Differential settlement, thermal load in load combination

[ttoonnyy]

Hi Guys

I got this concern while doing the load combinations. Would like to get some hints.
The background is process structure using AS 4100, 1170, 3600...

In a lot of structural design criterias, there is always word saying "apply diffrential settlement load, and thermal load when required or ask lead to confirm".

For thermal load, I can avoid it by adding the expansion connections when design over 20 m, AISC mentnioend 60m though. Won't discuss further about this here.
However, when it's not possible to aviod, (1) should the thermal load be combined in both ULS and WS condition? 1.2G+1.5Q+T & G+Q+T or 1.2G+0.6Q+T & G+0.6Q+T or just 1.2G+T & G+T;
AS1170 doesn't specify Q and T appears at same time. Cl 4.2.4 specify fire thermal actions like G+thermal +Q. Personally i'll just put in 1.2G+1.5Q+T for strength check.

Same as differential settlement load.

(2) Should differential settlement only combines in WS load cases because that's the realistic case?
If the differential settlement occurs, the ULS load combination will also suffer from it. Therefore, the load combo should be both 1.2G+1.5Q+DS, G+Q+DS ? I just put 1.2G+1.5Q+DS for strength check.

(3) Should the DS load combine with T as well? 1.2G+1.5Q+T+DS, G+Q+T+DS

When there is gantry load "C", (4) should gantry load be combined with DS and T as well? 1.2G+1.5Q+1.5C+T+DS, G+Q+C+T+DS
I personally won't combine DS with C in actural project, just discuss here.

Can anyone please share some design experience on this? Appreciated for the help.
Cheers,Tony

 

[canwesteng]

I'd recommend always detailing around thermal load, by having one end be a tower and the other a bent. Likewise allow some ability for the rack to rotate to accommodate the differential settlement. However, friction from thermal movement of the pipes can't be avoided - I usually take it as live load for simplicity.