If the torque in the spindle is T, then the force along the surface of a spindle of radius y is T/y. The separating force is the surface force times the sine of the tooth angle, or T/y sin(theta), where theta is the face angle.
A steeper face angle gives a smaller separating force for a given spindle torque, but also requires greater precision in manufacturing.
For a crank of length L and pedal load of F, the spindle torque T is at most FL, though it may be less if the crank is not horizontal when the load is applied.
The greatest separating force is thus F (L/y) sin(theta).
Suppose the peak pedal load is 200kgf, the crank is 180mm, the spindle is 24mm diameter, and the face angle is 5 degrees. Then the separating force is then 200 (180/12) sin(5) which is about 260kf.
The separating load is thus small compared to the 1600kgf bolt preload needed to resist the bending load. However, it may still cause problems.
The spindle bending load leaves the bolt load essentially unchanged unless the bending load gets so high that it fails the joint. That is, the bolt is tightened to a preload of B, and although the top and bottom loads may change by up to B/2, the bolt load remains at B. However, torsional spindle load causes the bolt load to rise.
The spindle's torsion load rises and falls once per stroke of the left pedal. Thus, the bolt is loaded and unloaded repeatedly. Cyclic loading can cause at least two problems. First, cyclic loading can also cause the bolt to unscrew. When the bolt gets tighter, the threads, which are ramps, tend to creep, pulled by the force. With enough repetitions, the bolt can loosen unless the bolt is sufficiently tight that the bolt friction exceeds the loosening force.
Second, cyclic loading can cause the bolt to fatigue. Even a small added load (much less than the peak torque load) can cause fatigue if the bolt stress is high. Thus, the bolt must be designed to have a low enough stress that the cyclic stress does not cause fatigue.
(Fatigue may seem like a ``high cycle'' issue. Note that at 100 RPM, the bolt goes through one million cycles in about 275 hours of riding, much less than a year for many cyclists and less than a month for some.)