Construction requirements: Requirements telescopic device in parallel, perpendicular to the axis of the bridge in both directions, can freely scalable, secure and reliable vehicle should be smooth, no sudden jump and noise; to be able to prevent the infiltration of rainwater and mud blocking junk; installation, inspection, maintenance, elimination of dirt to be simple and convenient. Set expansion joints, bridge deck railing and should be disconnected. Type 3 telescopic device: 1) galvanized sheet steel telescopic device. Fabricated in a small span girders bridge, when the deformation of the beam within the 20-40mm is often chosen. 2) steel extension telescopic device: its structure is more complex, and only in areas or large temperature difference on a larger span of the bridge was adopted. Steel telescopic device is also appropriate for use on the bridge. 3) Rubber telescopic device. It is a rubber band as a cross stitch materials. This telescopic device structure is simple, easy to use and good effect. A large amount of deformation in large-span bridge, you can use a combination of rubber and steel telescopic device.