Modern Convenience, Timeless Appeal

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Lasting 96 years in a place known for constant reinvention is a feat to be celebrated. Such is the case of the Spanish Revival-style facility at Hollywood Burbank Airport. Though it has gone by many names over the years—including United Airport, Lockheed Air Terminal, and Bob Hope Airport after the late comedian—the facility has always been known for two things: frequent celebrity usage (due to its proximity to major entertainment studios) and a highly convenient traveler experience. Hallmarks of this experience include expedient passenger pickups and drop-offs, short walks to and from gates, and a quick boarding/deplaning process complete with an outdoor walk along the tarmac.

Although the airport’s name changed to keep up with the times, its facilities did not. The size and speed of modern aircraft resulted in new Federal Aviation Administration standards that increased the required safety distance between concourses and runways, putting the airport out of compliance. The nearly century-old facility also lacked exterior space to expand cramped interior spaces with low ceilings and narrow corridors, some only 7-feet wide.

An up-to-date facility was desperately needed.

The new terminal opened last month, exactly one month shy of the 10-year anniversary of City of Burbank voters approving the project. Dubbed “The Icon,” the terminal features a 53% increase in square footage and is dotted with references to Hollywood’s golden age. Some references are subtle, like the perforated metal soffit panels inspired by Marilyn Monroe’s “Happy Birthday” dress. Other references are so obvious they command attention, like the three pairs of exposed, canted V-columns deliberately angled to mimic searchlights used at Hollywood movie premieres.

In addition to its glitz-and-glamour design, the new facility enhances the airport’s beloved convenience. These enhancements are immediately noticeable—drivers who are picking up/dropping off passengers will appreciate the 58% increase in curb space along the terminal, while those who need to park enjoy a much shorter walk: 645 feet instead of 1,675 feet. Once inside the terminal, travelers are treated to expansive two-story volumes and a centralized TSA checkpoint with greatly increased capacity.

Standing in juxtaposition to the airport’s leisurely convenience is the project’s highly aggressive schedule. Design, construction, and opening of the new terminal needed to occur less than four years from project award. Adherence to this schedule required submittal for the superstructure and foundation permit just nine months after award, with submittal for the full building permit following six months after. Design also needed to adhere to the Project Development Agreement approved by City of Burbank voters in 2016, which capped the new facility’s size at 355,000 square feet and ensured the number of gates stayed at 14. With these stipulations in mind, the progressive design-build team got to work.

The new terminal consists of several structurally discrete buildings linked by connectors with seismic expansion joints incorporated. All structures have a concrete slab-on-grade and utilize a shallow foundation system. The four primary structures are three concourse buildings (Modules A, B, and D) and the headhouse (Module C) (Fig. 2).

The concourse modules are one-story steel-framed structures with non-composite roof framing supported by steel columns. Typical roof height for these three modules is 18 feet. The two northernmost concourse structures, Modules A and B, are similar in plan dimensions: lengths are 300 feet and 360 feet, respectively, with widths of 90 feet. The concourse building to the south, Module D, is also 300 feet by 90 feet for the enclosed portion but connects to an outdoor structure used for baggage handling, resulting in an overall size of 300 feet by 200 feet. The baggage structure is single-story with non-composite roof framing supported by steel columns. It is open on three sides and contiguous with the enclosed concourse building.

The headhouse, Module C, is the largest structure. Inside its 750 foot by 240 foot space are several distinct areas, including ticketing, TSA screening, baggage claim, and a central concessions area. It is the only building with a second floor, which is approximately 18 feet above grade level. The roof of the headhouse has a curved form with an apex of 55 feet that extends east to form the entry canopy—the project’s chief architectural element. The curved roof transitions into a flat form to the north and south with heights approximately 39 feet above the first floor. Structural systems for the headhouse consist of non-composite framing for the high and low roofs, composite steel framing for the second floor, and concrete slab-on-grade for most of the first floor. Composite steel framing is used for areas of the first floor located over the basement level, described below. All framing levels are supported by steel columns.

A fundamental grid spacing of 30 feet by 30 feet was established for the column layout during initial design. To create the desired open atmosphere, the design team began looking for strategic opportunities to impact the feel of the space without also increasing project costs.
The gate and boarding areas within the three concourse modules and west side of the headhouse were the first to be studied. By increasing the depth of the roof beams in these areas from W16s to W24s, interior columns were able to be removed, which resulted in a 60-foot span in the east-west direction and a column-free experience for passengers waiting to board. The potential increase in project cost stemming from larger beams was offset by savings related to fewer columns and foundations.

Similar space-saving studies were done for the ticketing and baggage claim areas on the east side of the headhouse. Removing a row of columns in these locations created a 55-foot span that further emphasized the two-story volumes.

The most significant modifications to column locations were made in the central spine of the headhouse, where the barrel-vaulted roof and ceiling reach their highest points. Experienced by both departing and arriving passengers, this highly used, prominent area was designed to house the TSA security screening checkpoint (SSCP), central bar, and food court, as well as a hanging art installation for visual interest. With this in mind, the column grid within the SSCP was expanded in both the north-south and east-west directions to open up what is a commonly congested area in airports. This also provided space for additional TSA security lanes in the future. Enabling removal of the columns are curved W24 roof beams covering 60-foot spans in the north-south direction. The beams are supported by W40 and W36 girders in the east-west direction that allow for respective spans of 85 feet and 69 feet, resulting in a grand, voluminous space (Fig. 3).

Below a large portion of the headhouse (and some of Module D) is a basement with a floor-to-floor height of 15 feet. The basement consists of concrete retaining walls that also act as shear walls for the sub-grade level (Fig. 4). A tunnel to the east connects to the basement of the new six-story parking garage (engineered by Walter P. Moore) and provides a means to change out large baggage screening equipment. The basement lid is a 4.5-inch normal weight concrete slab over 3-inch metal deck. This lid configuration provided several efficiencies, including greater capacity for anchors placed directly in the deck, advantageous vibration performance for the high-traffic TSA checkpoint above, and 2-hour fire rating without the need for added fireproofing.

Developed side-by-side with the construction team, the basement walls were designed to cantilever during initial backfill operations; in their final condition, the walls function as propped cantilevers. Designing the walls in this way required an increase in the footing widths and reinforcing at the soil face, but in turn helped facilitate the aggressive schedule by avoiding the need for shoring. As the first elements constructed in the schedule’s critical path, the basement walls required constant structural attention to assess locations for utility penetrations and reinforcing. Engineers were frequently on site during the early phases of construction in a collaborative effort to keep the project on track.

Residents and airport officials alike wanted a design that anchored the airport to the community and provided a “statement of arrival,” which they found in The Icon design concept. The statement is immediately conveyed to drivers approaching the terminal by the project’s signature architectural element: A sweeping roof canopy that gradually morphs to imitate a classic Hollywood silver screen complete with signage displaying the airport’s name.

The canopy features multiple long spans bookended by cantilever beams at the north and south ends of the headhouse. The largest cantilever is on the order of 65 feet, achieved by a plate girder measuring 56 inches in depth with 3-inch-thick flange plates. At the end of the 65-foot cantilever is a perpendicular curved steel girder truss that serves as the backbone of the canopy. This 110-foot-long truss includes its own 40-foot cantilever span and supports secondary girders extending up to 85 feet from the terminal facade.

Supporting the girder truss is the largest of the three pairs of canted V-columns (Fig. 7) . These 24-inch-diameter, 67-foot- and 45-foot-tall AESS columns connect to a Cast Connex tapered clevis assembly at the base (Fig. 8). With its custom-cast shape, the clevis assembly was chosen over other connection options due to its smooth architectural appearance and ability to ease field fit-up of the large columns to the gusset plate. Anchoring the clevis are steel embeds cast into a pilaster connected to the basement wall of the parking structure.

Managing the thrust forces accumulated at the top of the canted V-columns was critical to the design. The searchlight-inspired angle of the columns introduces a natural instability and added significant complexity to the design. Adding to this inherent instability is a complicated column-to-truss connection that sits 40 feet from the canopy edge, resulting in an unbalanced asymmetrical profile. Providing stability for the V-column assembly is a network of round HSS cross-bracing concealed in the canopy framing, creating a horizontal truss that redirects unbalanced loads back into the headhouse moment frame system (Fig. 9). This cross-bracing is necessary as there are no frames beyond the east curtainwall of the headhouse.

A notable feature of the architecturally striking arrangement of the canopy is its bridging of two buildings with fundamentally different structural systems. On one side is the terminal with steel special moment-resisting frames and proprietary moment-frame connections; on the other, a six-story cast-in-place concrete parking structure utilizing special reinforced concrete moment-resisting frames. The contrasting stiffness, mass, and seismic response of these two buildings introduced substantial complexity in the canopy design.

To reconcile this complexity, the structural design team introduced a 24-inch seismic joint in the canopy to allow for the differential movement between the two structures. The joint is concealed within the canopy between two pairs of V-columns, hiding a team-oriented design decision in plain sight.

The new terminal was designed in accordance with the 2022 California Building Code with City of Burbank amendments. Occupancy and usage criteria required compliance with Risk Category III standards, including a seismic importance factor of Ie = 1.25. The project site is classified as Site Class D. For the seismic design, a site-specific response spectrum was utilized, with design spectral acceleration parameters of SDS = 1.521 and SD1 = 1.042. The structure is assigned to Seismic Design Category D. Although wind loading did not control the design of the primary lateral system, the design of exterior cladding and other exterior nonstructural components utilized a design wind speed of 101 mph and considered Exposure C effects.

Two options were studied at project outset for the primary lateral system: steel buckling-restrained braced frames and steel special moment-resisting frames. Ultimately, the team chose steel special moment-resisting frames due to a significant benefit in facilitating the desired spaciousness and a minimal difference in cost for the system.

The moment frames were placed around the perimeter as much as possible, particularly in the longitudinal direction of the concourse structures. In the concourse’s transverse direction, the frames are found along interior lines when needed to address bare deck diaphragm span limitations and achieve acceptable torsional behavior.

At the headhouse, moment frame locations were carefully selected to accommodate the wider grid spacing, ensure adequate function of various programmed spaces, and support the inherent complexity stemming from additional levels of framing, including the curved high roof. Where moment frame locations resulted in intersecting frames and potential bidirectional column moments, fix-pin “outrigger” beam bays were incorporated to transfer shear force from the beam to the column as axial load and avoid use of cruciform or boxed columns.

The seismic analysis utilized a modal response spectrum analysis. Although not required by code, the modal analysis was considered a more appropriate method to capture the seismic effects distributed across the unique geometry, particularly at the headhouse. Early analysis models incorporated pinned bases at the frames. However, as design progressed, the team opted for concrete grade beams tied into the frame columns at the base of most moment frames. These grade beams provided enough fixity to allow smaller frame members and a reduction in steel tonnage while still meeting drift limits. The initial “baseline” moment frame analysis and design incorporated conventional AISC-prequalified connections. With the baseline established, the team then explored alternative designs comparing two different proprietary connections. After assessing the options, the construction team selected bolted SidePlate connections due to savings in steel tonnage and reduction in installation time.

In addition to completing a code-based design, the owner requested the project team conduct a performance-based evaluation of the headhouse design, separate from the permitting process. The owner’s goal was to determine if the code-based design could provide “Immediate Occupancy” structural performance even though code only required Risk Category III measures be met. This performance evaluation was limited to the primary structural components of the lateral force-resisting system, including the beams, columns, grade beams, and SidePlate beam-to-column connections. A nonlinear static analysis was conducted using the procedures of ASCE 41 and the site-specific response spectrum based on the ASCE 7 design earthquake hazard level (which corresponds to BSE-1N in ASCE 41 terminology). The nonlinear modeling parameters and acceptance criteria for moment frame columns and grade beams were derived from ASCE 41 criteria; parameters and criteria for moment frame beams and SidePlate connections were derived from procedures outlined within ASCE 41 using test data provided by SidePlate.

Utilizing the frame and grade beam layout from the code-based design as the baseline and evaluating that same design against the owner’s performance criteria, the study concluded that the components of the primary lateral system (moment frame beams, columns, connections, and grade beams) meet the Immediate Occupancy structural performance objectives at the design earthquake target displacement. An additional study checked the structural performance at 150% of that target displacement and determined that the components of the primary lateral system additionally meet the Life Safety structural performance objectives of the higher demand level. These performance evaluations concluded the code-based design met the owner’s desire for enhanced seismic performance even beyond Risk Category III code requirements.

Passengers may not notice all the structural complexities of the new terminal, but what they will notice are shorter walks, a plethora of natural light and open space, and an updated sense of place that makes the airport worth the affection it has long enjoyed. Progressive design-build played a large part in realizing the aggressive design and construction schedules, but the largest component of this achievement is the highly cohesive project team that worked together to realize this ambitious design in a high-seismic region. ■

Todd Elayer, SE, DBIA, LEED AP is a Principal and Executive Director with Buehler with extensive design-build experience in the fields of aviation, education, civic, and commercial, where he is known for his creative exploration of structural systems. ([email protected])

Al Schuchard, SE, DBIA is a Principal with Buehler who has successfully delivered many high-profile design-build projects through construction completion, including international airports, civic facilities, and healthcare structures.

Phil Petermann is a Technical Writer with Buehler who got started in AEC performing historic concrete preservation at Alcatraz Island as a student at CSU Chico.