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Title: Reliability-Based Assessment of Concrete Strength in Existing Structures

Author(s): F. M. Bartlett

Publication: Symposium Paper

Volume: 198

Issue:

Appears on pages(s): 85-102

Keywords: compressive strength; concrete cores; evaluation; in-place strength; load; resistance

DOI: 10.14359/9992

Date: 3/1/2001

Abstract:
In 1988, the collapse of a supermarket roof in Burnaby, Canada, highlighted the need to distinguish between the specified strength and the actual strength of a material when evaluating existing structures. It is unsafe to calculate resistances using the actual strength instead of the specified strength in conven-tional resistance equations with customary resistance factors. This is the rationale behind current criteria for the evaluation of existing bridges in Canada, that require in-place strength data to be converted to equivalent specified strengths. In this paper, the statistical relationship between the specified strength and the actual in-place strength of concrete is examined. A method is summarized which enables concrete core compression strength data to be converted to an equivalent specified strength for structural assessment purposes. The method is illustrated by a case study involving 1200 40-year-old precast stringer bridges in Alberta, Canada.