Behind the scenes: Building the Skyway Bridge
Posted on 02.05.16
Those who like to cook know that sometimes the prep work can take longer than actually cooking the meal. Surprisingly, setting girders on the Skyway Bridge is no different.
The prep work to set girders on the bridge can take up to a week to coordinate and prepare, whereas it can take less than an hour to lift and set the giant girders on the piers.
Here is how it happens:
1. A week in advance of a girder placement, the trucking company that will deliver the girders submits a route permit application to the local jurisdictions. Officials can make sure the route the trucks will take to move the long girders is acceptable.
- If the delivery or placement work requires a road closure, the North Metro team also must submit a method of handling traffic (MHT)
- If major road closures are necessary, overnight work will occur to mitigate traffic impacts as much as possible.
2. Once the trucking route is approved crews will:
- Begin the coordination process to execute any needed traffic control
- Pull the necessary work permits
- Set up equipment rigs
- Perform a quality check on the compressive strength on the pier caps. The concrete in the pier needs to be at least 80 percent of the designed concrete compressive strength prior to the girder set.
3. The night before the girder set, crews load them onto trucks, typically one per truck.
- Girders for the Skyway Bridge vary in size ranging from 118 feet to 170 feet long.
- Oversized trucks can only travel on roads between 9 p.m. and 5 a.m. due to permitting requirements. To minimize impacts to the public, crews will often roll out of the yard at 1 a.m. to the delivery location.
- It would take you 15-30 minutes to drive your car from the storage yard to the delivery site. The same trip will take a truck carrying a girder weighing 60 to 80 tons 1-3 hours.
- Because the girders are so long, they are delivered on a semi with a steerable trailer, which is operated by a driver and a spotter who maneuvers the steerable trailer that the back end of the girder rests on.
4. Crews will already have 1-2 cranes mobilized on site when the girders are delivered. Typically two cranes are used for girder placement, but one crane can be used if girder size or work area constraints require it. For the Skyway Bridge, three girders span between the piers.
- Crews will set the middle girder first to ensure the weight on the pier is equalized and to allow space for chain hold-downs which are required to keep the girder stable.
- Setting each girder typically takes less than an hour, and crews usually can set six in one day.
The first girders on the Skyway Bridge were set in early January. Over the course of the next year, crews will continue to set girders on the bridge.