See Table 8-2: Actions in Combat in the PHB. Under the sub-heading 'Action Type Varies' you'll see that Disarm and Trip (and Grapple, but that isn't relevant to the spiked chain) have a footnote '7' which indicates that 'these attack forms substitute for a melee attack, not an action. As melee attacks, they can be used once in an attack or charge action, one or more times in a full attack action, or even as an attack of opportunity.'likuidice said:silly, slightly off on a tangent question, whirlwind attack allows a melee attack against all opponents within reach. is this just a regular (roll to hit, roll some damage) attack, or can you use the other attack options, such as disarm, trip, etc?
Note that the Sunder action is absent from that sub-heading and does not have footnote 7.