unbonded prestress connections
TRANSCRIPT
![Page 1: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/1.jpg)
UNBONDED PRE-STRESSED
CONNECTIONSProf. John F. Stanton
University of Washington,Seattle, Washington, USA
The ROSE School, Pavia.June 2009
![Page 2: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/2.jpg)
REFERENCE DOCUMENT
Design Guidelines for Precast Concrete Seismic Structural
Systems
John F. Stanton & Suzanne D. NakakiPRESSS Report No. 01/03-09
Available from PCI (and on Rose School website)
![Page 3: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/3.jpg)
UNBONDED PRESTRESSED CONCRETE FRAME:
GOALS• Zero residual drift (ZRD)
– Frame returns to vertical after earthquake
• Damped response
– Damping restricts peak drift
• Little damage even in a large earthquake
– Building can be re-occupied quickly
![Page 4: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/4.jpg)
POSSIBLE CONFIGURATIONS:(Continuous beams)
![Page 5: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/5.jpg)
POSSIBLE CONFIGURATIONS:(Continuous columns)
![Page 6: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/6.jpg)
CONFIGURATIONS
• Continuous Columns– Often used by precasters
• Continuous Beams– Long Heavy Beams– Columns must be accurately placed for bars to fit
![Page 7: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/7.jpg)
REINFORCEMENT CONFIGURATIONS
• Unbonded prestressing only– Simple to construct, but no hysteretic damping.– Damping could be supplied by external devices or
RC frames in parallel with UBPT frame.
• UB prestressing + rebar = “Hybrid Frame”– Internal hysteresis (damping) supplied by rebar– All-in-one package.
![Page 8: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/8.jpg)
UBPT Prestressed-only Frame
Shown with post-tensioned beams, multi-storey columns.Requires post-tensioning on site. Easy fit-up.
Post‐tensioning tendon
(unbonded) Post‐tensioning anchorage
![Page 9: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/9.jpg)
UBPT Prestressed-only Frame
Pre‐stressing tendon
Bonded region
Unbonded region
Shown with pretensioned beams, one-storey columns.Can prestress in plant. Columns must be accurately placed.
![Page 10: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/10.jpg)
UBPT Prestressed-only Frame Components
Unbonded PT tendon
Grout
![Page 11: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/11.jpg)
Hybrid Frame Components
Unbonded PT tendon
Bonded Rebar
Rebar locally debonded
Grout
![Page 12: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/12.jpg)
Deformed Shape
![Page 13: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/13.jpg)
Deformed Shape
![Page 14: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/14.jpg)
Deformed Shape
![Page 15: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/15.jpg)
Deformed Shape
![Page 16: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/16.jpg)
Hybrid Frame Components(Courtesy Nakaki Bashaw Group)
Pre-tensioned strands
Beam rebar (not continuous)
Sleeves for column bars (grouted)
Grout bed at interface
Column bar splices
Only the pre-tensioned strands cross the interface
![Page 17: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/17.jpg)
Hybrid Frame Components(Courtesy Nakaki Bashaw Group)
Mild steel (A706) (grouted)
Unbonded region
Post Tensioned Tendon (ungrouted)
Fiber Reinforced Grout
![Page 18: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/18.jpg)
UBPT FRAME CONCEPT
• PT tendon provides strength
• PT provides elastic restoring force
• Damping is minimal (use 5% critical)
![Page 19: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/19.jpg)
NON-LINEAR ELASTIC BEHAVIORLINEAR NONLINEAR
ELASTIC
INELASTIC
σ σ
σ
ε
εε
Elastic: Load and unload along the same pathInelastic: Load and unload along different pathsLinear: Load/unload path is a straight lineNonlinear: Load/unload paths are not straight.
![Page 20: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/20.jpg)
Hybrid Frame combines both features
Force - Deflection
•Returns to vertical•Nonlinear elastic•Low damping
•Residual drift•Nonlinear inelastic•High damping
PT only
Rebar only
![Page 21: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/21.jpg)
Hysteresis Loops - Combinations
100/0
25/75 0/100
50/5075/25
![Page 22: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/22.jpg)
DESIGN PROCEDURE
• Rational design procedure
• Design forces same as cast-in-place concrete SMRF
• Explicit evaluation of drift capacity
• Design of other parts of frame: per code
![Page 23: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/23.jpg)
ASSUMPTIONS
• All deformation occurs at the interface, not in the beam.
• PT is unbonded the entire length of the frame, except for bonded region at each end.
• cgp is at mid beam-height.
![Page 24: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/24.jpg)
LIMIT STATESWe need to define limit states at which the moment
strength will be computed.
• Nominal moment strength:• Corresponds to the design moment. • Used to size the reinforcement at the interface
• Maximum probable strength• Corresponds to the Maximum Credible
earthquake• Forms the basis for Capacity Design forces for
adjacent elements.
![Page 25: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/25.jpg)
NOMINAL STRENGTH LIMIT STATE
Smaller of • Onset of strain hardening in mild steel (if any).• Yield of PT steel.
Comparable to nominal strength of reinforced concrete frame
![Page 26: Unbonded PreStress Connections](https://reader033.vdocuments.mx/reader033/viewer/2022042517/589df2b91a28ab814a8be4c7/html5/thumbnails/26.jpg)
MAXIMUM PROBABLE STRENGTH LIMIT STATE
• Smaller of : • Strain at peak strength of mild steel.• Yield of PT steel.
System must have at least 3.5% drift capacity at MPS limit state.