Time-Dependent Stresses in Heated Concrete Structures

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Title: Time-Dependent Stresses in Heated Concrete Structures

Author(s): Ian J. Jordaan and Magdi M.A. Khalifa

Publication: Special Publication

Volume: 55

Issue:

Appears on pages(s): 321-346

Keywords: continuous beams; creep properties; deformation; finite element method; loads (forces); prestressed concrete; stress analysis; stress-strain relationships; structural analysis; temperature; tensile stress; thermal gradient; thermal stresses

Date: 8/1/1978

Abstract:
The time-dependent behaviour of concrete structures subjected to thermal gradients and, in addition, to mechanical loading is considered. Redistribution of stress with time results from two kinds of nonhomogeneity; firstly, there is a stress transfer from concrete to steel and secondly, the spatial variation of creep parameters (resulting from the temperature variation) causes stress redistribution. The constitutive laws for concrete creep are discussed in the light of recent experimental findings and a simple constitutive equation is found to account for the major features with sufficient accuracy in the analysis of static temperature fields. Because of the form of the equation, viscoelastic methods can be used; based on this fact, two approximate methods are proposed. Both use effective modulus calculations which must incorporate a spatially varying elastic modulus to account for the spatially varying creep properties; this is easy to achieve through the use of the finite element method. Two examples are given; the first is a reinforced cylinder subjected to internal pressure and a temperature gradient and the second is concerned with prestressed beams subjected to external loads and a temperature gradient. A comparison of the approximate methods with step-by-step calculations is given and good agreement is demonstrated.