The use of timber–concrete composite (TCC) bridges in the United States dates back to approximately 1924 when the first bridge was constructed. Since then a large number of bridges have been built, of which more than 1,400 remain in service. The oldest bridges still in service are now more than 84 years old and predominately consist of two different TCC systems. The first system is a slab-type system that includes a longitudinal nail-laminated deck composite with a concrete deck top layer. The second system is a stringer system that includes either sawn timber or glulam stringers supporting a concrete deck top layer. The records indicate that most of the TCC highway bridges were constructed during the period of 1930–1960. The study presented in this paper discusses the experience and per-formance of these bridge systems in the US. The analysis is based on a review of the relevant literature and databases complemented with field inspections conducted within various research projects. Along with this review, a historical overview of the codes and guidelines available for the design of TCC bridges in the US is also included. The analysis undertaken showed that TCC bridges are an effective and durable design alternative for highway bridges once they have shown a high performance level, in some situations after more than 80 years in service with a low maintenance level.
Nationwide, bridges are deteriorating at a rate faster than they can be rehabilitated and maintained. This has resulted in a search for new methods to rehabilitate, repair, manage, and construct bridges. As a result, structural health monitoring and smart structure concepts have emerged to help improve bridge management. In the case of timber bridges, however, a limited amount of research as been conducted on long-term structural health monitoring solutions, and this is especially true in regards to historic covered timber bridges. To date, evaluation efforts of timber bridges have focused primarily on visual inspection data to determine the structural integrity of timber structures. To fill this research need and help improve timber bridge inspection and management strategies, a 5-year research plan to develop a smart timber bridge structure was undertaken. The overall goal of the 5-year plan was to develop a turnkey system to analyze, monitor, and report on the performance and condition of timber bridges. This report outlines one phase of the 5-year research plan and focuses on developing and attaching moisture sensors onto timber bridge components. The goal was to investigate the potential for sensor technologies to reliably monitor the in situ moisture content of the timber members in historic covered bridges, especially those recently rehabilitated with glulam materials. The timber-specific moisture sensors detailed in this report and the data collected from them will assist in advancing the smart timber bridge.