Action Combination Factor
Action Combination Factor
(OP)
Hi everyone,
I have some questions in regards to the rules stated in the AS/NZS 1170.2 under Section 5 on the Action Combination Factors (Kc). The standard states that when the building has
2 effective surfaces: Kc = 0.9
3 or more effective surfaces: Kc = 0.8

However, I am a little bit confused on what constitutes as an effective surface. For the internal surface, I understood that it is considered effective if the |Cpi| > 0.2. But I am not sure about the Cpe. Can someone explain this to me? I have read several handbooks on the AS/NZS 1170.2 but still fail to understand this part. Thank you in advance for your help. I will appreciate it very much.
I have some questions in regards to the rules stated in the AS/NZS 1170.2 under Section 5 on the Action Combination Factors (Kc). The standard states that when the building has
2 effective surfaces: Kc = 0.9
3 or more effective surfaces: Kc = 0.8

However, I am a little bit confused on what constitutes as an effective surface. For the internal surface, I understood that it is considered effective if the |Cpi| > 0.2. But I am not sure about the Cpe. Can someone explain this to me? I have read several handbooks on the AS/NZS 1170.2 but still fail to understand this part. Thank you in advance for your help. I will appreciate it very much.





RE: Action Combination Factor
If looking at wind on a smaller element like a purlin for example, external pressure counts as one effective surface, internal as another if Cp,i is greater than 0.2. If only one surface then Kc =1 anyway so no effect.
If looking at an entire structure under wind then it's broken down into wind on roof being one effective surface, walls being another etc (as per the diagrams.
It's useful to understand the purpose of the factor, it's meant to represent the fact that the maximum wind pressures internally and externally over the full structure may not occur concurrently (due to the variations in pressure due to fluctuations in wind speeds), but on a local (smaller) element like an isolated beam, it's more likely that the wind pressures could be at their maximums.
RE: Action Combination Factor
Thank you for your reply. So, does that mean it the diagram has nothing to do with the location of the openings? For example design case 1 applies if the location of the opening is on the windward and leeward wall?
RE: Action Combination Factor
RE: Action Combination Factor
RE: Action Combination Factor
I apologize for the late reply and thank you so much for your explanation.