Progressive collapse simulation of concrete frame structures with floors

Progressive collapse, where a localized member failure causes widespread structural collapse, has become a critical concern nowadays, due to its potential to cause significant financial losses and loss of human life. Triggers include natural disasters like earthquakes and floods, as well as accidents, attacks and explosions. Reinforced concrete flat slab structures, which are eminent for their architectural flexibility and have larger spans, are particularly susceptible to disproportionate collapse, due to the lack of floor beams, which can redistribute loads after a column failure, unlike moment frame buildings. This research examines how multi-story reinforced concrete flat slab buildings behave, under prescribed gravity load combinations, compared to conventional framed buildings. The effects of removing columns at specified locations from an intermediate floor of the multistorey building are also examined. However, this investigation covers both the column removal approaches to check a possibility of disproportionate collapse which are; static removal and dynamic instantaneous removal. Furthermore, the research also assesses the efficacy of perimeter beams, in minimising the risk of gradual collapse in flat slab structures, by scrutinising their ability to reduce joint displacement, chord rotation, and demand capacity ratio. ETABS v18 was used to analyze all the 18 models. The findings revealed that buildings are more prone to progressive collapse when corner columns are removed, as opposed to edge and interior columns, due to higher Demand-Capacity Ratios (DCR) and joint displacement. In comparison to dynamic analysis, the static evaluation exhibited greater DCR values and vertical joint displacement. Furthermore, since they have a more efficient load redistribution mechanism, traditional framed structures performed better than flat slab models. The simulations additionally indicated that, adding edge perimeter beams, substantially lowered the possibility of progressive collapse in flat slab structures. Moreover, the tested flat slab building models, with and without perimeter beams showed no indications of progressive collapse, when specified columns were removed from the intermediate floors, since the DCR values of the crucial columns stayed within the permissible range of 2.0. In conclusion, structures built in compliance with IS 1893:2016 code and designed to withstand seismic loads demonstrate stronger resistance against significant damage, brought about by column failures.

To evaluate and ensure the safety of a prefabricated connection scheme for future engineering applications, this study investigates the life-cycle progressive collapse resistance of prefabricated reinforced concrete frame structures (PRCS) with steel tube stud connections. A simplified prefabricated column model was developed in SAP2000 using multi-segment linear plastic connection elements, and a six-story PRCS was established for analysis. Progressive collapse behavior of the PRCS and a comparable cast-in-place concrete frame structure (CPCS) was evaluated through the column removal method under four scenarios: corner column, long-side middle column, short-side middle column, and interior column removal. Time-history responses of internal forces and displacements were obtained. In addition, the effect of chloride-induced corrosion on the collapse performance of the structure was analyzed through pushdown analyses. The results indicate that the proposed connection model accurately reproduces the behavior of prefabricated column joints. Among the four scenarios, interior column removal had the most severe effect on PRCS, with displacement increasing by 72.2% compared to CPCS. Pushdown analysis revealed that PRCS exhibited 25.4% lower beam mechanism capacity when the corner column was removed, and 33.1% lower catenary mechanism capacity when the interior column was removed. Furthermore, long-term corrosion significantly reduced the progressive collapse capacity, underscoring the necessity of considering durability effects in design.

The growing need for blast-resistant designs in structural engineering is driven by the rising threat of terrorism, accidental explosions, and the significant risk of progressive collapse. This study presents a numerical procedure for analyzing the progressive collapse of Reinforced Concrete (RC) framed structures due to blast loads, addressing the gap in current methodologies. Traditional approaches such as the Alternate Load Path method, which are code-based and threat-independent, mainly focus on sudden column loss scenarios but do not fully capture the dynamic nature of blast-induced, threat-dependent collapses. Hence this study addresses the need for a computationally efficient and reliable method to predict and model progressive collapse under blast loading. This study employs a comprehensive numerical investigation using Finite Element Method where a seven-storeyed RC building is assessed for progressive collapse under blast loading. Progressive collapse analysis was executed using a commercially available Finite Element Analysis software, adhering to the Linear Static Procedure specified in the General Services Administration (GSA) guidelines, while blast load scenarios were examined through a nonlinear direct integration time history analysis. Different blast parameters, including charge weight and standoff distances, are varied to evaluate their impact on the structural integrity of the building. The study differentiates between threat-independent analysis, considering four column removal locations, and threat-dependent (blast-induced) scenarios with three distinct column removal positions. The scope of this study delves only into the perimeter blast scenarios neglecting the internal explosions. Demand Capacity Ratios (DCR) of columns were calculated to determine the susceptibility of the building to progressive collapse, with a DCR greater than 1 indicating failure. The numerical model was validated against the GSA baseline model. In threat-independent analysis, 30%, 60%, 22%, and 44% of the considered columns under corner, long side, short side, and interior column removal scenarios respectively exceeded the acceptable DCR criteria. In threat-dependent analysis, 100% of the considered columns under each blast induced column removal scenario exceeded the acceptable DCR criteria. This emphasizes the need for scenario-based planning in structural design to reduce collapse risks. The identification of critical columns, for threat-independent analysis as those directly above the removed column and on the topmost floor and for threat-dependent analysis as ground floor columns adjacent to the removed column, reveals potential weak points for progressive collapse initiation. The analysis of blast-induced progressive collapse reveals significantly higher DCR values than threat-independent assessments. Even the minimum percentage increases of DCRs when transitioning from threat-independent to threat-dependent analysis reaches high values up to 995%, 325%, and 981% for corner, long side, and short side column removal scenarios respectively. This specifies the importance of integrating blast resistance into the structural design of high-risk buildings. As a result, this study contributes to the understanding of structural dynamics under blast loads and offers a framework for the analysis of progressive collapse in RC buildings.

Progressive collapse of building structures under blast and impact loads has attracted great attention all over the world. Progressive collapse analysis is essential for an economic and safe design of building structures against progressive collapse to blast and impact loads. Because of the catastrophic nature of progressive collapse and the potentially high cost of constructing or retrofitting buildings to resist it, it is imperative that the progressive collapse analysis methods be reliable. For engineers, their methodology to carry out progressive collapse evaluation need not only be accurate and concise, but also be easily used and works fast. Thus, many researchers have been spending lots of effort in developing reliable, efficient and straightforward progressive collapse analysis methods recently. In the present paper, current progressive collapse analysis methods available in the literature are reviewed. Their suitability, applicability and reliability are discussed. Our recent proposed new method for progressive collapse analysis of reinforced concrete frames under blast loads is also introduced.

Progressive collapse is defined as the spread of an initial local failure of a critical load bearing structural element to the remaining structure, ultimately leading to the collapse of the entire building or of a large portion of it. After the partial collapse of the Ronan Point apartment tower in 1968, when a localised gas explosion ultimately led to the collapse of the whole corner of the building, progressive collapse firstly drew public attention due to its catastrophic consequences on human casualties and economic losses. Other recent collapse events, such as those of the Murrah Federal Building in 1995, Sampoong department store in 1995 and World Trade Centre towers in 2001, have further highlighted the importance of this topic and made engineering communities aware of the necessity to prevent the occurrence of progressive collapse in building structures. In the past decades, considerable research has been devoted to investigate progressive collapse of building structures. These research typically followed an alternate load path approach. This approach allows an initial failure to occur, while the remaining structure needs to seek alternate load paths to dissipate damage and prevent progressive collapse. In practice, the progressive collapse resistance of building structures is generally evaluated by notionally removing one or more load bearing structural elements, representing the initial failure. Despite all research efforts made, they have predominately focused on frame systems. Relevant investigations on reinforced concrete (RC) flat plate structures, a commonly used structural system, are still scarce. The flat plate system contains slabs, of uniform thickness, directly supported by columns without using beams, drop panels and column capitals. This provides structures with increased storey height, architectural convenience and significant savings in construction costs. Nevertheless, the slab-column connection is prone to punching shear failure, which may propagate to the vicinity of connections, potentially leading to progressive collapse. The present study aims at filling some of the current knowledge gap with comprehensive experimental, analytical and numerical investigations on RC flat plate structures. The experimental program consists of four quasi-static large-deformation tests performed on three 1/3-scale, 2×2-bay RC flat plate substructures subjected to critical column removal scenarios. The test specimens included one specimen tested under two consecutive corner column removal scenarios, one specimen under an edge column removal and one specimen under the scenario of concurrently removing both an edge and an interior column. For the loading scheme, a multi-point loading system was specially designed to simulate an increasing uniformly distributed load (UDL). The loading points of this system were equally positioned on the bays adjacent to the removed column(s) to apply the load until failure of the slab. Throughout each test, the structural behaviour of the slab was monitored by extensive apparatuses mounted to the slab both internally and externally. Failure and post-failure behaviours, failure modes, and collapse resisting mechanisms were observed and analysed. Additionally, a complement of analytical studies to the experimental tests, based on the observed yield lines, was carried out to estimate the flexural capacity of the test specimens. To numerically investigate the progressive collapse behaviour of RC flat plate structures, a set of 3D nonlinear finite element modelling approaches, using LS-DYNA software, was established. A total of five numerical models were explicitly created based on the four experimental tests in present research and one from the literature. The proposed modelling approach was basically composed of appropriate definitions of element types, bond-slip relationships, loadings and boundary conditions, and more importantly development of the material models for concrete and reinforcements and calibration of failure criteria for element erosion. A quasi-static loading scheme in displacement control in the numerical models was adopted, the same as that in the conducted tests, through explicitly modelling the multi-point loading system in order to replicate the true test conditions. The numerical models were respectively validated by comparing the load displacement responses, failure modes, crack patterns, and displacement and strain results against the experimental ones, which confirmed the appropriateness and reliability of the proposed models. The validated modelling techniques could be applied to further perform parametric studies of the progressive collapse resistance of RC flat plate substructures and prototype structures. In summary, the significant and original contribution of this research is to (1) obtain a solid understanding of the collapse behaviour of RC flat plate structures under critical column removal scenarios, (2) examine the analytical solution using the yield line theory to predict the flexural capacity of RC flat plate structures, (3) establish a set of numerical modelling techniques which can reasonably replicate the experimental process and provide valuable references of numerically analysing progressive collapse of RC flat plate structures, and (4) give design insights into Australian and international Standards in mitigating progressive collapse of RC flat plate structures.

Idealized structural unit method (ISUM) is now well recognized as one of the most efficient methods to analyze nonlinear behavior of large-sized structures under extreme or even accidental actions. This paper presents some techniques of ISUM modeling and surveys the literature on the ultimate limit state assessment of ship structures using ISUM. Theoretical formulations of ISUM elements for the progressive hull girder collapse analysis of ships that were implemented into ALPS/HULL computer code are outlined. Some benchmark studies are made by a comparison with physical test data and ALPS/HULL analyses on a frigate ship hull model under sagging moment tested by UK Royal Navy and on two double-skin tanker hull models under sagging or hogging moments tested by US Navy. Some ALPS/HULL application examples to progressive collapse analysis of a double-skin shuttle tanker hull under combined vertical and horizontal bending moments are then demonstrated. It is concluded that ISUM is very useful for the progressive hull girder collapse analysis of ships because it provides very accurate results while the computing time is very short.

Progressive collapse is defined as the spread of an initial local failure from a key element to adjacent elements, eventually resulting in the collapse of the whole structure or a disproportionately large part of it. As an abnormal dynamic load, blast load has the characteristic of rapid propagation, high peak value and short duration. And it is also one of the main reasons that might cause the progressive collapse of building structures. Based on the existing research achievements on the progressive collapse of building structures, in this paper the classification method for structural progressive collapse analysis is put forward. Then the current methods for progressive collapse analysis are further divided into two categories, i.e., the method for evaluation of structural progressive collapse resistance and the method for whole process analysis of structural progressive collapse. Recent progress on the evaluation of structural progressive collapse resistance and the method for whole process analysis of structural progressive collapse are presented from literatures. Finally, the conceptual design method, structural detailing and the procedure for progressive collapse resistant design of building structures against blast loading are put forward.

In this study, the progressive collapse potential of tube‐type buildings, such as diagrid and tubular structures, composed of lateral load‐resisting perimeter frames and internal pin‐connected gravity frames, was evaluated by nonlinear static and dynamic analyses. To this end, 36‐ and 54‐storey structures were designed as analysis models and progressive collapse analyses were carried out by removing first‐storey columns. According to the analysis results, the progressive collapse of tube‐type analysis model buildings occurred when perimeter columns corresponding to more than 11% of all member cross‐sectional areas were removed from one side of the structures. When the diagonals located around a corner were removed, the ratio was reduced to 8%. It was observed that the corner columns in the diagrid system helped prevent the propagation of member failure all around the perimeter. Copyright © 2009 John Wiley & Sons, Ltd.

Occurrence of progressive collapse events invariably leads to significant economic and human-life losses. Progressive collapse analysis and design of building structures have become a research hotspot worldwide. Existing studies have proved that development of extra load-carrying mechanisms could significantly improve the resistance of structures to progressive collapse. However, limited research has been conducted to quantitatively analyze these mechanisms. This study proposed a new and unified division method for mechanisms for resisting progressive collapse; furthermore, it provides a basis for their quantitative analysis. In addition, the progressive collapse behavior of a 1/3-scaled two-story, one-bay-by-two-bay reinforced concrete (beam–slab–column) frame with an edge column lost was experimentally investigated. Additionally, a 3 D solid finite element model was established and validated based on the test results. The effects of different extensive parameters, including ideal lateral constraints, slab thickness, and beam–slab interaction, on each resisting mechanism were quantitatively investigated. Finally, a new simple method for predicting the first peak load was proposed based on the contribution of each mechanism. The results from the simple method were in agreement with the simulation results of beam–slab–column structures.

Determination of dynamic collapse limit states using the energy-based method for multi-story RC frames subjected to column removal scenarios

In the past decades, several guidelines have been developed for designs against progressive collapse based on a number of experimental and numerical studies that have been conducted. However, the majority of the previous experimental and numerical investigations focused on the response of buildings under the scenarios of loss of interior or exterior columns. However, the loss of a corner column in the event of a terrorist attack is more likely to trigger progressive collapse given the paucity of surrounding elements that could help to redistribute the axial force initially resisted by the lost corner column. In order to investigate the progressive collapse of RC frames under the loss of a corner column scenario, an analytical model was proposed and subsequently validated through comparison with the experimental results. The influences of the beam longitudinal reinforcement ratio, beam depth, beam width, column width, and joint transverse reinforcement ratio on the progressive collapse performance ...

Over the last 10 years, two United States government agencies have developed guidelines for the design of their structures to resist progressive collapse: 1. The General Services Administration, "Progressive Collapse Analysis and Design Guidelines," (GSA Guidelines) and 2. The Department of Defense Unified Facilities Criteria 4-023-03 "Design of Buildings to Resist Progressive Collapse" (UFC 4-023-03). Although both documents incorporate some of the same approaches, there are notable differences in the application of these procedures. Within both approaches, the main direct design procedure is the Alternate Path (AP) method, in which a structure is analyzed for collapse potential after the removal of a column or section of wall. Different analytical procedures may be used, including Linear Static (LS), Nonlinear Static (NLS), and Nonlinear Dynamic (NLD). Typically, NLD procedures give better and more accurate results, but are more complicated and expensive. As a result, designers often choose static procedures which tend to be simpler, requiring less labor. As progressive collapse is a dynamic and nonlinear event, the load cases for the static procedures require the use of factors to account for inertial and nonlinear effects, similar to the approach used in ASCE Standard 41 "Seismic Rehabilitation of Existing Buildings" (ASCE 41). It is important that the design requirements incorporate appropriate dynamic and nonlinear factors such that the linear static and nonlinear static designs are more representative of the actual nonlinear and dynamic response of the structure.

Progressive collapse is a critical structural phenomenon where local damage triggers a chain reaction and potentially leads to disproportionate failure of the entire system. In this study, the progressive collapse behavior of multi-story reinforced concrete (RC) structures is investigated using numerical analysis methods. This situation poses a serious danger, especially for high-risk types of structures. In the study, the effect on the collapse tendency is evaluated by considering different structural models. Numerical analyses are performed using a nonlinear finite element method. This study offers a general exploration of the progressive collapse behavior of multi-story RC frames, focusing on robustness evaluation under various structural scenarios. The aim of this study is to improve the understanding of structural responses and to support the development of safer, more durable design strategies.

Structural robustness is vital to prevent disproportionate damage in a progressive collapse of a structure. Current assessment methods in building structures, such as the notional removal of structural members, are unable to capture cascading effects from debris impact loading and chained hazard scenarios. Vehicular impact with penetration into the building volume is an example of a plausible chained hazard scenario. In this study, the adequacy of notional damage methods was assessed for vehicular impact loading on building structures and a comprehensive framework was developed to address key limitations in conventional design methods against vehicular impact. The conventional approaches have relied on prescriptive forces and simplified models and have over-looked important phenomena, such as variable vehicle stiffness and energy dissipation mechanisms. The use of the vehicular impact framework has been exemplified using a model for progressive collapse to assess the consequences of successive time-delayed column loss on the structural response from the penetration of a lorry. The time-delay of successive column loss from vehicular impact was determined by considering the kinetic energy and energy dissipation mechanisms. Higher initial velocities lead to higher post-impact velocities after the initial impact on a column and to a reduction in time between successive failures, thus heightening the likelihood of cascading failures in structural columns and progressive collapse. Progressive collapse simulations revealed that a building structure may have sufficient robustness to prevent progressive collapse when subjected to the loss of single columns. However, successive column losses triggered an extensive progressive collapse.

Simplified nonlinear progressive collapse analysis of welded steel moment frames