OWNER & DEVELOPER: Madison 45 Co., NYC
ARCHITECT: Richard Cook & Associates, Architects, NYC
STRUCTURAL ENGINEER: Rosenwasser Grossman Consulting Engineers, NYC
MECHANICAL, ELECTRICAL & PLUMBING ENGINEER: Jaros, Baum & Bolles, NYC
CURTAIN WALL CONTRACTOR: Permasteelisa Cladding Technologies Ltd., Windsor, Conn.
STRUCTURAL STEEL FABRICATOR & ERECTOR: ADF Steel Corp. Montreal
CONCRETE CONTRACTOR: Carlton Concrete Corp., Floral Park, NY
EXCAVATION & FOUNDATION CONTRACTOR: Civetta Cousins JV, Bronx, NY
GENERAL CONTRACTOR: Pavarini McGovern Construction Co., NYC

Like a recipe, whose critical mix of ingredients can make the difference between an Epicurean delight and Ptomaine, the critical blend of steel and concrete at 360 Madison Avenue is has proven to be a Gold Medal winner for this complex endeavor.

As with any recipe, there is a starting point. For this $65 million project, it began with an existing steel structure that was built at the turn of the last century and then added to in the late 1970s.

The next ingredient was an adjacent building, 17 E. 45th St., which was demolished to make way for a new tower. Then came the blending - the challenge of making two structures as one.

Combined, the two structures total 355,000 sq. ft. The existing 120,000-sq.-ft., stone-clad 1910-structure, originally an Abercrombie & Fitch department store, was reclad with reflective glass curtain wall in the late 1970s and turned into an office building. Everything on this building was demolished down to the steel frame. Adjacent to this steel frame, a 26-story office building with a concrete superstructure rose. The steel frame was extended, and what had been 17 stories, became 23 stories. The solution to combining the two buildings as one was provided by the structural engineer.

The two buildings are intertwined because the developer wanted a large footprint for the office space. Enlarging a building by building on top of a previous enlarged building always presents a challenge because it has previously been reinforced. The new, five-story addition requires additional reinforcement with steel cover plates.

Another issue is the seismic code. Normally, he said, it would affect the new building. But, "the new building's footings did not have to be enlarged we could have created a seismic joint between the two buildings and enlarged the existing building for extra wind forces. Now, steel plates will be used to reinforce the existing building against wind forces."

Furthermore, the developer did not want a seismic joint between the two buildings because it would have created, in effect, two separate buildings. The solution was to build the new building using concrete to support additional forces the existing building could not sustain on its own.

In a sense, a new concrete building was because it would have been just as easy to put another steel building next door to it. It would have not had long-term shrinkage and creep of the columns. When you put two buildings together and add more floors to one of them, and you want level floors, then another solution is required.

To minimize variations in floor levels, a concrete joint with steel reinforcing with the rebar welded to the steel building to the underside of the flanges was designed. The separation between the two buildings is 1-ft. wide. So the concrete building is being built about 1-ft. away from the steel building to allow the floors to be level and remain level over time.

" In the new concrete building, the floors are being built slightly higher (about 0.1 in.) And monitored. So as the new building settles, it will remain as level as possible. The 1-ft. separation between the buildings will allow for an additional leveling of floors.

The skin of the building was also a challenge because the existing building was not in itself proportioned well due to the addition to it in the 1970s. The two structures would have different proportions, so a system that would accommodate both was developed. We did. This system consists of a clear, transparent skin which is meant to read like the surface of a pond - sometimes it will be reflective and at other times, completely transparent. Just as in a pond, sometimes you see the bottom, a fish or a reflection off the surface.

The skin is white-painted aluminum and glass because the white distinguishes the building and accentuates the surface of the pond aspect by contrasting with the glass.

Jury said this project's structural solution helped unite an existing building that received an addition with a new building to make them function as one structure on a floor-to-floor basis. The project team also had to deal with a constrained site and partial demolition of an existing structure.