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Condition Assessment of GFRP Composite Wrapped Timber Railroad Ties and Timber Bridge Piles Using Infrared Thermography

A large number of timber railroad bridges in the eastern United States are over 50 to 100 years old. In many cases, these bridges are part of critical supply routes for rural towns. The support structure (timber piles) for many of these bridges have developed significant areas of decay due to flooding in the underlying rivers or creeks. Due to the rising cost of bridge replacements, a more cost-effective approach is to wrap the timber piles and pile caps with glass fiber reinforced polymer (GFRP) composite fabrics. Such wrapping can greatly improve the strength and ductility of the members and prolong the service life of these timber bridges. In addition, old timber railroad ties can be encased in GFRP to form a strong and durable composite tie with wooden core. This procedure can lead to recycling of millions of deteriorated railroad ties by putting them back in service. Though composite wrapping or encasing offers many advantages, subsurface defects such as debonds and voids may be introduced during the initial rehabilitation or in-service stage, which can affect the structural integrity and durability of the rehabilitated structure. Hence proper quality control must be ensured during the initial rehabilitation process. In addition, timely detection and repair of the subsurface defects is needed during service in order to achieve best results. This paper presents infrared thermography case studies from several rehabilitated timber railroad bridges which are currently in service. The paper also includes infrared thermography studies in the laboratory and field setting for GFRP encased timber railroad ties. Infrared thermography has been found to be very effective in detecting debonds and voids between the GFRP wraps and the underlying timber member. The infrared thermography data demonstrates the usefulness of this nondestructive testing technique for quality control during the rehabilitation stage and for periodic in-service monitoring of rehabilitated timber railroad bridge components.

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