Shape of a structure to reduce wind loads on AS1170.2
Shape of a structure to reduce wind loads on AS1170.2
(OP)
Hi all
I'm analysing two tall structure, one is rectangular and one is circular. The drag coeffiecient for a rectangular structure is 2.2, for a circular structure is 1.2.
Does the 1170.2 allow you to reduce the wind loads based on the shape of the structure? Other international codes allow to reduce by 20-30% the action on a circular structure compare to a square structure.
I don't think that I am allow to do it with AS1170.2
Look forward to hear some comments
Cheers
I'm analysing two tall structure, one is rectangular and one is circular. The drag coeffiecient for a rectangular structure is 2.2, for a circular structure is 1.2.
Does the 1170.2 allow you to reduce the wind loads based on the shape of the structure? Other international codes allow to reduce by 20-30% the action on a circular structure compare to a square structure.
I don't think that I am allow to do it with AS1170.2
Look forward to hear some comments
Cheers





RE: Shape of a structure to reduce wind loads on AS1170.2
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RE: Shape of a structure to reduce wind loads on AS1170.2
I don't have any information on the transition of a square edge rectangle at 2.2 to a rectangular building at (0.7 + 0.5)x0.9 (from Table 5.2 and a combination factor of 0.9)
RE: Shape of a structure to reduce wind loads on AS1170.2
To calculate the effect of the wind on building you should use chapter 5 and use the following formulas:
Cfigi = Cpi Kci
Cfige = Cpe Ka Kce Kl Kp
None of the two formulas take into account the shape of the structure
My understanding is that AS1170.2 doesn’t allow a reduction of wind force if my structure is more aerodynamic compare to a box structure.
Any suggestion on codes that allow the shape on the wind force calculation?
Thoughts?
RE: Shape of a structure to reduce wind loads on AS1170.2
One of the appendices in AS1170 has calculations for cross-wind excitation for flexible structures which is more used for side to side sway and accelerations.
RE: Shape of a structure to reduce wind loads on AS1170.2
I know all of this thanks. My point is different. Right at the start of the project during pure feasibility stage when wind tunnel is not in the equation yet, the engineer should be able to check the building for strength and service with the code and should be able to calculate reduce wind loads based on code.
American code allow for reduction based on shape.
RE: Shape of a structure to reduce wind loads on AS1170.2
I have never done it myself and reducing the wind actions on the basis of a Cfig=1.2 compared to 2.2 is a big drop in force but this might be what a wind test reports.
If your a member of Engineers Australia there should be a webcast called "Structural Technical Presentation - Design Challenges of the Soleil Tower", the engineer quickly talks about the reduction in wind forces with chamfered corners but doesn't go too far into the topic.
RE: Shape of a structure to reduce wind loads on AS1170.2
Would love to know how different it is opposed to code based pressures.
Link
RE: Shape of a structure to reduce wind loads on AS1170.2
cfd is a way to do it but it's another black box software and you must be good at using it before believing the results.
The real point would be to try to use a code which allow you to reduce loads based on shape of structures
RE: Shape of a structure to reduce wind loads on AS1170.2
Australian study provided here
RE: Shape of a structure to reduce wind loads on AS1170.2
RE: Shape of a structure to reduce wind loads on AS1170.2
RE: Shape of a structure to reduce wind loads on AS1170.2
However, the originally quoted 1.2/2.2 will never be appropriate for buildings; they are only used structural section sized elements.
RE: Shape of a structure to reduce wind loads on AS1170.2
All i meant was that there is a different on bending moment between a similar size square structure and circular structure. The problem is that the code doesn't allow a reduction as such until you run wind tunnel tests you will not know the reduction so the schematic design became more conservative (which is frustrating).
Using CFD is ok but you should model the building around it to have true response. In Robot this is difficult to do.