08 October 2016

Swedish Bridges: 1. Barnhusbron, Stockholm

I recently visited Stockholm for the 19th Congress of the International Association for Bridge and Structural Engineering. This was a very good conference, but I don't think I'll have time to report it on any detail.

I did get a chance to explore a handful of Stockholm's bridges, and I'll share the photos here over the next few posts.

The first is Barnhusbron (translation: "Orphanage Bridge"), which connects the island of Kungsholmen to the Stockholm mainland. This is a tall highway bridge, some 290m long and 23m wide, constructed in post-tensioned concrete in 1969. The main span is 64.5m.

The bridge is notably taller than the next bridge along the waterway. This is reportedly because of an aborted plan to relocate the riverside Klarastrandslen highway above the numerous railway tracks below the bridge. However, the bridge's height does also allow it to connect directly into the Upper Norrmalm district.

The bridge parapets have been raised in height quite recently, although without taking the opportunity to address corrosion to the original parapet. The alteration was to improve bicycle safety. I have to note that these parapets don't look strong enough to me to survive any significant vehicular impact.

The bridge consists of two prestressed concrete box girders, which from the formwork marks appear to have been cast in-situ rather than precast segmentally. The void between the two girders is used for a number of utility ducts.

The girders are haunched over the main piers, in what I find quite an unattractive manner: the haunches are highly cusped ("pointy"), and the lower edge of the girder overhangs the edges of the pier. This gives the visual impression that forces in the girder are left hanging in mid-air, a defect which would normally be prevented by more careful design of the girder and/or the pier.

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