Abstract: A jack-up platform apparatus operable for effecting relative vertical motion between a leg chord of a platform and a deck of the platform.The jack-up apparatus includes at least one generally rectangular reaction member operable to be connected at one end thereof to the platform deck in a posture contiguous to but spaced from a leg chord of the platform. An abutment member is connected to the other end of the reaction member and first and second leg chord engaging members are mounted for selective translation along the reaction member between the abutment member and the platform deck. A jack asembly is mounted between the first and second leg engaging members for translating the members along the reaction member wherein selective actuation of the first and second leg engaging members and the jack assembly will function to effect relative vertical motion between the platform leg chord and the platform deck while the reaction member reacts bending moments across the width thereof.