Case Study #3: East Haddam Bridge,
East Haddam-Haddam
(click on image for larger view)
Bridge: Steel swing bridge built in 1913
Problem: Overstressed eyebars
Solution: Reinforce eyebars with new parallel members
According to two engineering analyses, the eyebars that form most of the upper chord of this large steel swing bridge appeared to be overstressed. These critical components, which carry the whole weight of the structure when open, were difficult to inspect and impossible to test in place. Consequently, the bridge was posted for a fifteen-ton limit while State transportation engineers considered methods of strengthening the bridge.
The answer was to supplement each set of eyebars with a pair of parallel bars running between the original members. The new bars are connected to the existing joints with high-strength bolts and connection plates. No original material was compromised by this solution. The new members are visually unobtrusive, and they are not likely to be mistaken for part of the original design.
Other components of the 1985 rehabilitation of the bridge were new steel-grate decks on both the fixed and movable spans, new guardrails, and improvements to the operating machinery. The eyebar reinforcement accounted for approximately one-fourth of the project's $1.5 million cost.