Subject: Capcity reduction for closely spaced epoxy anchor bolts
From: "Lee" <le98(--nospam--at)telusplanet.net>
Date: Mon, 22 May 2000 08:41:13 -0600
I want to ask Hilti people a question, and think it may be interested to
people in the group so I am sending it here.
We are extending a tower from 75 ft high to 100 feet. Tower is essetially a
pipe, 4 ft in diameter with 3/4" thick wall. The foundation is a 3000 psi
concrete slab, octagonal with 20 feet wide from side to side and 2.5 feet
Everything sounds ok except that we have to increase the number of anchor
bolts from 4 cast in place 3" diameter to 12 epoxy bond 1.5" diameter.
We are planning to use epoxy anchor bolts, with a bonding strength of 1800
psi, As the bolt circle diameter is about 5 feet, the spacing of 12 anchor
bolts comes to about 16", which is less than recommended minimum bolt
spacing 12*bolt diameter=18" (ACI SP130 Anchorage in Concrete).
1. Anchor pullout capacity = Bonding strength*contact area =
1800psi*3.14*1.5"*25" (embedment) = 212 kips
Do I have to multiply this capacity by a reduction factor less than 1 as in
the above reference?
2. Cone failure effective area: What is the effective area for calculating
capacity based on failure of the concrete cone? The effective area is
composed of 12 circles overlapped each others and some anchor bolts are in
tension, others are in compression (self weight and moment caused by wind
load) . Again, what is the reduction factor if i use an effective area of a