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LRFD and GDOT
Challenges and Solutions to Implementation
- f AASHTO LRFD 5th Edition
LRFD and GDOT Challenges and Solutions to Implementation of AASHTO - - PowerPoint PPT Presentation
LRFD and GDOT Challenges and Solutions to Implementation of AASHTO - - PowerPoint PPT Presentation
LRFD and GDOT Challenges and Solutions to Implementation of AASHTO LRFD 5 th Edition Ian Rish, P.E., Environmental Testing Branch Supervisor What is different about Load and Resistance Factor Design (LRFD) Factor of Safety (OLD) All the
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GDOT Work Flow for Bridge Foundation Investigations
Preliminary Bridge Layout Geotechnical Investigation Foundation Selection Bridge Foundation Loads LRFD BFI Final Bridge Plans
AASHTO 17th Edition Design
Geotechnical capacity controlled by factors of safety.
AASHTO LRFD 5th Edition Design
Geotechnical resistances based on resistance factors.
Preliminary Bridge Layout Geotechnical Investigation ASD BFI Final Bridge Plans
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Provide pile sizes based on their design Assumed Driving Condition (6.5.4.2)
- Severe
Provide factored and service loads to
- ptimize foundation design.
- Old estimated tips for piles based on maximum
allowable load instead of specific design load for foundation element.
Bridge Office Information
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Tolerances:
- Vertical Deformation
- Settlement
- Axial Resistance
- Horizontal Deformation
- Settlement
- Lateral Resistance
Service Limit State
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How much design done at service limit?
Spread footings
- Old method controlled for settlement of 1 inch.
- New method - what is tolerable?
Pile bents/footings
- L-pile analysis infrequent for piles.
Drilled shafts
- L-pile analysis routinely performed.
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Piles driven into soil Piles driven to soft rock
- Acts like soil
Piles driven to hard rock
- Loads controlled to reduce damage
- Rock is harder than the pile
Strength Limit State for Piles
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Strength?
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Scour
- Extreme rain events can scour out bridge piers
Downdrag
- Settlement can induce loads in piles
Lateral Loads
- Horizontal forces could bend a pile
Strength Limit State (cont.)
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Resistance Factors for Driving
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Resistance Factors (cont.)
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Old Practice (ASD)
- In-house developed method
- Source data not available
- Not able to come up with resistance factor
New Practice (LRFD)
- AASHTO approved method
- Driven 1.2 is free but no longer updated (has issues)
- In process of purchasing new software
Static Analysis
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What does this tells us?
Driven Output
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Why/when is this needed? What information is needed?
- Boring Log
- Hammer
- Pile Information
- Type (H-pile, PSC, MS)
- Size
- Physical Properties (fy, f’c, etc.)
- Length
Drivability Analysis
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Drivability Analysis Output
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Seismic
- Not usually an issue for Georgia
Scour
- This is our primary concern due to issues in the past.
Downdrag
- Normally taken care of with consolidation before driving
(Design – Bid – Build)
- Load included in pile or other options (Design Build)
Extreme Events
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Rock
- RMR
- No settlement
Soil
- Soil properties
- How much settlement?
Effective footing size?
Spread Footings
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Skin friction (soil/IGM)
- Methods are same as before
- Load tests recommended
End bearing (rock)
- Old practice based RQD and old data
- 5th and 6th edition based on RMR
- 7th edition based on GSI
- Load test?
Drilled Shafts
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Old BFI Template
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New BFI Template
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