Small Bar Spacing or Cover-A Bond Problem for the Designer


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Title: Small Bar Spacing or Cover-A Bond Problem for the Designer

Author(s): Phil M. Ferguson

Publication: Journal Proceedings

Volume: 74

Issue: 9

Appears on pages(s): 435-439

Keywords: bond (concrete to reinforcement); bonding; bond stress; cover; reinforced concrete; reinforcing steels;solicing; splitting tensile strength; stirrups.

Date: 9/1/1977

Two recent research reports about bond and development length indicate that both bar cover and bar spacing are very critical factors. For example, #9 bars, within heavy stirrups and having 2.1 in. clear cover over the bars, developed only 55 percent as much bond resistance when spaced on 2.5 in. centers as when spaced on 4.2 in. centers; and the latter spacing developed only 90 percent of that assumed in the 1977 ACI Building Code requirements for development length. Pending further Code revisions, the author suggests what the designer can do to avoid this weakness.