how compute the short and long term creep by aci318

[Ltdog]

I am designing a high-rise building and will provide information to the curtain wall design. One of the information is shore term creep (in the first three months) and another is long term creep.

The first question is:
According to the ACI318-08 clause 9.5.2.5, the deflection of the short term creep and long term creep is ?=???iw
Do you think the first question is right?

The second question is:
When we compute the immediate deflection of the short term, the load is included only the self-weight.
When we compute the immediate deflection of the long term, the load is included all of the dead-load and live-load.
Do you think the second question is right?

Your quick response is appreciated

 

[ishvaaag]

"shore term creep" = 3 months, well it seems they have provided you with the intent translation. They probably will contract not putting in place vertical members of their curtain wall before 3 months, so they will be happily discounting every creep you dump in the 1st three months. So be conservative and think it creeps at moderate pace, yet realistic.

On the second question, I do not think the full live load, needs be included for creep. Around 15% of full live load will be a far more representative loads for residential buildings. See Gaylord Gaylord Stallmeyer "Steel Structures" pages 7 and 8 for typical actual live loads on buildings.

Don't be overly conservaive for it will produce too wide visual recesses in the cladding, except that is acceptable in the intent. It may turn necessary, anyway, depending the case.

PCA had I think rundown tabulation of shortening publication on this kind of thing. In the inaccessible cabinet, sorry.

 

[asixth]

Creep is the increase in compression strain under sustained loading. So the additional deflections caused from creep under the sustained loads is the deflection multiplier multiplied by the deflections caused by those sustained loads. So your first question is correct, the deflection for short-term and long-term is:

?shortterm=?instant+?incremental

where

?incremental=??*?sustained

where ?? is your deflection multiplier and ?sustained is the deflection caused from your sustained loads.

The magnitude of ?? will vary from 3 months to long-term because creep is a long-term effect. The sustained loads during the first three months may also vary in the long-term depending on construction so that is something you also need to account for.