New Zealand's Bridges: Port Hills Overbridges across Route 73 in Christchurch (2)

March 2011 (-43.573 Degrees, 172.695 Degrees) Port Hills Overbridges 

 

I took this photo of the Port Hills Overbridges while standing between the bridge decks.

At-grade road crossings require a stop sign, a traffic light, or a traffic circle. However, if one of the roads is an expressway you need to separate them with a bridge (or maybe a tunnel). If they are both expressways, you usually need an interchange.

Typically, to carry vehicles onto a bridge you can use mounds of earth (embankments), retaining walls (like we saw on the Colombo Street Overbridge), or the bridge can start at grade and climb steeply with short and tall piers.

However, Port Hills Road is descending from hills, so instead of an embankment, Route 73 is in a cut section below the bridge. Note the crib wall holding back the toe of the slope. As I've said before, I've seldom seem earthquake damage to this type of earth retaining structure. Also note the steel keys keeping the girders from moving transversely. At Caltrans, our philosophy is to let the bridge move, and design for the displacement.

New Zealand's Bridges: Port Hills Overbridges across Route 73 in Christchurch (2) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

New Zealand's Bridges: Port Hills Overbridges across Route 73 in Christchurch (1)

March 2011 (-43.573 Degrees, 172.695 Degrees) Port Hills Overbridges

Driving south from Christhchurch to Lyttleton are these six span precast, voided slab bridges on hammerhead bents. At least one of these bridges was built in 1970 and the other may have been built later. If you look closely you can see the bridges were retrofitted with braces and brackets to hold it together during an earthquake. Another nice detail is the column by the far abutment, which is the same length as the others but isolated from the surrounding embankment with a hollow casing.

New Zealand's Bridges: Port Hills Overbridges across Route 73 in Chirstchurch (1) by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

New Zealand's Bridges: Fitzgerald Avenue Bridges across the Avon River in Christchurch

March 2011 (-43.526 Degrees, 172.651 Degrees) Fitzgerald Avenue Bridges

East of the Barbardoes Street Bridge, the Avon River forms a big ox-bow and at the other end are the two Fitzgerald Avenue Bridges. They are two span, precast voided slab bridges supported on seat-type abutments and with a pier wall in the river. Although it is not apparent in this photo, the riverbanks moved toward the river during the February earthquake, breaking some of the abutment piles.

New Zealand's Bridges: Fitzgerald Street Bridges across the Avon River in Christchurch by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.