Progressive Collapse Mechanism Research Articles

2D and 3D limit analysis of progressive collapse mechanism for deep-buried tunnels under the condition of varying water table

This paper aims to evaluate the pore water effect on the potential progressive failure subjected to varying water table. Theoretically, the falling blocks under the water level suffer from the pressure created by water while there would be no water pressure imposed on the failure above the water level. In this case, the previous failure mechanisms are no longer appropriate for the analysis of crown stability; therefore, a novel collapse mechanism should be introduced to characterize the velocity discontinuities. Based on this, and to better describe the 2D and 3D characteristics of progressive collapse, a novel 2D and 3D failure pattern composed of multi-surfaces in deep tunnels are proposed and then applied to estimate the impending roof collapse, respectively. On the basis of Hoek–Brown yield criterion, the upper bound solutions of collapsing blocks are obtained in the framework of plasticity theory with upper bound theorem and variational principle. In the application of kinematic approach, one assumption is made that the mechanical properties of rock materials are not influenced by the presence of underground water, which means that the geomaterials can be regarded as isotropic media with same values of strength parameters under and above the water table. Subsequently, the analytic and numerical results calculated in this literature are compared with existing research findings, which shows great consistency and validity of postulated progressive mechanisms. To analyze the influence of diverse parameters on the collapsing dimensions of surrounding rock masses, some examples and sensitivity analysis are conducted to gain the corresponding relationship from the perspective of 2D and 3D conditions.

Enhanced Residential Building Code for Tornado Safety

AbstractThe EF5 tornado that occurred in Moore, Oklahoma on May 20, 2013, provided a rare opportunity to study the effects of multiple major tornadoes on a single community in a relatively short timeframe. Data collected immediately after the tornado indicate an ordered progressive collapse mechanism for residential wood-frame structures with slightly different progressions for low-pitch and high-pitch roofs. This failure progression indicates that a continuous load path from the roof to the foundation is the most important aspect of design and construction for tornado resistance of residential structures. Performance of homes in a neighborhood constructed using more-robust methods indicates that the damage path caused by an major tornado can be narrowed by improving the overall structural system with a series of relatively simple items. Twelve code modifications proposed by the authors to create a more-robust structural system intended to withstand winds up to 60 m/s (135 mph), or an EF2 rating, are pre...

Progressive collapse mechanisms investigation of planar steel moment frames under localized fire

In this paper, the possible progressive collapse mechanisms of planar steel frames when one column failed under elevated temperature was studied through extensive case studies. An explicit dynamic solver was adopted, which could continue beyond local element buckling. The effects of analysis parameters such as mesh size and loading speed were investigated. And the numerical model was validated against experimental data and analysis results of other researchers. The investigated parameters included beam cross-sectional size, load ratio and location of heated column. Three progressive collapse mechanisms were found, namely, cantilever beam mechanism, pull-in force induced mechanism and high load ratio member failure mechanism, of which the last one is a new discovery. To evaluate progressive collapse of planar steel frames under fire, the cantilever beam mechanism and the pull-in force induced mechanism should be checked when the outer columns are heated, and the pull-in force induced mechanism and the high load ratio member failure mechanism need to be checked when the inner columns are heated. And the most adverse fire scenarios of a planer steel moment frame are when one of the following columns is heated: first floor column of the outmost, second and third outmost column lines or top floor column of the outmost, second and third outmost column lines.

Progressive collapse evaluation of RC symmetric and asymmetric mid-rise and tall buildings under earthquake loads

Plan irregularity causes local damages being concentrated in the irregular buildings. Progressive collapse is also the collapse of a large portion or whole building due to the local damages in the structure. The effect of irregularity on the progressive collapse potential of the buildings is investigated in this study. This is carried out by progressive collapse evaluation of the asymmetric mid rise and tall buildings in comparison with the symmetric ones via the nonlinear time history analyses in the 6, 9 and 12 story reinforced concrete buildings. The effect of increasing the mass eccentricity levels is investigated on the progressive collapse mechanism of the buildings with respect to the story drift behavior and the number of beam and column collapsed hinges criteria. According to the results, increasing the mass eccentricity levels causes earlier instability with lower number of the collapsed hinges which is necessary to fail the asymmetric buildings and at the same time mitigates the potential of progressive collapse. Moreover, the decreasing trend of the story drifts of the flexible edges is lower than those of the stiff edges and the mass centers and the amount of decrement in the story drifts of the stiff edges is approximately similar to those of the mass centers.

내부 폭발하중을 받는 철근콘크리트 코어의 연쇄붕괴 해석

논문에서는 철근콘크리트 코어 구조물의 내부폭발 효과를 폭발이나 충격해석에 특화되어 있는 하이드로코드인 Ansys Autodyn을 이용하여 조사하였다. 내부폭발의 경우 폭발하중의 반사효과로 인해 더욱 큰 파괴를 일으킬 수 있다. 그러므로, 본 논문에서는 UFC 3-340-02 를 사용하여 내부 폭발현상을 입증하였다. 추가적으로 Autodyn을 사용한 해석에 관하여 UFC에서 예제로 제시하는 폭발하중의 반사에 관한 실험 결과를 비교하여 Autodyn이 내부폭발 효과를 해석하는데 적합함을 증명하였다. 나아가, 초고층빌딩에서 가장 중요한 부분 중의 하나의 코어 구조의 붕괴메커니즘을 Autodyn을 사용하여 해석하였다. 내부폭발이 코어에 충격을 가할 때, 코어는 모서리와 폭발 정면 부분이 대부분 피해를 입었다. 그러므로, 코어 벽체가 피해를 입게 된다면 코어 구조물의 연쇄붕괴가 발생할 수 있다.

Improved capacity spectrum method with inelastic displacement ratio considering higher mode effects

Progressive collapse, which is referred to as the collapse of the entire building under local damages, is a common failure mode happened by earthquakes. The collapse process highly depends on the whole structural system. Since, asymmetry of the building plan leads to the local damage concentration; it may intensify the progressive collapse mechanism of asymmetric buildings. In this research the progressive collapse of regular and irregular 6-story RC ordinary moment resisting frame buildings are studied in the presence of the earthquake loads. Collapse process and collapse propagation are investigated using nonlinear time history analyses (NLTHA) in buildings with 5%, 15% and 25% mass asymmetry with respect to the number of collapsed hinges and story drifts criteria. Results show that increasing the value of mass eccentricity makes the asymmetric buildings become unstable earlier and in the early stages with lower number of the collapsed hinges. So, with increasing the mass eccentricity in building, instability and collapse of the entire building occurs earlier, with lower potential of the progressive collapse. It is also demonstrated that with increasing the mass asymmetry the decreasing trend of the number of collapsed beam and column hinges is approximately similar to the decreasing trend in the average story drifts of the mass centers and stiff edges. So, as an alternative to a much difficult-to-calculate local response parameter of the number of collapsed hinges, the story drift, as a global response parameter, measures the potential of progressive collapse more easily.

Influence of fire scenarios on progressive collapse mechanisms of steel framed structures

AbstractOpenSees is an open‐source object‐oriented software framework developed at UC Berkeley. The OpenSees framework has been recently extended to deal with structural behaviour under fire conditions. This paper presents the results of a numerical study, using OpenSees, of the progressive collapse of steel frames exposed to fire. After validating the capability of OpenSees against available analytical and experimental results of fire tests on steel members, a parametric study is carried out to find the progressive collapse mechanism of steel frames exposed to fire and corresponding influencing factors. The factors include load levels, lateral restraint, beam strength and fire scenarios. The catenary action of beams is considered by using a temperature‐dependent corotational beam/column element. The results show that different progressive collapse mechanisms can happen due to the sequence of the buckling of columns. High load levels lead to the downward collapse of the whole structure compared with the lateral collapse for low load levels. The existing of lateral restraint causes the premature buckling of bottom columns which triggers the whole frame collapse. As the beam section increases, the collapse mechanism of steel frames changes from beam failure mode to column failure mode. The fire scenarios have significant effect on the collapse mode of steel frames. The work presented in this paper is a preliminary study of the progressive collapse of steel frames. Further work is underway to combine the influence of the effect of concrete floors. A simple design method is then expected to be proposed to investigate the robustness of steel structures against progressive collapse due to fire.

Comparative study on the behaviour of Buckling Restrained Braced frames at fire

In this paper, the use of Buckling Restrained Brace systems (BRBs) in preventing the progressive collapse of the structural frame against fire is investigated using the stiffness reduction technique. Four-storey steel structures fitted with different bracing configurations were modelled using the Vulcan programme. For comparative purpose, the efficiency of BRBs in preventing the progressive collapse of the structure is compared with the Ordinary Concentrically Brace systems (OCBs) in the presence of edge and central bay fire exposures. In order to consider the effect of bracing member stiffness on the collapse prevention of the frame and to provide a comprehensive scheme of progressive collapse mechanism under fire condition, several cross sections of BRBs under different fire scenarios are considered. The results indicate that BRBs provide a higher global collapse temperature for the frame, owing to a greater stiffness and more symmetrical performance offered as compared to OCBs, and thus providing better progressive collapse resistance. Moreover, it is observed that BRBs are stiff enough to redistribute the sustained load by heated columns to adjacent members without any buckling occurrence in the bracing member, maintaining the stability of the whole frame through both heating and cooling phases of fire.

Progressive collapse potential of a typical steel building due to blast attacks

The recent terrorist attacks all around the world and the evidence of the threats found especially in the Kingdom of Saudi Arabia have prompted the concerned authorities to address the risks to the critical infrastructure of the Kingdom. Understanding of the progressive collapse mechanism is an essential step to protect buildings against blast attacks. Buildings are very vulnerable to progressive collapse if one or more columns are lost due to extreme loadings. It is also important to study the likelihood of progressive collapse of buildings in Riyadh to avoid catastrophic events. The paper presents progressive collapse analysis of a typical multi-storey steel framed building in Riyadh to establish its vulnerability when subjected to accidental or terrorist attack blast scenarios. A commercial finite element (FE) package (LS-DYNA) was used to simulate the building response under blast generated waves. The numerical modeling was validated using the results of a published example of tubular steel beam subjected to blast load. Based on the FE analysis results, recommendations are given to mitigate (or control) the progressive collapse potential of steel buildings.

Study of Model Tests on Large-Span Tunnel’s Damage Caused by Overload with Arch Cover Method

In the process of large-span tunnel excavation by arch cover method, how to ensure the safety of construction and to reduce the influence on the surroundings and environment has arising wide attention of scholars both domestic and abroad. But now it is still in the stage of experience as to the rock pressure and its instability failure, especially to the research on rock overload damage. Regarding the large-span tunnel rock failure mechanism of progressive collapse by arch cover method, large-diameter modeling test are adopted to do systematical research on the rock failure phenomena as load increase. Determine its ultimate failure state by increasing vertical load, then we can get its failure characteristics and instability criterion in different rock support section.

Progressive collapse vulnerability in 6-Story RC symmetric and asymmetric buildings under earthquake loads

Progressive collapse, which is referred to as the collapse of the entire building under local damages, is a common failure mode happened by earthquakes. The collapse process highly depends on the whole structural system. Since, asymmetry of the building plan leads to the local damage concentration; it may intensify the progressive collapse mechanism of asymmetric buildings. In this research the progressive collapse of regular and irregular 6-story RC ordinary moment resisting frame buildings are studied in the presence of the earthquake loads. Collapse process and collapse propagation are investigated using nonlinear time history analyses (NLTHA) in buildings with 5%, 15% and 25% mass asymmetry with respect to the number of collapsed hinges and story drifts criteria. Results show that increasing the value of mass eccentricity makes the asymmetric buildings become unstable earlier and in the early stages with lower number of the collapsed hinges. So, with increasing the mass eccentricity in building, instability and collapse of the entire building occurs earlier, with lower potential of the progressive collapse. It is also demonstrated that with increasing the mass asymmetry the decreasing trend of the number of collapsed beam and column hinges is approximately similar to the decreasing trend in the average story drifts of the mass centers and stiff edges. So, as an alternative to a much difficult-to-calculate local response parameter of the number of collapsed hinges, the story drift, as a global response parameter, measures the potential of progressive collapse more easily.

Simplified Models of Progressive Collapse Response and Progressive Collapse-Resisting Capacity Curve of RC Beam-Column Substructures

Based on analysis of a progressive collapse mechanism, this paper presents a simplified model for static analysis of progressive collapse response of RC beam-column substructures under midspan point loading. The proposed model expresses the load-deflection response directly, and it consists of three stages—beam mechanism stage, transient stage, and catenary mechanism stage. In the model, the influence of the span, the sectional dimension, and the reinforcement of the beam on progressive collapse behavior of substructures can be taken into account. The proposed model is validated by experimental results in literature. Last, progressive collapse-resisting capacity curves of substructures are established based on the energy conservation principle, which establishes a foundation for progressive collapse assessment of RC frame structures.

Investigation of bearing failure in steel single bolt lap connections

Bolted connections are more than ever used because of their ease of fabrication and erection but often can be a weak link in a structure. Among single bolt lap connection types of failure, bearing mode is generally dominant because of the necessity to ensure bolthole elongation that enables a progressive collapse mechanism. Although ductility represents a positive characteristic, excessive deformations limit the usefulness of a structure or cause the members it connects to fail. Because of the lack of research in representative conditions an investigation of the plastic behavior of single bolt lap connections with a special consideration of bolthole elongation was performed. This investigation consisted of experimental, numerical and analytical analysis. A detailed measurement of deformations during experimental testing was performed with an optical system that enabled the monitoring of strains in 3D. The results of experimental testing were used for the calibration of nonlinear numerical models and a parametric study of connections with different bolthole center to plate edge distances was performed. A larger set of results, derived from the parametric study served as a foundation for the evaluation of empirical expressions given in the European and American standards, and proposal of appropriate equations that enable a better prediction of ultimate and serviceability loads.

Investigation of Progressive Collapse Resistance for a Seismically Designed RC Building

The objective of this study is the vulnerability phenomenon to progressive collapse of a 7-storey Reinforced Concrete (RC) building in conformance with ACI 318-11/IBC 2009. Progressive collapse is defined as a disastrous structural phenomenon due to human-made and natural hazards. The progressive collapse mechanism involves a single local failure which could lead to major deformations ending up with the total collapse of the structure. The building was designed as a Special Moment Resisting Frame (SMRF) and assumed to have an Occupancy Category II per UFC 3-301-01. Tie Forces (TF) and Enhanced Local Resistance (ELR) methods according to Unified Facilities Criteria (UFC 4-023-03) and Demand Capacity Ratio (DCR) method based on General Services Administration (GSA) were incorporated to investigate the probability of progressive collapse. According to GSA, the study illustrated that the building’s columns did not require additional reinforcement to prevent progressive collapse. Also, the study revealed that additional reinforcement was required for all the three column removal cases to meet the progressive collapse requirements based on GSA. Furthermore, it was concluded that two-way slabs required additional reinforcement to meet UFC requirements.

Progressive Collapse Mechanisms of Steel Frames Exposed to Fire

OpenSees is an open-source object-oriented software framework developed at UC Berekeley. The OpenSees framework has been recently extended to deal with structural behavior under fire conditions. This paper summaries the key work done for this extension and focuses on the application of the developed OpenSees to study the fire-induced progressive collapse mechanisms of steel structures. The implicit dynamic analysis method (Newmark method) is applied and the influences of the load ratios, beam sizes and fire scenarios on the collapse behavior of frames are investigated. Single-compartment fire scenarios in the central bay and edge bay are considered, respectively. A total of four collapse mechanisms of steel frames are proposed by varying the three influencing factors. Most of the collapse of steel frames is triggered by the buckling of the heated columns. The thermal expansion of heated beams at early heating stage and their catenary action at high temperature have great influences on the collapse mechanisms. The most common collapse mode of steel frames are in the form of lateral drift of frames above the heated floor together with downward collapse of frames along the heated bay. As the load increases, the collapse behavior of structures is dominated by a downward collapse of the whole frame with little sign of the upper frame drift. The collapse modes of steel frames with strong and weak beams are column failure mechanism and beam failure mechanism, respectively. The former mechanism is due to the buckling of the columns below the heated floor represented by a global collapse of the frame and the latter is initiated by the premature development of plastic hinges at the ends of beams denoted by an obvious lateral drift of the heated floor. Generally, the edge bay fire is more prone to induce the collapse of structures than the central bay fire. It is found that the most dangerous situation is the frame subjected to high load ratios exposed to a central bay fire where its progressive collapse may occur as early as 250°C.

Seismic collapse propagation in 6-story RC regular and irregular buildings

One of the most important issues in progressive collapse mechanism of the buildings is evaluation of the collapse distribution in presence of the earthquake loads. Here, collapse propagation is investigated by tracking down the location and type of the collapsed beam and column elements, from the first element to the entire buildings. 6-story reinforced concrete ordinary moment resisting frame buildings with one directional mass eccentricity of 0%, 5%, 15% and 25% are studied to investigate differences among the progressive collapse mechanism of the regular and irregular buildings. According to the results of the nonlinear time history analyses, there are some patterns to predict progressive collapse scenarios in beam and column elements of the similar regular and irregular buildings. Results also show that collapse distribution patterns are approximately independent of the earthquake records.

Experimental study and numerical analysis of progressive collapse resistance of composite frames

A partial damage caused by an abnormal load could trigger progressive collapse of high rise buildings which may lead to terrible casualties. However, in the process of column failure, “catenary action” plays an important role in redistributing the internal load and preventing progressive collapses of the structure. Rigid composite joints, thanks to their high strength and good ductility, exert great influence in catenary action. Therefore, an experiment related to a 1/3 scale progressive collapse resistance with the use of rigid composite joints was conducted, and the results of the experiment were analyzed. Based on the experiment results, a FE model was developed and analyzed. This paper describes the experiment, the results analyzed, and the FE model in detail. The experiment showed that the progressive collapse mechanism of composite frame consisted of 6 stages: elastic stage, elastic–plastic stage, arch stage, plastic stage, transient stage and catenary stage. In catenary stage, catenary action evidently enhanced the resistance to the progressive collapse of the frames. The steel–concrete composite frame with rigid connections designed in accordance to current design standards showed a good resistance to progressive collapse. It is also found that horizontal restraining stiffness of the frame exerted great influence on the resistance in catenary stage.

Progressive collapse assessment of new hexagrid structural system for tall buildings

SUMMARY Hexagrid structure is an innovative tube-type system. It is constructed with hexagonal exterior structural grids. The hexagrid works as an effective lateral and gravitational resisting system. This paper presents the progressive collapse-resisting capacity of this new system and the common diagrid system based on the local failure of the structural elements in the story above the ground. The collapse behavior is evaluated by two different nonlinear static and dynamic analysis methods. This study was conducted to design two-type 28-story and 48-story building models to withstand wind load for both structural systems. With the analytical results, the hexagrid has enough potential of force redistribution due to its special configuration. It is observed that the new system had high resistance to progressive collapse than diagrids in similar condition. The complementary studies illustrate that resisting progressive collapse capacity, in both hexagrid and diagrid structures, is increased by using the buckling-restrained elements. The guidelines discussed here can help engineers to understand the mechanism of progressive collapse of the hexagrid structures. Copyright © 2013 John Wiley & Sons, Ltd.

The Numerical Analysis of Transmission Tower-Line System Wind-Induced Collapsed Performance

The numerical simulation of transmission tower-line systems' progressive collapse performance is considered as a major research hotspot and significant project, due to the increasing number of wind-induced collapse accidents recently. In this study, the finite element models for single tower and transmission tower-line system were established to simulate wind-induced progressive collapse by birth-to-death element technique in ABAQUS/Explicit. The wind field, based on the Kaimal fluctuating wind power spectrum and harmonic superposition method, was constructed by MATLAB commercial software. The current research focuses on the dynamic behaviour and the mechanism of a typical transmission tower-line system progressive collapse under wind action with clear step-by-step description. The numerical simulation results demonstrated that transmission tower-line system collapse mechanism depended on the number, position and last deformation of damage elements. Since the gallop effect of conductor and ground lines were ignored in the single tower model, the transmission tower-line system model, which has higher computational precision than the single tower model, is relatively accurate and recommended strongly in the design.

Analytical Study of Seismic Progressive Collapse in a Steel Moment Frame Building

Progressive collapse is defined as total or remarkable partial collapse of structure following the damage occurred at a small portion of the structure. In most cases, the study is focused on progressive collapse of structures due to explosion, vehicle impact, fire and other man-made hazards; with less attention on progressive collapse mechanism of structure due to earthquake. Although the post earthquake inspections show that structural elements, mostly columns in the corner of the plan, can be severely damaged during earthquake. If neighboring columns are not properly designed to resist and redistribute the additional gravity load that is imposed by the column loss, partial collapse of the structure will occur; which would lead to progressive collapse of the structure. In this regard, progressive collapse potential of a moment resisting steel building is investigated via analytical procedure under earthquake action. In this research, a corner-column of the building was weakened intentionally to navigate the damage toward a certain part of the structure. Then, nonlinear static analysis is carried out on the three dimensional model of the building and the total behavior of the structure is studied. The results indicate that after the failure of the corner-column, the lateral resistance of the frame in which the removed (failed) column was located decreases, and the failure of the other columns occurs. Large plastic deformations and the failure of the other members could cause progressive collapse in the whole structure and the expected ductile behavior of the structure would not be observed.