Correlation between Ambient Air Temperature and Effective Bridge Temperature Based on Long-Term Field Monitoring: A Case Study of a Concrete Girder Bridge in South Africa

This study investigates the long-term thermal behavior of an RC twin spine-beam bridge, the Van Zylspruit Bridge, located in central South Africa. This research utilizes 9 years of field monitoring data, including over 11.5 million data points from 41 thermistors as well as local meteorological information, to establish appropriate design correlations between the environment and the bridge’s thermal response. This study found that the temperature specifications for both ambient air temperature (AAT) and effective bridge temperature (EBT) in the South African Bridge Code, TMH 7, were overly conservative for this specific bridge and location. For instance, the design 50-year return period minimum and maximum AAT corresponded to actual return periods of 3,675 and 595 years, respectively. Similarly, the design EBT limits showed significantly longer actual return periods. Ultimately, this study underscores the critical importance of using appropriate thermal material properties alongside locally relevant environmental data for thermal design of bridges and proposes an adapted method for determining design effective bridge temperatures based on local meteorological data.