pbes seismic research at the university of washington john stanton, marc eberhard, kyle steuck,...
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PBES Seismic Research at the University of Washington
John Stanton, Marc Eberhard, Kyle Steuck , Jason Pang, Todd Janes,
Olafur Haraldsson, Hung Viet Tran, Phillip Davis, Gunnsteinn Finnsson, Jeffrey Schaefer.
University of Washington
FHWA P2P Exchange Workshop,Seattle, 2011.11.15
Partners
• WSDOT
• Berger-ABAM
• Concrete Technology Corporation
• Tri-state Construction
Acknowledgments• FHWA (Highways for Life)
• WSDOT
• PEER
• TransNOW
• Valle Foundation
• PacTrans
• NSF-NEES
ObjectiveDevelop a family of seismic bridge PBES connections for:
• Rapid construction
• Superior seismic performance
Designers can mix and match connections to suit local conditions.
Key Elements1. Large bars grouted in ducts. (Rapid construction)
Key Elements
2. Socket connections. (Rapid construction)
Key Elements3. Unbonded pre-tensioned columns. (Seismic performance)
Construction Procedure
1) Excavate footing.
2) Position and brace precast column.
Construction Procedure
3) Place footing reinforcement and cast.
Construction Procedure
4) Set cap-beam, grout bars into ducts.
Construction Procedure
5) Place girders, diaphragms and deck.
Construction Procedure
Precast
prestressed
c.i.p.
RC (ref)
Precast
RC
Cap-beam
to column
Column to
spread footing
Column to
drilled shaft
Connection
Details
Precast
prestressed
c.i.p.
RC (ref)
Precast
RC
Cap-beam
to column
Column to
spread footing
Column to
drilled shaft
Connection
Details
Large Bar Connection (Cap Beam)
• Bars grouted into ducts.
• Few, large bars simplify fit-up.
• Is development length a problem?
Large Bar Connection (Cap Beam) #18 Bar Anchorage Tests
- Pullout tests.
- Need 6db to develop yield, 10db to develop fracture.
- Bar can easily be anchored within cap beam.
Large-Bar Connection
Cyclic Lateral Load Testing
Large-Bar Connection
• Failure occurs in the column.
• PC Connection behaves the same as c.i.p.
Cyclic Lateral Load Testing
Precast
prestressed
c.i.p.
RC (ref)
Precast
RC
Cap-beam
to column
Column to
spread footing
Column to
drilled shaft
Connection
Details
Footing Connection: Construction
Headed bars
Footing Connection - PerformanceHeaded bars provide good load transfer.
Internal forces:
Strut and Tie Model.
Footing ConnectionHooked bars facing out(Conventional cip)
Load transfer is tangential to hook.
Poor transfer.
Spread Footing Connection
Vertical (gravity) load.
Lateral (seismic) load.
Spread Footing ConnectionConstructability:
• Column has no projecting bars.
• No “form-savers”.
• Easy to fabricate and transport.
Note: Top steel not yet in place
Spread Footing Connection
Structural Performance• Terminators provide better anchorage than
hooked bars facing outwards.• Failure occurs in column, not footing. • Seismic performance as good as, or better
than, conventional c.i.p. construction.
Precast
prestressed
c.i.p.
RC (ref)
Precast
RC
Cap-beam
to column
Column to
spread footing
Column to
drilled shaft
Connection
Details
Drilled-Shaft Connection
Drilled-Shaft Connection
DS-1 DS-2
Drilled-Shaft Connection
Performance depends on spiral in transition region.• 100% c.i.p. spiral failure in column.• 50% c.i.p. spiral failure in transition.
Hoop tension strength of transition region concrete appears to be important.• Third drilled shaft specimen (in lab now)
has thin concrete in transition region.
Precast
prestressed
c.i.p.
RC (ref)
Precast
RC
Cap-beam
to column
Column to
spread footing
Column to
drilled shaft
Connection
Details
Background
Unbonded prestressing tendons for elastic restoring force.
Yielding steel for energy dissipation.
Self-centering structural systems
Pre-Tensioned System
1.Pre-tensioning solves corrosion problems perceived to exist in post-tensioning.
2.Pre-tension in a plant.
• Good QC.
• No special equipment or extra site time needed (compare with post-tensioning).
3. Can add rebars for energy dissipation.
Pre-Tensioned System PC cap-
beamSleeved strand
Bonded strandc.i.p.
footing
Bonded rebar
Cracking plane
Test Specimens
Footing specimen
Cap beam specimen
Test Specimens- Footing
connection
Test Specimens- Footing details
Screw-thread adjustment deviceLoad cell
Strand chuck
Strand sleeve
Bonded region
Void under column
2% drift
Load vs. Displacement
-15 -10 -5 0 5 10 15-4000
-3000
-2000
-1000
0
1000
2000
3000
4000
Drift [%]
Mom
ent
[kip
-in.]
RC: does not re-center
-15 -10 -5 0 5 10 15-3000
-2000
-1000
0
1000
2000
3000
Drift [%]
Mom
ent
[kip
-in.]
UBPT: re-centers
Preliminary Results
1. System re-centers.
2. No strands broke.
3. No loss of strand bond.
5. Damage to concrete at interface, possibly promoted by stub bars from footing.
New pre-tensioned specimen in lab now:
1.Use HyFRC (Hybrid fiber reinforced concrete) in the plastic hinge zone to reduce crushing.
2.Use stainless steel rebars to increase drift capacity and energy dissipation.
Thank You
Background
Accelerate on-site bridge construction.
Use precast concrete components.
Connection details:
seismic-resistant
construct
Column-to-Cap-BeamConnection
Precast column
Precast cap beam
6 # 18 rebar
8.5” corrugated steel ducts
High strength grout
Cap-Beam Connection: Large bars
Column-to-FootingConnection
Pre-Tensioned System
2% drift
6% drift
Spread Footing Connectionafter seismic testing
Foundation undamaged.
Spread Footing Connection – Gravity Load Test
(Damaged) column crushed at: 3.5 * (1.25DL + 1.75LL).
No damage to footing. No sign of punching failure.
-15 -10 -5 0 5 10 15-4000
-3000
-2000
-1000
0
1000
2000
3000
4000
Drift [%]
Mom
ent
[kip
-in.]
-15 -10 -5 0 5 10 15-4000
-3000
-2000
-1000
0
1000
2000
3000
4000
Drift [%]
Mom
ent
[kip
-in.]
SF-1
• Hf/Dc = 1• Slots in column base• More diagonal rft.• 100% Caltrans
stirrups
SF-2 • Hf/Dc = 1• No slots• Less diagonal rft.• 50% Caltrans stirrups
Spread Footing Thickness
SF-1 and SF-2.
Hfoot = Dcol
SF-3.
Hfoot = 0.5 Dcol
-15 -10 -5 0 5 10 15-4000
-3000
-2000
-1000
0
1000
2000
3000
4000
Drift [%]
Mom
ent
[kip
-in.]
SF-1
• Hf/Dc = 1.0• Slots in column base• More diagonal rft.• 100% Caltrans stirrups
SF-3 • Hf/Dc = 0.5• No slots• Less diagonal rft.• Heavy beam shear
reinforcement
-15 -10 -5 0 5 10 15-4000
-3000
-2000
-1000
0
1000
2000
3000
4000
Drift [%]
Mom
ent
[kip
-in.]
SF Movie
After testing.
SF-3
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6
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12
SF-1 SF-2 SF-3
Dri
ft R
atio
(%
)
DS-1
• 100% transverse reinforcement in transition region
DS-2 • 50% transverse
reinforcement in transition region
Next Steps:
1.Test pretensioned, cap-beam specimen.
2. Bond tests on epoxy-coated strand.
3. Data analysis and design methodologies.
Looking Forward:
4. Methodology calibration tests (Grouted ducts, spread footings, drilled shafts)
5. High-performance materials (e.g. ECC at rocking interface).
Precast
prestressed
c.i.p.
RC (ref)
Precast
RC
Cap-beam
to column
Column to
spread footing
Column to
drilled shaft
Connection
Details
NEXT !