Wednesday, March 1, 2023

Beaming over our beams: SR 520 team celebrates Montlake Project’s final girder placement!

By Shoshana Wineburg

This past weekend’s closure of State Route 520 marked a major milestone for the SR 520 Montlake Project. Crews set in place the project’s final 37 girders. Thirty will support a new bike and pedestrian bridge over the highway in Seattle’s Montlake neighborhood. The other seven will support new bus and carpool ramps to and from the highway lid we’re building in Montlake.

These 37 weren’t any old girders. They marked the last batch of the 513 total girders crews have placed for the entire Montlake Project!

Wait a second. … what’s a girder?

Girders are beams that support the weight of what’s above – essentially the foundation of a crossing. A log placed over a creek is a girder that supports your weight while you cross.

With more complex structures, like bridges and highway lids, girders support the weight of the concrete deck slab above, plus the weight of soil and plants atop a landscaped lid’s deck, plus the weight of traffic and people moving across the structure. Girders keep bridges standing and people safe.

Girders can come in different shapes, sizes and materials. On the Montlake Project, they are made of reinforced concrete and most have an I-beam shape.

The girders are precast, meaning they are built off site, loaded on trucks and delivered to the work site, where cranes lift and lower them into place.

A worker checks steel rebar alongside massive concrete girders that will support the deck of a landscaped lid over SR 520 in Seattle’s Montlake neighborhood

What’s the purpose of the direct-access ramps?

This past weekend’s work included placing the seven girders that will support the Montlake Project's direct-access ramps. These ramps will give buses and carpools a separate, dedicated lane on and off the Montlake neighborhood’s new, three-acre lid and its regional transit hub. Rather than using SR 520’s existing on- and off-ramps in Montlake, the new ramps will provide transit, vanpools and 3+ carpoolers direct access to and from the highway and reduce travel times for commuters. The direct-access ramps, together with SR 520’s new HOV lanes, will give bus riders and carpoolers safer and faster trips between Seattle and the Eastside.

Why a bicycle and pedestrian bridge?

The remaining 30 girders set this past weekend are a key step in completing a much-anticipated bicycle and pedestrian bridge over SR 520 just east of the lid. This new crossing exemplifies our commitment to building a multimodal SR 520 corridor that serves all kinds of users and reconnects communities severed by the highway’s construction in the 1960s. The bridge will connect to the existing 520 Trail and provide a welcome alternative to crossing the highway along busy Montlake Boulevard.

Like the Montlake lid, the shared-use bridge will be landscaped. We’ll plant almost 15,000 plants and shrubs, including wildflowers and wild berries. And the paths leading up to the bridge will be lined with dozens of trees.

An interesting historical context precedes these new plantings. Before we first built SR 520 through Montlake 60 years ago, the footprint of the new bike and pedestrian crossing was part of the Washington Park Arboretum. Crews removed about 300 trees to make room for the new highway. Many of these trees were replanted in other locations, including 30 cherry trees that found a new home in the University of Washington Quad. Yes, those cherry trees.

In the foreground are the 30 girders placed over the Feb. 25-26 weekend for a bike/pedestrian bridge across SR 520. Further west are seven girders set in place for bus and carpool ramps to and from a regional transit hub we are building on the three-acre Montlake lid.

Where did the rest of the girders go?

Nearly half of the Montlake Project’s 513 girders – 225 of them – are in place on a 1.2-mile-long bridge we’re building over Union Bay. This structure, built to current seismic standards, will carry three lanes of eastbound traffic from Montlake to the SR 520 floating bridge. The project’s remaining girders support the three-acre Montlake lid.

At right is a new, seismically resilient bridge being built for eastbound SR 520 traffic. After it opens, the parallel span to the left will revert to a westbound-only bridge. In the upper right is the SR 520 floating bridge.

We expect to complete all these structures by the end of 2023. So there’s much more celebration to come!