A project undertaken by

TRANSIT NEW ZEALAND

in conjunction with OPUS INTERNATIONAL CONSULTANTS LIMITED

APEX PROJECT MANAGEMENT LIMITED

and

REGIONAL BRIDGE CONSULTANTS

S E I S M I C S E C U R I T Y O F S T A T E

H I G H W AY B R I D G E S I N

N E W Z E A L A N D

SCREENING & RETROFIT – PROGRESS SUMMARY

S E I S M I C S E C U R I T Y O F S T A T E

H I G H W AY B R I D G E S I N

N E W Z E A L A N D

SCREENING & RETROFIT – PROGRESS SUMMARY

2

OBJECTIVE & STATUS

• To identify bridges that justify a more detailed seismic assessment and, possibly, retrofitting

• Seismic screening completed

• Retrofitting underway

3

BACKGROUND

Project drivers:

• Experience from earthquakes – integrity of the roading network is vital

• Dramatic improvement in performance often achievable from simple measures, e.g. linkages

• Past practice - since 1933, bridges either monolithic or have spans interlinked

4

BACKGROUND

• Past retrofit policy – low cost seismic improvements in conjunction with work to raise service standards

• In early 1990s, 8 bridges in regions of higher seismicity retrofitted for linkages

5

BACKGROUND

• Wellington’s Thorndon Overbridge and the Auckland Harbour Bridge retrofitted

• A screening procedure was developed Refer 12th World Earthquake Conference (Chapman et al)

6

RISK ASSESSMENT

• Identification of structure vulnerabilities

• Classification of risk level for each risk event - likelihood & consequences

• likelihood derived from:

• peak ground acceleration causing risk event• seismicity of site

• consequences derived from:

• effect on safety• extent of traffic disruption

7

ECONOMIC RANKING INDICATOR (ERI)• For “high” and “significant” risks, an

“Economic Ranking Indicator” determined

• “ERI” was based on factors such as:• traffic volume

• duration & probability of disruption

• cost of traffic disruption

• cost of bridge damage (if significant)

• discounted cost (ROC) of retrofit

8

RANKING

• Ranking was based on factors such as:• Route priority

• Risk to Life

• ERI value

• Number of risk events

9

OUTCOME

• 3813 bridges & culverts screened• 2842 (75%) eliminated• 971 (25%) subjected to risk assessment• 381 (10%) “high” or “significant” risk level• 188 (5%) separately identified as having

linkage deficiencies• $850 per bridge for 2322 bridges

10

ASSESSING & RETROFITTING STRUCTURES• Top 50 ranked structures will be assessed

• Available specialist resources likely to constrain the timeframe for assessments

• Expenditure ~ $5M to ~$6M per annum

11

Bridge Seismic ScreeningStage 2

• Progress to date

– Linkage Retrofit

– Detailed Assessments

– Detail Design & Construction

• Programme Management

12

Progress to date• Linkage Retrofit

– P1 & P2 routes (130 comepleted)

• Detailed Assessments

– Re-prioritised 50 completed detail assessments

– On hold till first 25 bridges addressed

• Detail Design & Construction

– Retrofits complete 10

– Retrofits under construction 5

– Designs in progress 6

– Recommended for replacement 2

Programme Total P1 P2 P3

Detail Assessments 335 192 72 71

Linkages 173 92 45 36

13

Programme Management

• Delegated authority

• Project Team

– Rudolph/Gavin/John Wood/Howard Chapman

• Project Management Framework

– Basis of seismic design for existing bridges.

– Remaining life of structure & condition

– Mode of failure

– Performance indicators & risk profile

– Retrofit vs. replacement cost

– Route importance

– Bridge Design Statement