Progressive Collapse Analysis of Composite Structure

Two-dimensional reinforced concrete frames with the storey of different heights are simulated to the column removal scenario to understand the progressive collapse behaviour by using General Services Administration (GSA 2003) guidelines. Numerical modelling of 4-, 8- and 12-storey structures with different analyses procedures were evaluated such as Linear Static Analysis (LSA), Linear Dynamic Analysis (LDA) and Nonlinear Static Analysis (NLSA) using ETABS 2015. The liner results demonstrate the corner column removal and thus make the structure more vulnerable to progressive collapse when compared to the middle column removal and nonlinear results indicate that the progressive collapse of the structures decreases with increasing the height of the storey.

Interior brick-infill partitions are usually considered as\nnon-structural components and only their weight is accounted for in\npractical structural design. In this study, their effect on the progressive\ncollapse resistance of an RC building subjected to sudden column loss\nis investigated. Three notional column loss conditions with four\ndifferent brick-infill locations are considered. Column-loss response\nanalyses of the RC building with and without brick infills are carried\nout. Analysis results indicate that the collapse resistance is only\nslightly influenced by the brick infills due to their brittle failure\ncharacteristic. Even so, they may help to reduce the inelastic\ndisplacement response under column loss. For practical engineering, it\nis reasonably conservative to only consider the weight of brick-infill\npartitions in the structural analysis.

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 is a phenomenon in which a minor damage leads to total failure of the structure or the collapse of large parts of it. In this paper, influence of mass irregularity in height of the structures on the progressive collapse potential was investigated. To this end, four-, eight- and twelve-story steel moment resisting frame structures are designed and progressive collapse potential was evaluated using alternate load path method, recommended by the American General Service Administration 2003. Three dimensional buildings studied in the current paper were modeled using finite element method in ABAQUS software. Results revealed that in the cases with column removal in the first floor, increasing the number of floors, decreases progressive collapse potential. Maximum dynamic displacement under the removed column in regular 4-story building is about 1.41 times larger than that of regular 8-story building and about 2.16 times larger than that of regular 12-story building. Moreover, comparing performance of regular and irregular buildings showed that regardless location of column removal and story number, mass irregularity in height increases progressive collapse potential. Maximum dynamic displacement due to removed column in irregular buildings subjected to column removal in penultimate floor is 19, 20 and 22 percent larger than that of regular one for four-, eight- and twelve-story buildings respectively.

The Progressive collapse is a local failure which may cause the building to be severely damaged or entirely collapsed. Both US General Service Administration (GSA) and Unified Facility Criteria (UFC) have produced two different criteria to design new buildings and to check the safety of the existing structures against progressive collapse. The main objective of this article is to compare the results obtained by both linear static and nonlinear dynamic analysis methods suggested by GSA of a building originally designed according to the Egyptian Code of Practice, and to investigate the effect of adding bracing members in the first story to prevent the successive failure mode. The building has three bays in X-direction and two bays in Y-direction with seven stories. It was concluded that designing frames to sustain earthquakes, as well as adding bracing members in the perimeter of the first floor will enhance the structure behavior against progressive failure mode

Minimizing the possibility of progressive collapse is one of the most important tasks in ensuring the reliability of buildings This paper analyzes the regulatory frameworks of the world experience in ensuring resilience to progressive collapse to the current state of the national one. The purpose of the work was to search for basic information on ensuring resistance to progressive collapse in relevant foreign regulatory documents, in particular: minimum required characteristics of buildings to take into account progressive collapse at the design stage, accepted approaches to reducing the probability of progressive collapse, basic criteria for determining progressive collapse, parameters of modeling progressive collapse by the method of the sudden removal of the load-bearing structure. Current editions of foreign regulatory documents on ensuring resistance to progressive collapse contain similar provisions. The article compares the key provisions of the norms, in particular, the main attention is paid to the main approaches to reducing the probability of progressive collapse, namely the alternative path method. The alternative path method can be implemented in three ways: linear statics, nonlinear statics, and nonlinear dynamics. The minimum characteristics of buildings to take into account progressive collapse in the design are based not only on the building category (risk level, risk category), but also on additional parameters such as number of storeys, building purpose, new construction or reconstruction. The criteria for determining progressive collapse are generally characterized by the acceptance criteria for the rest of the building structure as a result of explicit consideration of resistance to progressive collapse (modeling of the progressive collapse process). The criteria vary from one regulatory document to another, but in general, these criteria are not allowed to be exceeded - localized failure of load-bearing structures is not allowed, except for the removed structure.

The design of new buildings using Progressive Collapse criteria has become better understood since the nation's largest landlord, the General Services Administration (GSA), incorporated progressive collapse design criteria into their standard design requirements. Other institutions, such as the Department of Defense (DoD), also have incorporated progressive collapse design criteria into their design requirements for both new and existing structures. The DoD presents their progressive collapse requirements in the Unified Facilities Criteria (UFC) document UFC 4-023-03 (25 January 2005), Design of Buildings to Resist Progressive Collapse. While there are numerous similarities between the UFC progressive collapse criteria and the GSA Progressive Collapse Guidelines, there are several key differences which can increase the time and cost of the design process, as well as the final construction cost of the project.

Design of safe structures with resistance to progressive collapse is of paramount importance in structural engineering. In this paper, an efficient optimization technique is used for optimal design of steel moment frames subjected to progressive collapse. Seismic design specifications of AISC-LRFD code together with progressive collapse provisions of UFC are considered as the optimization constraints. Linear static, nonlinear static and nonlinear dynamic analysis procedures of alternate path method of UFC are considered in design process. Three design examples are solved and the results are discussed. Results show that frames, which are designed solely considering the AISC-LRFD limitations, cannot resist progressive collapse, in terms of UFC requirements. Moreover, although the linear static analysis procedure needs the least computational cost with compared to the other two procedures, is the most conservative one and results in heaviest frame designs against progressive collapse. By comparing the results of this work with those reported in literature, it is also shown that the optimization technique used in this paper significantly reduces the required computational effort for design. In addition, the effect of the use of connections with high plastic rotational capacity is investigated, whose results show that lighter designs with resistance to progressive collapse can be obtained by using Side Plate connections in steel frames.

Buildings with the most diverse purposes are subject to extreme events, such as vehicle impact, explosions, and sudden loss of members essential to their stability. Progressive collapse can be defined as the process in which a localized damage leads to chain failure, causing the fall of an entire building or a large part of it. The sudden loss of an essential member due to exceptional loads can trigger the progressive collapse of a structure, causing enormous human and economic damage. Progressive collapse is a dynamic nonlinear phenomenon, so its modeling is complex. The most employed technique for evaluation of progressive collapse is the alternative load path method, which verifies the structure behavior after the sudden loss of a load-bearing element, checking its stress redistribution capacity and strength to load increase in critical situations. This work realized successive analysis of structural models of a reinforced concrete building, adopting a progressive complexity to each of them, using the alternative path method. At the end, the effectiveness and importance of each of the analysis steps employed at work were analyzed. The structure designed acoording to the reinforced concrete brazilian standard needed adjustments to meet the minimum resistance requirements of progressive collapse.

In this study, linear and non-linear static analysis of low-rise models representing two-bay two-story and three-bay three-story reinforced concrete framed structures designed as per Indian standard codes (IS 450:2000 and IS 1893:2016) for the high seismic region using Envelope loading combination are assessed with and without the Guidelines of U.S. (GSA) General Services Administration. The purpose of this study is to describe the applicability of Finite Element software in assessing the behavior of seismically designed low rise structure before and after losing vertical structural element column with and without considering dynamic increase factor, and the results indicate demand resistance ratios acquired from elastic linear analysis and the hinge formation pattern obtained from non-linear elastic analysis are similar for Envelope loading combination and GSA loading combination, thus the dynamic increase factor of 2 recommended by the U.S. General Services Administration guidelines for static analysis can be underestimated for low-rise reinforced concrete framed models designed seismically as far as progressive collapse resistance is considered, since both types of loading combinations (in which one combination considers only normal design load path method while the other combination considers alternate load path methods) acquire same type of results, thus confirms seismically designed low rise models does possess inherent property towards progressive collapse resistance. This study provides a good example and summary for the construction industry and can be used by design engineers while designing low-rise progressive collapse-resistant structures.

Recent research using the Applied Element Method (AEM) shows that the method is efficient in modeling progressive collapse analysis of structures. Recent research on progressive collapse design of structures based on the UFC code shows it can be used in optimizing the design for structures for which the alternate path method is required. This paper demonstrates the efficiency of the use of AEM in progressive collapse analysis of reinforced concrete structures by comparison to results of published experimental tests. A case study based on a typical seven-story reinforced concrete frame commercial building is used to demonstrate the advantages of using the alternate path method in progressive collapse design of concrete structures even for the cases where the code permits the use of the tie force method. The contribution of infill walls in resisting progressive collapse is also studied.

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 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.

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