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Post-earthquake fire events over the past few decades have become a major threat for buildings in seismic prone regions. Although post-earthquake fire events have caused many fatalities and high levels of damage, current building codes do not consider fire following an earthquake as a specific loading case. Furthermore, the current philosophies of seismic design permit a certain degree of damage to the structural elements which potentially makes structures more vulnerable when subjected to post-earthquake fire. This study is intended to address the fact that only limited research exists on the behaviour of earthquake damaged composite steel frames in a fire. The main objective is to improve the current understanding of post-earthquake fire behaviour of composite steel frames with a view to providing design recommendations. This study analysed a generic five-storey composite steel frame office building which is commonly used for modern buildings in seismic regions. For the first time, three-dimensional numerical models were developed to simulate the structural behaviour under fire following an earthquake. The finite element software ABAQUS v6.13 was used to model the structures. Steel beams and columns were modelled using two-node linear beam elements while concrete slabs were modelled using shell elements. A series of verification analyses were conducted to ensure that the results obtained from analysis give an acceptable level of accuracy. The finite element model was used to investigate the effect of earthquake damage on the fire resistance of composite steel frame buildings. A total of two types of earthquake damage; fire insulation delamination and residual lateral deformation, were investigated. Failure of the structure was defined using two measures, a beam deflection exceeding span/20 and column buckling. It was found that the earthquake damage can significantly reduce the fire resistance of the composite building. The reduction in fire resistance times results mainly from fire insulation delamination, particularly in the columns, rather than residual deformation. It was also found that fire insulation delamination on the protected beams, as might occur in an earthquake, considerably reduces the development of tensile membrane action. This has significant consequences for design because the benefits of tensile membrane action are often used for performance-based fire design of composite structures. Two methods of improvement are presented in this study to enhance the development of tensile membrane action concurrent with fire insulation delamination. Based on the results obtained, increasing slab thickness and improving fire protection rating can enhance the fire resistance of the whole building even with fire insulation delamination. The progressive collapse analysis of a 3D composite building under fire following an earthquake was also investigated. Several different locations of fire scenarios were first studied to investigate load redistribution path along two horizontal directions and the members' interaction within the composite building frame. Then, the effect of residual deformation after an earthquake on the progressive collapse analysis of the composite building was investigated. It is found that neither the load redistribution path nor the fire resistance of the building is considerably affected by the residual deformation. A series of progressive collapse analyses subjected to travelling fire resulting from fire compartment damage was also performed. It is concluded that the survival of the building can be greatly affected by the spatial nature of the travelling fire as well as the inter-zone time delay. Therefore, a range of travelling fire scenarios must be considered based on the compartment condition to guarantee that the building can withstand the 'worst case scenario'.

In a progressive collapse scenario, the immediate effect due to a local triggering failure, i.e. the loss of a column as considered in the present study, is exerted on the beams bridging over the lost column. The behaviour of such double beam assembly plays a critical role in determining whether a progressive collapse would occur or not. This study focuses on the realistic behaviour of such beam assemblies, particularly the plastic deformation concentration, the associated degradations in the connection regions, and how these in turn affect the overall resistance behaviour and the ultimate strength of the beam assemblies. To start with, a generic axially-constrained beam is analytically examined in order to better understand the full range response including the large deflection regime, the development of the plastic deformation, and how this in turn affects the overall resistance and the deformability. The load-deflection relationship and the associated plastic deformation are first analytically derived for a bending scenario, and then the effect of the catenary action is introduced. The analytical solution provides some quantitative insight, although under idealised conditions, into the limiting local criterion (material strain in this case) and the global deflection and deformability. A laboratory experimental study is then carried out on six reduced scale double beam assemblies. The purpose-designed connection details allow different local plastic mechanisms and local failure modes to develop, with an intention to represent relative weak connections so as to supplement the existing experimental literature in the coverage of relationship between connection failure limits and the overall resistance capacities. The test results have revealed that the specimens went through elastic and plastic bending stages; however, the catenary actions could not be developed sufficiently in most of the specimens whenever a premature local failure, such as material/weld fracture, bolt shear and concrete cracking, became dominant. The outcome highlighted the crucial importance of enabling the plastic deformation to "spread" in order to ensure a total plastic deformation capacity in the plastic zones as well as the importance of the axial capacities of the joint connections. In conjunction with the existing studies, the experimental exploration provided further evidences for the future experimental and numerical studies to focus on the design details in typical connection types and how these could transpire into the actual development of the plastic regions and effective catenary action. With representation of the realistic connection behaviour in mind and for practical applications, a new analytical framework is proposed in this study on the basis of component-based connection modelling, for the solution of the resistance function and the ultimate deformation limits. An analytical framework is realized by an in-house program written in MATLAB. In order to apply the analytical framework to double beam assemblies, the existing quantitative formulations for typical joint components of common steel joints are scrutinized. Examples of double beam assemblies with web-cleat and TSWA connection are carried out to verify the analytical solutions and demonstrate the key characteristics of the resistance functions involving these types of joints. Analytical results show good agreement with the corresponding test data. A dedicated study is then devoted to the development of a complete component model for a widely used connection in steel gravity frames, namely the fin-plate connection, which is however relatively less investigated in terms of the component modelling into the large deformation regime. Subsequently the overall behaviour of double beam assemblies involving such joints is examined using the analytical framework. In the development of the component model for the fin-plate joints, existing models and formulations to describe general plate bearing and bolt shearing behaviour are incorporated to establish the basic constitutive properties of the bolted lap-plate component set. Upon the initial verification, improvement of the constitutive descriptions is found to be necessary. To this end, high-fidelity finite element analysis is conducted, and on this basis, modifications to the plate bearing and bolt shearing behaviour are proposed. The analytical solutions with the modified lap-plate component properties are found to be in good agreement with the experimental results. The outcome of this thesis has provided new insight and evidence on the realistic behaviour of beam assemblies, and pointed out the directions for more robust design for improved progressive collapse resistance of the steel framed structures. The analytical framework and the associated solution provide a useful tool for the analysis of the resistance functions for the critical beam assemblies for practical applications. With this approach, the key to the reliability and soundness in the analysis of the resistance function lies upon the adequacy and accuracy of the description of the joint components. In this respect, the future work should focus on more comprehensive quantification of the properties and deformation limits of joint components for a variety of joint types and design details.

A structure subjected to extreme load due to explosion or human error may lead to progressive collapse. One of the direct methods specified by design guidelines for assessing progressive collapse is the Alternate Load Path method which involves removal of a structural member and analysing the structure to assess its potential of bridging over the removed member without collapse. The use of this method in assessing progressive collapse therefore requires that the vertical load resistance function of the bridging beam assembly, which for a typical laterally restrained reinforced concrete (RC) beams include flexural, compressive arching action and catenary action, be accurately predicted. In this thesis, a comprehensive study on a reliable prediction of the resistance function for the bridging RC beam assemblies is conducted, with a particular focus on a) the arching effect, and b) the catenary effect considering strength degradations. A critical analysis of the effect of axial restraint, flexural reinforcement ratio and span-depth ratio on compressive arching action are evaluated in quantitative terms. A more detailed theoretical model for the prediction of load-displacement behaviour of RC beam assemblies within the compressive arching response regime is presented. The proposed model takes into account the compounding effect of bending and arching from both the deformation and force points of view. Comparisons with experimental results show good agreement. Following the compressive arching action, catenary action can develop at a much larger displacement regime, and this action could help address collapse. A complete resistance function should adequately account for the catenary action as well as the arching effect. To this end, a generic catenary model which takes into consideration the strength degradation due to local failure events (e.g. rupture of bottom rebar or fracture of a steel weld) and the eventual failure limit is proposed. The application of the model in predicting the resistance function in beam assemblies with strength degradations is discussed. The validity of the proposed model is checked against predictions from finite element model and experimental tests. The result indicate that strength degradation can be accurately captured by the model. Finally, the above developed model framework is employed in investigative studies to demonstrate the application of the resistance functions in a dynamic analysis procedure, as well as the significance of the compressive arching effect and the catenary action in the progressive collapse resistance in different designs. The importance of an accurate prediction of the arching effect and the limiting displacement for the catenary action is highlighted.

A reinforced concrete flat plate structure is a type of structural system that consists solely of slabs and columns. Flat plate structures are popularly adopted worldwide due to their economic and architectural advantages. However, an inherent issue associated with this type of structures is that the slab-column joints (SCJs) are prone to brittle punching shear failure. In addition, the absence of beams in flat plate structures results in a lack of load redistribution path. Consequently, once a single SCJ fails, the initial failure has a high risk of propagating to the adjacent SCJs, which may eventually trigger a progressive collapse of the entire structure. Progressive collapse often causes severe loss of life and property. Since the progressive collapse incident of the Ronan Point Apartment Tower in 1968, scientific and engineering communities have been working devotedly to improve the progressive collapse resistance of building structures. A direct way to improve such resistance of flat slab structures is to enhance the punching shear and post-punching capacities of the SCJs, the latter is regarded as a second line of defence to progressive collapse. Strengthening methods, which are commonly applied in engineering practice, include strategies like enlarging the slab thickness at the SCJ, using various types of shear reinforcement and incorporating a post-tensioning system. To date, substantial researchefforts have been made to investigate the mechanical behaviours of the SCJs with these strengthening methods up until punching shear failure, which is within the small deformation stage. However, research on the mechanical behaviours of strengthened SCJs in the post-punching stage (i.e., the large defamation stage) remains scarce. To fill this knowledge gap, a comprehensive study consisting of experimental, numerical and analytical investigations on the strengthened flat plate SCJs are conducted in this PhD research. The strengthening methods include adding drop panels, shear studs and prestressing tendons in SCJs. [...]

Mass timber buildings, constructed with engineered wood products, such as Laminated Veneer Lumber (LVL), Glued Laminated Timber (Glulam), and Cross-Laminated Timber (CLT), are gaining international popularity. Despite this trend, the robustness level and progressive collapse behaviour of these structures are not well understood, and design guidelines for their robust design are still limited. So far, research on these structures has primarily involved either experimental studies on scaled substructures or numerical analyses on full-scale multi-story buildings using unvalidated finite element (FE) models, often yielding contradictory results. This PhD research aims to bridge this knowledge gap by studying the behaviour of multistory post-and-beam mass timber buildings through FE models validated against experimental studies previously conducted at Griffith University. The robustness of such buildings is quantified, and dynamic increase factors (DIF) are determined for use in design with static analysis. Additionally, this study evaluates the accuracy of pseudostatic analysis as a cost-effective method for assessing progressive collapse and presents a comprehensive parametric study aimed at identifying measures to enhance their robustness, understanding alternative load-bearing mechanisms after column loss, and clarifying failure modes. The findings indicate that a post-and-beam mass timber building designed according to Australian national codes can meet robustness requirements under accidental design loads if average strength values are assigned to structural components. A DIF factor between 1.7 and 1.8 is recommended for the design of these structures. Contrary to general consensus, one-bay CLT panels can provide an effective alternative load path through torsion, exhibiting slightly greater robustness compared to configurations with two-bay continuous panels. The study also reveals that while enhancing beam-to-column connections may increase robustness, such modifications must be approached with caution as they can lead to column damage and extensive collapse.

Flat plate systems, where slabs are directly supported by columns without the intermediary of beams, offer reduced storey heights and additional usable space. However, these beamless configurations are susceptible to high localised shear stresses at the slab-column joints, rendering them vulnerable to brittle punching shear failures. Such failures can lead to the redistribution of loads to adjacent joints, potentially triggering a chain reaction that culminates in disproportionate progressive collapse. Despite comprehensive research aimed at preventing the progressive collapse of flat plate structures through experimental, numerical, and theoretical studies, significant knowledge gaps persist. Predominantly, existing research has centred on static loading scenarios, neglecting the substantial dynamic responses during actual collapse incidents. While some studies have considered dynamic effects, they primarily examine structural behaviour under design load conditions, with limited exploration of responses in ultimate states. Furthermore, the commonly used research methodology, the alternative path (AP) method, assesses structural integrity after column removal. Although suitable for RC frame structures, this method may not fully capture the vulnerabilities unique to RC flat plate structures, especially those related to punching shear damage at the slab-column joints caused by slab overloading-a primary trigger for progressive collapse. Moreover, the application of dynamic increase factors (DIFs) in analyses, as recommended by the DoD and GSA guidelines, is considered overly conservative for flat plate structures. To fill the research gaps outlined above, this PhD investigation undertakes a series of experimental tests on reinforced concrete (RC) flat plate substructures, focusing on scenarios of both column failure (CF), as widely considered, and slab-column joint failure (JF), not being thoroughly considered so far. For the CF series, the study evaluated the dynamic collapse resistance of a specimen following the instantaneous removal of an interior column under varying gravity loads. The JF series commenced with a conventional push-down test to determine collapse resistance under quasi-static conditions. A subsequent test in the JF series more closely resembled real-world collapse scenarios by incrementally applying gravity loads without further intervention, effectively replicating the spontaneous failure conditions and dynamic effects inherent to flat plate structures. Enhanced by further numerical modelling and theoretical analysis, this research provides profound insights into the mechanisms of collapse resistance, patterns of load redistribution, and the impacts of dynamic effects on RC flat plate structures.

Following some incidents in high-rise buildings, such as Ronan Point London 1968, in which collapse of a limited number of structural elements progressed to a failure disproportionate to the initial cause, consideration of robustness was introduced in British Standard. The main method of preventing progressive collapse for providing robustness to steel framed buildings with precast concrete floor slabs focuses on the allowable tying forces that the reinforcement in between the slabs and in hollowcores should carry. However there are uncertainties about the basis of the practical rules associated with this method. This thesis presents the results of numerical and analytical studies of tie connection behaviour between precast concrete floor slabs (PCFS). It is shown that under current design regulations the tie connection is not able to resist the accidental load limit applied on the damaged floor slabs. By establishing the capability of a finite element model to depict and predict the behaviour of concrete members in situations such as arching and catenary action against several experimental tests, an extensive set of parametric studies was conducted in order to identify the effective parameters in enhancing the resistance of the tie connection between PCFSs. These parameters include: tie bar diameter, position, length, yield stress and ultimate strain; the slab’s height, length; and the compressive strength of the grouting concrete in between the slabs that encases the tie bar. Recommendations are made based on the findings of this parametric study in order to increase the resistance of the tie connection. Based on the identified effective parameters in the parametric study a predictive analytical relationship is derived which is capable of determining the maximum vertical displacement and load that the tie connection is able to undergo. This relationship can be used to enable the connection to capture the accidental limit load on a damaged slab. The identified parameters are examined in a three dimensional finite element model to assess their effect when columns of the structure are lost in different locations such as an edge, corner or internal column. Based on the findings of this study methods for improving the connections performance are presented. Also the effect of alternative transverse tying method is evaluated and it is concluded that although this kind of tie increases the load carrying capacity of the connection, its effect on the catenary action is not significant.

Progressive collapse can lead to sudden cascading structural failures in a building which raise critical concerns due to its catastrophic consequences. Despite the recent rise of awareness about this topic, further investigation is needed to better understand the effect of initial failure on the subsequent progression of damage within the system and failure mechanisms. In this research, the behavior of structural components, including beams and slabs is investigated to demonstrate their ability to redistribute the loads after the sudden failure of columns or other elements and their effects. The goal is to help structural engineers better understand how reinforced concrete buildings behave during progressive collapse for the purpose of improving guidelines and approaches for designing new structures and evaluating existing structures concerning their potential for progressive collapse. In this research, a series of numerical analyses were carried out to assess the role of floor slabs (with and without beams) and their impact on the performance progressive collapse of reinforced concrete buildings. These numerical analyses were conducted with computer models that were validated using experimental data from an actual building and three laboratory specimens. SAP2000 (2023) and ELS (2023) software were used for linear and nonlinear dynamic analysis of three-dimensional models. Parametric computational analyses are carried out on one of the laboratory specimens and the test building to specifically examine the impact of slab thickness, number of spans, span length, number of stories in the building, presence of interior beams and perimeter beams, and flat slab systems. Based on the numerical analyses, it was concluded that the reinforced concrete slab thickness strongly influences the load redistribution when multiple columns are sequentially removed from the computer models. In addition, the calculated results indicate that the span length greatly affects the progressive collapse response, while the number of stories and number of spans in the building show slight effect on the structural performance.

There are three main research conducted in this paper, including using deep learning methods with vision-based technologies on Structural Damage Detection (SDD), Structural Health Monitoring (SHM) and progressive collapse study. During the learning and improvement process, many goals of automation in SDD and SHM have been achieved, although there will be a large room for further improvement and development on these studies. In progressive collapse study, remote sensing technologies and data fusion are applied on a field experiment of a real building at the Central Campus of the Ohio State University. The major contributions of this paper are shown as follows:A few comprehensive experimental studies for automated SDD in extreme events using deep learning methods for processing 2D images. In the first study, a 152-layer Residual Network (ResNet) is utilized to identify multiple classes in eight SDD tasks, which include identification of scene levels, damage levels, material types, etc. The proposed ResNet achieved high accuracy for each task while the positions of the damage are not identifiable. In the second study, the existing ResNet and a segmentation network (U-Net) are combined into a new pipeline, cascaded networks, for categorizing and locating structural damage. The results show that the accuracy of damage detection is significantly improved compared to only using a segmentation network. In the third and fourth studies, end-to-end networks are developed and tested as a new solution to directly detect cracks and spalling in the image collections of recent large earthquakes. One of the proposed networks can achieve an accuracy above $67.6\%$ for all tested images at various scales and resolutions, and shows its robustness for these human-free detection tasks.Studies are conducted with a pipeline to automatically track and measure displacements and vibrations of structures or structural components in laboratory and field experiments. This novel framework that uses computer vision and deep learning methods to mimic human vision system for the dynamic performance assessment of in-service infrastructure with various camera placements. On one hand, the static deformations of cylinders and small-scale reinforced concrete beams in the laboratory tests are captured and measured by the proposed framework at first. Then two shaking table tests in the lab are utilized to assess the dynamic performance of the simulated structures. On the other hand, several bridges, including pedestrian, railway, and traffic bridges, are tested for their dynamic performance in field experiments with different camera placements: remote, structure-mounted, and drone-mounted cameras. To remove systematic motions of cameras and to capture the fundamental frequency of these tested structures, two techniques, displacement subtraction and frequency subtraction, are applied. To better understanding of practical applications, critical parameters for camera settings and data processing techniques, such as video frame-rates, window size and locations, and sampling rates on visual data are studied. It shows that not only the vibrations and the frequencies of the simulated structures (i.e., in lab tests) or the in-service structures (i.e., in filed experiments), but also the static deformation of structures or structural components, can be tracked and measured accurately by our proposed framework.The performance of a building in progressive collapse study is monitored and analyzed with the methods developed in previous studies. On one hand, we applied the proposed methods to detect structural damage on this reinforced concrete (RC) structure that was tested, including visual data from cell phones, inside and outside cameras, and drones. The experiments indicate that these solutions for automatic detection of structural damage using deep learning methods are feasible and promising. On the other hand, the proposed methods to measure the deformations and vibrations are utilized to process visual data from outside and inside cameras, and drones. Data from different sources are fused for capturing the performance of the structural elements under the scenarios of the sudden loss of the columns and slabs. The data fusion technique is useful to investigate the characteristics of this framed structure, especially when the traditional sensors such as strain gauges and Linear Variable Displacement Transducers (LVDTs) didn't work in the experiments. Since visual data acquisition and preparation, and techniques of data processing have been inclusively researched for real applications with deep learning, many experimental studies on SDD and SHM are carried out and promising results are obtained in this paper. In addition, the vibration-based technologies or traditional sensors are used as the reference. Our goal is to meet the needs for automatic detection of structural damage and accurate measurements for the performance of the structures or structural elements, thus, the efficiency and effectiveness of these frameworks are tested and analyzed. In summary, these research in this paper indicate that vision-based technologies with deep learning can be applied well on structural engineering domain, and facilitate structural engineers' job by providing reliable data and credential results. The methodologies developed in this paper can fill the gap of research and engineering applications in the future.

While the progressive collapse mechanisms of concrete and steel buildings have been widely researched, limited studies have been carried out on mass timber buildings. Experimental testing under given loading scenarios of the entire system or a representative large part of it, may be required to extend the knowledge and improve design rules. However, due to the limited laboratory space and budget restrictions, fullscale tests are rare and may not always be possible. In steel and concrete, tests are frequently performed on scaled down systems. Since timber is an inhomogeneous material, interpreting experimental results on scaled down timber structures may not always be straightforward. Knowing that connectors play a vital role in the performance and robustness of timber buildings, analysing the scale effect on the behaviour of connectors would therefore provide a solid understanding of how experimental results from scaled systems should be interpreted. Furthermore, current Australian and international design codes in timber structures recommend a linear elastic approach for designing beam-to-column timber connections. In the event of an unexpected loading or losing a main load-carrying element such as a column, connections may experience large deformations resulting from disproportionate shear and bending actions. Under such a scenario, the structure may undergo nonlinear plastic deformations. The connector’s capability in obtaining large rotations is a critical factor in the robustness of the structure with regards to a potential progressive collapse. In this context, the current study is aiming to (i) experimentally and numerically investigate the scaling effects in three types of beam-to-column timber connections used in mass timber buildings, (ii) to investigate the behaviour of connections subjected to shear and bending moment, (iii) introduce a connection that can undergo large rotations in a progressive collapse event, and numerically investigate the proposed connections’ response to combined shear and bending actions.

Progressive collapse, while rare in its occurrence, can lead to catastrophic results. Research on progressive collapse analysis of structures due to extreme loading has become more and more prevalent over the last 20 years. Progressive collapse surfaced as a potential failure mechanism in 1968, and since then progressive collapse analysis and design has advanced exponentially. Many governing agencies have released design guides on how to design for progressive collapse. Early versions of these codes/guides implemented very conservative guidelines on how to mitigate collapse. However, more recent versions have included sections permitting the use of advanced analysis software to assess progressive collapse.As analysis tools have advanced, so has the accuracy of results. In particular, the addition of slab influences has produced more accurate results when validating experimental data. Practicing engineers are faced with challenges of how to design for accidental loading without committing an extensive amount of time modeling and analyzing a structure. It is clear through previous research that high-definition finite element modeling (FEM) software will give accurate results, but many operating firms do not have the resources to appropriately utilize such highly advanced software. However, many firms have access to less advanced commercial software. The goal of this research is to validate the effectiveness of commercial software to simulate complex failure mechanisms associated with progressive collapse. Furthermore, this research focuses on creating design recommendations and considerations for practicing engineers when modeling progressive collapse using commercial software.SAP2000v19 is used to predict the behavior of a structure under a column-loss scenario. Experimental testing done by researchers at the University of Trento was used to validate the SAP2000 results. In addition, a parametric study of six ground story column-loss scenarios was conducted using a full frame model designed by the University of Trento.

The progressive collapse of a structure is of critical concern to structural design engineers as the progressive collapse can lead to tragic loss of life. Due to this major threat posed by progressive collapse, building design and analysis has pivoted to account for the prevention of progressive collapse as a structural design requirement. Years of research has already been undertaken to better understand progressive collapse in order to improve building structural design as well as develop new modeling techniques to evaluate existing structures for their progressive collapse potential. These computer models and analysis techniques still require data from field experiments in order to verify their effectiveness at evaluating progressive collapse potential.The goal of this research was to provide structural engineers with a better understanding of the progressive collapse behavior of buildings in order to refine the guidelines and approach to the design of new structures as well as the evaluation of existing structures for their progressive collapse potential. In this research both field experimentation and computer modeling for progressive collapse were conducted. The building tested was a reinforced concrete parking garage, North Cannon Parking Garage, located on The Ohio State University Medical Campus in Columbus, Ohio. The structure was tested by removing two load bearing columns. One removed column was supporting the roof helipad. The other removed column was in the fifth story directly below the first removed column location. During the column’s removal, changes in the strains of the columns adjacent to the column removed were measured as well as building vibrations in the area surrounding the column during its removal. The change in the strains in the adjacent columns were caused by the load redistribution in the building following the removal of the target column. LIDAR data was also collected before and after the column removals in order to measure any change in structural member lengths after the columns were removed. SAP2000 (2018) was the software used to conduct the modeling and analysis of the building using current GSA (2016) and UFC (2016) guidance. Three-dimensional (3-D) models were built using SAP2000 and evaluated for progressive collapse. Linear static and nonlinear dynamic analysis procedures used on the building models considered two load cases. The first load case was the unfactored dead load case. This was meant to represent the real-world loading conditions on the building during the column removals. The second load case was the factored dead load case. This was used in accordance with progressive collapse analysis guidance to determine the progressive collapse vulnerability of the building considering only the dead loads that were present during the experiment. Modal analysis was also conducted in SAP2000 to determine if the column removals altered the frequencies of the building. While the strain data was determined to be unusable due to external factors and noise in the data, preliminary summaries of ongoing LIDAR, accelerometer, and FLIR camera data analyses are presented in this thesis. Based off the current progressive collapse analysis procedures, the building was found to be vulnerable to progressive collapse based on the results of the linear static analysis. The nonlinear dynamic analysis results indicated the building would not be vulnerable to progressive collapse under its self-weight. Results of the unfactored dead load case for both linear static and nonlinear dynamic analysis indicated that the building behavior remained elastic even after both columns were removed. Modal analysis results of the building indicated that the mass and stiffness changes caused by the column removals only altered the first building frequency. This was due to the negligible change in mass and stiffness of the building over the course of the column removals.

Progressive collapse of structures caused by extreme or accidental loads may lead to significant loss of life and property. Considerable research efforts have been made to date to mitigate the probability of progressive collapse and its consequences. However, a vast amount of the existing knowledge is pertinent to the reinforced concrete (RC) frame structures whilst the understanding of progressive collapse mechanisms of RC flat plate structures is still limited. RC flat plate structures represent one of the most common construction systems used in residential buildings and car parks in Australia and internationally. The absence of beams, column capitals and drop panels which can help to redistribute the concentrated loads, makes flat plate structures susceptible to punching shear failure at their slab-column connections and subsequent damage propagation, potentially leading to a catastrophic progressive collapse. The post-punching shear behaviour of the slab-column connections and the load redistribution in the slabs are of particular interests, which essentially dominate the load-carrying capacities after punching shear failure. To investigate the progressive collapse mechanisms and resistance of RC flat plates, experimental tests were performed on two 1/3-scaled 2  2-bay RC flat plate substructures specimens under an interior column removal scenario. In addition to the uniformly distributed load (UDL) imposed on the slab, an incremental downward displacement was applied to the interior slab-column connection to simulate the column loss and subsequent collapse. Custom-built column load cells were designed and carefully calibrated to ensure an accurate measurement of the reaction forces and moments at column bases. The overall load-displacement responses, crack propagations, failure modes and strain developments, were recorded and analysed. The complete collapse-resistant behaviour and load redistribution pattern of the specimens were examined, from which three load-carrying mechanism phases, in the form of flexural, tensile membrane and a combination of oneway catenary and dowel actions were distinguished in resisting the applied concentrated load. To study the punching and post-punching shear behaviours of RC slab-column connections being isolated from their parent flat plate structures, a set of numerical modelling techniques was established and verified against the experimental results of eight slab-column connections. In this modelling strategy, the concrete was simulated using solid elements with calibrated Continuous Surface Cap material model (CSCM) and failure criterion for punching shear. The reinforcing bars were explicitly created using beam elements with material properties obtained from the uniaxial tensile tests as well as calibrated failure criterion for rebar rupture. As a result, a competent 3D nonlinear numerical model of RC slab-column connections without shear reinforcement was created, with which, the punching shear failure featuring a critical punching shear surface and an abrupt drop of the applied force in the load-displacement response was able to be accurately reproduced. The post-punching shear behaviour, taking the form of an increased load-carrying capacity which was ceased by rebar fracture in the suspension stage, was also well captured. Using the proposed numerical model, typical punching and post-punching shear failure mechanisms were studied in some detail, finally leading to a simple yet effective analytical solution to accurately and reliably predict the postpunching shear response of RC slab-column connections. To investigate the influences of critical slab design parameters on the progressive collapse resistance of RC flat plate structures subjected to an interior column loss, the already established numerical modelling strategy for RC slab-column connections was employed to simulate our own experiment of the 2  2-bay flat plate substructure under a concentrated load and a similar test under a UDL in the literature for model validation. In addition to the modelling techniques developed for RC slab-column connections, the modelling of bond-slip behaviour at the interface between concrete and reinforcing bars was also highlighted, which was found to have a significant impact on the structural performance of flat plate substructures in progressive collapse. The key structural behaviours of the substructures under large deformations including the tensile membrane and suspension actions were able to be replicated. Further, the validated numerical model being subjected to a concentrated load was used to conduct a series of parametric studies in which the influences of concrete strength, slab thickness and reinforcement ratio on the progressive collapse performance were examined. The outcomes of the parametric studies indicated that the concrete strength and the slab thickness only affected the flexural capacity to different degrees with no impact on the post-failure capacity, whereas the load-carrying capacity due to the tensile membrane action was primarily governed by the amount of slab reinforcement. This research, covering experimental, numerical and analytical studies of RC slab-column connections and flat plate substructures with a missing interior column, offers a further understanding of their punching and post-punching shear behaviours as well as collapseresistant mechanisms. The numerical modelling techniques developed for the substructures with an interior column loss can be readily used to simulate other column loss scenarios (edge column, corner column and multiple columns). Further detailed analyses of the 3D numerical models will help to establish a simplified numerical model to facilitate collapse simulations of entire flat plate structures induced by any potential column removal scenarios.

The design of critical buildings must consider extreme load effects from earthquakes, wind and tornado, blast and impact, among others. Many hazardous loads—such as wind pressures, blast impulses, and projectile impacts—originate at the facade system and are transferred via connections to the main structural system and, ultimately, to the foundation; resilient design for such extreme loads requires controlling damage along this load path. This research proposes a multi-hazard facade system (MHFS) design methodology capable of achieving multiple performance objectives for all credible hazards while focusing damage to easily replaceable connectors, thereby reducing operational downtime and repair costs following an extreme event. This methodology is supported by fundamental mechanics and dynamics, nonlinear static and transient analyses at the component, system, and building levels, and quasi-static experimental testing of multi-hazard ductile connectors (MDCs). A probabilistic framework for critical blast scenario parameters is also proposed to promote performance-based blast design for critical infrastructure. Facade-frame interaction during blast scenario analyses suggest adequate performance of typical building frames with MHFS, while seismic analyses suggest interaction that is not necessarily detrimental to performance but should likely be considered during lateral force resisting system (LFRS) design. Analysis of perimeter frame column loss scenarios (which may result from a deliberate explosive attack) indicate the MHFS is capable of substantially supplementing the frame’s capacity to redistribute demands to prevent progressive collapse, and the design may be altered to achieve a target floor load. The proposed MHFS is believed to be a practical and effective approach for improving building performance considering extreme events for both new design and retrofit of existing buildings.

Progressive collapse is a failure mechanism that occurs when a primary structural member fails, resulting in a propagation of failure through the adjoining structural members. The resistance method known as Alternate Path Method (APM) outlined by the UFC 04-23 (2013) is implemented to resist the progressive collapse failure. Steel moment frames are used to redistribute the load after a column is notionally removed. This study analyzes connections known as SidePlate, Welded Unreinforced Flanges with Welded Webs (WUF-W), and Reduced Beam Section (RBS), in terms of their ability to enhance the progressive collapse performance of a steel moment frame building using reliability analysis. In this research, RAM Structural Systems (2018) is used to design the superstructure of a mock-up structure using ASCE 7-16 (2016) and AISC 15th ed. (2018) recommendations. The mock-up structure represents a building design that would be produced in the practicing structural engineering field. The structural model is transferred to SAP2000 (2018) to perform a nonlinear dynamic analysis for APM using the guidance from UFC (2013). A newly developed tool is introduced to automate the process of APM in SAP2000. The tool is capable of accurately performing a column removal scenario for practicing engineers. The automated process is transferred to Matlab (2012) to perform a simulation-based reliability analyses. The performance of the steel moment frame connections is demonstrated by producing the probability of structural failure at different column removal locations. The reliability of each steel moment frame connections is calculated using a new state-of-the-art method called ESC adaptive kriging technique. Fragility curves are developed with respect to the total floor live load to provide practicing engineers with information on the optimal steel moment frame connection to select given a specified floor live load. The overall process is clearly displayed to show proof of concept and ease of replicability for future endeavors.

Two dormitory halls at the University of Nebraska-Lincoln known as Cather and Pound halls were demolished via controlled implosion on December 22, 2017. Cather and Pound halls were two thirteen-story reinforced concrete structures. The demolition of these two structures included the implosion of controlled charges at selected columns on alternating floors which initiated the progressive collapse of these structures. Three nearby structures in the vicinity of Cather and Pound halls were instrumented with high sensitivity uniaxial piezoelectric accelerometers to record the response of the adjacent structures during the event of the implosion and the progressive collapse. While these two thirteen-story reinforced concrete structures were also instrumented with sacrificial accelerometers to record the real-time response of the structures during implosion and progressive collapse, the focus of this thesis is the responses observed at the adjacent structures during the demolition sequence. The primary objective is to understand how a group of nearby structures response and interact during the implosion and progressive collapse of multistory buildings. To this end, ground motion parameters at three free field positions nearby these adjacent structures have been quantified to observe the variation of free field ground motions during the demolition event. Likewise, the acceleration response data obtained from adjacent structures and free field positions have been analyzed in the time and frequency domains. The analysis of response data has also been presented separately in terms of the blast and collapse sequence to differentiate and understand the response of adjacent structures during the blast and progressive collapse of the two 13-story reinforced concrete structures. An input-output study of the responses observed within three adjacent structures with respect to the ground motion recorded at free field positions indicated that secondary effects, such as the air wave generated by the blast, contributed to the structural response. Two of the adjacent structures are numerically modeled with a lumped mass approach in LS-DYNA, and the responses of these numerical models are compared to the experimental recordings. The numerical study further emphasized the significance of the air wave. Advisor: Christine E. Wittich and Richard L. Wood

In this research, experimental and analytical analysis of the progressive collapse potentialof existing building were evaluated. The progressive collapse design guidelines typicallyrecommend simplified analysis procedures involving instantaneous removal of specifiedcritical columns in a building. The design guidelines were developed based on a majorityof laboratory and numerical research. In this research, experimental data from the columnremoval from multiple structures is used to calibrate and validate numerical analysismethods. The current research involves one steel frame structure and three reinforcedconcrete structures. This data will be in addition to previous research conducted under acontinuing program at The Ohio State University. The overall objective of this research isto evaluate the appropriateness of existing progressive collapse analysis and designrequirements.

Progressive collapse is partial or complete collapse of a building, which is triggered by the sudden loss of load-bearing structural elements such as columns and walls. Many computational research studies have been conducted to investigate the progressive collapse mechanism and validation of current design guidelines. However, very few full-scale experiments have been conducted to produce experimental evidence and to evaluate and validate theoretical models. In this dissertation, the progressive collapse performance of masonry wall structures and a steel structure with infill walls have been investigated. Two existing wall structure buildings on the Ohio State University campus (Blackburn House and Nosker House) were tested by physically removing four exterior load-bearing walls consecutively. The mechanical response, including deflection of beams and strain variation in reinforced steel and CMU walls due to the sudden loss of walls, were measured by displacement sensors and strain gauges. Two-dimensional and three-dimensional models were developed using the structural analysis program SAP2000 to simulate the response of test buildings. The calculated response was compared with the experimental data measured in the field. The progressive collapse risk probabilities are evaluated by using current guidelines, and recommendations are made based on the numerical and experimental data generated in this research. New demand capacity ratio acceptance criteria are proposed for progressive collapse evaluation of masonry wall structures. A load increase factor is proposed to perform alternate load path analysis of masonry wall structures. The steel frame building with unreinforced masonry infill walls, Haskett Hall, was previously tested by removing a first story column. Progressive collapse performance of the structure and the contribution of infill walls are examined by modeling the masonry infill walls in the structural analysis program. Based on the numerical simulations, the effects and contribution of infill walls are investigated. The non-contact measurement approaches based on photogrammetry techniques are applied in this research to track the markers’ movements on the building facade during the wall removal experiments. It is concluded that the masonry wall structures have much more redundancy against progressive collapse. The gravity loads are redistributed uniformly through the slabs to load-bearing walls. Reinforced concrete beams turns to be the most critical structural elements, which need careful checks and evaluations for progressive collapse. Masonry infill walls help to stiffen the steel frame structure and contribute in progressive collapse resistance.

The threat of progressive collapse has been an increased concern for structural engineers in recent history. Current practice when designing structures to resist progressive collapse has focused on local strengthening of members and connections, and the addition of extra structural elements to “tie” the structure together. However, typical structures have a degree of inherent robustness that is not currently counted on by designers, which may lessen the need for these additional elements. Many of these elements that add integrity to the structure have not seen extensive experimental testing, and their strength and ductility are not fully understood. In an effort to fill this gap, a test program was designed and implemented to study the response of steel-framed composite buildings to the loss of a column. A prototype building was designed by Walter P. Moore to be consistent with current construction standards and practices. A test building was designed based on this prototype building, with spans and members scaled down slightly to accommodate the test frame. Test specimens consisted of a 2-bay by 2-bay section of the test building (in the case of an interior column loss) or a 2-bay by 1-bay section of the test building (in the case of a perimeter column loss). The effect of the surrounding building was simulated by the construction of a heavy restraining beam that circumscribed the test specimen, providing the restraint that would be present due to neighboring bays. A loading system and test protocol were designed to allow a uniform floor load to be applied to the test specimen while the column support is removed quasi-statically, with the potential for further uniform floor load to be added if the specimen survived column loss.

Abstract: The susceptibility of structures to extensive collapse when subjected to a localised failure due to an extreme loading event has in recent years gained considerable research attention. The scenario most often used to assess such performance, either experimentally or through finite element simulation, is the loss of a column, requiring the floor system to bridge across two building bays with the aid of arching and catenary actions. When a column is abruptly disengaged by an abnormal load, the resulting double-span beam must bridge over the removed column by developing a new equilibrium path to redistribute the load to the adjacent elements. This severe damage in a steel gravity frame, which is designed to carry primarily gravity loads, creates significant demands on shear connections. The response of steel shear connections as a component of steel gravity composite frame systems under the column removal scenario is still largely unknown due to the complex interaction between the slab and the steel framework at large deflections. While the slab itself can participate in maintaining the integrity of the overall floor system, its presence amplifies the demand on the steel connections after experiencing initial flexural action. This research investigated the behaviour of steel shear connections in composite frames under a simulated progressive collapse scenario. The research objectives, experimental protocols, and the most significant conclusions drawn from test observations are discussed. The present study describes the details of a comprehensive experimental and numerical program that has been completed to assess the behaviour of connections in composite floor construction by evaluating the failure mode, load carrying mechanisms, strength, and ductility of the connections. An experimental program consisting of 17 full-scale physical tests was performed on connections that included shear tabs and double angles. A variety of parameters were considered, including the connection type, connection depth, connection material thickness, and notional beam span. A testing procedure based on the proposed loading protocols was developed and executed on connections to simulate demands and deformations expected in a composite floor system under a column removal scenario. The second part of this research consisted of comprehensive finite element modelling and analysis techniques. Models were validated using the test results. They were also expanded to investigate the effects of critical parameters on the performance of shear connections in composite frames. Detailed three-dimensional prototype simulations were evaluated and compared with the simplified finite element models and physical tests. The overall capacity of the prototype systems was evaluated and compared with the integrity requirements stipulated in current Canadian and US building codes and design guidelines. Design recommendations based on the experiments and finite element models are proposed for calculating the capacity and ductility of shear connections in composite frames when subject to central column removal.

This research investigates the progressive collapse vulnerability of an existing steel building, Haskett Hall, on the Ohio State University (OSU) campus. The building was tested by removing one of the first-story columns to observe its collapse resistance. Progressive collapse is a partial or complete collapse of a structure due to the loss of a supporting element, a column in this case. Few researchers have been able to conduct full-scale experiments to understand progressive collapse. One previous OSU study tested the vulnerability for progressive collapse of a steel frame building in Northbrook, Illinois, and another steel building on the OSU campus. It was concluded that more detailed models are needed to account for nonlinearity, three-dimensional and dynamic effects in analysis of a building frame including beams and columns surrounding the removed column. To address these issues, in this research deflections and strains within the neighboring beams and columns were measured during column removal. A structural analysis program, SAP2000, is used to run linear static and nonlinear dynamic analysis to predict building response, which is then compared to the measured data. The goal of this study is to evaluate the accuracy of geometric and modeling assumptions of two-dimensional and three-dimensional models in analyzing a historic steel building for progressive collapse. By following the General Services Administration (2003 and 2013), Haskett Hall was calculated to satisfy strength and stiffness requirements to prevent progressive collapse.

The objective of this research is to develop a new probabilistic framework to facilitate reliability-based analysis and design of reinforced concrete (RC) buildings against progressive collapse. In this study, a two-scale numerical model is developed to investigate the probabilistic collapse behavior of RC buildings subjected to local structural damage. In this model, a set of coarse-scale cohesive elements is used to model the failure behavior of potential damage zones (PDZ) in various RC structural members. The constitutive properties of the cohesive elements and their probability distributions are determined from detailed stochastic finite element simulations of the PDZs by taking into account the uncertainties in various material properties. The two-scale model is validated both experimentally and numerically for different types of structural subassemblages. With this two-scale model, the nonlinear dynamic analysis is applied to study the collapse behavior of a 2D 30-story RC frame structure and a 3D 10-story RC building subjected to sudden column removal. The results of the present probabilistic analysis are discussed in comparison with the existing deterministic approach, which reveals the importance of the probabilistic method for analysis of progressive collapse. To further improve the computational efficiency of the proposed probabilistic method for reliability-based design optimization against progressive collapse, a linear elastic cohesive model inspired by the concept of energetic equivalence is developed based on the two-scale model. In this simplified method, the damage status of the PDZ is determined by comparing the elastic energy stored in the cohesive element with the actual energy dissipation capacity of the PDZ. This linear elastic cohesive model is combined with a sequential analysis method to identify different possible failure paths that could lead to collapse initiation. This energetic-equivalent model is applied to analyze the collapse initiation risk of a prototype RC building. The results are compared with those obtained by using the nonlinear dynamic analysis. It is shown that the simplified model is far more efficient than the conventional nonlinear dynamic analysis, and it yields a reasonable upper bound of the collapse probability. Finally, this energetic-equivalent cohesive model is incorporated into a general optimization method for the optimum retrofitting of RC buildings to achieve a target collapse risk.

Two full-scale composite floor slabs were tested at Ferguson Structural Engineering Laboratory at The University of Texas at Austin under two different column removal scenarios. The removal of a column and the associated response of a structure is an index of its resiliency under abnormal loads, such as those due to a terrorist attack or a vehicle collision. Previous computational studies have shown that floor slab contributions are extremely important in mitigating collapse, but the limited experimental data currently available provide inconsistent results. The aim of the experimental testing program was to identify basic behaviors of floor slabs and to estimate their ultimate capacity under the absence of a critical column. The two test specimens were representative of isolated sections of the gravity-load resisting system of a typical steel-framed building. Thus, all steel members were joined using simple connections. During testing, the critical column was statically removed under service loads. Next, the load on the floor slab was increased at a slow rate until the specimens completely collapsed. Overall, the ultimate load carrying capacity of the two specimens under the absence of a single column exceeded the required capacity from progressive collapse provisions. Detailed finite element models were developed and validated against the collected experimental data in which all the components of the floor system were explicitly modeled. The explicit nonlinear finite element software LS-DYNA® was employed to simulate the response of the experimental tests. Initially, individual components of the floor system were modeled and validated against experimental data available in the literature. The two specimens were modeled using a similar approach. The main components of the floor system were modeled using three-dimensional solid elements for the concrete and steel members, shell elements for the corrugated steel deck, and beam elements for the shear studs and reinforcement in the slab. Bolts and other connection components were explicitly modeled using solid elements, and contact was specified to account for the interaction among the connected parts. Good agreement was found between the tests and numerical simulations. Further analyses provided information about the sensitivity of the numerical models to several design parameters.

Progressive collapse research intends to evaluate and quantify the resistance of structural systems against local failures independent of how such failures may initiate. The present research program pertains to the simulation and analysis of a structural gravity frame with composite floor system under column loss scenarios. The ultimate goal of this research is to evaluate and possibly identify any potential deficiencies in the current progressive collapse guidelines. This thesis presents the construction, testing, and results of a test performed on a steel-concrete composite structure with shear connections under a perimeter column removal. The structure was designed based on typical design guidelines. After the column removal, the specimen was subjected to increasing uniform load and was found to resist the full progressive collapse design load without major failures. In addition, computational work pertaining to the composite floor system behavior and the interaction among the beams, the slab, and the shear connectors was conducted. The purpose of this work was to identify possible deficiencies in the current simulation techniques for composite structure modeling under progressive collapse scenarios. After the analyses were conducted, it was found that the majority of current simulation techniques are adequate for modeling composite floor systems, with the use of nonlinear springs being the most accurate and computationally efficient.

Progressive collapse is a structural failure that is initiated by the failure of a primary structural member due to manmade or natural reasons and causes a disproportionately large portion of the structure to damage and/or collapse. This thesis is focused on the computational assessment of the performance of steel gravity frames with composite floor systems under column loss scenarios. The ultimate goal is to provide step-by-step guidance to practicing civil/structural engineers on modeling and analyzing full-size structures by using simple structural analysis software with the purpose of determining progressive collapse resistance. In this research project, a steel frame structure with simple framing connections and a composite floor system was tested, modeled, and analyzed under an interior column loss scenario. For the computational analysis part of the research, a simplified modeling approach was developed and verified by comparing the analysis results with detailed finite element model results and available experimental data. Next, the test specimen was modeled with the proposed approach using the SAP2000 software, and an analysis was performed. Results of the analysis were compared with the test data to verify that the model accurately simulates the measured behavior of the structure. In the end, it was concluded that steel gravity frame structures with composite floor systems can be accurately simulated by using the proposed simplified modeling approach up to the point of first element failure. Moreover, it was shown that practicing civil/structural engineers can do quick and simple checks for their structure’s ability to resist progressive collapse by using the methods and approaches that are described in this thesis.

Abstract: There are many design methodologies and philosophies intended to provide structural integrity or increase structural robustness, thereby making structures resistant to progressive collapse. However, there is little information that reveals sources and levels of inherent robustness in structural steel members and systems. The present study seeks to begin the process of behaviour evaluation of components and assemblages initially designed for other purposes than progressive collapse, such as gravity loads, and make recommendations regarding their performance and possible methods for improvements for the new scenario. These recommendations can lead to more economical design and safer structural steel systems in the event of localised damage that has the potential to spread to a disproportionately large part of the structure. Connections play a major role in ensuring general integrity of different types of steel structural systems. Hence, numerical investigations have been performed to extend the current body of knowledge on connections and, consequently, the structural response in the event of progressive collapse. This study is intended to examine the response of steel frames with simple shear connections in the aftermath of unusual and extreme localized loads. The main goal of this research is to evaluate the behaviour of some prevalent and economical one-sided (i.e., connected only on one side of the supported beam web) shear connection types—shear tab, tee (WT), and single angle—in buildings, and perform numerical analyses on those connection configurations under extreme loading scenarios represented generically by the socalled “column removal scenario”. Characteristic features of the connection response, such as the potential to develop a reliable alternative path load through catenary action and ultimate rotational capacities, are discussed to provide a solid foundation for assessing the performance of buildings with these types of connections. Observations regarding the analysis results are synthesized and conclusions are drawn with respect to the demands placed on the connections. The results of this research project should contribute to a better understanding of the resistance of steel structures with one-sided shear connections to progressive collapse.

Abstract: The performance of structures under the effects of extreme loads can be a critical consideration in their design. The potential for disproportionate collapse following localized damage to a column can be mitigated by the provision of sufficient strength and ductility throughout a structural system to allow for the establishment of a stable alternative load path. An understanding of the behaviour of shear connections in steel gravity frames under the unique combinations of moment, shear, and axial force relevant to column removal scenarios is necessary to assess the vulnerability of a structure to disproportionate collapse. However, such an understanding is currently limited by a deficiency of physical test data. In order to investigate the inherent robustness of commonly used steel shear connections, an experimental program consisting of 45 full scale physical tests was completed. Specimens included shear tab, welded–bolted single angle, bolted–bolted single angle, bolted–bolted double angle, and seat and top angle connections combined with different types of shear connections at the beam web. A testing procedure was developed that imposes upon a connection the force and deformation demands that are expected following removal of the central column in a symmetric two bay frame. Various geometric arrangements of each connection type were tested, and each arrangement was subjected to a range of loading histories representing different column removal scenarios. The physical test results characterize the load development history, deformation mechanisms, and failure modes expected following column removal for each type of connection. Connection stiffness, strength, and ductility limits under the effects of combined loading are quantified. An approach to mechanical modelling that predicts connection response following column removal is presented and validated using the test results. The models are used to expand the database of results and study the effects of critical parameters on performance. Design recommendations based on the physical tests and mechanical modelling are presented, including connection detailing considerations and a simplified connection modelling technique that is suitable for whole-building column removal analysis.

Progressive collapse research aims to characterize and quantify the behavior of different structural systems in events of extreme local damage caused by bombings to improve the performance of targeted structures and to protect occupants. The focus of the research program described herein is the performance of steel gravity frame structures with composite floor systems in column loss scenarios. The goal of the project is to contribute to the development of rational design guidelines for progressive collapse resistance and to assess any potential weaknesses in current design standards. This thesis presents the results of a series of tests performed on a steel frame structure with simple framing connections and a composite floor slab under interior column loss. The specimen was designed and constructed in accordance with typical design practices and was subjected to increasing uniform floor loads after static removal of the central column. No significant structural damage was observed up to a load equivalent to the ultimate gravity design load. Further testing was performed after the deliberate reduction of the capacity of the steel framing connections, ultimately resulting in total collapse of the specimen.

Progressive collapse is a complex process in which failure of a single component leads to collapse of a disproportionately large part of the structural system. Recent building and bridge failures have highlighted the seriousness of such events and generated widespread research interest. The objective of this study is to address current gaps in the progressive collapse research area, focusing specifically on seismically-designed steel frame structures. Four different types of nonlinear dynamic computational models are created for a prototype 10-story special moment frame building. The models include a 3-D micro-model, 3-D macro-model, planar micro-model and planar macro-model. After calibration and validation, the models are used to conduct a comprehensive study of the effect of various types of modeling approximations on simulated collapse behavior. The numerical results show that accounting for 3-D effects, specifically the floor slab, is critical for accurate collapse modeling. It is also shown that well-calibrated macro-models can be accurate and that the results of planar analyses are not necessarily conservative. Simulation results suggest that the prototype building is more vulnerable to loss of columns in the upper stories than in the lower ones and is particularly vulnerable to loss of interior gravity columns at all floor levels. The simulation models are used to clarify the role of different structural components and parameters at the various stages of collapse response. The floor slab is shown to contribute significantly to the robustness of the structure, especially at the early stages of collapse; however, it is a double edge sword that can also be detrimental in the final stages of collapse. Design requirements in the Unified Facilities Criteria published by the US Department of Defense are evaluated using the developed models. Simulations studies show that the Tie Force Method is effective in protecting buildings from progressive collapse and can significantly reduce deformation under column loss scenarios. However, the Dynamic Impact Factor proposed in the document is deemed to be problematic and a new energy-based approach is proposed to assess the peak dynamic displacement. The new method is shown to be accurate and reasonably conservative.

A structure experiences progressive collapse when the following conditions occur: a primary structural member fails due to manmade or natural causes, the loads from the lost member are transferred to adjoining members, adjoining members fail due to the redistributed loads, and the process repeats until a disproportionate amount of the structure is damaged or collapses. This study investigates methods of collecting data from a test structure, modeling a structure, performing analysis, and ultimately developing a process to create a simplified model for engineers to use for fast and easy progressive collapse analysis of a structure.In this research, a reinforced concrete structure is tested and modeled for analysis. The building consisted of three above ground floors and a basement in a regular rectangular layout, thick reinforced concrete slabs with no beams on the lower floors, and circular columns with drop panels. 14 strain gauges were placed strategically on three of the first story columns near the same corner of the building prior to its demolition. Strain data was collected and monitored from the gauges during the demolition process where three external columns, including the corner column, were removed by a processor. This was done to simulate a multiple column loss triggering event for progressive collapse.Using the SAP2000 program, a detailed model is developed to represent the building and its behavior as accurately as possible. Various factors such as the loading conditions, development of structural elements with proper dimensions, and end constraints are modeled according to the building plans. Analysis is performed on the model and compared to the test data to verify that the model accurately represents the measured behavior of the structure. Various simplifications are then made to the detailed model including a reduction in the number of floors, a reduction in the number of bays, and replacing the thick slabs with equivalent beams. A series of sensitivity analyses are performed to investigate and justify all simplification steps made to the models. The test data is compared to the calculated results from the models after each major simplification is made to ensure relative accuracy is maintained. Ultimately, a procedure for creating a final simplified model consisting of only a few structural elements is developed. A spring model is also developed from the final simplified model which can be used in future research to perfect the proposed model.The research results provide valuable information to the study of progressive collapse as the behavior and response of a reinforced concrete structure subjected to multiple column losses is investigated and discussed at length. The proposed procedure and model are suggested for use by engineers for the quick and simple check of a structure’s ability to resist progressive collapse. The final simplified model consists of only a few frame elements and is developed for general use of analyzing different types of building structures.

There are a large number of reinforced concrete (RC) buildings in seismically active areas of the world that are not designed and constructed in accordance with modern seismic design provisions. These buildings are vulnerable to severe damage or collapse due to their low lateral displacement capacity and rapid degradation of shear strength during strong ground motions. Typically, columns in such buildings lack adequate strength and ductility in reverse cyclic loading and experience brittle shear failure and loss of axial load carrying capacity. To assess vulnerability to earthquake damage and decide on the required level of retrofit, expected behavior of the columns in terms of strength and deformation capacity must be evaluated. This can be achieved by estimating the load-deformation response considering all potential failure mechanisms associated with axial, flexure and shear behavior. This study presents an analytical model for estimation of lateral load-displacement response of reinforced concrete columns. In the proposed model, flexural deformations are calculated through fiber section analysis employing cracked concrete behavior while shear behavior is modeled through Disturbed Stress Field Model (DSFM). The interaction between flexural and shear mechanisms is considered through axial strains and concrete compression softening. The proposed model also considers other critical aspects such as deformations due to reinforcement slip, buckling of compression bars, enhancement in strength and ductility of the concrete due to confinement, concrete tension stiffening and tension softening, and concrete compression softening effects. The comparison of predicted responses with experimental data indicates that proposed model is a suitable displacement-based evaluation approach that can be employed to accurately estimate load-displacement relationships and failure modes. During a seismic activity, local structural failure in the lower-story columns can initiate vertical or progressive collapse in the buildings with inadequate ductility if gravity loads cannot be transferred to undamaged columns. After one or more columns fail, an alternate load path is needed to transfer the loads carried by failed member (s) to other structural members. If adjoining elements cannot resist and redistribute the additional loads, a series of failures will occur until entire or substantial part of the structure collapses. In order to investigate redistribution of gravity loads resulting from column failure, a study is presented using a progressive collapse model and experimental data. During the experimental phase, an existing reinforced concrete building of regular structural configuration was tested by physically removing one first-story exterior column. The structural response of the test building was monitored by recording strains and displacements of selected frame members in the vicinity of removed columns. During the computational phase of the research, two- and three- dimensional models of the test building were generated in SAP-2000. Linear static and non-linear dynamic analyses were performed for both two- and three-dimensional building models. The experimental and predicted structural performances are compared and effectiveness of currently available analysis and design methodologies is discussed.

Progressive collapse has been of an increasing concern in the structural engineering community, especially since the collapse of the World Trade Center towers in 2001. As a result of increasing catastrophic events in recent years, the prevention of progressive collapse is becoming a requirement in building design and analysis. A large number of studies have been performed to improve the design of the building against progressive collapse and to evaluate the progressive collapse potential of existing and new buildings by using computer programs and analytical tools. However, experimental evidence is still necessary to validate the computational analysis tools to better simulate the progressive collapse of structures. In this research, both experimental and analytical assessments of the progressive collapse potential of existing buildings were conducted. Two actual steel frame buildings, the Ohio Union building in Columbus, Ohio and the Bankers Life and Casualty Company (BLCC) building in Northbrook, Illinois were tested by physically removing four first-story columns prior to buildings’ scheduled demolition. During the field tests the changes in column axial forces were measured, and the recorded strains were compared with the analysis results from computer models. A commercially available computer program, SAP2000 was used to model and analyze the test buildings, following the General Services Administration guidelines (GSA, 2003). Two-dimensional (2-D) as well as three-dimensional (3-D) models of each building were developed to analyze and compare the progressive collapse response. Also, two different analysis procedures were evaluated for their effectiveness in modeling progressive collapse scenarios; linear static and nonlinear dynamic procedures.The measured strain data compared relatively well with the analysis results of SAP2000. In particular, 3-D model was more accurate than 2-D model, because 3-D models can account for 3-D effects as well as avoid overly conservative solutions. 3-D model had lower DCR values and vertical displacements than 2-D model, which was probably due to inclusion of transverse beams in 3-D model. 3-D model is believed to be more realistic than 2-D model for the progressive collapse analysis. Linear static analysis showed higher vertical displacements than nonlinear dynamic analysis for both 2-D and 3-D models. The amplification factor of 2 required for the dead load in linear static analysis may lead to very conservative analysis results. This research is an initial step in developing analysis tools and design guidelines that could be easily and effectively used to evaluate the progressive collapse potential of new and existing buildings. It is expected that the field experiments and SAP2000 analyses performed in this research could provide structural engineers with both practical and fundamental information on the progressive collapse response of buildings.

Recent tragedies involving the collapse of several large and prominent buildings have brought international attention to the subject of progressive collapse, and the field of structural engineering is actively investigating ways to better protect structures from such catastrophic failures. One focus of these investigations is the behavior and performance of shear tab connections in steel structures during progressive collapse events. The shear tab, a simple connection, is typically modeled as a perfect pin in standard design, but in progressive collapse analysis, a much more accurate model of its true behavior and limits is required. This report documents the development of a simple yet accurate shear tab model and its use in understanding the behavior and limits of shear tab connections in column removal scenarios. Particular attention is paid to the connections’ axial force limit state, an aspect of behavior that is typically unimportant in standard design.

Within the past 40 years, abnormal loadings resulting from natural hazards, design flaws, construction errors, and man-made threats have induced progressive collapse in structures all over the world. As progressive collapse behavior has become more prominent, it has made the necessity for design and analysis tools evident. In effort to provide one of these tools, Applied Science International, Inc. introduced its Extreme Loading® for Structures (ELS®) software, capable of progressive collapse simulation. This research evaluates the effectiveness of Extreme Loading® for Structures as an emerging, nonlinear dynamic analysis software package in modeling progressive collapse scenarios. The ELS® software utilizes the Applied Element Method (AEM) of numerical analysis, separating it from other available software packages. The software and analysis methodology's accuracy are investigated through simulation of two structural implosions. Comparing the predicted response to the documented response, each scenario is evaluated by analyzing the material models, failure criteria, local structural behavior, and global collapse behavior. The two case studies, Crabtree Sheraton Hotel in Raleigh, North Carolina and Stubbs Tower in Savannah, Georgia, each include an experimental and analytical investigation. The experimental investigations include gathering existing structural information, coordinating with the demolition contractor to simulate the implosion sequence, as well as observing and obtaining documentation from the actual event. The analytical investigation utilizes the Extreme Loading® for Structures software to construct a model for each structure, simulate the implosion sequence, and analyze the predicted behavior. To understand the effects of individual modeling parameters on the model's response, a parametric study was completed. Creation of an evaluation matrix allowed for systematic assessment of the parametric study, as well as the individual model's behavior. For the case studies, a completed evaluation matrix for each iteration can be found in the appendix, providing a rough quantification of the accuracy. Observations from this research show that the software is capable of successfully modeling progressive collapse scenarios. The software allowed for realistic construction of the models and was effective on various levels in predicting the local and global collapse behaviors. Inaccuracies were discovered in each model and were investigated through subsequent iterations of the analysis. A solution was found for some of the inaccurate aspects, while recommendations for future research are proposed to address the others. Allowing for the quick and effective assessment of structures, the Extreme Loading® for Structures software has the potential to become a valuable tool in design and analysis of structures for progressive collapse mitigation. Through continuous validation and verification, modeling techniques and parameters can be established, providing engineers with confidence when venturing into this relatively new realm. Eventually, the advancement in knowledge and computing integrated into this software could provide invaluable benefit to society, in the form of economic cost and life-safety.

Progressive building collapse occurs when failure of a structural component leads to the failure and collapse of surrounding members, possibly promoting additional collapse. Global system collapse will occur if the damaged system is unable to reach a new static equilibrium configuration. The objective of this research is to identify and investigate important issues related to collapse of seismically designed steel building systems using multi-scale computational models. Coupled multi-scale finite element simulations are first carried out to investigate the collapse response of moment resisting steel frame sub-assemblages. Simulation results suggest that for collapse resistant construction, designers should strive to use a larger number of smaller beam members rather than concentrate resistance in a few larger members and should specify ASTM A-992 steel rather than specifying generic steels. Improved behavior can also be achieved by increasing the shear tab thickness or directly welding the beam web to the column. Using information gleaned from the sub-assemblage simulations, computationally efficient structural scale models for progressive collapse analysis of seismically designed steel frames systems are developed. The models are calibrated and utilized within the context of the alternate path method to study the collapse resistance of multistory steel moment and braced frame building systems. A new analysis technique termed “pushdown analysis” is proposed and used to investigate collapse modes, failure loads and robustness of seismically designed frames. The collapse and pushdown analyses show that systems designed for high seismic risk are less vulnerable to gravity-induced progressive collapse and more robust than those designed for moderate seismic risk. Motivated by a number of deficiencies in existing ductile fracture models for steel, a new micro-mechanical constitutive model is proposed. Damage mechanics principles are used and a scalar damage variable is introduced to represent micro-structural evolution related to micro-void nucleation, growth and coalescence during the ductile fracture process in steels. Numerical implementation and parametric studies are presented and discussed. Calibration and validation studies show that the proposed model can successfully represent ductile fracture of steels. The models and simulation methodologies developed herein can be extended in future work to address the collapse resistance of three-dimensional models.

In recent years, progressive collapse as an engineering problem has become a topic of interest due to the observed performance of some structures following terrorist attacks. Due to its highly nonlinear and dynamic nature, rigorous analysis to resist collapse is not common in design offices. Current guidelines by the federal government and US military have addressed this issue and have provided simplified static analysis methods to help mitigate collapse. Past research, however, has suggested that these existing guidelines may be too conservative. This research study focuses on the estimation of equivalency factors for static linear and static nonlinear alternate load path analyses that can be used to achieve the same level of safety as computed from dynamic nonlinear analyses.