1625 Detailing of FRP Reinforcements

The development length of an FRP rebar is different from the development length of a conventional steel rebar. The properties of hooks in FRP rebars are also different from those in steel rebars due to the decrease in strength at the bends in FRP rebars. The ACI 440.1R-03 guide provides recommendations for detailing FRP rebar anchorages and splices so that the FRP rebar can develop its tensile strength at member ends, at hooks, and at locations where bars are overlapped or terminated. It should be noted that current recommendations are based on limited, and sometimes conflicting, data.

Failure due to insufficient development length is called a bond failure and may be due to splitting of the concrete surrounding the bar or due to pull-out of the bar itself. Two equations are provided by ACI 440.1R-03, one for splitting controlled failure and one for pull-out controlled failure. For splitting failure

V/c and for pull-out failure

2700 v 7

where 4>f is the development length and K2 ranges from 213 to depending on FRP rebar type and the source of the test data (ACI 440.1R-03 2003). Manufacturers of FRP rebars also provide data on development lengths for the bars they produce.

For hooked bars the development length is given as a function of the FRP rebar design strength. For FRP rebars with design strengths in the range of 75 to 150 ksi (typical of glass FRP rebars) the length of a hooked bar, ibfh, is given as

The tail length should not be less than 12 db or 9 in.

Tension lap splices for FRP rebars are based on recommendations for steel rebars and limited test data. For Class A and Class B lap splices the recommended development lengths are 1.3ldf and 1.6ldf, respectively.

FRP stirrups can be spaced at a maximum of d/2 (or 24 in.) and should have a minimum rb/db ratio of 3. The tail length of 90° hooks in the stirrups must be at least 12db. Minimum concrete cover for FRP rebars is db.

0 0

Post a comment