External Pressure Coefficient (AS/NZS 1170.2)

Question

External Pressure Coefficient (AS/NZS 1170.2)

Xaviera (Structural)

(OP)

8 Oct 17 06:02

Hi everyone,

I just wanted to ask. To get the external pressure coefficient of roofs, for the intermediate values of the ratios and angles, the standard stated that they could be linear interpolated. However, interpolation should only be carried out on values of the same sign. So, does that mean if the number at a is 0.0 and the number at b is -0.2, the number in between a and b should not be interpolated? Can anyone explain to me about this? Thank you in advance for your help. I will appreciate it very much.

apsix (Structural) · Answer 1 · 2017-10-11 00:31:56

Strict interpretation could mean that interpolation shouldn't be done in that case, but I DO use 0.0 to interpolate. This would seem to agree with the logic of the rule.

hokie66 (Structural) · Answer 2 · 2017-10-11 00:50:13

Interpolation midway between 0.0 and -0.2 give -0.1. If you get hung up on the sign, use -0.0.

Xaviera (Structural) · Answer 3 · 2017-10-11 01:44:52

Dear apsix and hokie66,

Thank you very much for the explanation. Just one last question, I was wondering about the linear interpolation for the gable roof when the h/d >= 1.

It states in Note 2 that the values in parentheses are for interpolation purposes. Does that mean that for value 2h to > 3h, the Cpe is derived from the interpolation of these two numbers? Thank you very much for your help.

hokie66 (Structural) · Answer 4 · 2017-10-11 04:55:39

No, the interpolation referred to is between h/d = 0.5 and h/d = 1.0. Since your h/d >=1.0, the two coefficients in the right hand column just define two different loading conditions.

Xaviera (Structural) · Answer 5 · 2017-10-11 06:20:48

Dear hokie66,

Does that mean there is no Cpe when the horizontal distance is from 2h to > 3h when h/d is >= 1.0?

hokie66 (Structural) · Answer 6 · 2017-10-11 06:45:47

When h/d > 1.0, there is no 2h to 3h on the roof.

Xaviera (Structural) · Answer 7 · 2017-10-11 17:37:47

Dear hokie66,

Thank you very much for the explanation. It's very helpful.

hokie66 (Structural) · Answer 8 · 2017-10-12 00:55:21

You are welcome. It is always a steep learning curve to know how to use the Wind Loading code.

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External Pressure Coefficient (AS/NZS 1170.2)