Completed in 1982 at a cost of more than $19 million, the post-tensioned box girder of the Houston Ship Channel bridge was cast in place without falsework 175 feet above some of the heaviest ship traffic in the United States. The structure carries four traffic lanes and has a 750-foot main span. The center span is flanked by two 375-foot spans to create a 1500-foot main structure, which forms part of a 4.2-mile link between two major highways. A concrete box girder was selected in part because of the Coast Guard requirements that the channel remain open to traffic, and also because of concrete's ability to withstand the high humidity and corrosive atmosphere of the area.
COOLING THE CONCRETE
The hot, humid climate which prompted selection of a concrete girder presented some problems in placing concrete. Ice was used in the mixes to keep the concrete cool and to avoid slump loss. Retarder and superplasticizer additives were needed to overcome slump loss due to a half hour travel time from one of the mix supplier's plants. Both pumps and crane and bucket were used in placing concrete in the various parts of the bridge.
BALANCED CANTILEVER CONSTRUCTION
The balanced cantilever method was used on the 1500-foot center section of the bridge. The process required that during construction a piece of freeway two-and-a-half football fields in length, 15 to 46 feet thick, balance atop each of the two piers nearly 200 feet in the air. The cast-in-place concrete segments called for a form traveler that could support a segment 59 feet wide with a height varying from 47.5 to 15 feet and still be easy to operate. The form travelers did this with a self weight of only 150 tons, while still being able to support a construction load in excess of 200 tons.