tests & modeling (pt bonded two-way slab)
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BEHAVIOR OF GROUT-BONDED VS.
UNBONDED PT CONCRETE STRUCTURES
University of Oklahoma
Civil Engineering and Environmental Science
May 3rd 2011
Thomas Kang Ph.D., P.E.
Assistant Professor
ACKNOWLEDGEMENTS
1. Substantial input from K.R. Chung & J.W. Park
( , Seoul, Korea)
2. Finite element analysis assistance of Y. Huang,
Ph.D. Student, University of Oklahoma
• Reference No. 1: PTI Journal (Next issue)
• Reference No. 2: Int. Journal of Theoretical & Applied
Multiscale Mechanics (Dec. 2010)
3. Funding support for student and faculty (U.S. DOT-RITA)
4. On-going industry collaboration: C. Hayek ( , USA)
BONDED PT SYSTEM (PT Transfer Girder)
Courtesy of C. Hayek
BONDED PT SYSTEM (PT Transfer Girder)
Courtesy of C. Hayek
BONDED PT SYSTEM (VSL Bonded Tendon System for Flat Plate)
BONDED PT SYSTEM (VSL Bonded Tendon System for Flat Plate)
BONDED PT SYSTEM (Freyssinet Bonded Tendon System for Flat Plate)
PT BLDG. IN DUBAI (Bonded PT Flat Plate)
Dubai, Arab Emirates
Residential & Office Building
24 Floors + 2 Basement Floors
Structural Design:
Dongyang (Korea)
Typical Module:
11.3 m x 9.6 m
(37 x 31.5 ft)
Drop Panel
Thickness:
350 mm (13.8 in.)
PT BLDG. IN DUBAI (Bonded PT Flat Plate)
Courtesy of K.R. Chung
PT BLDG. IN DUBAI (Bonded PT Flat Plate)
PT BLDG. IN SEATTLE (Unbonded PT Flat Plate)
Courtesy of J. Brink
PT BLDG. IN D.C. (Unbonded PT One-way Beam)
Courtesy of C. Hayek
RESEARCH NEEDS
Objectives
Review of prior experimental data
Developing FE models (both bonded and unbonded PT)
Comparison with the data and codes
PT slab-column connections
experienced punching damage
during Northridge EQ (1994).;
Four Seasons Bldg., Sherman
Oaks, CA – demolished (2005)
TESTING OF BONDED PT STRUCTURES
Mattock et al. (1971)
Seven simply supported PT
single-span beams and three
continuous two-span beams with
bonded or unbonded tendons
Cooke et al. (1981)
Twelve simply supported PT one-
way slabs with bonded or
unbonded tendons
Warnitchai et al. (2004)
Two PT bonded interior slab-
column connections with and
without drop panel
Simply supported PT one-way beam
(Mattock et al., 1971)
TESTS & MODELING (PT Bonded Beams)
Mattock et al. (1971)
One bonded PT beam and two unbonded PT beams; same prestressing
Cooke et al. (1971)
Three bonded and three unbonded PT one-way slabs; same other conditions
TESTS & MODELING (PT Bonded One-way Slabs)
Warnitchai et al. (2004)
A bonded PT interior two-way slab-column connection (unbonded not tested)
TESTS & MODELING (PT Bonded Two-way Slab)
Bonded PT slab-column
connection tested in Thailand
(Warnitchai et al., 2004)
Warnitchai et al. (2004)
A bonded PT interior two-way slab-column connection (unbonded not tested)
TESTS & MODELING (PT Bonded Two-way Slab)
TESTS & MODELING (PT Bonded Beams)
Mattock et al. (1971)
TESTS & MODELING (PT Bonded Beams)
Mattock et al. (1971)
TESTS & MODELING (PT Bonded Beams)
Mattock et al. (1971)
One bonded PT beam and two unbonded PT beams; same prestressing
Cooke et al. (1971)
TESTS & MODELING (PT Bonded One-way Slabs)
Cooke et al. (1971)
TESTS & MODELING (PT Bonded One-way Slabs)
Warnitchai et al. (2004)
TESTS & MODELING (PT Bonded Two-way Slab)
Warnitchai et al. (2004)
TESTS & MODELING (PT Bonded Two-way Slab)
Warnitchai et al. (2004)
TESTS & MODELING (PT Bonded Two-way Slab)
Warnitchai et al. (2004)
TESTS & MODELING (PT Bonded Two-way Slab)
Warnitchai et al. (2004)
TESTS & MODELING (PT Bonded Two-way Slab)
Analytical result
of tensile stress pattern
(under monotonic lateral loading) Observed crack pattern
(under reversed cyclic loading)
Warnitchai et al. (2004)
TESTS & MODELING (PT Bonded Two-way Slab)
Warnitchai et al. (2004)
TESTS & MODELING (PT Bonded Two-way Slab)
Strains in bonded tendon
(Exp. vs. FEA)
Shear stress distribution
at the critical section
(FEA)
Warnitchai et al. (2004)
TESTS & MODELING (PT Bonded Two-way Slab)
Strains in bonded tendon
(Exp. vs. FEA)
Shear stress distribution
at the critical section
(FEA)
BONDED VS. UNBONDED (Constructability Issues)
Tendon
Bonded
Unbonded
Slab
20
1
3
20
53.5
mm
Bonded rebar
Slab soffit
Duct
12.7 mm strands (dia.: 12.7mm or ½ in.)
16
1
6
20
44 m
m
Slab soffit
12.7mm strands
(dia.: 6mm, incl. cover)
c.g.s.
1~2 cm difference
For 200~250 mm thick
slab, unbonded is better
Reduced
effective depth
No change in
effective depth
Bonded Unbonded
New post-
tensioning
unnecessary
New post-
tensioning
necessary
If broken, tendon at other locations is okay. Once tendon is broken, no force exists.
BONDED VS. UNBONDED (Rehabilitation Issues)
Bonded Unbonded
No horizontal curve Horizontal curve
BONDED VS. UNBONDED (Constructability Issues)
Bonded Unbonded
Push strands into the duct Extruded tendons
BONDED VS. UNBONDED (Constructability Issues)
BONDED VS. UNBONDED (Constructability Issues)
Bonded Unbonded
Hard to fix, once grouted Adjustment on site is easy.
BONDED VS. UNBONDED (Constructability Issues)
Unbonded
250
Obstruction with column
longitudinal bars
Minimal obstruction by
column longitudinal bars
Bonded
BONDED VS. UNBONDED (Constructability Issues)
Bonded Type Unbonded Type Misc.
Cost regarding
tendons
Cost for Duct and Grouting,
Tendon Max Spacing Cost for anchorages
Unbonded is
better for thinner
members
Bonded
reinforcement
No req’t for minimum bonded
reinforcement (except for Mcr)
Minimum bonded
reinforcement
Cost/Area
Thickness
Bonded
Unbonded
Depends on the number of ducts
Not influenced by tendon layout and spacing
SUMMARY
1. For flat plates, unbonded PT systems dominate in the
U.S. (while there are some bonded PT projects in the
east coast)
2. For transfer girders and bridges, bonded PT systems are
more popular.
3. Structural performance is similar (while drift capacity of a
bonded PT slab-column connection may be lower than
that of unbonded PT connection)
4. Constructability issues – depends on the market and
project.
Thank You!
Any Questions? Kang’s research
on steel FRC
beams in shear
at U of Oklahoma
Kang’s research
on RC T-joints
under cyclic loads
at U of Oklahoma
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