Progressive Collapse Analysis of Two-Dimensional Reinforced Concrete Framed Structure

This research investigates numerically the potential failure of different framed structures after removal of a corner column. This study is directed towards the role of the joint above the removed column in terms of framed structures stability and internal forces redistribution utilizing linear static, nonlinear static and nonlinear dynamic analysis procedures. First, the preliminary linear static analysis as a part of more detailed nonlinear static and dynamic analysis to model reinforced concrete frames is performed. For nonlinear numerical models, three different moment-rotation capacity curves are considered for the joint above the removed column. These curves are taken according to FEMA 356 regulation according to the reinforcement condition at the joint location to represent normal joint, anchorage deficient joint and shear deficient joint. In linear static models, the results confirmed that, the more moment the joint can resist at the removed column location, the less moment is generated at the beam’s other end. In nonlinear static analysis, the model with normal plastic hinge properties recorded a higher carrying capacity than the model with both shear and anchorage plastic hinges. Nonlinear dynamic analysis with less assumptions offer the more representative modeling for the considered case study which is obvious from its closer perdition of internal forces and deflection compared to the reference findings.

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.

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

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.

Importance of ‘DAF’ in evaluating structural adequacy of gravity-load designed RC buildings

In this paper, a simplified analysis procedure to calculate the column removed point displacement at progressive collapse analysis of reinforced concrete structures is proposed. The energy absorption capacity under the column missing event is used for formulations. The approximate method is simple to utilize, user friendly, yet accurate. For progressive collapse analysis of structures, linear static analysis, nonlinear static analysis, linear dynamic analysis and nonlinear dynamic analysis can be performed. In this paper, the nonlinear static analysis from alternate load path method is used and the reason of initial local collapse has not been considered. In fact, an energy-based method by using load-displacement curve of RC frame and considering the effect of floor slab for the progressive collapse analysis is considered. The accuracy of the proposed method is demonstrated by comparing the results to three experimental and analytical results. Finally, the effects of the spans length, sections dimensions, material properties and the beams reinforcements of column removed spans on substructure behavior is studied, as well.

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.

The structural analysis involves the definition of the model and selection of the analysis type. The model should represent the stiffness, the mass, and the loads of the structure. The structures can be represented using simplified models, such as the lumped mass models, and advanced models resorting the finite element method (FEM) and discrete element method (DEM). Depending on the characteristics of the structure, different types of analysis can be used such as limit analysis, linear and nonlinear static analysis, and linear and nonlinear dynamic analysis. Unreinforced masonry structures present low tensile strength, and the linear analyses seem to not be adequate for assessing their structural behavior. On the other hand, the static and dynamic nonlinear analyses are complex, since they involve large time computational requirements and advanced knowledge of the practitioner. The nonlinear analysis requires advanced knowledge on the material properties, analysis tools, and interpretation of results. The limit analysis with macro-blocks can be assumed as a more practical method in the estimation of maximum load capacity of structure. Furthermore, the limit analysis requires a reduced number of parameters, which is an advantage for the assessment of ancient and historical masonry structures, due to the difficulty in obtaining reliable data. The observation of the damage in masonry buildings caused by earthquakes in the past has been shown that the masonry structures can be discretized into several macro-blocks and interfaces. The macro-blocks are portions of a structure with similar material properties and structural behavior, to which the mechanical properties of the material can be assigned or, by simplification, they can be assumed to be infinitely rigid. The interfaces in a macro-modelling represent, in general, the cracks associated to the failure mechanisms. However, in a micro-modelling strategy applied to masonry, in which the units and the joints are individually considered, the interfaces simulate the behavior of the joints. Furthermore, different criteria for the strength parameters of macro-blocks and interfaces can be considered. The limit analysis (Fig. 1) with macro-blocks is a simplified and powerful structural analysis tool to evaluate the ultimate capacity of masonry structures by static models, involving the equilibrium of the macro-blocks through the limit analysis basic concepts.

This paper presents a comparative review of three major seismic analysis methods used for reinforced concrete (RC) structures: linear static analysis, nonlinear static (pushover) analysis, and nonlinear time-history analysis. The study evaluates their underlying theory, modelling requirements, assumptions, accuracy, and level of computational effort. Published global and regional research was reviewed to assess when each method is appropriate for performance evaluation and design. The findings show that linear static analysis is simple and code-friendly but often unreliable for irregular, taller, or higher–mode-sensitive buildings. Nonlinear static analysis better represents inelastic behaviour, stiffness degradation, and hinge formation but may overlook torsional and higher-mode effects. Nonlinear time-history analysis offers the most realistic predictions of seismic response; however, it requires significant modelling detail, computational resources, and careful selection of earthquake records. This review highlights conditions where simplified methods are acceptable and where nonlinear approaches are necessary for accurate and safe seismic assessment and retrofit decisions.

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.

A general multidisciplinary procedure to approach the study of heritage building is synthesized in this PhD thesis considering the main features necessary to identify the structural behaviour of such type of buildings (historical inquires, geometric survey, material identification, in situ inquires) according to qualitative and quantitative methodologies. An in-depth survey has been carried out on the masonry of the Bell Tower of the “Santa Maria del Carmine” Church in the city of Naples, Italy. The analyses followed a multidisciplinary approach to identify its architectural and structural features, to identify the materials used and the state of damage and interventions made in various periods, to assess the stress state in the masonry under gravity loads, and to define its dynamic behavior. The information gathered represents the starting point for designing a seismic upgrade to meet the standards applied to historic monuments. A detailed historical, architectonical and structural inquires have been developed on the Bell Tower of “Santa Maria del Carmine” sited in Naples. These inquires have been preliminary to the study of the Tower by a finite element model for static and dynamic loads. The Bell Tower of “Santa Maria del Carmine” is an ancient (XVII century) historical masonry building located in city of Naples (Italy). The Tower is 68m high and is made by faced yellow tuff masonry along the initial 41 meters of height and by clay bricks along the upper levels. Internal and external walls are covered by decorative dark stone along the first nine meters. Geometrical and material surveys were performed to evaluate the actual damage state, the sequence of changes in the structures. Detailed experimental in situ investigations have been performed to define the geometry, to find the composing materials, to characterize their mechanical properties, to analyze damage condition and to identify the dynamic behaviour of the structure. The experimental results have been successively used to develop a numerical 3-D FE model. This model has been used to perform a linear static analysis under gravity loads to calibrate the mechanical parameters given by experimental results (i.e. the density of materials) and to check the safety condition for the vertical loads usually acting on the structure. Then, a linear dynamic analysis has been also accomplished to assess the values of Young’s modulus of materials and the constraint conditions offered by the surrounding buildings, based on parametric comparisons with the experimental results (natural frequencies and corresponding modal shapes obtained by dynamic in situ tests). This last study has been useful to understand the behaviour of the Tower under horizontal actions like an earthquake, considering that the structure is located in a medium risk seismic area. Therefore with the assumption of a ‘global behaviour’ of the Tower, a non linear static analysis (Push - over) was carried out based on the results of the previous inquiries, pointing out a low risk condition for the expected seismic actions (peak ground acceleration of 0.168g). Considering that previous numerical analysis evidenced that the Tower satisfied global checks for the expected seismic actions, in this paper attention is focussed on the study of local out-of-plane mechanisms activated by those actions. To prevent the activation of local mechanisms an innovative and low invasive intervention with FRP materials has been designed in the areas where local checks were not satisfying.

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

Reinforced concrete (RC) structures located in aggressive environment, for example, RC bridge piers close to the sea and experiencing chloride attacks, may be exposed to an increased seismic vulnerability. This requires practical yet effective safety assessment strategies aimed to determine the seismic behavior by incorporating corrosion deterioration phenomena. An easy‐to‐use phenomenological model is here developed to describe the seismic behavior of corroded RC elements based on a fiber hinge formulation wherein the corrosion‐induced mechanical degradation of concrete and steel is implemented through appropriate constitutive laws at the fiber level. The developed fiber hinge formulation is first validated against experimental cyclic tests of corroded RC columns from the literature. Then, the proposed approach is used for the seismic vulnerability assessment of the Zappulla multi‐span viaduct (southern Italy), whose RC bridge piers (with a box‐shaped, two‐cell hollow rectangular cross section) are exposed to carbonation and chloride‐induced corrosion. A comprehensive in‐situ testing campaign is conducted for the mechanical characterization of the materials in the RC piers. Corrosion potential mapping, carbonation tests and tensile tests on corroded bars extracted from RC piers are critically interpreted to calibrate the constitutive laws of the fiber‐hinge model. Motivated by experimental findings, numerical seismic analyses (including linear dynamic, nonlinear static and nonlinear dynamic analyses) are performed under two different corrosion scenarios to quantify the impact of corrosion on the resulting seismic vulnerability conditions of bridge piers with corroded bars. The proposed approach is characterized by low computational cost and lends itself to large‐scale seismic vulnerability assessment of other existing RC bridges placed in corrosive environment.

The gable wall of the conventional island of a nuclear power plant carries various pipeline loads connecting the nuclear island and the conventional island. If the gable wall collapses and is damaged due to the progressive collapse of the main plant structure of the conventional island, it will directly threaten the safety of the nuclear island. Therefore, it is of great significance to systematically study the resistance of the gable structure of the nuclear island to progressive collapse for the safe operation of nuclear power plants. Based on the SAP2000 finite element analysis platform, this paper established a model of the reinforced concrete frame structure of the first span of the shield building on the conventional island of a nuclear power plant, including the gable. According to the alternate path method, the node displacement and bearing capacity responses were used to determine the critical components in the gable, and single column failures of the top four in importance were selected as different analysis conditions. Nonlinear static and dynamic methods were used to analyze the displacement, internal force change, hinge sequence of the gable structure on the side of the nuclear island, and the ability of the gable to resist progressive collapse. The analysis results showed that the gable structure of the nuclear island had good resistance to progressive collapse under four single column failure conditions, whether by nonlinear static or dynamic analysis, and the overall vertical displacement obtained by the nonlinear static analysis was larger than that obtained by the dynamic analysis.