Corner Column Research Articles

МЕТОДИКА ЭКСПЕРИМЕНТАЛЬНОГО ОПРЕДЕЛЕНИЯ ПАРАМЕТРОВ ЖИВУЧЕСТИ СБОРНО-МОНОЛИТНОГО ЖЕЛЕЗОБЕТОННОГО КАРКАСА

The article presents a technique for carrying out experimental and numerical studies of reinforced concrete frame-fragments of a prefabricated monolithic reinforced concrete structural system of multi-storey buildings. The purpose of the research was to determine the nature of the change in the parameters of static-dynamic deformation and force resistance of the proposed structural system both at the stage of operation and during an emergency impact caused by the shutdown of one of the elements - the corner column of the first floor. To increase the resistance of the system under study to local or progressive collapse, new design solutions for the crossbars of the prefabricated monolithic frame are proposed, which make it possible to increase its resistance to a sudden change in power flows in the structural system under consideration. Analytical dependencies are proposed to determine the parameters of the intermedium contact zone in the prefabricated-monolithic structure of the crossbar. The solution of the problems under consideration was carried out using the LIRA-SAPR software package, taking into account material operation diagrams that take into account the static-dynamic nature of the loading of structures. The substantiation of the adopted design solutions for experimental designs of frame fragments for developing a program for conducting experimental studies of the structural system under consideration under special effects is given.

Experimental and theoretical analyses of the progressive collapse resistance of NSM strengthening RC frames after the failure of a corner column

When exposed to accidental loads, reinforced concrete (RC) frames are vulnerable to progressive collapse after the failure of a corner column, so necessary strengthening schemes should be employed for the frame. By strengthening the slab with near-surface-mounted (NSM) glass fiber-reinforced polymer (GFRP) bars and engineered cementitious composites (ECC) layer, this study experimentally revealed the effect of the strengthening method on the progressive collapse behavior of beam-slab systems after the removal of a corner column. Then, on the basis of experimental results, a theoretical analysis method of the peak capacity for the beam-slab system is proposed according to the principle of virtual work and the yield-line theory. The derived formula can accurately predict the progressive collapse resistance of the RC beam-slab system after the failure of a corner column and quantitatively evaluate the contribution of floor slabs to the structural capacity. The validity of the method is also proven by the application to the structural capacity of a flat-slab system and a beam-column system. Finally, according to the theoretical formula, the influence of several parameters on the structural capacity is investigated, such as the earthquake fortification intensity of the frame, the over-strength factors, the column spacing, and the depth-to-span ratio of the beam. The research results demonstrate that after considering the L-beam action, the capacities of the test specimens can be improved by 52%–65%. The capacity of the flat-slab system is the lowest among the above three structural systems. The structural progressive collapse resistance can be effectively improved through enhancing the constraint stiffness of the corner beam-column joint and utilizing building materials with high plastic development ability.

Seismic Performance of Buildings with Various Configurations in Hilly Regions

Structures on incline ground are vulnerable to earthquakes because of irregularities in plan and elevation. The structural configurations on slopes have been observed, with stepback and stepback-setback configurations being the most common. In mid to high rise buildings, shear wall and C-shaped shear wall cores are commonly used lateral load resisting components. The current research focuses on comparing the seismic performance of L-shear walls(LSW) at the corners, C shear-walls at core(CSW) and Reinforced concrete-filled steel tube column (RCFST) at corners and cores in stepback, and stepback-setback configurations buildings considering the base of the structures fixed designed for Indian codes using response spectrum analysis. The structural analysis tool ETABS 2017 was used to perform seismic analysis. Buildings on a hill slope with various configurations are studied: bare frame, concrete blockwork infill, LSW full bay at corners, LSW half bay at corners, CSW and RCFST column at corners and core. The characteristic parameters such as base shear, forces in the columns at the ground floor, storey drift, maximum storey displacement, time period, the bending moment in columns at every floor level and storey shear in structures will be determined and analysed for the different structures at the sloping ground. Structures with corner LSW perform better than buildings with centrally located shear walls at the core, whereas LSW at half bay in the corner and RCFST columns at corners and core serve the dual objective of space constraint and improved performance.

Study on Collapse Resistance of RC Frame under the Corner Column Removal Scenario.

The progressive collapse of buildings induces a variety of catastrophic consequences, such as casualties and property loss over the past few decades. The corner column is more prone to abnormal load events compared to the inner column and outer column; thus, it is easier to trigger progressive collapse. By considering the effects of floor slabs and adjacent bays on progressive collapse behavior, the pseudo-static loading method was used to study the progressive collapse test of a 1/3 scaled, one story, 2 × 2-bay cast-in-place reinforced concrete frame substructure under the removal condition of a corner column. The test results show that the flexural deformation principally concentrates upon the components of a directly affected part (DAP), and compressive arch actions are observed in members of the indirectly affected part (IAP). Moreover, the slab adjacent to the removed column and periphery elements contributes great resistance to a progressive collapse.

Axial compression behaviours of tubular sectioned C-shape continuous-supported steel walls in MSB

The ultimate strength behaviour of C-shaped continuous-supported walls employing hot-rolled structural hollow section (SHS) columns in modular steel buildings (MSB) was evaluated using two full-scale axial compression tests. The columns' width-to-length (D/B), width-to-thickness (D/t), and material strength were considered experimental parameters. A three-dimensional (3D) finite element (FE) model was validated against test results, accounting for geometry and material nonlinearities while projecting ultimate strength and failure behaviour. The size, spacing, number of columns, stiffener thickness and sidewall effects were evaluated in a parametric analysis. The columns compressive resistance was predicted using prediction equations from EC3:1-1, AISC360, and GB50017. The results revealed that the column nominal strength was reduced to achieve compression yielding due to columns stiffness differences, mutual constraints, and elastic buckling. If the buckling length is considered or omitted, the EC3:1-1 slenderness limit for Class 3 steel members becomes less conservative. Reducing column size and spacing or increasing stiffener size and number improves column and wall compressive behaviour; however, the sidewalls improved the corner columns constraint while weakening the front wall. GB50017 predictions were the safest; whereas, EC3:1-1 made the most unsafe predictions when buckling was not taken into account.

Dynamic response of RC beam-slab substructures following instantaneous removal of columns

High fidelity solid-element-based numerical modeling is employed in this paper to study the dynamic response of reinforced concrete (RC) beam-slab substructures following instantaneous removal of columns. After validation of the numerical model against experimental results, incremental dynamic analysis is conducted to obtain the dynamic structural resistance to progressive collapse. The numerical results for development of internal forces and distribution of stress and strain are used to illustrate the load redistribution and load transfer mechanisms of RC beam-slab substructures subjected to sudden loss of columns. The numerical model is further employed to explore parameters affecting the dynamic response and structural resistance of beam-slab substructures under sudden column removal scenario. The parameters studied include damping ratio, slab thickness, location of removed columns, multi-column removal sequence and interval. The numerical result shows that the dynamic progressive collapse resistance of the beam-slab substructure is much smaller than the quasi-static test result due to a dynamic increase factor (DIF) of 1.14. Moreover, a minimum slab thickness of 1/45 of span length is found vital for the improvement of progressive collapse resistance of RC beam-slab substructures through developing compressive membrane action (CMA) and tensile membrane action (TMA) as well as enhancing the development of compressive arch action (CAA) and tensile centenary action (TCA) of beams. When the damping ratio is smaller than 5%, the increase of damping ratio can significantly benefit the structural resistance against progressive collapse by producing smaller deflection and milder vibration. The additional loss of the corner column besides the penultimate perimeter column is found to form the most hazardous situation among the double-column removal scenarios. In contrast to the location of removed columns, the column removal sequence and interval tend to little affect the maximum deflection developed and consequently the progressive collapse resistance of substructures.

Impact of seismic retrofitting on progressive collapse resistance of RC frame structures

Most of the existing buildings in seismic prone regions have been built before the publication of modern design provisions against earthquakes, resulting in the need for structural retrofitting. Furthermore, some of those buildings are also subjected to additional hazards that may be either triggered by earthquakes (e.g., landslides, soil liquefaction, tsunamis) or associated with other natural or anthropogenic events, such as floods, vehicle collision, blast, and fire. A multi-hazard performance assessment of building structures is thus of paramount importance to implement integrated retrofit strategies, which otherwise would not be economically sustainable if oriented to structural risk mitigation against a single hazard. While retrofit strategies to improve the seismic performance of reinforced concrete (RC) structures have been widely investigated, structural retrofitting against progressive collapse has received very little attention. Within this context, the present paper illustrates a numerical investigation on the influence of seismic retrofitting on structural robustness of a four-storey, five-bay, RC frame building designed only to gravity loads. Seismic performance and structural robustness were respectively evaluated in OpenSees through pushover and pushdown analyses of a fibre-based finite element model. Structural robustness was evaluated under two relevant column-removal scenarios, i.e., the sudden loss of a central and a corner column, whereas earthquake resistance was assessed according to the N2 method, evidencing the need for seismic retrofitting. A retrofit measure based on carbon fibre reinforced polymers was then considered to avoid premature brittle failures. Analysis results show that this retrofit strategy was able to increase both seismic safety and structural robustness. Subsequently, a parametric analysis was carried out in order to evaluate the impact of beam span length and shear strength of the retrofitting system.

Robustness of multistory corner‐supported modular steel frames against progressive collapse

SummaryIn current practice, a relatively wide range of different interconnections and assembly systems is being used for the design of modular buildings made of volumetric prefabricated frames. The integration strategies and design criteria for providing structural robustness or prevention of disproportionate collapse for such buildings are completely different with those with conventional systems. This is mainly because of their fundamentally different configuration of joints and the redundancy they provide for the structure. This paper studies the robustness of multistory modular structures, made of prefabricated volumetric steel frames, against progressive collapse, which can be triggered by various column or module loss scenarios. In this study, the flexibility of modules and propagation of the damage inside the individual modules are taken into account, and the buckling of columns, as well as the effects of material nonlinearity on the responses and capacity of the entire system, are also considered. Load redistribution patterns and possible gravity‐induced collapse mechanisms are inspected in various collapse scenarios for a typical mid‐rise modular steel frame. In the numerical model, each individual prefabricated volumetric module is composed of discrete beam and column frame elements, connected through conventional rigid beam–column connections. The volumetric modular steel frames are connected via corner vertical and horizontal intermodule joints; each one is modeled utilizing one axial and two shear springs with predefined nonlinear force–displacement behavior in a 3D finite element analysis. The local damage scenarios are assumed to be due to instantaneous loss of columns or entire modules, for which the interactions between the modular units, overall structural robustness, load redistribution, possible collapse mechanisms, and progressive collapse response of the frames are investigated. The results indicate that the additional redundancy may help the modular steel frames survive from some corner column or single module removals but will not be able to maintain their robustness under combined module removal scenarios.

Progressive collapse resistance of reinforced concrete frame structures subjected to column removal scenario

The progressive collapse of a building occurs due to an unusual loading condition or when there is a sudden loss of the primary structural element. This could lead to a partial collapse or entire collapse of the building due to the failure of one or more structural elements. This study investigates the progressive collapse demand of the RC building by linear static analysis and vertical displacement responses using non-linear dynamic analysis. ETABS software is used for corner column removal, edge column removal, penultimate column removal and internal column removal scenarios. The RC buildings considered in this investigation are G + 6, G + 8 and G + 10 storey. The results showed that progressive collapse demand value of the bottom end of adjacent columns were found to be safe for all damage cases. However, the top end of the adjacent columns was found to be unsafe. The most critical damage case was found to be the penultimate column removal case that possessed highest PCD values. Finally, the vertical displacement of time history results is represented graphically and later the results of time history analysis is compared with linear static analysis results.

Comparison of Different Procedures for Progressive Collapse Analysis of RC Flat Slab Structures under Corner Column Loss Scenario

Progressive collapse is the failure of the whole structure caused by local damage, which leads to significant economic and human losses. Therefore, structures should be designed to sustain local failures and resist subsequent nonproportional damage. This paper compared four procedures for a progressive collapse analysis of two RC structures subjected to a corner column loss scenario. The study is mainly based on the methods outlined in the current Russian standard (linear static (LS) pulldown, nonlinear static (ND) pulldown, and nonlinear dynamic), but also includes LS and NS pushdown procedures suggested by the American guidelines and linear dynamic procedure. We developed detailed finite element models for ANSYS Mechanical and ANSYS/LS-DYNA simulations, explicitly including concrete and reinforcement elements. We applied the Continuous Surface Cap Model (MAT_CSCM) to account for the physical nonlinearity of concrete. We also validated results obtained following these procedures against known experimental data. Simulations using linear static pulldown and linear dynamic procedures lead to 50–70% lower results than the experimental because they do not account for the nonlinear behavior of concrete and reinforcement. Displacements obtained from the NS pulldown method exceed the test data by 10–400%. It is found that correct results for both RC structures can only be found using a nonlinear dynamic procedure, and the mismatch with the test data do not exceed 7%. Compared to static pulldown methods, LS and NS pushdown methods are more accurate and differ from the experiment by 28% and 14%, respectively. This relative accuracy is provided by more correct load multipliers depending on the structure type.

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.

Explainable models to estimate the effective compressive strength of slab–column joints using genetic programming

ABSTRACTIn this study, explainable models to predict the effective compressive strength of slab–column joints were proposed using genetic programming (GP). Effective compressive strength test results were collected from the literature, among which 81 were sandwich, corner, and edge columns, 44 were interior columns. With respect to the collected test results, random forest (RF), random forest–recursive feature elimination (RF‐RFE), K‐means clustering and linear regression analysis (KL) were applied to analyze the key features influencing the effective compressive strength. In addition, explainable models to predict the effective compressive strength were derived by using GP. The proposed models were verified by comparing with the existing equations, RF, and artificial neural network (ANN). Using the generative adversarial network (GAN), 20,000 fake data were additionally generated to strengthen the verification stage. The results showed that the proposed models exhibited the lowest root mean squared error (RMSE) among the existing equations, and RMSE of the proposed models was close to that of RF and ANN despite its conciseness.

Numerical Simulation on Dynamic Behavior of Slab–Column Connections Subjected to Blast Loads

Although many studies on the blast-resistant performance of structures have focused mainly on single members such as beams and columns, there is little research on the behavior of joints that are subjected to blast loads. In this study, the structural behavior of a slab–column connection subjected to blast load was investigated using a numerical analysis method. LS-DYNA was used as a finite element analysis program, and in order to improve the accuracy of numerical analysis, mesh size, material model, and simulation method of blast load were determined through preliminary analysis. The effect of different restraints of the joints, depending on the position of the columns in the slab, on the blast resistance performance was investigated. As a result, the highly confined slab-interior column connection showed better behavior than other edge and corner columns. The drop panel installed between the lower column and the slab was effective in improving the blast-resistance performance of the slab–column connection. For a more accurate evaluation of blast resistance performance, it was suggested that various evaluation factors such as ductility ratio, reinforcing stress, and concrete fracture area can be considered along with the support rotation, which is an important evaluation factor suggested by many standards.

Optimization of Diagrid Angle for High Rise Structure for Varying Bay Widths

The development of urban population, the lack of space and the high land costs has created the scope and necessity for the high-rise structures. In high rise structures, the design of lateral load resisting systems is more crucial than gravity load resisting system. There are many structural systems exists in literature to resist lateral loads. Diagrid structure is one among them which is proven to be both structurally and architecturally efficient structural system to resist lateral loads. The present study aims to investigate the best bay spacing for a particular high-rise structure and also optimizing the best diagrid angle to suit to the selected bay spacing. A numerical study is carried out with a 24 storied high-rise structure of plan area 36m x 36m considering with and without corner columns. The structure performance is checked with a bay width of 4m and with a bay width of 6m. Each structure is analyzed for four angles of inclinations of diagrid are formed by connecting 1, 2, 3, 4 stories respectively to optimize the diagrid angle. A comparative investigation is carried out for the structural responses like storey displacement, storey drift and base shear with different diagrid angles and with different bay width.

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.

Predictive model for bidirectional shear strength of reinforced concrete columns subjected to biaxial cyclic loading

Corner columns are subjected to bidirectional lateral loading in three-dimensional framed structures during seismic events, which can deteriorate their shear strength. The majority of the design codes do not consider the effect of biaxial lateral loading in the calculation of the column shear strength, and hence an accurate formulation that can predict the bidirectional shear strength is still lacking. Gene Expression Programming (GEP) was used in this research to predict the bidirectional shear strength of columns subjected to biaxial cyclic loads based on a database collected from different experimental studies found in the literature. Based on the previous experimental studies, it is found that the biaxial shear strength of RC columns are predominantly controlled by the column axial load, cross-sectional area of the columns, column shear reinforcement area, concrete compressive strength, and the height of the column. These parameters were used to develop the GEP models in this research. The models were statistically evaluated in order to ensure their applicability, and then they were compared to the ACI-318 formulation of the uniaxial shear strength. The R2 value obtained using the ACI-318 formulations is low compared to that obtained using the GEP models, where the R2 value obtained using the ACI formulation is 0.35, and that obtained using the first and second GEP models are 0.87 and 0.73, respectively. This confirms that the GEP models are more fitting to the experimental results compared to the ACI-318 formulation.

Strengthening of Edge and Corner Columns using Concrete Jackets

Strengthening of columns using concrete jackets depends on friction at the interface between them. So strengthening of edge and corner columns in only one story needs a large cross section area due to the shortage of friction length which leads to architectural issues. This research aims to study strengthening the edge and corner columns using a concrete Jacket in more than one story which increases the friction area between the Jacket and the original column. As a result, the load transferred from original column to the jacket will be increased. Thirteen models were done using ANSYS program to study the effect of various factors on the Jacket capacity such as the number of strengthened floors, the Jacket type (two sides or three sides), and whether there were shear connectors or not. The results showed that in the case of the edge and corner columns, it is preferable to strengthen the column by making a concrete Jacket on at least two or three floors to increase the surface area, which leads to increase the friction and thus increases the capacity of the strengthened column by an acceptable percentage. The results of ANSYS models were compared with the Indian code IS 15988 (2013) and the results were shown differently because the code equations depend on the presence of a full bond between the concrete column and the Jacket, which does not occur, but rather the load is transferred by friction between the Jacket and the original column. Doi: 10.28991/cej-2021-03091716 Full Text: PDF

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.

Dynamic response and failure mode of series isolation system under explosion load

The numerical model of the series isolation structure was established by using the finite element software to simulate the dynamic behavior of the series isolation structure after explosions occurred at different positions, and study the dynamic response and failure mode of the series isolation structure under explosion load. The results show that the vertical displacement and speed of the beams on each floor show a certain regularity with the passage of time. When columns at different positions encounter explosive loads, they will cause local collapse and damage of the structure, and the damage is mainly distributed in the longitudinal and transverse ranges where the columns are located. Compared with the inner column, the structural damage caused by the explosion load on the corner column and side column is more serious.

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.