ISSN: 1945-7553
CODEN: JTEVAB
Published Online: 11 December 2012
Page Count: 6

Analysis of Support Apparatus for Flexural Load-Deflection Testing: Minimizing Bias Caused by Arching Forces

Zollo, Ronald F.
Professor of Civil and Architectural Engineering, Univ. of Miami, Coral Gables, FL

(Received 30 July 2011; accepted 15 May 2012)

Abstract

It is in the best interests of standards development that bias and inter-laboratory variability be minimized in the reporting of test results. However, the apparatus sections of flexural test standards, such as ASTM C78, C1399, C1550, and C1609, may not adequately address important issues raised in this study that could adversely affect test results. Specifically, current standards specifications fail to address arching forces and effective span control. The mechanics of commonly applied journal-bearing-type support designs are analyzed and compared to an alternative ball or needle-bearing-type support design. The analysis demonstrates that significant bias can be introduced as a direct consequence of the mechanics that is the nature of journal-bearing-type supports. The analysis applies equally well to flexural tests involving small deformations of portland cement concrete or similar brittle materials, as it does to tests that are carried out involving relatively large deformations, such as with fiber-reinforced concrete.

Keywords:
flexural testing, beam-support design, large deflection apparatus, flexural test bias, flexural arching, fiber reinforced concrete

Paper ID: JTE104251
DOI: 10.1520/JTE104251
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