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

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



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



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



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



Wood Apartments

Over Conc ParkingOver Conc Parking

Over Weak 1st Story Parking

Higher Risk

Moderate Risk



Racked 2 story Apt Not as high risk as 3-story

Rear

Front


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



3 Story Collapse

Worst CaseWorst CaseWeak 1Weak 1stst story, story, older construction, older construction, and on poor soil and on poor soil



Aftershock Collapse does happen4 Story Buildings

1100hrsSat, 21Oct 89San Francisco

1105hrsSat, 21Oct 89San Francisco


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



Split level, Collapsed on garage

Racked Split Level HouseDamaged and ready to collapse



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


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



House Cripple Wall Failure

Most of these have been Retrofit


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



Roof Tile Hazards

NorthridgeQuake

Hurricane Iniki



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.


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



Fell off Jack Stands

Racked at base

Mobile Homes & Manufactured UnitsTypical quake issue at base


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



Typical URM -“Wall Fall” Hazard

Coalinga, CA 1984

San Francisco Loma Prieta 1989, 3 killed

Most of these have been Retrofit



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



Wall Connection Failure Wall falls out, adjacent roof collapses

Corner prevents Corner prevents collapse,collapse,

Redundancy Redundancy helpshelps



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



Damaged in Whittier 87 EQ

Collapsed Collapsed in in

AftershockAftershock

May Co GarageMay Co Garage



Precast Armenia Apartments

Parking Garages(Common in U.S.)



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


Prepared by David J Hammond, Structural Engineer Ret.What about Concrete Shearwall Bldgs?

They perform better than most, since they are cast in place



Concrete Shearwall Bldgs 12-story, Alaska EQ12-story, Alaska EQGood performanceGood performance

NASA AmesNASA AmesLower RiskLower Risk



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

Documents

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