truss analysis 2

[bsmet95]

I need to design a truss which will bear a distributed load and be laterally braced. I can go thru a hand analysis by the method of joints, but since I'll have several truss lengths to consider this may take a long time. Is there any software available to make the task a little easier?

 

[MiketheEngineer]

What kind of truss - wood, steel??

If wood - call your local truss supplier and they will do it quite quickly.

If steel, RISA or any of the structural software will do a nice job.

 

[msquared48]

Risa 2D or 3D works well for me.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[BAretired]

For hand analysis, the method of joints would be my last choice.

BA

 

[bsmet95]

Steel truss.

 

[msquared48]

For hand analysis, I would always use a Maxwell diagram if the truss is determinate.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[SteveGregory]

RAM Elements has some truss templates in their truss design module for more than 20 truss types. It works for steel, cold-formed steel or wood. Or you can make up your own truss within the general program.

 

[BAretired]

Parallel chord truss?

BA

 

[MiketheEngineer]

As M^2 says, Maxwell force diagrams are the quickest - but I haven't done one in 35 years!! I suppose an old structures book would show you how.

 

[bsmet95]

yes, parallel chord truss.

 

[csd72]

loads are very easy by method of sections. Take a section in the middle of the span to get the chord loads from maximum moment and at the ends to get the shear loads on the diagonals.

Deflection though is considerably more difficult.

 

[BAretired]

Forces in parallel chord trusses can be obtained very quickly using the method of sections...practically as fast as you can write them down.

Deflections are a bit more difficult if you want great precision, but simple beam formulae using the moment of inertia of the chords will provide a value which, when increased by a factor of 1.1 to account for deflection due to web members, should be accurate enough for most purposes.

BA

 

[msquared48]

I remember in 1978 that for the first truss I solved in the first structural office I was in, I used a Maxwell diagram. Impressed the boss! I, too, have not used the method since with the hard and software we now have.

But when the power goes off, I can still solve the problem, using a candle. My electric eraser just won't work, but then again, I rarely need that anyway. My slide rule will work too.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[BAretired]

Mike,
You probably don't need a curser either.

BA

 

[BAretired]

Oops...I meant cursor.

BA

 

[MiketheEngineer]

The first Maxwell I did was about 1973 - then I got so sick of it - I wrote software in about 1975 to do it. Actually used a matrix analysis that I found in the engineering library at school. I was still in college. My boss thought I was brilliant.

Never told him I just copied it out of a book.

Only thing I learned in college - how to find the information and how to read it.

 

[paddingtongreen]

We had to do a graphic solution, a method of sections and a method of joints analyses of the same truss as a night school homework exercise.

Method of sections works best for this problem.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[hokie66]

bsmet95,
All good advice from experienced truss designers. Be aware that all three manual methods mentioned assume pins at the truss nodes and will give axial forces only. You need to combine those axial forces with any chord bending.

 

[bsmet95]

Thanks, everybody.

 

[a2mfk]

If you are doing parallel chord trusses, follow along with all the SJI specifications, especially for bracing. This wheel has been invented and used for a LONG time now, make your life easy...