Concrete Pile Cap Design for Mooring Bollard

My suggestion would be to avoid H-piles at all costs, since they have very low transverse stiffness and the direction of load application is not known beforehand - might be 30, 45 or 60 degrees inclined with respect to principal axis of inertia. Use concreted circular hollow section steel piles, and batter them if the lateral load is too large to be resisted by bending.

A single reference for something like this just won't work. You are likely getting into anchorage loads, possibly cyclic loads, concrete design, and so on. You may want to get a structural engineer involved.

That being said....the CRSI handbook is a favorite for pile cap design.

Just to emphasise, mooring lines can be at a range of angles both vertically and horizontally and most ports put multiple mooring lines on a single bollard. You should consider the most onerous loadings for your piles. A 50 tonne rated mooring line will have a minimum break capacity of 50 tonne, not a maximum.

We did something similar once, not for bollards, but for a horizontal tie force with known directions. One unforseen issue we faced was eccentricity. If the force is at an angle in the horizontal plane, it can theoretically rotate the pile cap. In our case the construction was deep enough to mitigate this with active soil pressure.

Pretty sure there's no reference. Too niche. I've seen two camps. Shear ties and no shear ties. Shear ties weren't used until fairly recently. Don't know if design methods changed or bigger loads made them necessary. 50 tonners have definitely been done without shear ties.

Strut and tie isn't used for these. S&T doesn't handle multiple load cases well or the moment transfer at the pile heads. Just a usual frame analysis and pay attention to anchoring the bollard and piles into the cap.