×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

AS/NZS 1170.2 : Action Combination Factor (Kc)

AS/NZS 1170.2 : Action Combination Factor (Kc)

AS/NZS 1170.2 : Action Combination Factor (Kc)

(OP)
Hi everyone,

I am a bit confused in trying to determine the Kc of a structure using the AS/NZS 1170.2. It states in Section 5 of the standards that internal surfaces with |Cpi| < 0.2 is determined as an ineffective surface. However, in the table for the design cases, it asked how many surfaces are effective. If the Cpi of a single storey building is -0.1, does that mean there is no Kc? Can anyone give advice on how to determine the Kc correctly? Thank you in advance. I appreciate your help.

RE: AS/NZS 1170.2 : Action Combination Factor (Kc)

For starters I usually adopt Cpi = +0.2;-0.3 for a typical enclosed building. Thus Kci is always used. Net pressure coefficient on a surface is given by Cpn=Kci(Cpi)-Kce(Cpe). Remember to apply appropriate signs to pressures/suctions (+ve towards surface and -ve away from surface) and that the product of KaKc can't be greater than 0.8.
Example - take roof uplift on Rafter, whereby internal pressure and external suction combine
Cpe=-0.9 suction away from surface
Cpi=+0.2 pressure towards internal surfaces
Therefore Cpn=0.9(0.2)-0.9(-0.9)=0.9(1.1)=-1.0 (approx.) -- The negative indicates the net resultant is in the direction of the roof suction i.e. Upwards in this case.

When Cpi is less than 0.2, then yes Kce=1.0 and the internal pressure/suction is not included in the net resultant.
Generally
1 effective Surface causing structural response - 1.0 no reduction.
2 Effective surfaces causing structural response - 0.9 reduction
3 effective surfaces causing structural response - 0.8 reduction

Toby

RE: AS/NZS 1170.2 : Action Combination Factor (Kc)

(OP)
Hi Toby,

Thank you very much for your reply. It is very helpful and I could understand it now.

RE: AS/NZS 1170.2 : Action Combination Factor (Kc)

(OP)
Dear Toby,

I apologize for asking you again. I just wanted to know what constitute as surface as effective? For the internal surface I know that it is effective if |Cpi|> 0.2. But what about the other surfaces? Is it based on the situation and how the wind load acts on the building as shown in the diagrams? Thank you in advance for your help.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close