×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*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.

# AS1170.2 Combination Factor for Roof

## AS1170.2 Combination Factor for Roof

(OP)
5.4.3 Action combination factor (Kc)
Where wind pressures acting on a combination of surfaces of an enclosed building...
A surface shall be ..., a roof (the upwind and downwind roof shall be treated together as a single surface),...

First Kc only applies to enclosed buildings (roof and full perimeter walls (nominally sealed) from floor to roof level.) which excludes pitched free roofs.

From this clause I would say that rafters on one side of the roof would not have Kc applied, but that a roof truss would.
From this it would appear that if you cut the building at the ridge line to get a monoslope roof then Kc would not apply to that either, even though we now have the full roof. The labelling in Figure 5.2 would seem to support this interpretation.

What about a roof pitch of less than 10 degrees, where the ridge has no effect, and you don't have upwind and downwind slopes? Should Kc be applied? Again it seems to me that it should not.

### RE: AS1170.2 Combination Factor for Roof

Depend on whether you have internal pressure above 0.2, but assuming less than 0.2, I would say Kc = 1.00 for all the cases including a truss Table 5.5 (e) supports my interpretation.

http://www.nceng.com.au/
"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

### RE: AS1170.2 Combination Factor for Roof

(OP)
@rowingengineer
Table 5.5(f) shows Kc,e=Kc,i=0.9 for 2 effective surfaces, Roof pressures in combination with internal pressures.

### RE: AS1170.2 Combination Factor for Roof

Within an internal pressure coefficient of greater than +0.2, if the internal pressure coeff is less than 0.2 refer to (e) Hence we need to know if you talking about with or without internal pressure coefficients greater than +0.2.

Page 35 1'st paragraph last sentence explains this as to what can be considered an effective surface.

http://www.nceng.com.au/
"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

#### 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.

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:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!