Understanding what you really want from level 3 bridge
inspections and bridge load capacity assessments
Neal Lake
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Level 3
Bridge Assessment
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This Photo by Unknown Author is licensed under CC BY-NC
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Why undertake a Level 3 bridge load assessment• Heavy vehicle access requests
• Old design standard
• Deterioration reported from Level 2 inspections
• Reports of unusual bridge behaviour
• Suspected damage from major loading events
– Overload
– Flooding
– Damage from vehicle strikes
• Modification to the structure or additional dead loads
• No information on the original design
• Poor construction quality
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Take the risk
• Hope for the
best or
understand risks
Repair, Maintain,
Modify
• Maintain original
design capacity
Strengthen
• Upgrade the
bridge to a
higher capacity
Replace
• New design to
meet
requirements
When faced with a substandard bridgeOptions?
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Decision Making Process and Considerations
Basis of Decision making
• Review Context
• Define Objectives
• Factors Influencing
• Courses of action
• Alignment of stakeholders
• Plan
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The Rating Equation
AS5100.7
Rating Factor = 𝐴𝑣𝑎𝑖𝑙𝑎𝑏𝑙𝑒 𝑏𝑟𝑖𝑑𝑔𝑒 𝑐𝑎𝑝𝑎𝑐𝑖𝑡𝑦 𝑓𝑜𝑟 𝑙𝑖𝑣𝑒 𝑙𝑜𝑎𝑑 𝑒𝑓𝑓𝑒𝑐𝑡𝑠
𝐿𝑖𝑣𝑒 𝑙𝑜𝑎𝑑 𝑒𝑓𝑓𝑒𝑐𝑡𝑠 𝑜𝑓 𝑛𝑜𝑚𝑖𝑛𝑎𝑡𝑒𝑑 𝑟𝑎𝑡𝑖𝑛𝑔 𝑣𝑒ℎ𝑖𝑐𝑙𝑒
• WIM
• Ambient traffic
response
• Analytical load assessment
– Tier 1 Line model
– Tier 2 Grillage and Capacity
• Tier 3 Everything else
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Process for Bridge Assessment
• Austroads (2018) “Higher Order Bridge
Assessment in Australia”
Tier 1
Tier 2
Tier 3
Determination of the assessment
objectives
Data:• Cost of Tier 3 investigation• Potential for investigation
to achieve positive outcome
Undertake Preliminary Checks
Determine at a high level if a Tier 3 investigation is
appropriate and like to yield improvements considering
the various data inputs
Tier 3 assessment produces favourable results
Decide to Undertake Tier 3 assessment?
Yes
Leave stricture as is, update Tier 1 and Tier 2 processes and results to reflect the outcome
Consider strengthening / renewal or place service level
restriction / controlling the risk using structure management
plans
No
Yes
Yes
Tier 1 assessment has
favourable outcome
Preliminary Assessment
Conduct Desktop Study to identify relevant plans,
documents, standards
Conduct a Tier 1 assessment
Data:• Business Objectives• L2 Condition assessment• Strategic Service Level
Provisions- Safety- Function- Special requirements
• Design standards• Design specifications• Historical bridge data• Design vehicle or current
operation vehicle• Scenarios
No further action required. Service level provisions can be
enactedYes
Conduct a Tier 2 assessment
Yes
Are there drawings
No
Tier 2 assessment has
a favourable outcome
Yes
Use historical bridge family information and where
necessary undertake Tier 3 resistance model testing to
determine material parameters and dimensions
relevant for the material type e.g., concrete strengths,
reinforcing bar type, sizing and spacing
No
Update Tier 1 process and results
to reflect the outcome
Undertake preliminary checks
Determine at a high level if a Tier 2 investigation is
appropriate considering data
inputs
No
Conduct a Tier 3 assessment
NoTier 3 Assessments
should be considered
incremental in nature always
assessing potential gain vs cost
Decide to Undertake Tier 2
assessment
No
No
Assessment Request / Need
• As cycles increase
• Cost increases
• Sophistication increases
• Certainty increases (hopefully)
Only cycle if the potential gains will assist to achieve the defined objectives within the cost/risk/performance balance
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RFQ Issues
• Combining Level 3 investigations with
strengthening/retrofit
• Scope that will not achieve the objectives:
– Level 3 testing without considering whether the overall
objectives are likely to be achievable
– Scope with context
– Asked to pricing without context
– Load/Performance testing
• Scopes that are way to extensive for the actual
budget
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Load Testing
• Expensive
• At service levels tells you very little
about behaviour at ultimate
(cannot reliably use to calibrate
analytical models)
• Dynamic testing relates to service loads not ultimate loads and depends on many variables not part of the testing
• Proof loading can be effective but difficult to safely do if there are no drawings (More relevant when there is a family of bridges) (expensive)
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Load Testing
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Heavy Vehicle Applications
• Line model comparison should be the primary basis (can be based
on design era)
– span length
– span continuity
– design vehicle or known acceptable loading configuration
– L2 structure condition.
• Anything more: there should be a request for addition funding
• Use Level 3s to determine the impacts of deterioration / damage
on the intended design capacity
What should councils be expected to undertake
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Using AS ISO 13822
• Plausibility check – enables a critical review of any discrepancies
between the results of the analysis and the real-life condition of the
structure thus identified “plausibility gaps” can be used to identify
many solutions that may be cost effective that can still achieve the
required outcomes.
What should councils be expected to undertake
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Conclusions
• Faced with a substandard bridge; Take the risk,
repair, maintain or modify, strengthen replace
• Follow a decision making process RDFCAP
• Take an iterative approach to Level 3
investigations
• Make sure that any investigations will get you
closer to a decision
• Make sure service provider is not invested in a
certain outcome
• Get advice from someone knowledgeable in the
area
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QUESTIONS?
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Failure Investigations