Thermal Effects on Concrete Bridges in a Changing Climate

Abstract

The research presented herein aims to: 1) Investigate the suitability of AASHTO Bridge Design Specifications in quantifying the design thermal gradients that account for cold wave events, 2) Study the effect of different climate parameters on thermal gradients to help improve current guidelines and ensure that thermal gradients are derived based on the actual bridge location, 3) Quantify the effect of freezing temperature on the coefficient of thermal expansion (CTE) of concrete, 4) Analyze the structural response of a bridge structure to cold wave events, while considering the effect of temperature on the magnitude and sign of the CTE of concrete, and 5) Investigate the effect of climate change on thermal load.

The objectives of this work were achieved mainly using numerical finite element 3D models. Furthermore, the relationship between sub-freezing temperature and thermal strain was studied through experimental testing of concrete cylinders. A weather generator was used to simulate future climate conditions to study the impact of climate change on thermal loads.

The findings indicated that current guidelines fail to capture the true thermal load distribution within a bridge superstructure, which leads to an underestimation of the resulting structural implications, particularly the tensile stresses at the bottom of the cross section. It was also determined that a correlation exists between the direct normal irradiance at a specific location and the resulting thermal differential in a bridge. In addition, the effects of subfreezing temperature on the CTE of concrete were found to be significant and to strongly impact the structural behavior of bridges under cold wave events. For instance, a significant increase in tensile stress in both transverse and vertical direction was predicted during a high intensity cold wave event, an issue which can cause concrete cracking. Furthermore, a methodology to model future hourly climate data was developed, through which it was determined that climate change will have considerable effects on thermal loads on bridges in the future. For example, it was determined that climate change can cause an increase of about 5℃ and 6℃ in the absolute maximum positive thermal differential in bridges located in Toronto and Whitehorse respectively.