032011 March11 Houstonballet Web

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Vibration concerns set the stage for a new dance facility.

When it opens in early spring 2011, Houston Ballet’s Centeror Dance will be the largest proessional dance company acility in the United States. The sleek 115,000-sq.-t, six-story steel struc-ture will house nine dance studios or the Houston Ballet and its Academy, a 200-seat dance lab, administrative oces, and support spaces. The anticipated nal project cost is $53 million.

Located in the heart o the Theater District in downtown Hous-ton, the Center or Dance was constructed adjacent to WorthamCenter, the theater at which the Houston Ballet has perormedsince 1987. A private-access steel trussed bridge spans 130 t diago-nally rom the Center or Dance to backstage o Wortham TheaterCenter so the dancers can easily walk in costume rom the practiceacility to the perormance stage. The ultra-modern looking bridgeengages the public into Houston’s Theater District, the secondlargest theater district in the United States, as it spans over themain entrance to downtown rom the north.

The new acility will more than double the space that Hous-ton Ballet has had at its home since 1984, a renovated commer-cial building approximately three miles rom downtown. That structure was not designed or foor vibrations resulting rom

dancing, so occupants in conerence rooms and oces were oten

disturbed by vibrations resulting rom dancers leaping overhead. The new prime location, structural design to reduce vibration, andenhanced use o space make the new Center or Dance a tremen-dous improvement or Houston Ballet.

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The use o steel was an ideal choice or the Center or Dancedue to the unique requirements or the acility’s use o space, whichincludes underground parking, a ground-level vehicular drive-through and two-story dance lab, and support spaces, oces, andtwo-story studios or the academy and proessional dancers on theupper levels. These programming requirements resulted in 32 t foor-to-foor heights in the dance lab and studios to enable litingo ballerinas, spans up to 62 t in length, and transerring columnsabove the dance lab to provide a column-ree theater space.

Walter P Moore engineers conducted ull analyses o both aconcrete and a steel structure and determined the steel structure was more economical because o the post-tensioning required ora reinorced concrete structure with the long spans and the expenseo shoring the two-story heights. In addition, the atypical column

grid due to the distinctive requirements o each space would have

By Rachel calafell and KaRim ZulfiqaR, P.e.

MoDeRn steeL ConstRUCtion maRch 2011

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involved the use o many custom built ormsor the reinorced concrete option. Theducts required through the transer girdersand catwalks around the girders would havebeen dicult to accommodate with solid

concrete transer girders, while steel transertrusses have open regions and can be muchnarrower than concrete transer girders.

Double-angle inverted steel chevronbraced rames provide lateral support orthe new steel structure. Typical sizes o thebraces are 2l8×6×5 ⁄ 8 or the 33-t to 40-t spans between columns, and 2l6×4×or the shorter spans. All columns areW14s. The braces are hidden rom view in mechanical spaces, storage rooms, andalong the east wall.

Although all o the upper foors werebuilt o composite concrete raming, a 12-in.structural concrete slab was constructed at the rst elevated level to minimize the foordepth and thereore the amount o excava-tion required or the basement. The extent o excavation was a concern due to the high water table level at the project site.

Levels 2 through Roo Level are con-structed using 4-in. normal-weight con-crete on 2-in., 18-gage composite metal deck.Due to the thickness o the concrete deck, noreproong was applied to the steel raming

members. The roo level was constructed with a composite deck due to the mechani-cal equipment located on it, which is hiddenrom view by means o screen walls.

To provide a column-ree space in thetwo-story dance lab at ground level, two62-t-long trusses were required to transerthe column load rom upper levels to outercolumns at Level 3. Because a dance stu-dio is located on Level 3 directly above thedance lab, the transer truss designs werecontrolled by stiness. The transer trussesare 10 t deep, with W24×335 top chords

and W14×550 bottom chords. A 275-toncrane was used to erect the 50,000 and60,000 lb transer trusses. Due to the build-ing location in downtown Houston and thelimited space on site, the tower crane usedor steel erection was located in the centero the new building.

Some transer truss members had fangesmore than 2 in. thick that were welded with complete joint penetration welds, soultrasonic testing o the steel member and weld material was perormed to veriy that lamellar tearing and other deects were not present at the connections.

Rachel Calaell is a gradu-ate engineer and KarimZulfqar, P.E., is a principal and project manager withWalter P Moore. Both are AISC proessional mem-bers. They can be reached at

713.630.7300.

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Gd Vbra An extensive analytical vibration analysis

was conducted on the foors o the new acil-ity, including the dance studios and neigh-boring oce spaces and conerence rooms,due to the classes and rehearsals o Houston

Ballet that will occur in the studios. Engi-

neers used results rom a time history analy-sis to determine the required compositefoor thickness and girder sizes necessary tolimit vibrations to an acceptable level.

The procedure outlined by AISC SteelDesign Guide 11, Floor Vibrations Due to

Human Activity, was ollowed or areas with



rhythmic excitation. The jumping exercise loading was applied, which is more stringent than the general dance loading. In an eort to balance occupant comort and an economical design, engineersconsulted with the owner to determine the required level o vibrationcontrol or the structure. Optimization strategies employed in the vibration study included alternating the orientation o beams in adja-

cent bays and adding an additional girder in the center o some baysto reduce beam spans. In addition, based on recent industry research,the stiness o ull-height interior partitions was considered in the vibration analysis. Because the partition locations generally coincided with steel beam locations, stiness provided by the partitions wasaccounted or by applying modication actors to the beam stiness.

Without considering foor vibration the weight o the steelor this structure would have been 10 lb per sq. t (ps) to 12 ps.Because o the planned use o the building and its unusually longbay widths, providing the required stiness would have increasedthe steel weight to 22 ps. However, application o these optimiza-tion strategies lessened the required increase in tonnage resultingrom vibration design and resulted in a steel weight o just 16 ps.

For acoustical purposes, some o the new dance lab foors incor-porate foating slabs and the walls include 18 in. o air space orsoundproong.

Ballra Brdg The private-access Ballerina Bridge, a signature element o the

new Center or Dance, spans 130 t across the intersection o Smithand Preston Streets. The bridge is clad with uturistic-looking metalpanels, which have images o leaping dancers lightly screened ontothe top portion, while the bottom portion is slotted or ventilationand or lighting eect at night. Vehicles traveling under the bridgeor pedestrians might glimpse dancers traversing the bridge on theevenings o perormances.

The bridge cross section measures 8 t wide by 11 t tall and theconcrete abutments at each end are constructed on augercast piles. The typical size o the Pratt truss bridge diagonals and verticalsare 2l3×3×5 ⁄ 16. The bridge top chords are W12×26 and the bottomchords are W12×35. Steel moment rames using W12×65 members were provided above each abutment to resolve wind loads perpen-dicular to the bridge span. The 34-ton steel bridge was shipped intwo 65-t-long segments, which were spliced together at the siteprior to liting the bridge into place with two 90-ton cranes.

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Due to the site’s poor soil conditions and the water table being

almost at grade level, 18-in.-diameter, 95-t-deep augercast piles were a more economical option or the project than drilled piers.Proximity o the structure to the neighboring bayou made sitedrainage an important consideration. To alleviate drainage con-cerns, a building setback was incorporated and provisions weremade or a uture stairwell to the bayou.

Several value-engineering items were incorporated in the proj-ect to reduce the construction cost because the original cost esti-mate was approximately 50% over budget. These items includedeliminating a proposed seventh story o the new structure, reduc-ing the size o the foor plan, and selecting a cladding system o 3cm black granite, CMU and plaster on the east wall, and ceramic-etched glass as opposed to other cladding systems considered,

such as wood paneling.

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With its unique architectural appearance and structural eatures,the Center or Dance is an icon in Houston’s Theater District. This state-o-the-art acility allows Houston Ballet to signicantly expand its education and dance training programs and acilitatesits commitment to improving the art orm o ballet on all levels. When the Center or Dance opens in the spring o 2011, HoustonBallet will truly be dancing to a new beat.

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032011 March11 Houstonballet Web

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