Civil Engineering Reference
In-Depth Information
b
b
≥ 1.5
b
b
≥ 1.5
d
b
a
b
≥ 1.5
d
b
≥ 3.0
a
b
FIGURE 8.9
Minimum dimensions of grooves in NSM application.
the uncured adhesive in such a way as to roll out all entrapped
air. Surface preparations described earlier are needed prior to
applying the adhesive layer.
d. NSM bar placement
Grooves are cut to place NSM rectangular or circular bars
into the cover part of the section. Grooves are dimensioned as
shown in Figure 8.9 to allow enough adhesion around the bars.
Surface preparations must be performed as described earlier.
The manufacturer of the NSM system should be consulted on
the type of adhesive to use.
7. Alignment of the FRP sheets
FRP sheets should be properly aligned with the beam axis. Deviation
from the intended fiber angle orientation may lead to significant reduc-
tion in modulus and strength for angle differences as small as 5° (ACI
440.2R-08). Fabrics and fiber sheets should be carefully placed to
maintain fiber straightness. Any kinks or folds in fibers during installa-
tion may adversely affect the performance, so these should be reported
to the design engineer (ACI 440.2R-08).
8. Curing of resins
This is a temperature-dependent and time-dependent process. For res-
ins cured at room or ambient temperature, curing may take several days
for most of the cross linking to take place. For resins cured at higher
temperature levels, resin must be kept at a certain temperature for a
certain time span. The manufacturer's recommended curing process
should be carefully followed without deviations. Curing should be visu-
ally inspected, and problems with curing due to expired resins beyond
their shelf life should be reported to the designer.
REFERENCES
ACI 224.1R-07. 2007. Causes, evaluation and repair of cracks in concrete structures. ACI
Committee 224. Farmington Hills, MI.
ACI 440.2R-08. 2008. Guide for the design and construction of externally bonded FRP sys-
tems for strengthening concrete structures. ACI Committee 440. Farmington Hills, MI.
Search WWH ::
Custom Search