Shielding factor in Wind (AS1170) 2

[astonchamber]

In E2.3 Multiple open frames.

Cfig = Cfig,1 + SUM Ksh Cfig,1


Example
I am analysing the structure via Spacegass. I've got a 6 level of 6 columns steel structure (See diagram 1 below). Wanted to apply wind loading on to the model.

The wind is travelling North direction and will have pressure acting on the South Face of the structure. But the North beams and columns will be/not shielded by the South Beams

Assume the beams running EastWest is 5m per span
And the beams running NorthSouth is 7m per span
Height of each level is 4m.

My question now is:-

1.How to calculate Uniform Distributed Load on my beams and columns?

1a. How to calculate lamda (Frame Spacing ratio) for Table E2?

North
^
^
^
^

Plan view
*------*------*
| | | 7m
*------*------*
<-5m-><-5m->

Front view
|----|----|
| | |
|----|----|
| | |
|----|----|
| | |
|----|----|
| | |
|----|----|
| | |
|----|----|
| | |

Diagram 1
=========

Thanks heaps!
Aston

 

[sdz]

As I interpret it lamda=(spacing along wind)/(spacing cross wind). In your case lamda=7/5=1.4

For a steel frame your solidity will probably be small and hence shielding Ksh~1.0. Also consider effect of wind at an angle. It might be best to ignore shielding for columns. Beams could be a different matter.

You also need to consider wind load on installed plant, and possibly future cladding.

 

[dbuzz]

Isn't the spacing ratio, [&lambda;], equal to:
[ul]
[li]0.70 for northerly and southerly winds, i.e. 7m (frame spacing) [&divide;] 10m (projected width of building normal to the wind)[/li]
[li]0.71 for easterly and westerly winds, i.e. 5m (frame spacing) [&divide;] 7m (projected width of building normal to the wind)[/li].
[/ul]

You'll find that most open, steel-framed, industrial buildings have a solidy of around 0.8, but adopting 1.0 is not adversly conservative -- you'll probably end up with the same sheiding factor, K[sub]sh[/sub], anyway.

The UDLs on your members are calculated using the drag coefficients in AS 1170.2 Section E3, with the following allowances for shielding:
[ul]
[li]windward frame, no shielding[/li]
[li]second frame, shielding effect = Ksh[/li]
[li]third frame, shielding effect = K[sub]sh[/sub][sup]2[/sup][/li]
[li]fourth frame, shielding effect = K[sub]sh[/sub][sup]3[/sup][/li]
[li]etc.[/li]
[/ul]

I agree with sdz that you musn't ignore the wind loading on any installed plant, bins, hoppers, etc.

 

[astonchamber]

Thanks sdz and dbuzz for such detailed answer. Been very useful.

Seems like there's two different method of calculating lamda. My intepretation is the same as dbuzz.. But would like to hear from others as well.

Good point made by dbuzz regarding future cladding on to structure.

Aston