Experiment and Analysis on the Mechanical Behaviour of PC Simply-Supported Slabs Subjected to Fire

Abstract

Experiments on the fire resistance of 9 unbonded and 1 bonded prestressed concrete (PC) simply-supported slabs are completed. Calculation formula of the stress in the unbonded prestressing steel wires in PC simply-supported slabs subjected to fire is obtained based on the experimental results. Dividing the section of the slab into strips along its depth according to the distribution of temperature field, on the basis of invariable width of the slab in the surface exposed to fire, the transformed section of the slab subjected to fire can be obtained by multiplying the width of each strip by the elasticity modulus ratio of the strip concerned and the extreme strip in the surface exposed to fire. The stress in concrete and curvature in the researched section caused by load can be obtained based on equilibrium equations of force and moment on transformed section. Then, the methods for calculating concrete thermal strain, transient strain and creep at elevated temperature were introduced, and total strain of a point in the concerned section and total curvature caused by load and temperature can be calculated considering time-dependent effect. After the total curvature of the mid-span section was calculated, the actual stiffness of the critical section in the mid-span can be determined, moreover, the mid-span deflection of the PC slab can be calculated by the virtual displacement principle. The practical calculation formulas for the mid-span deflection of PC simply-supported slabs subjected to fire is presented considering the influences of the deflection of slabs at the ambient temperature, ratio of concrete cover to depth of slabs, load level, combined reinforcement index and span.

Keywords

prestressed concrete (PC)simply-supported slab fire resistance performance experiment thermal-mechanical coupling

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References

Anderberg

and Thelandersson

(1976). Stress and Deformation Characteristics of Concrete at High Temperatures, 2. Experimental Investigation and Material Behaviour Model, Bulletin 54, University of Lund, Sweden.

Bratina

Planinc

Saje

and Turk

(2003). “Non-linear fire-resistance analysis of reinforced concrete beams”, Structural Engineering and Mechanics, Vol. 16, No. 6, pp. 695–712.

Bratina

Saje

and Planinc

(2006). “The effects of different strain contributions on the response of RC beams in fire”, Engineering Structures, Vol. 28, No. 7, pp. 1236–1249.

Cooke

G. M. E.

(2001). “Behaviour of precast concrete floor slabs exposed to standardized fires”, Fire Safety Journal, Vol. 36, No. 4, pp. 459–475.

Eurocode 2 (2005). Design of Concrete Structures, Part 1–2: General Rules-Structural Fire Design, prEN 1992-1-2, British Standards Institution, London, British.

Gao

L. T.

Dong

Y. L.

and Yuan

A. M.

(2004). “Experimental investigation of the behaviour of continuous slabs of unbonded prestressed concrete with the end span under fire”, Journal of Building Structures, Vol. 25, No. 2, pp. 118–113 (in Chinese).

Gawin

Pesavento

and Schrefler

B. A.

(2003). “Modeling of hydro-thermal behaviour and damage of concrete at temperature with thermo-chemical and mechanical material degradation”, Computer Methods in Applied Mechanics and Engineering, Vol. 192, No. 12, pp. 1731–1771.

Guo

Z. H.

and Shi

X. D.

(2003). Behaviuor of Reinforced Concrete at Elevated Temperature and its Calculation, Tsinghua Press, Beijing, China (in Chinese).

Guo

Z. H.

and Li

(1993). “Deformation testing and constitutive relationship of concrete under different stress-temperature paths”, China Civil Engineering Journal, Vol. 26, No. 5, pp. 58–69 (in Chinese).

10.

Huang

Z. H.

and Platten

(1997). “Nonlinear finite element analysis of planar reinforced concrete members subjected to fires”, ACI Structural Journal, Vol. 94, No. 3, pp. 272–282.

11.

International Standard ISO 834-1-1999 (E). Fire-resistance tests-Elements of Building Construction-Part 1: General requirement.

12.

Khoury

G. A.

Majorana

C. E.

Pesavento

and Schrefler

B. A.

(2002). “Modeling of heated concrete”, Magazine of Concrete Research, Vol. 54, No. 2, pp. 77–101.

13.

Z. D.

and Xu

L. X.

(2003). “Analysis for structural responses of unbonded prestressed reinforced concrete frames in fire environments”, China Civil Engineering Journal, Vol. 36, No. 10, pp. 30–35 (in Chinese).

14.

Sanad

A. M.

Lamont

Usmani

A. S.

and Rotter

J. M.

(2000). “Structural behaviour in fire compartment under different heating regimes-part 1(slab thermal gradients)”. Fire Safety Journal, Vol. 35, No. 1, pp. 99–116.

15.

Shi

X. D.

Tom

T. H.

Tom

K. H.

and Guo

Z. H.

(2002). “Effect of force-temperature paths on behaviours of reinforced concrete Flexural Members”, Journal of Structural Engineering, ACSE, Vol. 108, No. 3, pp. 365–373.

16.

Zhang

H. Y.

and Zheng

W. Z.

(2006). “Experimental study on the creep and stress relaxation properties of 1770-φ^P5 prestressing steel wires at high temperatures”, China Civil Engineering Journal, Vol. 39, No. 8, pp. 7–13 (in Chinese).

17.

Zheng

W. Z.

and Zhang

H. Y.

(2006). “Experimental research on the mechanical properties of prestressing steel wire at and after high temperature”, Journal of Building Structures, Vol. 27, No. 2, pp. 120–128 (in Chinese).

18.

Zheng

W. Z.

M. X.

Shi

D. S.

and Hu

(2006). “Experimental study on spalling of concrete of pre-stressed slabs in fire”, China Civil Engineering Journal, Vol. 39, No. 10, pp. 48–53 (in Chinese).