Design wind speed AS/NZS1170.2

[apsix]

Asixth

Elsewhere you wrote;
"The 2002 (limit state) code specifies that a 2000 year wind event is used for ultimate design"

AS/NZS1170.0 refers us to the BCA for probability of exceedance to be used for design.

BCA table B1.2 directs us to use 1:500 for wind for 'normal' buildings.
Is there a reason why you use 1:2000?

 

[rowingengineer]

I was going to query this statement as well, and also this one:

"Creep and shrinkage are permanent actions and their actions should not be reduced when making checks for service. They should be treated as a dead load and load factor of 1 applied when checking service. Regardless of how variable creep and shrinkage may be in nature."

I always use wsQ or wlQ for serviceability combination's. normally ws being about 0.7 and wl about 0.4. Unless the combo service loading is great than 0.5 f'c, I don't use loadings in my creep and shrinkage deflections.

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it

 

[rapt]

rowingengineer,

I do not understand the last sentence. Creep calculations for deflection are done under the permanent load condition.

 

[rowingengineer]

rapt,
i read it now and it don't make sense to me. HaHaha, The deflections part is a not how i meant it to come across.

what i am trying to say is:
AS3600 uses a factor, defined as the basic creep factor, fcc.b, based on the ratio of the ultimate creep strain to the elastic strain for a specimen loaded at 28 days under a constant stress of 0.4f'c. I see no part in As3600 where the creep coefficient is related to applied loading but for the 0.4fc'.

however because the elastic strain is related to the loading then this is where the creep deflection picks up the loading thus gets the deflection.

does this make more or less sense. I'm reading it and it looks like less to me. even thou I'm Aust born and bread i wish my written English was better.

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it

 

[apsix]

born and bred?

brawn on bread?

 

[rowingengineer]

it's lunch time what can i say, I'm kinda hungry.

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it

 

[asixth]

I guess part of engineering is being able to justify and defend your decisions.

Design Wind Speeds:

The 2000yr wind event was off the top of my head what my last design involved. Looking over the design drawings the design was for a 500yr wind event, I made the 2000yr comment with reference to Appendix F of AS1170.0, a building in a non-cyclonic zone with an Importance level 3 and a design life of 100years. Using this table actually gives a return period of 2500years. I agree that the BCA is the controlling document that should be used in design, Appendix F is confusing and it should be removed if it isn't applicable for anything other than temporary loading. Recurrance intervals for temporary structures is something that I have been meaning to write a post for but have never got around to doing it.

Creep and Shrinkage:

What I was referring to and what I thought KBVT was questioning was to only allow for 50% of the creep deformations when checking serviceability. I think it is Section 21 of AS5100.2 which gives a good list of permanent and transient actions and it calls up creep and shrinkage as a permanent action and must be considered with other permanent actions. When calculating the additional deformations from creep I would use 0.4*LL as contributing to the permanent action for the majority of designs.

Wind Speeds and the BCA:

The AS1170.2 Table vs the BCA debate is a good one. You are not taught to much about the BCA at University (at least a BE(Civil) from UQ) and the degree is more aimed towards design principles and standards. So naturally when a graduate comes into the design office they immediately begin searching through the standards when looking for answers such as recurrence intervals.

What approach do others take? Do they design for a 500yr wind event and when do they refer to AS1170.0 Appendix F? I think appendix F should be used when designing for temporary structures and special structures which wouldn't fall in the BCA's description of 'normal building'? I was at a presentation at EngAust Queensland Branch hosted by Prof Wilson on Earthquake design and he also recommended that the BCA be used when determining recurrence intervals for Earthquake design. There should be a video stream of this presentation on the EngAust website for those interested.

 

[hokie66]

There is a statement in Appendix F which states that it does not apply to structures which are subject to the
BCA, so for wind loading we use the BCA provisions. 1:500 for most buildings, 1:1000 for assembly buildings, 1:2000 for post-disaster essential and hazardous facilities.

 

[rowingengineer]

Asixth,
well justified and defend.

I like the BCA v's AS1170.2 point, I think you have a good point here, the SA calls up higher requirements than the BCA for any structures that don't comply with the BCA. But why is this so???? (note table F2 50yr return importance 4, As1170 1:2500, BCA 1:2000, )

second of all for an engineer that has to make a descision regardsing the design life (assuming that it isn't legislative driven), bridges require a design life of 100years, so should an engineer in his right mind design all major structures for 100year?. assuming this is correct should he then use table F2 and design for 1:2500 yr event????

Arguing with an engineer is like wrestling with a pig in mud. After a while you realize that them like it