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RE: ANCHORAGE TO CONCRETE

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The CCD method as developed by 318 does include hooked bolts (J and L
bolts).  The minimum edge distance and spacing requirements included in the
method are intended to preclude the splitting failure mode, although I would
be a little cautious about this.

Splitting is not an issue that is confined to hooked bolts.  All anchorages
introduce splitting forces (in the form of hoop stresses) in the concrete.
These are dealt with either by providing sufficient concrete thickness
around the anchorage or by the placement of transverse reinforcement  (as
you would for a lap splice, for instance).

Park and Paulay (Reinforced Concrete Structures) provide a good discussion
of the testing and performance of hooked bars (Tom Hunt mentioned this
already), and touch on the issue of splitting.

J. Silva

> ----------
> From: 	Randy Hamilton P.E.[SMTP:rh-eng(--nospam--at)dakotacom.net]
> Reply To: 	seaint(--nospam--at)seaint.org
> Sent: 	Friday, November 12, 1999 8:44 AM
> To: 	sea list serve
> Subject: 	ANCHORAGE TO CONCRETE
> 
> 13                               Message:0013                           13
> --------------------------------------------------------------------------
> In my original post, I was trying to justify the anchorage that so many
> residential contractors in this area (Tucson, AZ)use for hold down anchor
> bolts in a concrete stem wall for 6" stud walls. I was attempting to
> justify
> it with a simple truncated cone on a j-bolt.  I now understand that the
> cone
> failure may not be very applicable for a j-bolt.
> 
> In my simple analysis I was not proposing to reduce the emedment length
> from
> 12 inches to 2.75".  I was only basing the failure cone to be that equal
> to
> a 2.75 inch embedment since the edge distance for a j-bolt embedded 12
> inches is only 2.75 inches on each side for an 6 inch stem wall. This was
> not adequate to develop the published load of a Simpson HD2A with a 5/8"
> anchor bolt much less develop enough to ensure a ductile failure of the
> bolt.  (All they are usually trying to develop is the 1800# uplift for the
> prescriptive braced wall panel required in UBC '94 2326.11.4).  I was
> looking for justification to use more surface area of the cone failure
> with
> 12 inches of embedment; however, it appears that I need to look at a
> different failure mode for a j-bolt.
> 
> Does the CCD method that John Silva referenced in the IBC 2000 address a
> smooth j-bolt (that is typically used) in a narrow stem wall.  Has anyone
> calculated the allowable service load for a 5/8" diameter j-bolt with 12
> inches of embedment in a 6 inch stem wall.
> 
> 
> 
> From: "Silva John (sj)" <Silva(--nospam--at)hilti.com>
> To: seaint(--nospam--at)seaint.org
> Subject: RE: Anchorage to concrete
> 
> Robert,
> 
> Let me try this one.  The idea of requiring an l/d of 8 was to force some
> measure of ductility, rightly or wrongly, into the anchorage.  It was
> assumed that for many cases, l/d = 8 would ensure steel rupture, and this
> should be encouraged by punishing shallower embedments.
> 
> In many cases, (stem wall anchors, for instance), the concrete capacity is
> severely limited by the geometry of the anchorage, and l/d = 8 cannot
> ensure
> steel failure at ultimate.  It is important to note, however, that if the
> ultimate capacity is limited by the concrete, increasing the bolt diameter
> will not increase the anchorage capacity, although it may increase the
> initial stiffness.
> 
> e.g., assuming you are not limited by near edges or adjacent anchors, and
> looking simply at tension, your 3/4" anchor (let's assume a standard hex
> A307 bolt) with 6" of embedment would develop a concrete capacity
> (concrete
> cone failure mode) in nominal 2000 psi concrete of approximately 26 kips.
> The tensile strength of the bolt at the threads (assuming an overstrength
> factor of 1.25) is about 25 kips.  The tensile strength of a 7/8" A307
> bolt
> is 33 kips.  Increasing the bolt diameter without increasing the embedment
> doesn't do much for you in this case.
> 
> With respect to your recommendation for designing embedments in stem walls
> or narrow foundations, I would agree that the use of equations based on a
> breakout cone failure for this case is inaccurate (this was the subject of
> a
> previous thread, as I recall).  Splitting will be the controlling failure
> mode for the concrete in many cases, and the equations for development
> length are based (at least in part) on this failure mode.
> 
> (The original post indicated reducing the embedment of the anchor bolt to
> 2.75" to avoid an edge distance reduction.  I would strongly recommend
> against this line of reasoning...)
> 
> Apropos strength design of embedments, I would recommend becoming familiar
> with the method adopted for the IBC 2000 (the so-called CCD method).  It
> is
> reasonably comprehensive and provides guidance for a wide variety of
> loading
> conditions.
> 
> Regards,
> 
> John Silva
> 
> 
>