a structural engineer with a BSCE degree from Lehigh University
and Anchor Systems Field Engineer with Simpson Strong-Tie gave a
PowerPoint presentation on post-installed concrete anchors to a
room of about 25.
types of post-installed anchors and how they work
affecting post-installed anchor performance
problems with post-installed anchors
discussed four different types of post-installed anchors:
Torque Controlled Expansion Anchors
are more commonly known as wedge anchors or expansion bolts and
are inserted into a pre-drilled hole. The wedges activate by tightening
a nut against the concrete surface. They tend to split the concrete
if installed too close to the edge. Also they also tend to loosen
under vibratory loads. They come in sizes up to 1.25" and have
allowable capacities of 12 kips in tension and 7 kips in shear.
Deformation Controlled Anchors
are partially split sleeves that are hammered into a pre-drilled
hole. A plug is inserted which is forced in by hammering a setting
tool and then a threaded rod is screwed into the sleeve. They are
normally used as hanger anchors in concrete ceilings, come in sizes
up to 0.75" and have allowable capacities up to 2.7 kips in
tension and 4.0 kips in shear.
Friction Screw Anchors
anchors look similar to masonry bits but with a large thread pitch.
They have a bolt head, are installed into a pre-drilled hole, work
well with vibratory loads, and are often used to bolt down sill
plates because they can be used closer to the concrete edge than
can wedge anchors. They derive their holding power by cutting treads
into the concrete as they are screwed in. The threads are not much
larger than the shank so a common installation problem is over drilling
the hole diameter, even by just leaning on the drill. They come
in sizes up to 0.75" with allowable capacities up to 4.7 kips
in tension and 6.2 kips in shear.
4) Adhesive (Bonded) Anchors
These are threaded
rods or rebar inserted into an oversized pre-drilled hole and bonded
with epoxy or other adhesive. They are sensitive to a clean hole
and demand a special cleaning procedure be followed. They are also
sensitive to water, temperature variations and mixing of the epoxy.
They have the highest load capacities (when epoxy is used) of the
post-installed anchors. They come in sizes up to 1.25" with
allowable capacities up to 31 kips in tension and 17 kips in shear.
presented on the four systems:
- All the
post-installed anchors discussed have group effect limitations
on their capacities if installed too close to each other.
- Greater embedment
depth than specified usually will not increase the documented
- Safety factors
used were 3.0 for the steel and 4.0 for the concrete. The 28-day
compressive strength used was 2000 psi. Higher
capacities may result for higher concrete strengths.
- Hole cleaning
is imperative prior to inserting the anchor to ensure full embedment.
Drilling a 6 inch hole makes about 2 inches of debris in the bottom
of the hole.