Long span aerial guideway construction
What to expect: Beginning the week of June 17, crews started working night shifts within the I-90 corridor. Night work is necessary to finish the elevated columns and construct the light rail guideway. Work activity will initially be focused near columns four and five (see inset map). Crews will construct the pier table (the structure on top of column that supports the bridge deck) at column five and begin installing a form traveler crane that will be used to construct the long span segmental bridges.
Work hours: Typical work hours are Monday-Friday (Saturday morning) 8 p.m. to 7 a.m., occasional night work may also occur on Saturdays (Sunday mornings). Since much of this work will occur over I-90 and I-90 ramps, crews will frequently need to close lanes below and adjacent to the work area. Due to the lane restrictions on I-90, this work will be performed during night shifts.
Noise: There will be noise from cranes, hydraulic pumps, steel beam erection, concrete trucks and associated equipment while crews set steel falsework, construct forms and place concrete in forms to build the bridge span. Vehicles will utilize broadband backup alarms.
Sound Transit's contractor is permitted to work expanded hours in the I-90 corridor and adjacent to Bellevue Way Southeast, including 24-hour work in this area. The allowable noise threshold is based on average construction noise produced over each one-hour period. There may be moments during an hour when construction noise exceeds the hourly average, but crews will take measures to stay below the average hourly threshold. Please contact East Link outreach with any feedback on nighttime noise. For after-hours issues that need immediate attention, Sound Transit maintains a 24-hour construction hotline.
Traffic impacts: Ramp and lane closures will shift as work progresses. Ramp and lane closures will be communicated in future alerts.
Form traveler construction: Form travelers are frequently used in balanced cantilever cast-in-place segmental bridge construction. This construction method utilizes a pair of form travelers which will be anchored to the top of the column pier cap. One form traveler will be installed on each side of the pier cap. While each traveler is a separate unit, they will operate as a pair. Once the travelers are installed, crews will build bridge sections moving at an equal pace outward from the column. As work progresses on long span bridges, the traveler will be moved from column four to column five and eventually the bridge spans will connect in the middle of the span. When complete, three bridges spanning 245' to 360' will form the East Link light rail guideway over I-90 and the I-90 ramps to Bellevue Way Southeast.
The American Segmental Bridge Institute published an animation which illustrates segmental bridge construction using form travelers.
