Behavior of concrete box-girder bridges exposed to environmental thermal loads: Experimental and finite element study

Most of the worldwide available bridge design codes specify provisions to control the stresses that arise in bridge superstructures due to the effect of the diurnal and the seasonal environmental changes. Recently, most of the design codes provide ranges for the maximum change in the bridge mean temperature and models for temperature gradients. This research aims to investigate the effects of the environmental thermal loads on concrete bridges and to introduce special design recommendations for concrete bridges in Turkey. The research composed mainly of four parts. The first is the experimental work, in which a full-scale concrete box-girder bridge segment was constructed and instrumented with concrete temperature, air temperature, solar radiation, and wind speed sensors. In the second part, a heat transfer 3D finite element analysis was conducted to investigate the temperature distributions in concrete box-girders, which was verified using the experimental results and utilized to conduct detailed parametric studies. This finite element model was used in the third part with long-term weather records to introduce design provisions for thermal effects on concrete bridges. Finally, a thermo-mechanical finite element analysis was carried out to study the structural behavior of the concrete bridges under environmental thermal loads. The experimental results showed that the hydration heat has significant effects on temperature distributions during the early age of concrete, and that the temperature differs from one fiber to another along and across the different parts of the superstructure. The recorded maximum vertical and lateral temperature gradients for more than one-year measurements were approximately 20oC and 19oC, respectively. From the experimental records, equations were proposed to estimate the maximum vertical and lateral temperature gradients. Based on parametric studies, ANOVA showed that density and surface emissivity are of negligible effects, while surface absorptivity has much more effect on concrete temperatures and gradients. The experimental, statistical, and numerical studies of this research, in addition to long-term extreme weather data for different Turkish cities were utilized, from which mean temperature and temperature gradient models were proposed and design procedures were suggested for thermal actions in concrete bridges in Turkey.