Risk Of Progressive Collapse Research Articles

Investigating post-earthquake progressive collapse resistance of irregular steel structures

Removal of load-bearing elements such as columns, can rapidly lead to structural failures and the compromise of building stability. These failures can be initiated by minor damage but can ultimately culminate in catastrophic events. In the line of progressive collapse resistance of conventional urban buildings, extensive studies have so far been performed; though relatively little attention has been paid to the impact of earthquakes on structural resilience under such failures, this is particularly the case in irregular structures as these structures have hardly received much attention. In this research, considering the presence of setback irregularities in many structures, the impact of the column removal scenario after different earthquake intensities of low, medium, and high on over 60 steel moment frame structures with 5 and 10 stories is investigated. The structures are first categorized into four vulnerability groups, from maximum to minimum resistance against progressive collapse, based on the damage percentage. After applying 12 earthquake records at the MCE level, the cases studied are assessed under column removal scenarios at different spans and stories. The results reveal that earthquakes, elevate the risk of progressive collapse. Moreover, increasing setback irregularity up to 13.33 % improves structural performance against progressive collapse, reducing responses by 21 % on average compared to regular structures. However, at higher setback irregularity percentages, responses increase by 82 % on average, diminishing structural resistance. Setting upper limits for this type of irregularity and imposing constraints on design parameters, while modifying minimum base shear and maximum period limit, can significantly reduce progressive collapse potential.

On the progressive collapse performance of RC frame structures under impact column removal

Currently, progressive collapse studies are mostly conducted based on an event-independent assumption. With studies employing an event-dependent premise mainly concerning explosion or fire events, the aftermath of impact loading is seldom reported. Meanwhile, interactions between reinforced concrete (RC) members and superstructures under impact loading need further evaluation. In this paper, finite element models of RC structures subjected to impact loading and progressive collapse are established and validated utilizing LS-DYNA. A valuing methodology of erosion parameters for the continuous surface cap model (CSCM) considering element size is proposed in this process. The influence of impact column removal (ICR) on the progressive collapse performance of RC frame structures is studied at sub-assemblage and structure levels. The parametric study indicates that the ICR process can be described by an impact loading stage and a gravity load stage. It is also found that structures experiencing ICR are exposed to a higher risk of progressive collapse, with the downward force exerted by the impacted columns being a significant contributing factor. Dynamic analyses demonstrate that the acceleration of the column removal point (CRP) can be used to validate and quantify the downward force. The hybrid force-displacement boundary conditions of frame columns give rise to the development of downward force. Recommendations for resisting progressive collapse considering ICR are proposed based on the analytical results of the paper.

Assessment of Different Methods for Enhancing Progressive Collapse Resistance of Irregular Reinforced Concrete Buildings Using Pushdown Analysis

Ensuring structures meet rigorous structural requirements is paramount in mitigating progressive collapse risk. In this comprehensive investigation, we scrutinize the impact of four distinct mitigation techniques on the propensity for progressive collapse in a six-story building featuring irregular structural attributes. The study adheres to the concrete building construction code ACI 318-14 and evaluates methods that include: (a) reinforcing the reinforced concrete (RC) slab with high-performance fiber-reinforced cementitious composites (HPFRCCs), (b) enhancing the RC slab with carbon fiber-reinforced polymers (CFRPs), (c) incorporating steel plate shear wall (SPSW) within specific columns, and (d) introducing an innovative approach named as the steel belt strip (SBS). In the context of 10 independent column loss scenarios conducted on the first floor, the nonlinear dynamic analysis reveals that HPFRCC effectively reduces vertical displacement under the removed column by up to 99.89% in certain scenarios. Meanwhile, the use of CFRP layers leads to reductions of up to 95% in vertical displacement, but with variations in effectiveness across scenarios. Notably, the SBS technique demonstrates remarkable potential by reducing vertical displacement by 97%, 89%, and 25.9% in different scenarios. This reduction, in conjunction with the mitigation of axial load on adjacent columns, makes the SBS a standout performer. Moreover, pushdown analysis indicates that, with the employment of these mitigation methods, the maximum loading factor can be increased up to 2.14 times in specific scenarios, significantly enhancing the structure’s resistance to progressive collapse. This pioneering research not only bolsters the resilience of irregular RC buildings but also holds profound implications for industry standards, risk assessment, and construction technology innovation.

Progressive collapse analysis and retrofit of a steel-RC building considering catenary effect

Despite their low probability of occurrence, the consequences of abnormal loads may be very important, both in economic terms and in terms of human lives. This has stimulated the development of strengthening and retrofitting techniques to mitigate the risk of progressive collapse of buildings. However, their application to real-scale buildings is still lacking. This paper describes the progressive collapse analysis and retrofit of a steel-reinforced concrete hospital building. The progressive collapse performance under different column removal scenarios is investigated using both nonlinear static and dynamic analyses. A two-step pushdown analysis procedure is developed to estimate the dynamic amplification factor (DIF) to partially compensate for the dynamic effects. The results have revealed the vulnerability of the building due to the low tensile axial resistance of the beam-to-column connections. Both the hypothesis of DIF = 2 and the almost inversely proportional relationship between DIF and vertical deflection have proven to be ineffective due to the catenary effect. A retrofit solution is proposed based on an outrigger-belt truss system on the rooftop level. The results show the effectiveness of the retrofit strategy. The displacement dynamic response of the retrofitted structure is significantly reduced if compared to the original structure since it goes from about 20 cm to less than 1 cm. However, the tensile strength of column-to-column connections of the top three floors is inadequate and should be increased. To this aim, a strengthening intervention is developed to increase the tensile strength from 565 kN to 965 kN, thus allowing the tensile axial forces caused by the column removed to be resisted.

A honeycomb panel-based protective device for steel parking structure against transverse impact

With escalating demand for urban parking structures, the columns within these structures are more susceptible to hazards resulting from vehicle collisions compared to other public buildings. Moreover, it is crucial to emphasize the significant increase in the risk of collapse in parking structures subjected to vehicle collisions, primarily owing to their heightened dynamic response and low required bearing capacity. Consequently, to prevent vehicles from directly crashing on the columns, besides providing an alternate load path, urgent implementation of protective measures utilizing energy-absorbing materials is necessary for parking structures. This study proposes a honeycomb panel-based (HP) protective device for steel parking structures aimed at absorbing energy and mitigating damage resulting from vehicle collisions. A simplified multi-scale simulation, considering reasonable material models and boundary conditions, is employed to study the performance of parking structures under transverse impact. The deformation patterns, impact loads, transverse deflections, internal energies, and horizontal reactions are compared for the parking structures with and without the HP protective devices. Innovatively, a classical progressive collapse loading scheme is employed to simulate the vertical residual resistance of the beam-column substructure after the transverse impact. Finally, a comprehensive investigation is conducted on the effects of critical parameters of HP protective device. The results demonstrate that a properly designed HP protective device can significantly enhance the resistance of parking structures to transverse impact, thereby effectively mitigating the risk of progressive collapse in such structures after impact.

The FAILNOMORE project – Practice‐oriented design recommendations against progressive collapse in steel and steel‐concrete buildings

AbstractStructural robustness is a specific safety consideration which is currently addressed in modern codes and standards, including the Eurocodes. It requires particular care from all professionals involved in the construction industry. The need for practical guidelines to mitigate the risk of progressive collapse has been emphasised by recent catastrophic events such as the 9/11 terrorist attack in New‐York. The lack of consistent design rules for practitioners is however clearly identified in existing normative documents and literature. Accordingly, various research projects were launched, particularly in Europe through RFCS research projects. Thanks to these research activities, significant scientific background has been developed, with the aim of understanding and characterising the behaviour of steel and composite structures subjected to exceptional events such as impact, explosion, or loss of a bearing member. Nevertheless, there was a need to consolidate the available scientific knowledge and to transform it into a consistent set of practical recommendations in order to facilitate the design of steel and composite structures for robustness. This was the purpose of a recent RFCS project “FAILNOMORE” (grant No 899371) which was concluded in June 2022. A brief summary and discussion of the main outcomes of this project are provided in the present paper.

Application of the tying force method in the design of alternative load paths in post-and-beam timber structures: A case building

This work aims to present an application of the tying force method recently proposed in the literature to a mid-rise post-and-beam timber building. Internal and edge column loss scenarios are analysed. A steel-to-timber connection is proposed and extensively evaluated as a potential solution to ensure the robustness of the structure, thereby satisfying the requirements imposed by the tying force method and effectively minimizing the risk of progressive collapse of the structure. Finally, a parametric analysis evaluating the variation of the tying force as a function of the chord rotation and different beam span lengths is carried out. The results obtained show that the tying force method represents a promising and rapid strategy for designing robust post-and-beam timber buildings falling in low and medium consequence classes.

Analysis of the Progressive Collapse Resistance Mechanism of an RC Frame Structure with an L-Shaped Plane

In order to improve the progressive collapse resistance of an RC frame structure with an L-shaped plane under local component failure, X-tension reinforcement and steel trusses are applied to the progressive collapse resistance design. In this paper, the finite element software MIDAS Gen v2.1 is used to establish the RC frame structure with 6-story X-type tension strengthening and the RC frame structure with a steel truss at the top. Nonlinear dynamic analysis and a comparison of the two structures after local structural failure are carried out. The results show that both X-tension reinforcement and steel trusses can improve the integrity of the RC frame structure with an L-shaped plane and reduce the risk of progressive collapse in the event of single-column failure, but the steel trusses have the best effect. After component failure, adding a steel truss to the top layer can transfer the load above the failure column to other columns and reduce some beam resistance, providing a more effective alternative load transfer path for the structure.

Soil–Structure Interaction Effect on the Resistance of a Steel Frame against Progressive Collapse Using Linear Static and Nonlinear Dynamic Procedures

In recent years, increases in terrorist attacks or other unexpected explosions have shown that their effects can cause critical damages to buildings and cause partial or total collapse of buildings. This chain collapse mechanism is named a progressive collapse. Subsoil effects on a building are often ignored in studies on progressive collapse. In this study, the effect of soil–structure interaction on the risk of progressive collapse of a steel frame is investigated by using the modified Vlasov model, which has not been used in the studies on progressive collapse before. For this purpose, a steel building model was investigated. A linear static procedure (LSP) and nonlinear dynamic procedure (NDP) with alternative path method were used for the analysis of the frame. SAP2000 software was used to model subsoil effect on the frame via an interface coded in MATLAB interactively. The results from the analyses showed that the soil–structure interaction effect can significantly affect the progressive collapse resistance of the building.

Numerical modeling for assessing progressive collapse risk of RC buildings exposed to blast loads

The safety of strategic structures against accidental loading (such as blast-generated waves) has recently received much attention from practicing structural engineers. Terrorist attacks in the proximity of urban environments may bring blast threats close to the perimeter of the buildings, thereby making them exposed to progressive collapse. This paper aims at investigating the progressive collapse possibility of an existing RC (reinforced concrete) building against blast-generated waves. Data was collected for a typical RC building constructed in a congested area in Riyadh city. A simple NLD (nonlinear dynamic) analysis approach was carried out to examine the progressive collapse possibility of the building when exposed to blast threat events. In this regard, 3D nonlinear two-stage FEA (finite element analysis) was conducted. In the first stage, a local model was created for a typical individual RC column. The local model was validated utilizing the published results of an RC column subjected to blast load. The goal of the local analysis is to evaluate the individual column response against blast load and to come up with the critical stand-off distance at which the column gets severely damaged. In the second stage, a global model (comprising shell and beam elements) was created for the whole building. The goal of the global analysis is to examine the global behavior of the building owing to the removal of the columns identified from the local model stage. The progress of damage caused to different structural elements and the state of stress in these elements was studied. The results enhanced the knowledge about the progressive collapse potential in RC buildings and will be helpful in the development of mitigation strategies.

Comparative Study of Progressive Collapse Potential of Steel Moment Resisting Frame and Braced Frame

Progressive collapse is a situation where local failure of a primary structural component leads to the failure of adjoining members, which in turn leads to spread of failure resulting in the collapse of an entire structure or disproportionately large part of it. In this paper, the effectiveness of inverted V type bracings on progressive collapse resistance of steel building is presented. 4-storey moment resisting steel frame building is considered for the study. Progressive collapse analysis is carried out under ten different column and/or bracing removal scenario from the ground floor level by following the U. S. General Services Administration (GSA) guidelines. Linear Static and Linear Dynamic analysis is performed to evaluate progressive collapse potential of 4-storey steel building considered for the study using SAP2000 software. Alternate Path Method (APM) is used to determine the Demand Capacity Ratio (DCR) of selected beam, column and bracing members located in surrounding of removed column. From the analysis results in terms of DCR of beams and columns, it is observed that the addition of bracing members, reduces the risk of progressive collapse.

Progressive collapse fragility of substandard and earthquake-resistant precast RC buildings

Several natural and man-made disasters have highlighted that precast reinforced concrete (RC) buildings often have insufficient levels of structural robustness, which is the last line of defence under extreme events. Even though robustness studies were originated by the progressive collapse of the Ronan Point precast RC building in 1968, such a structural feature of disaster resilience has been partially investigated in case of precast RC buildings to date. In this study, a precast RC frame structure representative of low-rise commercial buildings is analysed under different column loss scenarios, which can produce the partial or total collapse of the structural system. Two building classes are considered, namely, buildings designed only to gravity loads and buildings designed for earthquake resistance. Structural robustness is probabilistically assessed through a fragility analysis procedure, using three-dimensional fibre-based finite element models with nonlinear links simulating connections, large-displacement incremental dynamic analysis, and multiple performance limit states for damage assessment. The output of the study is threefold: (i) a detailed assessment of the effects of column loss on precast RC frame buildings, quantifying the major role of structural detailing and beam-column connections; (ii) a fragility-informed evaluation of beneficial effects of seismic detailing on structural robustness, which can drive designers in retrofitting of existing precast RC buildings and decision-makers towards prioritization-related issues; and (iii) the generation of typological fragility curves for progressive collapse risk assessment in both single- and multi-hazard environments. Progressive collapse fragility curves can be convolved with more classical fragility models describing the failure of single components (under, e.g., flow-type landslide impact, vehicle collision or blast) and hazard, to assess systemic structural risk.

Reliability-based assessment of progressive collapse in horizontally irregular multi-story concrete buildings

Structures’ resistance against progressive collapse varies depending on their design and taxonomy. However, despite numerous studies addressing the impact of geometric configuration, limited attention is given to the effect of irregularity. This study presents a reliability-based approach to evaluate the effect of horizontal irregularity on the progressive collapse potential of seismically designed concrete buildings. Incremental dynamic analysis is performed on three-dimensional nonlinear finite element models of six prototype buildings with different levels of horizontal irregularity subjected to four column removal scenarios. Probabilistic demand models are then derived to construct fragility curves based on the first-order reliability method. In addition, an analysis of covariance is performed to measure the sensitivity of demand models to column removal scenarios in terms of floor and location. The results show that the studied irregular buildings do not pose a greater risk of progressive collapse than the regular building. In addition, while the probability of collapse under sudden column removal is significantly low for the seismically designed concrete frames, all buildings are expected to experience significant damage under such abnormal loads.

Türkiye Bina Deprem Yönetmeliğine Göre Tasarlanan Betonarme Binaların İlerlemeli Çökme Davranışları

In this study, the progressive collapse response of reinforced concrete buildings designed for the ‘government buildings’ occupancy class was investigated numerically. For this purpose, two reinforced concrete framed buildings were initially designed according to the Turkish Earthquake Code published in 2018. Later, those buildings’ progressive collapse responses were evaluated using the Alternate Path direct design approach defined in the GSA-2016 and UFC 4-023-03 guidelines. Three different column removal scenarios were employed independently by applying the nonlinear dynamic analysis method. Nonlinear fiber hinges were used to simulate the plasticity of the structural load-bearing members. As a result of this study, it is deduced that a limited local collapse disproportioned to the initial failure was observed on the investigated buildings. In addition to the conventional seismic design methods, the buildings designed according to the Turkish Earthquake Code should also be assessed with respect to the explicit design approaches against unforeseeable extreme events to reduce their progressive collapse risk.

Progressive collapse risk of steel framed building considering column buckling

Steel buildings are generally susceptible to the risk of progressive collapse in case one or a few load-carrying members are lost in an extreme event such as blast, impact, or fire. Thus, to avoid the catastrophic collapse of steel structures, it is imperative to investigate and learn from the performance of existing steel buildings for progressive collapse potential. The Ohio Union building, a multi-story steel-framed building that existed on the campus of Ohio State University, was tested earlier before its demolition by one of the co-authors for progressive collapse assessment under the successive removal of four columns located at the first-story level. The aim of this study is to conduct NLD (nonlinear dynamic) analysis for the building considering buckling of columns to numerically assess its potential for progressive collapse and then compare it with test observations. The calibrated finite element (FE) model was then extended to incorporate more hypothetical sequential and simultaneous column-loss scenarios. As one of the most widely accepted documents used among practicing engineers for numerical assessment of progressive collapse potential of buildings, the 2003 GSA (General Services Administration) guidelines were also applied. The simplified LS (linear static) analysis approach of the GSA guidelines was used for assessing the progressive collapse risk of the building, and the results were then compared with both test observations and NLD analysis. New dynamic increase factors (DIFs) are recommended for both force- and deformation-controlled actions to be used with the LS analysis.

Experimental assessment of the residual capacity of axially loaded blast-damaged square RC columns

The aftermath of the Oklahoma City Bombing and the events of September 11, 2001 in the United States led to intense research into the response of infrastructure to explosion effects and the attendant risk of progressive collapse of building structures. The research has not addressed the residual capacity of blast-damaged columns. The challenge to structural engineers is determining the residual capacity of blast-damaged columns and deciding which should be demolished and which can be repaired cost-effectively. This paper presents the results of an experimental program designed to investigate the residual capacity of blast-damaged columns in the laboratory.The blast-damaged columns, from an earlier field test program, were first subjected to the design axial service load of 1000 kN. Columns capable of resisting the service load were subjected to additional lateral loading to determine their residual flexural capacity. The test results show that columns with reduced tie spacing exhibited higher post-blast residual capacity from the explosion at the same scaled distance. Also, a high axial load ratio was observed to adversely affect the flexural load capacity of the reinforced concrete columns in a numerical parametric analysis done using the finite element program LS-DYNA.

Experimental and FE study on strengthened steel beam-column joints for progressive collapse robustness under column-loss event

Strengthening of connections in steel framed structures is often required to mitigate the risk of progressive collapse initiated by column removal event. Steel framed buildings with simple shear connections between beams and columns are vulnerable to progressive collapse. Therefore, strengthening such structural systems for existing buildings as well as the designing of robust connections in the new structures is vital. This study was undertaken with the prime objective of investigating experimentally and numerically the efficient strengthening schemes for simple shear beam-column connections in order to minimize the risk of collapse in the incidence of sudden column loss. The experimental and numerical study includes testing a control test frame of a one-third scale single story shear-connection sub-assemblage consisting of two bays. A steel frame with an intermediate moment frame (IMF) connection was used as a target frame. Two schemes of strengthening beam-column connections were adopted for upgrading the control frame. The first scheme employed welded double side plates within the connection region, and the second scheme used pretensioned high-strength hot-rolled steel rods within the connection region. All specimens were subjected to dynamic loading in the vertical direction which essentially simulates extreme load cases like an explosion in which columns are removed. The efficacy of the strengthening schemes was evaluated based on the results of experiments and numerical simulation of the tested specimens.

High-fidelity FE models for assessing progressive collapse robustness of RC ordinary moment frame (OMF) buildings

Most of the buildings in Saudi Arabia were constructed using reinforced concrete (RC) ordinary moment frames (OMFs), which, in most cases, had discontinuous bottom beam rebars across the beam-column joints. Consequently, they may be susceptible to the potential of progressive collapse owing to accidental loss of one (or more) exterior column(s) in an extreme event. Therefore, it is imperative to examine the progressive collapse robustness of RC OMF buildings. In this paper, 16 half-scale RC OMF assemblies (skeletal frames comprising of multi-span beams and two-story columns) were investigated using validated FE modeling for progressive collapse potential in the event of middle column removal. The analysis was carried out with the help of LS-DYNA software. It incorporated nonlinear constitutive modeling of concrete and steel rebars considering the effect of strain rate, and modeling of bond-slip behavior at the interaction of steel rebars with concrete. Out of the 16 assemblies, 12 specimens represented the actual detailing of an existing 8-story building. The studied variables included axial load on columns, percentage of continuous bottom beam rebars across the beam-column joint (with respect to the total number of bottom rebars), and number of beam spans. The performance of the 12 assemblies was evaluated in accordance with mode of failure and characteristics of load–displacement envelope. A simple approach was suggested to assess the progressive collapse risk level of RC OMFs. Five risk levels were proposed, ranging from very low to very high. Very high to high risk was predicted for the 12 studied assemblies. The last four assemblies of the analysis matrix were newly designed to reduce the progressive collapse risk to a moderate (or low) level.

Shaking table test of the single-layer aluminum alloy cylindrical reticulated shell

Aluminum alloys have been increasingly used in reticulated shells due to their favorable properties. A single-layer aluminum alloy cylindrical reticulated shell model with a length and width of 3.6 m is designed to study its seismic performance. A shaking table test is carried out to test the natural vibration characteristics of the model. A dynamic response test of the reticulated shell model is conducted under frequent, rare and severe earthquakes. The difference in the stress characteristics of the reticulated shell affected by two horizontal seismic waves is compared. The acceleration, displacement, and strain responses of the model under different horizontal seismic waves are analyzed, and the collapse and failure characteristics of the reticulated shell model are studied. The non-linear code ABAQUS is used for numerical simulation, and the validity of the finite element (FE) model is verified by comparing the simulation and experimental results. The results show that the bending moment controls the stress of the cylindrical reticulated shell members under a horizontal earthquake. Under rare earthquakes, the reticulated shell model remains elastic. After reaching the plastic stage under a severe earthquake, the reticulated shell retains its high bearing capacity, indicating excellent seismic performance. The joints of the reticulated shell exhibit weakness under stress, thus, it should be considered in the seismic design. The test results show that the single-layer cylindrical reticulated shell has the risk of progressive collapse.

Effects of Non-Structural Walls on Mitigating the Risk of Progressive Collapse of RC Structures

This study aims to investigate the effect of the infilled frames through various important parameters (i.e., the openings’ percentage in infill walls - several columns on the first floor are removed - partial infilled) in the RC structures, subject to progressive collapse scenarios. To this end, 3D finite element models were constructed by using the software ABAQUS. Numerical and experimental results were compared to substantiate the finite element models’ capability of simulating the experimental models’ behavior of Al-Chaar et al. (2002) in an accurate manner. The results showed that there was good agreement between experimental and numerical results. Moreover, the results indicated that there was a significant effect, which cannot be neglected, on the progressive collapse resistance; the reduction ratios in vertical displacement at the regions removed columns can reach up to 80%.