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A variety of gripping systems have been developed to provide effective anchorage at the ends of the FRP bars in tension and to prevent premature failure. Castro and Carino (1997) developed a system involving embedding the bar ends in steel tubes with a high-strength gypsum-cement mortar. Similarly, Malvar (1995) designed special grips consisting of four aluminum blocks bolted together to characterize the tensile strength of different FRP bars. Tannous and Saasatmanesh (1998) adopted an anchor system consisting of coating both ends of the bar with a sand–epoxy mixture and then placing it in steel tube cut along its longitudinal axis to get two cylindrical shells. Schesser et al. (2014) highlighted that the key parameters for the effective design of all these gripping systems are grip length, steel-tube dimensions, and volume/thickness of the grout. It should be noted that the ASTM specimens have a longer gauge length (870 mm) than the CSA ones (760 mm). These lengths are around 45 and 40 times the nominal diameter of the GFRP bars. Wisnom (1999) indicated that the strength of composite materials tended to drop with increasing volume of material. Castro and Carino (1997), however, found no statistically significant influence on the mean tensile strength of FRP bars with a free-length to-diameter ratio of 40 to 70. Thus, it can be concluded that the gauge length did not produce the difference in the measured tensile strength between the ASTM and CSA specimens.

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Thank you Nasir Shafiq for your help!

Nasir Shafiq, do you have full reference of the works you cited?