SDOT answers questions about the work platforms on the West Seattle Bridge
Work platforms were raised up beneath the West Seattle Bridge on Monday morning July 20 as part of the Seattle Department of Transportation's (SDOT) efforts to stabilize the now damaged structure. It's been closed to traffic since March 23 when serious shear cracks were found to have grown longer and wider making the bridge unsafe for vehicle traffic.
The platforms will give workers access to the outside of the girders that form the bridge so that carbon fiber wraps can be applied. These wraps are extremely strong with a very high strength to weight ratio. The consist of carbon fibers in threads that form a kind of thin blanket or wrap. These wrap are then either soaked in epoxy or bonded to the surface with it giving the structure much higher tensile strength and crack resistance.
SDOT answered some questions for Westside Seattle about them.
The two platforms will be in place through tomorrow (or will they remain until next week to be then lowered and re-raised?)
We expect to lift the remaining platforms early morning Monday, July 27 (with some work possibility continuing the next day). Before that occurs, we will need to transfer the current platforms to the final rigging and remove the load from the winches so we can move them along the bridge. We then need to move the winches to the west side and make preparations for the last two platforms.
Were winches used to raise them on top of the bridge?
Yes, four winches were used for each platform resting on the bridge deck.
How big are the platforms?
52’10” x 60’
What are they made of?
Structural steel beam and corrugated metal decking
How many people will be on them during the process?
Up to 10 each
Will the carbon fiber wrap be applied in a criss cross pattern (as your previous example showed? How many layers are planned or optimal?
We do not expect to apply it in a criss-cross pattern.
Will you use a technique similar to what the State of Texas DOT tried in which small bore holes are drilled and the material “fanned out” at the surface wot provide up to a 50% increase in tensile strength?
Our contractors do not have access the contract documents for the project you are referencing.
How will you test the bridge load capacity to determine if the reinforcement worked?
We will repeat all the load testing we performed prior to any work at regular intervals during and following stabilization.