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RE: HSS Connections - Not Conventional
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: HSS Connections - Not Conventional
- From: "David Maynard" <davemaynard(--nospam--at)ceincorp.com>
- Date: Fri, 19 Aug 2005 14:26:31 -0600
for the input.
trying different truss configurations, I really exhausted that option. My
problems, unfortunately, weren't coming via the web members. It's
basically getting members good enough for the top and bottom chords. And,
according to the contractor, making the truss deeper isn't an option because
that would change his estimate for roof sheeting. *shakes head* I am
beginning to regret taking this task on. And nothing pisses me off more
than a contractor that gives me the money sob story when he went ahead and
bid the project before consulting with an engineer.
is, his idea is pretty good. He uses conventional wood framed
construction, but instead of using wood products, he uses all steel and welded
connections. Really not a bad idea. But there are some things, like
a 50' simply supported mono-sloped roof truss, that seem to fall outside his
realms of comfort. Hence the phone call to me. And now I have to
call him and tell him he has to spend more money on
kinda reminds me of an episode of Hell's Kitchen. Chef Ramsey was asking
for food to be done in a matter of 4 minutes and one of the apprentice chefs
said, "It's impossible to cook anything in 4 minutes. It defies the
laws of physics." That's how I feel when I talk to this guy and he keeps
asking, if I can do more to get it to work. No, I can't. It defies
the laws of physics. I cannot twist and bend the rules of logic in my
profession so that you can stay within your budget and still get an adequate
structure. AHHHHH!!!! TGIF!!!!
As long as your
analysis is sound and connections well detailed you are probably OK. One
thing I would consider is that if your sandwiched connections start getting
rather large with lots of welds your member ends may be more fixed than
pinned. You may want to run your analysis with both pinned and fixed
ends. There may be significant moments at the ends of your members,
depending on your configuration, which may need to be considered in your
If the members
have not yet been cut, you may also want to look at other types of truss
configurations. Changing the strut direction could possibly put the
critical members in tension rather than compression. If the cords are
the problem, making the truss deeper might help.
Thomas Hunt, S.E.
08/19/2005 12:40 PM
|HSS Connections - Not
Sorry for bugging everyone with these problems, but if there
is an area of the AISC design manual that isn't extremely clear, I believe the
HSS one to be it. Then again, it could be the lack of clarity results
from a VERY long week. Never the less....
My contractor made
the brilliant move of estimating a project that he is doing based on, what he
thought were, members sizes and geometry that would suit the purpose of a 50
ft mono-slope roof truss. He's using rectangular tube shapes, 2x4x14
ga., ASTM A588 (got the mill specs on this one to verify). However,
after running several analysis on varied geometries, I can't get a single 2x4
to work for his application, with respect to the top and bottome
His next option was to double up the members on the top and bottom, so
that two members would share the load. His connection option was to have
the web members "sandwiched" between the chord members, much like a typical
steel bar joists (bar ends are connected between the vertical legs of the
angles of the chords).
I have never done this type of connection and I
was hoping to get a little assistance on this. If I can develope enough
weld to make the connection (which may be a feet in and of itself, seeing as
how the walls are so thin), is this connection a viable option??? And if
so, what sort of local stresses should I be checking for this condition???
It isn't very conventional, but this is something that the contractor is
looking into in, what he believes to be, a cost saving option. (I tend
to not argue with contractors about "cost savings" when they come to me with
this type of post-proposed problem and ask me to "make it work") Any
assistance would be greatly appreciated.
David Maynard, PE