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2003 ECI Conference on Advanced Materials for Construction

of Bridges, Buildings, and Other Structures III % FILE:

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Switzerland% FILE:

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(cont)

Editors: % FILE:

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Mistry, P.E., Office of Bridge Technology, Federal Highway Administration,

USA

Dr. Atorod Azizinamini, Ph.D., P.E., Civil Engineering Department,

University of Nebraska, USA

John M. Hooks, P.E., Office of Infrastructure Research & Development,

Federal Highway Administration, USA

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(cont)

Year Paper

Seismic Performance of Precast

Column-Foundation Connection Assembled by

Post-Tensioning

Minehiro Nishiyama∗ Fumio Watanabe†



Seismic Performance of Precast

Column-Foundation Connection Assembled by

Post-Tensioning

Abstract

In order to develop design recommendations for column-foundation con-nection assembled by post-tensioning in seismic regions, cyclic loading testswere carried out on 14 test units simulating such kind of connections underearthquake loading. The tests were consisted of two series: Series A wasmainly for comparison between precast reinforced and precast prestressedconcrete column-foundation connections, and Series B for investigating dif-

ferences between test units with grouted and ungrouted tendons. The mainexperimental parameter other than the above was an axial load level.

∗Kyoto University†

Kyoto University

http://services.bepress.com/eci/advanced materials/5

Copyright c2005 by the authors.



SEISMIC PERFORMANCE OFPRECAST COLUMN-FOUNDATION CONNECTION

ASSEMBLED BY POST-TENSIONING

Minehiro Nishiyama and Fumio Watanabe

Built Environment Materials and Structural Systems

Department of Urban and Environmental Engineering

Kyoto University

Kyoto 606-8501, JAPAN

T & F: 81-75-753-5747; E: [email protected]

ABSTRACT

In order to develop design recommendations for column-foundation connectionassembled by post-tensioning in seismic regions, cyclic loading tests were carried

out on 14 test units simulating such kind of connections under earthquake loading.

The tests were consisted of two series: Series A was mainly for comparison between

precast reinforced and precast prestressed concrete column-foundation connections,

and Series B for investigating differences between test units with grouted and

ungrouted tendons. The main experimental parameter other than the above was an

axial load level.

INTRODUCTION

Post-tensioned precast construction has been getting popular in Japan because

of the following advantages over conventional cast-in-situ construction: 1) Easier

framing and less concrete casting at construction sites. 2) Shear transfer at the

interface between members which are connected is easily achieved by friction due

to prestressing force. 3) Full depth crack opening at the beam-column interface

under cyclic loading at a large inelastic deformation, which may result in pinched

hysteresis curves, is suppressed by prestress. 4) Permanent displacement after

major earthquakes is smaller than that for ordinary reinforced concrete.

One type of the post-tensioned connections used in practice is a column-foundation

connection. Ordinary precast reinforced concrete system is also often used. InJapan non-prestressed precast columns are more popular than prestressed ones.

However, from the viewpoint of construction and restriction of construction time,

there is a case that precast prestressed concrete system may be a better solution.

In Japan use of unbonded tendons for primary seismic resistant members like

girders, columns and structural walls had been prohibited. This year the code has

been revised and now unbonded tendons can be used for structural members if a

kind of displacement-based design different from the currently used allowable stress

based design is utilized, and some measures is taken against tendon fracture:

protection for girders from falling down.

1Nishiyama and Watanabe: Seismic Performance of Precast Column-Foundation Connection Assem

Produced by The Berkeley Electronic Press, 2011



In this paper, two series of loading tests are reported. One is Series A in which

dual-phase composite prestressing steel bars are used, and reinforced concrete

precast column-foundation connections are compared with prestressed ones in

terms of seismic performance. The other is Series B for investigating differences

in seismic performance between test units assembled by grouted and ungrouted

tendons.

EXPERIMENTAL WORK

The experimental work is divided into two test series; in Series A dual-phase

composite prestressing steel bars were used to assemble precast column-foundation

connections. Ordinary precast reinforced concrete column-foundation connections

were also constructed and tested. In addition, three test units were assembled

using ordinary prestressing steel bars. Test series B was planned for investigatingdifferences between precast prestressed column-foundation connections with

grouted and ungrouted tendons.

Series A

Dual-Phase Composite Prestressing Steel Bars

Unlike ordinary prestressing steel which was once heated to 900-1000°C, ferrite

with 0.48% carbon content was chauffaged to 850°C, which turned it to dual-phase

composite: ferrite and austenite. Water cooling changed the austenite into

martensite. This process produced dual-phase composite of high-strength martensite

and normal strength ferrite. Thus, it has a monotonic load-deformation relationship

which is better modeled by a trilinear than a bilinear approximation.

Fig. 1 schematically indicates the comparison of tensile force-strain relationship

between ordinary prestressing steel and dual-phase composite prestressing steel

Fig.1 Tensile force - strain relationship of

dual-phase composite prestressing steel

and ordinary prestressing steel bars

0

50

100

150

200

0 0.5 1 1.5 2 2.5 3 3.5

13mm Ordinary prestressing steel bar

15mm Dual-phasecomposite steel bar

L o a d ( k N )

Strain (%)

Dual-phaseOrdinary

15 13Dia. (mm)

176.7 132.7 Area (mm2 )

718 1100 Yield strength (MPa)

966 1145 Tensile strength (MPa)

17 12 Elongation (%)

Yield Load 127kN

Yield Load 146kN

Fig.2 Measured tensile force - strain

relations for ordinary and dual-phase

tendons

O

A

B

C

Dual-phase composite steel bar

Ordinary prestressing steel bar

Strain

F o r c e

D

Advanced Materials for Construction of Bridges, Buildings, and Other Structures III [2003], Vol. P05, Article 5

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bar. Since dual-phase composite steel bar should have a larger sectional area than

ordinary prestressing steel to have approximately the same yield tensile force, the

sectional area and the elastic stiffness of the dual-phase composite steel are larger

than the ordinary prestressing steel. In the dual-phase composite prestressing steel

bar the second point of change in stiffness (Point A) occurs when the high-strength

part (martensite) yields. Thefi rst point of change in stiffness (Point B) is used tomodel the nonlinear behavior due to yielding of the ordinary strength part (ferrite).

Initial prestress is expected to be introduced to a stress (Point C) between the

two points. Hysteresis loops between the two points contribute to the hysteresis

energy dissipation. Tensile force-strain curves obtained from the tensile tests of the

prestressing steel bars are shown in Fig. 2. They have approximately the same yield

tensile force. Therefore, the dual-phase bar has a larger sectional area, and larger

elastic stiffness than the ordinary bar.

Test Units

Eight precast column-to-foundation connections were constructed. Three of themwere conventionally reinforced by non-prestressed ordinary strength steel. The

other units were post-tensioned by prestressing steel bars. Their specifi cations are

summarized in Table 1. A typical post-tensioned test unit is illustrated in Fig.3.

The introduced prestress corresponded to the stress larger than the fi rst yield point

of the dual-phase composite prestressing steel bar. Thus, the dual-phase composite

prestressing steel bar was expected to be effective for hysteresis energy dissipation

in the early stage of loading. Effective prestressing forces at the time of testing were

426.7kN, 411.4kN, 418.9kN, 348.1kN and 356.5kN for PC1, PC2, PC3, PC4 and

Fig.3 Prestressed concrete test unit of Series A

25mmThick Plate

Column section

Longitudinal

Steel Bars

25mmThick Plate

4- 13PrestressingTendons

15mmMortar Joint

800

LoadingPoint

250

4- 9

15

φ

φ

50

250

150 50

D6 Ties

4- 13 PrestressingTendons

φ

(UNIT:mm)

D 6 @ 3 0

4- 9 Steel Barsφ

1 0 0

4 0 0

5 0 0

1 0 0

2 5 0

5 0

5 0

1 5 0





PC5, respectively. Immediately after introduction of prestress grout was injected into

the sheath. W/C ratio of the grout was 45%. The compressive strength of the grout

attained 38.0MPa.

The compressive strength of concrete used for the columns and the foundations

of the test units were 35.7MPa and 38.8MPa, respectively. The joint mortar at the

interface of the foundation and the column had a compressive strength of 56.9MPa.

Table 1 Test units in Series A

Test unit Longitudinal rebars Column axial load (kN)

RC1

8-D13 (SD395)

550 (0.25)*

RC2 980 (0.45)*

RC3 -224 (-0.46)**

PC1 Ordinary prestressing steel bars

4-φ13 (SBPR930/1080)

550 (0.25)*PC2 980 (0.45)*

PC3 -224 (-0.38)**

PC4 Dual-phase composite prestressing

steel bars 4-φ15

550 (0.25)*

PC5 -224 (-0.44)**

*(): N/f' c A

g , N : axial load, f'

c : concrete compressive strength, A

g : column sectional area

**(): N/f y A

s, f

y : yield strength of longitudinal rebar, A

s: total area of rebars

Testing Methods

After the specifi ed axial load was applied, horizontal load was quasi-staticallyapplied to the top of the column. The fi rst loading cycle was up to the fi rst cracking

load which was detected by a observer. Then, the load was reversed to the negative

direction to as large displacement as the positive loading. This loading cycle was

followed by a series of defl ection controlled cycles comprising two full cycles to each

of the column rotation angles of ±1/200, ±1/100, ±1/50, ±1/33 and ±1/25.

General Behavior of Test Units

Figure 4 shows the horizontal defl ection at the top of the column plotted against the

corresponding load of the column for each unit. The horizontal load plotted in Fig. 4

includes horizontal component of the axial load. All test units was able to be loaded

to the last loading cycles to the column rotation angle of 1/25.

Prestressed Concrete vs. Reinforced Concrete

The prestressed concrete test unit PC1 showed narrower hysteresis loops than the

reinforced concrete unit RC1. They were subjected to 550kN (0.25f’ c A

g ). Prestressing

force was equivalent to the axial compressive load of 0.19 f’ c A

g if loss of prestress

due to column shortening was not considered. Equivalent viscous damping of

each specimen is calculated and shown in Fig. 5. PC1 dissipated 1.58 times larger





hysteresis energy than RC1 at the column rotation angle of 1/100, but equivalent

damping factor of RC1 is larger than that of PC1 at the larger displacement: 48%

larger at 1/50 and 71% at 1/25 in the column rotation angle.

For the test units under the axial load of 980kN, PC2 and RC2, both units were

able to be loaded to a column rotation angle of 1/25. The hysteresis loops obtained

are stable without pinching and large capacity reduction. RC2 dissipated larger

hyseresis energy than PC2. Comparison of equivalent damping factor shows 21%

larger equivalent damping at 1/100 and 31% at 1/25 of RC2 than PC2.

For the test units subjected to tensile axial load, RC3 and PC3, less pinching of

PC3 had been expected because of prestressing force which connected the column

and foundation tightly. However, the actual hysteresis loops of PC3 are pinched

and narrow. This is not because of slip at the interface between the column and thefoundation or at the joint mortar. Displacements measured at the interface indicate

larger transverse displacement in RC3 than in PC3. One of the possible reasons

may be a stress-strain relationship of prestressing steel. Stiffness reduction due

-150

-100

-50

0

50

100

150

-30 -20 -10 0 10 20 30

L o a d ,

P ( k N )

1/100 1/50

Deflection, d (mm)

RC3

Axial load = -224kN (-0.46 f y As )Ordinary RC

-150

-100

-50

0

50

100

150

-30 -20 -10 0 10 20 30

L o a d ,

P ( k N )

1/100 1/50

Deflection, d (mm)

Axial load = -224kN (-0.38f y As )Ordinary ps steel bars

PC3

-150

-100

-50

0

50

100

150

-30 -20 -10 0 10 20 30

L o a d ,

P ( k N )

1/100 1/50

Deflection,d (mm)

Axial load = -224kN (-0.4 4f y As )Graded composite ps steel bars

PC5

-200

-100

0

100

200

-30 -20 -10 0 10 20 30

L o a d ,

P ( k N )

1/100 1/50

Deflection,d (mm)

Axial load = 550kN (0.25f'cAg)Ordinary RC

RC1

-200

-100

0

100

200

-30 -20 -10 0 10 20 30

L o a d ,

P ( k N )

1/100 1/50

Deflection,d (mm)

Axial load = 980kN (0.45f'cAg)Ordinary RC

RC2

-200

-100

0

100

200

-30 -20 -10 0 10 20 30

L o a d ,

P ( k N )

1/100 1/50

Deflection,d (mm)

PC1

Axial load = 550kN (0.25f'cAg)Ordinary ps steel bars

-200

-100

0

100

200

-30 -20 -10 0 10 20 30

L o a d ,

P ( k N )

1/100 1/50

Deflection,d (mm)

Axial load = 980kN (0.45f'cAg)Ordinary ps steel bars

PC2

-200

-100

0

100

200

-30 -20 -10 0 10 20 30

L o a d ,

P ( k N )

1/100 1/50

Deflection, d (mm)

Axial load = 550kN (0.25f'cAg)Graded composite ps steel bars

PC4

0.45f'cAg RC2 PC2

0.25f'cAg RC1 PC1 PC4

-0.46-0.38RC3 PC3 PC5

fyAs

RC Ordinary Dual-phase

Fig.4 Measured horizontal load - defl ection curves





to Baushinger effect may have occurred in the early stage of an unloading path to

negative (compressive) direction when the load was reversed in the post-yield range.

This sort of stiffness reduction in ordinary strength steel occurs on an unloading path

in the negative stress region. In high-strength steel like prestressing steel this may

occur in the earlier stage of unloading path even in the positive stress region.

Effect of Dual-Phase Composite Prestressing Steel Bar

PC4 with dual-phase composite prestressing bars has the least equivalent damping

factor in the displacement range of 1/100 to 1/25 among the test units subject to thecompressive axial load. At 1/200 its factor is slightly larger than that of PC1. PC5

subjected to tensile axial load indicates pinched hysteresis similar to PC3. Equivalent

damping factor of PC5 is as large as that of PC3 and 25% of RC3 at a column

rotation angle of 1/25, which were also subjected to tensile axial load. Therefore,

dual-phase composite prestressing steel bar was not effective for improving

hysteresis energy dissipation. However, hysteresis loops in the less displacement

range than 1/100 in a column rotation angle should have been examined in detail

during loading.

Series B

Test Units

Six test units were constructed. Three of them were assembled by post-tensioning

using grouted prestressing steel bars. The other three were post-tensioned by

ungrouted tendons. The test units in Series B are summarized in Table 2. A typical

test unit is illustrated in Fig.6. The column section is slightly smaller than that of

Series A. This is because of the loading setup used.

The concrete compression strength measured was 39.2MPa. The grout which

0

0.1

0.2

0.3

0 0.01 0.02 0.03 0.04

RC1

P C 1

P C 4

RC2

P C 2

RC 3

P C 3

P C 5

E q u i v a l e n

t d a m p i n g f a c t o r

Rotation angle (rad)

RC2 PC2

RC1 PC1 PC4

RC3 PC3 PC5

Fig.5 Equivalent damping factors for

Series A test units





was injected into the sheath of the grouted test units had a compressive strength

of 49.1MPa. The high-strength mortar used at the interface of the column and the

foundation attained a compressive strength of 59.8MPa and 51.0MPa for the grouted

units and the ungrouted units, respectively. D10 rebar used as longitudinal and shear

reinforcements in the columns had a yield strength of 363MPa. The 17mm diameter

prestressing bars (SBPR930/1080) had a yield strength of 1060MPa.

Table 2 Test units in Series B

Test unit Axial load (kN) Prestressing force

(kN)

grouted or

ungrouted

PCa-B1 330 (0.153)** 618.5 (0.287)**

groutedPCa-B2 660 (0.306) 610.5 (0.283)

PCa-B3 variable* 628.7 (0.292)

PCa-U1 330 (0.153) 603.4 (0.280)ungroutedPCa-U2 660 (0.306) 609.7 (0.283)

PCa-U3 variable* 606.2 (0.281)

*The axial load N varied linearly with the moment M from (M , N )=(-68kNm, 0) to

(68kNm, 660kN)

**(): Axial load or prestressing force/ Ag f'

c , A

g : gross area of column, f'

c : compressive

strength of concrete

The introduced prestress corresponded to the tendon stress 0.8f y , where f

y is the

nominal 0.2% offset yield stress of the prestressing steel. W/C ratio of the grout was

30 100 304545

3 0

1 1 0

3 0

2 5

17(SBPR930/1080)

D10(SD295)

30 190 30

30

170

170

30

D19(SD345)

D10(SD295)

26(SBPR930/1080)

250

2 2 0

75

50

75

50

50

50

50

50

50

50

25

10

15

30

600

800

Plastic pipe

Column section

Foundation section

2 5

4 0 0

Fig.6 Test unit of Series B





45%. The testing methods are similar to the ones for Series A. A series of defl ection

controlled cycles comprising two full cycles to each of the column rotation angle of ±

1/400, ±1/200, ±1/100, ±1/50, ±1/33, ±1/25, ±1/20 and ±1/13 was imposed.

Load-Displacement Relationships

The test units under the lower axial load failed in fl exural compression. Moment

at the column base - column rotation angle relationships are shown in Fig.7.

Additional moment due to P -δ effect is included. Load carrying capacity calculated

based on ACI318 is indicated by the horizontal straight line in the fi gures. For the

ungrouted units the tendon stress increament, ∆σ was estimated by ∆σ =0.75 σ e

+0.25 σ y

( σ e: effective prestress, σ

y : yield strength), which is proposed in AIJ design

and construction recommendations for partially prestressed concrete structures for

members subject to vertical loading.

Prestressing steel bars did not yield for all test units regardless of grouted or

ungrouted. Black circles ● indicate yielding of longitudinal mild steel reinforcement

in compression, and black triangles▲ indicate yielding of shear reinforcement.

PCa-B1 and PCa-U1 subjected to the lower constant axial load had stable hysteresis

loops with a slight reduction in load capacity beyond load cycles to 1/20. However,

PCa-B2 and PCa-U2 subjected to the larger constant axial load indicated the large

reduction in load capacity after they attained the maximum load at the column

rotation angle of 1/100. These units with the larger axial load were loaded up to the

column rotation angle of 1/20. Because during cycles to 1/20 the columns became

unstable and seemed not to sustain the axial load, the loading was stopped at these

cycles.

Ultimate Deformation

In this study ultimate deformation is defi ned as the deformation where load carrying

capacity reduces to 80% of the maximum load. Table 3 summarizes the ultimate

deformations for all test units in both positive and negative loadings. The test units

with ungrouted tendons have 11-36% smaller ultimate deformation than the units

with grouted tendons. This is because the ungrouted tendons in the compressionregion of the column cross-section did not work well as compression reinforcement

and concrete was subjected to larger compression load than that in the units with

grouted tendons.

Equivalent viscous damping factor

Equivalent viscous damping factors for the test units were calculated based on their

load-deformation curves and illustrated in Fig.8. Larger damping factors are obtained

from the units subjected to the larger axial load, PCa-B2 and PCa-U2. The other

test units show almost the same values. The larger damping factors for PCa-B2





Fig.7 Moment at the base of the column - column rotation angle relations

-100

-50

0

50

100

-8 -6 -4 -2 0 2 4 6 8

Rotation Angle (%)

PCa-B3

M o m e n t ( k N m )

longitudinal rebar yielded in compression

-100

-50

0

50

100

-8 -6 -4 -2 0 2 4 6 8

Rotation Angle (%)

+Mcal

-Mcal

PCa-B2




Yielding of shear reinf.

-100

-50

0

50

100

-8 -6 -4 -2 0 2 4 6 8

Rotation Angle (%)

+Mcal

-Mcal

PCa-B1


M o m e n t ( k N

m )


and PCa-U2 can be attributed to crushing of the compressed concrete. Non-linear

elastic hysteresis loops, which are typical for prestressed concrete members, are not

observed in these precast post-tensioned columns.

-100

-50

0

50

100

-8 -6 -4 -2 0 2 4 6 8

Rotation Angle (%)

PCa-U3





-100

-50

0

50

100

-8 -6 -4 -2 0 2 4 6 8

Rotation Angle (%)

+Mcal

-Mcal

PCa-U2





-100

-50

0

50

100

-8 -6 -4 -2 0 2 4 6 8

Rotation Angle (%)

+Mcal

-Mcal

PCa-U1

M o m e n t ( k N

m )







0

0.1

0.2

0.3

0.4

0 1 2 3 4 5 6

PCa-B1 (grouted, 0.15f'cAg)PCa-B2 (grouted, 0.31f'cAg)PCa-B3 (grouted, variable axial load)PCa-U1 (ungrouted, 0.15f'cAg)PCa-U2 (ungrouted 0.31f'cAg)

PCa-U3 (ungrouted, variable axial load)

E q u i v a l e n t d a m p i n g f a c t o r

Rotation Angle (%)

Fig.8 Equivalent damping factors for Series B test units

Table 3 Ultimate deformation of Series B test units

Test unit Loading

direction

Ultimate

rotation angle

(%)

Average

(%)

PCa-B1+ve 4.48

4.57-ve 4.66

PCa-B2+ve 2.10

2.42

-ve 2.74PCa-B3

+ve 3.363.36

-ve -

PCa-U1+ve 4.34

4.07-ve 3.80

PCa-U2+ve 1.84

1.87-ve 1.89

PCa-U3+ve 2.16

2.16-ve -

Axial strain at the centroid

Axial strain at the center of the column section - column rotation angle relationshipsare shown in Fig.9. The axial strain was obtained from the measurements in the

column hinge region whose length corresponded to the column hight, 250mm.

The moment-column rotation envelope curves are also plotted in the fi gures. In

PCa-B1 subjected to the lower axial load, the axial strain measured was almost

in tension. In PCa-U1 under the lower axial load and with ungrouted tendons, the

axial compressive strain increased rapidly after the loading cycles to 4%. This

corresponds to the ultimate deformation which is defi ned as the deformation where

the load carrying capacity reduced to 80% of the maximum load. For the test units

subjected to the larger axial load, PCa-B2 and PCa-U2, the axial compressive

strain started to increase at the loading cycles to 1.5-2.0%. Compared with the

0 Advanced Materials for Construction of Bridges, Buildings, and Other Structures III [2003], Vol. P05, Article 5




-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

-120

-80

-40

0

40

80

120

-8 -6 -4 -2 0 2 4 6 8

Axial strain

Moment envelope (+ve)Moment envelope (-ve)

A x i a l S t r a i n

M om en t ( k Nm )

Rotation (%)

PCa-U3

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

-120

-80

-40

0

40

80

120

-8 -6 -4 -2 0 2 4 6 8

Axial strain



M om en t ( k Nm )

Rotation (%)

PCa-U2

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

-120

-80

-40

0

40

80

120

-8 -6 -4 -2 0 2 4 6 8

Axial strain



M om en t ( k Nm )

Rotation (%)

PCa-B3

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

-120

-80

-40

0

40

80

120

-8 -6 -4 -2 0 2 4 6 8

Axial strain



M om en t ( k Nm )

Rotation (%)

PCa-B2

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

-120

-80

-40

0

40

80

120

-8 -6 -4 -2 0 2 4 6 8

Axial strain



M om en t ( k Nm )

Rotation (%)

PCa-B1

-0.04

-0.03

-0.02

-0.01

0

0.01

0.02

-120

-80

-40

0

40

80

120

-8 -6 -4 -2 0 2 4 6 8

Axial strain



M om en t ( k Nm )

Rotation (%)

PCa-U1

Fig.9 Axial strain in columns - column rotation angle relations with moment envelope

grouted units, the ungrouted units, PCa-U1, PCa-U2 and PCa-U3 showed large

axial compressive strains. This revealed that the ungrouted tendons did not work as

compression reinforcement and the compressed concrete had to share larger part of

the axial load than the units with the grouted tendons.

DESIGN RECOMMENDATIONS

The ungrouted test units showed smaller ductility than the grouted units as

illustrated in Fig.10 because the ungrouted tendons did not function as compressive





reinforcements and the larger part of the compressive force on the column had to be

borne by the compressed concrete.

Generally, the higher the axial load is, the more signifi cant the reduction in ductilityis. Equivalent damping factors of the test units with larger axial load are larger

than those of the units with lower axial load as shown in Figs.5 and 8. This energy

dissipation is mainly attributed to concrete crushing in the plastic hinge region. Even

the prestressed concrete test units under large axial load showed as large a energy

disspation as the ordinary reinforced concrete test units. However, It should be

discussed that energy dissipation due to concrete crushing can be justifi ed or not.

0

1

2

3

4

5

0 0.1 0.2 0.3 0.4

grouted ungrouted

M a x i m u m r o t a t i o n a

n g l e ( % )

PCa-U2

Axial load level (N/f' c A

g )

PCa-B2

PCa-B1

PCa-U1

Fig.10 Maximum rotation angle - axial load level relations

CONCLUSIONS

1. The dual-phase composite prestressing steel bars were not effective for

improing hysteresis loops of the precast prestressed concrete column-foundation

assemblies.

2. Hysteresis energy dissipation of the prestressed units under lower axial load

was smaller than that of the reinforced units. However, under larger axial load

the equivalent damping factors increased due to concrete crushing.

3. The ungrouted test units showed smaller ductility than the grouted units because

the ungrouted tendons did not work as compressive reinforcements.

ACKNOWLEDGMENTS

The authors would like to thank Netsuren, Co., Ltd. which provided the prestressing

steel bars used in the experiment.

REFERENCES

1. M Nishiyama, F Watanabe and H Sato, "Precast Connections Post-tensioned

by Graded Composite Steel", Concrete 95 Toward Better Concrete Structures,

Conference Papers Vol.1, Brisbane, Australia, 4-7 September 1995, pp.579-588.

2 Advanced Materials for Construction of Bridges, Buildings, and Other Structures III [2003], Vol. P05, Article 5

p.c cncrete

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