Bottom floor gets top priority in IRS project

August 11, 2010

When the Building Team began the $60.7 million renovation and modernization of the 1.4 million-sf Internal Revenue Service headquarters in Washington, it was obvious where to start. Sections of the building's slab-on-grade basement floor were sinking.

The initial deflection, which involved an area of 15 by 25 feet, later spread to other sections of the 186,000-sf slab. The failures were caused by underground voids, ranging in depth from two inches to as much as three feet, that resulted from settlement and consolidation of the subsoil. The slab failure cracked underground piping, which had to be replaced. New underground storm, sewer, and subsoil drainage was installed.

Before the new basement floor could be constructed, grout was injected beneath eight electrical vaults to prevent them from sinking.

Unlike its slab-on-grade predecessor, the new structural concrete floor is supported on new grade beams that bear on existing pile caps. The floor ranges in thickness from eight inches to 12 inches, and supports new underground piping.

Delayed reaction

The seven-story, steel-framed building, the first of seven completed in the Federal Triangle, was constructed between 1928 and 1936, according to Joseph Spina, project principal with the Washington office of Swanke Hayden Connell Architects.

Long before the IRS headquarters was constructed, a creek ran beneath what is now 12th Street. When tunnels for Washington's Metro rail system were constructed adjacent to the IRS site in the 1970s, it was necessary to dewater the soil, according to Jag Bhargava, project executive with the U.S. General Services Administration. This lowered the water table, and was apparently the principal reason for creation of the voids.

The project's initial scope was $22.7 million. The selection of options increased the total by $26 million, and owner-initiated changes by $12 million. "We're doing something pretty much everywhere in the building," says Kevin Mitchell, project manager for general contractor Grunley Construction, Rockville, Md.

The HVAC system was completely renovated. Prior to the installation of five new air-handling units, it was necessary to furnish temporary units at a slightly different location to accommodate the sequence of construction. A new 210-ton chiller was installed.

To protect the building against bio-chemical attack, fresh air intakes that were considered to be in vulnerable locations were relocated to the roof or to internal courtyards.

In order to provide blast protection, a laminated window system that meets a GSA Level C threat was installed interior to the building's existing steel-framed historic windows. Exterior work included the cleaning and repair of masonry walls.

Interior work included the upgrade of 70 bathrooms to conform to the Americans with Disabilities Act.

Although GSA did not designate this project to meet the criteria of the U.S. Green Building Council's LEED rating system, sustainability concepts were incorporated. For example, concrete from the original basement floor was pulverized and reused as backfill, thereby reducing construction waste. Recycled materials included flooring for the building's fitness center that was made from old rubber tires.

Construction was performed at night and on weekends so it would not interfere with operations of the building's 2,700 employees.

The project is scheduled for completion in October.

         
 

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