In the temperature change, concrete contraction, creep and load and other factors, the bridge beam length will change, so that the beam end displacement, in order to adapt to this displacement and keep the bridge traveling smoothly, it is necessary to set the bridge expansion device. With the rapid development of China's transportation, highways, elevated roads, overpasses, the construction of a large number of highway bridges, the increase in the amount of vehicular traffic, vehicle speed increases, the vehicle's load in the growth of people's comfort on the road and other requirements are more and more demanding, so the requirements of highway bridges, expansion and contraction of the device is also more and more demanding!