Truss Beam problem!
Truss Beam problem!
(OP)

In the picture a space truss beam is shown.
Its not a truss because the Webs are welded, not pinned and the main four exterior members are solid Members. So they can resist bending moment where in pure truss they only can resist Tension and compression.
Its basically a open web complicated beam.
Is there any analytical way to solve this type of truss beam?
Thanks.






RE: Truss Beam problem!
I would still analyze it as though it were pinned, I've seen trusses which are bolted and still treated as pinned.
RE: Truss Beam problem!
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Truss Beam problem!
another day in paradise, or is paradise one day closer ?
RE: Truss Beam problem!
His recommendation is to model the chords as a continuous beam. The web members are then pinned to an extremely rigid vertical member with a length equal to the noding eccentricity. The vertical member is fixed to the beam. This will induce a realistic bending moment into the chord, and allow the the web members to remain pinned, which is reportedly how they behave according to current research.
RE: Truss Beam problem!
Vertical webs are normally included to address a specific local loading item and I am wondering if this illustration is upside down...
The system looks like two 2D trusses with chord bracing between them rather than a 3D space frame truss, at least as I imagine them....
Just some observations.
RE: Truss Beam problem!
if you've got lateral load, then you need lateral bracing ... discrete truss members, or continuous webs.
another day in paradise, or is paradise one day closer ?
RE: Truss Beam problem!
RE: Truss Beam problem!
Unfortunetly I cant buy books right now. So, things get tough for me!
However, DamsInc, will you please Describe a little about it? specially "noding eccentricity", I havnt heard anything about it.
I guess the Chords will act as pure beams, So there should be a big error considering it as truss desertfox
Yes, I use it just as an example rb1957 Triangled
Ill go for FE analysis later KootK
RE: Truss Beam problem!
AISC 360-10 is available as a free download from the AISC website. That should allow you to use BadgerPE's information.
RE: Truss Beam problem!
@DamsInc: this is good to know. Is the fictitious rigid link a vertical element extending to the interior sides of the chords? Does it change how one should physically detail the joint or is making the member centroids coincident still appropriate?
Not so. The chords will act primarily as axially loaded members. Any frame action will be a secondary effect.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Truss Beam problem!
in the design world, the truss elements line of actions all intersect, but in the real world the diagonal truss element shears it's load into the chord member in a manner that'll introduce "kick" moments.
another day in paradise, or is paradise one day closer ?
RE: Truss Beam problem!
RE: Truss Beam problem!
KootK: Yes, that is correct, but it can extend on either side of the chord depending on if the eccentricity is positive or negative.
Depending on the ratio of the noding eccentricity to the member dimensions, the effect of the eccentricity can often be ignored.
I really recommend this book. It is a few years old now and some sections are now out of date based on more recent research.
RE: Truss Beam problem!
RE: Truss Beam problem!
RE: Truss Beam problem!
One major consideration is the size of the gap "g" between the web members. Too close and it won't be practical to weld. If the chord can handle the moment ok then the eccentricity isn't a big deal. Really it's just a fabrication/economics issue if the connection otherwise passes all the checks (there are 7 failure modes in the book). We spent a few weeks on the subject of these truss connections.
I got the impression that it is common in the industry to just consider the whole thing pin ended and be done with it.
That being said, I'm not a truss designer, I just finished his graduate class in December.
RE: Truss Beam problem!
RE: Truss Beam problem!
So I have got two ways.
1) Truss consideration:
i) Consider it as pure truss, 1st order analysis
ii) Consider the moments in joints, recalculate, 2nd order analysis
2) Beam consideration:
i) Consider chords as pure beam, 1st order analysis.
ii) Consider the web members as pinned and recalculate, 2nd order analysis
If 2nd order analysis of truss doesnt have much effect, I will go with simple truss calculation with pinned members. hokie66 KootK rb1957
A lot thanks DamsInc for your help.
I also thought that Its testing and software work, Thanks 48v
Yes I have downloaded one fegenbush . Thanks.
RE: Truss Beam problem!
Let us know how it works out, I would be interested to see how large the error might be, that was a concern you had if analysing as a simple pinned truss.
RE: Truss Beam problem!
Tried to use min potential energy method, but can be done using simple calculation.
Iteration process is probably the only way, which is very time consuming. May be impossible without software for More complicated frame.
Assumptions,
Deflection is very little to affect Beam length.
Moment at point B C and D are not considered. Left for 2nd degree analysis, which may be too much lengthy process!
Thanks.
RE: Truss Beam problem!
Integrator62, you should follow the link below...seems like a lot of great resources and they're all free if you register (takes 30 seconds to register).
http://www.cidect.org/en/Publications/
RE: Truss Beam problem!
axial members means the diagonal member is carrying the vertical load. this means the top member is in compression and the bottom member has zero load.
when you go to the next bay, the lower chord is reacting the horizontal component of the outer diagonal, the diagonal reacts any added vertical load, and the top chord reacts the outer top chord plus any diagonal component added in this bay.
a truss beam like yours, with single direction diagonals, is statically determinate.
now allowables, the compression allowable for the chords, ... that's a different question !
another day in paradise, or is paradise one day closer ?
RE: Truss Beam problem!
Thanks rb1957. But I hardly can understand. Ill be very grateful if you simplify this. I have added a photo...
RE: Truss Beam problem!
just draw FBDs at each joint.
if the pic posted is real, then i'd worry about lateral loads.
another day in paradise, or is paradise one day closer ?
RE: Truss Beam problem!
Thanks