Sudden Column Removal Research Articles

Dynamic performance of a real-scale reinforced concrete building test under a corner-column failure scenario

The topic of robustness and progressive collapse of structures has attracted significant attention within the field of structural engineering recently. This is reflected by the rise in the number of scientific papers published in recent years as well as efforts in reviewing and developing codes for design. Although important numerical and experimental studies have been carried out to date simulating the sudden removal of columns to reproduce the possible consequences of an extreme event, most of these studies focus on subassembly systems and internal columns. Edge and corner columns are most vulnerable to accidental events. This paper gives the results of a test carried out on a purpose-built full-scale reinforced concrete building with a specially designed corner steel column used for the sudden column removal. The test was highly instrumented, involving 38 strain gauges, 38 displacement transducers and 2 accelerometers to monitor the vertical and lateral response. The results were used to analyse the dynamic performance of the structure after the sudden column removal as well as the alternative load paths (ALPs) mobilised during the test (i.e. flexural and Vierendeel action). The test showed a clear dynamic amplification of the strains and displacements (with high peaks); dynamic amplification factors (DAFs) were obtained accordingly. The load initially carried by the removed column was redistributed through the entire building system (not just the neighbouring columns). Tests on full-scale buildings, including the one described here, can be used to compile a database to validate codes and future numerical studies.

ИССЛЕДОВАНИЕ ЖИВУЧЕСТИ ЖЕЛЕЗОБЕТОННОЙ КОНСТРУКТИВНО НЕЛИНЕЙНОЙ РАМНО-СТЕРЖНЕВОЙ СИСТЕМЫ КАРКАСА МНОГОЭТАЖНОГО ЗДАНИЯ В ДИНАМИЧЕСКОЙ ПОСТАНОВКЕ

The article presents the results of numerical simulation of the dynamic response of a reinforced concrete frame of a multi-story building with the sudden removal of load-bearing columns using a detailed 3D model in the LS-DYNA program, whichimplements the explicit finite element method. The model takes into account the nonlinear behavior of the material. The influence of the deformation rate of concrete and steel reinforcement is taken into account using the coefficient of increasing the strength of materials, normalized in SP 385.1325800.2018. The numerical results of the study showed that using the proposed calculatedmodel, it is possible in each moment to track the stress-strain state of load-bearing elements of frame-rod system frame high-rise buildings, to check criteria special limit state designs, and to answer the important practical question of the sustainability of a building to progressive collapse under a given beyond design action and as a result take in the design of necessary protection measures.

Deformation and failure of monolithic reinforced concrete frames under special actions

The results of experimental and theoretical studies of crack formation, deformation and failure of monolithic reinforced concrete frames under accidental action caused by the sudden removal of one of columns of the first floor. Experimental studies were carried out on the model of structural fragment of a three-story two-span reinforced concrete frame, designed from fine-grained concrete class B40 with reinforcement A500. The test of experimental structures is executed by the gravitational load, with use of specially designed lever loading device. Special effect in the form of sudden removal of central columns of the frame was modelled using a specially designed mechanism in the form of sudden switching-off device. The obtained experimental values of widths of cracks, deflections, pictures of cracking and failure of experimental structures of the frames before and after beyond-design action. The experimental values of these parameters are compared with the results of calculation by the method taking into account the specifics of static-dynamic loading of physically and constructively nonlinear structures under the considered special actions.

Vertical collapse safety margin assessment for steel frames against earthquake-induced loss of column

A quantifiable approach measuring the seismic structural collapse under sudden column removal is proposed using the interaction of the vertical collapse margin ratio (CMRV), the demand-to-capacity ratio (DCR) and the robustness (R). The assessment of CMRV needs the identification of the vertical maximum considered earthquakes. A classification of the ground motions based on the vertical-to-horizontal (V/H) ratios was used to obtain the vertical design spectrum. Six schemes of steel structures with various scenarios of sudden column removal were investigated to extract CMRV, DCR, and R. Then, a nonlinear regression analysis allows finding a general formulation of CMRV. A 15-story steel structure validates the proposed formulation of the CMRV. The two paths for estimating the minimum CMRV (CMRV, min) were the use of the recommended value of DCR and the minimum value of R inside the approximated CMRV expression, and the probabilistic distribution of CMRV, min from the analyses of different beam deformation states. The study of eighteen archetypes with 119 scenarios of sudden column removal reveals the value of the CMRV decreases when the V/H or/and DCR increase. The new maximum values of DCR with respect to R and its precise ranges are found with the use of the contour curves of CMRV, min.

Assessment of progressive collapse potential of special moment resisting RC frames – Experimental and FE study

The catastrophic collapse of the Twin-towers has further prompted structural engineers to understand and investigate the progressive collapse of multi-story buildings. This paper aims to simulate the response of reinforced concrete (RC) special moment resisting frame (SMRF) assemblies under column-loss scenarios through nonlinear finite element (FE) modeling. Besides the modeling of nonlinear rate dependent material behavior, bond-slip effects at the concrete-to-steel rebar interface have been considered. The FE model was calibrated against a scaled, single-story, two-bay by one-bay, RC SMRF model specimen with reinforcement detailing conforming to ACI 318-11 code. The specimen was tested under a middle column removal scenario. The calibrated FE model was subsequently employed for some parametric studies of interest wherein the effect of different parameters such as: type of assembly, column continuity, development of beam rebars at exterior joints, applied axial loads on columns and beam continuity at exterior joints, on the behavior of SMRF under a middle column removal scenario was studied. A simple procedure is also proposed for the progressive collapse assessment of RC SMRFs caused by sudden column removal.

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.

Probabilistic assessment of failure time in steel frame subjected to fire load under progressive collapses scenario

Consecutive loads can pose a serious threat to the safety of structures. The sudden removal of load-bearing elements such as columns is one of the causes of the progressive collapse in the structures. The local collapse caused by the sudden removal of the column could affect the response of the structure in the consecutive loads. The fire load is one of the loads that threatens the safety of the structure over the lifetime of the structure. The time a structure can resist the fire load is one of the main factors in the safety of structures against thermal loads. The local damage involved in the structure, including the sudden removal of the load-bearing elements, can affect the stability of the structures against the fire load as two successive events. This research aims to calculate the stability time of the steel frame during the consecutive loading from the sudden removal of column and the subsequent fire. Once designed, the 7-story steel frame is mechanically-thermally modeled and is subjected to the sudden removal of columns in different positions. The static and dynamic pushdown analysis is used to evaluate the structure response in the scenarios of sudden removal of the column. Different modes of thermal load are defined and applied to the structure in the positions of the removed column. Finally, the probability of structural failure is calculated under the fire load after the sudden removal of the column and presented at different times. The results show that the sudden removal of the column will have a great effect on the failure time of the structure and will increase the failure probability of the structure and reduce the failure and collapse time of the structure. Finally, the robustness index is also presented based on the probability of collapse time.

Experiments on the collapse response of flat slab structures subjected to column loss

Flat slab structures are prone to progressive collapse due to their relatively heavy self-weight and susceptibility to punching shear failure. In this study, three one-third scaled slab–column sub-assemblages were statically and dynamically tested to examine the collapse behaviour of such structures when either an edge or a penultimate column is removed. In the static tests, the development of an alternative load path bridging over the removed column was investigated with two specimens that were loaded to failure by a load-control procedure using concrete weights. In the dynamic test, a specimen that had been loaded by concrete weight up to 80% of the yield-line capacity was subjected to a sudden column removal, which was simulated by a quick-release mechanism. Based on the experimental observations, the potential failure modes of flat slab structures, the development of tensile membrane action as an alternative load path, and the dynamic effects resulting from sudden column removal are discussed.

Variance‐based global sensitivity analysis for fuzzy random structural systems

AbstractThere have been increasing advances in the sophisticated approaches like fuzzy randomness to handle different uncertainties in civil engineering; however, less attention has been paid to the formulation of a sensitivity analysis for fuzzy random structural systems. In this study, the main objective is to present the formulation of fuzzy Sobol sensitivity indices to quantify the influence of fuzzy random structural parameters. Meanwhile, uncertainty in derivation of limit states and acceptance criteria in collapse analysis is addressed briefly and treated using fuzzy model parameters. To show the application of the established sensitivity test, the collapse behavior of a steel moment frame subjected to sudden column removal is evaluated thoroughly. The proposed fuzzy sensitivity indices are determined for the problem and the overall influence of fuzzy acceptance criteria on the collapse assessment is shown using fragility analysis. The results show that the presented fuzzy sensitivity analysis can give detailed insight into the characteristics of fuzzy random systems, and the epistemic uncertainty in derivation of limit states can have significant effects on the reliability‐based collapse analysis. It is worth mentioning that to alleviate high computational demands in fuzzy probabilistic collapse analysis, a neural network metamodel is applied in conjunction with the genetic algorithm which is also of practical value to engineers and researchers.

Buckling of Compressed-Bent RC Elements of Frame-Bracing Structural System at “Unknown” Accidental Impacts

The paper presents the results of studies of the buckling of the bearing elements of the new structural system, which consists of reinforced concrete precast-monolithic panels-frames produced industrially under a special accidental impact caused by a sudden column removal from the building frame. It is established that under special accidental impact caused by a sudden column removal from RC precast-monolithic structural system consists of industrial panel-frame elements, the reason of the fracture spreading within and outside local damage (fracture) zone may be the buckling of compressed-bent elements.

Static and Dynamic Responses of Reinforced Concrete Structures under Sudden Column Removal Scenario Subjected to Distributed Loading

In this paper, static and dynamic experiments on reinforced concrete beam-column frames under single-column-removal scenario applying a multipoint loading method were conducted. One of the objectives was to investigate structural behavior compared with the single-point loading method, which has been popularly used in previous studies. By equally applying point loads at four locations of the double-span beam structure, the test setup successfully simulated the uniformly distributed loading condition, which is generally applicable for gravity loads in practice. Compared with the previously conducted static tests based on concentrated loading method, structural response from the static tests under multipoint loading condition differed not only on load-bearing capacity but also on failure sequence and displacement profile. On the basis of the test results, the analytical relationship between behaviors of the two loading methods was developed and verified. Compared with the static tests, the dynamic tests highlighted dynamic effects created by the column loss event and confirmed the structural behavior and failure modes observed in the static environment. The dynamic tests also verified the correctness and conservatism of the dynamic assessment framework using a previously proposed energy-based approach. Most important, both the static and the dynamic tests of structures under distributed loads showed less development of catenary action against progressive collapse compared with concentrated loading tests.

An evaluation of modelling approaches and column removal time on progressive collapse of building

Over the last few decades, progressive collapse disasters have drawn the attention of codified bodies around the globe; as a consequence, there has been a renewed research interest. Structural engineering systems are prone to progressive collapse when subjected to abnormal loads beyond the ultimate capacity of critical structural members. Sudden loss of critical structural member(s) triggers failure mechanisms which may result in a total or partial collapse of the structure proportionate or disproportionate to the triggering event. Currently, researchers adopt different modelling techniques to simulate the loss of critical load bearing members for progressive collapse assessment. GSA guidelines recommend a column removal time less than a tenth of the period of the structure in the vertical vibration mode. Consequently, this recommendation allows a wide range of column removal time which produces inconsistent results satisfying GSA recommendation. A choice of a load time history function assumed for gravity and the internal column force interaction affects the response of the structure. This paper compares different alternative numerical approaches to simulate the sudden column removal in frame buildings and to investigate the effect of rising time on the structural response.

Impact of two columns missing on dynamic response of RC flat slab structures

Sudden removal of columns caused by unexpected extreme loading may increase the bending moment and shear force at surrounding column-slab connections significantly, which may trigger punching shear failure at these connections and lead to progressive collapse of entire reinforced concrete (RC) flat slab structures. To quantify the dynamic load redistribution of flat slab structures subjected to different extents of initial local damage (one-column or two-column removal), two multi-panel RC flat slab substructures were tested subjected to simulated sudden column removal scenarios. These two specimens have identical dimensions and reinforcement details. One of the substructures suffered a loss of an interior column scenario while another one was subjected to a two columns (one interior column and one edge column) missing scenario. The dynamic response, deformation shape, failure mode, and local strain gauge results are presented. It is found that although both specimens had exceeded their yield load capacity, no collapse occurred as considerable compressive membrane action developed in the RC slab to help redistribute the loads. With the drop panels, no punching shear failure was observed in the slab-column connections after removal of the column. To further study the progressive collapse robustness of flat slab structures, finite element (FE) models were validated and parametric studies were carried out. Numerical analysis indicated that the axial force initial carried by the lost columns may amplify up by 1.25 times before redistribution into surrounding columns. Moreover, the dynamic ultimate load capacity of Specimens S1 and S2 are as large as 1.92 and 1.18 times of their design service load, respectively.

Experimental study on progressive collapse resistance of steel frames under a sudden column removal scenario

A comprehensive experimental apparatus for the progressive collapse testing of steel frames has been developed. The apparatus is suited for the testing of planar steel frames to study the load transfer process and the progressive collapse resistance of steel structures under a column removal scenario. In order to simulate a sudden removal of a middle column at the ground storey of the frames, a removable column unit has been designed to allow for an instantaneous knock-out by a pendulum hammer during the test. To avoid the out-of-plane instability of the planar steel frames, an out-of-plane restraining system has been designed and integrated into the test apparatus. Weights simulating the desired gravity loads were attached to the test frame through holding baskets, which were designed to minimize unwanted shaking and ensure that the suspended baskets moved together with the deformed steel frames during the tests. Experimental results showed that the column removal mechanism in the test apparatus was effective. Using this apparatus, the dynamic behaviour of three planer steel frames under a column removal scenario was investigated. Based on the measured deformations and strains, the dynamic response, collapse modes, load transfer path of the steel frames after the removal of the middle bottom column are studied.

Analysis of robustness of steel frames against progressive collapse

A finite element (FE) modelling study on the progressive collapse of steel frames under a sudden column removal scenario is presented. The FE models were developed with refined shell elements using the general purpose FE software package ABAQUS. The FE models were first validated by comparing the predicted responses with the measured results from an experimental study on the progressive collapse of three steel frame specimens. A new bearing capacity-based index was introduced to quantify the robustness of the steel frames. The robustness index takes into account the dynamic effects and the plastic internal force redistribution. By incorporating the experimental results and the numerical simulations, the dynamic amplification factor in the progressive collapse of the steel frames was assessed. The validated FE models were further applied to identify the collapse modes of planar steel frames and evaluate the influences of a range of mechanical and geometrical parameters on the progressive collapse and the robustness. The results showed that, for a column-instability induced progressive collapse mode, the influences of the damping is larger than the influences of the strain rate of material on the robustness. However, for the connection-failure induced progressive collapse mode, the influences of the strain rate is larger than the damping. The type of the steel frame (e.g. weak-beam strong-column or vice versa) and the location of the column removal were both found to play an important role in influencing the critical load and the robustness of steel frames.

An Investigation of the Effect of Semi-rigid Connections on Sudden Column Removal in Steel Frames

The semi-rigid behaviour of beam-to-column connections has an important effect on the performance of steel frame. This paper proposes a multi-spring component (MSC) model for assessing the rotational stiffness of semi-rigid beam-to-column connections. The main benefit of the MSC model is its ability to easily determine the response of semi-rigid beam-to-column connections in frame analysis. The MSC model is first validated through comparisons with 3D finite element method modelling and experimental test results, where good agreements of load rotation responses are generally observed. Then, using the MSC model, the semi-rigid connections in the frame were modelled by using rotational springs, and the ground floor columns were suddenly removed in sequence. The response of the remaining frame to this sudden removal was obtained through numerical simulation. The results of this simulation showed that the effect of the semi-rigid connection is crucial in the load-distribution and the frame deformation, and the influences of the column loss location and column removal time on frame response were discussed. The MSC model is design-effective and hand-calculable, and thus it brings convenience to the robustness assessment of steel frames suffering single column loss with considering semi-rigid connection and catenary action.

06.03: Dynamic increase factor for nonlinear static alternate path analysis of steel moment‐resisting frames against progressive collapse

ABSTRACTThe paper investigates the dynamic increase factor to be assumed in the nonlinear pushdown analysis of seismically designed steel moment‐resisting frames as a consequence of sudden column removal. The influence of the fundamental parameters, as well as the effect of various design variables, such as the number of stories, the number of bays, the location of the removed column and the level of seismic design load were investigated. The dynamic increase factor was estimated by direct comparison of static analysis with full nonlinear dynamic analysis. Eventually, the values obtained were expressed as a function of the vertical displacement at the location of the removed column and then compared with the GSA formulation based on the ductility factor.

Nonlinear Performance of Extended Stiffened End Plate Bolted Beam-to-column Joints Subjected to Column Removal

This paper presents a numerical study on the behavior of extended stiffened end plate bolted beam-to-column joints subjected to sudden column removal. To this aim, finite element analyses, validated against experimental tests available from literature, were carried out to investigate the response of the joints under catenary action. The influence of additional bolt rows, generally ineffective in case of design for pure bending response, was also examined and some practical design implications have been drawn up from the parametric study.

Assessment of eccentrically braced frames strength against progressive collapse

One of the most important and effective factors of structural strength against the risk of progressive collapse is the type of lateral load bearing system of a building. In this research, strength of dual steel moment frames equipped with a variety of eccentric bracings against progressive collapse was evaluated by using nonlinear static alternate path method. 6-floored building samples were designed with steel frame using a dual steel moment system together with 3 different types of bracing, including inverted eccentrically V-shaped bracing (chevron bracing), eccentrically V-shaped bracing and eccentrically X-shaped bracing, each with two different kinds of arrangement of bracings in the structural plan, in form of alternate and neighbor. The effects of sudden removal of columns on different floors of these buildings were examined. These studies showed that dual steel moment frames equipped with eccentric bracings generally exhibited desirable strength against progressive collapse. A change in the type of bracing resulted in significant changes in the system capacity in the progressive collapse. Among the different types of braces assessed, chevron type eccentrically brace showed higher strength against progressive collapse. Also, that alternate arrangement of bracings in structure plan demonstrated better performance than neighboring arrangement.

Experimental study on dynamic responses of reinforced concrete frames under sudden column removal applying concentrated loading

This paper focuses on structural behaviour of storeys above the targeted column that is suddenly lost due to accidental/terrorist events. The pertinent question is whether these storeys will remain stable, or the ensuing dynamic motion will cause them to fail during the free-fall stage. It is assumed that the two-dimensional frame structure above the targeted column is in pristine state. Previous quasi-static studies on reinforced concrete beam-column structures under missing column scenario have highlighted the potential of catenary action on providing alternate load paths to prevent catastrophic collapse. However, corresponding dynamic tests, either did not share the same loading configuration with the static tests, or did not have sufficient headroom and the specimen hit the ground before catenary action could be fully mobilised. On this paper, a series of dynamic tests was carried out for two-dimensional reinforced concrete beam-column frames simulating the sudden removal of a supporting column via a quick-release device. The specimens were loaded and hung by a mechanism which could be released to effect free vibration. Development of catenary action, which has not yet been confirmed in any previous dynamic tests, was well captured. The study also showed the influence of inertial and strain rate effects on structural response. Most importantly, the dynamic tests applied the same method of concentrated loading at the middle joint as the previous quasi-static tests conducted on similar specimens. As a result, comparisons could be made on damage patterns and failure modes between the dynamic tests and the static tests. Compared to static environment, the dynamic tests only took a few seconds and their behaviours are closer to the actual behaviour of the storeys that undergo free-fall acceleration.