From the current part 23 regs...
§ 23.473 Ground load conditions and assumptions.
(a) The ground load requirements of this subpart must be complied with at the design maximum weight ......
(d) The selected limit vertical inertia load factor at the center of gravity of the airplane for the ground load conditions prescribed in this subpart may not be less than that which would be obtained when landing with a descent velocity (V), in feet per second, equal to 4.4 (W/S) 1/4, except that this velocity need not be more than 10 feet per second and may not be less than seven feet per second.
Looks like the worst case requirement is a 10fps (=600fpm) landing; the equivalent part 25 text is somewhat different, but still ends up calling for 10fps at MLW.