Dallas Convention Center

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Dallas Convention Center
Dallas, Texas

Datum Engineers, Inc. is the structural engineer of record for the Dallas Convention Center expansion Phase I, Phase II, Phase III and the latest Phase IV Expansion.

PHASE IV
Owner: City of Dallas
Design Architect: SOM Chicago
Architect of Record: HKS
Structural Engineer: Datum Engineers

2003 AISC Engineering Award of Excellence
Award of Merit

Consulting Engineers Council of Texas 
Eminent Conceptor Award


The Dallas Convention Center Expansion and Renovation 2002 is the largest column free expansion space in the world, incorporating the latest technology and designs for convention centers.  SOM created a unique and world class architectural design.


Phase IV has all the same coordination problems due to spanning streets and Dart rail lines.  The foundations were coordinated to miss the street, rail lines, and major known existing utilities.  The contractor encountered several unknown structures buried in the site, creating conflicts with the foundations, requiring creative structural modifications.

The exhibition floor is a 400' x 400' column free space design to support 350 lbs. per square foot live load.  The roof is a structural steel frame hung from 2- 400' twin 50' tall  parabolic arch trusses constructed from a 4'- 0" diameter x 1_" to _" thick pipes.  At the ends of each parabolic arch is a 5'- 0" x 2" thick connection sphere tying it to the connection truss.  The exhibition floor is protected from vibration from six roadways and four train lines below by spring isolators.  The entry is created by a 900' long x 85' tall structural-architecturally exposed concrete wall.  The wall incorporates many structural design features to control the architectural finish and to control cracking.

Special Signature Concrete Wall Design Features Include:
•    Special pour sequence of the concrete
•    Specific detailing of the reinforcing
•    Concrete control joints to control cracking locations
•    Special concrete mix designs
•    Flexible foundations to release stresses in the wall

PHASE III
In 1986, Datum was selected by HLM Design and LMN Architects as the structural engineers for the Phase III expansion and an elevated vertiport.  The elevated vertiport was to have a 360 foot runway that would accommodate VTOL aircraft weighing 46,300 pounds.

The foundation of Phase III got more complex as the expansion proceeded westward toward the shale found in the Trinity River bottom. Therefore, the east end of the structure is supported on limestone and, as the limestone became thinner to the west, the foundations were drilled through the limestone and founded in the shale.  Special testing was required to identify the exact location where it would be required to drill through the limestone.

The roof system had to satisfy several constraints. Convention planners required a spacing of 120 feet between columns in the exhibit hall, and future expansion plans required these spans to be maintained at the perimeter of the building. Efficient mechanical design required a major air conditioning system to be centered on the roof of each exhibit hall. The combination of long spans and heavy loading indicated structural steel trusses for the primary structural frame.

All roof elements, including ductwork and other building services, had to be 35 feet clear above the exhibit hall floor. To minimize the overall building height, it was desirable to run the ductwork through the trusses.  Warren trusses were selected to provide adequate room for the major ducts. The Warren trusses also provide an attractive appearance for the roof structure, which is visible in the completed building.

The optimum spacing between trusses was determined to be 30 feet. Spacings of 20 feet and 40 feet (both equal divisors of 120 feet) were studied, and each resulted in increased steel tonnage. A benefit of the 30 foot spacing is that it matches the planning module for convention layouts, and corresponds to the layout of service boxes in the exhibit hall floors.

Bracing trusses are provided at a 30 foot spacing to stabilize the major roof trusses, for both gravity and wind uplift loading. These bracing trusses also support the roof joists, which are located at panel points to eliminate local bending in the truss chords.  Finally, the bracing trusses resist cladding reactions at the bottom chord elevation, thereby minimizing the vertical span of the cladding.

After consulting with steel fabricators and erectors, the steel trusses were limited to 14 feet depth, to allow unrestricted highway transportation.  Erection splices would allow the trusses to be transported in 60 to 75 foot sections.  The top chords of the trusses are sloped to provide roof drainage, while the bottom chords are horizontal.  All trusses are cambered to compensate for dead load deflections.

The final scheme consists of structural steel trusses with spans of 80 to 150 feet, and a 30 foot spacing.  The trusses support 24” deep steel joists spanning 30 feet.  A 3” metal deck spans 15 feet between supports, and an acoustic liner was included to control helicopter noise.  This scheme is shown on the attached plan.

Design loads include the dead load weight of the building components, 20 psf roof live load, a 10 psf hanging load allowance for exhibitors, wind loads and the effects of temperature.  Over the center bay of each exhibit hall is a 10,000 square foot fan room, containing all the HVAC equipment for the building.  Lateral forces are resisted by the concrete columns, which act as cantilevers from the exhibit hall floor level.

Due to the long spans for the roof, we were concerned about designing the trusses as simple-span.  While this solution allows the most efficient erection of the roof structure, we were concerned about the long-term effect of rotational movement at the truss supports.  This lead us to study making the trusses continuous and the connections rigid.  This solution makes more efficient use of materials, reduces live load deflections and eliminates rotational movement at the supports.  However early analysis ruled out the use of fully continuous trusses.  Chord connections at the supports would need to transfer the full axial capacities of the chord members, which were too large for economical connection detailing.  Lateral stability of the bottom chords was also a concern for fully continuous trusses.

The solution became clear. We should design the roof trusses to be simple-span for dead loads, and continuous for live loads and wind loads. The benefits of this solution are several.

1.    Straightforward erection, since members are simple-span
       for dead loads.
2.    Reduced quantity of materials, due to continuity
       at the supports.
3.    Reduced deflections, again due to continuity
       under long-term loading.
4.    Manageable chord forces at the support connections,
       since no dead load chord forces are transferred through
       the connections.
5.    No stresses in the chord connections under
       long-term loading.

The average weight of the roof structure (away from mechanical room area) = 9.2 lb./sq.ft., which represented a 12% reduction in tonnage of steel resulting from continuity.   This weight includes primary trusses, secondary trusses, bracing trusses, OWSJ and bridging.

Detailing of the roof structure went smoothly, with clear and open communication between the fabricator’s steel detailer and the structural designer.  The roof structure was erected using a mobile crane operating on a grillage system on the exhibit hall floor.

The result is a convention center which satisfies all the objectives of the design.  The roof structure is economical in its design and was efficient to construct.

PHASE II
In 1978, Omniplan commissioned a joint venture of Datum and Skilling, Helle, Christansen and Robertson as the structural engineer for the Phase II expansion that continued west over Griffin Street.  This expansion cost $34 million and added 400,000 square feet to the Convention Center.

All of the basic parameters established in Phase I were established for the structural design except one. After having six years of experience operating Phase I, the Convention Center management stated that they felt they could accept a smaller column spacing than 300’-0” x 300’-0”.  Datum designed a box truss and bar joist roof with spans of 90 feet and 120 feet.  This design was compared to the original 300 ft. x 300 ft. structural steel space truss and a savings of over $1,500,000.00 or over 4% of the total budget was realized and accepted by the Convention Center.

The 1978 expansion had several major structural considerations that the Phase I expansion did not have.  The floor was still to be designed for a 350 psf live load but the structure had to span 140 feet over Griffin Street and 115 feet over Ceremonial Drive.  This required major post-tensioned beams and girders to accomplish this requirement.

This project was featured on the cover of Engineering News Record and was recognized by The State Chapter of the Consulting Engineers Council as the outstanding engineering accomplishment of the year.

PHASE I
Datum Engineers have been actively involved in the design and maintenance of the Dallas Convention system since the first phase was designed in 1968.  The first phase was a 1,000,000 square foot $31 million addition to the Memorial Auditorium completed in 1973.  Datum performed local associate work on the Phase I project for Harrell and Hamilton Architects.  Datum designed the canopy of the escalator and all of the tall window mullions along with miscellaneous change order support.

During the design of the original Phase I project, several basic operational and functional decisions were made that impacted the structural design.  Some of these were:

1.    The floor would be designed to support 350 psf
       superimposed live load.
2.    The building module would be 30’-0” x 30’-0”.
3.    Electrical conduit would be installed in the structure with
       a pull box at 30’-0”x 30’-0”.
4.    The roof was designed as a space truss with columns
       spaced at 300’-0” x 300’-0” to provide maximum
       flexibility for the users of the space.
5.    The column spacing in the parking garage below the
       exhibit floor was established at 30’-0” x 60’-0” which
       moduled with the pull boxes cast in the floor at
       30’-0” x 30’-0”.
6.    The finished floor would be a 2 _” thick concrete
       topping slab.
7.    The exterior walls were to be sandblasted architectural
       exposed concrete walls.
8.    Hanging load capacity from the roof structure panel
       points for the exhibitors was established at 10 psf
       over and above the code roof live load.