The Steel-Framed Arched Roof of Dallas' American Airlines Center Is As

Arch hActionAct Arc ion

David A. Platten, P.E., hen American Air- 2,000 premium seats and three restau- and Lee W. Slade, P.E. lines Center opened rants. Located north of the historic Dal- with an Eagles con- las West End and east of Interstate 35E, cert in July 2001, the arena anchors the mile-long, 60- it captivated fans, acre, “Victory” development, an Wmedia and the community at large. The 8 million sq. ft, master-planned enter- center is the latest jewel in Dallas’ tainment, office, retail, hotel and resi- growing list of world-class civic build- dential complex. ings. Home to the NBA Dallas Maver- The rectangular arena building icks, the NHL Dallas Stars and other measures 390 ft by 500 ft, and is entertainment events, the new building bounded on all sides by city streets at headed off efforts by suburbs to attract the main concourse level. Signature the teams away from downtown. Its arches define the building’s four entry crossed-barrel-vaulted roof structure points, while minor arches define the The steel-framed inspires “wows!” as fans admire the building corners at street intersections. graceful arch that spans 140,000 sq. ft Canadian brick and glass are the pre- arched roof of Dallas’ with a structural depth of close to 13 ft. dominant façade materials, with lime- The American Airlines Center is a stone accent bands and granite American Airlines multi-purpose arena that seats 19,200 integrated into the design. Center is as skillfully for NBA basketball, 18,500 for NHL hockey and 20,000 for center-staged ORIGINALITY AND articulated as the events such as concerts and convoca- INNOVATION tions. The seating bowl incorporates The structural steel roof-framing action beneath it. 138 private luxury suites on two levels, system is a unique and economical re- separated by a club level featuring sponse to a complex architectural roof

Modern Steel Construction • November 2002 Opposite: The American Airlines Center anchors a 50-acre planned development.

Left, top: Front façade under construction.

Left, bottom: The roof structure was erected using four temporary erection columns.

Seats 18,500 hockey 19,200 basketball 20,000 concert Sports Teams NHL Dallas Stars NBA Dallas Mavericks Construction Cost $212 million Area 840,000 sq. ft Clear Roof Span 330 ft × 430 ft

shape. The American Airlines Center building was effectively shortened ■ A mix of structural steel, concrete demonstrates that this form can be by 15 ft, resulting in structural masonry units, cast-in-place con- structured economically using struc- frame-cost savings of an estimated crete, and site-cast concrete arch tural steel, but with a twist. $2 million, as well as savings in panels are used to support the com- ■ Walter P. Moore added an external, building façade and mechanical sys- plex building façade. The architec- post-tensioned-concrete tension tie tems. The design also provided a tural plan and elevation definition embedded in the upper-concourse long-span roof erection method that of the façade is highly articulated, floor framing to economically pro- was simple and safe. and does not dimensionally relate vide the lateral resistance usually ■ An innovative show-rigging sup- well to the interior floor plates. To provided by buttresses in tradi- port system is integrated into the resolve these incompatibilities, engi- tional barrel-vault construction. roof-truss design to improve econ- neers developed a cladding support This unique mix of structural steel omy, safety, aesthetics, and to system that stacks all load from the and post-tensioned concrete results streamline building operations. By full height of the façade down to the in a design that takes maximum ad- establishing a truss spacing of ap- ground level. Brick is supported vantage of the structural depth cre- proximately 11 ft, and designing the using load-bearing, grouted con- ated by the arch shapes of the truss bottom chords to resist rigging crete masonry units, which were cross-vault form. loads along their length, the engi- placed in plan to easily follow the ■ Internally tied structural systems neers eliminated the need for a sep- brick. Structural steel tubes and have been utilized on many recently arate rigging grid. This integrated wide flanges support window completed NBA/NHL arenas. solution provides riggers with safe walls. Brick arches are supported on However, the application of such a and easy access from the catwalk arched, site-cast concrete panels. system typically requires that the system, which in turn enables the Three site-cast concrete panels, building height be increased to pro- center to attract and prepare for a erected to form a true arch, support vide unobstructed fan sightlines. By variety of show events. the four large entrance arches. The using the external tension tie, the

Modern Steel Construction • November 2002 vault radius was flattened between the corners, and its apex was raised slightly relative to the short-side vault, resulting in the definition of a central framing rectangle 110 ft by 210 ft. The primary load-carrying structure is a “table-top” system: Four primary trusses occur at the perimeter of the central rectangle, or “table”; and four “leg” trusses extend from the corners of the rectangle at the valleys to the tension-tie elevation at the upper-con- Schematic view of the steel framing for the barrel-vaulted roof. course level. The externally-tied, roof-framing system allowed a column-free span of 330 ft by 430 ft to be framed with trusses having depths of only 13 ft. This shallow depth allowed for shop- welded fabrication of the trusses and shipping of complete truss sections in lengths of up to 60 ft, saving both time and money. The apex elevations of the two inter- secting vaults differ by 5 ft, with an av- erage elevation 65 ft higher than the tension tie at the upper concourse level. This large structural depth, combined with the stiff 14 ft by 2 ft concrete tension tie, resulted in an extremely stiff roof structure. As planned, the long- span roof deflected only 3 in. when the four erection towers were removed. Collaboration between the archi- tects and engineers resulted in simplification of the building geometry A view of the completed American Airlines Center. without compromising the desired roof form.

three-piece, site-cast arch is, in turn, framed economically using readily STRUCTURAL COMPLEXITY supported by cast-in-place concrete. available techniques and materials. The cross-vaulted exterior architec- ■ Innovative pour strips in the five In the original architectural design, tural roof design presented a complex levels of reinforced-concrete con- the cross-vault intersection occurred at structural engineering challenge, but courses eliminated the need for ex- a common elevation at the center of the the problem was complicated by addi- pansion joints in the huge building, building. Given the rectangular plan tional architectural constraints. First, reducing costs and improving the form, this resulted in very complex the interior form of the roof needed to efficiency of construction. Pour vault radii and intersection conditions. match the exterior form. Second, inter- strips were located at the mid- At the structural engineer’s suggestion, nal tension ties were discouraged, even length of each side of the building, this geometry was greatly simplified if unobstructed sightlines were pro- dividing it into four quadrants. The by the architect without compromising vided. Last, no catwalk or rigging strips allowed the contractor to the desired roof form. This approach framing was to be suspended below speed construction by constructing saved money and improved the build- the bottom chord of the roof trusses. and sequencing four separate building’s function. To standardize truss The ingenuity of the roof’s struc- ings, which were then intercon- shapes and simplify truss connections, tural-steel design solution lies in how it nected. cross-vault intersections were estab- simply satisfies these complex and com- lished at 45 degrees with matching peting structural criteria without com- SIMPLIFICATION WITHOUT vault radii in the corners of the build- promising economy or functionality. COMPROMISE ing. This created framing in the corners Integration of a radial-building grid The American Airlines Center de- that was symmetric about the valleys for the arena-seating bowl into a rec- sign illustrates how a complex architec- and was identical in all four corners, tangular building geometry further tural roof form can be simplified and which improved economy and con- complicated the design. Rectangular struction simplicity. The long-side public spaces located in the lower lev-

Modern Steel Construction • November 2002 els of the building occurred directly was completed on the original sched- below upper-seating sections, resulting ule. Construction cost savings of over in column placements that were not $2 million were achieved through the vertically compatible through the use of the innovative, structural steel building. Many upper-level columns roof. had to be creatively and economically No one can visit The American Air- transferred to match lower-level col- lines Center without appreciating that umn positions. Non-uniform seating engineering excellence in steel was a sections caused by the unique building crucial element of the building’s geometry complicated the raker beauty, function and success. beams. In some cases, adjacent raker beams were offset both in plan and David A. Platten, P.E., is Managing in elevation. Director of Walter P. Moore’s Dallas office. The desire to create an intimate set- Lee W. Slade, P.E., is Executive Director of ting in the bowl required the seats and Walter P. Moore’s Structural Engineering seating levels to be as close to the event Group. floor as possible. This imposed con- OWNER straints on the structural depth at the Hillwood Development Corporation, front of each level. These challenges Dallas, TX were met with a series of solutions: at- tachment of pre-cast fascia panels to DESIGN ARCHITECT the end of a 6-in. cantilevered slab at David M. Schwarz/Architectural the suite levels; and use of raker beams Services, Inc., Washington, DC at the club and upper-concourse levels, PRODUCTION ARCHITECT which support the first seating riser HKS, Inc., Dallas, TX from behind, instead of from below. STRUCTURAL ENGINEER EXCEEDING THE OWNER’S Walter P.Moore, Dallas, TX NEEDS ASSOCIATE STRUCTURAL The owner’s goal in building The ENGINEER American Airlines Center was “to cre- Charles Gojer & Associates, Inc., ate an atmosphere that is people Dallas, TX friendly, attractive and fills the community with civic pride.” The redevel- CONTRACTOR opment of a brownfield site has Austin Commercial, Inc., Dallas, TX transformed an eyesore into a city icon FABRICATOR AND DETAILER and clearly meets the needs of the North Texas Steel Company, Fort owner and the City of Dallas. Worth, TX (AISC member) Revenue from naming rights and STEEL ERECTOR advertising exceeded all projections, al- Derr Steel Erection Company, lowing the owner to increase the origi- Euless, TX (AISC and SEAA member) nal construction budget to include many unplanned amenities. Despite SOFTWARE the additional project scope, the center SAP2000

Modern Steel Construction • November 2002