PROJECTS Bridges ALSF 16L
Retained by the FAA, BPA designed the ALSF (Approach Lighting System with Sequenced Flashing Lights
) bridge project that supports the runway landing lights for Runway 16L at the SEATAC International Airport.
The total length of the system is about 730 m (2,400 ft), in which two 183 m (600 ft) long bridge segments are required to span over Interstate 528 and environmentally sensitive wetlands north of the airport.
In order to optimize the structure, a wind tunnel test was conducted to more closely understand the actual wind effects on the structure. As well, a time-history analysis was conducted in order to predict the performance of the system in an earthquake likely to occur in the Seattle Area. The time-history analysis subjects a computer model of the structure to a simulated earthquake. These tests resulted in savings of 15% on the structure weight for the two 183m (600 ft) long spans.