An actuator arrangement for moving a first component relative to a second component, the arrangement comprising: an actuator chamber for receiving a fluid under pressure, a side wall of the chamber being fixed relative to the first component; an actuating element fixed relative to the second component and located inside the chamber for sliding movement along the chamber, relative to the side-wall; and a sealing element which provides a corresponding sliding seal between the actuating element and the sidewall for maintaining an actuating fluid pressure differential across the actuating element thereby to drive the actuating element relative to said side-wall, under said fluid pressure differential, for driving said relative movement of the first and second components; wherein the arrangement further comprises an external side-wall brace connected to the second component for corresponding movement with the actuating element along the outside of the sidewall, the brace being slidably or rollably braced against the outside of the side-wall close to the sealing element thereby to provide respective local reinforcement of the side-wall at or near the sliding seal, in accordance with the position of the actuating element.