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International Journal of Steel Structures

, Volume 19, Issue 1, pp 147–156 | Cite as

Tension Chord Model and Flexural Stiffness for Circular CFST in Bending

  • Carlos ZanuyEmail author
Article
  • 34 Downloads

Abstract

The flexural behavior of circular concrete-filled steel tubes (CFST) is addressed in the present paper, with the aim of understanding the contribution of the concrete infill and the steel tube to the flexural stiffness under in-service loads. The provisions given by current codes of practice are oversimplified and they result in a very different contribution of the concrete infill from one code to another. In the present paper, a mechanical approach is proposed by taking into account the stress transfer mechanism from the steel to the concrete through bond stresses. The paper firstly addresses the response of the cracked section in pure bending. Secondly, a tension chord model for CFST is proposed, so that the contribution of concrete in tension between cracks (tension stiffening) can be evaluated. The model capabilities are compared with experimental results from the scientific literature and with own experimental results of the author, showing that the proposed approach can predict the flexural stiffness of CFST very satisfactorily. For the first time, a model with sound mechanical background is introduced to calculate the bending stiffness of CFST.

Keywords

Concrete-filled steel tubes Bending behavior Serviceability Tension stiffening 

List of symbols

Ac

Concrete area

Act,eff

Effective concrete area in tension

As

Steel area

D

Diameter

Ec

Concrete modulus of deformation

Es

Steel modulus of elasticity

EI

Flexural stiffness

EIcr

Cracked stiffness

EcIc

Flexural stiffness of the uncracked concrete infill

EsIs

Flexural stiffness of the hollow steel tube

M

Bending moment

T

Tensile force

Ts, Tc

Tensile force carried by steel and concrete, respectively

Us

Perimeter of the steel–concrete contact

fc

Concrete compressive strength

fct

Concrete tensile strength

fy

Steel yielding strength

sr

Crack spacing

srm

Average crack spacing

t

Thickness

x

Abscissa

xcr

Neutral axis depth

y

Vertical coordinate, from the center of the tube

z

Distance of a fiber of the cross-section from the neutral axis

αx

Semi-angle to define the effective concrete area in tension

εs, εc

Steel and concrete strain, respectively

εsm

Average strain at the centroid of the tension chord

κ

Curvature

κcr

Curvature of the cracked section

κm

Average curvature

θ

Angular coordinate

θcr

Angular coordinate of the neutral axis

σs, σc

Steel and concrete stress, respectively

τ

Bond stress

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Copyright information

© Korean Society of Steel Construction 2018

Authors and Affiliations

  1. 1.Department of Continuum Mechanics and Structures, E.T.S. Ingenieros de Caminos, Canales y PuertosUniversidad Politécnica de MadridMadridSpain

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