What size of "I" beam to use?

  • Thread starter richard7761
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richard7761

I live in a middle house of a block of three. The two partition walls, dividing the block into three houses, are made of concrete 22.5Cm thick.

On the ground floor, there is a brick wall, set in the middle, that runs from one partition wall to the other. The ceiling joists rest on the middle internal wall, they do not go from the front wall to the back wall without support in the middle. (In fact the joists are in length are just over half the distance of the width of the house, so they have to rest on the middle wall).

I'm going to remove one end of this internal wall. I'm removing a 3m length of it. So, I have to put up an "I" beam to hold the ceiling up- one end set into a partition wall, the other resting on the remaining middle internal wall.

Okay, what size should this "I" beam be? A friend did the same alteration and used a 9" x 4" beam. I thought 7" x 4" might be okay. What think? Thanks.
 
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richard7761

This picture shows pretty much the engineering situation. Except it's bedrooms on the second floor.

I could probably calculate the beam size, if I knew what the regulations were.

You see the "I" beam in red in the picture. That would be 3m in length.

:)

Let me just say I took the picture from here:

http://www.beamcalcs.com/instant/calc9_form.php

I could get a professional answer for £50, apparantly. :D
 
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RedHerring2

The professional answer should come with a degree of indemnity.
The opinion on here has no such indemnity.
 
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richard7761

The professional answer should come with a degree of indemnity.
The opinion on here has no such indemnity.

Hi. Yes. I'm figuring the "procedure" for this kind of DIY work, putting up an "I" beam, in the circumstances indicated, is to obtain a beam size based on a professional service. That will be required in many circumstances I imagine (if not all perhaps).

No doubt that folks here, by calculation or years of experience, could tell me the beam size and know that their advice is good and fulfills regulations.

But, I understand that few would want, and not unreasonably, to give the advice.
 
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RedHerring2

Is the work subject to BC? In which case BC will want a professional opinion.
 
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I could probably calculate the beam size, if I knew what the regulations were.

Here we go

Work out your loadings in kN and multiply by 1.4 or 1.6 for the design load

Use W/2 and WL/8 to get your max shear force and bending moment

Get a trial section modulus - Sx = Mu x 10^3/Pb

Check the bending moment of the section - Mc = Sx X Py x 10^3/10^6

Check the design shear capacity of the section - Pv = (0.6Py x D x t) / 10^3

Check for deflection - (5 x W x L^3 x 10^3) / 384 x E x I x 10 ^4

Then do the padstones - but that's for another thread

Alternatively, if your friend did the same alteration, and it is still standing, then why not just use the same beam?
 
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richard7761

Is the work subject to BC? In which case BC will want a professional opinion.

I assume you mean Building Control. I think this is this essential factor that I was not thinking of much in my first post. My home is not a private home so alterations wil be subject to Bulding Control.

So, it must surely be that I cannot avoid having to obtain a professional opinion. My friend does live in his own home, so I suppose he could get by without seeking professional assistance. I feel sure I do not have as much DIY scope with regard to how I come up with the size of "I" beam.
 
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Urm, are you saying this is a rented property or leasehold?
Either way you need permission from the property owner as well..

As far as the design of the beam goes i would recommend designing to BS5950 to comply with building regs part A.. you need to be a competent person to design the beam..
You will also need to assess the overall structure for stability, assess existing foundations to take the new loading, padstones and masonry checks if small piers are required..

In the end its often best to get something designed by a professional structural engineer who has some PI insurance..
 
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richard7761

In the end its often best to get something designed by a professional structural engineer who has some PI insurance..

Yep, I think I will have no option but to get a professional to state the size of the beam, irrespective of whether I can calculate it myself.
 

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