The Pedestrian Bridge Prototype Study for the Los Angeles International Airport (LAX) is part of the vision of rebuilding Los Angeles' most important gateway by transforming one of its most prominent structural element. These bridges, located in an area of high seismicity, are envisioned to replace the seven existing bridges that connect the existing parking garage to the airline terminals and range from 122 feet to 161 feet in span. Optimization techniques were utilized in generating the designs. Such techniques have been already successfully applied to structures in the aeronautical, automobile, and mechanical industries where natural force flows are modeled. These fundamental principles of optimization have been used to develop two novel responses to the long-span pedestrian bridge - The Optimized Orthotopic Steel Plate Prototype and the Optimized Truss Prototype. Both designs, though unique and simple, integrate the idea of topology optimization with modular design, resilient materiality, sustainable practices and visual transparency. By focusing the design effort of the bridge on structural optimization and weight reduction, the corresponding seismic forces have been reduced as well. The Optimized Orthotopic Plate Pedestrian Bridge is comprised of a lightweight steel-plated structure from which the walking deck is suspended. The steel material is located where it is utmost required allowing for steel cutouts which also serve as skylight for the bridges. The openings enhance the visual transparency. To minimize the steel material waste, the steel cut outs from the top and bottom plates of the Orthotopic steel deck would be reused to form the diaphragm plates. This approach enhances the sustainable qualities of the design, reducing waste by 12.5%. The Optimized Truss prototype utilizes the full height of the bridge for the structural truss depth, thus structural stiffness is maximized while material volume is minimized. The aerodynamic oval shape maximizes the walking surface while reducing wind loads. The truss members consists of steel pipe sections that are connected at the nodes with welded TYK joints. By virtue of a complete tube section, the truss has excellent torsional resistance and minimizes pedestrian-induced vibration. For both prototypes, the main structural module is expandable in the center, allowing for adaptability to the seven different spans. These forms can be easily prefabricated off site and lifted in place at night causing minimum disruption in airport operations. This paper summarizes the design techniques, prefabrication and connection details for both bridge prototypes.
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