UC San Diego

There is growing use of FRP composite materials in the civil infrastructure for rehabilitation of deficient bridge components including deck slabs and girders. However assessment of the effectiveness of rehabilitation over time and monitoring the progression of damage or change in load paths at systems level, caused by FRP strengthening of the components, has not been undertaken to date. Investigation was first carried out at "component level" on both unstrengthened and field-rehabilitated slab specimens cut out from a major highway bridge. The slabs were tested to failure and the progression of damage was characterized through instrumentation and NDE. The test data on the failure modes and capacity loads were compared to the available analytical models and design guidelines. The test capacity was also correlated to the bridge deck capacity based on local-global modeling. Research at the "systems level" was then undertaken, in which a three- girder two-span bridge deck system was tested to simulate behavior under field loading in which the deck slabs are found to be susceptible to punching shear type failures and the longitudinal girders are usually found to be deficient in terms of shear demand. The objective of the study was to evaluate damage progression in the FRP composite strengthened deck slabs and the longitudinal girders under simulated truck load and to study the changes in the overall response of structure at systems level caused by strengthening of individual components that might cause other components to reach their critical limit states under the higher load demands which can be resisted by the strengthened components. NDE techniques, including IR thermography and forced vibration based dynamic modal tests, were evaluated as means to quantify the damage localization and progression under simulated field loading as well as to quantitatively monitor, at systems level, changes in the response of the components caused by subsequent modifications of the structure through sequential FRP strengthening. The test data on the failure modes, capacity loads and specimen behavior were compared to both analytical and numerical models. Based on the limitations of the available design guideline for FRP strengthening, a modified design methodology was proposed for FRP strengthening of slab-girder systems