Masonry Magazine May 2010 Page. 18
CONNECTORS, ANCHORS
AND FASTENERS
Fastener selection
ANCHORS TO CONCRETE OR MASONRY can be torque
activated, hammer set expansion types, threaded screws, power
actuated pins, or hammer driven nails. Depending upon the tie
system selected, the length or type of fastener must comply
with the thickness of the base plate to be attached, plus the
minimum embedment required for the fastener to achieve the
loads induced. Since this fastener must partner with a plate or
tie assembly, the functional and material compatibility with the
tie is important.
turer regarding the appropriate installed torque and the
resulting induced clamping force). Stud-type expansion
anchors can take four to six turns of the nut to achieve the
installation torque. The stud projection from the plate sur-
face could be 1/4-to 3/8-inch above the surface of the nut.
The total anchor projection distance of 1/2- to 3/4-inch
can interfere with the placement of insulation or the verti-
cal travel of the adjustable tie in the base plate. Therefore,
a torque activated anchor having a hex head finish is best.
Typical torque type anchor
Typical threaded fastener
Torque applied anchors are an ideal solution for the
plate attachment. Besides providing a measurable clamp-
ing force, the installed anchor can be inspected. Applying a
4 foot-pound (48-50 inch-pound) torque can produce a
preload greater then 900 pounds. This is a typical installed
torque for 1/4-inch torque type anchors. Since the preload
exceeds the allowable load and allows for creep and relax-
ation of the installed torque (usually 35 to 50 percent), the
choice would be acceptable (check with anchor manufac-
Typical nail drive expansion
Typical toggle
The use of anchors other then torque-controlled expan-
sion has limited appeal. A nail drive system does not draw
the plate tight to the concrete or masonry surface. If not
properly inserted and activated the anchor can expand pre-
maturely, and the plate connection would be loose to the
surface. This will have a negative impact on the free play of
the tie and result in excessive deflection. Except for a visu-
al identification, a physical inspection is not possible that
would indicate the tie system is secured to the building.
This would be true of any nail or hammer driven anchor.
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A MITEK BERKSHIRE HATHAWAY CO.
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