Rules of thumb

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Rules of thumb

Postby steve » Wed May 09, 2007 11:40 pm

Heh guys, I'm doing a Structures exam shorthly in Arch Tech, and I'm just wondering if anyone can help me on a question Im having difficulty with. The question involves using the "Rules of Thumb" to approximate the depth of structural materials.....

Eg A Beam - (a) Lightly Loaded : Depth = Span/x (b) Heavily Loaded Depth = Span/x

Whats the value of x? There are 6 other members also, slab, catilever, truss, portal frame, and space frame....

Someone may have resources, or links that could help me...

Thanks in advance :)
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Re: Rules of thumb

Postby Bren88 » Sat May 12, 2007 1:40 am

surely if your doing an exam on the subject it must be covered in the subject lectures,
Beam, cantilever, slab and truss will al vary depending on type of each,
for example a castellated beam will be about 30% deaper than a solid web beam,
A hoolowcore floor is about 50% thicker than a wideslab floor etc
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Re: Rules of thumb

Postby Fionn » Sat May 12, 2007 11:58 am

Maybe you should have attended your lectures?
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Re: Rules of thumb

Postby steve » Sat May 12, 2007 4:22 pm

Fionn wrote:Maybe you should have attended your lectures?


I admire your candor :rolleyes:

Bren88 wrote:surely if your doing an exam on the subject it must be covered in the subject lectures,
Beam, cantilever, slab and truss will al vary depending on type of each,
for example a castellated beam will be about 30% deaper than a solid web beam,
A hoolowcore floor is about 50% thicker than a wideslab floor etc



No, I am not a student, so I didnt have lectures to attend.

But your right it does vary, ok its relatively easy to calculate mathematically the span/depth ratio of a member, but there are set of rules of thumb to estimate the values of each member. Which i dont know. :o Maybe I have posted in the wrong forum.

But thanks for your reply :)
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Re: Rules of thumb

Postby Bren88 » Sun May 13, 2007 3:39 pm

If your not a student, why are you sitting an arch. tech exam?

There are span/depth ratios, but as i said, there isn't a ratio simply for a beam, it varies depending on the beam type, tapered has one ratio, castellated has another, haunched another, solid web another,
i had a list of these last year for a project, but i dont know where there are now, but they vary so much.
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Re: Rules of thumb

Postby steve » Sun May 13, 2007 5:12 pm

Bren88 wrote:If your not a student, why are you sitting an arch. tech exam?

There are span/depth ratios, but as i said, there isn't a ratio simply for a beam, it varies depending on the beam type, tapered has one ratio, castellated has another, haunched another, solid web another,
i had a list of these last year for a project, but i dont know where there are now, but they vary so much.


Exactly, i understand completely what your saying, hence why Im having difficulity in answering the question. As to why Im sitting the exam, I did the course many years ago, but decided at the time that the profession was'nt for me and went to further my carreer doing something else. But recently, in the last year and half, I said I would go back and do my finals. Ive learnt to appreciate architecture. And yes Im doing this on my own merit, :) Its the only question that Im having difficulty with and would hate to go into an exam without knowing the answer.

I can only assume for a steel beam the ratio would be 1/20, and simply supported truss would maybe be 1/15, or even space deck would be 1/15. but thats just an estimation on my part. :)
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Re: Rules of thumb

Postby Bren88 » Sun May 13, 2007 7:20 pm

Thats roughly what there were from memory, but it varies alot. Some are 1/12, but can't remember which.
If its a roof or floor beam also makes a huge difference.
For example I just done a calculation for a 9m beam, domestic oading and it was 600mm deep, thats 1/15
Where are you sitting the exams? Waterford or Carlow?
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Re: Rules of thumb

Postby steve » Sun May 13, 2007 9:50 pm

Bren88 wrote:Thats roughly what there were from memory, but it varies alot. Some are 1/12, but can't remember which.
If its a roof or floor beam also makes a huge difference.
For example I just done a calculation for a 9m beam, domestic oading and it was 600mm deep, thats 1/15
Where are you sitting the exams? Waterford or Carlow?



Ya, usually for a roof member you would add 5, as the beam is lighter......
I've done sum research, and each site and engineering handbook has a different value, so here is an approximate. :) Depth = Span/x

A lightly Loaded beam x = 15
A heavily loaded beam x = 10

A slab = 20

Catilever fixed on one end only x = 3

A simply supported truss x = 15

A Portal frame x = 12

A continuos supported space frame x = 20
Spanning one way x = 12
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Re: Rules of thumb

Postby Bren88 » Sun May 13, 2007 10:15 pm

Cantilever looks a little low, possible doesn't include cantilevers where a beam continues past a support as a cantilever.
Its kinda strange you asked this question, as im right in the middle of my structures exam too, nice to get it out of the way first
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Re: Rules of thumb

Postby steve » Mon May 14, 2007 4:21 pm

Bren88 wrote:Cantilever looks a little low, possible doesn't include cantilevers where a beam continues past a support as a cantilever.
Its kinda strange you asked this question, as im right in the middle of my structures exam too, nice to get it out of the way first


Definately nice to get it out of the way, finally did today :)

the question wasn't even on the paper!!!!! oh well


Next question, anyone Hiring? lol
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Re: Rules of thumb

Postby Bren88 » Wed May 16, 2007 6:15 pm

Where you in DIT? The structure was today there
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