Corner Column Removal Scenarios Research Articles

Vierendeel action in progressive collapse of three-storey RC structures under corner column removal scenario

Previous studies have found that the Vierendeel action (VA) is one of the main mechanisms against progressive collapse of multi-storey reinforcement concrete (RC) frame structures in the event of corner column failure. However, the knowledge remains inadequate in terms of the behavior, mechanism, and quantitative contribution of the VA to the collapse resistance. To fill this gap, quasi-static tests were performed on a 1/3 scale single-storey RC substructure and a three-storey RC substructure with identical geometry, material, reinforcements and boundary conditions under corner column removal scenario. Test results found that, compared with the single-storey substructure experiencing no VA, the three-storey substructure developed additional plastic hinges at the beam ends near the corner column and at the lower end of the corner column as a result of the VA. The ultimate resistance of the three-storey substructure was 10.6% more than the triple ultimate resistance of the single-storey substructure. Then, numerical analysis was conducted to cognize the formation sequence of the plastic hinges and the effect of slabs. Furthermore, two coefficients were defined to reveal the mechanism of the VA in the three-storey substructure, i.e., the displacement-related coefficient ed and the coefficient associated with ultimate resistance eu. Finally, a simplified analytical model was proposed to predict the ultimate resistance of the three-storey structures with consideration of the VA.

Simplified multi-scale simulation investigation of 3D composite floor substructures under different column-removal scenarios

The robustness of structures to withstand progressive collapse is a significant theme. However, owing to the restricted experimental conditions, some issues regarding 3D composite floor substructures under a column-removal scenario remain unclear, such as different column-removal scenarios, boundary constraints, loading schemes, floor numbers, reinforced concrete (RC) floors, and structural or nonstructural components. To understand these issues, a progressive collapse study on 3D composite floor substructures subjected to uniformly distributed load (UDL) is carried out based on simplified multi-scale simulation. A 2 × 1-bay concrete-filled steel tubular (CFST) column-steel beam-RC floor substructure is employed to investigate the structural robustness under the corner column-, penultimate-edge column-, and middle-edge column-removal scenarios. It is found that the vertical resistance for the corner column-removal scenario is reduced by approximately 10–20% compared to the other two scenarios. The 3D substructure resists progressive collapse via the flexural action (FA), the catenary action (CA), and the RC floor. Compared with the real boundary constraints, the fixed and hinged supports at the beam ends can overestimate the CA, and disregarding boundary constraints can overestimate deformation performance. Moreover, the concentrated vertical load (CVD) severely underestimates the robustness of 3D substructures. The floor number, RC floor, shear wall, and steel brace significantly influence the progressive collapse performance of 3D substructures.

Experimental and Numerical Investigations of RC Frame Stability Failure under a Corner Column Removal Scenario

In recent decades, interest in the resistance of buildings and structures to progressive collapse has been increasingly sparked in research communities. Although several experimental, numerical, and analytical research projects on the robustness of building frames under a column removal scenario have been implemented, some aspects of this problem remain understudied. These aspects encompass failure mechanisms of reinforced concrete frames with slender columns, as well as criteria used to evaluate such failures. This paper focuses on experimental and numerical investigations of the structural behavior and failure of a scale reinforced concrete frame with slender columns under a sudden corner column removal scenario. In addition, we analyze the stability failure mechanism of a reinforced concrete frame with slender columns and the tangent stiffness criterion, which allow for evaluation of the ultimate state of a structure subjected to an accidental impact. A scale physical model of a reinforced concrete frame of a multistory building was designed and tested using the theory of functional similarity. For numerical study purposes, a finite element model was made that exactly the same as the test frame. We validated the findings by comparing simulation results and experimental data. The studies on the behavior of a reinforced concrete frame subjected to quasistatic loading with unequal concentrated loads identified the load transfer between columns through beams. Although these effects were minor in the frame under consideration, they can become more significant in cases of long-term loading. Numerical simulation and physical modeling of an accidental impact allowed for identification of the mechanism of load capacity exhaustion triggered by stability failure. Such failure was fragile. The moment of stability failure of the column of the experimental frame corresponded to the extremum on the force–displacement curve, indicating that zero tangent stiffness was reached. Hence, a criterion of tangent stiffness can be proposed for evaluation of the ultimate state of a structure subjected to an accidental impact.

Large-scale test of a 3D steel moment-resisting frame with composite slab subject to penultimate interior column loss

This paper investigates the structural behavior of a typical three-dimensional steel frame-concrete slab substructure (3D composite floor subassembly) subject to a penultimate interior column removal scenario. A two-by-two bay composite floor subassembly is one-third downscaled and quasi-statically pushed down to failure by a specially designed twelve-point loading tree in displacement control mode. Unlike the previous studies where progressive collapse propagates vertically, the current study reveals the possibility of horizontal progressive collapse of 3D composite floor structures that characterized by losing stability of the exterior column. The load-displacement relationships, failure modes, deformation pattern and beam end rotations of the test specimen are presented in detail. Based on the test results, the three load-transferring mechanisms, including flexural action, catenary action and tensile membrane action, are determined and discussed. Besides, the test results are compared with previous test results subject to interior column, edge column and corner column removal scenarios, based on which a structural design and analysis strategy of normal composite buildings against progressive collapse are recommended in this study.

Evaluation of Intermediate Reinforced Concrete Moment Frame Subjected to Truck Collision

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

Finite element modelling of the progressive collapse of post-and-beam mass timber building substructures under edge and corner column removal scenarios

The structural behaviour of mass timber buildings under a load bearing element removal scenario is complex. To well understand this phenomenon and ultimately develop scientifically based design guidelines against progressive collapse for this type of buildings, there is a need to develop a Finite Element model which accurately captures the non-linear response, load redistribution mechanisms (alternative load paths) and failure modes of such buildings. As such, this paper presents for the first time how mass timber post-and-beam systems can be accurately modelled using Finite Element under edge and corner column removal scenarios. The model was validated against published 2D and 3D experimental tests performed on scaled-down substructures. The non-linear structural responses of the main structural connections were experimentally quantified and inputted into the model using the component method. Results show that the model accurately replicated load redistribution mechanisms, ultimate loads, failure modes, and strain developments. The use of the model was then illustrated by running parametric studies to quantify (i) the influence of the Cross Laminated Timber (CLT) floor panels layout and (ii) one alternative load path, typically ignored in design, on the progressive collapse resistance capacity.

Effect of loading methods on progressive collapse behavior of RC beam-slab substructures under corner column removal scenario

In this paper, high-fidelity finite element (FE) models were developed to investigate the behavior of reinforced concrete (RC) beam-slab substructures to resist progressive collapse under a corner column removal scenario. The numerical models were validated by test results. Then, the validated FE models were employed to investigate the structural behavior under different loading methods, including concentrated loading (CL) and uniformly distributed loading (UDL) methods. Moreover, multi-story frames were built to capture the load redistribution behavior of substructures at different floors under different loading methods. The results indicated that the loading methods affect overall structural responses, load transfer mechanisms, and failure modes. It was demonstrated that the Vierendeel action could not be ignored for multi-story frames to resist progressive collapse caused by the loss of a corner column scenario. More significant Vierendeel action was developed in the structure subjected to CL method than that subjected to UDL method. It was also found that the load transfer mechanisms developed in the top story and bottom story for a multi-story frame are pretty different from those in the middle stories. The bottom story has the most remarkable load resisting capacity.

Effect of inter-module connections on progressive collapse behaviour of MiC structures

Modular integrated Construction (MiC) is a game changing construction approach which could significantly increase construction efficiency, quality, and sustainability. For steel MiC structures, modules are manufactured in the factories and assembled at the construction sites through inter-module connections. The concern of the vulnerability of these connections under abnormal hazards leading to disproportionate progressive collapse will impede industrial applications of MiC structures in the construction community. This study investigates the structural robustness of corner-supported modular steel buildings with the focus on different inter-module connections. A sub-structure extracted from a five-storey modular building is analysed by high fidelity finite element analysis under a corner column removal scenario. The load redistribution mechanism and failure modes are investigated thoroughly, based on which the simplified macro model is proposed where connections are modelled with rotational springs. Good consistence is found for the simplified model and the detailed FE analysis in terms of the pushdown curve. It is also found that the inter-module connection types will affect the beam-column joint properties which dominate the progressive collapse resistance of MiC structures. Therefore, attention should be paid when selecting different inter-module connections. The current rigid beam-column joint connection may lead to nonconservative evaluation.

Steel-concrete composite floor systems with different structural and loading configurations under a corner column removal scenario: Experimental tests

In this study, quasi-static tests were performed on three 3D steel–concrete composite floor systems under a column removal scenario with two variables, i.e., secondary beam connection type and pre-existing axial loads on columns. The work focused on the behavior of the three composite floor systems, including the load–deflection response, failure mode, load-resisting mechanism, e.g., flexure, catenary action and tensile membrane action (TMA), and load redistribution. It was found that secondary beam connection had a pronounced effect on the load–deflection response. Pre-existing axial loads on columns significantly influenced the load redistribution process and intensified the stresses in adjacent columns connected by the secondary beam to the removed column. For all the three specimens, a peripheral compressive ring with TMA was not observed in the composite slab due to a lack of rotational restraint from the perimeter beams and the main girder. However, at large deformation stage, when the composite slab deformed into an approximate hyperbolic-parabolic surface, the entire reinforcing mesh in the slab was in tension. It was observed that, at the early stage, the applied load was mainly resisted by flexure in the slab and the main composite girder and the secondary composite beam connecting to the removed column. But at large deformation stage, part of the applied load was resisted by flexure in the partially damaged slab and the main girder, and the intact secondary beam. Other load-carrying contributions came from catenary action in the main girder and TMA in the slab. In the end, most of the applied loads were redistributed to the columns adjacent to the removed column.

RESEARCH ON PROGRESSIVE COLLAPSE RESISTANCE CAPACITY OF COMPOSITE FRAME WITH CFST COLUMNS UNDER CORNER COLUMN REMOVAL SCENARIO

To study the progressive collapse performance of the composite frame with CFST columns under the corner column removal scenario, a 1/4-scale two-story-two-bay composite frame specimen was designed and tested. By the monotonic static loading of the residual structure after the corner column was damaged, the tests obtained the load-displacement relationship curves of the composite frame, the global/local failure modes of the structure and the strain developments of critical locations. The energy equivalence principle was used to analyze the progressive collapse dynamic effects. The resistance to progressive collapse of the composite CFST frame was evaluated. The experimental results show that the progressive collapse loading process of composite frame with CFST columns mainly includes four stages in the corner column removal scenario, i.e., elastic stage, elastic-plastic stage, internal force redistribution stage and damage stage. The damage of the specimen is mainly concentrated in the failure span. The failure characteristics are mainly on the fracture and distortion of steel beams, and the steel beams on the second floor are damaged before that on the first floor. It is also found that the composite slabs with profiled sheeting and concrete are separated from the steel beam and the shear studs are pulled off. When the flange of the steel beam on the second-floor is cracked, the internal force is transferred to the first-floor steel beam through the adjacent column. Based on the test results and the energy equivalence principle, it is found that the composite frame has 15.3% residual capacity to resist the progressive collapse in the corner column removal scenario.

Experimental study on the quasi-static progressive collapse response of post-and-beam mass timber buildings under corner column removal scenarios

This study presents the results from two quasi-static experimental tests performed on a ¼-scale, 2 × 2-bay, post-and-beam mass timber substructure, with Cross Laminated Timber (CLT) floors and Laminated Veneer Lumber (LVL) frames, subjected to corner column removal scenarios. One substructure was constructed and tested twice under different CLT panel configurations. In the first test (Test CM-1), the bay adjacent to the removed corner column consisted of three CLT floor panels, with two panels spanning one bay and one panel extending past the bay and spanning two bays. A constant Uniformly Distributed Pressure (UDP) was first applied to the bays not adjacent to the removed column and the UDP on the bay adjacent to the removed column was increased till failure through a six-point loading tree. As failure did not extend past the vicinity of the removed column in CM-1, the damaged elements were replaced and the specimen was re-tested by removing the diagonally opposite corner column. In this second test (Test CM-2), the bay adjacent to the removed corner column now consisted of one CLT floor panel spanning one bay and two panels spanning two bays. A similar loading protocol to that of Test CM-1 was used in CM-2. The substructure was assembled from a commonly used commercial beam-to-column connection. The failure modes, load redistribution mechanisms (alternative load paths) and overall behaviour are presented in this paper. The two test results showed that the applied load was mainly transferred to the three columns, the closest to the removed column. The ultimate load in Test CM-2 was 1.62 times higher than Test CM-1, demonstrating that the layout of the CLT panels plays a critical role against progressive collapse. A simplified analytical model, consistent with the current industry practice and pre-defined alternative load paths, was developed for the tested specimen to predict the ultimate resistance capacity and was also compared to the experimental tests. On average, the experimental failure load was 2.7 times higher than the predicted one, indicating that simplified current design practice is conservative.

A Parametric Computational Study of RC Building Structures under Corner-Column Removal Situations

Building progressive collapse is currently one of the hottest topics in the structural engineering field. Most of the research carried out to date on this topic has been focused on the structural analysis of the failure of one or more columns in a building to determine the Alternative Load Paths (ALPs) the structure can activate. Past research was mainly focused on extreme situations with high loads and large structural deformations and, to a lesser extent, research looked at lower loads used in design accidental situations, which requires a different set of assumptions in the analysis. This paper describes a study aimed at analysing accidental design situations in corner-column removal scenarios in reinforced concrete (RC) building structures and evaluating the available real ALPs in order to establish practical recommendations for design situations that could be taken into account in future design codes. A wide parametric computational analysis was carried out with advanced Finite Element (FE) models which the authors validated by full-scale tests on a purpose-built building structure. The findings allowed us to: (i) establish design recommendations, (ii) demonstrate the importance of Vierendeel action and (iii) recommend Dynamic Amplification Factors (DAFs) for design situations.

Experimental study on progressive collapse of reinforced concrete frames under a corner column removal scenario

Abstract A comprehensive experimental apparatus for the progressive collapse testing of Reinforced Concrete (RC) frames have also been developed. The loading apparatus has been studied for the testing of the threedimensional frame of progressive collapse resistance of the RC structure under a corner column removal scenario. Five storey RC samples were checked, one bare frame without wall load, one bare frame with wall load and one bare frame with Infilled walls. On the displacement screen at the top of the center column, the frame specimens are forced down quasi dynamically to check the progressive collapse mechanism of the RC frame with an emphasis on the effect of infill walls. This study includes the trend of Load Vs Deflection and crack pattern. The test results show that the infill walls can provide a suitable path of load transfer and improve the gradual collapse resistance of the RC frames.

Response of RC Beam-Slab Structure Strengthened with CFRP under Sudden Corner Column Removal Scenario

Response of RC Beam-Slab Structure Strengthened with CFRP under Sudden Corner Column Removal Scenario

Numerical study on steel-concrete composite floor systems under corner column removal scenario

In this paper, the authors assess the robustness of steel-concrete composite floor systems subjected to a Corner Column (CC) removal scenario based on numerical simulations. First, a modelling method is verified by previous actual test results conducted by the authors. Afterwards, using the reliable modelling method a composite floor system subjected to a corner column loss is simulated, producing the static load-displacement curve, the failure mode and load-transfer mechanisms. These results are compared with those of composite floor systems under an Internal Column (IC) removal scenario. Besides, the model is applied to simulate that the same composite floor system experiences a sudden column removal under six levels of loads. The dynamic displacement-time histories under all levels of loads are obtained, from which the loads and corresponding maximum deflections constitute the dynamic load-deflection response. They are used to evaluate the dynamic load capacity and deformability of this composite floor system subjected to a sudden CC removal scenario. Lastly, Dynamic Increase Factors (DIFs) are obtained through comparing the dynamic load-deflection response with the quasi-static one, which are further compared with DIFs under IC scenario.

Experimental study on the progressive collapse behaviour of RC flat plate substructures subjected to corner column removal scenarios

Reinforced concrete (RC) flat plate structures are broadly used in car parks, residential and office buildings due to their economic and architectural advantages. However, this structural system is inherently prone to punching shear failure, which may propagate horizontally and vertically, ultimately leading to the progressive collapse of the entire structure or of a large portion of it. This paper presents the experimental results from two quasi-static large-displacement tests performed on a 1/3 scale, 2 × 2-bay, RC flat plate substructure subjected to corner column removal scenarios. The specimen was tested twice with different corner reinforcement configurations: (i) firstly, one corner column, with torsional strips, was removed and the Uniformly Distributed Load (UDL) on the bay adjacent to the removed column was increased to failure (Test T1), and (ii) secondly, as the damage was concentrated in the vicinity of removed corner column in (i), the corner column diagonally opposite to the first removed one, without torsional strips, was removed. The UDL on the bay adjacent to the second removed column was also increased to failure (Test T2). Different failure and post-failure behaviours, failure modes, and collapse resisting mechanisms between the two tests were witnessed, presented and analysed. Results show that 80% to 110% of the applied load is transferred to the two edge columns adjacent to the removed corner column throughout the entire two tests. The ultimate load carrying capacity for T1 is found to be 1.7 times smaller than the one for T2.

Progressive Collapse Resistance of GFRP-Strengthened RC Beam–Slab Subassemblages in a Corner Column–Removal Scenario

In RC buildings, the unexpected sudden failure of a corner column is more likely to cause severe progressive collapse than the failure of an interior column or a side column due to the relatively weak tie force from the surrounding elements. Effective strengthening methods can improve the progressive collapse resistance of these structures. Fiber-reinforced polymer (FRP) has been widely used to retrofit RC structures due to its high strength, light weight, and corrosion resistance. In this study, the progressive collapse behaviors of glass FRP (GFRP)–strengthened RC beam–slab subassemblages under corner column removal were investigated. First, a quasi-static experimental test was adopted to study the progressive collapse resistance of the beam–slab subassemblages, including a control specimen and strengthened specimens. Two techniques applying externally bonded GFRP laminates and near-surface-mounted (NSM) GFRP bars were adopted to strengthen the subassemblages. The influences of the strengthening schemes on the behavior of the tested specimens were studied by comparing all the test results. The experimental results demonstrate that this strengthening technology can enhance the progressive collapse resistance of RC beam–slab structures. Finite-element (FE) analysis of the progressive collapse resistance of the beam–slab subassemblages was also conducted using the software package MSC Marc. The numerical model can predict the progressive collapse resistance of the subassemblages. In addition, the calculated results were used to better understand the stress distribution of the GFRP in a corner column–removal scenario.

Investigations of tensile membrane action in beam-slab systems under progressive collapse subject to different loading configurations and boundary conditions

Although catenary action in beams and tensile membrane action in slabs are generally believed as high-level analyses to mitigate progressive collapse in a reinforced concrete building, previous research studies did not clearly differentiate the contributions of the two mechanisms in combined three-dimensional beam-slab systems. Besides, most of the recent experimental studies on column removal scenarios focused on point load application as it is more difficult to apply the more realistic uniform distributed loads in the laboratory. In this paper, numerical analyses were first employed to investigate the combined effects of beams and slabs under both point load (idealised) and uniform distributed load (more realistic) conditions. The results show that differences between these two loading methods not only affect overall structural capacities, but also influence vertical deflections and failure modes. It is also observed that tensile membrane action in slabs was less sensitive to boundary conditions compared to catenary action in beams. Moreover, catenary action in beams which showed limited development in beam-slab structures can be conservatively neglected. Besides, under uniform distributed loading condition, scenarios with different locations of column removal were numerically investigated, showing that the loss of a penultimate column, rather than a corner column, could be the most critical case, contrary to conventional wisdom. In fact, in a corner-column removal scenario, tensile membrane action can still be partially mobilised owing to the presence of two stiff discontinuous edge beams. This phenomenon was well observed in a beam-slab test conducted in this study.

Dynamic increase factor for RC frame with specially shaped columns against progressive collapse

To investigate the dynamic increase factor (DIF) for nonlinear static (NS) alternate path analysis, the nonlinear dynamic (ND) and static analysis of a 6-storey reinforced concrete (RC) frame with specially shaped columns are carried out by utilizing OpenSees after the corner, side or inner column is removed respectively. Using the vertical displacement of removal column top node and axial force of adjacent column as control, reasonable value of DIF in the NS analysis are estimated according to the analysis results. A DIF about 1.8, 1.2 and 1.4 could capture the dynamic responses in corner, side or inner column removal scenario respectively when a static analysis is performed. The DIF in corner column removal scenario increases with the increasing of the floor on which the failure column locates and reaches the peak value at the top floor, while the DIF in inner or side column removal scenario decrease slightly. The DIF of inner or side column removal scenario increases linearly with the elongation of the beam span. The reinforcement of frame with specially shaped columns has little effect on the DIF.

Studying the Vulnerability of Steel Moment Resistant Frames Subjected to Progressive Collapse.

The guidelines of Unified Facilities Criteria (UFC) and U. S. General Service Administration (GSA) provide the design requirements to reduce the potential of progressive collapse for structures. According to these codes, progressive collapses are occurred due to loss of a main vertical structural element. In this study, the vulnerability of an official 10-story steel moment resistant frame, designed according to Iranian National Building Codes (INBC) is assessed. The following nonlinear dynamic analysis procedure is recommended by the UFC 4-023-03 guideline, which provides technical guidance for mitigation and protection of progressive collapse. Alternate Path (AP) method has been applied to evaluate the structure that can bridge over notionally removed column and nonlinear dynamic analysis procedure conducted. The investigated cases emphasize on the removal of a corner column in the ground floor, fifth floor, eighth floor, and just below the roof floor. Based on the results obtained in this research, steel moment resistant frames, designed according to Iranian National Building Codes, do not satisfy UFC acceptance criteria and have high potential for progressive collapse in corner column removal scenarios. Therefore some modifications have been conducted on the codes to satisfy the UFC limits.