Project Summary

The Blair Covered Bridge, completed in 1870, is a 295′ long, 2-span structure that spans the Pemigewasset River. The present structure is the second covered bridge to be erected at this site, with the stone substructure dating to construction of the first bridge in 1829. The bridge combines the patented Long Truss with supplemental arches. The purpose of the project was to address substructure movement and scour concerns, complete a full rehabilitation of the bridge and improve fire protection/detection. 

We performed a detailed inspection and analysis of the bridge, completed borings at each substructure element and retained a dry laid stone masonry expert for substructure recommendations. The major components of the project include installation of steel sheeting and stone rip rap around the center pier for scour protection, bridge abutment modifications to better distribute loads to the substructure, stone masonry wingwall reconstruction, repairs and replacement of bridge members, installation of fire detection and protection systems and minor approach improvements.  

A unique aspect of the project is in-place member stress testing to determine the loading effects of wedge driving in the trusses compared to design assumptions.  

Near full-time construction observation and administration services were provided following the NHDOT Local Public Agency program guidelines. The project is partially funded through the National Historic Covered Bridge Preservation Program. 

AWARDS: 
2015 Preservation Achievement Award, New Hampshire Preservation Alliance