Zakim Bridge: One of the Most Beautiful Bridges on Earth

Christian Menn, a world-renowned bridge architect from Switzerland, devised the cable-stayed design for the new span. The cable-stay design called for a 745-foot-long main span, flanked by two 295-foot-long side spans. It also called for an eight-lane main roadway to carry I-93 through traffic, plus two northbound lanes cantilevered from the main span. In effect, the 183-foot-wide roadway – the widest cable-stay roadway deck in the country – was to be asymmetrical.

The new Charles River Crossing was to be the first hybrid cable-stay bridge in the country, utilizing both steel and concrete in its design. Steel girders and beams frame the main span of the bridge. The north and south side spans were cast in place with post-tensioned concrete. Two additional northbound lanes (from the North End and Sumner Tunnel to northbound I-93) are cantilevered on steel beams from the eight-lane main span.

A network of 116 cable stays supports the roadway. On each side span, there are 24 cable stays leading from the median to the tops of the towers. On the main span, four sets of 17 cables were strung from the sides of the roadway to the spires. The longest of these cables is 500 feet long. There are 14 strands in each cable in the cables closest to the towers, and up to 73 strands in the strands furthest from the towers. The last three cables are anchored in 40-foot-long spline beams beneath the roadway. The south spline beam missed the old I-93 ramps by just two feet.

Despite its elegant, streamlined appearance, the new bridge was designed to be exceptionally strong. It was built to withstand winds of over 400 miles per hour, as well as hold up against a magnitude 7.9 earthquake.


~ by adhna on August 11, 2010.

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