When the 90-year-old steel pratt thru truss bridge over Big Bureau Creek in Princeton Township needed replacement, the Township dreamed of a timber covered bridge that would compliment the picturesque rural landscape of the area.  WHA’s innovative design made the bridge economical by requiring the minimum amount of wood possible.  The bridge uses a burr arch in combination with an inverted kingpost truss.  The burr arch was patented in 1804, and the kingpost truss was the most common truss used in the 19^th century for timber covered bridges.  The inverted kingpost truss has its diagonal members resisting the arches deformation when a live load travels across the bridge by having its diagonal members geometry orientated in a somewhat perpendicular fashion to the arch.  This allows the arch to carry a majority of the load while the truss keeps the arch in its desired shape.  This design allowed for the size necessary for a modern two lane bridge without distracting from the historic look and feel.

It was important to the client that the structure be entirely made of wood - a renewable, biodegradable, natural resource.  Rather than using timber solids, glulam (glue laminated wood) was used for the main load carrying components.  Glulam is stronger than solid timber and can be fabricated in any length.