I agree that if the member is top loaded, no significant connection is
needed, however I usually tend to specify at least two rows of 16d nails at
16" oc for attaching 1 1/2" or 1 3/4" members together. This at least helps
to equally share the load between members.
In the side loaded condition, assuming the multi-ply member is sized
correctly to carry the total load, you calculate the required number of
fasteners required using the yield mode equations in the 91 NDS. Attaching
members of different widths and strengths requires you to do an additional
calculation to determine what load each member carries based on relative
stiffness, but the calcs are straightforward.
This is how the multiple ply connection tables Trus Joist provides in their
literature were generated. If you have any old TJ specifier's guides you
can see the load capacity difference for a given nail pattern when attaching
2-1 3/4" members together compared to attaching 1-1 3/4" and a 3 1/2" member
together. Of course you need to consider the possibility of rotation when
you have multi-ply members greater than 6" in width.
Use of phenol formaldehye (PF) and phenol resorcinol formaldehyde (PRF)
adhesives can be enough to to transfer loads without fasteners if they are
properly used but generally this can't be accomplished outside of the
manufacturing facility. Trus Joist has made 3 1/2" wide members from 1 3/4"
members through secondary lamination with these type of adhesives. PF and
PRF adhesives are currently the most widely used adhesives in the engineered
wood products industry. These adhesives can be very effective for field
repairs in combination with fasteners, especially if you need to transfer
moment, and it also helps to limit fastener slip.
Albert J. Meyer, Jr., P.E.
----- Original Message -----
From: SEConsultant <seconsultant(--nospam--at)earthlink.net>
Sent: Tuesday, March 14, 2000 8:00 PM
Subject: RE: Double joist nailing pattern
> If this is to be a header I don't see the need to stitch them together
> inasmuch as the wall thickness for 2x4 studs is 3.5 inches. Typically, I
> have seen spacers used between the members used as headers to keep them
> flush with each face of stud.
> I learned my lesson in dry climates when I designed my home - a
> Southwest style with parapets and exposed wood headers and beams. I used
> headers and later regretted my choice as the headers twisted to some
> from the heat and drying differences inside and out. It may not be
> to most, but I can see every flaw and it speaks to me every day:o)
> If you are hanging joists or flush framing them to a built-up member, then
> can see why they should be stitched. You might want to consider following
> the suggestions of Trus-Joist for splicing Micro-Lam beams which are
> together in the field or delivered to the site spliced. I don't have the
> spec handy and possibly someone else can provide the information.
> I haven't had a need to splice conventional 2x members in the past, others
> might comment if an Alphatic Resin wood glue would add to the splice.
> Dennis S. Wish, PE
> -----Original Message-----
> From: JCohen [mailto:jccpc(--nospam--at)email.msn.com]
> Sent: Tuesday, March 14, 2000 9:25 AM
> To: seaint(--nospam--at)seaint.org
> Subject: Double joist nailing pattern
> Can anyone suggest how to effectively join two 2x12 timber beams using
> common nails? This seems to be a common construction practice, but the
> nailing I have observed seems less than adequate to effect a real
> connection. It also appears to be a particularly ineffective approach when
> adding a beam to share load as part of a repair.
> James Cohen