Forest City Ratner topped off the structural steel for the Barclays Center, the company announced today.

With the roughly $1 billion project’s 10,400 tons of steel in place, other portions of the arena can now progress including its roof, which a spokesman for the company said was in the process now of being closed over the arena floor and will likely be completed by the end of February.

Other elements of the 18,000 seat space also being finished, including most of the building’s concrete work, in preparation for its planned opening in September 2012.

The arena will be home to the NETs when the NBA team relocates from New Jersey to Brooklyn next season and is the centerpiece of a mixed use development Forest City is building on Brooklyn’s Atlantic Rail Yards that has drawn controversy from some neighborhood opponents.

The building can seat 18,000 people for basketball games and up to 19,000 for concerts according to information released by Forest City. The company, a large owner and developer in the city, owns 55 percent of the arena and 20 percent of the NETs. The Russian billionaire Mikhail Prokhorov owns the minority stake in the arena and the majority of the basketball team, which he purchased in 2009.

A concert featuring the rapper Jay-Z, who is also a part owner in the NETs, will be the first event in the space and is planned for September 28.

In a statement released by Forest City Ratner praised the union workers handling the construction.

“From day one, I said I want to develop great things that create jobs and that’s what we’re doing,” Mr. Ratner said in the statement. “And, most importantly, it’s all union, union, union as we continue to build important projects for the city and the state.”

In recent months, Mr. Ratner has stoked the ire of union workers for his plans to build residential towers abutting the arena using prefabricated modular construction methods, which would reduce the amount of work for construction workers at the site.

According to the company, the NETs gave the 500 workers involved in the construction 1,000 tickets to NETs games over the coming weekend.

Daniel Geiger, Staff Writer, is reachable at DGeiger@Observer.com

Kohl’s Department Stores is expanding its office presence at 1400 Broadway, and will eventually be taking over 100,000 square feet inside the midtown building, the company said in a statement.

  The office expansion, the third such space increase for Kohl’s inside 1400 Broadway since 2007, will be for the department store’s design studios, it said.

  W & H Properties is the owner of 1400 Broadway, according to the building’s website. Scott Klau of Newmark Knight Frank is the listed leasing agent for 1400 Broadway. He did not respond to requests for comment by press time. It was not immediately known who represented Kohl’s in the lease negotiations.

  Kohl’s design office first opened as a 23,000 square foot space at 1359 Broadway in 2007 to “have a presence in the heart of New York’s thriving fashion district and to be in close proximity to the design source and management of exclusive partnerships,” it said in a statement.

  In 2010, the design office relocated to 1400 Broadway, taking 59,000 square feet of office space. The company’s headcount also grew, from 30 office employees in 2007 to 140 designers today. Kohl’s will be occupying over 100,000 square feet by 2014.   The design team is responsible for the design and development of 13 brands like Simply Vera Wang, Princess Vera Vera Wang, Food Network, Candie’s, FILA Sport, and Jennifer Lopez.   A spokeswoman for Kohl’s did not return phone calls requesting comment.

Daniel Edward Rosen, Staff Writer, is reachable at DRosen@Observer.com