| The Susquehanna Area Regional Airport Authority (SARAA) selected PB as a key member of its design team for the New Terminal Project at Harrisburg International Airport (HIA). We were nearing completion of our design for this project, which included renovation and expansion of the existing terminal when the terrorist attacks occurred in the U.S. in September 2001. Later that month, SARAA, the project’s architect, and multiple PB specialists developed a schematic design for a new terminal building that would accommodate enhanced security measures while still providing the desired increase in capacity at the airport. Based on these efforts, we were asked to provide structural engineering design and construction drawings for the eight-gate new terminal building that was planned as part of the airport’s overall expansion and improvement program (Figure 1).
From the start, our team recognized that the key to project success was coordinating the space requirements of extensive security-related systems (including baggage handling) with those of other building systems. From early on, we focused on the accuracy and compatibility of our drawing files to facilitate file-sharing and design integration.
Design Challenges
While the majority of the structural elements used for this project 1 are very similar to those found in “high-end” commercial or institutional structures, three areas in particular provided opportunities for design of systems that are less typical:
- The large basement area, where there are widely varying groundwater levels in the surrounding soils
- The approximately 35-m (115-foot) long by 9-m (30-foot) wide elevated pedestrian bridge
- The large, featured, double cantilevered roof area.
Figure 1: Architect's computer generated rendering of new 8-gate terminal. |
Basement Area. The location and geology of the site adjacent to the Susquehanna River presented us with one of the project’s major design challenges, as we had to address a variable and potentially high groundwater elevation. The total area of the basement totals 8820 m2 (98,000 square feet), and would house mechanical and electrical equipment, baggage security screening functions, and baggage sorting. The design and detailing of basement walls, wall footings, basement floor slab, and column footings below the basement slab were coordinated with the detailing requirements of the waterproofing system that completely encases the basement.
In addition to the waterproofing system, a drainage system covers the entire perimeter and the underslab surfaces of the basement to prevent the groundwater from creating uplift pressure on the basement slab. Water collected in these drainage systems is diverted to several large sealed sump pits in the basement and removed from the building with sump pumps.
As an additional precaution against slab uplift, the team designed the basement slab as a two-way spanning slab anchored to the basement walls and column foundations. This slab and anchorage system were tailored to resist uplift water pressure based on the ground water at a level of at least 0.6 m (2 feet) above the basement floor slab but not more than could be safely offset by the structure’s dead load.
Figure 2: Elevation view of pedistrian bridge truss. |
Pedestrian Bridge. A “through truss” structure spans the full length of the pedestrian bridge that links the new terminal to a proposed new parking structure and multimodal transportation facility (MMTF). It bears on and is braced to steel columns at the perimeter of the terminal. The columns are supported adjacent to the MMTF by an integral steel moment resisting frame. The main bridge consists of floor and roof structures similar to the typical terminal construction supported by the bottom and top chords, respectively, by parallel, 35-m (115-foot) -long steel trusses. The truss design utilized the full available depth between the floor and roof, placing the wide-flange steel member chords 4 m (13 feet) apart with wide-flange steel web members arranged to form a modified Pratt truss 2(Figure 2).
Roof. The most noticeable architectural feature visible from airside is the significantly cantilevered end of the curved roof over the central area of the building. Project architects, the Sheward Partnership of Philadelphia, proposed that the curved roof form a cantilever approximately 5 m (15 feet) as it tapered toward the southeast edge. They asked us to identify a system that would allow the southwest and northeast edges to remain column free.
Figure 3: Cantilevered roof truss. |
Figure 4: Aerial photograph of HIA new terminal near completion. |
To achieve this objective, the structural engineering team developed a system comprised of an approximately 30.5-m (100-foot) -long, 1.4-m (4-foot-9-inch) -deep truss extending from the southwest edge of the roof toward the northeast edge. The truss is supported by two symmetrically located columns spaced 12 m (40 feet) apart and cantilevers 9 m (30 feet) at each end (Figure 3). This truss and the two noted columns provide support for members that cantilever toward the southeast edge of the roof. This roof area is clearly visible as the near edge of the curved roof in Figure 4.
Design Management and Coordination
Coordinating Elements of the Project. Design of any architectural structure involves identifying the space requirements of the various systems needed to make the structure function, including telecommunications, electrical and plumbing services, heating, ventilation and air conditioning (HVAC) and other elements. Unique to the airport terminal, coordination was also needed for the baggage handling and baggage security screening equipment.
The original baggage handling system design for the new terminal called for four conveyors to direct bags from the ticketing area down through penetrations in the ground floor structure to bag sorting and security screening equipment in the basement, and prepared for up to four conveyors to the bag make-up room and up to three conveyors to hand search screening areas, all returning up through the ground floor.
The positions of these openings and the paths of all of the conveyors were critical team coordination issues that were more readily evaluated and resolved by electronically overlaying AutoCAD files produced by all disciplines. The final baggage handling layout was modeled using the 3D capabilities of AutoCAD and referencing the previously coordinated plans developed by PB and the project’s architects.
During the design process, the effort of the HIA terminal team to maintain well coordinated drawings was enhanced by sharing electronic drawing files regularly. Plan drawings for all disciplines were developed as full scale models sharing a common coordinate system. To facilitate coordination with adjacent projects and to facilitate field survey layout of the terminal, the new terminal plans for all disciplines were tied to the Pennsylvania State Plane Coordinate System. We could easily determine open shaft area requirements and positions of mechanical equipment by inserting a file created by another discipline as a reference to the structural drawings.
This ability became increasingly important when the airport leaders determined, after construction was well underway, that additional facilities were needed. These included additional ticketing positions and an additional baggage conveyor that would travel from the ground floor to the basement. To accommodate this request, the baggage handling system consultant incorporated the additional conveyor into its 3D model by working with our team and the architect to find the optimum path through the ground floor framing.
Coordinating with Other Projects. The new term inal design needed to interface wi th adjoining projects that were being designed simultaneously and would be constructed simultaneously with the new terminal. On the airside, we coordinated the architectural design, passenger boarding bridge locations, and arrangement of emergency exit stair towers and, thus, the foundations and structure for each of these with the airplane parking and apron pavement layouts. On the landside, the de sign was required to interface with th at of a new roadway, curbside drop off area, and the MMTF.
After discussion with the MMTF design team and the architect for the new terminal, we identified locations for the two columns that support the end of the bridge that adjoins the MMTF. These locations, which placed the columns within 1 m (3 feet) of the MMTF perimeter column line, were chosen so that columns for both structures would be supported by single foundations, basically eliminating the potential for differential settlement at the interface. This relationship resulted in the need for very careful coordination of the layout, design, and construction of these foundations. To achieve this coordination, we provided the working load combinations for the bridge columns to the MMTF engineer for use in the design of pile groups and caps that would each support one MMTF column and one bridge column. We then verified that design and incorporated it into our construction drawings.
Summary and Thoughts for the Future
The HIA New Terminal Project provides a vivid example of the design and coordination advances that can be made by following established project standards for the use of electronic drawing tools. Of equal importance is the diligence and consistency of the design team in distributing current drawing information on a regular basis. Our team and the various teams that we interacted with distributed files by a number of methods, including overnight delivery of files recorded on CD, copies placed on the PB wide area network (WAN), attachments to e-mail, and the use of file transfer protocol (FTP) sites owned by PB2 and other team members.
While each of these methods of transfer served the needs of the design team, each had disadvantages, including the time and costs involved, limitations on file size, and the need for a specific communication to be sent to each team member who needed a given file.
Web site tools, such as ProjectSolve2, now provide a significantly more effective and efficient method of organizationing and sharing information. ProjectSolve2 provides a location where current information is stored and can be accessed by any authorized team member, and it can send automated notifications to all authorized team members when new information has been posted. These functions alone make a project Web site a valuable tool for all projects that involve team members from several PB offices or outside of PB. |
