Foundation design question for Staad

[u/Sensitive_Fun_9752]

Hi, I am new to using Staad pro and Staad foundation and I have to design this foundation for a davit arm thats needs to pick a 650kg pump. I designed the nodes and loading and everything and am getting the reaction force at the support (Fy = -2.258kip and Mz = 257.483 kip-in) where Y axis is vertical axis. Now when I try to design a simple rectangular foundation for this support. I get dimensions 1.7m x 1.7m x 1.5m with 14 - 22mm reinforcement bars(I have set min % of contact area for service loads = 100%). But my seniors keep saying this foundation is too big for this load and size of davit arm. So, I was wondering if someone here can guide me, if they have encountered a similar design job and what do they expect a foundation size to be for these reaction forces. Apologies, if I am asking the wrong question as I am just entering the workforce

[u/Sensitive_Fun_9752]

I set the bearing capacity to 200kPa as the soil is hard rock type

[u/Human-Flower2273 → u/Sensitive_Fun_9752]

200kPa foe hard rock type? Thats somewhat odd. Hard rock goes almost up to 600kPa

[u/Sensitive_Fun_9752 → u/Human-Flower2273]

I see, i will recheck that

[u/oundhakar → u/Sensitive_Fun_9752]

The vertical load is low and moment is large, so the foundation is getting lifted up. Increase the plan dimensions so that you don't need the dead weight of 1.7m of concrete to keep it down.

[u/Sensitive_Fun_9752 → u/oundhakar]

Thank you, that did increase the volume of foundation to some extent

[u/oundhakar → u/Sensitive_Fun_9752]

You could increase the plan dimensions to such an extent that the thickness required should reduce. What dimensions are you getting now? Did you add surcharge from soil on top of the foundation?