Hybrid Composite Beam Bridge Superstructure Design Considerations for Thermal Gradient

Abstract

The hybrid composite beam (HCB) is an innovative idea that incorporates traditional construction materials (i.e., steel and concrete) with fiber-reinforced polymer (FRP) composites in an efficient configuration to optimize the beam constituents’ performance. The HCB is comprised of three main subcomponents: a composite shell, a compression reinforcement, and a tension reinforcement. The shell is comprised of a glass-fiber-reinforced polymer (GFRP) box. The compression reinforcement consists of self-consolidating concrete (SCC) that is pumped into a profiled conduit within the shell. The tension reinforcement consists of galvanized-steel tendons anchored at the compression reinforcement ends. The HCB is a promising technology in bridge applications because it has several advantages over the conventional structural members (e.g., a prolonged lifetime and a lighter weight). This new technology was recently used to construct three bridges in Missouri. This research study performs the first investigation and analysis for an in-service HCB bridge superstructure’s behavior subjected to thermal loads and proposes a thermal design methodology. This investigation is crucial because the thermal stresses, if not accounted for during the design, can significantly affect a bridge superstructure’s durability, which this new HCB technology strives to address. Beam elements from the longest-spanning HCB constructed bridge in Missouri were instrumented with various strain gauges and thermocouples. The constituting elements’ temperatures and the corresponding induced strains were recorded over 6 months. The proposed algorithm was used to predict the induced strains. A two-step thermostructural finite-element analysis (FEA) was performed to analyze the HCB’s thermal behavior and further evaluate the proposed algorithm’s performance. The results of this study showed that the proposed algorithm was able to predict, with acceptable accuracy, the thermal stresses and strains in a HCB bridge superstructure. Subsequently, this algorithm is recommended as a useful tool for designing and analyzing HCB bridges that are undergoing environmental thermal effects. The current study also presents recommendations for modifying the thermal gradients recommended by AASHTO for the thermal design of reinforced concrete (RC) superstructures to better suit HCB bridges. Finally, the study proposed techniques for increasing the stiffness of a HCB bridge superstructure, while at the same time minimizing the induced thermal stresses under temperature fluctuations.