Eccentric Compression Research Articles

Analysis and calculation method for concrete-encased CFST columns under eccentric compression

This paper presents a computational method for concrete-encased concrete-filled steel tube (CFST) columns under eccentric compression, which adopts the form of equivalent rectangular stress integrated by material constitutive curve. When establishing finite element model via ABAQUS, confinement provided by stirrup was considered to modify the constitutive law of encased concrete, so that the numerical modeling was in good agreement with tests. By analyzing the simulation results, the applicability of basic assumptions, such as plane section assumption, was discussed, and a database of 207 models with various parameters was created. The developed method took into account the influences of geometric nonlinearities of section shape, and its accuracy was verified against various collected tests and the database. It turned out that the formula presented was applicable to a wide range and had sufficient precision, while the predictions of N-M interaction curves of concrete-encased CFST columns in EC4, AISC and CECS were conservative due to the ignorance of the exact integration about irregular section-shape.

Test and direct strength method on slotted perforated cold-formed steel channels subjected to eccentric compression

This paper aims to investigate the buckling behaviors of cold-formed steel (CFS) channels with slotted web holes determined by the Steel Stud Manufacturers Association (SSMA) under eccentric compression, and propose the simplified direct strength method (DSM) formulas for engineering practicing. An experimental study on 20 specimens was conducted, including 18 slotted perforated specimens with nine eccentricities increasing from −20 mm to 20 mm and 2 unperforated specimens subjected to axial compression. Two kinds of nominal lip lengths for cross sections were selected as 15 mm and 20 mm. The experimental results indicated that the failure modes of slotted perforated specimens subjected to eccentric compression depended on the position of the eccentricity. Compared with the slotted perforated specimens subjected to pure axial compression, the ultimate loads of specimens subjected to positive eccentric compression decreased by 21.70 % on average, while they decreased by 16.38 % on average for those subjected to negative eccentric compression. Moreover, a nonlinear elasto-plastic finite element model (FEM) was developed and validated against the experimental results. Furthermore, combined with the experimental results, extensive FE parametric analyses were conducted to predict the eccentricity impact coefficient formulas. Finally, based on DSM of unperforated CFS members subjected to pure axial compression in AISI S100-16 and the eccentricity impact coefficient formulas, the suitable DSM design formulas for slotted perforated CFS channels determined by the SSMA under eccentric compression were proposed, without the need to calculate the elastic buckling critical stress for slotted perforated CFS channels.

Testing and design on local-biaxial flexural interactive buckling behavior of high strength steel welded box beam-columns subjected to biaxial bending

A testing research on the local-biaxial flexural interactive buckling of high strength steel Q460C, Q550D and Q690D welded box slender section beam-columns subjected to combined compression force and biaxial bending is reported. A total of thirteen median long steel columns, of which four manufactured from Q460C steel, five from Q550D steel and four from Q690D steel, were loaded until failure under biaxial eccentric compression forces. The local-biaxial flexural interaction buckling behavior is investigated by analyzing the test results. As an addition to the test data, the finite element parameter analyses are performed. The ultimate bearing capacities obtained from the test in this study and the numerical results presented in this study or in the existent literatures are compared with the calculation results in accordance with the design methods recommended in the American Specification ANSI/AISC 360–16, Eurocodes BS EN 1993-1-1 and BS EN 1993-1-5, and the newly proposed Effective Yield Strength Method (EYSM) and Effective Section Method (ESM) to check whether the current technical provisions and the new methods are suitable to the high strength steel beam-columns examined in this paper. The experimental and numerical results show that after taking the resistance factor into account, the ANSI/AISC 360–16, EN 1993-1-1 and BS EN 1993-1-5 are very conservative for the high strength steel beam-columns with greater member slenderness ratios (λ = 80, 90, 100) or with smaller plate width-to-thickness ratios (square box sections with b/t = 40, or rectangular box sections with h/t = 40 or b/t = 17); the new proposed EYSM provides an excellent prediction of the ultimate bearing capacities of the beam-columns and thus suitable for the high strength steels; but the new proposed ESM gives a very conservative estimate, over the range of steel nominal yield stress fy = 460 MPa ∼ 690 MPa, plate width-to-thickness ratio b/t = 40–80, member slenderness ratio λ = 40–100.

Failure mode-based calculation method for bearing capacities of corroded RC columns under eccentric compression

This paper proposed a failure mode-based calculation method for bearing capacities of corroded RC columns under eccentric compressive loads, which considered corrosion-induced mechanical property degradation of steel bars, cross-sectional reduction of steel bars and cross-sectional reduction of concrete. Through analyzing the stress and strain distributions over the normal cross-section, four balanced failures and six failure modes were identified for corroded RC columns under eccentric compressive loads. Balanced corrosion degrees were defined and methods to calculate them were proposed. Based on corrosion degree and balanced corrosion degrees, the failure mode of an eccentrically compressed corroded RC column could be predetermined in advance. Then, the methods to calculate the eccentric compressive bearing capacity under each failure mode were proposed. Subsequently, a dataset of eccentric compressive tests on 118 corroded and 27 non-corroded RC columns was established. The eccentric compressive bearing capacities calculated by the proposed failure mode-based method were found in good agreement with the test results, which demonstrated the validity of the proposed method. The failure mode-based calculation method will contribute to not only rapid and accurate performance evaluation of existing corroded RC columns, but also fast and efficient time-dependent reliability analysis for planned RC columns.

Numerical Investigation of Axial Force–Bending Moment Interaction for FRP-Confined Reinforced Concrete Columns with Internal Steel Transverse Reinforcement

Externally bonded fiber-reinforced polymer (FRP) laminates are widely used in the retrofitting and rehabilitation of reinforced concrete (RC) columns because they can increase the axial and bending moment capacities of these columns through a confinement mechanism. The confinement produced by FRP laminates acts in addition to that exerted by the internal transverse steel, although the latter is often neglected in current design standards and guidelines. In this study, a recently developed FRP-and-steel-confined concrete constitutive model was employed to numerically investigate the axial force–bending moment interaction for FRP-confined RC columns modeled using finite-element (FE) analysis. The proposed model was first validated against experimental data available in the literature and then used to quantify, through an extensive parametric study, the effects of transverse steel confinement, FRP strength, FRP stiffness, FRP reinforcement ratio, column diameter, concrete compressive strength, and load eccentricity ratio on the strength of FRP-confined RC columns subject to combined axial compression and bending moment. It was found that the internal steel confinement can substantially enhance the strength of these columns, especially for low concrete compressive strengths, large cross sections, and small eccentricities. When design code provisions limiting concrete and FRP deformations were considered for eccentrically loaded columns, the contribution of the steel confinement increased for increasing FRP reinforcement ratio. Based on the parametric study results, this investigation proposed an extension to eccentric axial compression of two relative confinement coefficients, which were previously developed to describe the contribution of transverse steel confinement to the peak strength of FRP-confined RC columns subject to pure compression.

Analysis on Large Deformation in a Slender Beam subjected to Eccentric Compressive Load (In Case of a Slender Beam with Non-Rotation Fixed Supports)

Analysis on Large Deformation in a Slender Beam subjected to Eccentric Compressive Load (In Case of a Slender Beam with Non-Rotation Fixed Supports)

Simulation modeling and design of circular concrete-filled double-skin tubular slender beam-columns with outer stainless-steel tube

The stainless-steel tube has been used to construct Concrete-Filled Steel Tubular (CFST) columns because it has a high resistance to fire and corrosion, good durability, and aesthetic appearance compared to the carbon steel tube. However, there is very little published research on eccentrically loaded circular Concrete-Filled Double-skin Steel Tubular (CFDST) slender beam-columns composed of an outer stainless-steel tube and an inner carbon-steel tube. In line with this, this paper presents a fiber-based simulation model for predicting the structural performance of CFDST slender columns with external circular stainless-steel tube under eccentric compression. The simulation modeling of load-deflection curves and load-moment interaction diagrams for slender CFDST beam-columns is developed and verified by the experimental results. The verified simulation model is then used to study the effects of geometric and material properties on structural performance. The range analysis is applied to the orthogonal design to identify the relative significance of the factors that influence the structural response. The orthogonal design covers CFDST beam-columns with a hollow ratio ranging from 0.1 to 0.8. The results indicate that the column slenderness ratio is the most significant factor, followed by the loading eccentricity ratio, the outer tube thickness, stainless steel proof stress, concrete strength, and carbon steel yield strength. The accuracy of the design method specified in Australian standard AS/NZS 2327, and the proposed design methods are evaluated. The proposed equation provides accurate strength predictions of CFDST slender columns where the external skin is made of stainless steel.

Mechanical properties of BFRP-reinforced glued laminated wood hollow round column under eccentric pressure

The FRP-wood column elements are lightweight and high performance, meeting the social demand for sustainable construction. In this study, a basalt fiber reinforced polymer (BFRP) reinforced glued laminated wood hollow round column structure is proposed. Small eccentricity compressive tests and numerical simulations were carried out on glued wood hollow columns strengthened with BFRP to study the effect of BFRP arrangement on the mechanical properties of glued wood hollow columns with constant material, size and eccentricity. All samples are compression side of the wood first yielded, and then some samples tensile side of the end of the wood fracture or the central section of the wood was pulled off, which belongs to the typical compression bending failure and conforms to the characteristics of small eccentric compression. The compressive load capacity of the wood column after BFRP pasting was increased by 3.4%∼30.54%, and the lateral flexural stiffness was increased by 1.44%∼23.86%. Meanwhile, pasting BFRP at the end and middle of the wood column can effectively restrain the compression deformation at the end and bending deformation at the middle, and obtain higher load capacity and lateral flexural stiffness. The numerical simulation results agree well with the experimental results and can effectively characterize the mechanical properties of BFRP-reinforced glued laminated wood hollow round column under eccentric loading conditions.

Crack growth life calculation approach of surface cracked landing gear strut under eccentric compression load by bulging effect

The landing gear strut is mainly subjected to eccentric compression load during service, and the calculation of its stress intensity factor is often considered as a challenge to calculate the surface crack growth life. Based on the bulging effect, we modify the stress intensity factor of the surface cracked cube, and obtain the stress intensity factor formula of the surface cracked strut. It calculates the stress intensity factor by using geometric characteristics and load characteristics, and calculates the crack growth life without meshing finite element model. In the study of surface fatigue crack growth of steel strut under eccentric compression load, the proposed approach to calculate the crack growth life of surface cracked strut is proved to be feasible. The method is simple and conservative.

Behavior of double-skin truss-reinforced composite walls under eccentric compression

This paper presented an experimental and theoretical studies on double-skin truss-reinforced composite wall (DSTCW) subjected to eccentric compression. Five full-scale DSTCWs with different loading eccentricities, height-width ratios and truss spacing were conducted under uniaxial eccentric compressive. The effects of those variations on the failure mode, load- axial displacement curve, lateral deflection, strain distribution were discussed. Subsequently, the finite element (FE) models were built and verified to discuss the working mechanism of DSTCWs under eccentric compression, and an extensive parametric analysis was performed to find the vital parameters on the mechanical behavior of DSTCWs subjected to eccentric compression. Finally, based on Eurocode standard EC4, the Interaction model for DSTCW was proposed to estimate the bearing capacity subjected to eccentric compression. The proposed Interaction model was validated against the results from FE model analysis and experiments.

Behavior of UHPC columns confined by high-strength transverse reinforcement under eccentric compression

This paper presents the experimental and analytical studies on the compressive behavior of ultra-high performance concrete (UHPC) columns confined by high-strength transverse reinforcement under eccentric compression. Nine columns including test variables of spacing, strength and arrangement type of transverse reinforcements, steel fiber content and eccentricity were tested to analyze the load-lateral deflection behavior, failure modes and carrying capacity. The experiment results showed that the deformation capacity, peak load and residual carrying capacity of UHPC columns confined by high-strength transverse reinforcement under eccentric loading were significantly better than those of ordinary-strength transverse reinforcement. Reducing the spacing of transverse reinforcement and increasing the volume fraction of steel fiber could also improve the ductility and carrying capacity of UHPC columns. Then, a mesoscale model was proposed to characterize the tensile behavior of UHPC which considered the fiber inclination, fiber-matrix interface bonding and fiber embedded length. Based on the proposed tensile model, a simplified method for calculating the carrying capacity of UHPC columns under large eccentric compression was developed, where the tensile behavior of UHPC and the confinement effect of transverse reinforcements were considered. The errors between the theoretical and test values were within 10%, indicating that this method can be used to guide the design of UHPC columns.

Uniaxial Eccentric Load Behavior of L-CFSST Composite Column

This study presents the mechanical behavior of L-shaped concrete-filled square steel tube (L-CFSST) composite columns under uniaxial eccentric compression. Nine specimens were tested and the effects of eccentricity, steel tube thickness, steel yield strength, and slenderness ratio were investigated regarding failure modes, ultimate load, load-lateral displacement curves, and load-strain curves. Test results showed that, under uniaxial eccentric load, these columns showed favorable mechanical properties and steel tubes showed strong cooperative working performance. There were two types of failure modes for these columns: local buckling of the steel tube or overall bending of the specimen. ABAQUS was used to simulate the loading process and the accuracy of the numerical simulation results was verified by comparing failure characteristics, load-displacement curves, and ultimate bearing capacity with the test results. The N/Nu-M/Mu curves of the columns under uniaxial eccentric load with different parameters were simulated by the finite element method. A simplified formula for predicting the N/Nu-M/Mu relationship was established based on the finite element analysis results, which might be a workable approach for designing L-CFSST composite columns in engineering practice.

Behavior and design of circular concrete columns strengthened with textile-reinforced mortar subjected to eccentric compression

Textile-reinforced mortar (TRM) is a cheaper and eco-friendlier material for the concrete confinement than steel and fiber-reinforced polymer (FRP). The behaviors of plain concrete slender columns with circular cross-section strengthened with TRM under eccentric compression were analyzed both experimentally and analytically in this paper. The test results showed that TRM could effectively inhibit the extension of cracks in columns, and increasing the number of textile layers from one to three led to a 44% increase in ultimate load. Meanwhile, the secondary moment of columns relative to the total moment varied from 20% to 35%, which was positively related to the confinement effectiveness of TRM. Then, a comparison of the behaviors of confined concrete columns under axial load-flexural moment (P-M) loading demonstrated that the confinement provided by TRM was relatively insufficient when compared to steel and FRP, behaving a post-peak softening phase of compressive constitutive curves. However, the textile with high tensile strength improved the stress distribution of cross-section of eccentrically loaded columns, thereby observing a much slower reduction in ultimate load with the increase of the eccentric ratio. Finally, according to a cross-section bearing capacity analysis, the procedure of analytical calculations was proposed to predict the ultimate load of TRM-confined concrete columns at a given eccentric ratio. Furthermore, the proposed analytical calculations provided a parametric study to reveal the correlation between the eccentric ratio and the number of textile layers, and then a simplified regression formula for design purpose was developed. This research highlights the behavior and design of concrete strengthened with TRM under P-M loading, which would give researchers and engineers an insight.

Experimental and numerical investigation on the effect of concrete infill in pultruded GFRP CHS intermediate and long columns under axial and eccentric compression

The paper presents an experimental investigation of concrete-filled (CFFT) pultruded glass fibre-reinforced (GFRP) circular tubular columns under concentric and eccentric loading. The effective slenderness ratios of the CFFTs were 33, 44 and 55 and were tested under two different eccentricities of 28.5 mm and 57 mm. The failure modes observed for the CFFTs include localised hoop rupture and longitudinal splitting of the GFRP tube with concrete crushing. The axial load-carrying capacities of the CFFTs decreased with increasing eccentricity and slenderness. The strength and the ductility of the CFFTs were compared with their circular hollow section (CHS) counterparts tested in a previous study. A P-M interaction curve was developed, and its applicability was assessed against the experimental results for different slenderness ratios. The ultimate axial load and the locus and nature of the failure modes of CFFTs predicted from the developed finite element models were in good agreement with the experimental observations. The extent of damage of the GFRP tube in the CFFTs was compared to the damage of the GFRP CHS columns using FE analysis employing the Hashin damage material model for GFRP tube.

Numerical investigation and design of cold-formed steel built-up section beam-column members under moment gradients

This paper presents the numerical investigation and design of cold-formed steel (CFS) built-up section beam-column members experiencing non-uniform minor axis bending. Detailed considerations of material nonlinearity and initial imperfections were involved in developing finite element models of the thin-walled built-up section members undergoing eccentric compression. The finite element models calibrated against the existing experimental results were then employed for a parametric study. Numerical predictions of 279 built-up section beam-columns over a broad spectrum of cross-sectional geometries and moment distributions along the member length were obtained in this investigation. For the built-up open and closed section members included in the numerical analyses, non-uniformly distributed moments resulted in the strength enhancements by average of 39% and 37%, respectively. Furthermore, based on the 279 numerical predictions obtained in this investigation and 91 data collected from the literature, the nominal strengths predicted by the design rules codified in the current standards and proposed in the previous studies were examined for the CFS built-up section beam-column members with end moment ratios ranging from −1.0 to 1.0. Underpinned by the assessment results, design recommendations and modified design rules were provided for the CFS built-up open and closed section members undergoing synchronous axial load and non-uniform minor axis moment, respectively.

Performance of RC beam-column assemblies during and after elevated temperature to resist progressive collapse

In practice, fire is one of the accidental loads that can result in the progressive collapse of buildings but the commonly used alternate load path (ALP) approach often ignores the impact of fire. Therefore, numerical models based on the finite element software ABAQUS are employed to investigate the performance of reinforced concrete (RC) beam-column assemblies during and after high temperature to resist progressive collapse. The thermal–mechanical sequential coupling method is used for analysis. The effects of fire durations, boundary conditions (middle or penultimate column removal) and side column subject to fire are studied. Previous test results demonstrated that compressive arch action (CAA) and catenary action (CA) are developed in sequence to prevent progressive collapse for the assemblies at ambient temperature. However, the numerical results show that the in-fire assemblies could not develop CA owing to severe degradation of rebar elongation and thus, the load resistance of in-fire assemblies controlled by CAA capacity. Further increasing fire duration to 90 mins, the CAA capacity of the assemblies decreases over 70% compared with that at ambient temperature. Since the rebar can recover most of its mechanical properties after cooling down, the assembly after fire (i.e., exposed to fire then cooled down) can also successively develop flexural action (FA), compressive arch action (CAA) and catenary action (CA) to resist progressive collapse, which is similar to that of intact RC frame at ambient temperature. Under the penultimate column removal scenario, the exterior side column of the post-fire specimen suffers large eccentric compression failure, which causes the highest collapse risk.

Effects of structural size and corner radius on eccentric failure of rectangular CFRP-wrapped RC columns: Meso-scale modellings

The strengthening and retrofitting technique with fiber-reinforced polymer (FRP) composites on reinforced concrete (RC) columns has been widely popular. Compared with concentric compression behaviors of rectangular FRP-confined concrete columns, there are only limited investigations on their eccentric behaviors. Additionally, the applicability of existing design codes obtained from tested small-size columns in calculating load capacity of large-size columns has not been reasonably explained. In view of this, this paper developed a meso-scale numerical analysis method using a random aggregate model based on consideration of concrete heterogeneity. A series of rectangular carbon FRP (CFRP)-confined RC columns having different cross-sectional heights were modelled to investigate the influences of corner radius and size effect on their eccentric compression behaviors. Simulated results showed that there was a transformation of failure mode from brittle compression failure to ductile tensile failure with the increasing load eccentricity. An identical globally failure mode for rectangular columns having different cross-sectional heights was observed whereas crack widths became larger obviously with the increasing cross-sectional height. Regarding the axial load versus mid-height deflection relationship, the corner radius had a significant influence on maximum axial load and softening stage, especially at smaller load eccentricities. One can see that from nominal interaction diagrams, small-eccentrically-loaded columns exhibited more obvious size effect than large-eccentrically-loaded columns. The safety factor of load capacity decreased with the increasing cross-sectional height compared with existing design codes of ACI 440.2R-17 and GB 50608, illustrating that design codes appear to be not conservative for large-size specimens. Taking the influence of size effect into account, the design equations suggested by ACI 440.2R-17 were modified in this study, and the rationality of this correction methodology was verified against simulated data and results of tested large-size rectangular columns.

Research on the Seismic Performance of Prefabricated Bridge Piers Using UHPC Grout under an Eccentric Load

At present, research on prefabricated piers is limited to the axial compression state. However, many piers are under small eccentric compression in practical engineering. In this article, the seismic performance of ultrahigh performance concrete (UHPC)-grouted corrugated pipe-connected piers under small eccentric compression was studied. A pseudostatic test was carried out by using a prefabricated pier column model connected with UHPC-grouted corrugated pipes. The failure mechanism of the plastic hinge area of the column base was studied, and the failure mode, energy dissipation capacity, displacement ductility, and ultimate bearing capacity were compared with those of an ordinary axially compressed pier column structure. The result shows that compared to the conventional cast-in-place(CIP) pier, the overall energy dissipation capacity and the ductility factor of assembled pier with UHPC-grouted corrugated pipe-connection were decreased approximately by 5.0% and by 10%, respectively. The pinching phenomenon of the hysteresis curve of the precast pier was more obvious. When the assembled piers were under small eccentric compression, the overall energy dissipation capacity was close to that of conventional CIP piers and the ductility factor was improved by 20%. Comparison of two precast piers using the same UHPC grout connections shows that the stiffness degradation process of precast pier under small eccentric compression was similar to that under axial compression. But the ductility coefficient of precast pier under small eccentric compression increased by about 20%. The small eccentric compression caused different damage degrees in the plastic hinge zone at the bottom of the precast column. The ultimate load in the same direction as the additional bending moment was 55% lower than that of the opposite direction.

A nonlinear fibre beam-column model for partially encased composite columns incorporating local buckling effect

Partially encased composite (PEC) columns are being widely used as vertical load carrying members in high-rise building structures. The complex structural behaviour of PEC columns at ultimate and failure states, related to local buckling of steel section and confinement effect of concrete, has posed significant difficulties and computational costs for accurate analysis of these members. To address this issue, this paper presents a nonlinear fibre beam-column (FBC) model for efficient and accurate analysis of PEC columns. A 2D Euler-Bernoulli beam element based on geometrically exact beam theory is employed, which has fibre cross sections accounting for the material nonlinearity of steel and concrete. A generalised effective width method (GEWM) is developed and integrated in the FBC model to simulate the stress redistribution in the steel section due to the progression of local and post-local buckling. Numerical examples demonstrate that the proposed FBC model can reasonably predict the behaviour of short PEC columns under concentric and eccentric compression, as well as the global buckling behaviour of long PEC columns. The computational cost of the proposed FBC model is considerably lower than that of 3D finite element analysis. The numerical examples also show that the incorporation of the local buckling effect (GEWM) leads to decreases in the ultimate and post-peak loads predicted by the FBC model. The effect of local buckling becomes insignificant for long PEC columns with length-to-depth ratios greater than 15.

Finite element analysis and bearing capacity of CRACFDSST columns under eccentric compression

The mechanical behaviour of ceramic recycled aggregate concrete-filled double-skin square steel tubular (CRACFDSST) columns under eccentric compression, with changing slenderness ratio, eccentricity and hollow section ratio parameters, was investigated, and 12 columns were tested. The test results indicated that all specimens exhibited elastic–plastic instability failure. No cement-based materials attached to the ceramic glaze surface were observed at the crushed position. Additionally, the CRACFDSST columns had good ductility and bearing capacity. The constitutive relationship of ceramic recycled concrete constrained by the square steel tube was adopted to establish finite element (FE) models, which considered the plastic damage of concrete. The FE calculation results agreed well with the experimental results. FE analyses of ceramic recycled concrete and ordinary concrete members were conducted, and the stress distributions of the steel tubes and concrete, the load–deflection curves at the mid-span, and the interaction between the steel tubes and concrete of the members were compared. Subsequently, 312 FE examples were used to analyse the effects of the steel yield strength, concrete strength, hollow section ratio, nominal steel ratio, diameter-to-thickness ratio of the inner steel tube, slenderness ratio and ceramic coarse aggregate replacement rate on the moment-load curves. Ultimately, a simplified formula was proposed to predict the bearing capacity of CRACFDSST columns under eccentric compression.