Fibreglass (GRP) rock bolts are not all made the same!
The tensile strength in a fibreglass rod is dependent on how many glass fibres you can pack into a given diameter of rod. It’s easier to pack more glass into a small diameter tendon than a large one. That’s why Cutabolt uses small diameter fibre strength tendons pultruded along with standard glass fibres in their rods. Take a look at the end of the rod, you can see the strength members.
Cutabolt rods are typically stronger in tension per cross sectional area than other rods.
Like tensile strength shear strength is a function of the amount of glass you can pack into a rod. For the same reasons as tensile Cutabolt rods are typically stronger in shear per cross sectional area than other rods.
GRP rods are made from glass, resin and fillers (e.g. calcium carbonate). GRP bolts get their torsional strength from the resin. The lower the filler content the stronger the bolt in torsion. The rods used by Cutabolt typically have lower filler content giving the higher torsional strength. You can test it yourself with a vice and a torque wrench.
The transfer of load from the strata through the resin grout into the bolt. Cutabolt ensures good load transfer at the resin/bolt interface by using a spiral deformation on the surface of the rod. The spiral deformation compresses the rod during pultrusion maintaining the full integrity of the glass fibres. This prevents shear failure of the rod skin as can happen where the glass fibres have been broken to provide the surface deformation.
If a bolt is not fully encapsulated by resin grout load may be transferred into the thread and nut (termination). Cutabolt ensures the strongest bond between the fibreglass rod and the nylon thread by cutting a groove into the rod to provide a mechanical lock between them. This also allows the nut to take load even when it is right at the outer end of the thread.
Glass fibres will irritate the skin. Cutabolt’s use of a compressed deformation and allowing the resin to wet the outer surface of the glass minimises the risk of loose glass fibres.
Cutabolt believes it can offer the widest range of GRP bolts and accessories available from one source anywhere in the world.