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?

 

[ukbridge]

Im not a buildings guy but:

1. I think youll struggle to get a 300mm deep beam to work (depends on the loading regime and lateral restraint) but thats why you do a quick back of fag packet calculation.
2. Constructability I think you'll struggle as well although Im not sure about the context of this open space (is it in isolation or inside a larger building?"). Even if you splice it into two pieces youll have difficulty getting the splice to work due to the maximum moment occuring in the middle of the beam.
3. You will likely need to use props or similar, surely theres some design guidance about that illustrates how this is done in a pdf etc

gl

 

[oldestguy]

Hell, do as the famous architect did it. Frank LLoyd Wright just took them out. So the ceiling sagged, so what.

 

[dik]

Are the foundations adequate to support the new loads on the wall?

What loads is the new beam supporting?

What is the construction of the roof/ceiling?

For the span you could be looking at a beam in excess of 18" deep. You have to minimise deflection with masonry.

With any change in loading regime, you could be looking at cracking and the client should be made aware of this.

Dik

 

[dik]

OG: Great post...

 

[oldestguy]

dik: In his Spring Green, WI house you could see the result, but with his short stature, what the heck, he didn'b hit his head. Small height doors also his idea.

 

[dhengr]

Oldestguy:
Frank LLoyd Wright was actually just thinking ahead. Once he knew where the low spot in the roof was, he knew approx. where he would need to place a bucket to catch the leaking rain water which he was also well known for.

 

[hoshang]

Thanks

2. Constructability I think you'll struggle as well although Im not sure about the context of this open space (is it in isolation or inside a larger building?"). Even if you splice it into two pieces youll have difficulty getting the splice to work due to the maximum moment occuring in the middle of the beam.

It is inside a larger building

Are the foundations adequate to support the new loads on the wall?

What loads is the new beam supporting?

What is the construction of the roof/ceiling?

The beam will replace the two columns.
The new beam is supporting 18cm thick roof slab, self-weight and service load of 3kN/m2 as dead load and 1kN/m2 as live load
Do you mean the material? It's RC concrete

 

[dik]

OG: I understand that he was somewhat abusive to his staff...

Dik

 

[dik]

You may be looking at something like the attached... A W21x55 is stronger for approx the same cost.
Confirm with alternative design... this is a sample calc only. The beam sizes are part of a database that I can select from a dropdown list.

Dik

 

[dik]

OP: A W12x87 seems to work... I was just curious. Program includes the weight of the beam...

Dik

 

[ukbridge]

Putting two and two together, it doesn't seem particularly viable to me.

How are you going to get the beam in, through the window? Let alone all the equipment needed to break out the columns, retrofit the beam into the wall etc etc. Maybe a more experienced engineer has a good idea, draw some sketches showing the construction sequence and show it to the contractor if it cant be done it cant be done.

Nevertheless I don't think 300mm will be enough, do a simple 5minute hand calculation to size the beam wl^2/8 etc assume its unrestrained as theres no composite action between the slab and the beam.

loaded width B = 0.5*11 = 5.5m
1.35gk+1.5qk = 1.35*(3+0.25*0.18)+1.5*1 = 5.6kN/m2
UDL = 5.6*5.5 =31kN/m
M = wl^2/8 = 31*10^2/8 = 387kNm

For a LTB Lcr = 10m, a UB 356x171x67 gets you about 120kNm need a new plan i think

 

[dik]

UKbridge... I just used a WAG for spans and trib width due to the 2 span condition... might have an increase in 20% for this. Due to the flange being supported, I wouldn't consider LTB. Also based on CSA Standards... not Eurocode.

Dik

 

[ukbridge]

@dik yes apologies, agree with you there reasonable to assume fully restrained.

 

[dik]

No apologies necessary... fully understood what you had done. Purpose was to get a magnitude of the size. The spreadsheet is written using variables, and, I can cut and paste the beam design part so I may have 20 beams in s single sheet.

Dik

 

[hoshang]

Hi

UKbridge... I just used a WAG for spans and trib width due to the 2 span condition... might have an increase in 20% for this. Due to the flange being supported, I wouldn't consider LTB. Also based on CSA Standards... not Eurocode.

WAG for spans?
The spans are clear from the drawing
You wouldn't consider LTB?
Can you assume the flange being supported?
Do you assume composite section? There isn't shear studs.
I'm apologizing if I missed something.

 

[dik]

hoshang:

I was in a hurry and just 'roughly' did the sums... I would secure the flange to the slab and not worry about LTB... yes, the flange would be supported...I would not consider composite action... my spreadsheet is for simple span... I didn't even consider composite action, else I'd have used a different spreadsheet. I think you pretty much touched on everything.

Dik

 

[hoshang]

I would secure the flange to the slab and not worry about LTB... yes, the flange would be supported

Thanks.
Isn't there dry pack between the new beam and the existing RC roof?
How the flange is secured to the slab and supported?
A sketch of this situation would be helpful.
LTB of the beam is my first concern.

 

[JAE]

A similar thread here:
thread507-419492




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[dik]

Drypack if needed, and bearing pads at the ends...and, the natural camber of the beam upwards.

Dik