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Re: Anchorage to concrete

• To: seaint(--nospam--at)seaint.org
• Subject: Re: Anchorage to concrete
• From: Robert Shaffer <rkdn(--nospam--at)cruzio.com>
• Date: Tue, 09 Nov 1999 09:22:38 -0800

```A good article on anchorage to concrete was published in Bulding Standards
Magazine,  July/August 1993.  It runs through the whole shear cone area
developement,  including what to do with small edge distances.  If you are
asking about the large 7/8" diameter L-hook or J-hook anchors that are +/- 30"
long,  I have calculated those based upon the minimum developement length in
tension for smooth bar reinforcing per chapter 19 UBC,  not the section on
embedded bolts.

But while were on the subject of bolts,  I have a question on shallow c.i.p.
anchors per section 1632.2 which requires the use of Rp=1.5 versus 3.0 if the
anchor has an embedment depth 8x dia. or less.

If a 3/4" dia anchor is embedded 6" we satisfy this requirement and can use
Rp=3.0 and the connection exceeds our required load.  However in an attempt to
be more conservative in our design we use a 7/8" dia anchor with a 6" embed (
nothing else changes ) are we now forced to use the Rp=1.5 and the anchor no
longer meets our required load which has just doubled due to Rp=1.5 .

Robert Shaffer,  P.E.
Santa Cruz,  CA

"Randy Hamilton P.E." wrote:

> Can anyone lead me to a source to prove that a hooked anchor bolt (j-bolt)
> can develop the loads typically used for hold downs when cast into a stem
> wall.
>
> Using section 1925.3.2 ('94 UBC) with a phi factor of .85 (assuming the
> j-bolt is hooks around a horizontal bar) and an edge distance of 2.75 inches
> (assuming an 8 inch stem wall but the bolt is centered in a 5-1/2 inch 2x6
> plate), what should the value be for As?
>
> If I use concervatively a truncated cone with a diameter of 5.5 inches and
> an embedment length of 2.75" so as not to have to reduce for lack of edge
> distance, I come up with a tension value of 4045# for 2500 psi concrete.
> For service load design, this would need to be reduced by a load factor of
> 1.3 for wind and 2.0 for no special inspection which results in a value of
> 1555#.  This does not develop the load for even an HD2A bolted to a double
> stud.
>
> I assume it is acceptable to use more surface area then this conservative
> assumption but the question is how much and how is it justified?
>
> Thanks in advance for any input.
>
> Randy Hamilton P.E.
> Tucson, AZ
>

```