Seismic Retrofitting of Bridges Donald Kirkcaldie Seismic Retrofitting of Bridges Donald Kirkcaldie

1 Examples of Vulnerabilities

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3

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5 Common Vulnerabilities & Shortcomings Span Collapses arising from: No linkage between spans and support Inadequate overlap of spans with supports Inadequate structural detailing: No diaphragms between girders at supports Inadequate confinement and shear reinforcement of columns, pier walls and piles, especially at plastic hinge locations Main flexural reinforcement lapped in plastic hinges Insufficient shear capacity in pile caps Lack of joint shear reinforcement

6 Common Vulnerabilities & Shortcomings Ground instability issues: Instability of approach embankments at bridge abutments Liquefaction of the site subsoils Loss of soil strength in granular soils due to build up of pore water pressure Inward flow of soils towards the river channel or low ground Approach embankments raft on top of the inward flowing liquefied soils resulting in large forces on structural elements

7 SH7 Kowai River Bridge

8 SH7 Shale Peak Bridge

9 SH1 Otaki River Bridge

10 Wellington Urban Motorway Shell Gully Bridges

11 SH1 Waikanae River Bridge

12 SH2 Pakuratahi River Bridge

13 Wellington Urban Motorway Thorndon Overbridge

14 Some Papers on Seismic Retrofits Stuart CR, “Seismic Retrofitting of Highway Bridges in NZ”, Applied Technology Council Report ATC-12-1, 1985 Chapman H, Lauder M, & Oakden G, “Seismic Screening of Bridges in New Zealand”, 12 th World Conference on earthquake Engineering, 2000 Chapman HE, Kirkcaldie DK, Lauder M & Oakden G, “Seismic Security of State Highway Bridges: Screening and Retrofit – Progress Summary”, 2002 NZSEE Conference Kirkcaldie DK, Hobman H,& Saul GJ, “Seismic Assessment and Retrofit of the Shell Gully Bridges”, 2005 NZSEE Conference Wood JH, Chapman HE, Gregg GC & Kirkcaldie DK, “Seismic Assessment and Retrofit of Waikanae and Pakuratahi River Bridges”, 2007 NZSEE Conference Kirkcaldie DK, Brabhaharan P, Murashev M, & Kotze R, “Seismic Improvement of the SH3 Cobham Bridge and SH1s Clarence River Bridge”, 2009 Austroads Bridge Conference

15 Conclusion For areas of low seismicity the most important initial retrofit to consider is to prevent span collapses: Link spans to supports Provide adequate span – support overlap