Performance-based Seismic Design in 2014 Canadian Bridge Code 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 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 Service 50 year Prob. Life Line Emergency Other   Service Damage 10% Immediate All Immediate Emergency Repairable 5% 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 Major Route Other   Service Damage 10% Immediate None Minimal Service Limited Repairable 5% Service Disruption Extensive 2% Life Safety Probable 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 Lifeline Bridges Major-Route Bridges Other Bridges   Service Damage 10% Immediate Minimal Service Limited Repairable Service Disruption * Extensive * 5% Service Limited* Repairable* Service Disruption* Extensive* Life Safety Probable replacement 2% Service Disruption Extensive __ * 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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