A SAMPLING OF BRIDGE PERFORMANCE CRITERIA
BY MARK YASHINSKY, CALTRANS OFFICE OF
EARTHQUAKE ENGINEERING
Most bridge owners have adopted design criteria that limits
damage to specified levels based on the size of the earthquake and
the importance of the bridge. A good source of information for
bridge performance criteria is ATC-18, “Seismic Design Criteria
for Bridges and Other Highway Structures: Current and Future.”
However, a lot has changed since this report was written in 1997.
There are three parts to performance criteria:
1. The design earthquakes and their associated hazards.
2. Different categories of bridges.
3. Different damage states.
I) The Design Earthquake.
Japan’s Design Earthquake
All bridges are designed for three levels of earthquakes.
1. A high probability/low intensity earthquake and two very large, low probability
earthquakes.
2. a 1923 Tokyo subduction zone event
3. a 1995 Kobe crustal event.
For smaller, more frequent events both ordinary and important bridges are to survive without
damage. For larger, low probability events, ordinary bridges must survive without collapse
and important bridges must have limited damage.
New Zealand Design Earthquake
All bridges are designed for three levels of earthquakes.
1. A design earthquake with a return period of 450 years.
2. A smaller earthquake adjusted using a Poisson Distribution.
3. A very rare earthquake adjusted using a Poisson Distribution.
I) The Design Earthquake continued.
AREMA (Railway) Bridge Design Earthquake
Railway bridges are designed for three earthquakes
Ground Motion Level
1
2
3
Frequency
Occasionally
Rare
Very Rare
Average Return Period (yrs)
50-100
200-500
1000-2400
Level 1 ground motion that has a reasonable chance of being exceeded during the life of the bridge.
Level 2 ground motion that has a low probably of being exceeded during the life of the bridge.
Level 3 ground motion for a rare, intense earthquake. The return period for each limit state is
determined by multiplying the difference in the average return period in the table above by an
importance classification factor ‘I’; dividing the product by 4; and adding the result to the
minimum return period.
Chapter 9 of the AREMA manual
provide maps from the USGS that give
the peak rock accelerations for 100 year,
475 year, and 2,400 year return period
earthquakes for Canada, the United
States, and for Mexico. Base acceleration
coefficients (as a percentage of g) are
taken from the 100 year, 475 year, and
2,400 year maps and linearly interpolated
with the return periods obtained using the
importance classification factor to obtain
the acceleration for the three limit states.
I) The Design Earthquake continued.
AASHTO LRFD DESIGN EARTHQUAKE (2001)
Probability of Exceedance for Design Earthquake
Performance Level
Life Safety
Operational
Rare Earthquake (MCE) 3% in 75 years
Service
Significant
Immediate
Damage
Significant
Minimal
Frequent or Expected Earthquake 50% in 75 years
Service
Immediate
Immediate
Damage
Minimal
Minimal
Design Earthquake
The upper-level earthquake considered in these provisions is designated the Maximum Considered Earthquake, or
MCE. In general the ground motions on national MCE ground motion maps have a probability of exceedance of
approximately 3% in 75 years. However, adjacent to highly active faults, ground motions on MCE maps are
bounded deterministically. When bounded deterministically, MCE ground motions have a probability of exceedance
higher than 3% in 75 years.
The performance objective for the frequent or expected earthquake is either explicitly included as an elastic design
for the 50% in 75 year force level or results implicitly from design for the 3% in 75 year force level.
Caltrans Design Earthquake
Safety Evaluation Ground Motion (Up to two methods of defining ground motions)
 Deterministically assessed ground motions from the maximum earthquake as defined by the Division of Mines and Geology Open-File
Report 92-1 (1992).
 Probabilistically assessed ground motions with a long return period (approx. 1000-2000 years).
For important bridges, both methods shall be given consideration, however the probabilistic evaluation shall be reviewed by a CALTRANS
approved consensus group. For ordinary bridges, the motions shall be based only on the deterministic evaluation. In the future, the role of
the two methods for these bridges shall be reviewed by a CALTRANS approved consensus group.
Functional Evaluation Ground Motion:
Probabilistically assessed ground motions that have a 60% probability of not being exceeded during the useful life of the bridge. A
CALTRANS approved consensus group shall review the determination of this event.
Although the performance criteria provide functional evaluation requirements for ordinary bridges, these structures do not require an
explicit functional evaluation if they meet the safety evaluation performance criteria. In other words, Caltrans designs ordinary bridges for
only one event, the deterministically assessed ground motion from the maximum earthquake.
I) The Design Earthquake concluded.
Designing bridges for different return periods makes sense in regions
where large earthquakes are rare. However, in California, there is only
a moderate difference between the 100 year event and the 10000 year
event as shown in the figure below.
II) Bridge Categories.
Japan’s Bridge Categories
Bridges shall be classified into two groups of importance considered in relation with road
classes and bridge functions and structures:
Class A bridges are of ordinary importance.
Class B bridges are of high importance.
New Zealand’s Bridge Categories
Bridges are divided into three categories based on traffic and importance (jurisdiction).
Caltrans Bridge Categories
After the Northridge Earthquake (Housner, 1994), Caltrans adopted performance criteria for
important and ordinary bridges, where an important bridge meets one of three criteria:
A bridge required for secondary life safety, such as providing the only access to
a hospital.
A bridge formally designated as critical by a local emergency plan.
A bridge whose loss would cause a major economic impact.
All other bridges are considered ordinary.
AASHTO LRFD Bridge Categories
Bridges are divided into three categories of importance, but these categories are not
specifically addressed in design.
II) Bridge Categories concluded.
US RAILWAY (AREMA) Bridge Categories (2000).
The Importance Classification Factor ‘I’ is the sum of a bridge’s immediate safety value, its immediate value, and its replacement
value (all multiplied by different weighing factors).
IMMEDIATE SAFETY VALUE (factors are summed and the total < 4).
Occupancy Factor
Freight Service only
1
Less than 10 passengers per day
2
More than 10 passengers per day
4
0 to 4
Hazardous Material Factor
0-4
Community Lifeline Factor
IMMEDIATE VALUE (factors are summed)
Railroad Utilization Factor
Under 10 million gross tons annual traffic
1
Between 10 million to 50 million gross tons annual traffic
2
Over 50 million gross tons annual traffic
4
Detour Availability Factor
No Detour Available
1.00
Inconvenient Detour Route
0.50
Detour Route Readily Available
0.25
REPLACEMENT VALUE (factors are summed and the total < 4)
Span Length Factor
Less than 35 ft
1
Between 35 and 125 ft
2
Between 125 and 250 ft
3
Greater than 250 ft
4
Bridge Length Factor
Less than 100 ft
1.0
Between 100 and 1000 ft
1.5
Greater than 1000 ft
2.0
Bridge Height Factor
Less than 20 ft
0.75
Between 20 and 40 ft
1.00
Greater than 40 ft
1.25
III) Damage.
Japan’s Bridge Damage
For smaller, more frequent events both ordinary and important bridges are to survive without
damage. For larger, low probability events, ordinary bridges must survive without collapse
and important bridges must have limited damage.
Safety Factor a, for Reducing the Lateral Force on Concrete Piers.
Bridge Importance Type
Type I Ground Motion
Type II Ground Motion
Type B – Important Bridges
3.0
1.5
Type A – Standard Bridges
2.4
1.2
New Zealand Bridge Damage
1. After a design event, the bridge should remain usable for emergency traffic, although
some repairs may be needed. Moreover, the bridge should be repairable to its initial
condition.
2. After an event with a return period significantly smaller than the design value, damage
should be minor, and without disrupting traffic.
3. For an event with a very large return period, the bridge should not collapse. Moreover, it
should be usable to emergency traffic after temporary repairs and it should be capable of
being brought back into service, perhaps at a lower level of service.
AREMA (Railway) Bridge Damage
The serviceability limit state provides for train safety after a moderate event.
The ultimate limit state provides structural integrity after a large event.
The survivability limit state prevents bridge collapse for intense events.
III) Damage continued.
Caltrans Performance Criteria for New Bridge Design.
Ground Motion at Site
Ordinary Bridge
Important Bridge
Functional
Evaluation
Ground Motion
Functionality – Some Loss
Functionality – Slight Loss
Damage State – Moderate
Damage State – Minor/Slight
Safety
Evaluation
Ground Motion
Functionality – Considerable Loss
Functionality – Some Loss
Damage State – Major/Extensive
Damage State - Moderate
AASHTO LRFD PERFORMANCE CRITERIA (2001)
Probability of Exceedance for the Design
Performance Level
Life Safety
Operational
Earthquake
Rare Earthquake (MCE)
Service
Significant
Immediate
3% in 75 years
Damage
Significant
Minimal
Frequent or Expected Earthquake
Service
Immediate
Immediate
50% in 75 years
Damage
Minimal
Minimal
Service Levels
Immediate Full access to normal traffic shall be available to traffic following an inspection of the bridge.
Significant Disruption Unlimited access (reduced lanes, light emergency traffic) may be possible after shoring, however the bridge may
need to be replaced.
Damage Levels
None
Evidence or movement but no notable damage.
Minimal
Some visible signs of damage. Minor inelastic response may occur, but post-earthquake damage is limited to narrow flexural cracking in
concrete. Permanent deformations are not apparent, and any repairs could be made under non-emergency conditions with the exception
of superstructure joints.
Significant
Although there is no collapse, permanent offsets may occur and damage consisting of cracking, reinforcement yield, and major spilling
of concrete may require closure to repair. Partial or complete replacement of columns may be required in some cases. For sites with
lateral flow due to liquefaction, significant Inelastic deformation is permitted in the piles, whereas for all other sites the foundations are
capacity-protected and no damage is anticipated. Partial or complete replacement of the columns and piles may be necessary if
significant lateral flow occurs.
III) Damage continued.
The FHWA Retrofit Manual uses damage criteria developed by Mander
and Basoz in their “Seismic Fragility Curve Theory for Highway
Bridges” to prioritize bridges for retrofit.
Categories of Bridge Damage (Mander, 1999).
Damage State
1) None (pre-yield)
2) Minor/Slight
3) Moderate
4) Major/Extensive
5) Complete/Collapse
Functionality
Required Repairs
No Loss.
None
Slight Loss.
Inspect, Adjust, Patch
Some Loss.
Repair Components
Considerable loss. Rebuild Components
Total loss.
Rebuild Structure
Expected Outage
None
< 3 days
< 3 weeks
<3 months
>3 months
It uses NBI fields to determine the bridge fragility.
NBI Data
1
8
27
34
42
43
45
46
48
49
52
Definition
State
Structure number
Year built
Skew
Service type
Structure type
Number of spans in main unit
Number of approach spans
Length of maximum span
Structure Length
Deck Width
Other Use
To infer type of code design
General identification number
Infer whether or not a seismic design
To select only highway bridges
Single or multi-span
To infer base fragility curve
To infer whether it’s a major bridge
To infer if it’s a major bridge
To infer span length and replacement value.
To compute replacement value
III) Damage continued.
FHWA RETROFIT MANUAL EXPECTED DAMAGE METHOD FOR THE
RANKING AND PRIORITIZATION OF BRIDGES
This method compares the severity of damage to each bridge due to the same
earthquake. The bridges are ranked by the amount of damage, RCRT or the total cost
of repair, TLOSS.
RCRT   ( RCR i  PDS i S a )  1.0
5
i2
PDS i S a 
= probability of being in Damage state DSi for a given spectral acceleration
Sa at structural period, T = 1.0 sec.
RCR = repair cost ratio for ith damage mode
Damage
1 none
2 slight
3 moderate 4. extensive
5 collapse
RCR  2
 1.0
# spans
RCR
0
0.01 to 0.03 0.02 to 0.15 0.10 to 0.40
TLOSS = BLOSS +HLOSS Where BLOSS =cost of structural damage and HLOSS =indirect
loss.
B
 U B  L  RCR
i
i 5
i
LOSS
$
T
2
2
U$ = unit construction cost in $/m (in 2000 it was $1100/m ).
B = width of bridge deck.
L = total bridge length.
III) Damage concluded.
IV) CONCLUSIONS.
1. Higher performance criteria (above ‘no collapse’) is exceedingly
difficult to achieve. When ductility is limited, displacements are
reduced and accelerations are greatly increased as shown in the figure
below.
IV) CONCLUSIONS.
For instance, the Southern Freeway Viaduct was retrofit to have a
ductility demand of 4.0, but due to weak soil and large ground motion,
the retrofit ended up costing 1.3 times the replacement cost of the
structure.
IV) CONCLUSIONS.
Originally, BART engineers were hoping to keep their trains running
after a major earthquake. However, they soon realized that anything
beyond Life Safety had an unacceptable benefit to cost ratio.
IV) CONCLUSIONS.
The Performance Criteria for all the new, important bridges, such as the
East Bay Crossing, the new Benecia Martinez Bridge, and the I-880
replacement was to simply reduce the ductility demand to 3.0.