D i Phil h fD i Phil h fDesign Philosophy for Design Philosophy for Regions of LowRegions of Low--toto--ModerateModerateRegions of LowRegions of Low--toto--Moderate Moderate

Seismicity within the U.S.Seismicity within the U.S.yyByByByBy

Dominic KellyDominic KellySimpson Gumpertz & HegerSimpson Gumpertz & Heger

Historical Design PhilosophyHistorical Design PhilosophyHistorical Design Philosophy Historical Design Philosophy East of the RockiesEast of the RockiesEast of the RockiesEast of the Rockies

•• CT CT -- Earthquakes really only occur in CA, Earthquakes really only occur in CA, d l d d i i d i il 1989d l d d i i d i il 1989amendment excluded seismic design until 1989 .amendment excluded seismic design until 1989 .

•• Because the code requires us to design for Because the code requires us to design for earthquakes, we’ll charge our clients higher fees, but earthquakes, we’ll charge our clients higher fees, but we won’t worry whether our design is good.we won’t worry whether our design is good.

•• 1975 MA Building Code: “to protect life safety by 1975 MA Building Code: “to protect life safety by limiting structural failure”limiting structural failure”gg

Evolution of Philosophy EastEvolution of Philosophy EastEvolution of Philosophy East Evolution of Philosophy East of the Rockiesof the Rockiesof the Rockiesof the Rockies

•• Earthquakes can happen, but not very often. Earthquakes can happen, but not very often. Let’s design for earthquakes RLet’s design for earthquakes R--factors and factors and semisemi--ductile or nonductile details.ductile or nonductile details.

M hi i i h 1999 BOCA iM hi i i h 1999 BOCA i–– Memphis: current practice with 1999 BOCA is to Memphis: current practice with 1999 BOCA is to set Aset Avv = 0.195 for Category C (Av = 0.195 for Category C (Av 0.2) instead 0.2) instead

f Df Dof Dof D

Current West CoastCurrent West CoastCurrent West Coast Current West Coast PhilosophyPhilosophyPhilosophyPhilosophy

P i 1997 UBC “ i il f dP i 1997 UBC “ i il f d•• Purpose in 1997 UBC “primarily to safeguard Purpose in 1997 UBC “primarily to safeguard against major structural failures and loss of life, not against major structural failures and loss of life, not to limit damage or maintain function ”to limit damage or maintain function ”to limit damage or maintain function.to limit damage or maintain function.–– Engineers expect most buildings to be repairableEngineers expect most buildings to be repairable

•• Damage control code provisionsDamage control code provisions•• Damage control code provisions Damage control code provisions –– Ex.: new flat plate and flat slab provision in IBCEx.: new flat plate and flat slab provision in IBC

Shift t P fShift t P f B d D i li t liB d D i li t li•• Shift to PerformanceShift to Performance--Based Design as clients realize Based Design as clients realize their true risks.their true risks.

East Compared to WestEast Compared to West•• LowLow--toto--moderate zones should focus on protection moderate zones should focus on protection

of life while the high seismic zone should moveof life while the high seismic zone should moveof life while the high seismic zone should move of life while the high seismic zone should move towards performance based design.towards performance based design.

•• What is fundamentally different about earthquakes What is fundamentally different about earthquakes East of the Rockies that should lead us to a differentEast of the Rockies that should lead us to a differentEast of the Rockies that should lead us to a different East of the Rockies that should lead us to a different design philosophy?design philosophy?

–– Damaging Earthquakes are much less likely to occur in Damaging Earthquakes are much less likely to occur in lowlow--toto--moderate zonesmoderate zoneslowlow toto moderate zonesmoderate zones

PGA for CitiesPGA for Cities

10% / 50 yr10% / 50 yr 2% / 50 yr2% / 50 yr

BostonBoston 0.05g0.05g 0.17g0.17g

CharlestonCharleston 0.17g0.17g 0.79g0.79g

MemphisMemphis 0 16g0 16g 0 80g0 80gMemphisMemphis 0.16g0.16g 0.80g0.80g

New YorkNew York 0.06g0.06g 0.25g0.25ggg gg

San FranciscoSan Francisco 0.53g0.53g 0.76g0.76g

f S l A l if S l A l iRatioRatio of Spectral Acceleration at of Spectral Acceleration at 0 2 sec for 2%/50 yr hazard to0 2 sec for 2%/50 yr hazard to0.2 sec for 2%/50 yr hazard to 0.2 sec for 2%/50 yr hazard to

10%/50 yr hazard10%/50 yr hazard

A lA l 11Los AngelesLos Angeles 1.71.7San FranciscoSan Francisco 1.71.7New York CityNew York City 3.33.3CharlestonCharleston 5 05 0CharlestonCharleston 5.05.0MemphisMemphis 5.15.1

From Nordenson and Bell, EERI Spectra, Feb. 2000

Systems with low ductilitySystems with low ductilitySystems with low ductility Systems with low ductility did not make sensedid not make sensedid not make sensedid not make sense

•• Designing for a 10% / 50 yr EQ with semiDesigning for a 10% / 50 yr EQ with semi--ductile or nonductile or non--ductile detailing would notductile detailing would notductile or nonductile or non ductile detailing would not ductile detailing would not necessarily protect against collapse necessarily protect against collapse prevention in a MCE eventprevention in a MCE eventprevention in a MCE event prevention in a MCE event –– For a reinforced concrete beam FEMA 273 For a reinforced concrete beam FEMA 273

allows a plastic rotation angle of 0.02 for lifeallows a plastic rotation angle of 0.02 for life--safety and 0.025 for collapse preventionsafety and 0.025 for collapse prevention

Development of anDevelopment of anDevelopment of an Development of an Appropriate PhilosophyAppropriate PhilosophyAppropriate PhilosophyAppropriate Philosophy

•• Building StockBuilding Stock

•• What the building stock is designed forWhat the building stock is designed for

T f d t t f th b ildiT f d t t f th b ildi•• Type of damage to expect for the building Type of damage to expect for the building stockstock

Building Stock on East CoastBuilding Stock on East Coast

•• Highrise BuildingsHighrise BuildingsSteel Braced frames in core w/ perimeter momentSteel Braced frames in core w/ perimeter moment–– Steel Braced frames in core w/ perimeter moment Steel Braced frames in core w/ perimeter moment framesframesC t f ith h ll t l t dC t f ith h ll t l t d–– Concrete frames with shear walls at elevator and Concrete frames with shear walls at elevator and stair coresstair cores

Building Stock on East CoastBuilding Stock on East Coast

•• Midrise BuildingsMidrise Buildings–– Steel StructuresSteel Structures

•• Steel braced frames w/ composite slab and metal deck, offsets in Steel braced frames w/ composite slab and metal deck, offsets in brace locations are commonbrace locations are commonbrace locations are commonbrace locations are common

•• Ordinary (nonductile) moment framesOrdinary (nonductile) moment frames•• Steel frame with masonry infillSteel frame with masonry infillyy

–– Concrete StructuresConcrete Structures•• Nonductile frames including flatNonductile frames including flat--slab and flatslab and flat--plate framesplate frames•• SemiSemi--ductile framesductile frames•• Frames with masonry infillFrames with masonry infill

Building Stock on East CoastBuilding Stock on East Coast

•• Lowrise BuildingsLowrise Buildings–– Warehouses and industrial buildingsWarehouses and industrial buildings

•• SteelSteel--joist roof with braces and moment frames joist roof with braces and moment frames jjcladded with metal siding or precastcladded with metal siding or precast

•• Prefabricated steel buildingsPrefabricated steel buildings•• Older concrete flatOlder concrete flat--slab buildingsslab buildings

–– WoodWood--framed buildingsframed buildingsWW gg–– SteelSteel--joist buildingsjoist buildings

East vs. West Building StockEast vs. West Building Stock

•• Buildings are older on average in EastBuildings are older on average in East•• Probably a greater percentage of unreinforced Probably a greater percentage of unreinforced

masonry buildingmasonry buildingy gy g•• More precast buildings and untopped parking More precast buildings and untopped parking

garages in Eastgarages in Eastgarages in Eastgarages in East•• TiltTilt--up buildings in West are not common in up buildings in West are not common in

EastEastEastEast•• Buildings with tall brick facades exist in EastBuildings with tall brick facades exist in East

Philosophy should considerPhilosophy should considerPhilosophy should consider Philosophy should consider damage recorddamage recorddamage recorddamage record

•• Study damage from lesser events in regions of Study damage from lesser events in regions of higher seismicity that have similar types of higher seismicity that have similar types of buildings as the Eastern and Middle U.S.buildings as the Eastern and Middle U.S.bu d gs as t e aste a d dd e U.S.bu d gs as t e aste a d dd e U.S.

1993 Scotts Mills Earthquake1993 Scotts Mills Earthquake1993 Scotts Mills Earthquake 1993 Scotts Mills Earthquake in Northwest Oregonin Northwest Oregonin Northwest Oregonin Northwest Oregon

•• Modified Mercalli Intensity of VIIModified Mercalli Intensity of VII

•• PGA 0.05g to 0.1g in area of damagePGA 0.05g to 0.1g in area of damage

B ildi d i d d i f S i iB ildi d i d d i f S i i•• Building code required design for Seismic Building code required design for Seismic Zone 2 per UBC (PGA of 0.2)Zone 2 per UBC (PGA of 0.2)

Molalla High School (PGA 0.1g)

Saint Mary’s in Mount Angel (PGA 0.1g)

Residence between Molalla and Mt. Angel (0.1g)

1999 Izmit, Turkey 1999 Izmit, Turkey

•• 7.4 Mw7.4 Mw

•• PGA near epicenter 0 3gPGA near epicenter 0 3g•• PGA near epicenter 0.3gPGA near epicenter 0.3g

•• 115 km away at Proctor & Gamble site the 115 km away at Proctor & Gamble site the estimated PGA is 0 06gestimated PGA is 0 06gestimated PGA is 0.06gestimated PGA is 0.06g

Expected Major Damage in Expected Major Damage in LowLow--toto--Moderate Regions for Moderate Regions for

10% / 50 EQ10% / 50 EQ10% / 50 yr EQ10% / 50 yr EQ•• Unreinforced MasonryUnreinforced Masonry•• Unreinforced MasonryUnreinforced Masonry•• Precast Concrete Parking Garages and Precast Concrete Parking Garages and

B ildiB ildiBuildingsBuildings•• Irregular Nonductile BuildingsIrregular Nonductile Buildings•• FlatFlat--plate / Flatplate / Flat--slab moment framesslab moment frames•• Warehouse Buildings with precast concreteWarehouse Buildings with precast concrete•• Warehouse Buildings with precast concrete Warehouse Buildings with precast concrete

walls and steel joist or prefabricated steel walls and steel joist or prefabricated steel systemssystemssystemssystems

Falling HazardsFalling Hazards

•• Precast and stone facadesPrecast and stone facades•• Brick and terra cotta from infilled framesBrick and terra cotta from infilled frames•• Masonry parapets and chimneysMasonry parapets and chimneys•• Masonry parapets and chimneysMasonry parapets and chimneys•• Interior masonry firewalls particularly in Interior masonry firewalls particularly in

assembly buildingsassembly buildings

Appropriate design Appropriate design philosophy for regions of philosophy for regions of

ll tt d t i i itd t i i itlowlow--toto--moderate seismicitymoderate seismicity

Design to pre ent b ilding collapse in aDesign to pre ent b ilding collapse in a•• Design to prevent building collapse in a Design to prevent building collapse in a 2%/50 yr event2%/50 yr event

•• Address falling hazards.Address falling hazards.•• Have more stringent requirements forHave more stringent requirements for•• Have more stringent requirements for Have more stringent requirements for

structures on loose sands and soft claysstructures on loose sands and soft clays

What is different about What is different about design that might effect the design that might effect the

Phil h ?Phil h ?Philosophy?Philosophy?

•• Inherent strength of the gravity systemInherent strength of the gravity system

Th t f di l t th t tTh t f di l t th t t•• The amount of displacement that a system The amount of displacement that a system will experience is lesswill experience is less

Steel Frame w/CompositeSteel Frame w/CompositeSteel Frame w/Composite Steel Frame w/Composite DeckDeckDeckDeck

•• Inherent lateral strength of gravity system is 5 Inherent lateral strength of gravity system is 5 to 10% g. to 10% g.

•• Lateral strength may be increased by as much Lateral strength may be increased by as much f f i i f l df f i i f l das a factor of 2 in regions of low or moderate as a factor of 2 in regions of low or moderate

seismicity.seismicity.

Steel Joist SystemSteel Joist System

•• Stack of cards when steel beams are not Stack of cards when steel beams are not provided to frame between columns. provided to frame between columns.

•• Lateral strength is from the lateral system Lateral strength is from the lateral system llonly.only.

We should expect greater variation in the seismicvariation in the seismic

performance of buildings with i il l t l t b tsimilar lateral systems but different gravity systems.

Expected LateralExpected LateralExpected Lateral Expected Lateral Displacement for MCEDisplacement for MCEDisplacement for MCEDisplacement for MCE

•• In Charlestown and Memphis it is equivalent In Charlestown and Memphis it is equivalent to West Coastto West Coast

•• In New England and New York, I estimate In New England and New York, I estimate h h f di l i / / f hh h f di l i / / f hthat the roof displacement is 1/3 to 1/2 of the that the roof displacement is 1/3 to 1/2 of the

displacement for a similar building in the displacement for a similar building in the West CoastWest Coast

Expected Roof Drift* for MCEExpected Roof Drift* for MCE

San FranciscoSan Francisco Ne YorkNe YorkSan FranciscoSan Francisco New YorkNew YorkShear WallShear Wall 1.5%1.5% 0.5%0.5%

Braced FrameBraced Frame 2%2% 1%1%

MomentMoment 3%3% 1 5%1 5%Moment Moment FrameFrame

3%3% 1.5%1.5%

* Very Rough Estimates

SAC Research on SteelSAC Research on SteelSAC Research on Steel SAC Research on Steel FramesFramesFramesFrames

Analysis results indicate that the frames do not lose stability until about 12%do not lose stability until about 12% inter-story drift

Exterior of Building5161 Lankershim North Hollywood5161 Lankershim, North Hollywood

Typical Chevron Braced Frame

Avoiding Stout Braces

P P 2PPT1 PC1

Just Before Buckling:

PT1 + PC1 = 2Pbuckling

P PPost-Buckling Strength:

PT2 = Abrace Fy = Pt yield

PC2 = Pbuckling

PT2 PC2

0.2 to 0.4

Want PT2 + PC2 > PT1 + PC1PT i ld > 2Pb kli - Pb kliPTyield > 2Pbuckling PbucklingPTyield > 1.7Pbuckling for = 0.3

Upgraded Braced Frame with Zipper Column

Broken Braces ConcentratedBroken Braces ConcentratedBroken Braces Concentrated Broken Braces Concentrated on one flooron one flooron one flooron one floor

•• 4 stories maximum in California (2% 4 stories maximum in California (2% concentrated in 1 story equates to 8% concentrated in 1 story equates to 8% y qy qinterstory drift)interstory drift)

•• 8 or 10 stories maximum in New England or 8 or 10 stories maximum in New England or New York (1% concentrated in 1 storyNew York (1% concentrated in 1 storyNew York (1% concentrated in 1 story New York (1% concentrated in 1 story equates to 8%)equates to 8%)

SummarySummary•• The design philosophy should be different in lowThe design philosophy should be different in low--toto--

moderate regions of seismicitymoderate regions of seismicitymoderate regions of seismicity.moderate regions of seismicity.•• Designs in LowDesigns in Low--toto--moderate regions should prevent moderate regions should prevent

collapse for the MCE eventcollapse for the MCE eventcollapse for the MCE event.collapse for the MCE event.•• We should expect a greater variation in how We should expect a greater variation in how

buildings with similar lateral systems perform due tobuildings with similar lateral systems perform due tobuildings with similar lateral systems perform due to buildings with similar lateral systems perform due to the inherent lateral strength of the gravity system the inherent lateral strength of the gravity system

•• Displacement based design will allow use to moreDisplacement based design will allow use to more•• Displacement based design will allow use to more Displacement based design will allow use to more realistically assess how the designs may be differentrealistically assess how the designs may be different