Strengthening of a 19th-century roadway metallic bridge using nonprestressed bonded and prestressed unbonded CFRP plates

This paper summarizes the strengthening of a historically significant 122-year-old roadway metallic bridge using nonprestressed bonded carbon fiber reinforced polymer (CFRP) plates. Prior to the bridge strengthening, sets of laboratory tests were conducted to characterize the mechanical properties, glass transition temperature, and CFRP-to-steel bond strength of two different epoxy adhesives (linear and nonlinear) commonly used for structural retrofitting. Furthermore, the field application complexity, as well as the short- and long-term efficiency of the developed nonprestressed bonded system, was compared with the existing flat prestressed unbonded retrofit (FPUR) system. Short-term measurements, including sets of truck-loading tests performed before and after strengthening, demonstrated that the tensile stresses were reduced by approximately 15% and 44% in the bridge cross-girders after strengthening by the proposed nonprestressed bonded and FPUR systems, respectively. The long-term measurement results, obtained from a wireless sensor network (WSN) system installed on the bridge, revealed that because of the mismatch of the steel-CFRP thermal expansion coefficient, diurnal temperature changes can cause significant thermal-induced stress cycles in the nonprestressed bonded CFRP plate. These diurnal cyclic stresses must be considered in the design of bonded CFRP strengthening solutions.