Rehabilitation for pedestrian use is a practical and popular way to preserve these historic structures. But the American Association of State Highway and Transportation Officials (AASHTO) Guide Specifications for the Design of Pedestrian Bridges (AASHTO 1997) throws an obstacle in the way. It mandates modern wind load design criteria. Structural engineers attempting to rehabilitate historic bridges from former highway to modern pedestrian use often discover that the old structures lack the strength to resist the AASHTO wind load criteria. This can contribute to either a “heavy-handed” design approach, which is both expensive and detrimental to the historic character to be preserved in the first place, or condemnation of the bridge.
A dichotomy presents itself: On the one hand, historic truss bridges often do not possess “code-compliant” lateral resistance for current wind load requirements. Yet in case after case observations reveal no physical evidence to suggest that wind has caused damage or distress, even after a century of exposure. At this age, bridges have indeed weathered many severe windstorms.
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