Earthquakes in San Francisco, California - Structural Engineering Solutions -

Why Do Earthquakes Occur? Earth’s Lithosphere (crust) made up of numerous plates Plates can move on earths asthenosphere: Solid, but in geological timescales is relatively viscous Plates move slowly - creep Plates can become “Locked” to each other - earthquakes

Why is San Francisco at Risk? San Andreas fault Major fault line between North America and Pacific plates: 800 miles long, can extend to 10miles deep Right lateral strike slip Geologists estimate the total displacement 350 miles Surveying shows drift of 2inches/year

Geology of San Francisco The geology of San Francisco amplifies the problems caused by earthquakes Much is alluvium and sand deposits that lack rigidity

The Great 1906 Earthquake 5:12 AM 18 th April 1906 Death toll up to 3000 Earthquake strength estimated at 7.8 on Richter scale Max observed displacement 20feet Main shock 45-60s Economic centre of the west coast Cost of damage $450m ($650b in 2006) Up to 300,000 out of 410,000 left homeless Most damaged caused by fires

Pictures from 1906 Earthquake

Engineering Solutions Earthquakes produce two types of vibrations: Horizontal movement Vertical movement For buildings and their contents horizontal movement is the most dangerous There are two basic methods to protect against earthquakes: Isolate the building from the grounds movement Make the building strong enough to withstand it

Engineering Solutions Base Isolation: Allows for horizontal movement of the ground under the building Isolation need a significant level of mechanical damping Rubber DampeningRolling Dampening

Engineering Solutions New Modern Techniques: PTED Frames No welding between beams and columns Beams and columns can twist and move without structural damage Still in the testing stages ‘Energy dissipating’ bars – Reduce the cyclic movement within the frame Post tensioned bars keep the frame together under movement

Engineering Solutions New Modern Techniques: Tuned Mass Damper Large weight positioned at the top of a building Tapia Oil dampeners connected to the steel ball stop movement of the building due to the inertia of the mass Method currently used Also helps with wind dampening Tapia 101 building, Taiwan. Tuned Mass Damper on 88 th floor.

One Rincon Hill Situated in San Francisco South of the North Bay Reduce sway: This is the first residential building in America to make use of a liquid tuned mass damper A water system is used, the energy from the swaying building is dissipated through filters/screens.

One Rincon Hill Make the building strong: The building has large steel outriggers that transfer load into the serpentine rock It is the highest US Skyscraper to have ‘buckling resistance braces’ and the first ever to have these as outriggers The outriggers transfer the load from the central core down into the base foundations At 48ft they are braced back onto the concrete cored for extra strength