on multi-hazard design of highway bridges -...

D E P A R T M E N T OF C I V I L & E N V I R O N M E N T A L E N G I N E E R I N G

On Multi-Hazard Design of Highway

Bridges

M. Ala Saadeghvaziri and Nick Carlson


Outline

• Concept of multi-hazards

• Structural Design: Forces and Systems

• Seismic Design

– Brief Background and State-of-the-Art

• Other hazards

• Multi-hazard design considerations

– Progressive collapse

– Anti-gravity forces

• Conclusions

– Research needs

• Multi-hazard approach with seismic benefits


Hazards

• Natural Hazards: 4 elements – Earth: earthquake

– Water: flooding, wave effects

– Wind

– Fire

• Man Made Hazards: Blast

• Environmental: corrosion, temperature, material dependents demands, etc.

• Collision


Source: Google


Structural Question of the Day

Q.) How much does a house weigh???

A.) Just a tad more than a rural two-lane bridge can hold, apparently.


Earthquakes

Source: USGS


Floods


Hurricanes


Terrorists Tactics and Targeting Stat.

Maritime3% Hospitals

3% Government14%

Journalists3%

Tourists18%

Financial3%

Educational1%Corporate

4%

Airports5%

Mass Transit5%

Ports4%

Places of Worship

4%

Places of Gathering

16%

Oil Industry5%

Military Police12%

Source: Venske (2006).

“Jihadi Tactics & Targeting

Statistics.” Intel Center,

Alexandria, VA.


Load Carrying

System: Buildings

Elevation

Plan


Load Carrying System: Bridges


Past EQs and Performance

• 1923 Kanto, Japan earthquake one of the largest

to hit a industrial area (M 7.9).

• 1964 Alaskan,1970 Madang and 1971

Earthquakes

• Damage these EQs damage is attributed mostly

– to weakness in soil and substructure

– Limited bridge vibration cause of damage

• San Fernando EQ of Feb 9, 1971

– Turning point for seismic design of highway bridges

– PGA of 0.6g and 1.0g in horizontal and vertical

– Bridge vibration critical


San Fernando EQ of Feb 9, 1971 • Inadequate transverse reinforcement in the columns to

provide shear resistance and ductility

• Small seat width, inappropriate location of expansion joints, inadequate footing reinforcement causing pull out


Loma Prieta EQ of 1989 Highlighted Importance of

longitudinal motion, joint

detailing and site conditions


Northridge EQ 1/17/1994

• Magnitude 6.6, 61 deaths, $30 billion in damage (at the time most costly natural disaster in US history)

• Widespread damage due to:

– EQ epicenter at metro area

– Thrust rather than lateral fault:

unusually large vertical

acceleration.

• Highlighted importance of

near fault ground motions.


Kobe EQ of Jan 17, 1995

• Shallow EQ & near infrastructure

• Lessons important to low seismic areas in US as: – Predominant type of bridge is steel

on girder superstructure.

– Difference between the maximum credible EQ and design EQ very large: an earthquake of this size was considered a rare event for this part of Japan.

• Premature failure of some bearings appear to have acted like a fuse.


Chi-Chi (Taiwan) EQ of Sept 20 1999 • Failure of bridges due to large

permanent ground deformation.

• Provided significant amount of

data on bridge performance in

near-fault regions.

• Near fault affect known as “fling

step” that can create large

unidirectional velocity pulses in the

fault-normal direction. – This characteristics of ground motion

have led to failure of several decks.

– Must be considered in design of bridges

for near-fault regions but challenging.


Turkey EQs of 1999

• Highlighted the importance of near source effects and fault rupture crossing the bridge site.

• Progressive collapse

Right lateral offset of 1.5 meter

Surface Fault Trace


Seismic Code Development

• Prior to 1971: Very simple and without much consideration to bridge vibration and site condition: – EQ = CW

– Where C ranges from 0.02 to 0.06 and W is bridge weight.

• 1971 – Present: Life safety philosophy – No to minor damage during moderate EQ

– Damage under larger EQ OK but no collapse

– Most recent adopted by AASHTO in 2007

• Future: Performance-Based Engineering


AASHTO 2007: New Concepts

• New Soil Factors

– One of the most significant changes.

– Different factors are recommended for short and long

period range.

– An increase in site factors with decreasing accelerations

(nonlinear response effects of soils).

• New Spectral Shapes

– Decays as 1/T for long period (vs. 1/T2/3).

• Present Justifications for 1000-yr Return Period

(which is approx. 7% probability of exceedance

in 75-yr).


AASHTO 2007 (cont’d)

• No Analysis Design Concept: an important new addition.

• Capacity Spectrum Design Procedure – Similar to CalTrans’ displacement approach.

– Assess adequacy after designing for non-seismic.

– No need to determine bridge period.

– Future research should expand range of applicability.

• Displacement Capacity Verification (Pushover) Analysis.


SD1 for New Jersey

Max SD1, = 0.14 = 3.5*0.04

Entire state of NJ is no analysis

Rock

Soil


SDCs Core Flowchart


Multi-Hazard Approach to Design

• Seismic

• Blast

• Hurricane/

flooding

• Fire

• Wind

• Collision


Shortcomings and Opportunities within a

Multi-hazard Design Framework

• Too prescriptive

– Quality not rewarded

– Need to enhance engineer role

• Unexpected performance

• Lateral force design

– For bridges basically a column design

• Vertical component is not considered

• Multi-hazard requires emphasis on vertical

strength and stability


Unexpected Performance

• Many buildings have survived earthquakes

much stronger than what they were designed

for:

– Conservatism in design

– Ignoring structural elements not part of lateral force system

– Recorded motion not really representative of what goes

into the structure

– Analytical methods inaccurate

– Good engineering

Sigmund Freeman, “Why properly code designed and constructed buildings have survived major earthquakes,” 13 th WCEE,

Vancouver, BC, 2004, paper no. 1689


Vertical Motion: why not considered

• Peak ground acceleration smaller

– Measurements have shown this is not true, especially

for near fault and thrust type events

• Difficult to specifically attribute failure during past

earthquakes to vertical motion. – Shear failure

– Confinement

– Elephant foot buckling

• Inherent factor of safety in the vertical direction

– While this might be true for building not for bridges


Effective Mass


Simple Example: Girders/Beams

• I = 4256 in4; A = 190 in2, L = 40 ft

• f = 4.3 Hz or T = 0.23 sec

• This is in the range of high energy of vertical component. Say vertical ground acceleration, Sva,= 0.5g

• Dynamic amplification = 2.5 – 4

• Beam/girder acceleration = 1.25g – 2g

• Max. total vertical acceleration = gravity + vertical = 1g ± 2g

• This is: 3g downward, and 1g upward


NYCDOT Draft Provisions


Shear Capacity: Anti-Gravity?


EQ Damage: Potentially due to Vertical Motion


Prestressed Shear and Principal Stress

by Nawy


Pre-stressed Cross-section

Shear strength under flexural-shear

cracking:

Shear strength under web-shear

cracking:

NOTE:

Vd = shear due to unfactored DL

Vp = vertical component of effective

prestressed force at the section.


Vertical Motion: possible modes of

damage (cont’d)

• Connections – Higher demand, especially hold-down devices; and

changes to load transfer mechanism at the bearings.

• Response of base isolation system – Fluctuating normal force causing additional dynamic

effect


Flood Loads


Flood Loads (cont’d)


Buoyancy Forces on Bridge Deck

Source: Robertson, et al., JWPCOE, ASCE


Katrina: Parking Structure

• As many as 10-parking structures failed in

Biloxi-Gulfport region

• Damage to 2nd floor

• Cause of damage due

to hydrodynamic uplift

and/or buoyancy

• Precast double-tee used

– Uplift due to buoyancy

estimated as much as 153%

of gravity

Source: Robertson, et al., JWPCOE, ASCE


Parking Garage Failure • The center columns were crushed, resulting in caving-in of

the floors and extreme bending of the external columns.

– Structure failed because

of brittle vertical load

carrying system,

– Need exists to provide

ductile load path in beams

/girders intended only to

resist dead and live loads

– Brittle nature of the

collapse caused the

system to collapse even before the structure was subjected to

significant horizontal acceleration

Source: Englekirk & Beres (Concrete Int., Oct 1994)


Northridge Fashion Center

• Englekirk & Beres (Concrete Int., Oct 1994):

– Structure failed because of brittle vertical load carrying

system,

– Need exists to provide ductile load path in beams/girders

intended only to resist dead and live loads,

– Because the precast-prestressed vertical load carrying

members failed in shear,

– Brittle nature of the collapse caused the system to collapse

even before the structure was subjected to significant

horizontal acceleration.


Anti-gravity loading Damage

Concrete slab ruptured by

hydrostatic pressure

(buoyancy) induced by the

floodwaters of Hurricane

Katrina

Twin-Tee roof panel lifted as a

result of the combined effects of

wind uplift and pre-tension.

Tornado (Missouri, May 2003)


Anti-Gravity Loading Damage (cont’d)

Failure of post-tensioned concrete

slab exposed to uplift forces due

to storm surge (Photo credit:

Jack Hayes, USACE)

Photograph of the damage to the

U.S. 90 Biloxi Bay bridge caused

by Hurricane Katrina.


Reinforcement of Floor Slab


Support Movement: Katrina


Support Movement:

Kobe EQ


Blast Load

Source: FEMA 426

Z = scale distance = R / W1/3


Anti-gravity forces

Source: FEMA 426


Blast Effects on Bridges

Source: Winget, et al.


Blast Effects on Bridges (cont’d)

Source: Winget,

et al.


Buildings: Transfer Girders

Source: Smilowitz, Weidlinger Assoc.


Case Study: An Actual Simple Bridge

• Column Brisance: total loss of load

carrying capacity

• Progressive Collapse

–Superstructure

–Bearings

• FEA Modeling

– Element death

and birth option

utilized


Bending and Catenary Actions:

Bridges


Bending and Catenary Actions:

Buildings


Results

• Catenary action important

– Lower deflections and rotations

– Can it be mobilized?

• Reversed moment and shear in superstructure

• High tensile force in the superstructure


Multi-hazard Considerations

• Provide both bending and shear

– More than integrity reinforcements

– Perhaps called:

Multi-hazard reinforcements


Response: Blast vs. Seismic

Sources: FEMA and Smilowitz, Weidlinger


Stresses: Blast vs. Seismic

Blast Seismic


Mid-Height Failures during various EQs

Source: USGS

1st Story Column,

Mexico City EQ 1985 Olive View Hospital

San Fernando EQ., 1971

Foothill Freeway, Failure

attribute to combined V&H;

San Fernando EQ., 1971


Conclusions

• Multi-hazard approach requires

additional emphasis on vertical strength

and stability of the structural system.

–Ductile load path for gravity load

–Design for anti-gravity forces oThis will have significant seismic benefits


Conclusions (cont’d)

• For Bridges

– Thoroughly review bridge performance during

Katrina

oMany implications

– Ensure that the superstructure can withstand

higher and/or reversed flexural and shear

stresses due to various hazards.

oWe need to think about providing multi-hazard

reinforcements in the deck

Source: www.rjwatson.com

http://www.rjwatson.com/



– Provide bearings with

much higher rotational

capacity (>4%)

Source: www.rjwatson.com

– Cap beams must be able

to redistribute forces o Use integral connection to girders

o Use more than 2 columns

o Provide adequate seat length (both

directions)

http://www.rjwatson.com/



– Ensure robust load transfer mechanism so that

large catenary action and/or hydrodynamic

forces are transferred.

Clearance?

Strength?



– Provide strong shear keys to

prevent lateral movement

– Provide hold-down devices


Recommendations

Thermal

• Develop knowledge base

– Comparative review of buildings/bridges

performance during past hazards

• Formulate multi-hazard

design framework and

guidelines

• Develop new designs and

technologies


Knowledge Base: Directionality Effect

of Blast Load


Directionality Effect: Point a


Directionality Effect: Point c


Design Implications


Blast Damage Simulation

150 mm (6 in) thick concrete slab

fc‘ = 35 MPa (5 ksi)

20 kg (44 lb) TNT blast

1 m (3.3 ft) standoff


Pressure Time History


Blast Damage without Water Jacket


Blast Damage with Water Jacket


Blast Damage with Water Jacket (cont’d)


Thank You!

on multi-hazard design of highway bridges -...

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