Ladder clamping structure for ladder racks

A ladder rack for work vehicles comprises a pair of side rails held in parallel, spaced relation by a pair of crossbars. Extending between the crossbars is at least one hook bar. The side rails, crossbars and hook bars comprise aluminum extrusions incorporating clamping ridges adapted to be engaged by clamps for rendering the structure rigid. No welding is required. A latch mechanism is affixed to a rearmost crossbar for releasably securing ladders on the rack. It comprises a crank on a rotatable shaft held by brackets affixed to the rear crossbar for rotation about an axis parallel to the crossbars. A rear hook is keyed to the shaft and aligned with a front hook affixed to the hook bar. The front and rear hooks can be made to engage spaced ladder rungs. An air spring connected between the rack frame and the rotatable shaft resists rotation of the rear hook member.