Thomas Z. Scarangello, P.E., otel guests usually notice The resort was designed by archi- and Bryan Tokarczyk the size of their rooms, the tects at Hnedak Bobo Group of Mem- quality of the bath towels phis, TN, and structural engineer of and the friendliness of the record Uzun & Case of Atlanta, GA. staff; but rarely is the roof a The entire complex covers 60 acres and Hmajor point of interest. However, when includes 1,400 guest rooms, 200,000 sq. ft a hotel roof spans unsupported across of convention space and 150,000 sq. ft a 10-story-high atrium for several hun- of meeting rooms, in addition to the fa- Innovative steel dred feet, and supports four acres of cility’s signature atria features. The glass, perhaps some people will take central atrium is themed to recall the designs for the note of the structural spectacle. historic Florida city of St. Augustine, Such roof-gazing is entirely plausi- while smaller atria on either side re- massive atrium roofs ble at the new Gaylord Palms Resort semble Key West and the Everglades. and Convention Center in Orlando, FL, Each atrium includes spaces for public at Orlando’s Gaylord where guests have the rare treat of en- entertainment, shopping and dining. joying an airy, sunny, semi-tropical The boundaries of the atria vary from Palms Hotel create Florida environment—in an enclosed adjacent hotel buildings to glass walls bright and airy spaces and air conditioned space. The $350 and open clear spans. million Floridian-themed hotel sur- for guests to enjoy. rounds three glassed-in atria with en- SMALLER ATRIA tertainment spaces for visitors. A huge The Key West and Everglades atria two-acre atrium features towering posed several major engineering chal- palm trees, cascading waterfalls and lenges for engineers. Each large roof mock historic buildings. Thornton- covers an acre of land, and has contin- Tomasetti Engineers designed the uous support only on the two sides structural systems of these atrium roofs nestled into the corner of an L-shaped with careful attention to both structural hotel building. The third side runs par- efficiency and aesthetic detail. allel to the face of one of the main hotel

Modern Steel Construction • November 2002 Opposite page: The Ever- glades Atrium features an acre of glazed roof. Four Pratt trusses, 11’ deep, form the primary structure.

Left, top: The Grand Atrium contains 100,000 square feet of landscaped space under glazed canopy 150’ above.

Left, bottom: Gaylord Palms Resort and Convention Cen- ter under construction. The Grand Atrium is the central feature of the resort. buildings, and the fourth side bears on The glass wall is supported by 5-ft- atypical support arrangements and ex- a 70 ft tall wall of windows subject to deep vertical trusses of 6-in., 8-in. and treme loads. The canopy bears on the severe wind loads during hurricanes. 10-in. square steel tubes. This mix of roof levels of the two buildings at the Further complicating the design was sizes allowed for economical atrium’s perimeter, eight to nine stories an architectural requirement for a 150 “stepped” welded connections sug- above grade. Because the canopy rests ft by 170 ft, column-free space below gested by detailing consultant Ferrell on two separate structures, it had to be the glass roofs. Super-efficient drainage Engineering. The trusses are spaced at designed to tolerate simultaneous also was required to prevent pools of intervals of up to 19 ft, delivering wind movements in different directions water from collecting on the glass roofs loads to a ground-floor concrete base while maintaining its shape. Moreover, during tropical cloudbursts. wall and to the atrium roof framing. its rooftop location places the glass The resulting solution was a clean Where the main roof trusses meet the canopy in an elevated and exposed and simple one. Four Pratt trusses 11 ft glass wall, the vertical trusses are built position that subjects it to increased deep form the primary roof framing. in pairs and connected by “middle wind pressures. These pressures are at They are composed of steel wide- chords” for extra weight-bearing ca- least 60 psf throughout the roof, rising flange chords and verticals with dou- pacity to carry the roof. as high as 80 to 120 psf in some areas ble-angle diagonals, and span 150 ft for both inward and outward (uplift) from posts behind the glass wall to THE GRAND ATRIUM directions. supports on the L-shaped hotel build- The central, St. Augustine-themed The Grand Atrium roof takes the ing. Triangular trusses of WT and space, or “Grand Atrium,” is signifi- form of an octagonal faceted dome wide-flange elements span 56 ft be- cantly larger than the Key West and topped with a cupola. The radial ribs of tween the main roof trusses, creating Everglades atria. It contains 100,000 sq. ft the dome are tied arches that reach 46- three gabled roofs that provide good of ground-floor planting areas, ft deep at the center of the roof. Each drainage. Guided bearings permit ther- streams, and walkways covered by a rib includes a 13-ft-deep steel truss of mal movement and truss-end rotations glazed canopy located more than 150 ft wide-flange and double-angle mem- where the roof framing rests on sur- above. This roof presented the most bers. The trusses carry roof framing rounding buildings. At the same time complex design challenge of the entire and resist unbalanced loads. Beneath they resist forces due to gravity, lateral project due to its tremendous size each rib, a wide-flange bottom tie winds and uplift. (spanning 364 ft between supports), member resists the dome’s outward

Modern Steel Construction • November 2002 Above: A schematic view of the framing for the Grand Atrium.

Right: Completed view of the Gaylord Palms Resort.

thrust, since the surrounding buildings framing to resist unbalanced roof and the Everglades. The openness of are not relied upon to resist spreading. loads. Bringing all eight ribs to the cen- the atrium designs at Gaylord Palms At the edge of the roof, circumferential ter would eliminate ring framing while provides bright and airy environments trusses form a tension ring that pro- creating a major barrier below the for the Floridian locales mirrored in Or- vides additional resistance to spread- cupola. The solution was a system in lando’s new hotel. And even if the ing while also supporting joist and which only four of the eight main ribs hotel guests don’t stop to look up and cross-truss infill framing that carries meet at a central hub. A light compres- appreciate the roof that protects them the glazed roof. sion ring is included to receive forces from the central Florida weather, they Stability against lateral buckling from the four shorter ribs and from in- are certain to enjoy the sunny, airy (and comes from both a 5/8 in. diameter steel fill framing. This system provides a vi- air conditioned) atrium spaces during rod X-bracing in four of the dome’s sually light and open appearance, their stays. facets, and a 14 ft wide horizontal resists unbalanced loads efficiently and perimeter ring truss. Unlike traditional allows for straightforward fabrication Thomas Z. Scarangello, P.E., is a man- dome structures that rely on infill ma- and erection. aging principal of Thornton-Tomasetti En- terial for structural behavior, the over- gineers, New York, NY, and Bryan all atrium roof will not be affected by ATRIUM CONSTRUCTION Tokarczyk was formerly a project engineer damage to or replacement of any glass Steel for the Grand Atrium dome with Thornton-Tomasetti. panels. The domed roof bears only on was erected using a single, main erec- the eight corner points plus two more tion tower, thanks to the roof’s sym- ARCHITECT points at extensions beyond the octa- metric design. This avoided both the Hnedak Bobo Group, Memphis, TN gon, so each bearing plays an impor- scheduling complications of relocating tant role. The bearings allow lateral shoring during staged roof construc- STRUCTURAL ENGINEER movements of up to 5 1/2 in. in both tion and the excessive localized deflec- SER: Uzun & Case, Atlanta, GA plan directions, rotation of nearly 0.5 tions and stresses that can result from Atrium Roofs: Thornton-Tomasetti degrees, gravity loads of up to 425 tons the use of temporary supports. The Engineers, New York, NY and net uplifts of up to 163 tons. Work- work of other trades could continue ing together with bearing supplier Cos- below the roof during erection thanks DETAILER mec, engineers developed unique and to close coordination with the engi- Southern Steel Detailers, complex bearings for use on the dome. neers at Williams Erection. Lexington, SC (NISD member) Atop the Grand Atrium dome sits a All together, Thornton-Tomasetti’s 90-ft-wide glass cupola that expands design, Williams’s erection methods, DETAILING CONSULTANT the airy openness of the space. At its FabArc Steel’s fabrication and South- Ferrell Engineering, Birmingham, AL peak the cupola rises 28 ft above the ern Steel’s detailing produced a quick, (NISD member) top of the main roof. The design team methodical system to fabricate, ship, worked to achieve a good balance stage and piece together the structural FABRICATOR among the openness below the cupola, steel, joists and glass systems in only a FabArc Steel Supply, Anniston, AL lightness of structural framing and effi- few months. This allowed time-con- (AISC member) ciency of the roof system. A compres- suming landscaping work to move sion ring at the base of the cupola could ahead under atrium enclosures and have kept it completely open, but the turn a construction site into miniature ring would have needed bulky steel versions of St. Augustine, Key West

Modern Steel Construction • November 2002