The characteristics of earthquake ground motions which have the greatest importance for buildings are the 1.) Duration: How long the shaking lasts. Shaking for longer=more damage 2.) Amplitude Size of the shaking. BIGGER shaking=more damage (displacement, velocity and acceleration) 3.) Frequency Speed of the shaking This one is a bit involved so…. SLINKY DEMO ?? Courtesy of Multidisciplinary Center for Earthquake Engineering Research (MCEER)

FREQUENCY(f) How many times something “wiggles” back in forth LOW FREQUENCY HIGH FREQUENCY BUT it MAY BE easier to understand if we talk in terms of PERIOD PERIOD(T): How long it takes for a full “wiggle” (cycle) to happen T = 1 / f SHORT PERIOD LONG PERIOD COURTESY OF: The Physics Classroom and Mathsoft Engineering & Education, Inc.

RESONANT FREQUENCY & NATURAL PERIOD a building's vibrations tend to center around one particular frequency, Which is known as its natural, fundamental, or resonant frequency. Resonant Frequency = the number of times per second that a building will TEND vibrate back and forth per unit time (2 cycles/sec) Natural Period = the time it USUALLY takes for the building to make one complete vibration (1 sec/2cycles=.5sec/1cycle) buildings suffer the greatest damage from ground motion at a frequency close or equal to their own natural frequency

RESONANT FREQUENCY & NATURAL PERIOD If ground motion period/frequency=buildings natural frequency then this motion is CONSTRUCTIVE (adds together) =EVEN MORE MOTION IN BUILDING Courtesy of (MCEER)

SO… We need to know… 1.) what kind of history of EQ in certain areas. *What type of frequencies/periods are common in an area and DON’T build them to match. 2.) The kind of material in an area. (Essen. Pg. 212/Fig. 9.11) *Unconsolidated vs. consolidted (bedrock) a.) If building is on bedrock=high frequency seismic waves then Build a flexible tall building. b.) If on unconsolidated materials =low frequency seismic waves then go with short stiff building.

Two Main Ideas For Foundation Design 1.) Tie the foundation to the bedrock so that the ground and building shakes as a single unit 2.) The other is to have a “boundary” like shock absorbers, rollers, rubber doughnuts- Base Isolation (ND pg. 83/fig. 3.31) **Check out for some COOL techniques **It is the inertia of the building the is the problem (Fig. 2 Essentials, pg. 215) Courtesy of (MCEER) inertia Courtesy of (MCEER)

HOW DO WE MAKE BUILDINGS STRONGER TO RESIST LATERAL MOTION ??? THINGS TO CONSIDER (Essentials pg. 215 sidebar) 1.) different wings of same building respond differently 2.) foundation-wall interface. 3.) resultant swaying increases with height-”wobbley” lever 4.) buildings too close hit each other. 5.) Long axis orientation 6.) “soft” first story BAD = “soft” first story. (ND pg. 85/fig. 3.33) see results (ND pg. 76/fig again)

GOOD DESIGN ELEMENTS 1.) Shear walls: a.) Help to transmit horizontal energy back into the ground b.) solid c.) need to be symmetric in floor plan to resist torsion/twisting d.) See ND pg ) Braced Frame: a.) “nested triangles” provide lateral support. b.) should be made with ductile material. c.) Back to ND pg. 81 d.) meterstick demo? Photo: Courtesy of Godden Collection/Earthquake Engineering Research Center/University of California, Berkeley

3.) Moment –resisting frame:The problem is that the joints usually fail. a.) House of cards analogy-edges/connections fail… b.) So these connections need to be SRONG c.) prefered by architects because they provide less obstructions than shear walls. d.) inherent structure behavior is rigid so material needs to be ductile (steel) GOOD DESIGN ELEMENTS (continued) Courtesy of (MCEER)