MOMENT DESTRIBUTION METHOD FOR SIMPLE FRAME

[CESSNA1]

HELLO ALL: It has been over 30 years since I have worked witn the moment distribution . I am really rusty. By the way this is not a homework problem this is a real world problem. Here is the problem I am trying to solve.

A simple 2 dimensional frame with 8" legs and an 11 inch top cross piece. Both legs are anchored so they carry a moment, shear and axial loads. The crosspiece on the top is 11 inches long and has a 1000 pound load 5 inches from the left end. The technical information is:

material: steel - E=30,000,000 #/sq in
Moment of inertia - each 8" leg - .0088 in^4
Moment of inertia - crosspiece - .019 in^4

I have referred to Roark for a solution and a 1928 Structural Book I have. Neither seemed to work. I would like to go back to basics. Although the Moment Distribution Method yields only moments I will draw free body'd of each member to obtain shear and axial forces.

I would like to see the step by step solution. I will send my E-mail address for a copy of the solution.

Cordially
Dave

 

[JAE]

For an 8" leg that is a very small moment of inertia. You might want to check it.

 

[CESSNA1]

JAE: Thank you for your response. You are correct. The 8" leg is flatbar that is 2" wide and .375" thick. The moment of inertia is:

(1/12)*(2)*(.375^3) =.0088

This is part of a small bracket that fits on the front of a vehicle and I am trying to determine the loads and stresses involved.

Thank you again
Regards
Dave

 

[JAE]

Is it bending about the strong or weak axis? Your calcs indicate that it is bending about the weak axis (flat side bending).

In any case, the moment distribution method is dependent upon relative stiffnesses instead of absolute stiffnesses.

I think that teaching or describing the Moment distribution method on a site like this is a bit much. Get a good structural analysis textbook and it should have the method and steps required. Or invest in a cheap 2D program. I believe there are some out there.

Good Luck!

 

[CESSNA1]

JAE:Thank you for your response. The bending is about the flat side, as you noted. I understand your concern about space but I wanted someone to work the problem, in detail, and then scan and E-mail the results to me. I have the textbooks and I am muddleing through them But I would like someone with more and later experience/knowledge than I. If someone volunteers to do this I will post my e-mail adress. A finite element model would be acceptable also. I need the moments at each node.

Regards
Dave

 

[MiketheEngineer]

Archonengineering.com has a very simple frame program - I think it is $40 or $50.

Most of us do not have time to do others work... and don't want the liability...Sorry


The moment distribution method is quite easy to do and is well defined in any good structures book.

 

[ToadJones]

try this....i've never used it.

 

[msquared48]

There are also several older books out there on moment frames like Seeyle (spelling). I have a copy packed away somewhere, but rarely use it. I just use RISA.

Mike McCann
MMC Engineering