NORTH LITTLE ROCK — The steel arch on the now-closed Broadway Bridge over the Arkanasas River between Little Rock and North Little Rock, which was scheduled to come down at 10 a.m. Tuesday, hit a snag when the steel superstructure proved to be stronger than anticipated.

With cuts in the metal placed strategically along with explosive charges, the entire span was supposed to collapse into the water when the charges were detonated.

Although the charges blew as planned, the arch stayed stubbornly in place, appearing from a distance to be virtually unscathed, although officials said the explosives and the cuts in the steel beams would have destabilized the structure, making attempts to pull it down very risky.

“The structure is severely weakened and could fall at any moment,” said Danny Straessle, a spokesman for the Arkansas Highway and Transportation Department, a few minutes after the failed attempt. “It’s very dangerous right now so the contractor has to figure out how to bring it the rest of the way down as safely as possible.”

The arch fell into the river just before 3 p.m., as a crew worked to nudge it out of place, using a steel cable attached to a crane positioned on a barge.

“About five hours, that’s what it took,” said Straessle, adding that the delay required clarification on the 24-hour window given to clear the channel.

“We’re trying to figure out if they have 24 hours from the time the structure came down or the time they closed the channel this morning. Because there was a delay in bringing it down, we’re trying to get some clarification on that,” be said.

Twenty minutes after the 10 a.m. explosions, the barge, with a large crane positioned on the deck, was put into place by a tugboat, and a cable attached to the crane lifted two workers in a “man basket’ to survey the archway. Sometime later, the barge was moved so the cable could be attached to the north end of the archway. Then, using the crane and attached steel cable, workers tried to pull the archway over sideways, but were unsuccessful.

The barge and crane were repositioned and the cable reattached to the arch, this time in the center, for another attempt. Finally, just before 3 p.m., the arch toppled into the river.

Straessle said as soon as the structure came down, workers swung into action to begin the task of clearing the debris.

“They’re going to work on it right now. They’re starting to lift those pieces out of the water and dispose of the arch,” he said.

Massman Construction Co., a Kansas City, Mo. construction firm, was awarded the contract after submitting a bid of $98.4 million to replace the aging bridge, which carried 24,000 vehicles a day between Little Rock and North Little Rock.

The company has 180 days from Oct. 1 to have the new Broadway Bridge in place. The work is scheduled to run 24 hours a day, seven days a week, including holidays, to finish the job on time.