Analysis tools for 2-span continuous glulam beam with cantilever span at one end? 1

[AELLC]

I don't have anything available to design this, it has uniform loads that vary in intensity along its spans and a few concentrated loads. The concentrated load at the cantilever end is large and worrisome.

I have my own Excel which can do a 2-span continuous beam, but this has the cantilever span in addition at one end.

I have used STRUDL and similar major programs in the past but don't have the time to re-learn something complex or the resources.

Is there anything user-friendly with minimal learning effort, and less than $300 in cost? Is Enercalc capable of this?

If not, I will patch this together by using my Excel and superimposing the 2-span continuous and cantilever conditions as an approximate analysis.

 

[JedClampett]

Can't you just add a concentrated moment in place of the cantilever end and use your spreadsheets? Then design the cantilever separately.

 

[msquared48]

I use BeamPro, and it's under $50.00 if I remember correctly. Very user friendly and I have used it for years. Does cantilevers too.

Mike McCann
MMC Engineering

 

[AELLC]

Jed,

yes, that would work. The spans are 21.2', 12.1', then a cantilever of 4'

How would I approximate the deflection at the cantilever end?

 

[AELLC]

Mike,
I started to d/l the BeamPro free demo, but when I saw all the junkware that came with it, I pulled the plug.

I recently had a horrible computer malfunction experience because of junk/malware)

 

[Strukter]

AELLC

I am new to these forums (fora?) but I noticed you mentioned Beamanal in another thread.

You can input a 2-span, pinned support, continuous beam model,and then input a moment at the end support where you have the cantilever,and add a concentrated load there also.

 

[AELLC]

Strukter,

Yes, very good. I just noticed it gives a slope evaluation, I have a deflection at the cantilever now.

I have this thing pretty much buttoned down as a 5-1/8" x 18 GLB, 24F-V8, and a 6 x 8 post at the interior support between the 21.2 and 12.1' spans, and a 6 x 6 post at the end support where the cantilever is. It look ballpark, and all the deflections are very small.

The only thing that surprised me was the negative bending moment at the 6 x 8 support was much higher than I first estimated.

 

[AELLC]

I am getting a stability/volume factor of 0.92, does anyone think that looks reasonable? The beam bottom edge is not laterally supported or braced.

 

[Strukter]

Aellc

I got another idea - I tried this and it seems to work -

Input as 3-span on Beamanal - all pinned - spans of 21.2',12.1',300' (yes 300)

Place concentrated load at end as located 4' to right of support 3, and any uniform load 0' to 4' to right of support 3 - that gives very close results compared to true cantilever of 4'

 

[JedClampett]

AELLC, I didn't have my best thinking cap on this morning. If I would of, I would of suggested slope deflection as an exact manual method of doing this problem. Two equations; two unknowns, easy peasy.
I'm not even sure they teach all those manual methods (slope deflection; moment distribution; moment area, etc.) anymore. But they're pretty easy, especially if you use them every day. I don't, but I break them out every once in a while just to refresh my memory.

 

[AELLC]

Jed,

We were taught all those methods at University, plus modern methods which lend themselves to computer-automated methods - stiffness method and flexibility method...I just don't remember any of it, never having used any at work.

These beams usually have complex loadings, and we have to check for bending moment, shear and deflection - I have a tendency to just go with the easy plug and chug computer method, and I like to have all my calcs done on Excel.

 

[AELLC]

Strukter

That is actually a great idea. The third span would be so flexible, it probably behaves close to a cantilever span condition.

 

[hokie66]

Strukter,
I have never used the program in question, but that is a clever manipulation. Instead of just plugging and accepting, a bit of thinking goes a long way.

 

[AELLC]

Hokie,

Beamanal is a very good continuous beam analyzer, and it has an AISC steel beam design module (in ASD)

It is Excel, and it is free on the AISC website - if you wish, I can attach here in this thread.

 

[Triangled]

Don't forget your compression face bracing requirement.

 

[AELLC]

Triangled,
The stability factor there is 0.90, does that sound ballpark? The volume factor is higher, so I am using the 0.90 to adjust F'b

 

[Triangled]

Not having my references in front of me, here are some thoughts,
Volume effect is, in addition to geometry, contingent upon species and somewhat upon loading configuration, and, 0.90 doesn't seem out of line, and may be conservative for your beam, but, need more data. O just noticed you said 24f v8 so looks like DF.
Beam stability could be, I think, much lower than 0.90. What is your bracing scheme? at columns only? (And don't forget column bracing.)
It seems that no moment will exceed the simple span moment for your 21’ span, so I'd probably look at that as a double check for your section.
The simple span moment for your short span, assuming the same loading, is around only 33%~50% of the long span moment, and you cantilever length is long for a 12' backspan, which, depending on true loading and whether you have to consider possibilities of skipped live loads, suggests worst case possibility of your 12’ span being in compression it's entire length. So I think your bracing scheme is important.
Regarding cantilever deflection, your serviceability requirements are important as that strikes me as a long cantilever for the given column spacings. But 5-1/8 x 24 is pretty big beam, but, only you know the cantilever load. Nice thing about glulams, you're fabricator should be able to camber up for your dead load deflection if you want. Good luck!

 

[AELLC]

Triangled,

This is a large custom home, and the beam support posts are within 2x6 stud walls.
The analysis did show the beam in negative bending the entire 12'-2" length. I am going to re-check what I have for calculating C sub L in general.

 

[Triangled]

The strength gained to cost expended ratio for Glulam compression face bracing is generally pretty good.

 

[AELLC]

The beam is the same depth as the floor trusses, so that sshould be pretty easy. Because we are almost always limited to floor truss depth, that is why these residential beams frequently need to be more than 2-pont bearing.