SALEM - Concerns over the safety of a fourth-floor balcony will keep the Salem State library closed for several weeks as the college conducts a review of the entire building.

Officials will investigate the strength of an interior overhang on the top floor that holds an office, archives and storage, college officials said yesterday. The college abruptly shut down the library Monday night after engineers raised concerns about the structural safety of the building.

"We want to take the time to do it carefully and correctly and not try to rush things through," college spokeswoman Karen Cady said.

In particular, engineers will examine the load-bearing capacity of the fourth-floor overhang to determine whether it can support the weight of the desks and fully stocked shelves it holds now.

"Part of the question is that construction standards have changed through the years," Cady said. "So what may have been considered adequate load-bearing capacity in 1970 is different in 2007."

It's not the first time the library has faced serious structural problems.

The library was built in 1971, but it remained closed for three years because of construction flaws, said Neil Olson, who served as chairman of the library's construction committee from 1966 to 1974.

Just before the library was set to open in 1971, officials discovered that steel rods inside the building weren't strong enough to reinforce the concrete flooring, Olson said.

"It was muffed by everybody," Olson said, "mostly by the people who were supposed to check the basic mathematics of the steel construction and didn't do it. ... It was a real pain in the neck to everybody involved."

For three years, the library's grand opening was delayed while the state spent millions of dollars to strengthen the support of the building, he said.

As a result, the floors were actually made stronger than they had to be and capable of withstanding about 150 pounds per square inch of pressure, Olson said.

"If they put lead weights on every single one of those shelves, I don't think they'll get up to 150 (pounds per square inch)," he said. "You could drive a truck on those floors and they wouldn't buckle."

However, the role of the building has changed over the years as the college has grown, and it now holds more office space, computer equipment and other furnishings.

It's used by an estimated 3,000 students and holds offices for 90 faculty and staff, as well as computer labs and classrooms.

Yesterday, the college identified alternative places on campus to move all the classes, offices, academic advising and other services offered inside the building.

"Maybe not the most optimal space, but it's space," Cady said. "We're being very creative."

The college made the decision to shut down the library after hearing from state engineers who were conducting a study on scheduled renovations there.

"There are certain areas of the building that may be overcapacity, and that's what's being looked at in more detail," said Kevin Flanigan, spokesman for the state Division of Capital Asset Management.

College officials insist they're simply erring on the side of caution. The building hasn't suffered any recent damage and is in no danger of collapse, Cady said.

It's still too early to know how extensive any needed renovations might be or how much they would cost, Cady said. Last week, Gov. Deval Patrick submitted an education bond bill that included $41 million to upgrade the building.

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Staff writer Chris Cassidy can be reached at 978-338-2526 or by e-mail at ccassidy@ecnnews.com.