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Benjamin Franklin Bridge Main Suspension Cable Investigation

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As the City of Philadelphia and neighboring New Jersey communities began to grow, so did the need for the much planned, yet long overdue Delaware River crossing. As chief bridge engineer, Ralph Modjeski designed what would be the longest suspension bridge of its time in the early part of the 20th Century. Today, the Benjamin Franklin Bridge feeds regional towns, including Philadelphia – the nation’s fourth largest city economy – with over 100,000 vehicles daily, plus an additional 50,000 passengers carried on the bridge’s two outboard PATCO rail lines. In recent years, the Delaware River Port Authority has laid out a plan to proactively keep up with the area’s increasing transportation demands. This included a detailed investigation of the main suspension cables to identify any changes in their condition.

As active partners, our engineers worked with the DRPA and steel construction contractors to wedge open and inspect the main cables at several panel locations. Modjeski and Masters also oversaw the material testing of wire samples, and on-site wire splicing using ferrule connectors. Next, our problem solvers performed a cable strength evaluation. And much like Ralph Modjeski’s use of deflection theory for the original design, our technical experts used the latest practices and methodologies to determine the factor of safety of the main cables.

Bridge Geometry
Main Span 1,750 feet
Total Length 7,456 feet
Lanes on Structure Seven lanes, two rail lines, two sidewalks

The Benjamin Franklin Bridge main suspension cable investigation is exemplary of our commitment beyond completion. Our long-term relationship with the DRPA was established over 85 years ago with our founder’s design of the iconic bridge.