Seismic Progressive Collapse Research Articles

Seismic collapse assessment of single-column bridge piers using the applied element method

Several single-column-bent bridges have collapsed in the past under earthquakes. Different factors associated with poor structural design and/or construction including inadequate and/or prematurely terminated longitudinal reinforcement (LR), insufficient concrete confinement, or insufficient transverse reinforcement (TR) were identified and reported. Different alternative designs or retrofitting solutions were also proposed and examined. One of the well-known samples of this bridge type was the elevated Hanshin Expressway Bridge (HEB), which collapsed in the 1995 Kobe earthquake. In that incident, 18 circular single-column piers (SCPs), monolithically connected to the deck, failed and collapsed. Here, the seismic progressive collapse behaviour of SCPs of the HEB was investigated using non-linear dynamic analyses of three-dimensional numerical models created by way of the applied element method (AEM). The results obtained agreed well with field observations after the earthquake. Two alternative design solutions for improving the seismic response of the original model were also considered and the efficiency of the solutions was assessed. Results showed that the AEM is capable of modelling the progressive collapse procedure for concrete bridges with sufficient accuracy. The results proved greater effects of the anchorage length of the LR as well as the space between the TR in the collapse behaviour of the pier.

Effects of Earthquake Components on Seismic Progressive Collapse Potential of Steel Frames

Effects of Earthquake Components on Seismic Progressive Collapse Potential of Steel Frames

Evaluating the Fragility Curve in Steel–Concrete Structure Undergoing Seismic Progressive Collapse by Finite Element Method

Evaluating the Fragility Curve in Steel–Concrete Structure Undergoing Seismic Progressive Collapse by Finite Element Method

Novel seismic–progressive collapse resilient super-tall building system

Accidental events that may lead to a progressive collapse (e.g., explosions and collisions) and earthquakes are two types of destructive hazards for super-tall buildings. The study of the resilience of super-tall buildings against these hazards has become a crucial issue. Corresponding research outcomes have important social, political, and economic value for damage/loss assessment and the post-disaster recovery plans for important buildings. A resilient structural system usually exhibits significantly reduced consequences and recovery time after hazards. Therefore, based on the resilience concept and the widely adopted “frame–truss–core tube” system, a novel seismic–progressive collapse resilient super-tall (SPCRST) building system and the corresponding design method are proposed in this paper. Detailed case study results indicate that, compared with the conventional system, the proposed system has significant advantages in controlling the dynamic responses of super-tall buildings during accidental events and earthquakes (e.g., vertical displacement after local column failure, and floor accelerations and inter-story drifts under earthquakes) and in improving the seismic–progressive collapse resilience of the structure.

Comparison of seismic and gravity progressive collapse in dual systems with special steel moment-resisting frames and braces

Progressive collapse studies generally assess the performance of the structure under gravity and blast loads, while earthquakes may also lead to the progressive collapse of a damaged structure. In this study, the progressive collapse response of concentrically braced dual systems with steel moment-resisting frames was assessed under seismic loads through pushover analysis using triangular and uniform lateral load patterns. Two different bracing types (X and inverted V braces) were considered, and their performances were compared under different lateral load patterns using the nonlinear static alternate path method recommended in the Unified Facilities Criteria (UFC) guideline. Eventually, the seismic progressive collapse resistance of models was compared to their progressive collapse response under gravity loads. These studies showed that models under the seismic progressive collapse loads satisfied UFC acceptance criteria and limited rehabilitation objective. The structures had better performance under seismic progressive collapse than models under gravity loads because of more resistance, ductility, suitable load redistribution, and more structural elements that participated in load redistribution. Furthermore, despite studies on progressive collapse under gravity loads, the dual system with X braces showed better progressive collapse performance (more resistance, residual reserve strength ratio and ductility) under seismic loads than the model with inverted V braces.

Seismic progressive collapse mitigation of buildingsusing cylindrical friction damper

The occurrence of progressive collapse induced by the removal of the vertical load-bearing element in the structure, because of fire or earthquake, has been a significant challenge between structural engineers. Progressive collapse is defined as the complete failure or failure of a part of the structure, initiating with a local rupture in a part of the building and can threaten the stability of the structure. In the current study, the behavior of the structures equipped with a cylindrical friction damper, when the vertical load-bearing elements are eliminated, is considered in two cases: 1-The load-bearing element is removed under the gravity load, and 2-The load-bearing element is removed due to the earthquake lateral forces. In order to obtain a generalized result in the seismic case, 22 pair motions presented in FEMA p 695 are applied to the structures. The study has been conducted using the vertical push down analysis for the case (1), and the nonlinear time-history analysis for the second case using OpenSEES software for 5,10, and 15-story steel frames. Results indicate that, in the first case, the load coefficient, and accordingly the strength of the structure equipped with cylindrical friction dampers are increased considerably. Furthermore, the results from the second case demonstrate that the displacements, and consequently the forces imposed to the structure in the buildings equipped with the cylindrical friction damper substantially was reduced. An optimum slip load is defined in the friction dampers, which permits the damper to start its frictional damping from this threshold load. Therefore, the optimum slip load of the damper is calculated and discussed for both cases.

Proposal of an Energy Based Assessment of Robustness Index of Steel Moment Frames under the Seismic Progressive Collapse

One of the aims of earthquake engineering is to build secure structures against random loads and also various damage types under lateral loads. Progressive collapse, a word that has attracted attention of many researches after the failure of the World Trade Center, can occur under abnormal loads such as explosion or natural causes like earthquakes. Resistance to progressive collapse is expressed by a parameter called Robustness. The purpose of this study is to survey various methods of calculating robustness index under lateral loads, especially seismic loads, in steel moment frames. So three steel structures with 4, 8 and 15-story and intermediate moment frames were designed and analyzed subsequently. Different methods of measuring the robustness indexes were compared and eventually presented a simple method to assess robustness index based on nonlinear dynamic analysis. Robustness index introduced using this method, which is based on the types of Pancake and Zipper collapses and energy parameters, tries to express an appropriate standard for structural strength against earthquakes.

Comparison of seismic progressive collapse distribution in low and mid rise RC buildings due to corner and edge columns removal

One of the most important issues in structural systems is evaluation of the margin of safety in low and mid-rise buildings against the progressive collapse mechanism due to the earthquake loads. In this paper, modeling of collapse propagation in structural elements of RC frame buildings is evaluated by tracing down the collapse points in beam and column structural elements, one after another, under earthquake loads and the influence of column removal is investigated on how the collapse expansion in beam and column structural members. For this reason, progressive collapse phenomenon is studied in 3-story and 5-story intermediate moment resisting frame buildings due to the corner and edge column removal in presence of the earthquake loads. In this way, distribution and propagation of the collapse in progressive collapse mechanism is studied, from the first element of the structure to the collapse of a large part of the building with investigating and comparing the results of nonlinear time history analyses (NLTHA) in presence of two-component accelograms proposed by FEMA_P695. Evaluation of the results, including the statistical survey of the number and sequence of the collapsed points in process of the collapse distribution in structural system, show that the progressive collapse distribution are special and similar in low-rise and mid-rise RC buildings due to the simultaneous effects of the column removal and the earthquake loads and various patterns of the progressive collapse distribution are proposed and presented to predict the collapse propagation in structural elements of similar buildings. So, the results of collapse distribution patterns and comparing the values of collapse can be utilized to provide practical methods in codes and guidelines to enhance the structural resistance against the progressive collapse mechanism and eventually, the value of damage can be controlled and minimized in similar buildings.

Collapse Distribution Scenario in Seismic Progressive Collapse of RC Buildings Caused by Internal Column Elimination

Prediction of the safety margin in the buildings against the progressive collapse mechanism due to the earthquake loads is a significant issue in the structural and earthquake engineering. In this paper, modeling of the collapse distribution and propagation in the structural elements, one after another, is investigated by tracking down the collapsed locations among the beam and column structural elements in the moment-resisting reinforced concrete short buildings, and the effects of the column removal are studied on the expansion and development of the progressive collapse due to the earthquake loads. A three-story reinforced concrete building designed with ordinary moment frames is modeled, and potential of the progressive collapse mechanism due to the internal column removal is studied using the results of nonlinear time history analyses in the presence of the two-component ground motion records proposed by FEMA_P695. According to the results, some approaches and proposals are presented to seismic optimization of the reinforced concrete short buildings against the progressive collapse mechanism. Also, a collapse distribution pattern is introduced to predict the progressive collapse propagation scenario due to the earthquake loads and the internal column removal.

Robustness analysis of steel structures with various lateral load resisting systems under the seismic progressive collapse

Abstract Robustness is called to non-sensitivity of a structure to local damage. In the literature of Civil Engineering, the sensitivity of structures to the local damage which can cause a progressive collapse is called Robustness Index. After 9/11, progressive collapse drew the attention of researchers and since that time, increasing the Robustness Index in a structure has been considered as one of the factors in strengthening the structure against progressive collapse. The aim of this study is assessing the Robustness Indices of steel structures having various lateral load resisting systems. So, 8-story, 4-story and 15-story structures with Moment Frames, Concentrically Braced Frames and Eccentrically Braced Frames were modeled and assessed under Robustness analysis. For a progressive collapse analysis, the Alternative Load Path method was used and after emerging local damage, the potential of progressive collapse was assessed using the Robustness Index. First, Robustness analysis was carried out on the basis of Robustness Index assessment using Stiffness and Base Shear methods. Subsequently, it continued by introducing a simple method based on Energy. The results show that despite their simplicity, the methods which are based on Stiffness and the Base Shear, have lots of disadvantages. But, the Energy method has better capabilities for understanding the behavior of structure under seismic loads in progressive collapse scenario. Furthermore, structures which have bracing had a better reaction in progressive collapse scenario.

Effect of Earthquake characteristics on seismic progressive collapse potential in steel moment resisting frame

According to the definition, progressive collapse could occur due to the initial partial failure of the structural members which by spreading to the adjacent members, could result in partial or overall collapse of the structure. Up to now, most researchers have investigated the progressive collapse due to explosion, fire or impact loads. But new research has shown that the seismic load could also be a factor for initiation of the progressive collapse. In this research, the progressive collapse capacity for the 5 and 15-story steel special moment resisting frames using push-down nonlinear static analysis, and nonlinear dynamic analysis under the gravity loads specified in the GSA Guidelines, were studied. After identifying the critical members, in order to investigate the seismic progressive collapse, the 5-story steel special moment resisting frame was analyzed by the nonlinear time history analysis under the effect of earthquakes with different characteristics. In order to account for the initial damage, one of the critical columns was weakened at the initiation of the earthquake or its Peak Ground Acceleration (PGA). The results of progressive collapse analyses showed that the potential of progressive collapse is considerably dependent upon location of the removed column and the number of stories, also the results of seismic progressive collapse showed that the dynamic response of column removal under the seismic load is completely dependent on earthquake characteristics like Arias intensity, PGA and earthquake frequency contents.

Seismic progressive collapse of MRF–EBF dual steel systems

Designing structures to resist progressive collapse during an earthquake is a key challenge for structural engineers working in seismic zones. This paper introduces a more appropriate brace configuration based on an upper-bound estimation of the probability of seismic progressive collapse in moment-resisting, eccentrically braced frames designed to the third edition of the Iranian seismic code. The code currently only has provisions for the capacity of moment frames, with no detail given for bracing elements. A numerical modelling study of low- to mid-rise residential and office buildings was undertaken. The results show that for five-storey buildings the optimum number of braced bays is 10–20% of the building's perimeter bays, whereas for eight-storey buildings the optimum proportion is 20–30%. Results also show that regular bracing in internal bays is more appropriate for resistance against progressive collapse.

SEISMIC PROGRESSIVE COLLAPSE ANALYSIS OF CONTROLLED STEEL FRAME STRUCTURES

Any element loss in the concentrically-braced frames (CBF) system significantly affects its seismic performance. The research presented in this paper aimed to understand the behavior of this system against seismic progressive collapse due to the failure of a column. A collapse of this magnitude may lead to the entire collapse of the structure, or else it could avoid or even localize the disaster by redistributing the released load to the surrounding structure. The progressive collapse phenomenon was investigated through analyzing a building equipped with CBF system during a seismic event. Four cases of failed beams were considered, depending on the location of the column loss and the configuration of the braces surrounding them. Through OpenSees simulation, the results showed the seismic and gravity loads increased and rapidly reached the ultimate state of the structure from 0.6 sec after the time of failure. The model for each scenario, regardless of the direct collapse of the structure due to the column loss, indicated the CBF system limited the plastic hinge formation around the failed element. Finally, the results showed the braces working in tensile are more reliable in terms of collapse resistance than those working in compression.

Seismic progressive collapse assessment of 3-story RC moment resisting buildings with different levels of eccentricity in plan

Margin of safety against potential of progressive collapse is among important features of a structural system. Often eccentricity in plan of a building causes concentration of damage, thus adversely affects its progressive collapse safety margin. In this paper the progressive collapse of symmetric and asymmetric 3-story reinforced concrete ordinary moment resisting frame buildings subjected to the earthquake ground motions are studied. The asymmetric buildings have 5%, 15% and 25% mass eccentricity. The distribution of the damage and spread of the collapse is investigated using nonlinear time history analyses. Results show that potential of the progressive collapse at both stiff and flexible edges of the buildings increases with increase in the level of asymmetry in buildings. It is also demonstrated that "drift" as a more easily available global response parameter is a good measure of the potential of progressive collapse rather than much difficult-to-calculate local response parameter of "number of collapse plastic hinges".

The Effect of Local Damage on Energy Absorption of Steel Frame Buildings During Earthquake

Progressive collapse is a kind of failure in which whole or large part of a structure collapse when a local damage occurs and distributes to other parts. Many researchers focus on the column removal analysis and study of the structure behavior under effect of gravity loads, so these investigations are mostly carried out on the tall building. Earthquake inspections indicate structural element can be damaged during earthquakes and this initial damage distributes to the other parts, so seismic progressive is proposed as a research issue. In this article, seismic progressive collapse of a steel-frame building is investigated. A local damage in a part of the structure was created by weakening a column intentionally so, the initial damage was navigated toward a part of structure then the lateral loads were applied to the model and the structure behavior subjected to seismic progressive collapse is evaluated. In the next step, the effect of differentiating length and numbers of spans in both directions is studied and finally structure failure pattern cased by seismic progressive collapse is obtained.