The DFW International Terminal D Parking Garage blends technology, beauty, and culture

The new International Terminal D for the Dallas/Fort Worth International Airport (D/FW) operates as the ultimate gateway to the state of Texas. It is an architectural work of art that serves as a model for future airport terminal designs. Similarly, the new Terminal D Parking Garage serves as the perfect gateway to the terminal itself.

Completed as part of a $2.7 billion Capital Development Program, the 3.1-million-square-foot garage provides more than 8,000 parking spaces and is one of the largest parking garages in North America. The structure rises eight levels above the ground with an unusual, elongated octagonal floor plate of 475 feet by 910 feet. Three lines of expansion joints divide the garage into six independent structures that comprise the contiguous parking floor areas and two independent elevator/stair towers. The perimeter of the garage hosts a cascading dual ramp system that is a first of its kind.

Designed around the special requirements of the new international terminal, this state-of-the-art parking facility helps travelers quickly find a parking space and gets them to the new terminal via beautiful landscaping, a sculpture garden, and main pedestrian walkways that lead to graceful cable-suspension bridges guiding passengers to the terminal. Architectural details not typically reserved for parking structures—a durable cast-in-place post-tensioned concrete structure and "smart-garage" technology—make the D/FW Terminal D Parking Garage an unrivaled parking facility. Integral to the distinctiveness and success of the garage are its parking features and aesthetic achievements, but implicit in these assets are structural challenges that were overcome to make the vision a reality.

Prompt parking

D/FW Airport officials requested that the garage allow patrons to easily and quickly find a parking space. With a facility this massive, the latest in parking technology had to be relied upon to realize this directive. To combat the exponential increase in time spent locating a decreasing number of available spaces drivers are guided by means of "smart-garage" technology.

The design team embraced a loop-count system in which the garage is divided into many zones. Sensors embedded in the concrete structure track the progress of vehicles by counting the number of cars passing between the zones. Numerous dynamic message signs, which are located at entry points and throughout the garage, and are fed information from the loop-count system, alert drivers to how many parking spaces are available on each level and in each zone.

As drivers enter the facility, the cascading double express ramp system allows proper visibility of dynamic message boards indicating the number of available spaces on the specific level. This process allows drivers to select a spot close to their gate. The perimeter express ramp system also allows for flat garage floors that let travelers effortlessly find the terminal during their departure and easily find their car again upon arrival. The nature of the ramps allows swift travel between distinct zones, upon which the smart garage loop-count system is dependent.

By drastically reducing the time required to find open spaces, the smart-garage system significantly reduces traffic, along with the resulting vehicle emissions.

Appealing architecture and alluring art

The designers of the D/FW Terminal D Parking Garage used architecture and art to provide patrons with added visual interest while they quickly find a parking space and make their way to the terminal. This experience starts as soon as the exterior of the garage comes into view from the primary entrance off of the main airport thoroughfare. The precast concrete spandrel panels of the garage façade have an angled profile that creates multiple shadow lines. A portion of the precast panels are double-walled to form landscaping planters akin to large, continuous window boxes. The panels are interrupted only at the perimeter ramps, which are highlighted by transparent and translucent polycarbonate panels in an applied curtain wall system that complements the architectural finish of the adjacent terminal.

The "Welcome Wall"— the airport logo marker surrounded by a large bed of manicured landscaping—greets visitors at the main entrance of this vast structure. Inside, the typical bays are 30-foot by 60-foot and are wide-open, well-lit, and safer because of the flat parking levels. After parking with ease, the typical traveler proceeds to one of four air-conditioned moving walkways that serve as beacons within the interior of the vast building. These ferry patrons to one of five core areas housing the elevator and stairs.

The garage’s wayfinding system uses a Texas wildflower theme, such as the bluebonnet or Indian Paintbrush, for each level. In addition to intricate and colorful mosaic-tile designs in the floors, all of the signage on the level ties into its wildflower theme.

Several links take travelers to the Terminal D building. Those running late may choose a more direct route, such as one of the three elegant skywalks connecting the garage and the terminal. However, travelers with time to spare may prefer to enjoy the landscaping and sculptures in the plaza between the garage and terminal. The plaza showcases sculptures on loan from Dallas’ renowned Nasher Sculpture Center. Overhead, a tensile fabric canopy sweeps 200 feet between the garage and the terminal. This signature feature takes the form of an enormous sculpture in its own right that stands guard over the garden below.

Sound structural design

Sound structural design makes possible many of these features and much of the form of the D/FW Terminal D Garage, many of which the public do not see.

The structure consists of a 5,000 pound-per-square-inch, cast-in-place concrete, post-tensioned 36-inch-deep beam and 8-inch-thick slab system with lateral loads resisted by concrete moment frames. These considerations make the structure quite durable. Compared to a typical precast parking garage, the Terminal D Garage will require significantly less maintenance and experience a significantly longer lifespan—features that owners appreciate.

Many of the features that make the garage so user-friendly also presented significant structural challenges to the design team. As an example, the cascading double express ramp system is crucial to the traffic flow in the garage, but it presented some difficulty with the structural detailing of the building and prevented reuse of typical designs on multiple floors in many instances.

Also vital to the parking design of the facility is the smart-garage loop-count system. Miles of conduit lie hidden in the slab to support this system. The conduit shares its place in the slab with the reinforcing steel and the post-tensioning. Precise coordination was required during the construction phase of the project to ensure that the structural system and the smart-garage counting system were carefully integrated within the slab to provide optimal performance of each.

Several of the aesthetically appealing aspects of the facility also represented a structural challenge simply because of the additional loads they imparted on the structure. For example, the heaviest landscaped areas at the sculpture garden plaza and the "Welcome Wall" had to be supported above additional parking levels below. In addition, the sculptures themselves weigh as much as 20,000 pounds each. Each heavily loaded condition had to maintain the requirements of the 36-inch structural depth in order to satisfy clearance and to maintain a well-lit, safe garage. A careful post-tensioned design was used to combat gravity and fulfill the aesthetic design.

Post-tensioning helped to solve other challenges imposed by heavy loading that stemmed from the parking design of the garage. The series of zones that the smart-garage loop-count system relies upon requires a rigid traffic flow pattern. Simply painting the floor does not guarantee that vehicles will pass through specified zone entrances/exits where sensors are located. An intricate network of 6-inch curbs was utilized to control traffic flow. These curbs impart significant additional load to the concrete slabs and beams that complicated their design and again prevented reuse of typical designs in many instances because of the atypical placement of the curbs.

In a few cases, the rigid traffic flow pattern also necessitated inconspicuously moving columns off of grids for one level only. Post-tensioned transfer girders solved this problem without compromising the 36-inch floor depth. Harped tendon profiles were used to efficiently carry the high concentrated load of each transfer column, and a fully bonded, grouted multi-strand post-tensioning system was specified as an extra safeguard for these critical components.

One of the largest structural challenges on the project lay with the signature element of the terminal project: the 200-foot-span tensile fabric canopy. The canopy imparts a sustained lateral load on the structure that required special consideration in the global stability and lateral analyses of the structure, but the greatest challenge presented by the canopy was its attachment to the structure. The canopy’s cables react against the garage structure at 14 distinct locations with loads of up to 220,000 pounds each. The canopy cables connect to 3-inch ear plates that are welded to large, embedded plates that locally transfer the load into the structure. A thick, studded plate and continuous reinforcing bars welded to the embedded face plate serve as the primary mechanism of force transfer, but post-tensioning plays an important supporting role.

The embedded plate extends into the anchorage zone of the post-tensioning, allowing the force from the embedded plate to transfer into the anchorage zone and then into the post-tensioning strands. A post-tensioning force in excess of the canopy reaction is supplied continuously at the center-of-gravity of the concrete section, permitting this mechanism to provide a separate and redundant load path for the entire canopy force. The continuous reinforcement and post-tensioning work together to control cracking and fully develop the force from the canopy reaction across the entire width of the structure.

Innovative structural solutions, such as the method for dragging the canopy force into the garage structure, combined with traditional structural engineering approaches applied in extreme ways allow parking characteristics and aesthetic accomplishments to be featured prominently at the D/FW Terminal D Parking Garage.

A successful conclusion

Quick and easy parking, a graceful canopy, world-class artwork, abundant landscaping, exceptional wayfinding, the ambience of safety produced from the open environment, and many other details catapult the D/FW Terminal D Garage into a league of its own. The goal to transform the chore of parking a vehicle at the airport into a positive, rewarding experience was exceeded by the design team. The D/FW International Terminal D Garage makes parking a pleasant, efficient, and easy experience and is a model for all future large-scale parking facilities to follow.

Joseph Dowd, P.E., is an associate and senior structural engineer and Mike Hsu, Ph.D., P.E., is a senior associate and structural project manager. Both are in the Dallas office of Walter P Moore and can be reached at 214-740-6200.

Design & Construction Team

Project name: Dallas/Fort Worth International Airport Terminal D Parking Garage
Owner: Dallas/Fort Worth International Airport, Texas
Managing architect: HKS, Inc., Dallas
Architect of record: Gresham Smith and Partners, Dallas
Lead structural engineer of record: Walter P Moore, Dallas
Associate structural engineer: Campbell and Associates Consulting Engineers, Dallas
Managing structural engineer: L.A. Fuess Partners, Dallas
General contractor: Austin Commercial, Dallas
Post-tensioning steel provider: Suncoast Post-Tension, Houston

Photo credits: Blake Marvin/HKS, Walter P Moore