Corner Column Research Articles

The Effect of Out of Plane Perpendicular Beams on the Ductility Demand of Steel Moment Framed Structures during Progressive Collapse

Unexpected loading, induced by severe earthquake or blast, could cause local damage to a structure. In this case, the structure has the potential of progressive collapse phenomenon. Hence, further consideration is required to mitigate the consequences of such loading. This study is aimed to evaluate the progressive collapse capacity of steel moment frames with different heights under column removal conditions. Seven and twelve story buildings modeled in different conditions in order to view effects of various parameters like the out of plane frames, column removal location, and the height of buildings in the results. One of the middle column and/or the corner columns is removed in order to evaluate the effect of column removal location in response of structures. The General Services Administration and the Department of Defense guidelines are considered for defining load combination for the analysis of the collapse. Nonlinear dynamic analysis is conducted in order to obtain the ductility demand of structures when the out of plane effect is considered. The structures have welded cover plate connections, designed for high-seismic zone area. For evaluating the response of the structures, for each connection at the point of column removal, maximum vertical displacement is measured. For Finite Element analysis, a sub-assemblage of structures is modeled using ABAQUS software and the ability of beams deformation and it’s out of plane effect is measured.

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.

Testing robustness: A full-scale experimental test on a two-storey reinforced concrete frame with solid slabs

This paper presents the results of a full-scale robustness test carried out on a two storey building with two square reinforced concrete slabs (25 cm deep) with a span of 6.6 m, in which a corner column was suddenly removed. Despite the extreme action, and the fact that the slab was not designed for it, only relatively minor damage was observed, with a maximum deflection around 22 cm and apparently controled cracking patterns. The slab started working as a simply supported element along the symmetry axis of the structure supported on only 3 columns. The tests was modeled using Finite Element Analysis. It was observed that the model could capture very well the behaviour of the real structure, predicting very similar cracking patterns and deflections. The structure was shored two hours after the test because deflections were not yet fully stabilized. It is suspected that this increase of deflections could be related to the deterioration by torsional effects of the connection between the slab and columns on the first floor.

Seismic behavior of steel reinforced concrete L-shaped columns under compression-bending-shear-torsion combined action

The L-shaped column is usually used as a corner column in buildings, which can be one of the weak members in the structural system. Because of the asymmetry of an L-shaped column, it is more complex in structural layout and mechanical performance. To study the seismic performance of steel reinforced concrete (SRC) L-shaped columns under compression-bending-shear-torsion combined action, twelve SRC L-shaped columns were tested in this paper. The main variables included the shaped-steel layout, the torsion-bending ratio and the ratio of limb height to limb thickness. Based on the test results, the failure modes, hysteretic curves, ductility, stiffness degradation and energy dissipation were compared and analyzed. The results show that the failure modes of SRC L-shaped columns mainly depended on the torsion-bending ratio, which could be divided into bending failure, bending-shear failure and bending-torsion failure. The shaped-steel layout had an effect on the final damage degree of the specimens. Increasing the torsion-bending ratio could improve the torsion resistance of the specimen, but the bending capacity became weaker and the stiffness degradation was faster. The ductility and energy dissipation of SRC L-shaped columns could be enhanced by reducing the ratio of limb height to limb thickness. Comprehensive analysis showed that the empty-web T-section SRC L-shaped column had superior seismic performance under compression-bending-shear-torsion combined action.

Experiment on crack resistance of prestressed CFRP tendons-steelreinforced concrete members under eccentric tension

In our country, there are many eccentric tension members, such as steel reinforced concrete truss transfer layer straining beam, low-rise building corner column. For these members, large-scale cracks easily appear during normal use stage. Aiming at these problems, this paper took the light, high-strength and anti-corrosion carbon fiber reinforced polymer composite (CFRP) tendons as the prestressed reinforcement, the prestressed CFRP-steel reinforced concrete structure system was designed by combining CFRP tendons with prestressed steel reinforced concrete, which can effectively restrain the crack. And on this basis, a systematic study on the crack resistance under eccentric tension was carried out. A total of eleven members were designed and fabricated with the prestress level, eccentricity, longitudinal reinforcement diameter and profile flange thickness as the main parameters, and eccentric loading was achieved through the self-developed tension-compression conversion truss system. The results indicate that the crack resistance of the prestressed CFRP tendons-steel/concrete members is greatly strengthened. Compared with the ordinary eccentric members, the cracking loads of the large tension members with prestressed CFRP tendons are increased by 64.8%–102.3%, the cracking loads of the small tension members with prestressed CFRP tendons are increased by 61.7%–117%. The crack resistance of the member is positively related to the prestress level, longitudinal reinforcement diameter and steel flange thickness, and negatively related to the eccentricity. With reference to the combined structural design specification, three positions of the neutral axis of the prestressed CFRP tendons-steel reinforced concrete members during the cracking stage are proposed, and the calculation formula of cracking load is derived. Compared with the test value, the agreement is perfect, which can provide a reference for the application of other composites in the prestressed eccentric tension system.

Performance of typical plan concrete buildings under progressive collapse

Many engineers are interested in the progressive collapse phenomenon, considering multi-user typical buildings, construction bias toward economization and thus, reduction of material consumption. The key factor in progressive collapse is the disproportion between the initial and final damage which sometimes can lead to the destruction of the whole building. So, the efforts are focused to prevent the expansion of initial damage through some strategies such as strengthening some load-bearing elements or choosing a proper plan. GSA and UFC regulations are two very reliable resources regarding the progressive collapse in which the alternative path method (APM) is one of the most common methods to evaluate building response to progressive collapse. In this study, the influence of typical concrete building plans (i.e. square and rectangular) on progressive collapse is investigated by 3D modeling of the buildings using LS-DYNA finite element software and removing a corner column using APM, considering GSA and UFC regulations. The results indicate that removing a corner column in the rectangular building has more intense effects including doubling the downward collapse rate, increasing the shear and axial loads in columns by 1.5 times, reciprocating motion of shear loads and higher energy absorption rate in comparison with those in the square building.

Dynamic Punching Assessment of Edge Columns after Sudden Corner Column Removal

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Progressive collapse of RC flat slab substructures with unbonded posttensioning strands after the loss of an exterior column

Reinforced Concrete (RC) flat slab structures are mainly composed of load-bearing columns and RC slabs, which are vulnerable to collapse once one or several local load-bearing columns fail due to accidental loads such as terrorist bomb attack or vehicle collision. To investigate the progressive collapse performance of flat slab structures after the loss of an exterior column, static collapse tests were conducted on three 1 × 2 bay RC flat slab substructures. Effect of prestress and layout of the unbonded posttensioning strands (UPSs) on the progressive collapse of flat slab structures was discussed. Experimental results showed that punching shear failure (PSF) foremost occurred at the slab-column connection (SCC) of the failed exterior column during collapse, and then successively occurred at the SCCs close to the corner column and the exterior column adjacent to the failed column. Primary cracks on the top slab surfaces around the failed exterior column generally presented arc-shaped distribution; while primary cracks on the bottom slab surfaces radially propagated from the failed exterior column. Comparing with the flat slab substructure without UPSs in the slabs, the load-bearing capacity of the substructures with UPSs in the slabs significantly improved. Flexural action was the fundamental collapse resistance mechanism in the initial collapse stage, and tensile membrane action gradually formed during collapse. The flexural action, the tensile membrane action, as well as the post-punching behaviors of the slabs resisted the collapse load together before the final collapse occurred. Most of the load applied on the failed exterior column mainly transmitted along the shorter slab bay under the exterior-column-removal scenario. Arranging posttensioning strands in the slabs contributed to reducing vertical deformation of the slabs. The UPSs in the column strip passing through the failed column played a more important role in resisting collapse load than those arranged in the middle strip. The residual flat slab substructures still possessed satisfactory load-carrying capacity even if PSF occurred in one or several SCCs.

Numerical Study on the Behavior and Bearing Mechanism of Flat Slabs in Column Loss Events

This study investigates the behavior and the load-bearing mechanism of a typical flat slab with rectangular panels in several scenarios including the removal of a corner, penultimate, and internal columns. The scenarios are rather similar to those used in the conventional evaluation of the progressive collapse potential; however, application of the uniformly distributed loading over panels adjacent to the removed columns was not limited to twice the value of the initial load. Thus, load-deflection curves were drawn up to the point in which a great number of longitudinal slab bars ruptured. Introducing 5 stages on each curve, finite element outputs on concrete cracking pattern and rebar stress state were presented. A significant increase in the stresses along the diagonals of the slab panels accompanied by bar ruptures around columns adjacent to the removed column proved contribution of an important load-bearing mechanism in addition to the behavior called “quasiframe action.” Consecutive rupture of bars showed formation of a zipper-type collapse mode as well as a great tendency to transfer load share of missing column mainly along shorter direction of slab panels. Moreover, the findings indicated that the slab damaged zone could exceed the panels under uniform overloading.

Improved progressive collapse resistance of irregular reinforced concrete flat slab buildings under different corner column failures

As the flat slab building with irregular geometric configurations is commonly designed to advance urban development and for architectural demands, its behaviour to resist progressive collapse must be examined. The building's progressive collapse occurs when one or more vertical structural load-bearing elements such as columns are removed due to an extreme load caused either by natural or manmade hazards. The present analytical research examines the failure criteria and improvement in the progressive collapse resistance of five and ten-storey irregular R.C flat slab building by incorporating perimeter beams along with strengthened perimeter columns in the building. The progressive collapse study is conducted by removing different corner columns on the ground floor as per the GSA guidelines (2003) and assessing the spread of damage. Static analysis is performed using the structural analysis program ETABS 2016. For each case, the results have been taken in terms of demand capacity ratio (DCR) at critical sections and, chord rotation and joint displacement at locations of removal of columns. The results showed that the presence of strengthened columns provides sufficient stiffness and the perimeter beam provides load paths for the building's gravity loads, thus making it resistive to progressive collapse under column failure.

Evaluation of seismic torsional response of ductile RC buildings with soft first story

This study investigates the inelastic torsional response of plan asymmetric ductile RC buildings with a soft first story. The buildings of Rectangular, L, T, and U plan shapes are considered for the study. Force-based fiber beam-column elements are modeled for the inelastic response prediction of the buildings. Masonry infill walls are uniformly distributed in the plan and considered for the evaluation of torsional response. The pushover methods, Extended N2 and Extended Capacity Spectrum Method – FEMA 440 are adopted to estimate the inelastic torsional response. Bi-directional nonlinear time history analysis is carried out on the buildings considering near-field and far-field ground motions. Story drift ratio and curvature demand-capacity (D/C) ratio of columns are reported at the stiff, flexible side of buildings. The torsional response of infill wall buildings is compared with that of bare frame buildings. It was observed that the torsionally irregular ductile buildings with soft first story exhibit higher seismic demand on the flexible side corner columns. Infill wall interaction amplifies the torsional response at the bottom story, causing an increase in displacements higher at the flexible side and moderate near the stiff side. This study concludes that the flexible side corner column in plan asymmetric building with a soft first story can be conservatively designed for 1.5 times the design forces obtained from the analysis. This conservative design ensures stable energy dissipation in the corner column under load reversals, without significant strength reduction under higher excitation levels. The designer shall properly distribute lateral load resisting elements in a plan to prevent premature failure of the columns located internally and close to the initial center of rigidity. The designer can avoid the collapse of columns located internally in the buildings with stiff peripheral frames by designing for forces 1.5 times higher than obtained.

Case study on strengthening methods for progressive collapse resistance of RC flat slab buildings

The progressive collapse of buildings may result in major financial losses and fatalities, so reducing the chances of such occurrences is of paramount importance. Due to the absence of beams for redistribution of gravity loads that were initially resisted by the missing column, flat slab buildings are more prone to progressive collapse than moment frame buildings. Thus, flat slab buildings should necessarily be assessed for progressive collapse and strengthened accordingly in order to avoid the likelihood of progressive collapse. This study evaluates the efficacy of three different strengthening methods for reducing the potential for progressive collapse of a validated 3-bay by 3-bay 4-storey flat slab building simulation model, subject to alternate, simultaneous and sequential removal of columns in the first storey. Corner, edge and interior columns of each building model are statically and instantaneously removed and the static and dynamic response of the building is compared for different removal sequences. The three strengthening strategies investigated are the addition of perimeter beams, the addition of shear walls and the addition of both perimeter beams and shear walls. The results are evaluated in terms of the vertical displacements at the top of the removed columns and the DCR of the sectional forces of critical adjacent columns, for which the acceptance criteria provided for DCR by the GSA is used to assess the vulnerability of the studied building to progressive collapse. The results show that perimeter beam, shear wall and combination of both perimeter beam and shear wall improve the progressive collapse resistance of the studied building by reducing DCR of critical columns by up to 67.0% and reducing the vertical displacements at top of the removed column by up to 81.0% depending on the different column removal cases.

Flexural behaviour of stiffened and multi-cell L-shaped CFSTs considering different loading angles

Stiffened and multi-cell L-shaped concrete-filled steel tubular (CFST) members are often subjected to the loads from different loading angles as corner columns. Moreover, the flexural behaviour is the basis for the research of beam-columns and the determination of axial force-bending moment interaction curves. However, little work has been done on the flexural behaviour of these kinds of members at different loading angles. In this study, a total of 11 L-shaped CFST specimens with the variables of sectional type and loading angle were tested under pure bending. The failure mode, bending moment-deflection curves, moments-strain curves, deflection curves, flexural capacity and stiffness were investigated. It was found that the influence of loading angles is significant. The flexural capacity and stiffness of the specimens are highest at 135°, middle at 0° and 180°, and lowest at 45° and 225°. Setting longitudinal stiffeners or using multi-cell cross-section can improve the flexural capacity by about 20%. Then a finite element model was developed incorporating residual stress and cold-formed effect. Considering the effect of loading angles on the basis of the design model at 0°, the simplified formulas for flexural capacity of the stiffened and multi-cell L-shaped CFST members were proposed.

L-shaped concrete-filled steel hollow-section columns under diagonal cyclic loading

L-shaped concrete-filled steel hollow-section (CFSHS) columns have the potential to be widely used as corner columns, and have the advantage of creating larger usable areas in buildings. However, few experimental tests of this kind of column under diagonal cyclic loading have been reported. Tests on eight L-shaped CFSHS columns with equal legs were conducted to study their hysteretic behaviour; the test variables were: loading angle, concrete compressive strength, axial load level and presence or absence of stiffeners. The failure process and modes, stiffness degradation, ductility and energy dissipation were observed, and lateral load–displacement hysteretic curves and envelope curves were plotted. The results show that L-shaped CFSHS columns have generally good hysteretic behaviour and that the displacement ductility coefficients are in excess of 3 in most cases. Columns with a loading angle of 45° have >10% decrease in ultimate strength but a slightly higher ductility than columns with a loading angle of 0°. The ultimate strength, ductility and energy dissipation of columns all decrease with increasing axial load levels. Discontinuously welded stiffeners can improve the ultimate strength and ductility, but the amplitude is limited. Finally, a finite-element model was developed; the predicted results agree well with the test results.

Influence of wind speed on a Reinforced Concrete tall building

This study is conducted to assess the influence of wind on a 17-storey multipurpose Reinforced Concrete Tall Building according to the revised wind code of IS 875 (Part 3): 2015 compared to its previous version i.e., IS 875 (Part 3): 1987. The study covers all basic wind speeds of 33, 39, 44, 47, 50 and 55m/s as specified in the Indian standards. Dynamic effects due to ‘Along wind’ and ‘across wind’ are considered in the analysis using ETABS evaluation software. The Lateral load, Lateral sway and Longitudinal Rebar Percentage (LRP) are found to be increased as per the revised version. The LRP in the Middle, Edge and Corner columns are also reported. An increase of total Rebar quantity by about 3.7% (beams and columns) in the entire structure for a basic wind speed of 50m/s is observed.

Building wall corner structures, its microclimate and seismic resistance

Widespread low-rise residential buildings with a seismically resistant concrete frame and brick infill walls have lower microclimate levels in cold seasons due to low temperatures on the inner wall corner surfaces.These temperatures are lower if there is a corner column. For Bishkek, this temperature is 4.6 °C lower than that for permissible microclimate, even when the external wall has the required 70 mm of mineral wool slab insulation. It is caused by the negative effect of the wall corner thermal bridge. This effect is determined by ArchiCAD 20 software packages by visualizing the temperature distribution in the cross-section of the corner, which needs an additional thermal insulation layer of 40 mm. Using the LiraSAPR 2013 software package, the authors reduced the square cross-section dimensions of the column by 40 mm to allow for that additional thermal insulation layer. The optimal width of this layer is determined for different options for the meeting angle of two external walls from 70° to 180°. For a typical 90° angle, an acceptable width is 860 mm. With this insulation, it is possible to achieve the required temperature at the corner. The authors eliminated the negative thermal effect of the corner by rounding it with cement-sand plaster. Using the isotherms, it was determined that the rounding radius of 300 mm allowed for equal temperatures on the corner and inner surface of the external walls. The achieved results show that the microclimate formed as in a room without external wall corners.

Simulation analysis on continuous collapse resistance of assembled building structure under multi-dimensional earthquake

Under the multi-dimensional earthquake, the random damage of the building column structure is large, and the analysis of the continuous anti collapse performance of the building structure is limited. Therefore, the simulation analysis of continuous anti collapse of assembled building structure under multi-dimensional earthquake is proposed. Through the analysis of the undamaged structure of the building, it is found that under the action of multi-dimensional earthquake, if the long side column, corner column and inner column of the building structure are damaged, it may lead to the collapse of the assembled building structure. The test results show that the continuous collapse caused by inner column demolition is the strongest, followed by long central column, corner column demolition will not cause the continuous collapse of the building structure.

Progressive collapse analysis study of rc building:a review

The progressive collapse of building is that the collapse of whole building or a part of building in progressive manner thanks to spread of local failure from element to element. thanks to progressive collapse there'll be severe loss of building and lifetime of humanity as progressive collapse happens suddenly. Toavoid the loss got to design a building by proper study and analysis of building for progressive collapse. thanks to earthquake, blast, vehicular sudden impact, etc if the column isn't capable to face up to sudden impact then column may get failed and due that other columns also get failed, which causes loss of whole structure. A linear static analysis and non-linear dynamic analysis using time history method is administered using finiteelement software. Two column removal eventualities particularly corner and middle column removal situation area unit thought of. In Linear Static analysis Demand capability Ratio(DCR)values and member acceptance criteria area unit thought of and Non-linear Dynamic Analysis (NDA)Time vs Displacement, most Axial force, bending moment results wherever the column is removed associate obsolete as base for comparison area unit calculated to know the potential for progressive collapse of a structure. Key Words - RC frame buildings, Progressive, Linear Static, Non-linear Dynamic.

Progressive collapse of reinforced concrete buildings considering flexure-axial-shear interaction in plastic hinges

Progressive collapse assessment of a reinforced concrete (RC) building designed only for gravity loads and lacking a dedicated lateral load resisting system was carried out using the alternate load path (ALP) method and finite element method (FEM) numerical model created in software SAP2000. Plastic hinge capacity of the members was evaluated considering flexure (M), axial force (N) and shear force (V) interaction and a validated procedure was devised to incorporate the plastic hinge capacity based on M-N-V interaction into the results obtained from the FEM model. It was found that consideration of M-N-V interaction resulted in plastic hinge capacities that were lower than the flexure-only capacity of the plastic hinges available in the FEM software which caused the progressive collapse to initiate at a lower load and also resulted in increased collapse area. In the second part of the study, it was demonstrated that the progressive collapse resistance of the building for the interior and the edge column removal scenarios was appreciably improved after ordinary moment frames were cost-effectively designed at selected locations without increasing member cross-sectional dimensions. However, key element design concept approach was needed for improving the progressive collapse performance for the corner column loss scenarios. Relative reduction in the plastic hinge capacity due to M-N-V interaction as compared to flexure-only hinge capacity was found to be lower for the redesigned building due to improved member capacity.

Progressive collapse assessment of precast prestressed reinforced concrete beams using applied element method

Due to the repetitive progressive collapse events, it became necessity to form theories of designs against those cases of loadings. Prestressed reinforced concrete elements become widely used in construction field due to various properties that contribute to enhancing the overall structural stiffness, increasing the loading capacity, and elevating the crack resistance threshold compared to the non-prestressed elements. However, few researches in prestressing members and its capacity towards progressive collapse is covered. According to the Unified Facilities Criteria (UFC) and the General Services Administrations (GSA) guidelines, the pre-stressed precast structure’s assessment under progressive collapse are taken into consideration using approximate solutions for analysis. The UFC stated the types of the structure under progressive collapse assessment regardless of the structural system used. This is a great challenge needs a lot of experimental and numerical testing and validation. In this research, a numerical analysis is carried out for a typical five-story framed prestressed precast reinforced concrete structure subjected to column loss (corner column, edge column and internal column near to the structure’s edge), and designed according to Precast/Prestressed Concrete Institute (PCI) and (ACI 318−14). Non-linear dynamic analysis for the structure was carried out using Extreme Loading for Structures (ELS) software depending on the AEM. The investigation was done on two levels. Total collapse took place in case 1. As a result, the necessity of extending the research to include case (2) is essential for having an overview assessment of this type of structures. Case 2 showed high capability to resist progressive collapse against all column removal scenarios. The results are indicated in terms of; prestressed beam behavior, prestressing cable contribution, and flexure and axial loads’ changes with respect to time. Beam and column rotations are calculated and compared to the UFC limitations to assess its safety towards progressive collapse.