Behavior Of Columns Research Articles

Axial behavior of UHPC columns with new emerging mixtures and varying confinement

Using advanced materials to optimize designs and make structures resilient is becoming of crucial importance. Advanced rapidly growing materials with superior mechanical properties, like ultra-high performance concrete (UHPC), can make structures better in terms of strength and service life when compared to conventional concrete. Behind the excellent performance of UHPC stands its dense packing theory and usage of steel fibers or even carbon nanofibers (CNF) in emerging UHPC mixtures. UHPC is mostly used in small-scale applications like bridge field joints and overlays, but research is extending UHPC to full structural applications such as girders and columns. To expand existing knowledge on UHPC columns and add new results from emerging and recently commercialized UHPC mixtures, this study uses, for the first time, two new UHPC mixtures with white cement and CNF enhancement to investigate axial behavior of nine full-scale columns with varying confinement. An extensive experimental program considers two groups of columns from two different mixtures with several other variables such as transverse reinforcement detailing, cross-section, and percentage of steel fibers. The paper presents results from companion material tests along with a detailed discussion of the global and local behavior of the columns, i.e. force, axial strains, reinforcement strains, and stiffness. Test results are interpreted in light of existing ACI 318 Code provisions and guidance is provided for axial design capacity estimation and transverse reinforcement detailing.

Cyclic performance of precast steel beam-to-CECFST column exterior sub-assemblages with dry connections: Experimental studies and mechanism analyses

Combining advantages of both reinforced concrete (RC) and concrete-filled steel tube (CFST), concrete-encased concrete-filled steel tube (CECFST) members demonstrate superior structural performance over pure RC or CFST counterparts. Nevertheless, current research in this domain has primarily focused on member and connection behaviour of CECFST columns, with no attention given to frame-level performance. This significantly impedes applications of this form of high-performance composite members into actual engineering practice. To bridge this research gap, a novel precast steel beam-to-CECFST column composite system is proposed in this study. This is followed by a comprehensive experimental programme, where seven precast steel beam-to-CECFST column exterior sub-assemblages were tested under cyclic loads. In the test specimens, three types of connections, including beam-to-beam (B-B), column-to-column (C-C) and beam-to-column (B-C), were incorporated to establish a precast steel beam-to-CECFST column sub-assemblage. Horizontal displacement versus shear force relationship and failure mode of the test specimens are reported, followed by a detailed analysis of test results and findings. Furthermore, a comprehensive mechanism analysis is presented, with emphasis on energy dissipation behaviour and deformation mechanism of the proposed precast composite system. The test results show that the proposed precast composite system has comparable load-carrying capacity and energy dissipation capacity in comparison with conventional cast-in-place counterparts. This indicates that despite using precast beam-to-beam and column-to-column connections, structural performance of the composite frame system would not be significantly affected, showing that this form of precast steel beam-to-CECFST column composite system has considerable potential to be adopted in actual engineering practice.

Axial compressive behavior of low-alkalinity seawater sea-sand concrete column reinforced with hydrophobic longitudinal SFCBs and FRP hoops

To address corrosion problem of steel bars and shortage of freshwater and river sand in marine and offshore structures, a novel hydrophobic-modified longitudinal steel-FRP composite bars (SFCB) and FRP hoops reinforced low-alkalinity seawater sea-sand concrete (SWSSC) is developed. However, axial compressive behavior of hybrid SFCB and FRP reinforced columns is not clear and the applicability of existing design methods is low. Here, nine hybrid reinforced columns have been designed and tested. Typical failure modes of columns and axial compressive behavior of constituent materials (i.e., hydrophobic reinforcements and low-alkalinity SWSSC) are investigated. It is found that the synergistic confining effect formed by hybrid reinforcement are significant. The mesh confinement formed by densely distributed FRP hoops and longitudinal SFCBs improves the local buckling behavior, and effectively constrains the lateral expansion of concrete core, resulting in improved compressive strength and ductility of column. The compressive contribution of single longitudinal SFCB to ultimate load capacity of column can be enhanced effectively, up to 36.3 %, by increasing steel content of SFCB. Based on this, a prediction model of hybrid reinforced columns is proposed, which can accurately evaluate the ultimate load capacity. This work provides valuable experimental observations and load capacity model for hybrid reinforced column, which promote its design and application in marine engineering.

Experimental and numerical characterization of column webs/faces loaded out-of-plane in steel joints

This paper presents a comprehensive investigation into the behavior of column webs/faces under out-of-plane loading within steel joints. The experimental component of the study involves testing five profiles, encompassing both open and closed sections with varying web slenderness and steel grade, subjected to direct out-of-plane tensile loads through bolted connections, utilizing both single and double rows of bolts. Concurrently, numerical simulations are conducted using finite element models, thoroughly calibrated with the experimental results. Drawing upon the calibrated numerical models, the paper systematically explores the influence of key parameters, including web slenderness, bolt arrangement, and analysis methods, through a parametric study involving 167 cases. A careful comparison of the observed behavior of the component from experimental tests, numerical models, and analytical models for initial stiffness is presented. Finally, the initial stiffness formulation derived from a recent model developed by the authors is improved to align with the observations from the experimental and numerical results.

Axial partial compressive behavior of round-ended concrete-filled steel tubular columns

The paper conducted 19 partially and 5 fully loaded tests on round-ended concrete-filled steel tubular (CFST) columns. These tests revealed that the ultimate strengths of round-ended CFST columns under partial load declined as the cross-sectional aspect ratio or partial compression area ratio increased. However, the use of a top plate effectively enhanced their ultimate strengths. In addition, a finite element model (FEM) was utilized to generate 487 large-size models to explore the confinement effect, stress distribution, and parametric effects. Since there are no specific design standards available for round-ended CFST columns, the paper has evaluated the applicability of design methods provided in Eurocode 4, AISC 360–16, and Chinese code GB50396 which are intended for circular, square, or elliptical CFST columns for round-ended CFST columns under partial load. However, these existing design techniques showed inaccurate and dispersed resistance predictions for round-ended CFST columns. Therefore, an effective simplified method for forecasting the resistance predictions of round-ended CFST columns under the partial load has been proposed based on the testing results and FEM analysis.

Compressive behaviour of self compacting concrete column strengthened by hybrid confinement of fibre reinforced polymer sheet and fibre rope

AbstractThe compressive behavior of self-consolidating concrete columns strengthened by hybrid confinement of polypropylene fiber rope and glass fiber-reinforced polymer sheet was investigated experimentally. We cast and tested eight column specimens under axial compression load. (Six confined SCC columns and two conventional SCC columns.) The concrete grade utilized is SCC M40. For reinforcement, the SCC columns are enclosed with GFRP wrap and polypropylene fiber rope in various volumetric ratios. The compressive resistance of a confined SCC column, strength enhancement, stress-strain relationship, ductility ratio, and load deflection relationship are the parameters studied. The results are compared to establish the adequacy of the confinement. The wrapping of GFRP increases the load-carrying capacity and modulus of elasticity.

Shear behavior of thin-walled concrete-filled steel tubular columns

Shear failure is a brittle type of failures, which should be avoided in any structure as it could cause property loss and human casualties. The shear behavior of thin-walled concrete-filled steel tubular (CFST) columns was hence investigated in this study, involving the tests of 24 thin-walled CFST columns and considering the following parameters: shear span-to-depth ratios = 0.15, 0.3, 0.5, 1, 1.5, and 2; confinement factor = 0.63, 1.27, 1.44, and 1.70; and axial load ratios = 0, 0.2, 0.4, and 0.6. The test results revealed the insights of the initial shear stiffness, failure modes, ultimate bearing capacity, load-deflection curves, load-strain curves, and ductility of the specimens. Based on the failure modes, a method is proposed to evaluate the load resistance, and explain the relationship between the shear span-to-depth ratio and the peak bearing capacity. A compression strut mechanism considering the confinement provided by the steel tube flange is also proposed. The effect of axial load on the shear strength of the concrete core is negligible when the axial load ratio doesn’t exceed 0.4. The predicted results from using the proposed simple model agree generally well with the experimental results.

Behavior and design approach of ultra-high-performance concrete slender columns

The existing literature concerning the behavior of slender columns made of reinforced ultra-high-performance concrete (UHPC) is severely limited. Furthermore, current design standards lack specific guidelines for reinforced UHPC (R–UHPC) slender columns. Based on this, a comprehensive experimental investigation was conducted on four columns with 2 % steel fiber content subjected to compression to explore the influence of eccentricity ratios (e/h0 = 0, 0.15, 0.3, and 0.6) on the compression behavior of the R–UHPC slender columns. The results revealed that all R–UHPC slender columns experienced failure due to compressive zone UHPC crushing, with no observed concrete spalling. Moreover, a detailed parametric study was conducted on 3000 R–UHPC slender columns using a validated finite element model. By analyzing the parameters and employing the moment magnification method, a statistically derived design equation for effective flexural stiffness (EI) was formulated. The results indicated that EI decreased with increasing eccentricity ratio and increased with rising slenderness ratio. Additionally, calculation formulas for determining cross-section strength were proposed for R–UHPC slender columns, accounting for the contribution of tensile zone UHPC to the overall section strength. Finally, the proposed design approach was validated by comparing predicted results with available experimental data.

Effects of enhanced confinement on cyclic behavior of concrete bridge columns with partially unbonded seven-wire steel strands

The effects of enhanced confinement on the proposed bridge columns under lateral cyclic loading were investigated in this research by testing large-scale column specimens. The proposed column used nonprestressed partially unbonded seven-wire strands as elastic elements to increase the post-yield stiffness of the column to reduce the residual displacement under seismic loads. The enhanced confinement included rectilinear transverse reinforcement with an increased amount (specimen CSCR) and reduced spacing or innovative five-spiral reinforcement (specimen CSCS). Test results showed that all the specimens exhibited a positive post-yield stiffness ratio of 3.5–6.4 %. However, the enhanced confinement reduced the post-yield stiffness by 42–45 % but increased the lateral strength of the column, which is beneficial for controlling the residual displacement. The enhanced confinement did not affect the drift ratio when the positive post-yield stiffness ended (6 %) but significantly increased the deformation capacity by 15–31 % and the energy dissipation capacity by 37–63 % of the column. Even with a smaller amount of transverse reinforcement, the specimen with the innovative five-spiral reinforcement showed deformation and energy dissipation capacities better than the other specimens with conventional rectilinear transverse reinforcement. A pushover analysis model was developed and modified to better account for the effect of the enhanced confinement and the strand slip, and to consider the end point of positive post-yield stiffness. The comparison with the test result showed that the proposed pushover model well captured the envelope responses of the specimens. Finally, a simplified method was proposed for estimating the moment strength of the proposed column.

Compressive behavior of RC columns strengthened with FRP and prefabricated UHPC blocks

The combined strengthening method of cross-sectional shape-modification and lateral FRP confinement has been proven to be capable of significantly improving the compressive behavior of RC column and the FRP confining efficiency. However, the traditional shape-modification method using a cast-in-place concrete jacket has a complicated construction process and a long curing period. Additionally, the application of normal concrete substantially increases the cross-sectional area and weight of the column, resulting in poor seismic performance of the strengthened column. In this study, a novel strengthening method using FRP and modular prefabricated ultra-high performance concrete (UHPC) blocks is proposed for strengthening RC columns. An experimental study was conducted to investigate the axial/eccentric compressive behavior of RC columns strengthened with this novel method. The test results demonstrated the high efficiency of the proposed method in enhancing the load-carrying and deformation capacities of the RC columns under axial or eccentric compressive loads. The significant roles of the strengthening components in the novel method in improving the compressive behavior of columns were also verified.

Behavior of Circular Hollow Steel-Reinforced Concrete Columns under Axial Compression

The circular hollow steel-reinforced concrete (HSRC) column consists of an inner circular hollow steel tube and outer circular hollow reinforced concrete (RC). This design provides several advantages, including being lightweight, having a wide sectional profile, and having a high flexural stiffness. This paper aims to investigate the behavior of the circular HSRC columns under axial compression through testing and finite element (FE) modeling. An FE model was established to simulate the circular HSRC columns under axial compression, which was validated against the test data. Additionally, the load distribution and the interface stress between the outer hollow RC and inner steel tube were analyzed. Subsequently, a systematic parametric analysis was conducted on the diameter (d) and thickness (t) of the steel tube; slenderness ratio (λ); strength of concrete (fcu); yield strength of steel tube (fsy), longitudinal rebar (fly), and stirrup (fgy); as well as the stirrup spacing (s). The critical influencing factors of the circular HSRC columns under axial compression were identified. fcu, λ, d, fly, and fsy dramatically influence the bearing capacity, and the stiffness is notably affected by λ and fcu. Finally, three simplified design methods were summarized and evaluated for calculating the bearing capacity of the circular HSRC columns under axial compression.

Experimental study on the behavior of damaged CFRP and steel rebars RC columns retrofitted with externally bonded composite material

The structural behavior of concrete columns reinforced with CFRP bars has been the focus of many researches over the past two decades. There is a dearth of comprehensive research concerning the axial compressive performance of retrofitted CFRP bars reinforced concrete (RC) columns. To fill this gap a thorough investigation was carried out to understand failure mode, load–displacement response, axial deflection, axial load-bearing strength, ductility index (DI), stiffness index (KI), and strength index (SI) of retrofitted CFRP bars RC columns. The experimental matrix comprised 14 short circular columns, seven reinforced with CFRP bars and hoops and the other seven with steel bars and hoops. Initial damage was induced through axial loading until a 35% reduction in peak axial strength was observed, after which damaged columns were repaired and retrofitted using CFRP sheets. The parameters of the study include concentric and eccentric compressions, transverse reinforcement spacing, CFRP wrapping, steel, and CFRP reinforcements. According to the findings, lowering transverse hoop spacing enhanced the utmost capacity and ductility of both types of retrofitted columns. The average peak strength and corresponding axial displacement of CFRP RC columns were 22.63% and 14.87%, and ductility (at a 20% load decrease) was 118% higher after CFRP retrofitting. The axial stiffness of damaged CFRP bars RC columns after strengthening with CFRP sheet were not fully rehabilitated and on average SI under concentric loading was 3.22% lower while DI under eccentric loading was 2.71% higher than steel RC columns.

Slenderness effect on the behavior of composite RC columns under eccentric loads

Slenderness effect on the behavior of composite RC columns under eccentric loads

Experimental and numerical investigations of the impact resistance of socket and pocket connections for precast bridge columns

This study investigates the dynamic performance of precast bridge columns under pendulum impact testing, including socket connection, pocket connection, and cast-in-place (CIP) columns. The study focuses on comparing the impact behavior of CIP and precast columns regarding failure modes, impact force-time, and deflection-time histories. Furthermore, the mechanism by which the socket or pocket connection configurations affect the impact resistance of the precast columns is discussed. The results indicate that the development of cracks in the precast and CIP columns is consistent under the same impact conditions. Notably, the shear resistance mechanisms and failure modes vary significantly at the bottom of the two columns. For the precast specimens, substantial local damage occurs at the connections with consecutive impacts. Specifically, punching shear failure is observed at the pocket connections, whereas the connection sections of the socket columns may pull out from the grooves. Local damage to the column-footing connections reduces the global stiffness of precast columns, leading to higher deformation, greater residual displacements, and lower impact forces than those of CIP columns. A simplified finite element modelling method is proposed to simulate the characteristics of precast column connections, and its accuracy is verified using the test results. The numerical findings show that increasing the friction coefficient at the connection interface promotes the formation of diagonal compression struts within the connection, effectively resisting impact loads and preventing excessive shear stress produced by sliding at the interface. Furthermore, amplifying the minimum embedment depth of the socket-connected precast column to 1.0 D is recommended to ensure safe performance under impact loading.

Eccentrically compressed behavior of UHPC columns considering the P-delta effect

Eccentric compression is a critical behavior observed in arches and columns, particularly in structures constructed with ultra-high performance concrete (UHPC). Compared to normal concrete structures, those made with UHPC exhibit distinct behaviors that need to be clearly investigated. This study comprehensively investigates UHPC columns under eccentric compression load through experimental study and theoretical analysis. Various experimental parameters, including slenderness ratio, eccentricity distance, fiber content, and stirrup ratio, were examined across 26 UHPC columns. Failure modes were evaluated using digital image correlation (DIC) methods. The load-displacement responses indicated that slender columns subjected to significant eccentricity exhibited load decreases during yielding stages, whereas short columns experienced load increases. This discrepancy in yielding stages was attributed to P-delta effects. In addition, theoretical models were developed to determine the ultimate bearing capacity of columns experiencing compression-controlled and tension-controlled failures, considering the P-delta effect caused by the different slenderness ratios. The moment magnifying coefficients for UHPC were calibrated based on theoretical analyses of the limit curvature of eccentric compression members. The proposed theoretical models agreed well with the experimental results, with an average ratio of 1.02. The second-order effect for the case of UHPC short column with a slenderness ratio of 5 can be ignored as per Eurocode 2, which is less than 10 % of the corresponding first-order effect.

Eccentric compression behavior of L-shaped column fabricated by thin-walled square steel tubes based on self-drilling screw connections

In this study, a new L-shaped column fabricated by thin-walled square steel tubes (LFTST columns) based on self-drilling screw connections is proposed. The LFTST columns consisted of square steel tubes, U-shaped parts, angle parts, gusset plates, and self-drilling screw connections. LFTST columns possess several advantages including easy transportation, rapid assembly, and eco-friendliness. Consequently, they are suitable for low-rise buildings, such as village-building, low-rise dormitories, and low-rise office buildings. However, the compression behavior of LFTST columns remains silent. Five full-scale LFTST column specimens were subjected to eccentric compression tests. The variables under consideration included eccentricity (with values of 0 mm, 40 mm, and 80 mm), thickness (2 mm and 4 mm), and the number of gusset plates (0, 1, and 3). The failure modes, bearing capacity, load–displacement response, and strain development of the LFTST specimens were obtained. Subsequently, finite element (FE) models of LFTST columns were established and used to analyze the eccentric compression behavior of LFTST columns. The FE modeling results agreed well with the experimental results. A detailed parameter analysis was conducted to evaluate the effects of various factors. These factors included the thickness of the plates (2 mm, 3 mm, and 4 mm), the width of the gusset plates (100 mm, 150 mm, and 200 mm), limb spacing values (0 mm, 150 mm, and 300 mm), and eccentricity (0 mm, 20 mm, 40 mm, 60 mm, and 80 mm). In addition, the calculation formula for estimating the ultimate bearing capacity of the LFTST columns was derived employing the double coefficient product method. The proposed formula was validated by experimental and FE results.

Experimental study on axial compressive behavior of concrete-filled corrugated steel tubular columns

Concrete-filled corrugated steel tubular (CFCST) column is a novel type of steel-concrete composite column, comprising four corrugated steel plates, four square-section steel bars at the corners, and infilled concrete. The transversely placed corrugated steel plates can effectively prevent their premature local buckling, release the axial load, and provide lateral confinement effects on the infilled concrete. This paper investigated the axial compressive behavior of CFCST columns through experimental, numerical, and theoretical approaches. Experiments were conducted on 20 specimens, focusing on their axial load-resistant behavior. The specimens demonstrated excellent axial bearing capacity, ductility, and residual bearing capacity. Besides, the mechanical behavior of corrugated steel plates throughout the loading process was analyzed through the development of the horizontal and vertical strains. Furthermore, a finite element (FE) model was developed to simulate the axial compressive behavior of CFCST columns, which was validated against the experimental data. The FE model was used to analyze the compressive behavior of each part in CFCST columns, revealing that the infilled concrete and steel bars primarily bear the axial load, while the corrugated steel plates mainly provide lateral supports to the infilled concrete. Finally, a simplified method for calculating the critical width of corrugated steel plates and a formula for the axial bearing capacity of CFCST columns were proposed. It was indicated that the limiting width-to-thickness ratio of the corrugated steel plates was larger than that of the steel elements in conventional CFST columns. These formulas were demonstrated to be accurate enough and suitable for the engineering designs.

Experimental and analytical study on eccentrically loaded Fiber concrete columns reinforced longitudinally with GFRP bars

In this paper, experiments were carried out to analyze the behavior of the square columns reinforced longitudinally by GFRP bars along with different ratios of hooked end fibers under eccentric compressive loading. Eight short square columns with a cross-section dimension of 150x150mm and a height of 1200 mm, were fabricated to conduct the experimental program. A 150 mm enlargement in column-cross at both ends was considered to develop an eccentric axial load. The columns were tested under different load eccentricity ratios (0.26, 0.5, 1). Different tie spacings (50, 100, 120) mm. Different ratios of steel fibers 0 %, 0.5 %, and 1 % were incorporated into the concrete mix. It was observed that columns with steel fibers demonstrated good characteristics, including higher ultimate load, increased ultimate deflection, and enhanced ductility and toughness compared to the columns without steel fibers due to multiple cracking behaviors. The ductility of the columns reinforced with GFRP bars was enhanced by 46.8 %, and 68 % for steel fiber volume ratios of 0.5 % and 1 %, respectively. The energy absorption was increased by 42 % and 77 % for steel fibers ratios of 0.5 % and 1 %, respectively. When GFRP bars were used as longitudinal reinforcement, there was an improvement in the bond behavior between the concrete and the GFRP bars. All concrete columns reinforced by GFRP bars failed due to flexure-compression failure. There was no observed rupture of GFRP bars during the experimental test and the maximum strain did not reach 40 % of their ultimate strain capacity. Nonlinear Finite Element analysis was conducted to simulate the behavior of tested columns. The equations from previous studies and the codes were established to predict the nominal peak capacity of columns considering all parameters. In general, there was a reasonable level of agreement observed between the experimental data and the theoretical results determined for seventy-column specimens in the current study and from previous studies in the literature.

Numerical simulation of axially loaded circular concrete-filled steel tubular short columns with localized corrosion

Concrete-filled steel tubular (CFST) columns are widely utilized in structures owing to their cost-effectiveness, high strength, ductility, and proven fire resistance. Despite these advantages, concerns persist regarding the performance of CFST columns with locally corroded steel tubes, impeding their widespread adoption in offshore structures. This research employs three-dimensional finite element (FE) simulations for circular CFST stub columns subjected to axial compression, validated against experimental data. Verification includes full load-displacement histories, ultimate axial strengths, and failure modes. The validated FE models are then employed to assess and compare the structural behavior of CFST columns with various shapes of localized corrosion, analyzing overall load-deformation curves, interaction stress-deformation responses, and composite actions. To acquire critical data for understanding stub column behavior, 81 specimens underwent non-linear finite element analysis, with local corrosion represented by artificial notches in steel tubes. Test parameters, such as notch orientations, lengths, depths, widths, and concrete compressive strength, are varied. Results elucidate the impacts of these parameters on different aspects of stub column responses with corroded steel tubes. Furthermore, the accuracy of existing design models in predicting the ultimate axial strengths of CFST columns with corroded steel tubes is assessed. Finally, through parametric analysis of test results, a practical model is proposed and verified for computing the peak resistance of a CFST stub column with a locally corroded steel tube.

Selective online model updating in hybrid simulation of a full‐scale steel moment frame

AbstractThis study presents the implementation of an online model updating algorithm within a full‐scale hybrid simulation (HS) of a six story, four bay steel moment frame. The experimental substructure consists of a cruciform subassembly generating critical data on the nonlinear behavior of the first story column and two beams with reduced beam sections (RBSs) on each side. The updating algorithm focuses on the modeling parameters of plastic hinge elements representing the RBSs in the numerical model. A smooth plasticity model is utilized for beam plastic hinges with updating parameters identified from on‐line experimental data through a modified version of the unscented Kalman filter. The HS shows that the numerical beam hinges based on simple hysteretic model with updated parameters are able to capture the characteristic behavior observed in experiments. Due to fracture of beam flanges is observed in the experiments, a selective updating concept is proposed to allow for updating multiple numerical components accounting for asymmetric behavior and variability in the response. The selective updating method is validated through virtual HSs that are better able to identify and isolate the effects of fracture and other behavioral characteristics. The combination of results from physical and virtual tests highlights the benefits of model updating on the local and overall system‐level response.