Closing the Loop

McCabe, Raymond; ,

Closing the Loop

by Raymond McCabe, (M.ASCE), Assoc; HNTB, Fairfield, NJ,

Serial Information: Civil Engineering—ASCE, 1993, Vol. 63, Issue 7, Pg. 64-66

Document Type: Feature article

Abstract:

The 5.1 mi Cooper River Bridge, the longest in South Carolina, completes the I 526 Mark Clark Expressway around Charleston. It is a two-way, four-lane structure with the capability of expansion to six lanes. The bridge is designed to withstand hurricane-force winds of 155 mph at deck level, earthquakes causing ground accelerations of .15 g, and the impact of barge collisions. The bridge is also aesthetically pleasing. The most distinctive feature is the main span truss, which was designed with no vertical member or sway bracing to provide more open space. With a navigation clearance of 155 ft over a 700 ft open channel, the steel parallel chord truss design was $17 million less than the concrete, cable-stayed alternative. The bridge deck is also unusual in that it's fully continuous for 1,600 ft with no stress relief joints to cause maintenance problems. In September 1989, the partially erected truss survived Hurricane Hugo. Damage to 250 prestressed girders and pier caps cost $5.2 million to repair and delayed the project by one year. Despite the setback, the project was completed at a cost overrun of less than 1% excluding the extra costs resulting from Hugo. It was completed in June 1992 at a cost of $141 million.

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