Table 5-3. FRP reinforcement material properties
Type Dia. Area Tensile Modulus Elongation
 (in.) (in2) Strength (ksi) at rupture
 (ksi) (%)
 Glass Rod 0.750 0.4580 90 5900 2.00
 Carbon Rod 0.375 0.1100 405 22500 1.80
 Carbon Grid N/A 0.0097 100 9200 1.05

 Results, Observations and Discussion

 The load displacement curves (Fig. 5-11) for specimens 1 and 2 have 3 distinct

areas. The initial portion of the curves is linear up to first cracking, which occurred at

approximately 7.5 kips for specimen 1 and 5.5 kips for specimen 2. After cracking the

slopes are reduced due the reduction in cross-section stiffness from flexural cracking yet

remain linear up to the plateau. The plateau seen in the load-displacement curves (see

Fig. 5-11), was attributed to a combination of the following three factors: (1) concrete

confinement, (2) the post peak curve that GFRP bars exhibit prior to rupture and (3) the

shape of the cross-section of the piles. The shape of the cross sections was tubular for

both cases once concrete spelling took place. The square pile had a tubular reinforcement

arrangement and therefore once the cover concrete spalled it had the same compression

zone shape as the round pile. That was the reason the square pile had a plateau associated

with its load-displacement curve. For specimen 1 a noticeable loss in capacity was

observed before the plateau which was attributed to spelling of the top cover concrete.

 The information available by the manufacturing company of the GFRP bars

indicated a post peak curve for the bars (Hughes 2002(a)). Chaallal and Benmokrane

(1996) reported that the GFRP bars they used in concrete beams also exhibited some post

peak behavior rather than rupturing at peak load.