STEEL BEAM STRENGTH

[Sandbags89]

just a quick one. throwing up an I Beam for the middle of a flat roof for garage for joists to sit on.

Planning to get a 203x133x25UB which I think should be more than ok. Not along of weight going on top. But I was shopping about and saw that 254x102x25UB was the same price and it made me wonder if one is stronger than the other or more or less the same. I understand that this stuff usually requires architect/engineers to plan etc. but I'm only looking for a rough answer from some of the experienced members. I'll prob go with the 203 either way, but its just a curiosity more than anything.

Some details if they help.

Single skin 7n block garage about 6mx7m.
Steel 5600 length sitting on 150mm padstone on pier either side.
Flat roof constructed of 6x2 going on top.

cheers

 

[freddiemercurystwin]

Steel is charged per weight, so each beam is 25kg per metre so the same price per linear metre, it will be desirable to use one rather than the other depending on the situation for example if a wall was 100mm thick then a 102 wide beam would be a more practical choice than a 133 wide beam.

BTW the rule of thumb for the depth of steel beams is it should be about 1/20th of the span.

 

[Sandbags89]

Steel is charged per weight, so each beam is 25kg per metre so the same price per linear metre, it will be desirable to use one rather than the other depending on the situation for example if a wall was 100mm thick then a 102 wide beam would be a more practical choice than a 133 wide beam.

BTW the rule of thumb for the depth of steel beams is it should be about 1/20th of the span.

ah I see, so its really about the last number for the weight per m rating. thanks

1/20th... so 5600/20=280 so according to the sizes I see available that would need a a min of 305x102x33UB? Sounds bit overkill for what I've got, or is that rule of thumb for general structural use holding up another floor/walls etc.

 

[Dereekoo]

Tables showing max bending moment each steel can take for comparison purposes, 203 x 133 x 25 is the stronger

 

[Dereekoo]

ah I see, so its really about the last number for the weight per m rating. thanks

1/20th... so 5600/20=280 so according to the sizes I see available that would need a a min of 305x102x33UB? Sounds bit overkill for what I've got, or is that rule of thumb for general structural use holding up another floor/walls etc.

Rule of thumb means nothing as you say it all depends what you are supporting (small or large area of flat roof, large or small depth of wall ,etc.etc,etc)

 

[^woody^]

ah I see, so its really about the last number for the weight per m rating

No, its not the weight of steel, but how its formed that matters. And it's not a case of one beam being stronger than another, but of one being more resistant to factors such as bending, shear, buckling and deflection.

A deeper beam may be more resistant to bending for any given load, whereas a wider beam may be more resistant to bucking for instance - even when the beam contains the same amount of steel.

 

[Sandbags89]

thanks for all the reply guys, very helpful.

I appreciate its not black and white answer on this sort of topic, but the info has helped, thanks