Simpson Strong-Tie, Inc. has a division that sells concrete anchors
called Simpson Anchor Systems®. Their double expansion anchor is sold
as the DMSA machine screw anchor - an acronym for double machine screw anchor.
The DMSA has an expanding cone at each of its two open ends to allow
the DMSA to expand the entire length of the anchor and to provide better
performance in base materials with questionable strength.
DMSA Federal Specifications
DMSA all meet federal specifications A-A-1923A, Type 3, with an exception made for the 1/4” DMSA25 and the 5/16” DMSA31.
DMSA Base Materials
The DMSA machine screw anchor can be used in a variety of base
material, such as concrete, brick or block. In most cases, the DMSA is
more versatile than the single expansion anchor SMSA because it can be
used in base material of questionable strength.
DMSA Diameters
The DMSA is a female anchor and its internal threads of the anchor
determine the size designation. The DMSA comes in four diameters from
1/4” to 1/2”, and other brands, such as www.concretefasteners.com, have
diameters of 5/8” and 3/4”. All of the threads on the DMSA are national
coarse machine threads and will accommodate any bolt or threaded rod
with the same national coarse threads.
DMSA Diameter of Hole
The hole that is drilled in the base material for the DMSA machine
screw anchor must be drilled with a hammer drill and a carbide bit that
meets ANSI standard B212.15. The diameter of the hole drilled is the
same diameter as the outside diameter of the anchor (see chart below).
Depth of Hole
The deeper into the base material the anchor is inserted the
better the DMSA holding values may be. The holding values of the DMSA
anchor are dependent on the holding strength of the base material. The
DMSA must be embedded a minimum distance into the base material. The
DMSA machine screw anchor requires that the anchor be inserted the
length of the anchor at minimum, so that the end of the anchor is flush
with the surface of the base material (see chart).
Thickness of Concrete
The thickness of the concrete that the DMSA machine screw anchor
is placed into must be no less than 1.5 times the embedment depth of the
anchor. If a 3/8” DMSA machine screw anchor is being used then the
concrete must be at a minimum 2.44” thick.
DMSA Length of Bolt
The length of the bolt used with a DMSA anchor must be long enough
to engage a minimum 2/3 of the threads on the expansion cone. To
determine the overall length of bolt needed, add the thickness of
material being fastened plus the depth of embedment of the anchor.
DMSA Product Information Chart
|
DMSA25
|
1/4” -20
|
1/2”
|
1-1/2”
|
100
|
|
DMSA31
|
5/16” - 18
|
5/8”
|
1-3/4”
|
100
|
|
DMSA37
|
3/8” - 16
|
3/4”
|
2-1/4”
|
50
|
|
DMSA50
|
1/2” - 13
|
7/8”
|
2-3/4”
|
25
|
DMSA Installation Instructions
Caution: Holding values may be reduced if the anchor is
placed in a hole that is oversized, which prevents the anchor from being
expanded properly.
1. Using a hammer drill, drill a hole into the base material with
a carbide bit that meets ANSI standard B212.15. Make sure that the
diameter of the bit is equal to the diameter of the hole required for
the diameter of DMSA being installed. Drill the hole to a depth of 1/8”
deeper than the intended anchor embedment, making sure that the hole
depth is a at a depth at least equal to the anchor length.
2. Using a vacuum, compressed air or a wire brush, clean out the hole of all debris and dust.
3. Insert the DMSA machine screw anchor into the hole with the
threaded cone first. A hammer many be used to tap the DMSA machine
screw anchor into the base material until the anchor is at least flush
with the surface.
4. Move the hole in the fixture to be fastened over the DMSA
machine screw anchor until the holes line up. Insert a bolt through the
fixture and into the DMSA machine screw anchor. Turning the bolt
clockwise will engage the threads and expand the anchor. Turn the bolt
until it is tight against the fixture being fastened. Remember to make
sure that a minimum of 2/3 of the treads are engaged by the bolt.
As with any anchoring project, it is important to keep safety in mind and follow instructions carefully. Always remember to wear safety goggles, handle all tools with extra care and follow all technical specifications. This article is meant to serve only as a basic explanation of concrete fasteners. Always refer to manufacturer's instructions or consult a contracting expert during any anchoring project.
Article Written By:
Bob Carlisle, President of Concrete Fasteners
Concrete Fasteners, Inc. has over 40 years of experience selling concrete fasteners. We can ship out one box or a whole pallet of concrete anchors. Our products are of the highest quality... "your satisfaction is guaranteed". We ship all orders the same day the order is received.