Design Issues - Strengthening Design of Reinforced Concrete with FRP - page 75

other hand, the resin matrix protects the fibers in general from alkalinity and acid-
ity. However, it may only retard deterioration of glass fiber. Accordingly, carbon is
the fiber of choice in applications having high alkalinity and high relative humidity.

4.6.4 t hermal e xpanSion
As stated previously, the coefficient of thermal expansion varies drastically between
the fibers, matrix, and FRP system at various orientations. Along the fiber direction,
CFRP has a coefficient of thermal expansion of zero while GFRP has a coefficient of
thermal expansion comparable to concrete. The coefficient of thermal expansion of
polymers is around five to seven times that of concrete. Thus, the transverse direction
of an FRP system has much higher coefficients of thermal expansion. Differences in
thermal expansion may potentially affect bond with concrete. However, this effect is
limited for a temperature range of ±50°F (±28°C) (ACI 440.2R-08).

4.6.5 e leCtriC C onDuCtivity
GFRP and AFRP are known to be electric insulators. On the other hand, CFRP is
conductive and should therefore be kept away from steel to avoid potential corrosion.

4.6.6 D urability
This is a subject of ongoing research. It is worth mentioning here that the use of
FRP systems to completely seal the concrete surface is cautioned wherever moisture
vapor transport is anticipated. Whenever possible, exposed concrete surfaces need to
be allowed to enable moisture escape.

Chapter Problems

Problem 4.1
A library building has a simply supported rectangular concrete beam reinforced
with four No. 6 bars in tension and two No. 3 bars in compression and No. 3 stirrups
at 6 in. (152 mm) on center in shear. The details of the beam are shown in the follow-
ing table. As part of the library upgrade, the beam is subjected to a 40% increase in
live load, as shown in the table. Determine the adequacy of the bare-beam section to
resist the upgraded loads in flexure and shear in case of fire.

Span 20 ft 6.1 m

B 12 in. 305 mm

H 20 in. 508 mm

f c 4 ksi 27.6 MPa

f y 60 ksi 414 MPa

Top bars #3

ϕ = 9.5 mm

Main bars #6

ϕ = 19 mm

W DL 0.9 k/ft 13.14 kN/m

W LL 0.9 k/ft 13.14 kN/m