Removing existing columns 4

[hoshang]

Hi

Please find the attached file.
The object is to remove the two columns to have a larger open space. The thicker walls are stone masonry built about thirty years ago; the thinner walls (extension) are hollow concrete blocks built about ten years ago. I have the thought of introducing permanent W12 beam supported by two W8 columns spaced 9.8m clear distance located in the the thicker and thinner wall interaction (before cutting off the columns). The columns are to be supported on single footings. I have a limited depth for the beam of 30cm due to the clear height required for the ceiling. My concerns are
1- The lateral- torsional buckling of the beam
2- Constructability due to the enclosed area. I suppose the beam to be cut into two pieces and spliced.
3- Immediate deflection of the slab
4- Should I use nonlinear analysis?

 

[dik]

JAE: clicked the forum policies, by accident and nearly read them <G> Just realised that I've never read the forum policies. Good link and the summation of the work was good. Missed it, somehow.

Dik

 

[dik]

Just noticed the loading on my sheet was wrong... corrected. W18x55 no longer OK, need a W21x55. I've highlighted the loading, trib width and span. Your live load seems a little light. Ignore B02 and B03... that was from another project and has used your design loads. I'll update my spreadsheet so that the loading is carried forward.

Dik

 

[hoshang]

Hi
For LTB restraining, could these be options:
1- Custom wide flange with cap Channel

https://www.screencast.com/t/FimMajImEN

2- Instead of W shape as beam, using Channel as beam

https://www.screencast.com/t/FV2jxQdLFx

3- Instead of W shape as beam, using Tube as beam

I tried with HP 16x183, it's OK. What do you think?

 

[dik]

Why add a channel when you can secure the flange to the concrete? Just an added expense and a more difficult shape to move/transport.

Why the hangup on LTB. Best if you can avoid it by securing the flange. Using a channel is a backward approach, and you may not find a channel large enough. With a channel comes greater instability.

An HP16x183 is 3 times the weight. It is far more costly, being a less common section and may not be available in higher strengths and is far less common. It is also far more difficult to install in a confined location. Consideration of same is really 'silly' to quote Monte Python. I've updated my spreadsheet to include for Class of section, and if you use Zx and not Sx, the W18x55 works (I don't know what other codes allow).

Dik

 

[hoshang]

Hi

I tried W12x210. It seemed OK. What do you think?

 

[BridgeSmith]

hoshang, you seem to be trying to use shallower and heavier sections than others are proposing. Is there a depth limitation for the beam? Otherwise, a deeper and lighter section is far less expensive, stiffer, and doesn't add as much load to the foundation.

 

[hoshang]

Is there a depth limitation for the beam?

Hi
Please read the original post (the first post). Besides, LTB is the main concern. So I try finding section with wider flanges to have less lateral torsional buckling concerns.

 

[dik]

You might be able to get by with something lighter... New improved spreadsheet... again, your live load seems light.

Dik

 

[dik]

LTB is the main concern.

From an earlier post, "Why the hangup on LTB. Best if you can avoid it by securing the flange."

Dik

 

[BridgeSmith]

I thought maybe there was something later about the depth limitation that I missed, since Dik was proposing W21x and W18x sections. Anyway, it doesn't take anything very strong to provide lateral support against LTB, but it probably would mean attaching an angle or something to the top flange to lock it in. Heavier and simpler vs. lighter and more complex - I guess whether it's worth it, depends on how much weight you can save by providing lateral support. It wouldn't have to be continuous; maybe discrete bracing could be an option?

 

[hoshang]

again, your live load seems light.

Hi
I changed Live load to 2kN/m2. I tried W12x190. It seems OK.
Other concerns:
1- My thought is to use 3 pieces of the beam (2.5m on each sides, about 4m in the middle) and splice them. What do you think?
2- I'm familiar with American steel sections (not familiar with Europe steel sections); here only Europe steel sections are available (Turkish make). Does this section has equivalent in Europe?

 

[BridgeSmith]

If it has to be 3 pieces, then so be it, but if you can do it with 2 pieces, even if the splice ends up near the middle, one larger splice is more economical than 2 splices. Presuming your design code is similar to the AASHTO bridge code, a minimums for the splice (size, number of bolts, etc.) may dictate the 2 splices end up the same size as if you just used one. Do you know the maximum piece length you can use?

 

[dik]

Revised spreadsheet. With shallower beams end plate splices become a bigger issue, too.

Dik

 

[hoshang]

Hi dik
Thank you.
I'm sorry. I tried a little bigger span (I used 10x10m)
W12x170 doesn't verify.
Mry/(Fib*Mny) = 1.06 > 1.00 LRFD (H1-1b) Not verified
uzt = 4.4 cm > uzt max = L/240.00 = 4.2 cm Not verified
What about my concerns in my post on 9 Jul 18 at 17:20?

 

[dik]

W12x170 doesn't verify... are you using the Plastic section modulus? I get a Mr=1030+ just a quick calc... and a Mf=695 based on the trib width and span. Def'l is slightly below L/180. Maybe different codes? Fy = 350 MPa, and phi = 0.9 and Zx = 275 in^3. For Canadian codes, if you have a Class 1 or Class 2 section, you can use the plastic section modulus and not the elastic one.

I'm not sure what the difference between 4.4 and 4.2 cm is... looks like a couple of millimeters.


Dik

 

[hoshang]

Hi dik
Thank you
Not very different. I think W12x170 is OK.
What about my concerns in my post on 9 Jul 18 at 17:20?

 

[hoshang]

Hi
Other concerns:
1- My thought is to use 3 pieces of the beam (2.5m on each sides, about 4m in the middle) and splice them. What do you think?
2- I'm familiar with American steel sections (not familiar with Europe steel sections); here only Europe steel sections are available (Turkish make). Does this section has equivalent in Europe?

 

[hoshang]

Hi
Are there any thoughts on my concerns?

 

[hoshang]

Hi

If I couldn't find equivalent Europe steel shapes for wide W12x170, I'm thinking of using built-up section.

 

[BridgeSmith]

Well, if you have only 12" of depth to work with, you'll have to go that way anyway - a W12x170 is 14" deep, as is the European HE 320M, which would be the rough equivalent.

Is the roof deck something you could make composite with the beam? If you're going to have something fabricated, it may become advantageous to add some type of shear connectors, if the roof deck can be used as a composite top flange. Otherwise, providing lateral bracing at a few location should become easier.