[REQUEST] How to design mat foundation resisting 3 columns for Tower

[miquan]

With telecom tower, there're 2 types: self support and guy mast towers.
The layout of guy mast tower is too small (0.5x0.5m) with dimension of foundation. So approximatively we can consider axial force only.
With self support tower (36m, 45m hight), we can use SAFE for analysis. Foundation is model ed as thick shell, soil is modeled as spring (need some iterations for spring stiffness).
This matter is solved as same manner with pad foundation of building.

[Devil_Red]

Munykong,

Frankly, i think this shall be able to calculate by hands.

As for the 4 legged tower, presumably you have the same (or somewhat similar) axial load. Then it is the 'reverse' flat slab.

As for the the 3 legged tower, it's a combination of the flat slab and the 3 pile caps group.

It's a good practice, and i always advise my juniors, to start with manual calculation before proceed to any programs.

[oanm2000]

Each problem has its focus.
For telecommunications towers, with three or four supports or legs, the most critical load is the traction, not the soil capacity of the land, which is the secondary verification.
In my country, and in coastal areas where wind loads are significant (without going to extremes of hurricanes), it is verified that the structure is sufficiently anchored in the ground, assuming a load in tension or uplift equal to the weight itself structure plus an additional factor. This verification is done for each leg, and then to the slab, considering the maximum resulting on the first analysis and their situation over the slab.
After verifying the stability uplift loads, it performs the analysis of ultimate bearing capacity; probable settlement are verified at the end.
Normally, for purposes of initial analysis, it neglects the weight of the earth over the foundation, for incorporate it into the subsequent analysis. Now, if the slab can not "embedded" in the field, and should be flat with the surrounding land, the weight of the foundation slab must be equal to or greater than the probable maximum tensile load (maximum load plus an uplift factor additionally, it can be seen between 1.10 and 1.30).
It is a common practice (in my Country) that the first calculation and verification is done manually (you determine the weight of the tower, estimates the maximum uplift load, is applied to the foundation, placing the burden on the position of each of the legs, one at one time, and recess is verified on the ground. Subsequent verifications (allowable capacity and settlements) can be done with software. Personally, I do all the calculations by hand, and then verified using software later, to avoid mistakes.

Regards
oanm2000

[fsalmario]

One more pointer, please check also the foundation rotation as this criteria is significant for the alignment of antenna.

[Munykong]

Dear all of you:

Any body have examples of my questions or any books inherent?

Best Regards yours