• Structural Engineering and Mechanics
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• 제83권3호
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• pp.387-400
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• 2022

The practice of using encased steel-concrete columns in medium to high-rise structures has expanded dramatically in recent years. The study evaluates existing methodologies and codal guidelines for estimating the ultimate load-carrying characteristics of concrete-encased short columns experimentally. The present condition of composite column design methods was analyzed using the Egyptian code ECP203-2007, the American Institute of Steel Construction's AISC-LRFD-2010, Eurocode EC-4, the American Concrete Institute's ACI-318-2014, and the British Standard BS-5400-5. According to the codes, the axial load carrying characteristics of both the encased steel and concrete sections was examined. The effect of load-carrying capacities in different forms of encased steel sections on encased steel-concrete columns was studied experimentally. The axial load carrying capacity of twelve concrete-encased columns and four conventional reinforced columns were examined. The conclusion is that the confinement was not taken into account when forecasting the strength and ductility of the encased concrete, resulting in considerable disparities between codal provisions and experimental results. The configuration of the steel section influenced the confining effect. Better confinement is achieved with the laced and battened section than with the infilled steel tube reinforced and conventionally reinforced section. The ECP203-2007 code reported the most conservative results of all the codes used.

• Steel and Composite Structures
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• 제22권4호
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• pp.797-820
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• 2016

This paper simulates the hysteretic behavior of steel reinforced recycled concrete (SRRC) columns under cyclic loads using OpenSees software. The effective fiber model and displacement-based beam-column element in OpenSees is applied to each SRRC columns. The Concrete01 material model for recycled aggregate concrete (RAC) and Steel02 material model is proposed to perform the numerical simulation of columns. The constitutive models of RAC, profile steel and rebars in columns were assigned to each fiber element. Based on the modelling method, the analytical models of SRRC columns are established. It shows that the calculated hysteresis loops of most SRRC columns agree well with the test curves. In addition, the parameter studies (i.e., strength grade of RAC, stirrups strength, steel strength and steel ratio) on seismic performance of SRRC columns were also investigated in detail by OpenSees. The calculation results of parameter analysis show that SRRC columns suffered from flexural failure has good seismic performance through the reasonable design. The ductility and bearing capacity of columns increases as the increasing magnitude of steel strength, steel ratio and stirrups strength. Although the bearing capacity of columns increases as the strength grade of RAC increases, the ductility and energy dissipation capacity decreases gradually. Based on the test and numerical results, the flexural failure mechanism of SRRC columns were analysed in detail. The computing theories of the normal section of bearing capacity for the eccentrically loaded columns were adopted to calculate the nominal bending strength of SRRC columns subjected to vertical axial force under lateral cyclic loads. The calculation formulas of horizontal bearing capacity for SRRC columns were proposed based on their nominal bending strength.

• Steel and Composite Structures
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• 제45권1호
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• pp.23-38
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• 2022

This paper presents experimental and analytical studies of eccentrically loaded concrete-filled double steel (CFDST) and concrete-filled double skin tube (DCFST) columns having outer stainless steel tube. Eighteen CFDST and DCFST column specimens were manufactured and tested to examine the strength and load-deflection responses. In the study, the main parameters were concrete strength, load eccentricity, cross section and slenderness. The strengths, load-deflection diagrams and failure patterns of the columns were observed. In addition, the tested CFDST and DCFST columns were analyzed to attain the capacity and load versus lateral deflection responses. The obtained theoretical results were compared with the test results. A parametric study was also performed to research the effects of the ratio of eccentricity (e/H_o) slenderness ratio (L/r), H_o/t_o ratio, H_i/t_i ratio and the concrete compressive strength on the behavior of columns. In this work, the obtained results indicated that the ductility and capacity of columns were affected by cross section, concrete strength, steel strength, loading eccentricity and slenderness.

• Steel and Composite Structures
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• 제20권3호
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• pp.571-597
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• 2016

A new unified design formula for calculating the composite compressive strength of the axially loaded circular concrete filled double steel tubular (CFDST) short and slender columns is presented in this paper. The formula is obtained from the analytic solution by using the limit equilibrium theory, the cylinder theory and the "Unified theory" under axial compression. Furthermore, the stability factor of CFDST slender columns is derived on the basis of the Perry-Robertson formula. This paper also reports the results of experiments and finite element analysis carried out on concrete filled double steel tubular columns, where the tested specimens include short and slender columns with different steel ratio and yield strength of inner tube; a new constitutive model for the concrete confined by both the outer and inner steel tube is proposed and incorporated in the finite element model developed. The comparisons among the finite element results, experimental results, and theoretical predictions show a good agreement in predicting the behavior and strength of the concrete filled steel tubular (CFST) columns with or without inner steel tubes. An important characteristic of the new formulas is that they provide a unified formulation for both the plain CFST and CFDST columns relating to the compressive strength or the stability bearing capacity and a set of design parameters.

• 국제초고층학회논문집
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• 제7권4호
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• pp.327-342
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• 2018

Geopolymer concrete (GPC), which is recognised as an environmentally friendly alternative to ordinary Portland cement (OPC) concrete, has been reported to possess high fire resistance. However, very limited research has been conducted to investigate the behaviour of geopolymer concrete-filled steel tubular (GCFST) columns at either ambient or elevated temperatures. This paper presents the compressive test results of a total of 15 circular concrete-filled steel tubular (CFST) stub columns, including 5 specimens tested at room temperature, 5 specimens tested at elevated temperatures and the remaining 5 specimens tested for residual strength after exposure to elevated temperatures. The main variables in the test program include: (a) concrete type; (b) concrete strength; and (c) curing condition of geopolymer concrete. The test results demonstrate that GCFST columns have similar ambient temperature behaviour compared with the conventional CFST counterparts. However, GCFST columns exhibit better fire resistance than the conventional CFST columns. Meanwhile, it is found that the GCFST column made with heat cured GPC has lower strength loss than other columns after exposure to elevated temperatures. The research results highlight the possibility of using geopolymer concrete to improve the fire resistance of CFST columns.

• Steel and Composite Structures
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• 제39권5호
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• pp.583-598
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• 2021

The composite steel reinforced concrete (SRC) columns have been widely used in Structural Engineering due to their good performances. Many studies have been done on the SRC columns' performances, but they focused on the ordinary types with conventional configurations and materials. In this study, nine new types of steel reinforced lightweight aggregate concrete (SRLAC) short columns with cross-shaped (+shaped and X-shaped) steel section were tested under monotonically axial compressive load; the studied parameters included steel section ratio, steel section configuration, ties spacing, lightweight aggregate concrete (LWAC) strength, and longitudinal bars ratio. From the results, it could be found that the specimens with larger ties ratio, concrete strength, longitudinal bars ratio, and steel section ratio achieved great strength and stiffness due to the excellent interaction between the concrete and steel. The well-confined concrete core could strengthen the steel section. The ductility and toughness of the specimens were influenced by the LWAC strength, steel section ratio, and longitudinal bars ratio; in addition, larger ties ratio with smaller LWAC strength led to better ductility and toughness. The load transfer between concrete and steel section largely depends on the LWAC strength, and the ultimate strength of the new types of SRLAC short columns could be approximately predicted, referring to the codes' formulas of ordinary types of steel reinforced concrete (SRC) columns. Among the used codes, the BS-5400-05 led to the most conservative results.

• Steel and Composite Structures
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• 제17권4호
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• pp.431-452
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• 2014

The present study focuses on the mechanical behaviour of concrete filled double skin steel tubular (CFDST) stub columns confined by fiber reinforced polymer (FRP). A series of axial compression tests have been conducted on two CFDST stub columns, eight CFDST stub columns confined by FRP and a concrete-filled steel tubular (CFST) stub column confined by FRP, respectively. The influences of hollow section ratio, FRP wall thickness and fibre longitudinal-circumferential proportion on the load-strain curve and the concrete stress-strain curve for stub columns with annular section were discussed. The test results displayed that the FRP jacket can obviously enhance the carrying capacity of stub columns. Based on the test results, a new model which includes the effects of confinement factor, hollow section ratio and lateral confining pressure of the outer steel tube was proposed to calculate the compressive strength of confined concrete. Using the present concrete strength model, the formula to predict the carrying capacity of CFDST stub columns confined by FRP was derived. The theoretically predicted results agree well with those obtained from the experiments and FE analysis. The present method is also adapted to calculate the carrying capacity of CFST stub columns confined by FRP.

• Steel and Composite Structures
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• 제13권3호
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• pp.277-293
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• 2012

The interaction between steel tube and concrete core is the key design considerations for concrete-filled steel tube columns. In a concrete-filled steel tube (CFST) column, the steel tube provides confinement to the concrete core which permits the composite action among the steel tube and the concrete. Due to construction faults and plastic shrinkage of concrete, the debonding separation at the steel-concrete interface weakens the confinement effect, and hence affects the behaviour and bearing capacity of the composite member. This study investigates the axial loading behavior of the concrete filled circular steel tube columns with debonding separation. A three-dimensional nonlinear finite element model of CFST composite columns with introduced debonding gap was developed. The results from the finite element analysis captured successfully the experimental behaviours. The calibrated finite element models were then utilized to assess the influence of concrete strength, steel yield stress and the steel-concrete ratio on the debonding behaviour. The findings indicate a likely significant drop in the load carrying capacity with the increase of the size of the debonding gap. A design formula is proposed to reduce the load carrying capacity with the presence of debonding separation.

• Steel and Composite Structures
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• 제23권6호
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• pp.669-682
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• 2017

The use of ultra high performance concrete (UHPC) in composite columns offers numerous structural benefits, and has received recent research attention. However, the information regarding the behavior of steel tube confined concrete (STCC) columns employing UHPC has been extremely limited. Thus, this paper presents an overview of previous experimental studies on circular STCC columns with taking into account various concrete strengths to point out their distinctive features. The effect of the confinement factor and the diameter to thickness ratio on both strength and ductility in circular STCC columns employing UHPC was investigated. The applicability of current design codes such as EC4, AISC, AIJ and some available analytical models for concrete confined by steel tube was also validated by the comparison of ultimate loads between the prediction and the test results of Schneider (2006) and Xiong (2012). To predict the stress-strain curves for confined UHPC in circular STCC stub columns, a simplified model was proposed and verified by the comparison with experimental stress-strain curves.

• Steel and Composite Structures
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• 제47권5호
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• pp.645-661
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• 2023

Concrete-filled steel tubular columns with double inner steel tubes (CFST-DIST) are a novel type of composite members developed from conventional concrete-filled steel tubular (CFST) columns. This paper investigates the structural performance of circular CFST-DIST stub columns using nonlinear finite element (FE) analysis. A numerical model was developed and verified against existing experimental test results. The validated model was then used to compare circular CFST-DIST stub columns' behavior with their concrete-filled double skin steel tubular (CFDST) and CFST counterparts. A parametric study was performed to ascertain the effects of geometric and material properties on the axial performance of CFST-DISTs. The FE results and the available test data were used to assess the accuracy of the European and American design regulations in predicting the axial compressive capacity of circular CFST-DIST stub columns. Finally, a new design model was recommended for estimating the compressive capacity of CFST-DISTs. Results clarified that circular CFST-DIST columns had the advantages of their CFST counterparts but with better ductility and strength-to-weight ratio. Besides, the investigated design codes led to conservative predictions of the compressive capacity of circular CFST-DIST columns.