5th Tongji-UBC Symposium on Earthquake Engineering
Performance-based Seismic
Design in 2014 Canadian
Bridge Code
Sharlie Huffman, P.Eng.
PERFORMANCE-BASED SEISMIC DESIGN
Performance-based design provides a consistent outcome from differing tectonic environments
allows designers the flexibility of choosing materials, design options and construction methodologies to
more accurately reflect the seismic environment and configuration of the designed structure
describes the performance:
Clear, easily understood terms, explicity demonstrated
Does not restrict methodology
Currently needs some prescriptive boundaries
provides owners, regulatory agencies, designers and the public to have a consistent expectation of the
structure performance during designated levels of seismic events.
provides owners and regulatory agencies flexibility to risk-manage expenditure and performance
Enables vital retrofits to suit individual circumstances rather than a prescriptive bar.
May require more sophisticated analysis to understand or demonstrate the required performance.
PBD or FBD
While all seismic design in all categories can use performance-based
design, Table 4.11 specifies where PBD is required. Where Table 4.11 shows
FBD is permitted, the Authority having jurisdiction may require PBD instead.
Regular bridge requirements
SINGLE SPAN BRIDGE EXEMPTION
S6-06
Only a few bridge types when single span required detailed seismic
analysis.
At one time, single span bridges were generally small and regular
and with a few exceptions such as trusses and arches.
Currently single span bridges can be girder, truss, arch, cable-stay,
spiral etc.
S6-14
Only a few bridge types when single span are exempted from
detailed seismic analysis.
PERFORMANCE LEVELS
Implied Performance Levels S6-06 Commentary
50 year
Prob.
Life Line
Service
10%
Immediate
All
5%
Immediate
Emergency
Damage
Emergency
Service
Damage
Other
Service
Immediate
Emergency
Damage
Repairable
Repairable No Collapse
S6-06 does not provide descriptions of the service and damage states. Going to
other Codes that also use such terms provides significant variation in definition.
PERFORMANCE-BASED DESIGN
Performance Levels S6-14
50 yr
Prob.
Life Line
Service
Damage
10%
Immediate
None
5%
Immediate Minimal
2%
Service
Limited
Repairable
Major Route
Service
Other
Damage
Service
Damage
Immediate Minimal
Service
Limited
Repairable
Service
Disruption
Extensive
Service
Limited
Repairable
Service
Probable
Extensive Life Safety
Disruption
Replacement
S6-14 provides descriptions of the service and damage criteria in primarily operational
terms with some prescriptive criteria. All criteria must be met – not only the prescriptive
PERFORMANCE-BASED DESIGN
Cost drivers for structural performance:
The human cost – deaths, injuries, social dislocation, economic loss
Structural cost – cost of repair/replacement due to direct damage and the impact on the
overall capacities to respond to multiple demands – regulatory, owners/agencies, funding,
professionals, constructors, suppliers, transporters.
Downtime – impact locally and regionally on loss of the asset in terms of direct financial
impact (tolls, taxes), emergency response, social and economic recovery impacts .
These drivers have been incorporated into the performance criteria for the respective
importance categories.
PERFORMANCE-BASED DESIGN
In use in BC for seismic design for over a decade
Initially a combined prescriptive and performance-based approach for seismic retrofits
Subsequently implemented for major projects in BC
Sea-to –Sky Highway 2010
Pitt River Bridge 2011
Port Mann/Highway 1 project 2009-2015
South Fraser Perimeter Road 2012-2014
RETROFITS
S6-06 essentially required retrofits to new bridge design level.
This was problematic for agencies with inventory of bridges that
were not well designed for seismic but were otherwise in
acceptable structural condition. It was not always possible to either
achieve new design level with the old structure or to do so
economically.
Many jurisdictions designated reduced levels of capacity for
retrofits.
RETROFITS
Recognizes the potential limitations on retrofit of older structures.
Addresses the public expectation of post retrofit capacity
Places the performance levels within the Owner/Regulatory
Authorities control.
Utilizes PBD which enables Owners and Authorities to proceed with
vital retrofits at reduced levels to suit individual circumstances.
The PBD approach also provides the ability for increased capacity
through the selection of only some of the criteria from a higher
category where that is technically feasible and would provide an
improved cost-benefit.
PBD provides an easily communicated performance expectation for
discussions with owners or public to occur.
RETROFITS
Sample PBD Grid for Retrofits – to be determined by owner/Regulatory Authority
50 year
Probability
10%
5%
2%
Lifeline Bridges
Major-Route Bridges
Service
Damage
Service
Damage
Immediate
Minimal
Service
Limited
Repairable
Other Bridges
Service
Damage
Service
Extensive *
Disruption *
Service
Service
Probable
Repairable* Disruption Extensive* Life Safety
Limited*
replacement
*
Service
Probable
Extensive Life Safety
Disruption
replacement
* Optional performance levels
__
__
Challenges to PBD
Explicit
demonstration
Optimizing
effort
Explicit Demonstration
One of the main challenges to the PBD requirement is the explicit
demonstration that the performance criteria have been met.
Analysis requirements in codes tend to be based on structure importance
rather than structure configuration, complexity and response.
Using non-linear dynamic analysis and full FEM today’s software will
enable designer to confirm member properties and displacements sufficient
to confirm performance compliance.
The minimum requirements of code are just that – minimum – but do all
bridges require that level of analysis?
Can partial or simplified models be effective?
Optimizing effort
Designers use “safest”, most extensive methods – excess effort
Designers look for exemptions to minimize effort – insufficient effort
Hit and miss – over time methods and results get optimized/corrected
University research and studies (that are reproduced) to provide optimization
It is important that meeting the performance criteria is understood and
demonstrated by the designer – and structure specific
Research
Universities have an important role to play in moving codes forward, to facilitate
implementation of seismic PBD, to contribute to ongoing design quality and future code
updates. There are many opportunities for research, such as:
Matching analysis levels to structure types and performance levels
Effective modelling
Damage testing to confirm damage levels relative to inputs
Testing consistency within the levels of performance criteria
Algorithms for measuring and predicting damage (SHM)
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THANK YOU
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