• Computers and Concrete
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• v.14 no.5
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• pp.613-633
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• 2014

A double-skinned composite tubular (DSCT) column, which consists of concrete and inner and outer tubes, was finally developed to overcome the weaknesses of concrete filled tube columns by reducing the self-weight of the column and confining the concrete triaxially. Research pertaining to the stiffness and strength of the column and the confining effect in a DSCT column has been carried out. However, detailed studies on the confining stress, especially the internal confining stress in a DSCT column, have not been carried out. Internal and external confining stresses should be evaluated to determine the effective confining stress in a DSCT column. In this paper, the confining stresses of concrete before and after insertion of an inner tube were studied using finite element analysis. The relationship between the internal or external confining stresses and the theoretical confining stress was investigated by parametric studies. New modified formulae for the yield and buckling failure conditions based on the formulae suggested by former researchers were proposed. Through analytical studies, the modified formulae were verified to be effective for economic and reasonable design of the inner tubes in a DSCT column under the same confining stress.

• Steel and Composite Structures
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• v.23 no.4
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• pp.483-491
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• 2017

This paper presents an experimental study on the behavior of concrete-encased composite columns with multiseparate steel sections subjected to axial and eccentric loads. Six 1/4-scaled concrete-encased composite columns were tested under static loads. The specimens were identical in geometric dimensions and configurations, and the parameter of this experiment was the eccentricity ratio of the applied load. Each two of the specimens were loaded with 0, 10%, and 15% eccentricity ratios. The capacity, deformation pattern, and failure mode of the specimens were carefully examined. Test results indicate that full composite action between the concrete and the steel sections can be realized even though the steel sections do not connect with one another. The concrete-encased composite columns can develop stable behavior and sufficient deformation capacity by providing enough transverse reinforcing bars. Capacities of the specimens were evaluated based on both the Plain Section Assumption (PSA) method and the superimposition method. Results show that U.S. and Chinese codes can be accurate and safe in terms of bending capacities. Test results also indicate that the ACI 318 and Mirza methods give the best predictions on the flexural stiffness of this kind of composite columns.

• Steel and Composite Structures
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• v.1 no.1
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• pp.51-74
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• 2001

A series of tests on concrete-filled SHS (Square Hollow Section) stub columns (twenty), columns (eight) and beam-columns (twenty one) were carried out. The main parameters varied in the tests are (1) Confinement factor (${\xi}$) from 1.08 to 5.64, (2) concrete compression strength from 10.7MPa to 36.6MPa, (3) tube width to thickness ratio from 20.5 to 36.5. (4) load eccentricity (e) from 15 mm to 80 mm and (5) column slenderness (${\lambda}$) from 45 to 75. A mechanics model is developed in this paper for concrete-filled SHS stub columns, columns and beam-columns. A unified theory is described where a confinement factor (${\xi}$) is introduced to describe the composite action between the steel tube and filled concrete. The predicted load versus axial strain relationship is in good agreement with stub column test results. Simplified models are derived for section capacities and modulus in different stages of the composite sections. The predicted beam-column strength is compared with that of 331 beam-column tests with a wide range of parameters. A good agreement is obtained. The predicted load versus midspan deflection relationship for beam-columns is in good agreement with test results. A simplified model is developed for calculating the member capacity of concrete-filled SHS columns. Comparisons are made with predicted columns strengths using the existing codes such as LRFD (AISC 1994), AIJ (1997), and EC4 (1996). Simplified interaction curves are derived for concrete-filled beam-columns.

• Steel and Composite Structures
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• v.24 no.2
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• pp.201-211
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• 2017

This study evaluates the reliability of present European codes in predicting the collapse load of columns made with perforated cold-formed steel (CFS) profiles under combined axial load and bending. To this aim, a series of experimental tests on slender open-section specimens have been performed at varying load eccentricity. Preliminarily, stub column tests have also been performed to calculate the effective section properties of the investigated profile. By comparison of experimental data with code-specified M-N strength domains, the authors demonstrate that present code formulations may underestimate the collapse load of thin-walled perforated open sections. The study is the first step of a wider experimental and numerical study aimed at better describing strength domains of perforated CFS open sections.

• Structural Engineering and Mechanics
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• v.53 no.4
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• pp.745-765
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• 2015

A nonlinear Finite Element (FE) algorithm is proposed to analyze the Reinforced Concrete (RC) columns subjected to Cyclic Loading (CL), Cyclic Oriented Lateral Force and Axial Loading (COLFAL), Monotonic Loading (ML) or Oriented Pushover Force and Axial Loading (OPFAL) in any direction. In the proposed algorithm, the following parameters are considered: uniaxial behavior of concrete and steel elements, the pseudo-plastic hinge produced in the critical sections, and global behavior of RC columns. In the proposed numerical simulation, the column is discretized into two Macro-Elements (ME) located between the pseudo-plastic hinges at critical sections and the inflection point. The critical sections are discretized into Fixed Rectangular Finite Elements (FRFE) in general cases of CL, COLFAL or ML and are discretized into Variable Oblique Finite Elements (VOFE) in the particular cases of ML or OPFAL. For pushover particular case, a fairly fast converging and properly accurate nonlinear simulation method is proposed to assess the behavior of RC columns. The proposed algorithm has been validated by the results of tests carried out on full-scale RC columns.

• Journal of Korean Society of Steel Construction
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• v.9 no.2 s.31
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• pp.277-285
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• 1997

To investigate the shear strength and hysteretic behavior of SRC column to H steel beam joints, seven cruciform specimens were fabricated and tested. The test specimens showed stable hysteresis behavior with a little pinching. The strength decreased with increase in deflection after the speciemens reached at the maximum strength. The shear strength of panel zones increased with increased in the concrete amount of SRC column sections. The shear strength may conservatively be estimated by the sum of shear yielding strength of steel column web, plastic bending strength of steel column flange and ultimate shear strength of concrete in the panel zone.

• Steel and Composite Structures
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• v.26 no.3
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• pp.315-328
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• 2018

Built-up Double-I (BD-I) columns consist of two hot rolled IPE sections and two cover plates which are welded by fillet welds. In Iran, this type of column is commonly used in braced frames with simple connections and sometimes in low-rise Moment Resisting Frames (MRF) with Welded Flange Plate (WFP) beam-column detailing. To evaluate the seismic performance of WFP connection of I-beam to BD-I column, traditional and modified exterior MRF connections were tested subjected to cyclic prescribed loading of AISC. Test results indicate that the traditional connection does not achieve the intended behavior while the modified connection can moderately meet the requirements of MRF connection. The numerical models of the connections were developed in ABAQUS finite element software and validated with the test results. For this purpose, moment-rotation curves and failure modes of the tested connections were compared with the simulation results. Moreover to avoid improper failure modes, some improvements of the connections were evaluated through a numerical study.

• Steel and Composite Structures
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• v.33 no.4
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• pp.489-507
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• 2019

In order to obtain high bearing capacity and good ductility simultaneously, a structural column with hybrid normal and high strength steel (HNHSS) welded box section has been developed. Residual stress is an important factor that can influence the behaviour of a structural member in steel structures. Accordingly, the magnitudes and distributions of residual stresses in HNHSS welded box sections were investigated experimentally using the sectioning method. In this study, the following four box sections were tested: one normal strength steel (NSS) section, one high strength steel (HSS) section, and two HNHSS sections. Based on the experimental data from previous studies and the test results of this study, the effects of the width-to-thickness ratio of plate, yield strength of plate, and the plate thickness of the residual stresses of welded box sections were investigated in detail. A unified residual stress model for NSS, HSS and HNHSS welded box sections was proposed, and the corresponding simplified prediction equations for the maximum tensile residual stress ratio (${\sigma}_{rt}/f_y$) and average compressive residual stress ratio (${\sigma}_{rc}/f_y$) in the model were quantitatively established. The predicted magnitudes and distributions of residual stresses for four tested sections in this study by using the proposed residual stress model were compared with the experimental results, and the feasibility of this proposed model was shown to be in good agreement.

• Structural Engineering and Mechanics
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• v.50 no.3
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• pp.323-347
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• 2014

This paper proposes a Particle Swarm Optimization (PSO) algorithm, which is improved by making use of the Harmony Search (HS) approach and called HS-PSO algorithm. A computer code is developed for optimal sizing design of non-linear steel frames with various semi-rigid and rigid beam-to-column connections based on the HS-PSO algorithm. The developed code selects suitable sections for beams and columns, from a standard set of steel sections such as American Institute of Steel Construction (AISC) wide-flange W-shapes, such that the minimum total cost, which comprises total member plus connection costs, is obtained. Stress and displacement constraints of AISC-LRFD code together with the size constraints are imposed on the frame in the optimal design procedure. The nonlinear moment-rotation behavior of connections is modeled using the Frye-Morris polynomial model. Moreover, the P-${\Delta}$ effects of beam-column members are taken into account in the non-linear structural analysis. Three benchmark design examples with several types of connections are presented and the results are compared with those of standard PSO and of other researches as well. The comparison shows that the proposed HS-PSO algorithm performs better both than the PSO and the Big Bang-Big Crunch (BB-BC) methods.

• Computers and Concrete
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• v.15 no.4
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• pp.643-671
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• 2015

Chloride induced reinforcement corrosion is widely accepted to be the most frequent mechanism causing premature degradation of reinforced concrete members, whose economic and social consequences are growing up continuously. Prevention of these phenomena has a great importance in structural design, and modern Codes and Standards impose prescriptions concerning design details and concrete mix proportion for structures exposed to different external aggressive conditions, grouped in environmental classes. This paper focuses on reinforced concrete column section load carrying capacity degradation over time due to chloride induced steel pitting corrosion. The structural element is considered to be exposed to marine environment and the effects of corrosion are described by the time degradation of the axial-bending interaction diagram. Because chlorides ingress and consequent pitting corrosion propagation are both time-dependent mechanisms, the study adopts a time-variant predictive approach to evaluate residual strength of corroded reinforced concrete columns at different lifetimes. Corrosion initiation and propagation process is modelled by taking into account all the parameters, such as external environmental conditions, concrete mix proportion, concrete cover and so on, which influence the time evolution of the corrosion phenomenon and its effects on the residual strength of reinforced concrete columns sections.