The most important thing in designing foundation of tower crane using pile group

Hey there.. what s up?? haha.. it s not a bad day is it? but next several day going to be bad day for me.. haha.. lemme tell you something, u know  that I just a graduated last 4 mounth ago, and now in my work, my boss just asked me to design the foundation of tower crane. Fistly I design it and use raft foundation,, a very big foot plate about 5 x 5 m and 1,5 m of thicknes. I m enough confidence for it,, but u know what? he asked me to change it using pile group.. because it s cheaper than the raft. It reduce your volume of concrete, and so do the main rebar

Then I just design it with the deep foundation formula,, calculating maksimum P for single pile from NSPT test, analizing forces and moment at the pilecap and design the dimension and the rebar. the results is 3 x 3 m and 1,5 of thickes with adding 4 square pile (45 x 45 cm) with 20 m depth.

Then the drafters draw shop drawings of the foundation which I ve designed. It showed the detail between the pile and the pilecap, there should be overlapping where the pile sink into the pile cap for 20 cm of depth. But there is rebars after 7 cm from the surface of the bottom. And I checked in the site, how was they make it. THERE IS NO OVERLAPPING!!! damn suddenly I m scared…!!

So it just the 5 x 60d strand wire of the pile in the concrete block which transfer all the forces from the pile to its cap. damnn,,, they just sucked me! I design it with the assumption that it fixed join between the pile and its cap, so when the tower crane got rolling moment, pilecap will pull the piles so it is keep the balance. But what if there is only 5 x 60d of strand wire which thansfer the pulling force? Do you belive in them? what if it got busted? Or the bounding between the wire and concrete is bad? so when it transfers the pulling force it s slipped?? what can you say if your tower crane collapse??

DAMNN… here I m gonna tell you, that for your safety,, you better design the foundation of tower crane using raft foundation. It is expensive but it s safe if you have enough financial back up. But if you don’t,, there is some things you should more consider when designing using pilegroup.

-          You should calculate the bounding force between the strand wire of the pile and the concrete of it s cap.

-          It s better use longer strand wire embedded in the pilecap, minimum 1 m of length

-          Actually the capacity of the strand is higher than normal rebar, but just check the fy and make sure that it can transfer the pulling force without fail.

-          make sure you calculate the friction force between the soil and the pile, and when it got the maximum rolling moment, the pile can hold the balance of it.

-          and the last,,, damn,, you should told me this before I tell you now!!!

That’s all… safe your life before its collapse!! and comment….