Post on 28-Dec-2015
Introduction to Earthquake Hazards in Common Structures
Prepared by David J Hammond, Structural Engineer Ret.
Short Course for Earthquake Preparedness
Recognizing Common Structural Hazards
Feb10
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/ 1st 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/ 1st story garages
3-story are worst, but 2-story also
Wood houses w/ Brick Chimneys
Split level wood houses
Wood structures with brick veneerTaller are higher risk – falls on your head
Wood structures w/ heavy tile roofingThey are fire-resistant, but falling hazard
Introduction to Earthquake Hazards in Common Structures
Prepared by David J Hammond, Structural Engineer Ret.
One or more Story can Collapse in Aftershock - M 5+
Elec
GasWater
Heavy Roofg ?Balconycontents
Racked walls ?• plywood• diag shtg• stucco only• stucco on gyp
Broken glass
Wood Apartments – Hazard Checklist
Introduction to Earthquake Hazards in Common Structures
Prepared by David J Hammond, Structural Engineer Ret.
Wood Apartments
Over Conc ParkingOver Conc Parking
Over Weak 1st Story Parking
Higher Risk
Moderate Risk
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
Rear
Front
Introduction to Earthquake Hazards in Common Structures
Prepared by David J Hammond, Structural Engineer Ret.4 Story Apt – High Risk Bldg has weak 1st story & “Open Sides”- can offset
Introduction to Earthquake Hazards in Common Structures
Prepared by David J Hammond, Structural Engineer Ret.
3 Story Collapse
Worst CaseWorst CaseWeak 1Weak 1stst story, story, older construction, older construction, and on poor soil and on poor soil
Introduction to Earthquake Hazards in Common Structures
Prepared by David J Hammond, Structural Engineer Ret.
Aftershock Collapse does happen4 Story Buildings
1100hrsSat, 21Oct 89San Francisco
1105hrsSat, 21Oct 89San Francisco
Introduction to Earthquake Hazards in Common Structures
Prepared by David J Hammond, Structural Engineer Ret.Split-level HouseSplit-level House Collapse Hazard
Initial condition Collapse projects weak story away
roof & floor overweak garage areprojected away
chimney breaksat roof or fire box
Introduction to Earthquake Hazards in Common Structures
Prepared by David J Hammond, Structural Engineer Ret.
Split level, Collapsed on garage
Racked Split Level HouseDamaged and ready to collapse
Introduction to Earthquake Hazards in Common Structures
Prepared by David J Hammond, Structural Engineer Ret.
Most likely Aftershock hazards = Falling heavy objects
Cripple Wall Type Hi - Footing
Rackedcripple wall
SeparatedEntry Roof
Roof Tilefalls off
Gas &Water
Masonry veneerfalls off
Elec
Brick chimneycracked & mayfall
Wood House Hazard Checklist
Introduction to Earthquake Hazards in Common Structures
Prepared by David J Hammond, Structural Engineer Ret.1 to 3 Story House w/ weak crawl 1 to 3 Story House w/ weak crawl spacespace Most have been retrofit in CA – Banks requireMost have been retrofit in CA – Banks require
cripple wall
Weak cripple wall racks and allowshouse to move as much as it’s height
chimney can fallas far as it is tall
discontinuous roofcan be knocked off
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
NorthridgeQuake
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 BuildingsMany 1 and 2 story in SF Bay Area, inc Moffett FieldCritical issue is connection of walls to bldgSome have been retrofit – no Ordinance
Precast Parking GaragesPoor 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 UnitsTypical 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.
Fell off Jack Stands
Racked at base
Mobile Homes & Manufactured UnitsTypical quake issue at base
Introduction to Earthquake Hazards in Common Structures
Prepared by David J Hammond, Structural Engineer Ret.URM Building Hazard Checklist
Most Hazards are Brittle & Lethal falling objects
Elec
GasWater
Slip offbearing
Unsupportedroof & floorURM
corner
Crackedwall piers
Cracked parapets& split or peeled walls
URM can fall20 ft frombldg. face
Looseequip
Introduction to Earthquake Hazards in Common Structures
Prepared by David J Hammond, Structural Engineer Ret.
Typical URM -“Wall Fall” Hazard
Coalinga, CA 1984
San Francisco Loma Prieta 1989, 3 killed
Most of these have been Retrofit
Introduction to Earthquake Hazards in Common Structures
Prepared by David J Hammond, Structural Engineer Ret.
TU Buildings Hazard Checklist
Crackedwalls
Leaningwalls
Separation of roof membersfrom wall bearings
Slip at allinterior roofconnections Wall top tension failure
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 Corner prevents collapse,collapse,
Redundancy Redundancy helpshelps
Introduction to Earthquake Hazards in Common Structures
Prepared by David J Hammond, Structural Engineer Ret.
Elec
Gas
Crackedwalls w/broken connsOverload fromupper collapseLoose debris
Partly fallen slabs & beams
Cracked corbelsBeam collapse ?
Leaning wallcheck conns
Water
Aftershocks cause loosely connected parts to shift & fall.Debris piles of large parts can shift & trap rescuers
Precast Concrete Hazard Checklist
Introduction to Earthquake Hazards in Common Structures
Prepared by David J Hammond, Structural Engineer Ret.
Damaged in Whittier 87 EQ
Collapsed Collapsed in in
AftershockAftershock
May Co GarageMay Co Garage
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 localsWeak 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 EQ12-story, Alaska EQGood performanceGood performance
NASA AmesNASA AmesLower RiskLower Risk
Introduction to Earthquake Hazards in Common Structures
Prepared by David J Hammond, Structural Engineer Ret.
The Heavier the building, the greater the Forces Light, tough structures perform better
Wood Bldg w/ plywood sheathingSmall Metal Bldgs, w/ good connectionsThe 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/ 1st story garagesBrick Chimneys with wood housesSplit level wood housesUse of brick and concrete finishes on wood bldgs
Key Learning Points