Failure Modes Of Columns Research Articles

Behaviour of tapered CFDST columns with large hollow ratio under combined loads

Tapered concrete-filled double-skin steel tubular columns with large hollow ratio (LHR-CFDST) have a good application potential in wind turbine towers, where they are commonly subjected to the combined action of compression, bending, shearing and torsion. Up to now, research work on the behaviour of tapered LHR-CFDST columns under combined loads is seldom reported and relevant experimental data are limited. This paper presents an experimental and numerical study on the tapered LHR-CFDST column under combined compression-bending-shear-torsion loads. Seven specimens with different parameters including the tapered angle, the hollow ratio, the torsion-to-bending ratio, the axial compression ratio and the height-to-diameter ratio were tested. The experimental results in terms of failure modes, load versus deformation relations and strain responses were discussed. Reliable finite element models were established to conduct numerical analysis in an extended parameter range. The mechanism of columns and the effects of torsion-to-bending ratios, axial compression ratios, height-to-diameter ratios, tapered angles, hollow ratios, diameter-to-thickness ratios of steel tubes and the material strength were revealed. The suitability of the existing ultimate capacity prediction method was evaluated for tapered LHR-CFDST columns. It is found that the failure mode of columns under compression-bending-shear-torsion loads is related to the torsion-to-bending ratio. The columns behave in a ductile manner under moderate axial compression. Tapered angle has a slight effect on the bending capacity of the column, whereas the capacity declines with the increase of hollow ratio and torsion-to-bending ratio. The existing method gives a conservative prediction for the ultimate capacity of tapered LHR-CFDST columns.

Prediction of Seismic collapse behavior of deep steel columns using Machine learning

Steel Column Net (SCNet), a dataset of more than nine hundred experimental and numerical results of deep wide flange (W-shape) columns with different attributes is compiled. Three failure modes are distinguished in SCNet: local, global, and coupled modes while column rotation capacity is expressed in terms of its cumulative inelastic rotation until failure. The efficiency of five machine learning (ML) classification models is explored to identify the failure modes of columns subjected to combined axial and lateral loading in a randomly assigned test set from SCNet. Among the ML classification techniques used, support vector machine and decision trees provide the best performance with a prediction accuracy of 89%. The efficiency of four ML regression models is explored to predict the cumulative inelastic rotation until failure and categorize highly ductile behavior of the columns in the test set. Of these, the gaussian process regression exhibits superior performance with an accuracy of 87%. The performance of the ML regression models is compared with the current AISC highly ductile limits for W-shape columns and found to provide a 30% improvement in classification accuracy with respect to the number of correctly classified highly and non-highly ductile columns in the test set. Based on these results, it is suggested that machine learning algorithms that are continually updated with new experimental and computational data could inform future generations of design specifications.

Mechanical Performance of Circular Ultrahigh-Performance Concrete–Filled Double Skin High-Strength Steel Tubular Stub Columns under Axial Compression

This paper proposed a new type of stiffened circular ultra-high performance concrete-filled double skin steel tubular (UHPCFDST) column, in which stiffeners were applied to connect both inner and outer steel tubes. It efficiently delayed the local buckling of steel tubes and enhanced the integral of the section. This new type of UHPCFDST can be named multicells ultra-high performance concrete-filled double skin steel tubular (MUHPCFDST) column since the stiffener divided the sandwich space between the two steel tubes into multicells. Both the UHPCFDST and MUHPCFDST stub columns were fabricated and tested under centrally compression loading to investigate the axial mechanical behavior. The parameters considered in this study included specimen size, diameter-to-thickness ratio, the quantity of stiffener, and hollow ratio. Based on the tests, specimens’ column failure mode, axial load-shortening curves, local buckling behavior, compounding strength, strength index, and ductility coefficient were obtained and discussed. Then, the authors proposed a uniaxial stress-strain function of ultra-high performance concrete under compression and established three-dimension finite-element (FE) models with this stress-strain model to simulate the axial behavior of UHPCFDST and MUHPCFDST columns. Compared with the experimental results, the average deviation of the FE analysis in predicting the column bearing capacity and corresponding axial shortening was −3% and −5.5%, respectively. Finally, parametric studies were carried out, and a calculation method was proposed. The parametric analysis results and predictions from different methods (including the proposed method and methods suggested by existing design codes) were compared. The proposed method and calculating methods provided in AIJ-2008, EC4, and AS/NZS 2327 can reasonably predict the ultimate bearing capacity of both circular UHPCFDST and circular MUHPCFDST columns.

Evaluation on story-based stability in multistory frame under various restraining conditions

To estimate the critical buckling load, the effective length approach isolates a critical column inside a frame and analyses the rotational and translational stiffness of its end restraints. Although designers proportion leaning columns with K = 1, which is the correct K-value based on the column failure mode, buckling analysis fails to predict these values due to the influence of nearby columns and beams. In current design practise, beam-to-column and column-base connections in steel frames are typically idealised as wholly pinned or totally stiff connections. Various studies have demonstrated, however, that the semi-rigid behaviour of the systems beam-column connections affects the internal efforts in the structural parts, therefore the buckling critical loads and corresponding effective lengths of the compressed elements were also taken into account. In this study, a numerical analysis of the Effective length of column in multi-storey frames with single bay and dual storey (G + 2) is tried with variation in storey heights using rigid and semi-rigid jointed frames with rigid and semi-rigid jointed frames is undertaken. Webber's empirical equations are efficient in rigid frame systems for calculating the effects of adjoining columns and their critical buckling loading of the isolated column. The effective length K factor with the variance in critical length with different storey heights acquired a greater value when compared to other models. Moment rotations in semi-rigid jointed frames were influenced by differences in fixity factors in semi-rigid frames. The rigidity coefficient dropped as the stiffness coefficient increased, leading in an increase in the effective length factor.

Experimental study on axial compressive behavior of full-scale masonry columns strengthened with reinforced high ductile concrete (RHDC)

The present paper demonstrates the results of an experimental study on full-scale masonry columns strengthened with reinforced high ductile concrete (RHDC) system. This technique can be applied for existing masonry structures as a strengthening technique or for new construction as RHDC-masonry composite columns. Three unreinforced masonry (URM) columns and nine RHDC-strengthened columns were prepared and subjected to concentric axial loads. Each column had a rectangular cross-section and a heigh of 2400 mm. The variables considered in the tests were different configurations of RHDC system. The axial behavior of full-scale columns was discussed and analyzed including modes of failure, axial load-deformation response, peak load, and deformation capacity. Overall, the failure mode of columns was improved by RHDC system, preventing masonry from seriously crushing. Moreover, RHDC system increased both axial capacity and corresponding displacement of full-scale masonry columns, with maximum increases of 168% and 34%, respectively. Due to the enhanced stiffness and cross-sectional area of columns, the results from the current investigation allowed using a stability coefficient higher than that of URM structures for the prediction of the axial capacity of RHDC-strengthened columns. Finally, the effect of initial masonry strength and vertical stress on the load-bearing capacity of columns was analyzed theoretically. The strength reduction coefficient of HDC obtained from analysis can be used in engineering.

Axial performance of seawater sea-sand concrete columns reinforced with basalt fibre-reinforced polymer bars under concentric compressive load

Combined use of basalt fiber reinforced polymer (BFRP) and seawater sea-sand concrete (SSSC) in civil engineering could avoid the consumption of freshwater and river sand and solve the Chloride-induced corrosion problems. To promote the application and development of BFRP bars and SSSC, this paper presents an experimental study on BFRP bar reinforced SSSC columns under axial compression. Eight full-scale SSSC columns reinforced with BFRP bars were tested under axial compression. Failure modes, load–axial deformation curves, lateral deformation distributions, strains in BFRP bars and SSSC, initial axial stiffness, ultimate loads, and ductility of these column specimens were investigated. The effect of tie spacing, concrete strength, reinforcement ratio (i.e., longitudinal bar size) and slenderness ratio on the structural behaviour (e.g., ultimate load, initial stiffness, ductility, and strain distribution) of columns were analysed. Owing to the low modulus of BFRP, strength of BFRP is not fully utilized and the ultimate capacity of columns is mainly controlled by the compressive strength of concrete. Reducing tie spacing could increase the concrete compressive strength due to the confinement effect. Buckling of BFRP bars was postponed by increasing the confinement effect and bar size, resulting in an increase in the ultimate strain in bars. Although the slenderness ratio is low (=10.4–18.9), second-order effect exists in columns as evidenced by the failure modes of columns and the unequal axial strains of BFRP bars in the extreme tensile and compressive sides. Finally, design formulas are proposed to estimate the load-bearing capacity of BFRP bar reinforced SSSC columns and the prediction matches well with the experimental results.

Shear strength model and prediction of failure mode for multi-spiral column

The damage of reinforced concrete columns due to shear is often serious, so this type of failure should be avoided from the design. In this paper, a model derived based on the discrete computational method is proposed to calculate the shear strength of column carried by multi-spiral transverse reinforcement, accounting for the effect of compression depth. Furthermore, based on this model, a method is proposed to predict the failure mode of multi-spiral columns. The test database of multi-spiral columns from previous studies is used to validate both the shear strength and failure mode predictions. The proposed model with a crack angle of 40 degrees gives the best estimation of the shear strength of multi-spiral columns, and the proposed method predicts well the failure mode of these columns. To avoid shear failure, the ratio of the minimum shear strength calculated from the proposed model with a crack angle of 40 degrees to the shear force based on the moment-curvature analysis is suggested to be larger than 1.2.

The effect of CFRP-shear strengthening on existing circular RC columns under impact loads

In recent decades, accidents involving derailed train collisions have increased, owing to the rapid development of railway construction worldwide. Reinforced concrete (RC) columns in train stations are likely to be subjected to derailed train collisions, resulting in a brittle shear failure of the columns and catastrophic damage to the entire structure. In view of these problems, this study investigated the effectiveness of carbon fiber-reinforced polymer (CFRP) shear strengthening in improving the failure modes of circular RC columns. A drop hammer impact test was performed on a plain circular RC specimen and a CFRP-shear-strengthened circular RC specimen with fixed supports. The tested specimens were scaled from a regular train station column in China, and the impact height was selected as 2/9 of the effective span length, in accordance with the dimensions of a high-speed train locomotive. The test results revealed that wrapping a layer of CFRP sheets can effectively mitigate the shear damage of the concrete, and transform the failure mode of the column specimen from brittle-shear to ductile-flexural. In addition, finite element (FE) models were developed and verified based on the experimental results. Using the verified FE models, the structural design-related parameters (e.g., the longitudinal reinforcement ratio, transverse reinforcement ratio, impact location, concrete compressive strength, and axial load ratio) were extensively analyzed, aiming to further investigate the effectiveness of CFRP strengthening on RC columns. The results demonstrated that wrapping existing RC columns with CFRP can achieve a consistent good strengthening effect, despite variations in these basic design parameters.

Performance of axially loaded masonry columns confined using textile reinforced concrete (TRC) added with short fibers

Textile-reinforced high ductile concrete (TRHDC) (Li et al., 2020) is an optimized textile reinforced concrete (TRC) by using short polyvinyl alcohol (PVA) fibers. This work presented an experimental study on the compressive behavior of masonry piers confined with TRHDC jacket. The considered parameters were textile types, number of textile layers, together with a group of fiber reinforced polymer (FRP) confined columns as a reference set. Although the strength was greatly improved by the FRP wraps, the brittle failure and rather weak post-peak behavior were observed in the FRP strengthened columns. By contrast, TRHDC composites changed failure mode of columns with multiple thin cracks opening on the jacket. The compressive strength, ultimate strain and energy absorption capacity were improved by the TRHDC confinement. Analytical models from the literature were evaluated for their applicability to estimate the compressive strength of masonry piers confined with FRP or TRHDC jacket. Predictions were in good agreement with experimental data, which can be adopted in the engineering application.

Collapse Mechanism of Ordinary RC Shear Wall-Frame Buildings Considering Shear Failure Mode

Most commercial buildings among existing RC buildings in Korea have a multi-story wall-frame structure where RC shear wall is commonly used as its core at stairways or elevators. The members of the existing middle and low-rise wall-frame buildings are likely arranged in ordinary details considering building occupancy, and the importance and difficulty of member design. This is because there are few limitations, considerations, and financial burdens on the code for designing members with ordinary details. Compared with the intermediate or unique details, the ductility and overstrength are insufficient. Furthermore, the behavior of the member can be shear-dominated. Since shear failure in vertical members can cause a collapse of the entire structure, nonlinear characteristics such as shear strength and stiffness deterioration should be adequately reflected in the analysis model. With this background, an 8-story RC wall-frame building was designed as a building frame system with ordinary shear walls, and the effect of reflecting the shear failure mode of columns and walls on the collapse mechanism was investigated. As a result, the shear failure mode effect on the collapse mechanism was evident in walls, not columns. Consequently, it is recommended that the shear behavior characteristics of walls are explicitly considered in the analysis of wall-frame buildings with ordinary details.

Strengthening of RC Circular Short Columns with Fibrous Jacket

This research presented a wide study about the structural behavior and strength of RC circular short columns when strengthened with concrete jackets strengthened with steel fiber. A total of 17 circular columns were designed, fabricated, and tested experimentally under monotonic load. An experimental investigation was carried out to assess the efficiency of the fibrous jacket in the retrofitting of RC column. The parametric study was conducted which included using four columns as control specimens with different cross-section dimensions. The remaining 13 column specimens included strengthening the column by different parameters such as steel fibers ratio and type, jacket thickness, bond by epoxy, and full and limited jacket height. The ultimate stress and strain, crack pattern, failure modes, ductility, and toughness capacity of the specimens were studied. The experimental outcomes exhibited that the fibrous jacket enhanced the ultimate strength capacity, ductility, and changed the failure mode of columns. The increase in the steel fibers ratio (1%, 1.5%, and 2%) enhanced the ultimate load capacity by (194%, 71%, and 126%) respectively. Strengthened columns by FRC jacket with thicknesses (25, 35, and 45) showed enhancement in the stress carrying capacity by (126%, 242%, and 171%) respectively. Using epoxy appeared a different behavior in comparison with square columns. The use of epoxy showed lower stress capacity by (21% and 24%) for (1% and 2%) hooked steel fibers ratio respectively. Use of hoop jacket case enhanced the ultimate stress capacity better than composite case. straight fibers were better than hooked ones in the improvement of ductility and energy absorption.

Failure Mode Recognition of Columns Using Artificial Neural Network

Columns are one of the most vital segments in bridgessince its post-seismic behaviour is of much importance. The retrofitting methods and rehabilitation strategies of bridges mainly rely on the identification of the failure mode of columns. It has been witnessed in various studies on columns that the mode of failure highly depends on section and material properties and there is no specific boundary between the modes, which makes their identification more sophisticated. This paper uses an artificial neural network to predict the modes of failure by analysing the effects of such soft computing methods. In this study, machine- learning models were generated from the experimental data of 253 columns of rectangular cross-section and its accuracy of failure mode prediction was evaluated by considering failure modes mainly flexure, flexure-shear, and shear. The optimal input parameters have also been evaluated for the machine-learning algorithm that enhances the efficiency of failure mode prediction.

Study on the compression performance of steel reactive powder concrete columns

In this study, the mechanical properties and failure characteristics of steel reactive powder concrete columns with different strength grades were investigated through compression testing. Six steel reactive powder concrete columns were tested; three columns underwent axial compression testing and three columns underwent eccentric compression testing. The results of the axial compression testing showed that steel and reactive powder concrete could work cooperatively at the initial stage, and the final column failure mode was primarily splitting failure at the end of the column, with the formation of a main crack in the longitudinal direction extending to the middle of the column. The results of the eccentric compression testing showed that the eccentrically loaded steel reactive powder concrete columns had comparatively strong deformability. The columns presented ductile failure mode under the eccentric load with 0.2 eccentricity. The final failure of the column involved a sudden increase in the horizontal crack width on the tension side, the steel flange on the tension side reached the yield state, the reactive powder concrete in the middle of the compressive side was crushed, and the reactive powder concrete surface layer burst open and partially spalled off. According to the test results and with reference to the relevant standards, equations for calculating the approximate ultimate bearing capacities of axially and eccentrically compressed reactive powder concrete columns were proposed.

Experimental analysis of hysteretic behavior and strain field of external diaphragm joints between steel beams and CFDST columns

External diaphragm joints with high structural reliability are used widely in composite steel and concrete structures. In this study, the external diaphragm joint was improved to be a steel beam-to-concrete filled double steel tubular column connection. The digital speckle correlation method was used to measure and investigate the strain field in the panel zone and relative beam-to-column rotation in a low-cycle reciprocating loading test. The obtained hysteresis curves of moment-rotation ( M-θ) and shear force-deformation ( V-[Formula: see text]) showed that the external diaphragm joints had higher strength, higher ductility, and better energy dissipation capacity. Decreasing the axial compression ratio resulted in the deterioration of initial rotational stiffness. Wider external diaphragm produced better ductility and larger initial shear stiffness. The ribbed anchorage web was effective to increase the bending resistance by 10%. Beam-to-column bending stiffness ratio can not only influence the bending resistance and energy dissipation capacity significantly but also affect the shear deformation capacity in the joint core. The magnitude of the shear strain in the panel zone was large, especially for the specimens under column failure mode, and shear deformation in the panel zone should not be neglected for it accounted for 30%–40% of the beam-to-column rotation. Beam-to-column rotation and shear deformation obtained by the digital speckle correlation method offered better predictions to analyze the mechanical behavior of external diaphragm joints in the concrete filled double steel tubular structures.

Mechanical performance of parallel bamboo strand lumber columns under axial compression: Experimental and numerical investigation

This paper presents an investigation on the mechanical performance of parallel bamboo strand lumber (PBSL) columns under axial compression. Experimental test and numerical analysis were performed for 40 PBSL columns with various slenderness ratios. Failure modes, ultimate capacity and load-strain response are reported and evaluated. Compressive failure is the typical failure mode of columns with small slenderness ratios, however, buckling failure is commonly observed for longer columns. Elastic eigenvalue analysis is found effective to predict critical buckling load of long columns, as buckling occurs within elastic range. However inelastic behavior has significant effect on critical load when the buckling stress exceeds proportional limit of the material. As a result, inelastic approaches provide more accurate prediction of critical load for columns with a slenderness ratio lower than the elastic threshold (λy). The presented experimental results and numerical analysis validated the feasibility of the elastic/inelastic buckling analysis approaches on determination of ultimate capacity of axial loaded PBSL columns.

Structural Behavior of Digitally Fabricated Thin-Walled Timber Columns

This paper aims to investigate the structural behavior of digitally fabricated thin-walled timber sections with edge connectivity provided by integral mechanical press-fit joints. Experimental, numerical, and analytical investigations have been developed to accurately characterize the press-fit section behavior and their failure modes. Plywood fiber orientation, material thickness, and connection tightness are considered as potential factors that may affect the performance of the press-fit jointing system. Experimental testing of square hollow sections (SHSs) under uniaxial compressive loading showed failure of sections through both conventional crushing and novel pop-off bifurcation failures. Pop-off buckling behaviors were shown to be governed by the integral joint transverse stiffness and its magnitude relative to a critical edge stiffness value. Columns with joint transverse stiffness value less than the critical edge stiffness value exhibited pop-off failures. These joint stiffness values were obtained from testing of unloaded joints and were used to obtain accurate predictions of column failure modes. Joint stiffness values for loaded joints were then predicted with an interpolation model mapping axial strain to a tighter connection tolerance and these were used to obtain accurate estimations for column failure load in most of the tested column types. Comparative investigations showed thin-walled sections with integral joints only to be capable of matching the compressive capacities of glued sections, for instances where crushing governed. Similarly, the weight-specific compressive capacity of timber sections was found to be comparable to thin-walled steel sections when crushing governs.

Machine Learning–Based Failure Mode Recognition of Circular Reinforced Concrete Bridge Columns: Comparative Study

AbstractThe prediction of failure mode of columns is critical in deciding the operational and recovery strategies of a bridge after a seismic event. This paper contributes to the critical need of f...

FRP-confined concrete core-encased rebar for RC columns: Concept and axial compressive behavior

In the ultimate failure mode of columns in RC structures under seismic load, the longitudinal reinforcement generally suffers from severe buckling due to the axial compressive load, spalling of concrete cover and dilation of concrete core. Proper configuration of RC columns to postpone or prevent the buckling phenomenon can enhance the seismic performance and make full use of the strength of steel reinforcement. In this paper, a new concept and configuration of FRP-confined concrete core-encased rebar (FCCC-R) for RC columns is proposed. The concrete surrounded the longitudinal rebar is confined by an FRP tube, which can prevent the rebar from premature buckling. The axial compressive behavior of the hybrid bar considering different parameters, including the slenderness ratio, FRP tube diameter, mortar strength, and bar position was studied experimentally. Furthermore, finite element (FE) simulation was carried out and calibrated by test results. Based on the FE model, additional discussion and a parametric study was performed. Finally, the minimum FRP tube diameter required for the FCCC-R considering the compressive behavior enhancement effect was calculated, and design curves for 3 types of steel bars with nominal yield strengths of 400 MPa, 800 MPa, and 1100 MPa were proposed.

Analysis of seismic collapse mechanism of concrete frame structures subjected to near-fault ground motions

The characteristics of near-fault ground motions are significantly different from far-field ground motions. There are also great differences in the damage of concrete structures caused by these two kinds of ground motions. Earthquake damage indicates that the damage of concrete frame structures subjected to near-fault ground motions is more serious and collapse mechanism is more complicated. In this paper, the traditional alternative path method (APM) in the analysis of collapse was improved. Collapse mechanism of reinforced concrete frame was studied by numerical simulation method. A typical ten-story reinforced concrete frame model was established. Three harmonic waves and three practical near-fault ground motions were selected as acceleration time history input. The results show that different damaged parts of structure caused by strong earthquake have little effect on the final collapse mode when the structure is under free vibration. The failure mode of columns subjected to different ground motions is almost the same. Simple harmonic excitation whose period is close to the predominant period of ground motion can approximately simulate the failure mode of structure caused by earthquake.

Numerical Study on the Relevance of Columns Hidden Failure Modes in the Seismic Capacity of Non-Ductile RC Frames

ABSTRACT In simplified seismic structural analyses, not all the deterioration modes are adequately considered. This work discusses the relation among the hidden failure modes of columns of non-ductile reinforced concrete building frames and their global collapse mechanism. With this aim, a numerically efficient model is developed and implemented in OpenSEES. Two benchmark problems are analyzed with this model: the well-known Van Nuys Hotel and a prototype building designed for gravity loads only; in this last case, the results are compared with experiments on a one-third scale model. The obtained results confirm that simplified models grossly overestimate the building capacity.