Proposed Design Method for Thermal Bridge Movements

Bridges expand and contract due to temperature changes. These movements are estimated in design, and expansion joints and bridge bearings are designed to accommodate the movements. Integral construction is another means of adapting to thermal movements. If the design movements are too small, the bridge may be damaged during extreme conditions. If the movements are too large, less economical joint and bearing systems may be selected, and higher long-term maintenance costs will be incurred. An improved thermal movement design procedure is developed and compared to existing AASHTO Specifications and field observations. The recommended design temperatures are developed from more than 60 continuous years of weather data after considering the relationship between bridge temperature and climatic conditions for different bridge types. The recommended temperatures provide a realistic indication of actual bridge performance and eliminate the ambiguity of present design methods. Strategies for defining design movements and design installation temperatures for different joint and bearing systems are also developed. The design recommendations result in significant changes in predicted movement for some bridges, and the recommendations are compared with field measurements of bridge temperatures and movements to verify the proposed limits. The proposed design provisions are presently under consideration by AASHTO Committees for adoption into the AASHTO Specifications.