Bridge and structural engineers have been designing new bridges and retrofits to increase
sustainability of the infrastructure today.
By doing so, plans of keeping older structures in good
condition are a main priority, so the need to retrofit is now. What is retrofitting? By definition, it
means “to install, fit, or adapt (a device or system) for use with something older” (retrofit,
dictionary.com). In recent times, “it has been said that retrofitting is of major importance for the
future because by 2032 an earthquake of a magnitude of 6.7 or higher has a 38 to 85 percent
chance of occurring, however when its 6.0 to 6.6 the rate is increased to 80 to 96 percent
chance.” (Lincoln Electric, 2010) The specific faults in the region “that are most likely to rupture
are the San Andreas Fault and the Hayward- Rodgers Creek Fault, with probabilities of
producing a magnitude 6.7 or greater earthquake of 21% and 27% respectively. The aggregate
probability of one or more magnitude 6.7 or greater earthquakes within the next 30 years from
2003 to 2032 in the SFBA (San Francisco Bay Area) is estimated to be 62%” (Allen, R.M., 2006,
pg. 372). Thus in layman’s terms, with percentages like the ones shown, retrofitting is a must.
In California, the California Department of Transportation (Caltrans) has been developing many
new ideas and ways to retrofit bridges and buildings in its surrounding areas.
For all intensive
purposes, this proposal will be centered on the retrofitting of the Dumbarton Bridge.
was built in 1927, but then was reconstructed in 1982 which is located
State Route 84 between
San Mateo and Alameda counties near Newark and East Palo Alto, California (MTC, 2009).
bridge in question is also a toll bridge which is partaking in a seismic retrofit program to improve
its life span. “Caltrans and BATA evaluated the seismic safety of the bridge and determined it
requires seismic retrofit work to make the bridge safe during a major earthquake. There is
currently a bill (AB 1175) in the California Legislature to add the Dumbarton Bridge to the Toll
Bridge Seismic Retrofit Program” (MTC, 2009). This proposal is created for those purposes.
Also, the composition of the bridge is one with steel box girders and a pre-stressed concrete
approach which spans the entirety of the bridge.
In Appendix A, pictures show the bridges two
column piers that are rectangular in shape, and this will affect our retrofit design in some way.
All infrastructure pieces will be taken in account and thoroughly discussed when planning the
Description of Magnitude and Number of Earthquakes in Affected Areas
Understanding seismic retrofitting begins with the knowledge of earthquakes and magnitudes. In
Seismic Design and Retrofit of Bridges written by Calvi, Priestley, and Seible, it was explained
that “magnitude of an earthquake is a measure of the energy released at the source; and intensity
is a measure of the effects of the ground motion at a given location” (1996, pg. 69). The scale