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Title: Compressive Stress-Strain Relationships for North American Concrete under Elevated Temperatures

Author(s): Adam M. Knaack, Yahya C. Kurama, and David J. Kirkner

Publication: Materials Journal

Volume: 108

Issue: 3

Appears on pages(s): 270-280

Keywords: creep; elastic modulus; strain; structural fire design; temperature; Young’s modulus

Date: 5/1/2011

This paper focuses on the compressive stress-strain behavior of North American unreinforced concrete under elevated temperatures from fire. Multiple least-squares regression analyses are conducted on existing experimental data to propose temperature-dependent relationships for the concrete elastic modulus, strain at peak compressive stress, and ultimate strain. These relationships are then combined with a previously developed relationship for the peak compressive stress (that is, strength) to produce a predictive concrete stress-strain model under fire. It is shown that the results provide a reasonable statistical fit to the available data, especially considering that the proposed relationships use relatively simple regression models suitable for design. The concrete stress-strain model is then extended to conditions of time-dependent temperature and strain, including the thermal, creep, and transient strain components to estimate the total strain. Several hypothetical analyses are employed to investigate time-dependent effects on the compressive stress-strain behavior of concrete. For the cases studied with elevated temperatures not exceeding several hours (such as from a building fire), the numerical experiments indicate that the mechanical strain makes up the largest portion of the total strain and the creep strain makes up the smallest component.


Electronic Materials Journal


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