Progressive Collapse Mechanism Research Articles

Performance of a 3D printed cellular structure inspired by bone

Biological thin-walled cellular structures have intricate arrangements that facilitate lightweight and high energy absorption. A prime example is trabecular bone, which possesses a unique thin-walled cellular structure of connected rods or plates, to minimise weight whilst meeting the loading demands from the body. For example, the femur has a closed cell structure of plates to transmit heavy loads to the ground, whereas a carpal bone has an open cell structure of connected rods. Although existing lightweight thin-walled cellular structures with controlled arrangements have been investigated extensively, such as those with re-entrant geometries, asymmetric instability due to local buckling can hinder their energy absorption capacity. Mimicking the features of trabecular bone can offer the designer a greater degree of control over the buckling and collapse mechanisms of thin-walled cellular structures. This can lead to the development of high-performance protective systems with superior energy absorption capabilities. This study employs 3D printing and finite element analysis techniques to mimic and investigate several key features of the plate-like thin-walled cellular structure of trabecular bone. The performance of the developed bioinspired structure is benchmarked against traditional hexagonal and re-entrant designs. The controlled and progressive buckling and collapse mechanisms observed in the bioinspired structure result in superior energy absorption over its re-entrant and hexagonal counterparts. • Developing a framework for automatically generating a finite element model and 3D printed sample of a bone-like structure. • Benchmarking the performance of the bioinspired structure against existing cellular structures, including hexagonal and re-entrant. • Identifying several parameters that can guide the design of biomimetic thin-walled cellular structures in the future.

Kinked rebar configurations for improving the progressive collapse behaviours of RC frames under middle column removal scenarios

For reinforced concrete (RC) frame structures, applying more continuous longitudinal bars in the beams is the most effective way to improve the progressive collapse resistance. However, an RC frame has the possibility to experience multiple collapse mechanisms. An RC frame may not only experience progressive collapse caused by critical column removal but may also experience lateral collapse under strong earthquakes. The strong column-weak beam (SCWB) requirement in seismic design does not allow excessive longitudinal reinforcement in the beams. To solve this contradiction, a previous study proposed a novel kinked rebar (KB) configuration to enhance both the seismic and progressive collapse resistances of RC frames. This study was carried out to conduct further experimental validation and investigation of progressive collapse behaviours of RC frames with KB configurations. First, a quasi-static progressive collapse test involving 9 RC frame substructures was carried out. The test results indicated that the application of KBs could increase both the loading and deformation capacities under the catenary mechanism of RC substructures. For RC substructures, the influences on progressive collapse behaviours from various structural parameters were also investigated. Second, finite-element simulations were carried out to model the behaviours of the test specimens. This study experimentally verified that the KB configuration can improve the progressive collapse resistances of RC frame structures and clarified the progressive collapse mechanism of novel RC frame substructures with KB configurations.

Collapse Distribution Scenario in Seismic Progressive Collapse of RC Buildings Caused by Internal Column Elimination

Prediction of the safety margin in the buildings against the progressive collapse mechanism due to the earthquake loads is a significant issue in the structural and earthquake engineering. In this paper, modeling of the collapse distribution and propagation in the structural elements, one after another, is investigated by tracking down the collapsed locations among the beam and column structural elements in the moment-resisting reinforced concrete short buildings, and the effects of the column removal are studied on the expansion and development of the progressive collapse due to the earthquake loads. A three-story reinforced concrete building designed with ordinary moment frames is modeled, and potential of the progressive collapse mechanism due to the internal column removal is studied using the results of nonlinear time history analyses in the presence of the two-component ground motion records proposed by FEMA_P695. According to the results, some approaches and proposals are presented to seismic optimization of the reinforced concrete short buildings against the progressive collapse mechanism. Also, a collapse distribution pattern is introduced to predict the progressive collapse propagation scenario due to the earthquake loads and the internal column removal.

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

The existing RC buildings in urban habitat comprises of buildings mostly constructed either before evolution of seismic provisions or has been designed only for resisting gravity loads. These buildings are found to be vulnerable for any accidental damages to any of the critical load-bearing member in the form of progressive collapse. Hence, accurate estimation of structural adequacy is imminent in transforming the existing vulnerable building stock into a sustainable building environment. Progressive collapse of structural systems is often resulted from the failure of critical structural members and change of load transfer path. The progressive collapse potential can be accurately estimated using nonlinear dynamic analysis. However, in engineering practice, a simplified linear static analysis (LSA) is often carried out with a dynamic amplification factor (DAF) to approximate the dynamic forces. In this study, the correctness of estimation of dynamic demand during progressive collapse mechanism is investigated using DAF for structural models comprising of G + 3 story, G + 10 story and G + 12 story hypothetical RC building models. The structural models are designed as per IS 456: 2000, and progressive collapse mechanism is initiated by identification and removal of load bearing critical column member leading to global failure of the structure. Nonlinear static and nonlinear dynamic analysis (NLD) is carried out using SAP2000. Structural adequacy is ascertained by computing the demand-capacity ratios (DCR) of the requisite structural members identified to be inadequate during nonlinear analysis. It has been observed from the results that DAF is inconsistent in estimating the dynamic demand for high rise buildings. The outcome of the analysis is checked with the structural behavior of existing building structure (located in Warangal city, Telangana state, India) presented in case study and can be concluded that nonlinear dynamic analysis appears to be the only alternative for analyzing the structural behavior of important high-rise buildings.

Effect of infill walls on mechanisms of steel frames against progressive collapse

In this study, the effect of masonry infill walls on the progressive collapse mechanisms of steel frames is investigated. Three two-story by four-bay steel frames are designed: a bare frame, frame with full-height infill walls, and frame with partial infill walls. The applied vertical load, horizontal displacement, failure modes, stress development, and load redistribution mechanisms are investigated under center column pushdown scenarios. The influences of critical material properties and opening dimensions of partial infill walls are also investigated in this study. The results indicate that masonry infill walls significantly enhance the maximum applied vertical load and initial stiffness; however, they decrease the ductility and can alter the failure modes of the steel frames. The outward movement of the steel frames is a result of the diagonal compressive actions of the infill walls, and the changes in the bending positions of beams are a result of the bracing effects of the infill walls. The mortar joints and opening dimensions significantly influence the progressive collapse performance of infilled steel frames. In addition, different modeling strategies for masonry infill walls are developed and compared. Finally, a preliminary design procedure adopting masonry infill walls to protect the steel frames against progressive collapse is proposed.

Functional Catastrophe Analysis of Progressive Failures for Deep Tunnel Roof Considering Variable Dilatancy Angle and Detaching Velocity

The phenomena of progressive failures are very common and important in geotechnical engineering. In this paper, a reliable prediction model is proposed to interpret the progressive failure phenomenon of roof collapse in deep tunnels using the functional catastrophe theory. The progressive collapse mechanisms and collapsing block shapes of deep circular tunnels under conditions of plane strain are investigated. The analytical solutions for the shape curves of the collapsing blocks of circular tunnels are derived based on the nonlinear power-law failure criterion considering variable dilatancy angle and detaching velocity. Moreover, criterions with variable dilatancy angle on progressive failure occurrence for deep tunnels are obtained. Then, the analytical predictions obtained in this paper are compared with experimental testing results, which indicate that the impacts of variable detaching velocity on the shape curves of the several continuous collapsing blocks should be considered to obtain more consistent prediction results with the corresponding experimental testing results.

Identification of critical members for progressive collapse analysis of single-layer latticed domes

This paper presents a method to identify the critical member in a single-layer latticed dome, which in the context of progressive collapse is defined as the member whose removal causes the most severe damage. The distribution of critical members in four typical types of single-layer latticed domes, including the Kiewit dome, the Ribbed dome, the Schwedler dome and the Lamella dome, is investigated through a comprehensive Alternate Path analysis scheme composed of hundreds of individual dynamic nonlinear analyses. The Alternate Path analyses also confirm the progressive collapse mechanism of single-layer latticed domes, i.e., the nodal snap-through buckling at either end of the initially removed member. On this basis, a critical member identification method is established, using an index that implicitly estimates the relative vulnerability to node buckling following the removal of a member to determine the criticality of this member. This method along with two other methods, using either static axial force or free vibration response, are evaluated via comparison against the nonlinear dynamic Alternate Path analysis results, and this proposed method shows a beyond-compare accuracy. Furthermore, based on the established understanding of the progressive collapse mechanism and the factors influencing the node buckling resistance, three methods for increasing the progressive collapse resistance of single-layer latticed domes are presented.

Progressive structural capacity loss assessment-A framework for modern reinforced concrete buildings.

By the virtue of burgeoning terrorism, the exponential growth of advanced weaponry, and allied aids for explosions, it is quite evident that infrastructural facilities in the world have increasingly become more susceptible to sabotaging activities. The ever enhancing employment of reinforced concrete (RC) in the construction industry around the globe, the progressive collapse mechanisms, and respective mitigation strategies in the context of terrorism have garnered quite an attraction by the structural engineering community. The proficiency to envisage the complete collapse under the chain reaction of structural failures, partial collapse of key structural members, or the strength degradation of fundamental structural elements under the blast or impact loading can deliver significant information to cope with partial or complete structural failure. It is quite convenient to say that during the service life, a structure may experience extreme loading conditions. The current study has proposed a new methodology to cover the effect of uncertainty involved in loading on key structural elements of new and complex structures by emphasizing a very realistic structural capacity loss mechanism that allows the incremental reduction in the structural capacities of pivotal structural elements against any sort of impact loading instead of their complete annihilation. To demonstrate the application of the proposed methodology, a 13-story complex structure was selected that was comprised of a diverse structural configuration. The outcomes and results ensured the structural integrity against the applied loadings, as well as the effectiveness of the proposed methodology.

Experimental Investigation of a Steel-Framed Building for Disproportionate Collapse

This paper presents the experimental and numerical investigation of the progressive collapse vulnerability of an existing steel building, Haskett Hall, on the Ohio State University campus. The building was tested by removing one of the first-story columns to observe its collapse resistance and to evaluate the effectiveness of current modeling and analysis guidelines. Progressive collapse is a relatively large partial or complete collapse of a structure due to the loss of a vertical load-carrying element—a column in this case. Few researchers have been able to conduct full-scale experiments to understand the progressive collapse mechanism. In this research, deflections and deformations of steel structural components were measured during the field experiment. Computational models and simulations were examined and compared with the experimental data from the field tests. The contribution and effects of infill walls to progressive collapse resistance of frame structures were investigated. The test data collected in this research can be used to help develop recommendations for improved procedures for progressive collapse analysis of frame buildings.

Assessment of the combined in‐plane and out‐of‐plane behavior of brick infill walls within reinforced concrete frames under seismic loading

SummaryUnderstanding the out‐of‐plane response of masonry infill walls and preventing their progressive collapse mechanisms is very important for earthquake‐prone countries to prevent loss of life and economic loss. In fact, having a realistic collapse mechanism assessment allows suitable prevention measures to be adopted. With this purpose in mind, two full‐scale one‐bay one‐story substructures of reinforced concrete frames (RCF) with infill walls were tested on a shake table. These 2 specimens were designed to represent the response of a typical RC Frame at the fifth floor of an 8‐story building, namely the out‐of‐plane failure of its infill wall under combined bidirectional seismic load. Both specimens were composed of a single‐leaf clay brick infill wall surrounded by the RC Frame. However, while the first specimen corresponds to an unreinforced masonry configuration, the second specimen includes horizontal bed joint reinforcement as a strengthening/retrofitting technique. The main novelty of this study is the application of a bidirectional and simultaneous dynamic loading to the specimen, such that in‐plane and out‐of‐plane effects are evaluated together. This work presents several interesting experimental results, with particular emphasis on the bearing capacity of the specimens against out‐of‐plane failure. As expected, the in‐plane capacity of the reinforced infill specimen is larger than that of the unreinforced infill specimen. Nevertheless, the out‐of‐plane bearing capacities of the two specimens are very similar, in contrast to their ductility capacity, which is significantly increased in the reinforced masonry specimen. The capacities of the two specimens for both in‐plane and out‐of‐plane directions, as predicted by formulations in the literature, are given. The differences found between these calculations and the results of the tests are discussed, and may possibly be explained by the parameters considered in the different formulations.

Research Status on the Collapse Mechanism and Prevention Measures of Mega Composite Structural Systems

Mega composite structural system presents wide application prospects in high-rise and super high-rise buildings. However, research concerning the important issues of the seismic behavior, collapse mechanism, and prevention from progressive collapse for such new structural systems under severe earthquakes is quite limited. This paper will summarize the current research status, followed by the discussions on the collapse and prevention mechanisms of high-rise and super high-rise mega composite structural systems under severe earthquakes, the theoretical basis on progressive collapse mechanisms, numerical simulation techniques, and test methods. The failure modes of high-rise mega composite structures were studied firstly, followed by the collapse mechanisms and the associated criteria and indices. In addition, a new numerical technique for simulating the non-linear structural collapses considering large deformations will be presented, along with the relevant test results. This study shows that analysis method, damage accumulation model, failure criteria, appropriate preventive measures, and improved collapse experimental verification methods are all important seismic design considerations for high-rise and super high-rise mega composite structures. Based on the study results, recommendations for collapse and prevention mechanisms of high-rise buildings are proposed.

Refined dynamic progressive collapse analysis of RC structures

Post-earthquake field investigation has revealed that if reinforced concrete (RC) structures in seismic regions were not designed to the level required by modern seismic design codes, they are vulnerable to severe damage or even progressive collapse when subjected to strong earthquakes. To gain insight into the mechanism and prevention of progressive collapse, it is imperative to develop an effective and efficient approach to capture the physical collapse of RC structures by numerical simulation. Finite element method (FEM)-based numerical simulation is one of the most widely used approaches for progressive collapse analysis, but some uncertainties still exist in its element removal algorithms. This paper refines FEM-based dynamic progressive collapse simulation for RC structures by introducing the concept of degree-of-freedom (DOF) release. With the concept, a RC beam-column element removal is a natural consequence of release of all DOFs of the element. This concept is implemented in an open-source finite element code of OpenSees. The test results of a RC beam with two ends fixed under a static load and a RC column with light transverse reinforcement under lateral pseudo-static load are first used to assess and demonstrate the advantages of the DOF release over the beam element removal. The refined progressive analysis method is then applied to a RC frame structure to demonstrate its dynamic progressive collapse with catenary effect included. Finally, a two-span continuous RC bridge with a two-column pier is taken as an example to demonstrate its flexure-shear-axial failure predicted by the proposed method.

Experimental evaluation of the interaction between a masonry infill wall and the surrounding frame

AbstractThis paper studies the interaction effects between a masonry infill wall and its surrounding frame. A new experimental technique is developed aiming at evaluating the loading dependent interaction effects. This includes the stage where the infill wall accumulates severe damage and cracking that are difficult to monitor with conventional devices (strain gauges and displacement transducers) or optical techniques such as digital image correlation (DIC). The experimental concept is based on detection of strains along the surrounding frame, their conversion into stress resultants, and the translation of the latter into interfacial contact tractions. It also aims at identifying the regions of contact and detachment between the frame and the infill wall and their changes during the loading path. A large‐scale experimental setup that realises the concept and demonstrates its ability to provide important new information is constructed. A complementary DIC analysis that serves as reference for the above monitoring system is also conducted. This experimental setup with its complementing combination of sensing methods allows measuring the infill wall‐frame interaction effects in a case of horizontal loading that simulates lateral seismic loads, as well as vertical loading that simulated a mechanism of progressive collapse triggered by failure of a supporting column. The paper presents the experimental concept and its implementation in the large‐scale experimental setup and explores its capabilities. Emphasis is given to the interaction effects in the deep non‐linear region where optical monitoring is adversely affected by the developing damage. The proposed experimental technique is found to be very effective and provides new information regarding the interaction of the infill wall with the surrounding frame. It is demonstrated by an experimental study simulating the loss of a frame supporting column thus enhancing the understanding of the infill wall role in the frame resistance and its contribution to avoid progressive collapse.

Experimental study of the progressive collapse mechanism of excavations retained by cantilever piles

An increasing number of catastrophic progressive collapses of deep excavations have occurred throughout the world. However, the research on progressive collapse mechanisms is limited. In this paper, two categories of model tests were conducted to investigate the mechanism of partial collapse (sudden failures of certain retaining piles) and progressive collapse. The model test results show that partial collapse can cause a sudden increase in the bending moments of adjacent piles via an arching effect. The load-transfer coefficients are defined to be equal to the peak increase ratios of the maximum bending moments in adjacent piles (peak moments caused by collapse over the values before the collapse). When the maximum load-transfer coefficient is larger than the bearing capacity safety factor of the piles, the partial failure will lead to progressive collapse. The influential factors of the progressive collapse mechanism, such as the partial collapse extent, excavation depth, and capping beam, were also investigated. During progressive collapse, the previous failed pile could cause new stress arching; simultaneously, the soil behind certain nearest intact piles could become loosened and destroy the arch springing of the stress arching, causing the progressive collapse to cease gradually.

Seismic rehabilitation effect in a steel moment frame subjected to tow critical loads

PurposeThe purpose of this paper is to present a probabilistic assessment and verify the effectiveness of seismic improvement schemes against earthquake, blast and progressive collapse. The probabilistic analysis is performed by taking into account the uncertainties in loading such as planar configuration and amplitude of the blast loading. A standard Monte Carlo (MC) simulation method is employed to generate various concepts of the uncertain parameters within the problem. For a given concept, various local dynamic analyses are performed within a certain range of distance, in order to quantify and locate the damage induced by impact wave on structural elements. In the next step, a limit state analysis is performed in order to investigate whether a progressive collapse mechanism forms under the acting loads or not.Design/methodology/approach( | ) and ( | ) are blast fragility and seismic fragility, respectively; ( ) and ( ) are annual occurrence rate of earthquake and blast, respectively. The purpose of the current study is to calculate for the primary structure as well as the retrofitted structure. Annual occurrence rate of earthquake can be calculated by using probability seismic hazard analysis for the site of interest, where the structure is located. In this paper, blast fragility and seismic fragility are defined rather differently; in other words, seismic fragility is defined as the probability of structural collapse given a specified level of seismic intensity whereas blast fragility is defined as the probability of collapse given that a significant blast event takes place. Both blast and earthquake loading conditions involve the activation of energy dissipation mechanism and, as a consequence, both can be resisted employing ductility enhancing techniques, such as column wrapping or jacketing and steel bracing.FindingsThe current paper aims to present a probabilistic assessment of progressive collapse under blast and earthquake loads. Non-dependent and incompatible events are considered to obtain a general rate of collapse. Finally, probabilistic collapse rate was obtained for a moment frame before and after modifying with convergent steel brace (CBF). The purpose of doing so is to investigate whether seismic improvement schemes can reduce collapse risk of different critical events or not.Originality/valueObjective of the present work is to present a methodology for calculating the annual risk of collapse for a civil structure subjected to both seismic and blast loads, using a bi-hazard approach. Given that a blast event takes place, the probability of progressive collapse is calculated using a MC simulation procedure. The simulation procedure implements an efficient non-linear limit state analysis, formulated and solved as a linear programming problem. The probability of collapse caused by an earthquake event can be calculated by integrating the seismic fragility of the structure and the seismic hazard for the site.

Behavior of Steel Structures under Elevated Temperature

The purpose of this paper is to investigate the damages of an industrial steel building affected by a fire event. The author's main objectives are to identify different types of damages produced by fire to the building structure and nearby built environment, highlighting the idea that nowadays the fire safety must be seen as a sustainable practice. The presented research is based on a case study regarding the damages of an industrial steel building subjected to fire. Structural design of buildings exposed to fire requires the achievement of two main objectives; the first one is to reduce the loss of life and the second one regards the load bearing resistance of the building for a specified period of time. The behavior of steel structures under elevated temperature can be assessed using both numerical simulations and experimental studies. There are a lot of studies regarding the behavior of multi-storey steel buildings under fire conditions and progressive collapse mechanisms. Unfortunately, little information regarding the industrial steel buildings subjected to fire can be found. Analyzing the behavior of single storey steel buildings at elevated temperatures, it can be conclude that not always the collapse of an element leads to the collapse of the entire structure. A correct expertise of the damage level of steel structures exposed to fire, in order to identify the elements which can be kept and which have to be replaced, in most of the cases lead to a lower consumption of materials and financial resources.

Progressive collapse analysis of a steel frame subjected to confined explosion and post-explosion fire

Fire is a common secondary disaster following blast events. Because the strength of steel is sensitive to temperature, the steel structure that survives an explosion threat may collapse in the post-explosion fire. Thus, it is significant to investigate the progressive collapse mechanism of steel structures subjected to explosion and post-explosion fire. This article presents an accurate analytical model for evaluating the progressive collapse potential of a steel frame subjected to a confined explosion and post-explosion fire. The macro-model of the shear tab connection is established, and a material model that can reproduce the nonlinear dynamic behaviour of connections under combined hazard is compiled as subroutines. The finite element package AUTODYN is adopted to calculate the internal blast load to accurately analyse the effect of blast-induced damage on the fire resistance of the steel structure. The analytical results indicate that the gravity columns and columns in the interior moment resisting frames are key components for structural stability under combined hazards. The blast not only results in geometrical damage to the structural members, improving the load–displacement effect, but also leads to failure of the shear tab connections which increases the effective length of the column. Therefore, the failure time of the column under the combined hazard of blast and fire is earlier than the fire only case. Blast damage to the connection may also result in connection failure before column buckling in a fire, leading to local collapse prior to progressive collapse. Moreover, the collapse time–charge weight interaction diagram is generated to determine the weakest area of the steel frame. The membrane action of the floor is the only mode to redistribute load after the failure of the damaged column in a fire. Thus, increasing the reinforcement ratio in the floor may help mitigate the progressive collapse potential of the steel frame.

Study of the progressive collapse mechanism of excavations retained by cantilever contiguous piles

Abstract An increasing number of catastrophic progressive collapses of deep excavations have occurred throughout the world. However, the mechanism by which partial failures evolve into large-scale progressive collapses has rarely been studied. In this paper, long-strip excavations and square excavations retained by cantilever contiguous piles under partial failure were simulated using the explicit finite difference method (FDM). The results show that a partial collapse can cause sharp increases in the internal forces in adjacent intact piles through the horizontal arching effect. Therefore, the concept of a load transfer coefficient is proposed, which is equal to the ratio of increase of the internal force in an intact pile. The relationship between the maximum load transfer coefficient Tmax and the safety factor of the piles determines whether progressive collapse will occur. Furthermore, the influences of a number of important factors on the load transfer mechanism, such as the capping beam, the extent of partial failure, the soil strength, the excavation depth and the corner effect, were examined. A continuous capping beam can reduce the maximum load transfer coefficient Tmax. Within a certain range of the extent of partial collapse, a larger partial collapse extent will produce larger load transfer coefficients and have a greater influence over a larger area. For the same retaining structure, a higher soil strength will result in larger load transfer coefficients. Moreover, when the lateral stiffness of the retaining piles is lower, the maximum load transfer coefficient will be smaller and the range of influence will be larger. In an excavation with a corner effect, when the number of failed piles is above a certain threshold, the maximum load transfer coefficient decreases with an increasing number of failed piles. Therefore, the progressive collapse evolving toward the corner will terminate when the maximum load transfer coefficient decreases below the safety factor. The corner effect can be recognized as a cause of the natural termination of progressive collapse.

Study of the mechanics of progressive collapse with simplified beam models

Methods for assessing structural robustness need to move away from the traditional norms of prescriptive rules and become more similar to those used in conventional structural design. They should therefore be based on a sound understanding of the mechanics of the problem and provide quantitative indication of its effects. Several Codes and Design Guides consider the sudden column removal approach as their principal method for progressive collapse assessment. The level of robustness is defined based on the capability of the remaining structure for sustaining the additional loading imposed by the column loss. Most likely, the beams adjacent to the lost column and their supporting connections form the principal load paths. The present paper presents a detailed study of the response of those components under the conditions experienced following column removal. Suitable analysis approaches that have been previously developed at Imperial College London are employed to investigate the basic features of the behaviour, while several simplifications are applied for exploring particular effects. The study concludes with the development of a simplified method for simulating the nonlinear dynamic response of axially restrained and unrestrained beams following column removal. The capability of the new simplified method to accurately describe performance is demonstrated through a set of suitable applications presented in a separate publication.

Experimental study on the progressive collapse performance of RC frames with infill walls

The interaction between the infill walls and the reinforced concrete (RC) frame members in the progressive collapse process was examined experimentally in this study. Two 1/3 scaled, four-bay, two-story RC frame specimens, one of which was featured without infill walls while the other with infill walls, were tested. The frame specimens were designed in such a way that the center column of the first story was missing, in order to simulate the failure of the structural component due to abnormal loads or design flaws. The frame specimens were quasi-statically pushed downward at the top of center column under displacement control to investigate the progressive collapse mechanism of the RC frames, with a focus on the effects of infill walls. Specifically, the physical quantities and phenomena of great interest in this study include the collapse resistance force and mechanism, strain variation and crack development in structural components, and local and global failure modes of the frames. The test results showed that the infill walls can provide alternative load paths for transferring the loads originally only supported by the beams, and thus, improve the collapse resistance capacity of the RC frame. The infill walls, however, may reduce the ductility of the RC frame and may change the failure mode of the frame. It is concluded that the infill walls may affect (i.e., either improve or impair) the performance of RC frames against progressive collapse in different aspects.