tests & modeling (pt bonded two-way slab)

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 (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.)


Courtesy of K.R. Chung


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)


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)


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)


A bonded PT interior two-way slab-column connection (unbonded not tested)




One bonded PT beam and two unbonded PT beams; same prestressing

Cooke et al. (1971)

TESTS & MODELING (PT Bonded One-way Slabs)



Analytical result

of tensile stress pattern

(under monotonic lateral loading) Observed crack pattern

(under reversed cyclic loading)



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 Unbonded

Push strands into the duct Extruded tendons



Bonded Unbonded

Hard to fix, once grouted Adjustment on site is easy.


Unbonded

250

Obstruction with column

longitudinal bars

Minimal obstruction by

column longitudinal bars

Bonded


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

tests & modeling (pt bonded two-way slab)

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