Progressive Collapse Analysis and Retrofit Design Using the Unified Facilities Criteria

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

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.

Progressive collapse assessment of multistory reinforced concrete structures subjected to seismic actions

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 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.

The Alternate Load Path (ALP) is a useful method that has generated a considerable recent research interest for the assessment of progressive collapse. The outcome of the ALP analysis can be assessed either using the force-based approach or the energy-based approach. The Unified Facilities Criteria (UFC- 4- 023-03) of progressive collapse guideline - have outlined that the force-based approach can either be analysed using static or dynamic analysis. The force-based approach using static analysis is preferable as it does not require a high level of skill and experience to operate the software plus no effort is required in scrutinising the validity of the analysis results output. However, utilising the static approach will eliminate the inertial effect in capturing the actual dynamic response of the collapsed structure. In recent years, the development of the energy-based progressive collapse assessment is attracting widespread interest from researchers in the field; as the approach can produce a similar structural response with the force-based dynamic analysis by only using static analysis. Most of the current energy-based progressive collapse assessments are developed following the requirements which are given in the progressive collapse guidelines provided by the Unified Facilities Criteria. However, little attention is given to the development of the energy-based approach using the Eurocode standards as a base guideline. This article highlights the merits of utilising the energy-based approach against the force-based approach for a collapsed structure and explains the collapse mechanism of a steel frame in the perspective of the energy concept. The state of the art of energy-based progressive collapse assessment for a structural steel frame is reviewed. The comprehensive review will include insights on the development of the energy-based method, assumptions, limitations, acceptance criterion and its applicability with the European standards. Finally, potential research gaps are discussed herein.

In this study, a numerical progressive collapse response evaluation was performed on a 40-story high-rise building designed according to the Turkish Earthquake Code of 2018 (TEC-2018). The alternate path method specified in the General Services Administration of 2016 (GSA2016) and the Unified Facilities Criteria (UFC 4-023-03) was used for the evaluation. A total of 18 scenarios were investigated for column and shear wall removals. In the cases where hinges were observed, the extent of damage was evaluated using the performance criteria given in the Turkish Seismic Code and the American Society of Civil Engineers (ASCE) 41-17. In this study, the most damage was observed when the corner column was removed at the bottom floor, while the least damage was observed on the shear walls close to the center and core of the building. For all the scenarios evaluated, no collapse was observed. The study deduced that the high-rise building designed according to TEC-2018 showed sufficient resistance to progressive collapse.

In the past few decades, effect of natural hazards such as earthquake, wind etc. on existing structures has attracted the attention of designers. Progressive collapse is nothing but a condition of indigenous failure of prime structural element which in turn leads to the collapse of connecting members and then it leads to the additional collapse. For the case of progressive collapse, damage is included in the model through the elimination of important structural component like column. The progressive collapse design guidelines primarily suggest the simplified analysis actions occurred due to the sudden removal of specific columns in a building. The study of analytical approaches for evaluating progressive collapse is carried out by linear static analysis using Alternate Path Method (APM) recommended in General Service Administration (GSA) guidelines and the same is presented in this study. This study involves the use of various general methods of progressive collapse design & evaluation based on numerical mock up and experimental information. For this study, a multistoried composite building (i.e. G+7) is considered. The prime objective of this study is to analyze the composite building by removing columns at different locations and finding out critical location of column vulnerable to progressive collapse and also prevention of progressive collapse of structure using linear static analysis. Location of removed column, Number of floors, vertical irregularity were studied and their influence was also carried out in this research.

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.

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.

Investigation of progressive collapse resistance and inelastic response for an earthquake-resistant RC building subjected to column failure

During the entire life cycle, the facilities are experienced to force and environmental actions of various nature and intensity. In some cases, such influences can lead to a loss of the bearing capacity of the structural elements of a building, which in turn can lead to a disproportionate failure of the entire structural system. Such phenomenon was called progressive collapse. Major accidents at facilities, such as the collapse of a section of the Ronan Point high-rise residential building (London, 1968), the Sampoong department store (Seoul, 1995), the Transvaal Park pavement (Moscow, 2004), the World Trade Center (New York, 2011) and others, clearly demonstrated the urgency of this problem. In this regard, the regulatory documents of the USA, Great Britain, EU, China, Australia, Russia and other countries established requirements for the need to calculate structural systems of buildings for resist to progressive collapse after sudden localized structural damage. However, the steady increase in the number of new publications on the problem of progressive collapse observed in the world scientific literature indicates that the results of such studies do not yet provide exhaustive answers to all questions related to this phenomenon. In this regard, the proposed review article is aimed at systematizing, generalizing and analyzing new research results on resistance to progressive collapse of facilities, identifying new trends and proposing new research directions and tasks to improve the level of structural safety of design solutions for buildings and structures. In order to achieve this goal, the following aspects were considered: the nature of the impacts leading to progressive collapse; features of modeling the progressive collapse of structural systems of buildings and structures; mechanisms of resistance to progressive collapse and criteria for evaluation of a progressive collapse resistance. Particular attention in the scientific review is paid to the analysis of works related to a new direction of research in the area under consideration, associated with the assessment of the bearing capacity of eccentrically compressed elements of structural systems, the effect on their resistance to progressive collapse of the parameters of the loading mode, degradation of material properties and the topology of the structural system. The significance of the proposed scientific review is that, along with the well-known and new results presented in the English-language scientific literature, it summarizes and analyzes the original approaches, methods and research results published in Russian-language scientific publications, primarily included in the RSCI Web of Science.

The article provides a comprehensive analysis of the current state and future development prospects of the system of protective structures for the civilian population in Ukraine under conditions of ongoing armed aggression and heightened threats to public safety. Special attention is given to the transformation of the civil protection system in response to new security challenges, which require not only prompt response but also the implementation of long-term strategic solutions. Modern approaches to integrating protective elements into the architectural and structural design of new buildings are examined in detail. Particular emphasis is placed on ensuring structural reliability and resistance to extreme external impacts, including explosions, shock waves, progressive collapse, missile and artillery shelling, fragment impacts, and other force majeure circumstances. In addition to new construction, the article analyzes the possibilities for adapting, reconstructing, and modernizing existing buildings and underground structures in order to convert them into fully functional protective shelters for the population. Practical approaches to converting basements, underground parking facilities, and other suitable spaces are considered. Engineering solutions aimed at strengthening load-bearing elements, increasing structural rigidity, and minimizing the risk of progressive collapse are outlined. Considerable attention is devoted to technical measures, including the sealing of premises, installation of blast-resistant doors and protective structures, arrangement of safe and accessible emergency exits, and implementation of reliable ventilation systems with filtration capabilities. The article also addresses organizational and regulatory aspects. It examines requirements for engineering support, classification of protective structures, occupancy standards, and maintenance rules. Particular attention is given to the implementation of relevant measures, including financial support, coordination between state authorities and private developers, technical supervision, and raising public awareness.

ABSTRACTPavement evaluation surveys represent the key element for efficient pavement management and for assuring pavement mission capability. In the Department of Defense (DOD), the Unified Facilities Criteria (UFC) 3-260-03 Airfield Pavement Evaluation provides the current guidance for pavement structural evaluations. During structural surveys, FWD tests are executed at different locations within the same section, with the objective of obtaining a full assessment of the section’s structural capability. The availability of multiple deflection measurements for the same section raises the challenge of identifying the deflection basin best representing the entire section and its use in the backcalculation routine to determine the section’s structural strength. This manuscript proposes a fuzzy-based approach for the selection of a representative basin over multiple deflection basins collected for a specific section. The approach accounted for the spatial variability enclosed within the basin membership function obtained by fuzzy c-mean partitioning. The proposed methodology showed promising results for flexible pavements by offering more robust structural assessment that can account for spatial variability and thus minimise some aspects of mission risk that had a large effect on funding allocation and mission readiness.

While the U.S. Army Corps of Engineers (USACE) conducted two pilot Building Information Modeling (BIM) designs in 2005, published their BIM Roadmap in 2006, and hopes to be “fully BIM capable” by 2012, the U.S. Air Force (USAF) has only recently (Fall 2008) embarked on their BIM journey. Indeed, the USAF was much later than the USACE in promulgating their support of BIM, but their delay has the benefit of increased industry BIM knowledge and awareness. Consequently, the USAF initiative has the possibility of greater immediate Return on Investment (ROI) than the Army’s BIM initiative. This research assessed BIM’s impact on the design and construction phase of the two Army Corps of Engineers pilot construction projects and compared that to the USAF BIM approach based on Dynamic Prototyping. By establishing baseline data according to the Unified Facility Criteria (UFC) standard use category codes used across the Department of Defense, these BIM-based projects were evaluated for statistically significant performance differences compared to recent projects of similar use according to three metrics. These three metrics were cost growth, schedule growth, and construction timeline growth. After evaluating the data it was determined that all the BIM-based projects analyzed experienced statistically significant differences in their productivity metrics compared to recently constructed projects of the same type that have similar use. However, there was no significant trend in either positive or negative performance in the construction phase.