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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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