Foundation stability combinations

[SeanLee3]

Dear engineers,

i am designing a foundation for a telecom pylon.
the major effect is the wind effect.
the system is similar to a big billbord 15m height subjected to wind effect.
The foundation is designed to withstand overturning due to the wind.
can anyone give me the right load combinaison to use to check the stability.
Is 0.9G +1.6Wind valid (ACI)?

Regards

 

[SteelPE]

All load combinations should be checked for stability, but usually you can narrow them down to one or two different combinations that will control.

I usually carry out all of my stability checks at service level not strength level. However, with the new wind procedures the code writers may soon get their wish in forcing me to get everything in strength level.

 

[SeanLee3]

Thanks SteelIPE
i appreciate ur help. i checked lots of calculations and the stability (Stabilising Moment over overturning momnet) is took on ultimate combinaisons
i used to use G+W
1.35G +1.5 W
G +1.5 W
but i found a calculus made on G+1.75W , i thought it is too much but i found in ACI someyhing similar 0.9G+1.6W .
So i am lost if i use it of not knowing that my foundation size will varry alot depending on this combo.

Mike thanks for your time ...

 

[SteelPE]

Well, you need to follow what the code tells you to do. In my jurisdiction I need to follow the IBC. The load combinations in the IBC overrule the combinations in ACI/AISC. I have always felt that the combinations located in ACI/AISC are provided just in case you have no other code to follow. In any case the stability of the foundation needs to have a factor of safety. This is built already built into the load combinations provided to me in the IBC.

I have never run an analysis of comparing a strength level stability calculation to a service level calculation.... but you should at least end up in the same ballpark.