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Materials and Structures

, Volume 43, Issue 10, pp 1327–1341 | Cite as

Effect of high temperature creep on the fire response of restrained steel beams

Original Article

Abstract

At room temperature, and at service load levels, creep has little effect on the performance of steel structures. However, under fire conditions, creep becomes a dominant factor and influences fire resistance of steel members. Under fire conditions, significant forces develop in restrained steel beams and these forces induce high stresses in the steel section. The extent of creep deformations is affected by magnitude and rate of development of stress and temperature in steel. In this paper, the effect of high temperature creep on fire response of restrained beams is investigated. Current high temperature creep models are compared. Finite element model created in ANSYS was validated by comparing the predictions with fire test data. The validated model was applied to investigate the effect of load level, heating rate, fire scenario and fire induced axial restraint on the extent of creep deformations. Results from the parametric study indicate that the influence of high temperature creep increases with the increase in axial restraint, heating rate, and load level. Generally, neglecting high-temperature creep effect stiffens the structural response and leads to reduced deflections but larger restraint forces. Therefore, neglecting high temperature creep in fire resistance analysis of steel structures can lead to unconservative predictions.

Keywords

Structural steel Creep deformations Creep model Beams Restraint High temperature creep Fire response 

List of symbols

B, n

Constants in Dorn’s creep formulation, that depend on the type of steel

ΔH

Activation energy of creep (Btu/lb mole)

c1,…,c7

Experimental coefficients of ANSYS creep model (see text for units)

θ

Dorn’s temperature-compensated time (h)

Q

ΔH/R = Constant of the compensated time formula in Dorn’s model (Rankine)

R

Gas universal constant (Btu/lb mole R)

SΦ(σs)

Temperature–stress-dependent function in Dorn’s formulation of creep strain rate

σs

Stress in steel (MPa)

t

time (min)

Ts

Steel temperature (°C)

TR

Steel temperature (Rankine)

Z

Zener-Hollomon experimental parameter (h−1)

Notes

Acknowledgments

The research presented in this paper is supported by the National Science Foundation (Grant No. 0652292) and Department of Commerce/National Institute of Standards and Technology (Grant No. 60NANB7D6120). Any opinions, findings, and conclusions or recommendations expressed in this paper are those of the authors and do not necessarily reflect the views of the sponsors.

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Copyright information

© RILEM 2010

Authors and Affiliations

  1. 1.Department of Civil and Environmental EngineeringMichigan State UniversityEast LansingUSA

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