Why do you feel that the "Rilem Data Bank" must simultaneously keep data you want on "bond strength" AND "GFRP bars"? Their newest database is on creep and shrinkage!

So try your search elsewhere for the second terms only:

https://scholar.google.com/scholar?q=+%22bond+strength%22+%22GFRP+bars%22

If you really must use Rilem then give them one keyphrase at a time to avoid getting nothing:

http://www.rilem.org/gene/main.php?base=04&q=Bond+strength

http://www.rilem.org/gene/main.php?base=04&q=GFRP+bars

How about going to your heavy structures lab and making some measurements on Glass Fibre-Reinforced Polymer rebars yourself?

https://scholar.google.com/scholar?q=+%22bond+strength%22+%22GFRP+bars%22