E.1 BAIL/SUPPORT NUT TOO
STRONG
If the Bail/support nuts are too strong the support will not tension properly
in certain situations. The primary function of the bail/support nut is to hold
the shel of an expansion anchor in place until the plug begins to expand it into
the borehole wall. Once this occurs the bail/support nut is no longer necessary
and should break away. If the bail/support nut does not break away it will
prevent the bolt from being drawn up through the plug as it is rotated. With a
support nut this will cause most of the tension to occur between the plug and
the support nut. When this situation occurs the result can be high installed
torque with low tension, erratic tension, springy bolt, the anchor breaks on
installation, or the bolt breaks on installation. Check bail/support nut using
procedure listed in section A.5. The breaking
torque of the bail/support nut should not exceed the installed torque of the
support system.
E.2 BOLT INSERTION TOO FAST
Often time when bolts bend on installation or when spinners are prevalent the
cause is due to the operator inserting the bolt too fast. Certain expansion
anchors offer more resistance than others when pushing through a grout cartridge
and some grouts offer more resistance than others. In either case the more rapid
the bolt insertion the greater the forces applied to the expansion anchor and
bolt. In some cases the bail/support nut can break and the expansion shell will
become dislodged from the plug resulting in a spinner. When long bolts are used
the result can be that the bolt bends before it is fully inserted in the
borehole. If any of the above problems are occurring instruct the operator to
slow down the bolt insertion. If that does not alleviate the problem then
consider changing the grout, the expansion anchor or using a stronger
bail/support nut.
E.3 GROUT LUBRICATING BOREHOLE
In this situation the grout acts as a lubricant and prevents the shell from
anchoring in the borehole wall. Because the shell cannot get a "bite"
in the hole the entire unit just spins on the bolt until it runs out of threads.
A stronger bail/support nut could help by holding the shell in place long enough
for the plug to expand the shell, which would allow the serrations to cut
through the grout, and contact the borehole wall. If the bail/support nut is too
strong other problems can be encountered (see E.1 ).
Sometimes pre-expanding the anchors will eliminate the problem, however,
pre-expanding the anchors too much can interfere with the grout flow around the
anchor, causing the bolt to bend on insertion.
E.4 GROUT CARTRIDGE MATERIAL
INTERFERES WITH ANCHOR PERFORMANCE
This condition is very difficult to detect. If after using grout from a
different lot or manufacturer you start encountering spinners or tension/torque
problems the grout cartridge could be responsible. If you suspect that the grout
cartridge contact both the grout manufacturer and the bolt manufacturer.
E.5 ANCHOR DESIGN
Not all expansion anchors are suitable for use with grout. Many of the older
expansion anchors were not designed for use with grout. Anchors specifically
designed to be used with grout are available from all manufacturers. These
anchors have more streamlined shapes and often have passages in them to allow
the grout to flow more smoothly.
