At 42 years old, The Colonie Center Mall is one of the oldest enclosed shopping centers in America. To look at it today, though, you would never guess that fact. The Albany, NY, mall is sporting a brand-new look and feel with the addition of more than 100,000 square feet of space to house upscale eateries like The Cheesecake Factory and P.F. Chang's China Bistro, as well as an L.L.Bean, a Barnes & Noble and a 13-screen Regal Cinemas.
The trip, however, from faded to fabulous was not without its engineering challenges. The main challenge for the team of architects and engineers was to come up with the design of a third-floor addition that would accommodate the added tenants – including the 2,800-seat movie theater. Further, the disruption of the mall's 120 tenants had to be minimized, a task complicated by a construction start date coinciding with the arrival of the holiday season.
The largest challenge was to accommodate the seismic provisions of Appendix K of the New York State (IBC) Building Code. This code requirement would have required reinforcement of the existing building structure for the seismic loads from the new building elements as well as the existing building structure. The previous New York State Building Code to which the building was designed only required the design of the building structure for gravity and wind loads, which were much less than the seismic design loads.
The solution was to create an independent third-floor structure going through and above the existing mall rather than have it carry the addition's extra loads. The key to the design was thinking big: eight 100-foot-long by 43-foot-tall trusses weighing 48 tons each and a 390-foot-long by 43-foot-tall truss weighing 203 tons – the kind normally seen on bridges, not for the support of a theater. The 390-foot-long truss is held up by six super columns, the kind usually reserved for tall buildings. The super columns are freestanding for 38 feet and are a total of 81 feet tall. They are made of a W36x262 with two continuous 2.5-inch-thick by 35-inch-wide side plates (to form a box member) and weigh 27 tons each.
The super columns had to be located where they would cause the least disruption in the existing retail spaces below. To this end, only six were used. The 100-foot trusses, which span front to back in an east-west direction, had to be located in the theater demising walls. The conflicting requirements for the super column and truss locations resulted in most of the 100-foot trusses not falling on the super columns. As a result, a 390-foot truss spanning north-south was required to run over the super columns to pick up the 100-foot trusses. The ends of the 390-foot truss cantilever 10 feet over the end super columns to pick up the two exterior, 100-foot trusses.
The super column with the largest loads had to support a 1,970-kip gravity load (1 kip = 1,000 pounds). The bases of the super columns were fixed to give stiffness to the building so as to limit side sway from lateral loads. The base fixity resulted in a maximum moment of 1,430 foot-kips at the column base. The column base plates were 42 inches by 56 inches and 5 inches thick. Spread footings, which had to be located to miss footings for the existing mall columns, were constructed in an “L” shape. Because of the large loads on the footings, they had to be designed so that the center of area was as close as possible to the column to minimize eccentric loads on the footings. The largest footing was 35 feet by 25 feet and 5 feet thick, requiring 134 cubic yards of concrete.
One of the biggest challenges was erecting the 82-foot super columns, which came in two pieces. The lower one measured 40 feet long and weighed 13 tons. This meant 6-foot by 7-foot holes were cut in both the roof and second floor to allow the columns to be set. The base plates were left off to minimize the holes required for the columns.
Setting the columns was a task best described as threading a gigantic needle. Great precision was required by the crane operator, whose job was complicated by the fact that he could not see where the columns were going through the relatively small holes. Once in position, the base plates were set on the footings, and the columns were welded to the base plates. The top portions of the super columns were then welded to the lower parts.
Designing a building on top of a building is one thing. Designing a multiplex movie theater on 38-foot-tall, freestanding columns is a separate issue entirely. Normal considerations in a multiplex fit-out include the accommodation of heavy partitions as well as the high (up to 32 feet clear) headroom for stadium seating. But in this case, additional factors like the location of extra-large trusses and columns, as well as deflection, had to be considered.
For sound attenuation, typical theater demising walls are made with three layers of 5/8-inch-thick gypsum board on each side of metal studs and weigh approximately 650 pounds per liner foot. At the truss locations, the demising walls had to be widened to 32 inches to allow the trusses to fit in the walls. These walls were constructed of two faces of metal studs with three layers of 5/8-inch-thick gypsum board that sandwiched the trusses.
When movie theater architects design a multiplex, they are typically designing it with a slab on grade in a big field. The contractor levels the ground and creates the stepped concrete floors that usually step down at the front. In this case, there was no field, so the stepping had to take place within the new building structure. The new floors were concrete slabs at elevation 42 feet 6 inches on composite steel deck supported by composite steel beams. Each theater had a 2-foot well in front for the lowest stadium seating with a floor elevation of 40 feet 6 inches. The stepped seating was placed on the floor slab, supported by concrete slabs on Styrofoam at the lower levels and by concrete slab on steel deck spanning to light-gauge steel stud-bearing walls at the upper levels.
Deflections were a critical issue with this project, as the combined deflection of the beams, the 100-foot trusses and the 390-foot truss had to be considered. The total deflection of the new construction had to be limited so as not to put pressure on the building below. Even after the new members deflected, they had to be clear of the existing mall roof below, which was at an elevation of 37 feet. At the theater wells, the floor beams were limited to heavy W24 beams. These beams had to span up to 68 feet and could not deflect more than 2 inches under both dead and live loads.
Neither cold nor throngs of holiday shoppers could delay the start of construction, which took place in November 2005. To avoid inconveniencing tenants and customers, work was done at night when the stores were closed. By 7 a.m. each morning, construction crews were out and cleaning crews were in to prepare the site for the mall's 9 a.m. opening.
Three years later, the finishing touches are now being added to the transformed mall. Inside and out, the resulting look is sophisticated, warm and welcoming. New amenities include a two-story fireplace, natural lighting, earth-tone tiles, and painted surfaces. Plush ensemble areas feature leather chairs, lamps and plasma TVs, and redesigned columns enhance the line of vision.
The atmosphere is decidedly more contemporary and attractive to a wider range of ages. There are popular restaurants providing leisurely alternatives to the food court, a Barnes & Noble has moved into the new space, and Regal Cinemas opened in the spring.
The “above and through” solution was able to satisfy developers, tenants and, most importantly, patrons. Business was able to go on as usual – a not-so-simple feat during a three-year, massive remodel that proceeded while 8 million people per year continued to shop.
Editor's note: Malcolm McLaren, W. Richard Mahoney and V. Douglas Platt Jr. are professional engineers with McLaren Engineering Group, a full-service engineering firm based in West Nyack, NY.