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Mariposa Land Port of Entry, Nogales, Ariz.

Mariposa Land Port of Entry, Nogales, Ariz.

By American Institute of Steel Construction | May 5, 2016

Photo: Bill Timmerman

Owner: General Services Administration, Region 9, San Francisco

Owner’s Rep: GSA - Design + Construction, San Francisco

*Architect: Jones Studio, Phoenix

Structural Engineer: Bakkum Noelke Consulting, Phoenix

General Contractor: Hensel Phelps, Phoenix

Fabricator: S&H Steel, Gilbert, Ariz. (AISC member / AISC certified fabricator and erector)

Erector: S&H Steel, Gilbert, Ariz. (AISC member / AISC certified fabricator and erector)

*Firm that entered the project in the IDEAS2 contest

The Mariposa Land Port of Entry in Nogales, Ariz., is one of the busiest land ports in the U.S., processing over 2.8 million northbound vehicles each year. The port serves as the entry point to 37 percent of the produce imported to the U.S. from Mexico and was in need of modernization and expansion due to the growth in trade since it was built in the 1970s. Completed in August 2014, and certified LEED Gold, the 55-acre site contains 270,000 gsf of buildings, inspection facilities and kennels for both south and northbound traffic. Total cost was $187 million.

The circulation design consists of four parallel linear zones: a southbound traffic zone; a northbound privately owned vehicles (POV) zone; the oasis; and a northbound commercial traffic zone. The central spine of the port is the oasis, a desert garden which runs the length of the main buildings, and uses landscape to provide respite from the harsh Sonoran climate and from the day-to-day stress of security and border protection. The Sonoran Desert is characterized by huge amounts of rainfall during the monsoon season set against many months devoid of precipitation. The pavement and roof structures throughout the Mariposa campus are designed to collect the rainfall when it is available and convey it to a 1 million gallon underground storage tank until it is needed to support the landscape throughout the year. The large steel scuppers throughout the project celebrate the collection of rainwater and make it visible as an “event.” This was a major contribution to the project’s LEED Gold recognition for sustainable design.

The material palate of steel, concrete and glass at the Mariposa Port was selected to minimize long-term maintenance. The inspection canopies, trellises, and roof structures are constructed of raw, mill-finish steel, protected by a layer of natural rust which adds to the richness of the port as it weathers over time. The natural faced, insulated concrete is designed to be rugged and thermally efficient. A pattern of footprints are cast into the exposed material alluding to the journey and experience of migration and responding to differing program elements throughout the port. The ample glazing around the port is carefully placed to take advantage of garden zones while connecting workers to their adjacent natural environment.

The most distinguishing feature of the Mariposa Land Port of Entry is the amount of exposed structural steel elements throughout the site. The most prominent of these structures is the large shade canopy spanning across the entry to the port. These trusses provide shade from the desert sun, facilitate overhead inspections of vehicles by way of a continuous catwalk, and create the dynamic red, white, and blue threshold of entry to the U.S.

In addition to the port’s entry canopy, each of the main buildings have large structural steel overhang trellises. The extreme length of the two main buildings on the port (over 1,000 feet long) offered challenges for the thermal expansion of the exposed steel from the significant fluctuations in desert temperatures, which can range from winter lows in the 20s to summer highs in the 100s. These shade structures and roof overhang structures all consist of long-span, custom-designed steel trusses carefully articulated to direct rainwater movement. The trusses were designed and detailed in the structural engineer’s office for each span and loading condition as the architecture required different steel shapes than those in typical pre-fabricated trusses. All steel connections are expressed and custom detailed.

The trusses along the largest canopy structure span on average of 64 feet with additional 18-ft cantilevers at each end. The trusses are spaced at 15-ft and 5-ft on center and support 3’ x 18-gage steel decking and hollow structural section (HSS) lattice tubes while accommodating vehicular movement below. The trusses span to and bear on deep custom steel joist girders. The girders span 38 feet and are supported on high-strength structural hollow pipe columns. These girders are nearly 1,000 feet long, transitioning from the inspection canopy, to the interior of the main processing lobby, and back to exterior canopy.

The majority of the custom trusses consist of hollow structural pipe sections for the top and bottom chords and a combination of hollow structural pipe and channel sections for the web members. A large portion of the hollow pipe sections were required to be high strength steel due to the large internal stresses induced. The majority of the steel was fabricated in a steel shop, however some of the longer span trusses were fabricated in sections and assembled on site.

Some of the other unique structures on the port consist of serpentine shade structures for pedestrian crossing at the international border. These structures consist of rigid steel bents spaced at approximately 10-ft on center and made of wide-flange shapes and steel channels. Smaller HSS members infill to create a unique shade pattern.

Construction of the Mariposa Port occurred over four phases, spanning 58 months. The new facility was constructed in the footprint of the previous facility and the team knew from day one that there could be no interruption of port operations at any point during construction. The orchestration of multiple tenant moves became an art unto itself as temporary facilities wove between the new structures. These efforts were further complicated by the reality of needing to keep thousands of semi-trucks rolling through the facility without obstruction. Conceptual phasing plans developed by the design team were refined and implemented by the contractor. The site team worked closely with the port directors to ensure the port remained operational at all times, yet still allowed for construction activities. The Mariposa Port’s primary tenants appointed liaisons to participate in weekly project meetings to allow for a close collaboration with the project team. Not only was the project delivered on time (and some portions early), the project team also was able to accommodate and integrate more than $20 million in tenant-requested added scope without any time loss on the project.

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