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SR522 Seismic Isolation Bearings Report C8128 .pdf



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SR522 Seismic Isolation Bearings
November 13, 2015

Prepared by:
WSDOT Bridge and Structures Office

Participating Authors:
Amy Leland, SE
Ralph Dornsife, SE
Richard Zeldenrust, SE

SR522 Seismic Isolation Bearings
Introduction
The Snohomish River Bridge is located on SR522 in Washington State near the city of Monroe. As its
name indicates, this bridge crosses over the Snohomish River. The bridge is an eight span steel girder
bridge. (Figure 1) Due to poor soil conditions, the superstructure sits on seismic isolation bearings to
minimize the amount of lateral load transferred into the substructure. The substructure is designed to
remain elastic during a design seismic event. The seismic isolation bearings are Earthquake Protection
System (EPS) triple friction pendulum bearings. (Figure 2 ) These bearing were sole sourced, and a
purchase agreement was included as part of the contract.

Figure 1 – Snohomish River Bridge Framing Plan

1

Figure 2 - Schematic of EPS Triple Friction Pendulum Bearing

Less than a year after opening the bridge to traffic, water and apparent corrosion were observed in
many of the bearings. This apparent corrosion concerns WSDOT, the owner, because the long-term
performance of the bearings is vital in preventing substructure failure in a future seismic event.
Corrosion typically increases over time and since this bridge is early in its design life, WSDOT is
concerned that the apparent corrosion will continue to negatively affect the bearing performance over
the 75 year expected design life.

History of Construction
The bearings were delivered to the bridge site in late September of 2012. (Figure 3)

Figure 3 – Bearings Delivered to Bridge Site

2

They were then protected by a tarp by early October. (Figure 4)

Figure 4 – Bearings Under Tarp

On October 24, 2012 the bearings began to be placed on Piers 5 through 9. Then on November 1, 2012
the first girders were placed in Span 5. The girders were set on the bearings. (Figure 5)

Figure 5- Span 4 Girder Placement

3

On November 15, 2012 the final first phase girders were set in Span 8. All girders are set between Piers
5 and 9. (Figure 6)

Figure 6 – Span 8 Girder Placement

On December 13, 2012 the overhang brackets for the deck formwork began to be placed. (Figure 7)

Figure 7 – Span 4 Deck Formwork Bracket

4

In December 2012 the grout pads were poured around the bearings. (Figure 8)

Figure 8 – Grout Pour at Pier 5 Girder D Bearing

In January 2013 the deck formwork began to be placed, and was completed in March. (Figure 9)

Figure 9 – Formwork Complete for Spans 5 through 8

5

In June 2013, the concrete bridge deck began to be poured between Piers 5 and 9 (Figure 10), and
bearings began to be placed on Piers 1 through 4 (Figure 11).

Figure 10 – Deck Placement Beginning Near Pier 9

Figure 11 – Pier 1 Bearings

6

In October 2013 the launched girders were set on top of the bearings at Piers 1 through 4, and then the
last girder segments were placed on the bearings at Pier 5. (Figure 12)

Figure 12 – Span 4 Girder Placement

In December 2013 the brackets for the deck formwork began to be placed along with a working
platform. (Figure 13)

Figure 13 – Working Platform

7

In January 2014 the grout pad were poured around the bearings on Piers 1 through 5.
Deck formwork was complete by early April 2014 (Figure 14), and the deck was poured in June (Figure
15).

Figure 14 – Formwork Complete for Spans 1 through 4

Figure 15 – Deck Placement near Pier 5

8


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