Gov. George Pataki, Mayor Michael Bloomberg and Fire Commissioner Nicholas Scoppetta were present at the ceremony, at which "Taps" was played.
The 30-foot girder survived when the twin towers collapsed into a mountain of 1.8 million tons of rubble. For months it was covered by debris, but as the pile shrank the column was revealed, still standing where it was planted when the south tower was built more than 30 years ago.
Workers topped it with a flag, and covered the sides with spray-painted messages and photographs of victims.
Bill Harris, a 50-year-old construction worker from Pearl River, N.Y., said the mood among construction workers was somber. They had formed a bond with site, which many feel is now sacred ground, and were morose that the recovery effort was over, he said before the ceremony.
"It was so big, you thought it would never end," said Harris, who had been working at ground zero since the recovery effort started Sept. 11. "I think they're going to have to tie them up and take them away. They don't want to go. They're proud to be here."
Lee Ielpi, a retired firefighter whose son's remains were found in December, said construction workers deserved similar praise that was bestowed upon firefighters and police officers who died during the attacks.
"They are absolutely the best," Ielpi said. "They have gone through everything we have gone through, and they have not gotten the recognition we have."
"It means a lot to people — it's like a flag, which is a piece of cloth, but it represents our country and an idea. The idea of the beam is our strength, our resilience," said Richard Streeter, 34, who has operated an excavator at the site since Sept. 12.
Hundreds of construction workers who have labored at the site watched as the column was cut and draped with a flag. The ceremony is the first of three — for construction workers, rescue workers and families — that make up a gradual farewell to the round-the-clock recovery operation.
On Thursday, the beam will be removed from the site in a procession past an honor guard during the city's formal ceremony, which begins at 10:29 a.m., when the north tower collapsed.
A fire department bell will ring the signal for a fallen firefighter, then a stretcher with a folded flag will be carried out of the site, honoring the victims whose remains have not been found.
Lt. John Ryan of the New York and New Jersey Port Authority Police Department, which lost 37 members in the attacks, said he had "mixed emotions" about Thursday's symbolic ceremony ending eight months of grueling, sorrowful work.
"I realize at this point a lot of the people who were lost here may not be recovered but I also look at it from the standpoint that it has been a tremendous effort to get to the point we're at," Ryan said.
Of the 2,823 people killed in the attack, the remains of just 1,092 have been identified. But nearly 20,000 body parts have been recovered, and the medical examiner expects to continue identification work for at least eight more months.
Thursday's ceremony, which officials expect will draw tens of thousands to lower Manhattan, will last just 20 minutes from 10:29 a.m., marking the minute when the second of the 110-story buildings collapsed in a heap of crushed concrete, steel and glass. It is intended for city officials, ground zero workers and victims' families.
Several family groups had asked Mayor Michael Bloomberg to schedule the service on a weekend, so that work and school schedules would not be disrupted. The mayor said the city avoided the weekend so it would not conflict with religious observances.
Jennie Farrell, whose brother died in the attack, wrote to Bloomberg protesting the date on behalf of the families.
"This ceremony holds such emotional and symbolic significance," wrote Farrell, a leader of Give Your Voice, one of several family groups. "We have lost our brothers, sisters, mothers, fathers, husbands, wives, sons and daughters, and at the very least should be given a day that will not add to the nightmare we live in every day."
To accommodate those who could not attend on Thursday, the family groups have planned their own service at ground zero on Sunday. The city has issued permits for the event.
One of the survivors of the collapse of the buildings who also worked on the recovery, New York Fire Department Lt. Mickey Kross, said he had "very strong feelings" about Thursday's event.
"I was deeply involved in this, not only as a fireman but as a person who was trapped in the building when it came down," Kross said. "I do get a sense of peace of mind when I'm there, if I stay away too long I get fidgety. This is going to be an experience when this ends for me."
Plans for some kind of memorial and redevelopment of the site are being discussed and could be announced as soon as July, city officials said.
The Lower Manhattan Development Corporation, which was established after the attacks to help guide the rebuilding, has begun public hearings on what kind of buildings would replace the World Trade Center. The twin towers dominated the lower Manhattan skyline from their completion in 1973, symbolizing New York's financial might in the world's most important business district.
"It's very unlikely that any buildings 100 stories tall will be built again," said corporation Chairman John Whitehead. "People sometimes like the symbolic aspect of even higher buildings but people don't want to work in a 100 story building downtown anymore."