D.1 POOR SYSTEM DESIGN
In a well designed combination system the tensioning section i.e., the
mechanical section, is the weakest part. Failures should not occur in the
couplers or the anchorage section (deformed bar). If these types of failures are
occurring contact the manufacturer.
D.2 DEFECTIVE COUPLER
To check if the couplers are defective the combination system should be sent
to a testing lab.
D.3 TORQUE INHIBITOR TOO
STRONG/WEAK
To check if the torque inhibitor is functioning properly, put the deformed
bar end of the bolt in a vise and turn the mechanical bolt into the coupler
until the torque inhibitor breaks. If the torque inhibitor does not break the
couplers should be replaced. If the torque inhibitor did break, then drill a
hole that is 3" or 4" shorter than the bolt length. Next, install and
rotate the bolt to mix the grout as per the manufacturers instructions. After
the grout is mixed turn the bolt counter-clockwise 2 rotations, then turn by
hand clockwise. Keep turning until the bolt stops. Now using a torque wrench
continue turning until the torque inhibitor breaks. This torque reading is the
break-away torque and should not exceed 70% of the installed torque (unless
otherwise specified by the manufacturer). If it appears that the torque
inhibitor cannot be broken and the bolt springs back this means that the bolt is
at the end of the coupler threads because the torque inhibitor was too weak and
broke during the mixing cycle. If after conducting several of the checks the
break-away torque is too high or too low the shear mechanism is not functioning
properly and the couplers should be replaced.
D.4 HORIZONTAL STRATA SHIFTING
Usually when a coupler breaks from pure axial tension the break will be clean
and straight across the coupler. When a coupler breaks in bending or is sheared
the couplers will usually have a ragged break and will have the appearance of
being torn. This type of failure is most likely do to horizontal shifting of the
roof strata. If you suspect horizontal shifting is responsible for the failures
look up the hole that the failed bolt came out of to determine if the strata has
shifted. If a fall has occurred and the borehole is no longer intact, drill a
test hole in another place and periodically check for strata shifting.
