"RicodJour" wrote:

Deck screws are too light, and 3" is too short - only 1.5" of
penetration?

In this application, fasteners are strictly in shear, so penetration
is
not an issue.

Don't like 3", use 3-1/2" or 4".

Deck screws that size are about the same as 16d common nails which
would do the job, if your arm is in shape to handle a 24 OZ framing
hammergrin.

And how many is "some"?

How about 3"-4" spacing or whatever looks good in the shower.

Most engineering designs fail
in the connections and the lack of detailing.

This is about as classic a design as it gets. The fasteners are in
shear, supports are in compression. I wouldn't expect these joints to
weaken the design.
===================================
If I'm understanding you, you're trying to give the OP a design for
a
full length truss with no intermediate support, but it's not really a
truss. A truss joist has diagonals that are opposed. Where one
diagonal is pushing or pulling, the meeting one is resisting that
force - there is no distance between where those forces are applied.
In your design you are relying on the 2x6s on flat to resist those
forces, there is a distance between where the forces are applied, and
the screws at the ends of the 2x12 blocks will be required to carry
more load than 1.5" of penetration will allow. This will tend to sag
over time. I didn't run the numbers, but it will happen.
=================================
Not quite.

The bottom 2x6 is in tension, the top 2x6 is in compression, and the
2x12
web provides the diagonal support.

No details have been specified for the end terminations; however, the
beam must rest on an adequate support.

Fasteners will not carry the load by themselves.

I'm lost about your fastener concern?

====================================
A swing set should be designed with a large factor of safety and it
should be designed for the occasional show off adults competition
really going at it.
====================================
Yep.

====================================
There's also the cyclical nature of the applied
loads, the combined tension and shear load on the screws with the 2x12
design, etc.
===================================
You lost me.

====================================
A #12 wood screw has something like 200 lbs of pullout
resistance in SYP (PT wood) per inch of embedment - 1.5" =~300 lbs. I
would think you'd need a minimum of seven or eight hundred pounds per
fastener for the end conditions with the 2x12 design instead of three
hundred.
====================================
You lost me. The beam must rest on an adequate support.

Fasteners in tensile will fail.

====================================
It would be better if the OP skipped the 2x12, which has problems
with
shrinkage and twisting, and used some 3/4" pressure treated plywood as
the web. Even better would be to use the 3/4" plywood and PT 2x6s
(might be able to get by with smaller 2xs) and build a box beam joined
with construction adhesive and 2.5" epoxy-coated deck screws at 4" -
6" on center.
====================================
Building a box truss with plywood is certainly an approach; however,
using pressure treated lumber for anything other than a ground contact
member is way down on my list of acceptable materials.

Exposed exterior construction would require considerable preventative
maintenance, thus wasn't considered.

====================================
The top of the beam should be covered so there's no standing water
on
top of the beam and water won't enter the edge of the plywood. The
plywood joints should be staggered and - belt and suspenders - screw
and glue plywood scabs to join the ends of the plywood pieces to each
other.
=============================

Having the swings hung from the top of the beam is definitely
preferable with a truss or box beam. I have no idea what sort of
hardware is available for a swing set, so I can't recommend any
specific method of attachment. Another poster mentioned the hardware
is expensive, I'd price that stuff before finalizing a design.
==================================
3/4", 3 strand nylon, replaced every other year.

Works for swings and dock line for my boat.

Have fun.


Lew