Progressive Collapse Design Research Articles

Historical review of prescriptive design rules for robustness after the collapse of Ronan Point

After the collapse of Ronan Point tower building in 1968 there was an unprecedented discussion about the issue of progressive collapse in structural design. In particular, recommendations were published that precast panel structures should include tying elements to hold a structure together after an element loss. The initial investigation into the causes of the collapse and the majority of the subsequent discussion was focused on ensuring precast structures had the same monolithic behaviour as conventional forms. However, the prescriptive recommendations were then applied to all structural forms without amendment to account for the different mechanical behaviour. This paper presents the findings from a novel bibliographic study of historical documents published soon after Ronan Point collapse which influenced the development of relevant design guidelines. The technical information was analysed chronologically to determine the intended purpose of such requirements and the assumptions they were based on. It then traces the development of progressive collapse design requirements to the current Eurocodes to consider if they are being applied as intended. This critical review is timely since robustness considerations in Eurocodes and other international codes are currently being reviewed and general misconceptions regarding existing prescriptive rules have been identified among practitioners in the UK and internationally.

A non-iterative progressive collapse design method for RC structures based on virtual thermal pushdown analysis

Disproportionate progressive collapse is a structural failure mode with low probability and high consequences. Due to this nature, progressive collapse design is usually treated as a secondary design; namely, a design check after the design for primary loadings. Various design procedures have been recommended, notably the alternate load path method through nonlinear pushdown analyses. However, most of these design procedures are iterative by nature to satisfy the design acceptable criteria. To improve the design efficiency, this study presented an innovative design technique that allows to directly determine the proper amount of reinforcement in beams and slabs of a reinforced concrete (RC) structure in order to withstand the gravitational loads under column removal scenarios. Inspired from fire-induced progressive collapse research, the proposed method employs a virtual thermal pushdown analysis, in which the temperature increase affects only the strength of reinforced steel. With carefully developed strength-temperature relationships of the rebars, the virtual thermal analysis produces a displacement-temperature curve that represents the genuine nonlinear relationship between the amount of reinforcement and structural performance (often represented by vertical displacement). This curve is then used to directly determine the amount of reinforcement at the prescribed performance target. Two beam-column sub-assemblage examples and the Alfred P. Murrah Federal Building were analyzed and redesigned to demonstrate the effectiveness of the proposed method. All three examples showed that the proposal virtual thermal pushdown method can accurately determine the appropriate amount of reinforcements to meet the performance target.

Improvement to composite frame systems for seismic and progressive collapse resistance

Steel-concrete composite frame is one of the widely used structural systems. Earthquake and progressive collapse due to accidental localized damage are the main hazards that affect the safety of steel-concrete composite frames. Therefore, a seismic and progressive collapse resistant composite frame (SPCRCF) structural system is proposed based on a comprehensive consideration of the seismic and progressive collapse design requirements. The seismic and progressive collapse performances of the proposed SPCRCF were compared with the conventional steel-concrete composite frame using the experimental results of four specimens. The general-purpose finite element software, MSC.Marc, was used to simulate the specimens. The experimental and simulation results show that the proposed SPCRCF has better seismic resilience (low damage, self-centering, and easy repair) and larger progressive collapse resistance compared to conventionally designed steel-concrete composite frames.

Improving the tie force method for progressive collapse design of RC frames

PurposeThe purpose of this paper is to recover the deficiency of existing tie force (TF) methods by considering the decrease in section strength due to cracking and by selecting limit state of collapse according to section properties.Design/methodology/approachA substructure is selected by isolating the connected beams from the entire structure. For interior joints, the TFs in the orthogonal beams are obtained by catenary action. For corner joints, the TFs are assessed by beam action. For edge joints, however, the resistance is gained by greater of the resistance under catenary action for periphery beams and beam action for all the connecting beams in both directions. For catenary action, the TF capacities must satisfy Equation (20). On the other hand, for beam action, the TF must satisfy Equation (16), while R is calculated from Equation (17). In the case where the length of the connecting beams is similar, Equation (19) can be used.FindingsClosed form solutions are available for TFs on both beam and catenary stages.Originality/valueThe proposed formulation makes designing more practical and convenient. However, the proposed formulation had good agreement with experimental results.

Performance limit states for progressive collapse analysis of reinforced concrete framed buildings

The definition of performance limit states for progressive collapse design and assessment of civil structures is an open issue and deserves special attention in view of future building codes and standards. In this study, the main findings of a multilevel sensitivity analysis are presented to characterize the progressive collapse capacity of a selected class of modern European buildings having a reinforced concrete framed structure. After that a group of capacity model properties are assumed as random variables on the basis of earlier studies, the sensitivity of both ultimate load capacity and corresponding maximum and residual drifts to the ultimate steel strain and location of column‐removal scenario is assessed. Then, the influence of the capacity model properties on maximum drift demand corresponding to a code‐compliant design gravity load is evaluated. Finally, five performance limit states associated with increasing levels of damage are introduced and the corresponding load capacity is quantified under varying capacity model properties. Analysis results indicate a high sensitivity to the ultimate steel strain, column location in plan, beam span and yield steel strength.

Performance evaluation of WT connections in progressive collapse

In conventional design, shear connections are generally assumed to resist no significant moment or tension. However, since current progressive collapse design guidelines ask engineers to design robust connections that maintain their integrity in a double-span “column removal” scenario, it is important to investigate anticipated shear connection performance under this specific type of loading. There are several types of simple shear connection used in steel structures. WT connections are one relatively common option, but there is limited information about how they would perform under these conditions. In this research, the results of a numerical study conducted to characterize the performance of WT connections under combined shear, moment, and tension are presented. The results are verified with available experimental data. Finite element models consist of a central column stub connected to adjacent beams. The WT connections are modelled as being bolted to both the column flange and beam web. The central stub column is pushed down, while the connection demand and performance are monitored at each stage. It is observed that the tension and moment that develop interact with the shear in the load transfer mechanism. Important aspects of the mode of failure are distinguished and compared with existing test data. Based on the results of this study, models are proposed for WT connections in the column removal scenario. An extensive parametric study is performed in order to investigate the effects of different design parameters, such as WT geometric properties, bolt size and type, and also connection depth. Finally, an equation, based on the connection depth, is proposed to predict the rotational ductility of this connection type when an adjacent column is removed. This study will help to shed lights on the behaviour of WT connections in the column loss event.

Experimental study of a novel multi-hazard resistant prefabricated concrete frame structure

Reinforced concrete (RC) frames are one of the most commonly used structural systems worldwide. Earthquake actions and progressive collapse caused by accidental local damage are two critical hazards increasing collapse risks of multi-story RC frames. A significant difference is well recognized between the structural seismic design and progressive collapse design. Whilst the seismic design focuses on resisting the lateral forces due to earthquake, the progressive collapse design deals with resisting the unbalanced vertical load induced by a localized failure. Existing research has revealed that considering the two different designs individually for a structure may lead to an undesirable overall structural performance and unnecessary waste of construction materials. In this study, a novel Multi-Hazard Resistant, Prefabricated Concrete (MHRPC) frame system is proposed to satisfy the demands of both structural seismic and progressive collapse designs. Cyclic and progressive collapse tests are conducted to validate the performance of this newly proposed structural system. The mechanisms of the MHRPC frame system under both cyclic loads and a middle column removal scenario are analyzed based on the experimental results and numerical simulations using OpenSees. The results indicate that the proposed fame system exhibits such characteristics as large rotation, low damage, self-centering, and ease of repair. The system is also proven to be able to meet the multi-hazard design requirements of RC frames against both earthquake actions and progressive collapse.

Seismic and Robustness Design of Steel Frame Buildings

In this paper, a design procedure that combines both progressive collapse design under column removal scenario and capacity design to produce a hierarchy of design strengths is presented. The procedure develops in the context of the European Standards, using the classification of European steel sections and considering the seismic design features. Three-dimensional models of typical multi-storey steel frame buildings are employed in numerical analysis. The design for progressive collapse is carried out with three types of analysis, namely linear static, nonlinear static and nonlinear dynamic. Since the behaviour following sudden column loss is likely to be inelastic and possibly implicate catenary effects, both geometric and material nonlinearities are considered. The influence of the fundamental parameters involved in seismic and robustness design is finally investigated.

Effects of Masonry Infill Wall on the Performance of RC Frames to Resist Progressive Collapse

Masonry-infilled (MI) panels, which serve as partitions in buildings, are normally considered as architectural elements. Their weights are considered in progressive collapse analysis, but the resistance of the walls is normally ignored in design guidelines. Simple structural analysis predicts that the infill walls, which are commonly equivalent to compressive struts, increase not only the lateral load resistance but also the vertical load resistance of the reinforced concrete (RC) frames. Because extra vertical resistance might reduce the risk of failure, it is necessary to quantify the effects of MI walls on the load resisting capacity of RC frames to mitigate progressive collapse. However, few studies, especially experimental studies, have been carried out on this topic. Thus, six multistory by multibay RC subframes were designed and tested, subjected to push-down loading regimes. The six subframes were categorized into two groups: (1) bare frames without MI walls and (2) infilled frames with MI walls. The failure modes, load-displacement curves, deformation shapes, and strains of the specimens are measured and compared. The effects of the MI wall on the load resisting capacity, initial stiffness, and load resisting mechanisms of RC frames to resist progressive collapse were also evaluated and discussed. The experimental and analytical results indicated that ignoring the effects of MI walls in progressive collapse design may result in substantial inaccuracy in predicting the stiffness, strength, and failure modes of infilled frames to resist progressive collapse. Infill walls with low height/span ratio may fail in splitting of the equivalent compressive struts prior to crushing.

Progressive Collapse Analysis and Design of Steel Structure

Progressive Collapse Analysis and Design of Steel Structure

Effects of Seismic and Progressive Collapse Designs on the Vulnerability of RC Frame Structures

AbstractBuildings are exposed to multiple natural hazards over their service lives. Multihazard analysis and design of building structures has become a research hotspot worldwide. For these structures, earthquake and progressive collapse are two of the most commonly encountered hazards. However, little research has been conducted to examine the effects of the seismic and progressive collapse designs on the resistance of buildings against multiple hazards. In this study, a series of six-story reinforced concrete (RC) frames are considered, and their seismic and progressive collapse designs are performed independently according to the corresponding design codes. Fragility curves are used to assess the seismic and progressive collapse resistance. The interactions between the two designs are discussed by analyzing the fragility curves and the collapse modes. Results show that the progressive collapse design of the RC frame may lead to an undesirable failure mode (i.e., strong-beam-weak-column) under earthquak...

A Method for Modeling Successive Removal of Columns in Macromodeling Frameworks

As a well-known technique, alternate path method (APM) has been widely used to evaluate progressive collapse potential of structures. This method investigates the capability of structures to redistribute loads carried by a removed element in the remainder. However, in most cases the initiating event is so intensive that it destroys more than one load bearing element. If the destruction of members does not occur concurrently, dynamic removal of columns in APM could not be correctly modeled in common macromodeling frameworks. This problem has resulted in progressive collapse analysis and design guidelines to define less element removal cases than has been expected. In this paper, the method chosen for modeling successive removal of columns is capable of improving the guidelines to consider more realistic collapse scenarios. This method can be easily implemented by practicing engineers in commercial or open source programs. Moreover, a simple case study is defined to emphasize significance of the proposed method.

An Energy-Based Assessment on Dynamic Amplification Factor for Linear Static Analysis in Progressive Collapse Design of Ductile RC Frame Structures

Progressive collapse is a mechanical process that exhibits nonlinear and dynamic characteristics. The nonlinear dynamic effect on the progressive collapse resistance demand can be accurately evaluated by the nonlinear dynamic (ND) method. In engineering practice, however, the simplified and easy-to-use linear static (LS) method is often adopted. That is accomplished by using a dynamic amplification factor (DAF) to correct the LS resistance demand to approximate the true ND resistance demand. In this paper, the analytical expression of the DAF is established based on the energy conservation principle. The collapse-resisting substructure is firstly simplified as a single-degree-of-freedom (SDOF) equivalent. Then the energy conservation equation and the static balance equation of the SDOF equivalent are established to obtain the ND and LS demands. Finally, the DAF is obtained by dividing the ND demand by the LS demand. The DAF is validated through a series of the numerical examples including a SDOF system, a 3-storey planar frame and an 8-storey 3-D RC frame model structures.

Economic Design Issues of RC Structures against Progressive Collapse

Progressive collapse of structures is defined as the damage incurred on the structure as a result of abnormal and occasional loads which result in initiation of a chain reaction mechanism ending with progressive and disastrous failure. In this study, the economic cost of designing RC structures located in non-earthquake hazardous regions to meeting progressive collapse design requirements is estimated. Therefore, a typical reinforced concrete has been modeled to achieve the above objective. The Occupancy Category II per UFC 3-301-01 has been chosen for this structure. Tie Forces for the whole structure and Enhanced Local Resistance for the corner and penultimate columns at the first story are the design requirements for this OC. It was concluded that the cost of reinforcement for this OC level in order to meet UFC criteria and maintain safety requirements was around 15% compared to reinforcement requirements of ACI 318-08/IBC 2009 for non-seismic region. The importance of progressive collapse as a major concern has led to addition of explicit requirements regarding the redundancy of the structures in seismic codes throughout the world. Specific codes related to progressive collapse analysis of structures have been published by the Department of Defense (UFC 4-23-03) and the General Services Administration (GSA 2003). Most of the countries located in non-seismic regions are not designed properly against earthquakes according to the relevant seismic codes. Hence, the majority of typical RC buildings are exposed to progressive collapse in such regions.

Experimental and analytical progressive collapse assessment of a steel frame building

A field experiment and numerical simulations were performed to investigate the progressive collapse potential of an existing steel frame building. Four first-story columns were physically removed from the building to understand the subsequent load redistribution within the building. Experimental data from the field tests were used to compare and verify the computational models and simulations. Due to the scarcity of data from full-scale tests, the experimental data produced during this research is a valuable addition to the state of knowledge on progressive collapse of buildings. The progressive collapse design guidelines typically recommend simplified analysis procedures involving instantaneous removal of specified critical columns in a building. This paper investigates the effectiveness of such commonly used progressive collapse evaluation and design methodologies through numerical simulation and experimental data.

Alternate Path Method Analysis of RC Structures Using Applied Element Method

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

DoD Research and Criteria for the Design of Buildings to Resist Progressive Collapse

The collapse of conventional/nonhardened structures was a concern of the U.S. Department of Defense (DoD) for years before the collapse of the World Trade Center (WTC) towers during the terrorist attacks on September 11, 2011 (9-11), owing to the bombings of the Murrah Federal Building in Oklahoma City, the U.S. embassies in Africa, and the U.S. Marine barracks in Lebanon. Since 9-11, motivated by the lack of any meaningful U.S. progressive collapse design requirements, DoD has worked with the civilian community on a number of significant efforts to improve the design of buildings to resist disproportionate collapse. The DoD efforts have included laboratory and field experiments, numerical simulations, and development of design requirements. Synergy and coordination with the civilian community resulted in combined programs with the General Services Administration, guidance and feedback provided by the ASCE Structural Engineering Institute (SEI) Committee on Disproportionate Collapse Standards and Guidance (DCSG) and its members, and adoption of some European civilian approaches to progressive collapse design. A significant result of the DoD effort was the creation of Unified Facilities Criteria (UFC) 4-023-03, Design of Buildings to Resist Progressive Collapse. The approaches employed in UFC 4-023-03 are currently being evaluated and modified for civilian applications by the SEI DCSG committee. The development and underlying approaches used in UFC 4-023-03 are briefly summarized in this paper, as are the previous DoD laboratory and field tests and numerical simulations.

Progressive collapse design of seismic steel frames using structural optimization

This paper uses structural optimization techniques to cost-effectively design seismic steel moment frames with enhanced resistance to progressive collapse, which is triggered by the sudden removal of critical columns. The potential for progressive collapse is assessed using the alternate path method with each of the three analysis procedures (i.e., linear static, nonlinear static, and nonlinear dynamic), as provided in the United States Department of Defense United Facilities Criteria (UFC) Design of Buildings to Resist Progressive Collapse. As a numerical example, member sizes of a two-dimensional, nine-story, three-bay regular steel immediate moment frame are optimally determined such that the total steel weight is minimized while the design satisfies both AISC seismic provisions and UFC progressive collapse requirements. Optimization results for the example frame reveal that the traditional minimum weight seismic design, which does not explicitly consider progressive collapse, fails to meet the UFC alternate path criteria associated with any analysis procedure. Progressive collapse design optimization using the linear static procedure produces the most conservative and consequently heaviest design against progressive collapse. In contrast, the more accurate nonlinear static and dynamic procedures lead to more economical designs with UFC-acceptable resistance to progressive collapse, at the expenses of considerable modeling and computing efforts.

Progressive Collapse Analysis of RC Frames Subjected to Blast Loading

Progressive collapse of a building can be triggered by damage to certain critical load-carrying elements immediately following a blast. The initial damage can be followed by a chain of events which progressively destabilize the building. The modelling of progressive collapse is very complex and must take into account the nature and extent of damage inflicted to the individual elements, the behaviour resulted from the damage and the structural interaction between the elements. Importantly, the chain of events to be modelled is dynamic in nature. This paper critically compares some analysis methods available for progressive collapse design from the very simple linear elastic static analysis to the most rigorous and time consuming nonlinear dynamic analysis which takes into accounts both the primary and secondary effects of the blast loading. Inelastic non-linear dynamic finite element analyses and computational fluid dynamics have been employed in the evaluation which revealed certain deficiencies with the simplified methods including the non-linear dynamic analysis method which does not take into account the direct impact of the blast loading.