AS 1170 Combinations
AS 1170 Combinations
(OP)
I'm new to Australian codes. AS 1170.0-02 clause 4.2.2 (Strength Combinations) gives two similar combinations;
(b) Ed = [1.2G, 1.5Q]
(c) Ed = [1.2G, 1.5ΨlQ]
The second combination includes the long-term factor which is less than or equal to one. When would combination (c) ever govern over (b)?
Thanks for your help.
(b) Ed = [1.2G, 1.5Q]
(c) Ed = [1.2G, 1.5ΨlQ]
The second combination includes the long-term factor which is less than or equal to one. When would combination (c) ever govern over (b)?
Thanks for your help.





RE: AS 1170 Combinations
Doug Jenkins
Interactive Design Services
http://newtonexcelbach.wordpress.com/
RE: AS 1170 Combinations
I'm not following you. How is the ultimate (strength) capacity time dependent?
I understand that the imposed actions in (c) are long-term (i.e. sustained) loads. It seems that the imposed actions in (b) cover any load duration, or should they only be short-term (intermittent) loads? Are (b) and (c) meant to be used together?
Perhaps a quick example would illustrate the difference. Say we're designing a beam that supports a lab. Take G to be say 300 kNm at midspan, while the long-term live load (benches, equipment, etc) is 150 kNm, and the short-term live load (people, materials, etc.) is 200 kNm. Assuming distributed loads I take the long-term factor to be 0.6.
(b) Ed = 1.2(300) + 1.5(150 + 200)= 885 kNm - my interpretation?
(c) Ed = 1.2(300) + 1.5(0.6)(150) = 495 kNm
If (b) includes the long-term live load as well as other live loads then it should always govern.
Sorry if I'm missing the basic philosophy but my experience is North American.
RE: AS 1170 Combinations
Hence the ultimate limit state capacity is time dependent depending on the loading type.
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RE: AS 1170 Combinations
RE: AS 1170 Combinations
RE: AS 1170 Combinations
For timber the strength for loads that include transient loads is greater than for permanent/long term loads only.
Both combinations only need to be checked for materials with time dependant strength such as timber.
RE: AS 1170 Combinations
That answers it. I'm working with steel and concrete and didn't see the rationale.