1. Structures Design Age Building materials

2. Measuring force on structures Acceleration Resonance

3. Acceleration A measurement made on structures relative to gravitational force 1 g = 32 ft/sec squared or 9.8 meters/second squared Building codes are at about 40-60 percent of that or written as.4 to.6

4. Acceleration Added strength is needed to maintain a structure’s integrity when subjected to lateral accelerations Structures are built to maintain their integrity due to gravity

5. Accelerographs are placed on man-made structures to measure performance during an earthquake

6. Acceleration readings vary with earthquakes What type of fault would produce the highest accelerations? Acceleration

7. -Horizontal accelerations reached 1.19 and 1.02 g at the base and 1.8 g on the roadway. -The Los Angeles River sediments underlie this bridge. -What happened? Freeway Collapse

8. Freeway collapse

9. Simi Valley freeway collapse due to high accelerations. Northridge Earthquake

10. Increase with building height Acceleration San Jose High School, 1906 earthquake: stiff building material and increase acceleration with height

11. Decreases with distance from epicenter Acceleration

12. Period and Resonance Period is the amount of time it takes one wavelength to pass a point Seismic waves with a long wavelength have a larger period (2-4 seconds) Seismic waves with a short wavelength have a shorter period (1/2-20 cycles/sec) Wavelength

13. Period and Resonance Buildings also have a period The period (long or short) is determined by the number of stories Resonance occurs when the seismic waves pass through the earth material producing a particular wavelength and this wavelength matches the buildings period (wavelength). Remember: frequency is inverse of period

14. Resonance causes the motion of the bldg to increase 0.1 second for a one-story building 1-2 seconds for a 10-20 story building Period and Resonance

16. Common Building Failures Resonance: when the period of the seismic wave matches the period of a structure 30 seconds of shaking put the structure into resonance

19. Wood Shear Wall Construction

20. Structural Failure associated with the Loma Prieta Earthquake

21. Bay Bridge failure First pier into bay mud off Yerba Buena Island (bedrock) Connection failed due to low frequency seismic waves (mud) and high frequency seismic waves (bedrock)

22. Cypress structure, Oakland Reinforced concrete failure 1950 structure: lacked seismic design Earth material: bay mud Seismic waves amplified Liquefaction

23. Marina District Earth material: unengineered fill Liquefaction Seismic waves amplified Soft story: a floor of a multiple story building that lacks the structural strength or symmetry of the other floors

24. Downtown Santa Cruz Earth material: unconsolidated sediments deposited by the San Lorenzo River Seismic waves amplified Liquefaction Unreinforced masonry (URM) failed

25. Structural Failure Man-made structures: –Structural design and age –Building materials –Fire –Infrastructure failure: gas lines, water lines, electrical wires or transformers, cell phone towers

26. Soft Story: one floor has less support than the adjacent floors

28. Soft Story Collapse Parking garage is a soft story Scenes like this were familiar near the epicenter Where have you seen this type of structure?

29. Soft story: inadequate lateral bracing Structural failure, Northridge Eq

30. Kobe, Collapse of 5th Story Another example of soft story collapse 5th floor restaurant Open structure Stories above and below have more support

31. Stiff building material Pakistan, 2005: Mw 7.6 8:50 AM, local time 80,000 fatalities 200,000 injuries

32. Unreinforced Masonry

33. Wall Failure Traditional structures failed- unreinforced brick

34. L’Aquila, Mw 6.3 April 4, 2009

35. Seismic waves travel horizontally and vertically Failure occurs at the connections Increase in acceleration with height Irregularly shaped buildings

36. Irregularly shaped structures

37. Irregularly shaped buildings T-shaped structure Communication center in Mexico City The city lost international communication after the 1985 earthquake

38. Resonance Resonance: when the period of the seismic wave matches the period of a structure 30 seconds of shaking put the structure into resonance Mexico City, 1985

39. Earth material Loosely consolidated sediments and water saturated mud or sand amplify seismic shaking Liquefaction often occurs Failure at connections where earth material varies Bay Bridge Cypress Structure Moss Landing

40. House falls off foundation Foundation Sill plate House attaches to the foundation through the sill plate

41. HOG: house over garage Open, weakly supported garage fails with heavier and sturdier structure above

42. Cripple wall failure The wall between the sill plate and the house

43. Mexico

44. Silent earthquakes

45. Yellow: GPS data –Slow slip or silent earthquakes –Early- 2002, mid-2006 Red/Green: seismic stations –Circled area, earthquakes Silent earthquakes: indicative of earthquakes

46. Shallow and then becomes more steep under Mexico City Mexican subduction zonezone

47. Mexico City Earthquake 50 x 170 kilometers of displacement along the subduction zone M 8.1 Mexico city is 400 kilometers away City was built on the sediments of Lake Texcoco

49. Mexican subduction zonezone Cocos tectonic plate is subducting under the North American Plate Two plates lock Stress builds and energy is stored Stress exceeds frictional force Release of energy in terms of an earthquake

50. Earthquakes are more shallow than other subduction zones Mexican subduction zonezone

51. Mexico City Drained Lake Texcoco Clay sedimentary layers Low frequency surface waves amplified 1-2 second frequencies Matched the periods of buildings 6-16 stories

52. Mexico City: Common Building Failures Top floors fail- resonance T-shaped structures Flexible structures between stiff structures

53. Mexico City: Building Failures Hammering Soft story collapse

54. Chile, Mw 8.8, 2010

56. Uplifted terrace with lighthouse Intertidal fauna exposed 3-6 feet of uplift along the coast

57. Conception:L-shaped structure failure

58. Failure of URM and soft story

59. Balcony beams and weak internal wall caused buckling of building.

60. Conception: failure of concrete walls

61. Liquefaction induced failures

62. EarlyEarly seismic construction Huaca Pucllana Lima, Peru 200-700 CE Bricks built in a trapezoid pattern with spacing Accommodates seismic shaking

63. Which structural designs tend to fail during ground shaking? Soft story Structures constructed from stiff building materials One weak point initiates other failures Irregularly shaped structures Structures that move into resonance Earth material fails Hogs House off foundation Cripple wall failure

64. Constructing model buildings and subjecting to shaking Building must be: –At least 30 cm high –At least 3 stories –No central post or uprights Materials are limited Complete construction in limited time