Introduction to Earthquake Hazards in Common Structures Prepared

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Short Course for Earthquake Preparedness Recognizing Common Structural Hazards Feb 10

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Earthquake – General Rules Earthquake shaking causes damage to structural load resisting system Then Gravity causes structural collapse The Heavier the building, the greater are the Forces Light, tough structures perform better Wood Bldg w/ plywood sheathing Small Metal Bldgs, w/ good connections The newer the better – lots of plywood wall sheathing Discontinuities in structures and the use of dis -similar materials are vulnerable to quake shaking Wood structures w/ 1 st story garages Brick Chimneys with wood houses Split level wood houses Use of brick and concrete finishes on wood bldgs

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Higher Risk Wood Structures Wood structures w/ 1 st story garages 3 -story are worst, but 2 -story also Wood houses w/ Brick Chimneys Split level wood houses Wood structures with brick veneer Taller are higher risk – falls on your head Wood structures w/ heavy tile roofing They are fire-resistant, but falling hazard

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Wood Apartments – Hazard Checklist One or more Story can Collapse in Aftershock - M 5+

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Wood Apartments Moderate Risk Higher Risk Over Weak 1 st Story Parking Over Conc Parking

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Racked 2 story Apt Not as high risk as 3 -story Front Rear

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. 4 Story Apt – High Risk Bldg has weak 1 st story & “Open Sides”- can offset

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. 3 Story Collapse Worst Case Weak 1 st story, older construction, and on poor soil

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Aftershock Collapse does happen 4 Story Buildings 1100 hrs Sat, 21 Oct 89 San Francisco 1105 hrs Sat, 21 Oct 89 San Francisco

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Split-level House Collapse Hazard chimney breaks at roof or fire box Initial condition roof & floor over weak garage are projected away Collapse projects weak story away

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Racked Split Level House Damaged and ready to collapse Split level, Collapsed on garage

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Wood House Hazard Checklist Most likely Aftershock hazards = Falling heavy objects

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. 1 to 3 Story House w/ weak crawl space Most have been retrofit in CA – Banks require chimney can fall as far as it is tall discontinuous roof can be knocked off cripple wall Weak cripple wall racks and allows house to move as much as it’s height

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. House Cripple Wall Failure Most of these have been Retrofit

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Brick Chimneys are very Hazardous 1 story w/code reqd ties 2 -story is also Hazard to Adj. House

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Roof Tile Hazards Northridge Quake Hurricane Iniki

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Other Structures – Poor Performance Mobile Homes & Manufactured Units Unreinforced Masonry Walls - URM Most have been retrofit or replaced in CA due to Statewide Ordinance Critical issue is connection of walls to bldg Tilt-up Wall Buildings Many 1 and 2 story in SF Bay Area, inc Moffett Field Critical issue is connection of walls to bldg Some have been retrofit – no Ordinance Precast Parking Garages Poor performance in most of U. S. – better in CA.

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Mobile Homes & Manufactured Units Typical quake issue is connection at base On Jack stands About 2 ft off ground Vulnerable to racking & utility connection issues

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Mobile Homes & Manufactured Units Typical quake issue at base Fell off Jack Stands Racked at base

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. URM Building Hazard Checklist Elec URM corner Gas Water URM can fall 20 ft from bldg. face Unsupported roof & floor Slip off bearing Loose equip Cracked wall piers Cracked parapets & split or peeled walls Most Hazards are Brittle & Lethal falling objects

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Typical URM -“Wall Fall” Hazard Coalinga, Most of these have CA 1984 been Retrofit San Francisco Loma Prieta 1989, 3 killed

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. TU Buildings Hazard Checklist Cracked walls Aftershocks can cause added wall & roof collapse

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Wall Connection Failure Wall falls out, adjacent roof collapses Corner prevents collapse, Redundancy helps

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Precast Concrete Hazard Checklist Elec Partly fallen slabs & beams Leaning wall check conns Gas Cracked walls w/ broken conns Overload from upper collapse Loose debris Water Cracked corbels Beam collapse ? Aftershocks cause loosely connected parts to shift & fall. Debris piles of large parts can shift & trap rescuers

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. May Co Garage Damaged in Whittier 87 EQ Collapsed in Aftershock

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Precast Armenia Apartments Parking Garages (Common in U. S. )

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Cast in Place Concrete Structures Are heavy, so potential hazard May be 1 to 30 stories Ones w/ concrete walls perform better Generally better in CA than other locals Weak concrete in Haiti, Iran, Pakistan, etc CA bldgs built prior to 1985 are higher risk

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. What about Concrete Shearwall Bldgs? They perform better than most, since they are cast in place

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Concrete Shearwall Bldgs 12 -story, Alaska EQ Good performance NASA Ames Lower Risk

Introduction to Earthquake Hazards in Common Structures Prepared by David J Hammond, Structural Engineer Ret. Key Learning Points The Heavier the building, the greater the Forces Light, tough structures perform better Wood Bldg w/ plywood sheathing Small Metal Bldgs, w/ good connections The newer the better – lots of plywood wall sheathing Discontinuities in structures and the use of dis-similar materials are vulnerable to Quake. Wood structures w/ 1 st story garages Brick Chimneys with wood houses Split level wood houses Use of brick and concrete finishes on wood bldgs