Influence of Friction in Supporting Rollers on the Apparent Flexural Performance of Third-Point Loaded Fiber Reinforced Concrete Beams

Abstract

Abstract Existing beam-based ASTM test methods for the assessment of post-crack performance of Fiber Reinforced Concrete (FRC) and Fiber Reinforced Shotcrete (FRS) contain detailed specifications for many components of the test apparatus including the yoke assembly for measuring specimen deflection and the control system required for the test machine. However, there is limited attention paid to the design of the supporting rollers with the result that laboratories have been left to develop their own designs for this component of the test apparatus. Simple free-body force calculations for a cracked FRC beam indicate that friction in the supporting rollers can significantly influence the apparent post-crack performance of a beam. The present investigation has confirmed experimentally that the apparent post-crack performance of a third-point loaded FRC beam will be biased as a result of friction in the supporting rollers. Rollers that fail to roll during a test will lead to over-estimated post-crack performance. Due to the potentially serious consequences of unconservative FRC performance estimation a “standard” design for a supporting roller has been proposed for use in all ASTM beam tests. Use of this supporting roller design will lead to a reduction in performance variability between laboratories and improve the confidence users can have in the post-crack properties of FRC.