Main structural (and any other) impact of hard landing
here are the main parts at risk for structural integrity after a hard landing: 

the landing gear itself and the attachment points of the gear to the fuselage and/or wings

the fuselage-to-wing attachment structures

the engine-to-wing (pylon) or engine-to-fuselage attachment structures

the main fuselage structure in the immediate vicinity of the wing attachment points

If the hard landing involves a tail strike, then the integrity of the aft pressure bulkhead is at risk.

Note that the structural integrity risk is not simply one of prompt failure due to an overstress impulse load, but also subsequent premature fatigue failure arising from microcracks caused by the hard landing stresses- especially if that cracking occurs in a location which is inaccessible for inspection.