James Lewan, an experienced forensic engineer and owner of Chicago-based J28, LLC, completed a structural engineering report for the circa 1850 George Street bridge last fall, courtesy of Landmarks Illinois.
• Many deck boards are warped, cupped, damaged, loose or missing.
• The guardrails are bent or loose.
• While the limestone support walls generally are in good condition, there are cracks.
• The sill beams – believed to be cut from hearty southern yellow pine – are generally in fair condition. However, they show signs of age.
• Many of the fasteners between heavy timber members are corroded or missing.
• The most significant deterioration was “end grain” decay on the sill beams and stringer beams. Sill beams rest on top of the foundation walls. In bridge construction, stringers are lightweight, longitudinal beams that lie parallel to the bridge's length. They are the primary members the deck rests on.
Recommended repairs include:
• Replacing the existing corroded fasteners with new stainless-steel fasteners.
• Repairing the loose guardrail posts.
• Replacing the sill beams at both limestone stem walls and repoint the walls.
• Replacing half of the sill beams supporting the pedestrian extension to the north.
• Repairing half of the stringer beam ends.
• The bents –which transfer weight from the bridge's superstructure down to the foundation – are generally in good condition. However, there is decay at the top of the southernmost pile that requires repair. Piles are the long, vertical structural columns driven into the ground to support a bridge's foundation.
• Remove and replace the deck boards
• Remove and replace the portions of the pedestrian extension along the grade-supported approaches.
