Shallow Foundation for a Concrete Column 10

[Bill002]

Hello,
I am designing a shallow concrete foundation for a 2ft x 2ft column. I have a concern because my moment (450 ft*k) is considerably greater than the axial load (70 ft*k). This is creating a large eccentricity at the base (e=450/70 = 6.4ft). To make this work on a shallow foundation I would need the width of the foundation to be e<b/6 so b = 38.5ft. This seems way to excessive for a 2ftx2ft column. Can somebody please tell me if there are any other methods of looking at this foundation?
Thanks!

 

[csd72]

and its even worse than that since the bridge must span over a void and your sliding force acts toward this void.

I suggest you look at the anchorages as hokie has suggested or the whole thing could end up the the river.

 

[Bill002]

There is definitely going to be an underground deadman anchor at either ends of the bridge where the cable will be finally tied off.

But looking at the cable on the saddle situated at the top of the tower there are two different angles, one for the incoming cable (from main span) and outgoing cable (to deadman) this combined with the dynamic movements induces a frictional load on the tower top. As many have said, 25% might be an exaggeration of that load.

 

[OHIOMatt]

Sorry, late to the party, but it seems as if you are designing the foundations for the temporary construction condition, ie drapping and pulling the cables. If this is the case, simply have the towers shored, braced or tied back during this period of time.

 

[hokie66]

If the cable forces must be at different angles to the horizontal, you could incline the towers to suit rather than trying to take the force in bending. I see the frictional components as largely irrelevant, but suspension towers need to be compression only members to be economical. As you have found, introducing bending quickly leads to big numbers.