On 9 Feb 2007 17:58:08 -0800, "Lawrence"
wrote:

On Feb 9, 2:17 pm, (lp13-30) wrote:
I always want things like this to be many times stronger than actually
needed, but this is not going to require some 1/2" thick steel brackets.
Look at the weight a joist hanger will support vs. how light and flimsy
they look. Larry

A joist hanger works with gravity supporting the load from underneath
with multiple nails. Other larger nails also hold the joist in
place. If you want to support the beam it from above then it must be
supported from above perhaps with steel cables and turnbuckles. It
would be more than unusual.

Roof joists or collar ties are not usually large boards but they are
vital to the structural integrity and must be supported from
underneath and they should not be attached to the beam in the way
suggested. Rather, steel cable could be attached to the ridge beam
which could be beefed up would be a more likeley solution in this
unusual scenario.

No, it is not impossible but a more conventional approach can most
likely be used. If the OP insist one this wacky idea I suggest he
hire an experienced carpenter or engineer to OK the framing design.
From a practical standpoint I think the beam could be inside the room
and made to look nice with some moulding. That is a more conventional
solution and easier to design and execute.

The beam doesn't care whether the load it's supporting is above it,
below it, or tacked to the side. The only issue is making sure
that the hangars are capable of supporting the load on the joists.

Since these are 2x6s, one assumes that the span tributary to the
beam isn't more than 10'. If the joists are 16" o.c.,
that's 13.33 (call it 14) square feet. Since OP is
willing to have the beam above the joists, one assumes that
it's not a load bearing floor, so we can call it pessimistically
30 PSF, or 420 pounds per hanger.

I don't think there's any commonly available steel with a yield
strength of less than about 20,000 psi, but lets use 10,000.

The easiest way to support the joist is to wrap the strap
around the bottom of it, run it up both side, up one face
of the beam, so there's one strap up each side of the joist,
and hook both ends over the top of the beam. Each half
needs to support 210 pounds. On the other hand we're bending,
twisting, and drilling holes in it, so we'll triple that
value, and call it 630 pounds. Since our cheap-ass
recycled steel bar-stock supports 10,000 psi, that means
we need a strap with a cross section of .063 square inches.

Half-inch strap iron 1/8th inch thick is, conveniently
0.0625 square inches in cross section.

Hmm... common box nails, in sheer, 3" penetration
.... call it 100 pounds per nail. which works out
to 6 nails per strap.. That seems excessive to
me, but hell, the point is to make stupid overbuilt...

So put 3 nails slanted one way, 2 the other, up the face
of the beam, and a sixth on on top.

Attach the brackets to alternating side of the beam
on each successive joist, so it won't be tempted
to roll. Put blocking between the joists near the
beam so that even if some nut-case screws a swing
into one of the joists, it can't pull sideways and
behead the nails one at a time.

Remember:
Goedjn is not an engineer.
Goedjn is an anonymous voice on the internet.
Do your own math.

--Goedjn