Truss Beam problem! 5

[Integrator62]

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.

 

[Integrator62]

Ill do it a little days later I hope. Just made a little try for a very simple model and Stuck!
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.

 

[CANPRO]

I'm working through a similar problem....trying to determine the effective length of an unsupported compression chord. I just started doing some research into the topic, and this thread has given me a good start.

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/

 

[rb1957]

your pic is indetminate (though solvable), but your assumptions of fixed end moments is causing the problem (not simple axial members).

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 ?

 

[Integrator62]

A lot thanks CANPRO . This will help me a lot!

Thanks rb1957. But I hardly can understand. Ill be very grateful if you simplify this. I have added a photo...

 

[rb1957]

i think you've got it ... diagonal BD reacts the applied load P (the vertical component of the load in BD = P). the diagonal induces load in the top member AB (the horizontal component of the load in BD). BC and CD have no load in them.

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 ?

 

[Integrator62]

Yes I got the point! BC and CD will face very little I guess, so neglected. All is left is a 3 member frame! Load along BD later apply force on DC member, and again increase the Moment on AB by bending DC! Things get rough! I hate to do iteration! I am tired of it! Ill try some days later!

Thanks