Design Issues - Strengthening Design of Reinforced Concrete with FRP - page 73

Steel and concrete strengths are reduced at elevated temperature according to ACI
216R-89, while FRP strength is ignored. The resistance of the member at elevated
temperature R n θ may be determined based on testing or ACI 216R-89 guidelines.
Equation (9.2) of ACI 440.2R-08 needs to be satisfied:

(4.2)

RS S
n

=+

θ DL LL

where S DL and S LL are the load effects of the upgraded loading due to the addition
of f F R P.
Glass transition temperature T g is conservatively taken as the critical temperature
below which FRP needs to be kept to sustain its functionality. More research is
needed to accurately identify critical temperatures for different types of FRP, as seen
in Figure 4.1 (Naser et al. 2014).

4.5 OVERALL STRENGTH OF STRUCTURES
It is the responsibility of the designer to make sure that the overall strength of struc-
ture is adequate under different upgraded loads for various strengthened members.
Slab-punching shear, column capacity, and footing-bearing capacity must be satis-
fied when slabs and beams are upgraded. In most of the cases, this works out well
due to the reduction in dead- and live-load factors required by ACI 318-11 and ACI
440.2R-08 compared to those required by early versions of ACI 318 code. An exam-
ple on strengthening of a reinforced-concrete slab designed according to ACI 318-83
is presented in Chapter 5.

1200

1000

VG/CFRP interface
FE VG/CFRP interface
CFRP/Concrete interface
FE CFRP/Concrete interface
ASTM E119

800

600

400

200

0 0

50 100 150 200 250 300

Time (min)

FIGURE 4.1 Experimental and numerical comparison of heat progression in CFRP-
strengthened T-beams under fire (Naser et al. 2014. Courtesy of Multi-Science Publishing).