapse of structure is evaluated by Monte Calro simulation and Tornado diagram. The analysis results show that the behaviour of model structures is highly sensitive to variation of the yield force of beams and the structural damping ratio.

• Journal of Ship and Ocean Technology
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• 제10권1호
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• pp.38-46
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• 2006

The objective of this paper is to summarize current ultra-deepwater (i.e., up to 3,500 meters water depth) pipeline mechanical design methodologies as part of the limit state design. The standard mechanical design for ultra-deepwater pipelines in the Gulf of Mexico (GOM) is based on API RP 1111. API code also has been used for deepwater projects in west Africa. DNV code OS-F101 was mostly used for deepwater projects in offshore Brazil and Europe. Some pipeline designs in the GOM have started to incorporate parts of the DNV design methodology. A discussion of failure under collapse only and combined loading (i.e. pressure + bending) is presented. The best design criteria are obtained from physical full-scale collapse testing. The comparison of the physical test data and collapse calculations using the DNV and API codes will be presented. It was found that the conservatism still exists in the collapse prediction for ultra-deepwater pipeline using modem design codes such as DNV OS-F101 and API RP 1111.

• Geomechanics and Engineering
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• 제23권5호
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• pp.441-454
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• 2020

The tunnel collapse, large deformation of surrounding rock, water and mud inrush are the major geological disasters in soft rock tunnel construction. Among them, tunnel collapse has the most serious impact on tunnel construction. Current research backed theories have certain limitations in identifying the collapse risk of soft rock tunnels. Examining the Zhengwan high-speed railway tunnel, eight soft rock tunnel collapse influencing factors were selected, and the combination of indicator weights based on the analytic hierarchy process and entropy weighting methods was obtained. The results show that the groundwater condition and the integrity of the rock mass are the main influencing factors leading to a soft rock tunnel collapse. A comprehensive fuzzy evaluation model for the collapse risk of soft rock tunnels is being proposed, and the real-time collapse risk assessment of the Zhengwan tunnel is being carried out. The results obtained via the fuzzy evaluation model agree well with the actual situation. A tunnel section evaluated to have an extremely high collapse risk and experienced a local collapse during excavation, verifying the feasibility of the collapse risk evaluation model. The collapse risk evaluation model proposed in this paper has been demonstrated to be a promising and innovative method for the evaluation of the collapse risk of soft rock tunnels, leading to safer construction.

• 국제초고층학회논문집
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• 제7권4호
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• pp.375-387
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• 2018

This paper presents a review on progressive collapse mechanism of steel framed buildings exposed to fire. The influence of load ratios, strength of structural members (beam, column, slab, connection), fire scenarios, bracing systems, fire protections on the collapse mode and collapse time of structures is comprehensively reviewed. It is found that the key influencing factors include load ratio, fire scenario, bracing layout and fire protection. The application of strong beams, high load ratios, multi-compartment fires will lead to global downward collapse which is undesirable. The catenary action in beams and tensile membrane action in slabs contribute to the enhancement of structural collapse resistance, leading to a ductile collapse mechanism. It is recommended to increase the reinforcement ratio in the sagging and hogging region of slabs to not only enhance the tensile membrane action in the slab, but to prevent the failure of beam-to-column connections. It is also found that a frame may collapse in the cooling phase of compartment fires or under travelling fires. This is because that the steel members may experience maximum temperatures and maximum displacements under these two fire scenarios. An edge bay fire is more prone to induce the collapse of structures than a central bay fire. The progressive collapse of buildings can be effectively prevented by using bracing systems and fire protections. A combination of horizontal and vertical bracing systems as well as increasing the strength and stiffness of bracing members is recommended to enhance the collapse resistance. A protected frame dose not collapse immediately after the local failure but experiences a relatively long withstanding period of at least 60 mins. It is suggested to use three-dimensional models for accurate predictions of whether, when and how a structure collapses under various fire scenarios.

• KIEAE Journal
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• 제10권5호
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• pp.151-157
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• 2010

This study is connected with evaluation of the progressive collapse resisting capacity for sustainable RC super tall building design. As the progressive collapse is not considered in current design codes in Korea, differences between linear static and dynamic analysis based on the GSA guidelines was analyzed for better evaluation, and the analysis model of flat plate system was determined. Finally, the progressive collapse resisting capacity was evaluated for structural system of super tall building. According to this study, the results by linear dynamic analysis were underestimated than the results by linear static analysis. Thus, the dynamic coefficient value of 2 provides conservative approach. The Effective Beam Width's model, currently used in field, is useful for the analysis about lateral force, but this model does not consider the effect of load redistribution by the slab. Hence, finite element analysis considering slab element will be needed for progressive collapse resisting capacity of the flat plate system. Finally, analysis model of 80-story building designed based on KBC(Korea Building Code) shows the weakness against progressive collapse because the DCR value is over 2. Thus, the countermeasure for alternative loading path such as installment of spandrel beam and reinforcements around slab is required to prevent the progressive collapse.

• Steel and Composite Structures
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• 제46권2호
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• pp.279-292
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• 2023

Structural design against the progressive collapse has been a vital necessity for decades due to occasional tragic events. The question of whether designed structures against the progressive collapse are still robust if subjected to multi-hazard scenarios containing column removal and successive localized fires is ad-dressed in the current study. Two seven-story steel structures with an identical area but different structural configurations of 4- and 5-bays are designed against the progressive collapse; the structural components are also fireproofed for a 60 min fire resistance. The structures are then subjected to different column re-moval scenarios over different stories followed immediately by localized fires. Results indicate that the structures are not able to keep their stability under all of the considered scenarios; the 4-bay structure is more vulnerable than the 5-bay structure. It is also indicated that upper stories are more sensitive toward the considered scenarios than lower stories. To advance structural safety, two strategies are adopted: in-creasing the thickness of the insulation materials to reduce the thermal effects, or, increasing the safety fac-tor (ΩN) of the structures when designing against the progressive collapse. As for the first strategy, provid-ing a 35% and a 25% increase in the insulation thicknesses of the structural components of the 4-bay and 5-bay structures, respectively, can prevent a progressive collapse to trigger. As for the second strategy, in-creasing ΩN by 10% can enhance the structural integrity to where no collapse occurs under all of the sce-narios.

• Earthquakes and Structures
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• 제18권3호
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• pp.367-377
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• 2020

Incremental dynamic analysis (IDA) widely uses for the collapse risk assessment procedures of buildings. In this study, an IDA-based collapse risk assessment methodology is proposed, which employs a novel approach for detecting the near-collapse (NC) limit state. The proposed approach uses the modal pushover analysis results to calculate the maximum inter-story drift ratio of the structure. This value, which is used as the upper-bound limit in the IDA process, depends on the structural characteristics and global seismic responses of the structure. In this paper, steel midrise intermediate moment resisting frames (IMRFs) have selected as case studies, and their collapse risk parameters are evaluated by the suggested methodology. The composite action of a concrete floor slab and steel beams, and the interaction between the infill walls and the frames could change the collapse mechanism of the structure. In this study, the influences of the metal deck floor and autoclaved aerated concrete (AAC) masonry infill walls with uniform distribution are investigated on the seismic collapse risk of the IMRFs using the proposed methodology. The results demonstrate that the suggested modified IDA method can accurately discover the near-collapse limit state. Also, this method leads to much fewer steps and lower calculation costs rather than the current IDA method. Moreover, the results show that the concrete slab and the AAC infill walls can change the collapse parameters of the structure and should be considered in the analytical modeling and the collapse assessment process of the steel mid-rise intermediate moment resisting frames.