Guide for Lap Splice and Development Length of High Relative Rib Area Reinforcing Bars in Tension and Commentary
|Publication Date:||1 October 2009|
Evaluation of lap splice and development lengths of coated and uncoated bar reinforcement in tension shall be limited to bars having a high relative rib area, conforming to Sections 2.1.1 through 2.1.5:
The relative rib area is at least 0.10, but no larger than 0.14;
The ribs shall be in accordance with (a), (b), and (c).
(a)Ribs shall be at an angle of 45 to 65 degrees inclusive with respect to the axis of the bar;
(b)Ribs shall not cross; and
(c)Use of X patterns and diamond patterns for ribs is not permitted.
The rib spacing is at least 0.44 of the nominal diameter db of the bar reinforcement.
The average rib width is not greater than one-third of the average rib spacing.
The bar size does not exceed No. 11 (No. 36).
This guide is provided to help designers take advantage of higher bond strength exhibited by high relative rib area bars (Darwin and Graham 1993; Darwin et al. 1996a; Zuo and Darwin 1998) in the calculation of tension lap splice length and development length of bar reinforcement. It includes expressions for development and lap splice length applicable only for high relative rib area bars. This document has been updated to reflect improvements to the provisions of ACI 408.3-01 (ACI Committee 408 2001) proposed by Darwin et al. (2005). Because experimental data are available only to evaluate the development and lap splice lengths of straight high relative rib area bars in tension, the integrity of high relative rib area bars in compression or as hooked bars in tension should be evaluated using appropriate Chapter 12 provisions of ACI 318-08 (ACI Committee 318 2008).
To use this guide, ASTM A615/A615M for carbon-steel reinforcing bars should have the supplementary requirements imposed by the "Recommended Supplement to ASTM A615/A615M for High Relative Area Bars" that is appended to this document. With modifications to the section reference numbers, this supplement can be adapted for use with ASTM A706/A706M for low-alloy steel reinforcing bars.