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The sudden loss of columns due to abnormal loads demonstrates a remarkable example of a localized failure that might ultimately result in the progressive collapse of the complete steel-framed structures. In this study, finite element (FE) simulations are implemented by utilizing ABAQUS-Explicit to investigate the progressive collapse of two-storey steel reduced beam section (RBS) frames with web openings. The reliability and accuracy of the FE models are validated by comparing the obtained results with currently available experimental test results. A numerical investigation is conducted on twenty-eight RBS frames, each with a distinct web opening form (i.e. circular, square, and hexagon holes), different sizes of (D = 75, 90, and 105 mm), and varying distances of (25, 50, and 100 mm) from the center of the flange-reduced to the web opening. The failure modes, load-displacement characteristics, and development of catenary action are evaluated. The results showed that the specimens with square holes showed a greater degree of damage and lower load-carrying capacity compared with the specimens that have circle and hexagonal holes. In addition, an increased opening size resulted in a decrease in load-bearing capacity at small distances, thereby resulting in an increased capacity at a large distance.

Bridge structures are often subjected to extreme conditions such as rough weather, earthquakes, impacts from traffic accidents, and even blasts. Such extreme loads can cause damage to the anchorage zones as a result of high stress concentration and can lead to cable loss. Such extreme loads can cause dam-age to the anchorage zones as a result of a highstress concentration and can lead to cable loss. One of the main targets of this study is to develop an analytical method that increases our understanding of the behavior of long-span cable-supported bridges in the case of the failure of one or several cables,through this method, a formula can be deduced to calculate dynamic amplification factor (DAF) more accurately, which could be useful for academic research. In this study, a parallel-load bearing system is considered as a conceptual model of long-span cable-supported bridges. The objective is to investigate the structural robustness of long-span cablesupported bridges in a cable-loss scenario. The conceptual model consists of a beam suspended from cables (tension elements). A simplified model is intentionally selected to make the analytical approach easier. If examining the simplified model shows a certain phenomenon, a similar phenomenon in more sophisticated models can also be expected. The study considers multiple cable failures and employs an analytical approach, developing an approximation function for stress magnification factor in cable break scenarios, using least squares method. The proposed approximation function is accurate and less than 5% error-free in all tested systems, except for minor β values, and increasing β reduces stress magnifica-tion factor. The parameter β influences the calculation of the cable load. For systems with high β values, smaller design loads are necessary, allowing long-span cable-stayed bridges to be segmented into zones with varying β values. This approach enables the determination of minimum design loads for each zone, ultimately reducing cable design costs in cases of cable loss.

Abstract Today, considering the increased cases of terroristic operations, structural design engineers are starting to acknowledge blast-induced loads alongside other design parameters. Since a blast-induced load exhibits a much shorter period than the natural period of the structure, it is unlikely to induce general damages or stimulate the entire structure immediately after the loading, but rather local damages in individual structural elements are the common form of damage. These local damages, however, can set the scene for the gradual failure of the structure. The present study on structures with moment-resisting frames, buckling-restrained braces (BRBs), and conventional steel braces was conducted through an alternative load path (ALP, also known as column elimination) and exact modeling of the blast on the steel frames was undertaken using LS-DYNA software. In this work, the behavior of three five-story steel frames under a blast-induced load of 100 kg TNT equivalent at a distance of 10 m from the structural columns for a period of 100 ms was investigated. Results of analyzing the blast-induced effect on the frames showed that the frame equipped with buckling-restrained braces (BRB) exhibited improved overall peak displacement across the entire frame, peak induced velocity, and peak induced acceleration by 30%, 30%, and 46%, respectively, as compared to other steel frames exposed to blast loads.

In accidental design situations, the loading mode of reinforced concrete structures includes two typical stages such as long-term deformation under constant or slowly varying load and dynamic impact. The purpose of the presented research was to reveal the peculiarities of stress-strain state of concrete under two-stage static-dynamic loading caused by an emergency situation. To achieve this purpose, the experimental investigations of concrete specimens in the form of prisms were carried out under different loading modes, including quasi-static and dynamic loading. The influence of the presence or absence of a long-term loading stage was also considered. It was shown that long-term loading at a stress level of 0.6 of the ultimate strength had a positive effect on the strength of concrete both in quasi-static tests and in dynamic loading. The hardening coefficient in quasi-static tests was 1.07 for the first series specimens and 1.10 for the second series specimens. The dynamic hardening was 1.20 for the first series specimens and 1.32 for the second series specimens.

This study investigates the resilience of dual-system reinforced concrete (RC) structures impacted by progressive collapse where the local failure of a primary structural component leads to the sequential collapse of adjoining elements. The study is conducted on buildings designed in the United Arab Emirates in the context of extreme events. Nonlinear dynamic analysis of twenty-seven different building models is performed to evaluate the impact of critical variables, building height, and column spacing on progressive collapse potential under the Unified Facilities Criteria (UFC) regulations. The research methodology aims to study impacts associated with sudden removal of critical columns (corner, edge, and internal) that replicate severe accident scenarios in buildings. The structural responses were assessed based on the ASCE 41 performance design criteria. The formation of plastic hinges was analyzed to determine the ductility and resilience of the structures. The study finds that buildings with removed corner columns exhibit more significant vertical displacements than those with edge or internal column removals. The results also indicate that columns adjacent to the removed ones generally remained elastic and within their structural capacities, showing structural resilience to localized damage. However, the flexural strength of RC flat slabs near removed or adjacent columns demonstrates insufficient flexural capacities. This study underscores the imperative for enhanced design strategies and emphasizes the critical importance of bolstering structural resilience against extreme events. Moreover, it intends to draw the attention of policymakers locally to the need to consider progressive collapse when designing reinforced concrete structures.

The studies on progressive collapse have primarily focused on threat-independent methods, wherein a sudden column removal is suggested in codes. However, a real collapse scenario is necessarily threat-dependent. Focusing on blast- and impact-induced progressive collapses, the current study considers cases in which damage is concentrated in a single member, without resulting in complete column loss. It is demonstrated that the progressive collapse performance under specific threats can be better or worse compared to that of sudden column removal. Thus, dynamic column removal does not necessarily guarantee the most critical scenario, as the response in a damaged system can sometimes exceed expectations. A simple analytical model is proposed to describe in detail the observed phenomena and emphasizes the development of catenary forces in the column under lateral extreme loading scenarios. The results provide a deeper insight into the progressive collapse performance of frame systems and the involved member-level resisting mechanisms.

The effect of service life of a reinforced concrete building frame on its robustness parameters in the case of sudden failure of the outermost column has been investigated. The reinforced concrete frame of a philharmonic hall was chosen as the study subject. In order to evaluate its robustness, a relative robustness index, which is related to the parameters of the failure load for a system with and without initial local failure, has been utilized. Quasi-static modeling using the finite element method taking into account physical and geometric nonlinearity was performed as a part of the study. The physical nonlinearity of concrete, considering long-term operation of the structure, was accounted for by modified bilinear constitutive models of the material. Such models differed for elements with different stress-strain states in long-term operation. The parameters of the constitutive models were obtained using the integral deformation modulus proposed by Bondarenko. This approach has been employed to analyze the deformations and forces in the elements of the load-bearing system in the scenario of the outermost column failure. The curves for the percentage of destroyed elements of the load-bearing structure versus the parameters of the failure load have been plotted for the models with and without initial local failure of the outermost column, as well as for short-term and long-term operation. It is shown that the values of the failure load parameter and the relative robustness index decrease when the service life of the structure is accounted for.

Introduction. Spatial rod metal structures of high level of responsibility are the most frequently used as structural systems for covering large spans of buildings and structures. However, progressive destruction can actively develop in these systems under unfavorable combination of factors. The aim of the research is to develop scientific justification of new approaches to the design of optimal spatial metal structures resistant to the development of progressive collapse of high level of responsibility with guaranteed levels of reliability of key and secondary elements.Materials and methods. The main research methods in the work are methods of structural mechanics in the form of the finite element method, methods of similarity theory, and methods of the theory of reliability of building structures.Results. As a result of the research work for the considered structures, a 2-stage algorithm for assessing reliability was developed, which differs from the previously developed ones by the possibility of assessing the development of progressive collapse. The results of its testing for frame-cantilever structures of coverings over stadium stands are presented in the form of established values of reliability indicators for a set of key elements. A similar assessment was made for the implemented reconstruction project of the long-span covering of the “Ilyichevets” sports complex (Mariupol).Conclusions. To assess the reliability of the studied structures, taking into account the tendency to the development of progressive collapse, a universal algorithm is proposed and tested in practical design, the main components of which are computer modelling of the process of successive failures of structural elements, and the establishment of failure probability values for the selected set of key elements. The studies carried out on the basis of its algorithm made it possible to identify a set of key elements of the cantilever part for the frame-cantilever coverings above the stadium stands, the failure of which initiates the beginning of an avalanche-like collapse, and to set limits for them to change the values of safety characteristics and survivability reserve. Additionally, the main provisions of the developed approach were experimentally tested during the development and implementation of the project of reinforcement of large-span bearing structures of the covering of the “Ilyichevets” sports complex (Mariupol).

Abstract This paper investigates the progressive collapse potential of eight-story reinforced concrete framed buildings with several atypical structural configurations and compares results with a typical structural configuration. The alternative load path mechanism, the linear-static analysis procedure amplified by dynamic increase factors, and the demand capacity ratio criterion limits from the U.S. General Services Administration guideline were used to evaluate the vulnerability of the different atypical and typical framed structures. Variations in bay size, plan irregularity, and closely spaced columns were used to represent the atypical structural configurations. The extracted demand-capacity ratio (DCR) of the global structural response showed that the demand-capacity ratio for the longitudinal frame with short-span beams had a larger DCR than the transverse frame with longer beam spans with significant potential for progressive collapse. Furthermore, atypical building configurations with closely spaced columns failed by shear and showed the highest DCR limits. In addition to the global structural response, the local member end actions were also evaluated. The evaluation showed that the critical atypical frame configuration with closely spaced columns had a 91% and 127% maximum shear force and support bending moment value difference, respectively, when compared to a baseline typical frame configuration.

The design of structures to resist progressive collapse primarily focuses on enhancing structural safety and robustness. However, given the low probability of accidental events, such designs often lead to a negative cost–benefit. To address this problem, this paper uses risk analysis to optimize the progressive collapse resistance design of steel frame structures. The elements’ cross-section design for the progressive collapse resistance of steel frame structures is optimized using genetic algorithms and SAP2000 23, which identify the structural model with the minimum robustness index while ensuring safety. The results show that the risk-based robustness index can effectively assess the cost of progressive collapse design. More importantly, the optimization model can rapidly identify the most cost-effective structural design solution that complies with progressive collapse resistance guidelines, enhancing the simplicity and usability of the structure design optimization process. Additionally, the integration of the SAP2000 API with Python 3.8 automation streamlines the parameterization process, minimizes manual errors, and enhances the precision and efficiency of the structural design optimization. Finally, the model’s effectiveness is validated through a case study, where the refined single-frame structure shows a reduction in initial construction and collapse-related costs by 2.4% and 9.1%, respectively. Meanwhile, the three-dimensional frame shows a 2.9% rise in initial costs but a 13.5% decrease in total collapse-resistant design costs, illustrating the model’s ability to balance safety with cost-effectiveness.

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.

La socavación de las cimentaciones puede causar fallas estructurales con graves consecuencias. El proceso de socavación tiene un carácter progresivo y, dependiendo de las condiciones en las que se desarrolla, los efectos de este proceso podrían ser controlados oportunamente para evitar el colapso de las estructuras. Este artículo presenta los resultados de la modelización numérica mediante elementos finitos del colapso del puente de la calle Arturo Sandez en el cantón Girón, Ecuador. El análisis se realizó en un modelo de elementos finitos sólidos en el programa Midas Civil. El estudio del estado tenso-deformacional del puente se realizó en diferentes etapas de socavación y los resultados obtenidos demuestran que, si durante una valoración física se detectan daños en una estructura, entonces es necesario realizar una evaluación numérica de su estado tenso-deformacional. Esta acción permitirá pronosticar la evolución del estado tenso-deformacional de la estructura y tomar las medidas correctivas de manera técnica y oportuna para prevenir el colapso. Este estudio muestra que la socavación inicialmente detectada casi un año antes del colapso constituía un 5.86% de la superficie de cimentación, el inicio del fallo del estribo izquierdo se produjo cuando el área de la socavación alcanzó el 25.48%, y el fallo irreversible de la estructura se produjo cuando la socavación alcanzó un el 39.41% de la superficie de cimentación. Los resultados expuestos demuestran que una modelización numérica pudo prevenir el colapso del puente y permitir tomar las medidas necesarias de mitigación. Abstract Foundation scour can cause structural failure with serious consequences. The scour process has a progressive character and, depending on the conditions under which it develops, the effects of this process can be controlled in a timely manner to avoid the collapse of structures. This paper presents the results of the numerical modelling of the collapse of the Arturo Sandez bridge in Girón, Ecuador. The analysis was performed in a solid finite element model in the Midas Civil software. The study of the stress-strain state of the bridge was carried out at different stages of scour and the results obtained show that, if damage to a structure is detected during a physical assessment, it is necessary to carry out a numerical evaluation of its stress-strain state. This action will allow the stress-strain state of the structure to be predicted and corrective measures to be taken in a technical and timely manner to prevent collapse. This study shows that the scour initially detected almost one year before the collapse constituted 5.86% of the foundation area, the onset of failure of the left abutment occurred when the scour area reached 25.48%, and the irreversible failure of the structure occurred when the scour reached an area of 39.41%. The above results demonstrate that numerical modelling was able to prevent the collapse of the bridge and allow the necessary mitigation measures to be implemented.

Abstract The alternative load path (ALP) method is an important modern design approach to prevent progressive collapse of buildings by redesigning adjacent structural elements to provide an alternative load path in case of partial collapse. This may lead to tangible changes in the mass and stiffness of the building, which means a change in the seismic behavior of the building. This shows the fact that choosing and designing an alternative load path is not an easy task. Studying the improvement in the seismic behavior of the building, whether direct or indirect, as a result of using the ALP, is the main objective of this paper. To achieve this goal, this study examined approximately 96 models, including the study of the possibility of progressive collapse occurring, whether there is or isn't an alternative path for the loads using non-linear static and dynamic analysis, as well as evaluating the study models using various seismic evaluation methods, where both the nonlinear static pushover analysis method and the FEMA-P58 method were used and compared. The study models are divided into two sections, with and without (ALP). The study models are also categorized by building height using heights of 6, 9, 12 and 15 floors. The models were also divided based on the locations of weak points in the original design that may be susceptible to damage and lead to progressive collapse, whether they are internal, side, or corner weak columns. The findings from the examined models indicate that the efficiency of (ALP) systems is more prominent in low and mid-height buildings compared to tall buildings. Additionally, the results demonstrate that the FEMA-P58 method yields similar predictions regarding building behavior as traditional seismic assessment methods like pushover analysis, but in a simplified manner that benefits non-engineers by providing clear insights into the financial and temporal aspects of different structural system solutions.

Some examples of failures of structures, buildings, where the lack of robustness was recognized, are analyzed. Several author’s definitions for robustness are presented and discussed. Special emphasis is given to the fact that define robustness as an intrinsic structural property and the other hand it as a property of the structure and its environment. Some related concepts are presented and discussed.The most important proposed measures for robustness are also present-ed including some illustration examples. Finally, a comparison between them is made and the respective shortcomings are identified. After anal-ysis of the robustness nature, a new structural oriented definition is pro-posed. Based on the highlighted shortcomings of the existing measures, in particular those related with the application to deteriorated structures, a conceptual framework for robustness assessment is proposed.

Introduction. Calculation methods and current normative documents used in the calculation of buildings for resistance to progressive collapse are considered. The key methods of analysis are listed and fundamenta.rules of each of them are stated. The advantages and disadvantages of these methods are analyzed.Materials and methods. The calculations of stability to progressive collapse have been carried out for a multi-span flat frame at the failure of the middle post of the ground floor. The software complex LIRA-SAPR 2021 R1.2 was used to perform calculations. The task was solved by several methods: the static calculation, quasi-static calculation and dynamic calculation. The nonlinear functioning of construction and material was considered by step-methods with using the flow curve from SP 16.13330.2017. Quasistatic calculation was performed in two variants: pulldown and pushdown analysis. The dynamic calculation was carried out by direct integration of the equations of motion using the module “Dynamics in Time”. Two variants with different element elimination time were considered.Results. The results are analyzed and summarized in Table 2. The static calculation yields force and displacement values that are clearly underestimated as compared to other methods. Forces and displacements obtained by quasistatic analysis are greater than those obtained by dynamic analysis. The results obtained in the pulldown and pushdown analyses are close in value.Conclusions. Quasistatic calculations give higher forces and displacements than dynamic calculations. The results of pushdown analysis correlate better with the results of calculations in the dynamic formulation. In order to determine forces more accurately when using quasi-static calculation, a justification of the dynamical coefficient is necessary.

The collapse failure of rock surrounding caverns involves a progressive collapse process. Based on the nonlinear Hoek–Brown failure criterion and the upper limit theorem, the whole process curve of the progressive collapse of the surrounding rock of a large-span cavern is outlined in this paper. The progressive collapse process of the surrounding rock of the large-span cavern is experimentally studied using an independently developed visualized large-span-cavern geomechanical model test device with variable angles. The results show that, through theoretical calculation and model tests, the surrounding rock at the top of the large-span cavern undergoes three collapses. Under the condition of rock mass and the shape of the cavern, the larger the span of the cavern, the more times the surrounding rock collapses; with the increase in surrounding rock pressure, the first collapse occurs in the middle part of the arch roof. When the overlying load reaches a certain level, the arch foot becomes the weakest part, and the rock undergoes shear failure along the arch foot, gradually extending upwards, accompanied by multiple collapses, forming a progressive collapse process. The theoretical calculation results of this paper are basically consistent with the scope of the model test, and the research results can provide a basis for the construction and support design of the large-span cavern.

A possible way to improve the structural safety and robustness of precast building structures is to develop effective precast frame systems with layered beams, which combine prefabricated parts with cast-in situ ordinary concrete, high-performance concrete, fiber concrete, or FRP. The paper provides a new type of precast reinforced concrete frame system with layered beams for rapidly erected multi-story buildings resistant to accidental actions. Using a combination of the variational method and two-level design schemes, a simplified analytical model has been developed for structural analysis of the precast reinforced concrete frame system, both for serviceable and ultimate limit states as well as for accidental actions. The proposed model allows for determining shear deformations and the formation and opening of longitudinal cracks in the intermediate contact zone between precast and monolithic parts of reinforced concrete structural elements of the frame, as well as the formation and opening of normal cracks because of the action of axial tensile force or bending moment in these elements. The design model was validated by comparing the calculated and experimental data obtained from testing scaled models of the precast reinforced concrete frame system with layered beams. The paper investigates and thoroughly analyzes the factors affecting the stiffness and bearing capacity of the intermediate contact zone, discusses the criteria for the formation of shear cracks along the contact zone of precast and monolithic concrete, and examines the change in the stiffness and dissipative properties of layered elements at different stages of their static–dynamic loading. The robustness of the experimental models of the structural system was not ensured under the specified load, section dimensions, and reinforcement scheme. Following an accidental action, longitudinal cracks were observed in the contact joint between the monolithic and prefabricated parts in the layered beams. This occurred almost simultaneously with the opening of normal cracks in adjacent sections. A comprehensive analysis of the results indicated a satisfactory degree of agreement between the proposed semi-analytical model and the test data.

Highlights Progressive collapse was studied in RCSWs frames considering soil–structure interaction. A parametric study of structure and substructures was done on progressive collapse. Vulnerability of frames for progressive collapse was assessed by sensitivity index.

Due to the sudden nature of hull girder collapse caused by extreme loadings, the ultimate strength of ships, i.e., ultimate capacity, has to be evaluated. Ultimate strength analysis procedures have already been provided within the rules of the classification societies for sea-going ships. However, rules for inland vessels are not fully addressing the issue. In addition, literature data on the ultimate strength of inland vessels are almost negligible, which is alarming, considering the frequency of grounding and overloading events in inland navigation. Moreover, inland vessels' structural elements are prone to buckling due to their slender plates. In order to evaluate ultimate strength, an inland waterway (IW) barge is chosen for progressive collapse analysis (PCA) employment. PCA has demonstrated that the buckling collapse of structural elements vastly governs a vessel's ultimate capacity. Results show the extent of the safety zone between the actual loss of the ultimate capacity and the linear-elastic behavior of the structure.

Abstract The progressive collapse of the structure caused by the partial failure of the structure will cause severe consequences and massive losses, and structural progressive collapse resistance has always been a hot topic of current research. In order to study the progressive collapse mechanism of base-isolated structures, the test study and numerical simulation of the base-isolated structures were carried out based on the vertical Pushover method and analysis of the variation rule of the capacity of the remaining structure and influence mechanism. The isolation bearing failure position, the size of the beam of the seismic isolation layer, the type of the isolation bearing, and the horizontal stiffness of the seismic isolation layer on the capacity of the remaining structure were compared and analyzed. The results show that the non-uniformity of the beams and the concentrated loading at the nodes were easy to form a linear catenary mechanism, resulting in more severe beam end damage than mid-span damage. In the case of side isolation bearing failure, due to the lack of sufficient lateral restraint, the capacity was significantly lower than other conditions, which were more likely to cause partly collapse. Therefore, setting more transfer paths to improve the structure’s resistance to progressive collapses was necessary. Increasing the size of the beam of the seismic isolation layer could improve the capacity of the remaining structure of the alternate load path in the base-isolated structure. The changes in the horizontal stiffness of the seismic isolation layer and the type of the isolation bearing have little effect on the progressive collapse resistance capacity of the remaining structure.

The problems of non-equilibrium and nonlinear processes in the evaluation of reinforced concrete structural systems robustness potential in ultimate states are considered. The definition of concept of “robustness exposition” is given for a quantitative assessment of the robustness potential. A calculation model based on the generalization of the well-known classical relationship between the current relative deficit change rate of the reinforced concrete stress-strain state with respect to each fixed time value is proposed to describe in time non-equilibrium processes of structural materials force resistance depending on the mode and level of loading. On the basis of the linear creep theory, aging materials, an algorithm was developed to determine the measure of creep, corrosion-damaged concrete and reinforced concrete and to determine the parameter “robustness exposition” of a reinforced concrete statically indeterminate structural system, taking into account non-equilibrium and nonlinear processes of its deformation in time. An example of a single-span rigidly clamped reinforced concrete beam calculating the robustness potential from the position of a special limiting state criterion is considered.

As building structures in different parts of the world become increasingly exposed to extreme events, there has been a notable research and professional effort to ensure the design of more robust buildings which are insensitive to local failures. At the same time, several works performed in the field of forensic structural engineering have contributed to advancing knowledge on causes and risk factors of structural failure. This includes the creation of several collapse databases, most of which focus mainly on the underlying hazards causing failure. While such databases have provided invaluable insights for preventing structural failures, they do not lend themselves well to the analysis of how failure propagates, which can be useful for improving the progressive collapse resistance of buildings. To this end, a novel database of building collapses is presented in this article which systematically collects information on the hazards, initial failures and their corresponding propagation mechanisms. In addition, key information related to the context and the consequences of collapse is also gathered. Based on the information compiled in the database, this article provides an in-depth analysis of the most commonly occurring initial failures and propagation mechanisms, with significant conclusions extracted from the study of past collapses. The application of different consequence models for estimating fatalities and reconstruction costs is also presented, leading to recommendations for improving such models and related data collection strategies.

Statistics of human losses and financial casualties induced progressive collapse, as one of the new and modern concepts in the field of civil engineering, have doubled the importance of having knowledge about this phenomenon and strategies to reduce its effect. Progressive collapse starts with a local failure with loss of local load-carrying capacity of a small portion of the structure and spreads throughout the structure from element to element. These consecutive failures may cause the collapse of either the entire structure or a major part of it. This paper studies the effect of adding a bracing system to the steel moment frames designed for seismic loads through a nonlinear dynamic method according to GSA-2003 and UFC-4-023-03 criteria. The study was conducted using computational simulation of building models with two different elevations of three and six floors located in a moderate seismicity region. The simulation results showed higher resistance against the progressive collapse of the structure in the braced steel moment frames and less sensitivity to the removal of the column in the braced spans in comparison to the spans without bracing. The prediction of possible progressive collapse in the UFC-4-023-03 criterion is more conservative than the GSA-2003 criterion. Although, generally there is no significant difference between the analysis results of these two criteria.

The steel frame structure plays an important role in strategic deployments and is widely used in heavy machinery, metallurgy, military, and other important industries. To study the impact of explosive loads on the anti-progressive collapse performance of steel structures, this paper proposes to establish the vulnerability characteristics of steel frame structures and provides a method for calculating vulnerability characterization indicators. A finite element model is used to analyze the dynamic response of steel frame structures under the action of close-range explosive loads, and factors influencing the anti-progressive collapse of steel frame structures are proposed, including the number of stories and diagonal bracing. A comparison is made between the various column types of steel structures under explosive loads, such as corner columns, long-edge middle columns, short-edge middle columns, inner columns, also in various coupling conditions. The results show that the progressive collapse of steel frame structures is greatly influenced by the position of the explosion and less affected by the amount of explosive material. The simultaneous failure of corner columns and long-edge middle columns is more likely to cause overall structural failure. The addition of diagonal bracing significantly improves the anti-progressive collapse ability and prevents the lateral displacement of steel frame structures; increasing the number of stories provides more alternative load transfer paths for steel frame structures, thereby preventing their collapse.

Standard structural assessments of ship hulls include the evaluation of the elastic structural response. Elastic analysis neglects extreme and unpredicted loadings, which can produce catastrophic outcomes, such as the loss of the ship’s ultimate strength. Moreover, hull elements are considered unaffected by age-related degradation. Therefore, this study models and quantifies the effect of corrosion-induced structural degradation on the ultimate strength of a high-tensile-steel (HTS) cargo ship using progressive collapse and nonlinear finite element methods. Uniform and pitting corrosion are modeled through selected scenarios, which hull elements might encounter during exploitation, producing a total of 148 calculation models. The findings show that corrosion-induced degradation can significantly decrease the ultimate strength of the hull (up to 30% for the most severe scenarios assessed). Furthermore, ultimate strength decreases almost proportionally to the amount of wastage considered. It was found that stiffener corrosion has a significant effect on the total ultimate strength. This study’s aim is to emphasize the vast importance of including ultimate strength along with ageing effects in industry-standard structural assessments of large HTS ship structures, designed to last for several decades whilst exposed to excessive and unpredicted bending moments.

In order to study the effect of the support mode of a staggered truss system on the continuous collapse resistance performance of a steel structure, four finite element models were established based on the bracing arrangement of a five-story steel frame structure. The situations of different columns on the first floor removed were classified into eight scenarios, and five models of each scenario were analyzed with nonlinear dynamic analyses. Finally, a computational metric based on energy robustness was proposed to evaluate the robustness of the structure. The results of nonlinear dynamic analyses indicated that the staggered truss system significantly improved the resistance to progressive collapse of steel frame structures and effectively increased the redundancy of steel frame structures. All four bracing methods effectively reduced the vertical displacement at the point of failure, with the peak displacement at the point of failure reduced by a maximum of 84 percent and a minimum of 41 percent compared to a pure frame structure. Moreover, the staggered truss system can reduce some axial force peaks in the adjacent columns adjacent to the failed columns. The structural robustness coefficients of Model A, Scheme 1, Scheme 2, Scheme 3, and Scheme 4 are 1.144, 1.339, 1.306, 1.584, and 1.176, respectively, according to the proposed robustness calculation method, which shows that the braced steel frame structure has improved robustness over the original structure. The staggered truss system improves the robustness of the steel frame structure so that the steel frame structure has better resistance to progressive collapse.

In order to increase plasticity during destruction along inclined sections and to protect against progressive collapse of reinforced concrete frames of multi-storey buildings, a variant of cross reinforcement of crossbars in such frames is proposed. The results of a numerical study of the reinforced concrete frame of a multi-storey building with a special impact in the form of an extraordinary hypothetical removal from the work of one of the columns are presented. The modeling of the deformation of the frame is carried out in three versions: the frame of the entire building in the rod setting, a fragment of the building in the column removal zone and a fragment of crossbars adjacent to the column being removed using volumetric finite elements. The obtained results showed the effectiveness of the proposed variant of cross-reinforcement of crossbars to protect a multi-storey frame building from progressive collapse, as well as the effectiveness of using the proposed variant of three-level models for calculating the parameters of static-dynamic deformation of the carcasses of multi-storey buildings under the considered special impacts.

The paper provides the conclusions of a comparative analysis of various approaches, design models, methods for analysis of a loaded structural system and the results of such analysis for a sudden failure of a structural member. It shows that the analysis methods recommended by Russian and foreign standards are based on the same methodology. And the recommended options for choosing secondary design schemes in static, quasi-static and dynamic formulations have different complexity, however, give results which are close enough and acceptable for practical purposes. Some differences in the results are associated with different approaches to consider the reaction redistribution time for the removed structural member, i.e., in essence, with the mode of failure of this member. The issue of criteria for a special limiting state is also discussed. The authors present the expediency of including an additional criterion in regulatory documents that considers the second-order effects on the buckling of the structural elements under accidental impacts and, accordingly, provisions for protecting structural systems against the exhaustion of the bearing capacity due to the loss of stability. As such criterion, the achievement of the limiting equilibrium point on the diagram “axial force vs. transverse deflection” can be adopted.

Experimental determination of the parameters of the force resistance of reinforced concrete structures aimed at protecting them from emergency beyond design impacts is an important direction in improving the safety of buildings and structures. In this connection, the purpose of the study was an experimental assessment of the deformation parameters in the complexly stressed elements of reinforced concrete frames under special impact in the form of a sudden column removal. Experimental studies were carried out for two frames, one of which was tested when removing the middle column, the second - when removing the extreme. Experimental two-span structures of reinforced concrete frames are designed with three floors in height, reinforcement was made with spatial reinforcing cages that provide resistance to torsion with bending. The results of experimental and theoretical studies of reinforced concrete frame structures under special influences and an assessment of displacements, cracking and destruction of the considered complex-stressed structural elements under such influences are presented. It is established that the type of stress state, the formation and width of crack opening significantly affect the dissipative properties of the structural system.

This study investigates the effect of spans length, reinforcement ratio and continuity of flexural reinforcement on the progressive collapse performance of double span beams over failed columns. The investigations focus on initial flexural resisting mechanism to prevent the progressive collapse. Detailed nonlinear finite element simulation of double span beam-column sub-assemblages subjected to residual gravity loads that initially carried by the failed column is adopted for the investigations. Nonlinear static pushover analysis is conducted in which capacity curves are derived and compared with demanded capacities. The effect of spans length, reinforcement ratio and number of continuous bottom flexural reinforcement on progressive collapse are considered in the investigations. Analysis results show that the strength to resist progressive collapse has decreased by 25.4 % and the ductility increased by 103 % following the increasing in span length from 5 m to 7 m. On the other hand, increasing reinforcement ratio of top flexural reinforcement from 0.447 to 1.089 leads to 26.27 % increasing in strength accompanied with a decrease in ductility equal to 16.42 %. In addition, extending all bottom bars rather than the minimum specified two bars resulted in 12 % increasing in strength and 40.28 % decreasing in ductility.

In this paper, a comprehensive state-of-the-art review on types, current modelling, analysis, and design trends of arch, continuous girder, cable stayed, suspension, and steel truss bridge types prone to progressive collapse is presented. Moreover, the effect of different parameters and respective damage mitigation techniques are also delineated based on the findings of compiled case-study reports, and numerical investigations. Finally, from the reviewed literatures, specific knowledge gaps, future bridge engineering practice implications, and unforeseen future study areas are outlined.

In this study, the progressive collapse of reinforced concrete structures due to vehicle collision to the columns of the ground floor was modeled and examined. For this purpose, a four-story reinforced concrete building with the intermediate moment frame system was designed using ETABS software followed by the simulation of impact loading by SAP2000 software. Performing non-linear time history dynamic analysis, the critical forces required to the column failure were determined via trial and error by considering different live load contribution. Then, the corresponding critical velocities for 4, 8, and 12 ton vehicles were determined. Finally, the progressive collapse of the building was examined by the sudden removal of the column. The results showed that by increasing the percentage of live load contribution, the force and critical velocity for the instability and damage of the column will decrease. Furthermore, comparing the perimeter and corner columns showed that the corner columns are the most critical columns for occurrence of the progressive collapse. In addition, during the assessment of the progressive collapse, it was found that the number of damaged springs in the corner column removal scenario is less than that of the perimeter column removal scenario.

Tensegrity structures have a high degree of indeterminacy. Occurrence of initial partial failure at one point of these structures can lead to the propagation of failure throughout the structure. One of the influential factors in the propagation of initial failure is the initial starting point of failure. The first failure can occur in a member that is considered as "critical member" and causes further damage to the structure, or it can occur in a member that has caused minor damage to the structure and maintain the overall stability of the structure. Identification of critical members in tensegrity barrel-vaults, due to the application of these structures in the roof covering of meeting halls, passenger terminals, industrial halls and aircraft hangars, etc. can lead to important and effective results in preventing the occurrence of progressive collapse and possible damages. Therefore, in this paper, the critical members of a two-layer tensegrity barrel-vaults consisting of square simplexes are identified by performing nonlinear dynamic analyzes using Abaqus software. Abaqus software uses the Model Change settings to simulate the initial failure. The stability of the structure under the dynamic effects of failure of different members is investigated and finally, the critical and non-critical members is introduced. It was found that failure of members of the modules are closer to the center of the structure in the longitudinal direction of the barrel vault show more critical behavior than the members of other modules. It was also observed from the results of the analysis that members with maximum stress are not among the most critical members.

Abstract In this essay, to investigate the progressive collapse of the reinforced concrete (RC) frames, a nonlinear static pushdown analysis was performed with column removal scenarios from the first story. At first, a numerical model was simulated and verified with the experimental model in SeismoStruct software without soil–structure interaction (SSI). Afterward, the foundation, soil, and the RC frame were modeled simultaneously in FLAC software and verified with the numerical model of the SeismoStruct software. Furthermore, the effect of SSI was studied on the progressive collapse of RC frames based on the sensitivity index (SI). The sensitivity index is defined as the ratio of the residual capacity under gravity loading of the structure by removing the column to the value of the undamaged structure. The results showed that by considering SSI, the sensitivity index decreases. Then, a parametric study of the framed structures (thickness of the foundation) and substructures (soil density, soil types, soil layers, and the soil saturation conditions) was performed to evaluate the progressive collapse-resisting capacity based on the sensitivity index. The results showed that by considering SSI, with an increase in the soil density and decrease in the groundwater level, the conditions would be better for preventing progressive collapse. It was also shown that rock and silty sands (SM), compared to other studied soil types, and SM and silty sands—silty clay with low plasticity—silty sands (SM-CL/ML-SM), compared to other studied soil layers, are better for preventing progressive collapse.

This paper studies the dynamic response of corner-supported modular steel buildings with a core wall system, under progressive collapse scenarios, associated with corner module removals. Since using secondary systems such as concrete core in mid- to high-rise buildings is currently unavoidable, understanding their impact on load transfer between modules during collapse scenarios becomes essential. The designated four-, eight-, and twelve-story buildings were modelled using the macro-model-based finite element method in Abaqus. In addition, three different locations are considered for the concrete shear core within the building plan, leading to nine various case scenarios. Each vertical and horizontal inter-module connection was modelled by one axial and two shear springs with predefined nonlinear force-displacement behavior. The local and global buckling, which plays an essential role in the building’s stability, was considered to obtain accurate results. Finally, parametric studies on the building response were carried out, including the intra-module connection rigidity and inter-module connection stiffness. The results demonstrated that the core wall could maintain the robustness of a modular steel building through two mechanisms dependent on its location within the plan. In addition, preventing plastic hinges from forming in beams could be introduced as an anti-collapse mechanism in the corner module removal scenarios.

The traditional fixed boundary could not transmit the elastic-plastic stress waves in the progressive collapse analysis of the truss structures, leading to discrepancies in understanding the true response of structures. To solve the critical problem, a new dynamic artificial boundary is proposed and integrated into the truss structure to transmit elastic-plastic stress waves. The new dynamic artificial boundary is established through the integration of the elastic-plastic constitutive model into the governing equation of the stress wave. This boundary is subsequently implemented within the ABAQUS finite element software for the purpose of conducting progressive collapse analysis of the truss structures. The progressive collapse simulation of the truss structures involves a comparative analysis between the new dynamic artificial boundary and the traditional fixed boundary. Numerical analysis demonstrates that the dynamic artificial boundary led to varied initial failure and collapse compared to the fixed boundary. The failure typically occurs at the mid-span under the dynamic boundary. In contrast, additional failures occur near the support columns under the fixed boundary due to stress wave reflections. The dynamic artificial boundary more closely reflects the physical reality and provides a new method for the progressive collapse analysis of the truss structures in practical applications.

The results of a numerical study of a fragment of a reinforced concrete frame of a multi-storey building with a special impact in the form of a sudden hypothetical removal from operation of one column are presented. For a more rigorous assessment of the stress-strain state of reinforced concrete frames of multi-storey buildings, it is proposed to take into account the elastic-plastic work of the junctions of structural elements. Two options for connecting a crossbar with a column are considered: the first is absolutely rigid, the second is taking into account nonlinear compliance in the areas: "bending moment-angle of rotation", "transverse force-deformation", "longitudinal force-deformation". According to the results of numerical analysis, a change in internal forces (up to 30%) in the elements of reinforced concrete systems is shown due to the non-linear operation of both structural materials and the geometric non-linearity of the change in the dimensions of the design model due to the compliance of nodes. The revealed differences in the nature of the change in the stress-strain state are explained by an increase in the plastic properties of the carrier system. The established phenomena require further experimental verification, taking into account various types of structural element connections.

According to regulations and standards, all buildings and structures must fulfil the requirements for mechanical safety. At the same time, the safety of structures must be ensured throughout their entire service life. The annual increase in the number of accidents due to terrorist acts, domestic gas explosions, collisions of vehicles with load-bearing structures, etc. has led to the creation of normative documents on the protection of buildings from progressive collapse. At the same time, the issue of buildings sustainability, which were designed without taking into account these requirements and which may have suffered localized damage during operation, remains open. Such buildings include monolithic houses with flat slabs, which have been erected since the beginning of the XXI century. The aim of the work is to study the resistance of these frames to accidental impacts and the influence on the survivability of structures of local defects in the most critical zone of the column-slab junction. Calculations on stability assessment in case of emergency of a fragment of a 9-storey monolithic building have been performed and it has been established that at certain combinations of damages in the support zones, progressive destruction of neighboring structures may occur.

Introduction. The results of the studies analysis on the protection of multi-storey buildings from progressive collapse are presented, which indicates insufficient attention to structural systems made of precast reinforced concrete, as a result of which design standards orient the designer to the use of not always effective monolithic structures. In particular, the problem of protection against progressive collapse with the exclusion of prefabricated crossbars of floors and coatings has not been practically studied. The purpose of the study is to develop a method for calculating a continuous system of hollow plates made by the method of formless molding.Materials and methods. When designing the protection of multi-storey buildings from prefabricated elements, a static calculation is usually carried out with the exception of vertical structures (walls, columns) and the reinforcement of floor crossbars and coatings by ensuring their continuity. There are constructive methods of reinforcing prefabricated floors by creating continuous plates of adjacent spans with the help of connecting elements made of plastic reinforcing steel, but the calculation of such systems has not been developed. A method for calculating a system of two plates according to a rigid thread scheme is proposed.Conclusions. Currently, theoretical methods have been developed to solve various problems of protecting buildings and structures from progressive collapse. However, there are many design requirements for the protection of multistorey buildings from progressive collapse, which have not yet received experimental and theoretical confirmation for the effective solution of practical problems. It seems that in this article one of these problems is partially solved.

Abstract The possibility of the occurrence of a second punching shear failure and of a Progressive Collapse after a punching shear failure had occurred in one flat slab column connection is investigated in two building structures, using Eberick and SAP2000 softwares and the Yield Line Method, and codes ACI318:2019, EUROCODE2:2004 and NBR6118:2014. It is shown that slab column connections should be designed and detailed to prevent Progressive Collapse and that Integrity Reinforcement should always be present, and that the remaining capacity of floors after punching failures depends on the i) post-punching resistance of the connection being punched; ii) post-punching resistance of the neighbors’ connections; iii) flexural resistance of the slabs, and that the flexural resistance of the slab’s floors can be evaluated by the Yield Line Method.

Beam-column joints are one of the most critical components of RC structures, affecting the structure's performance under different types of loads. In recent years, some researchers have considered high-performance fiber-reinforced cementitious composites (HPFRCCs) as an alternative to conventional concrete for improving the performance of beam-column joints. The effects of HPFRCC materials on the robustness of reinforced concrete structures subjected to progressive collapse were investigated in this study. To this end, the method proposed by Fascetti et al. was utilized to assess the robustness of three five-story RC buildings with a moment-resisting frame system. The buildings were designed as special moment frames (SMF), intermediate moment frames (IMF), and intermediate moment frames with HPFRCC at joints (IMF-H) per ACI 318–14. The OpenSees finite element platform has been widely used for 3D buildings simulation and nonlinear analysis. In this study, the analyses and calculated robustness indices indicated that using HPFRCCs materials in beam-column joints significantly improved the robustness of concrete moment frames subject to progressive collapse. Furthermore, the damage distribution based on plastic rotation results confirmed that the robustness of concrete moment frames with HPFRCC joints subjected to progressive collapse was significantly improved.

This paper investigated progressive collapse analysis of three-dimensional (3D) reinforced concrete (RC) frames that are optimized for carrying structural loads by introducing a unique simultaneous multi-column removal load path using Machine Learning. The investigation includes formulating an integrated computational framework that incorporates a self-training machine learning algorithm. This algorithm is used to train the largest machine learning models of 3D RC frames containing more than 600 optimized structures to predict the posterior based on the trained priors. The efficiency of the computational framework was shown by conducting a comprehensive study on the optimization and behavior of structures considering seismic loading, alternative load path due to progressive collapse, and second order (P–delta) effects. The results show that the proposed framework ensures that system solutions meet both structural integrity and constructability requirements of the ACI and the Unified Facilities Criteria.

To investigate the effect of nano carbon-fiber-reinforced polymer (nano CFRP) on retrofitting reinforced concrete (RC) structures, this article presented the progressive collapse performance of two half-scale four-bay RC frames including one control specimen S1 and specimen S2 with nano CFRP retrofitting beam ends. The progressive collapse performance was discussed by comparing crack patterns, failure mode, load–displacement curves, horizontal displacement, strains, and rotational and energy dissipation capacity. The test results demonstrated that nano CFRP did not change the ductile beam-hinge failure mode, but improved the load-bearing capacity and ductility efficiently, and postpone shear failure of the joint core region obviously. Due to the insufficient development of plastic hinges limited by nano CFRP, S2 failed to enter catenary action, which revealed its own defects in anti-progressive collapse. It was shown that the retrofitting strategy using nano CFRP can substantially improve the mechanical characteristics and implement the strong column-weak beam failure mode.

Previous studies indicate that low-rise buildings are more prone to progressive collapse rather than high-rise ones. In this research, an innovative method of probabilistic analysis of progressive collapse has been applied based on the concept of fragility curves. In order to develop the fragility curves, the column reaction is considered as the Intensity Measure (IM) and the displacement at top of the removed column as the Damage Index (DI). Based on these measures, the fragility curves of a 4-story steel Intermediate Moment Frame (IMF) structure were developed. Six scenarios of progressive collapse including removal of corner, perimeter, and middle columns were investigated. The scenarios were considered in all columns of structural stories. The simulations were conducted in OpenSees software. The structural analyses were performed by the nonlinear time history approach in a three-dimensional framework. The verification of the numerical modeling process was performed using the available experimental data. The results showed that the IDA capacity curve of the upper stories was weaker than the lower stories. According to the results, at every considered DI and assumed performance level, damage to the removed columns occurs at lower axial force on the upper stories than on the lower ones. Furthermore, the potential of the progressive collapse in different columns was investigated. It was shown that the capacity curve of the middle columns was lower than other columns due to the high gravity loads. The probabilities of the fragility of the corner and the perimeter column in the stories were the highest and the lowest, respectively. In order to reach the corner and the perimeter column to CP performance level, 93% axial force and 105% of the axial gravity load in the opposite direction of the column reaction were required. Finally, the overall fragility curves of the structure were investigated. According to the results, upon removing 100% of the column reaction in each column of the considered 4-story structure, the structure exceeded the CP performance level.

In this study, the potential of progressive collapse of a four-story steel structure due to the collision of an 8-ton truck with the ground floor columns was investigated. For this purpose, a 4-story steel structure (with intermediate steel moment frame system and special concentric steel bracing in the x-direction and intermediate steel moment frame system in the y-direction) was modeled and designed in ETABS software. ABAQUS finite element software was used to simulate the structure under collision scenarios. In this research, 6 scenarios of truck collision with adjacent columns of the structure have been considered by performing nonlinear dynamic analyzes. The vehicle speed is assumed to be 20 meters per second. The results showed that corner columns are more vulnerable to impact than perimeter columns. The presence of braces reduces the collapse and deformation in the desired scenario. The horizontal displacement in the impacted column in the direction of the moment frame was about 3 times that of in the direction of the dual system. this shows the positive effect of bracing system in reducing the structural responses to impact.

The approach to numerical modeling of fiber reinforced concrete slab (FRCS) under blast load is considered. The slab is used for coverings of buried protective structures. The stress-strain state of this structure is investigated in the dynamic setting. The loads in this case change in time in terms of both intensity and area. The calculation makes provision for the consideration of rigid and deformable structure of support units. The damping properties of the structure are evaluated for its resistance to progressive collapse. Concrete dilatation and softening are factored in the numerical simulation. The bond between the fiber concrete and the reinforcement was modeled by introducing interpolation elements that simulate the absence of deformation in the area of their contact. The interaction of FRCS with the deformed support was modeled using the linear contact. The transition from the elastic-plastic deformation stage to the rigid stage was performed by introducing gap elements. The geometric nonlinearity, as well as the physical nonlinearity for fiber-reinforced concrete and reinforcement, was taken into account in estimating the ultimate loading. The load absorbed by the structure through the thickness of the ground during detonation explosion of a charge on its surface was considered. To realize numerical integration of the system motion equations, an implicit scheme was used. It is based on a modification of the Newmark step method in which effective matrices of fiber concrete and reinforcement stiffness are constructed at each step considering the loading history of the structure for its deformed state. The possibility of effective regulation of the stress-strain state of FRCS was established, which allows the design of effective and safe structures of this type.

In order to investigate the effects of engineering cementitious composite (ECC) used as post-cast materials and anchorage length of beam longitudinal rebars in the ECC cast-in-place joints on collapse behavior of precast reinforced concrete (PRC) structures, static pushdown collapse tests on scaled PRC beam-column (BC) sub-assemblages were carried out. Three BC sub-assemblage specimens having a double-span beam and a middle column joint were designed and fabricated with the same geometric dimensions, including one monolithic specimen BC0 and two PRC specimens BC1 and BC2. The specimen BC0 was cast in site with normal concrete, while the double-span beams of specimens BC1 and BC2 were first cast with normal concrete and then the middle column joint was post cast with ECC. The anchorage length of beam longitudinal rebars embedded into the middle joint was 29d, 20d, and 10d (d is the diameter of beam rebar) respectively for specimens BC0, BC1, and BC2, which could produce different splice length in the middle joint. On the basis of tests, refined finite element (FE) models were established and reasonably verified by a detailed comparison between numerical and experimental results. Based on the validated FE models, a parametric analysis was performed to study the effects of horizontal constraint stiffness, anchorage length, and bond strength between beam longitudinal rebars and ECC on collapse resistance of PRC sub-assemblages. The results showed that the application of ECC as the post cast material in the joint of PRC sub-assemblages could achieve similar collapse behavior to the monolithic counterpart and reduce the anchorage length of beam longitudinal rebars with a suggested lower limit of 20d. The bond strength between rebar and ECC in the joint had obvious influence on the collapse resistance and deformation capacity at large deformation stage.

The use of old building design codes and improper execution of recent seismic design practices resulted in substandard and vulnerable reinforced concrete building stock, the majority of which is built with weak beam-column joint connections (i.e. joint panels having no transverse reinforcement and built in low strength concrete). In order to understand the seismic response and damage behavior of recent special moment resisting frame (SMRF) structures with the defect of weak beam-column joints, shake table tests were performed on two 1:3 reduced scale two storey and one bay RC frame models. Reference code design and weak beam-column joint frame models were subjected to unidirectional dynamic excitation of increasing intensities using the natural record of 1994 Northridge Earthquake. The input scaled excitation were applied from 5 % to 130 % of the maximum input peak ground acceleration record, to force the test models from elastic to inelastic stage and then to fully plastic incipient collapse stage. The weak beam-column frame experienced flexural cracking of the columns, longitudinal bar-slip in beam members, cover concrete spalling and severe damageability of the joint panels under multiple dynamic excitations. The deficient frame was able to resist only 40 % of the maximum acceleration record as compared to the code design frame, which was able to resist up to130 %. Based on the experimental observations, a drift-based damage scale was developed for different performance limits states that can be employed for the global performance assessment of deficient weak beam-column joint RC frames.

This research studies the performance of two- and four-story steel building models against progressive collapse in two cases: (1) skewed beam–column connections, and (2) straight cleated beam–beam connections. Nonlinear static and dynamic analyses were performed and then the time history analysis was performed under the simultaneous effect of the two horizontal components of three earthquake records and two column removal scenarios. The results showed that the 60-degree skewed connection had a weaker performance than the straight connection, and, according to the plastic hinge distribution, it was observed that the mentioned connection did not provide the life safety performance level.

Since the effect of the irregularity in height of medium and tall structures has a great influence on lateral behavior of structures and it also affects the design of the sections, in this study, various scenarios of sudden column removal in different locations of steel structures with and without geometric irregularities in height have been investigated. The Alternate load Path Method (APM), Nonlinear Dynamic Analysis (NDA), and OpenSees software were used to investigate 10, 15 and 20-story buildings with three types of irregularity in four different column removal scenarios.