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Fire Technology

, Volume 46, Issue 1, pp 67–89 | Cite as

Ultimate Behavior of Idealized Composite Floor Elements at Ambient and Elevated Temperature

  • K. A. Cashell
  • A. Y. ElghazouliEmail author
  • B. A. Izzuddin
Article

Abstract

This paper is concerned with the ultimate behavior of composite floor slabs under extreme loading situations resembling those occurring during severe building fires. The study focuses on the failure state associated with rupture of the reinforcement in idealized slab elements, which become lightly reinforced in a fire situation due to the early loss of the steel deck. The paper describes a fundamental approach for assessing the failure limit associated with reinforcement fracture in lightly reinforced beams, representing idealized slab strips. A description of the ambient-temperature tests on isolated restrained elements, carried out to assess the influence of key material parameters on the failure conditions, is firstly presented. The results of a series of material tests, undertaken mainly to examine the effect of elevated temperature on ductility, are also described. A simplified analytical model is employed, in conjunction with the experimental findings, to assess the salient material parameters and their implications on the ultimate response at both ambient and elevated temperature.

Keywords

structural fire behavior composite floors slab strips failure conditions 

Notation

As

Area of steel reinforcement

d

Reinforcement bar diameter

Ec

Elastic Young’s modulus of concrete

Es

Elastic Young’s modulus of steel at ambient temperature

Es,EC4

Elastic Young’s modulus of steel at elevated temperature as specified in Eurocode 4

Es,exp

Normalized values for elastic Young’s modulus of steel at elevated temperature

Es

Elastic Young’s modulus of steel at elevated temperature θ

Ff,test

Total experimental load at failure

fp

Characteristic proportional limit steel reinforcement at elevated temperature θ

fp,exp

Normalized values for characteristic proportional limit steel reinforcement at elevated temperature

fp,EC4

Characteristic proportional limit steel reinforcement at elevated temperature, as specified in Eurocode 4

fult

Characteristic ultimate strength of the steel reinforcement at ambient temperature

fult,exp

Normalized values for characteristic ultimate strength of steel reinforcement at elevated temperature

fult

Characteristic ultimate strength of the steel reinforcement at elevated temperature θ

fy

Characteristic yield strength of the steel reinforcement at ambient temperature

fy,θ

Characteristic yield strength of the steel reinforcement at elevated temperature θ

hc

Assumed distance of contact point from level of reinforcement

L

Half span of member

P

General term for half the member mid-span load

Ts

Tensile force in reinforcement at crack location

U

General term for vertical displacement

Uf

General term for vertical displacement at failure

Uf,calc

Calculated term for vertical displacement at failure, using reduced expression

Uf,pred

Predicted term for vertical displacement at failure, using the simplified analytical approach

Uf,test

Experimental vertical displacement at failure

αc

Coefficient of thermal expansion for concrete

αs

Coefficient of thermal expansion for steel

δc0

Axial shortening of the concrete

Δc

Shortening of concrete along thermally curved reference line

Δs

Extension of steel reinforcement along thermally curved reference line

εav,θ

Average strain in reinforcement at temperature θ

εult

Ultimate strain of steel at ambient temperature

εult,θ

Ultimate strain of steel at elevated temperature θ

θ

Temperature of steel reinforcement

ρ

Reinforcement ratio

τb

Bond stress

Ψu

Parameter related to normalized failure deflection at ambient

∇θ

Thermal gradient over cross section

Notes

Acknowledgements

The support provided by the Engineering and Physical Sciences Research Council (EPSRC) in the UK under Grant No EP/C511204 for the work described in this paper is gratefully acknowledged. The authors would also like to thank the technical staff of the structures laboratories at Imperial College London, particularly Mr. Trevor Stickland, for their assistance with the experimental work.

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Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  • K. A. Cashell
    • 1
  • A. Y. Elghazouli
    • 1
    Email author
  • B. A. Izzuddin
    • 1
  1. 1.Department of Civil and Environmental EngineeringImperial College LondonLondonUK

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