Durable UHPC Columns with High- Strength Steel...2019/07/26 · Durable UHPC Columns with...

Durable UHPC Columns with High-Strength Steel

Mahmoud Aboukifa

Mohamed Moustafa, PhD, PE

Ahmad Itani, PhD, SE

Department of Civil and Environmental Engineering

University of Nevada, Reno

ABC-UTC Research Seminar, July 26, 2019

Outline

• Introduction

• Experimental Program

• Results and Discussion

• Comparison against NSC Column

• Conclusions & next steps

2

• Ultra-High Performance Concrete (UHPC) is a new generation of cementitious materials with superior durability and mechanical properties (e.g. low porosity, high ductility, tensile capacity, etc.)

• UHPC is attracting larger attention in the bridge industry specially for Accelerated Bridge Construction (ABC) and connections

• UHPC is not widely used at larger scales for full structural elements (e.g. columns or girders)

• Some of Challenges:

Higher cost Lack of trained work force for construction Lack of knowledge on structural performance of full members

Introduction

3

Introduction

- Higher strength more compact cross-

sections & efficient structures

- High durability longer service life and

minimal maintenance costs

- Suitable for harsh environments (e.g.

coastal bridges)

Mission Bridge Seismic Retrofit, British Columbia, Canada (LAFARGE)

Why Seismic? e.g. UHPC Column Jackets

NSC Column UHPC Column

??

Focusing on bridge columns…

If UHPC to replace normal strength concrete

4

GoalsOverall goal:

Conduct fundamental research to understand the basic structural and seismic response of UHPC columns with high-strength steel

How this benefits ABC:

• Enhanced understanding of structural behavior of columns for future/subsequent use in prefabricated/precast columns

• Compact cross-sections leads to lighter structures (easier transportation and handling, faster construction time)

• High durability is crucial for bridges in harsh environments (e.g. marine structures) where precast construction is commonly used

5

1. Investigate the seismic performance of four large-scale UHPC

columns under combined axial and lateral loading.

2. Determine the damage progression and the mode of failure of the

UHPC columns.

3. Investigate the effect of longitudinal reinforcement detailing on the

design capacity of UHPC columns

4. Conduct a comparison between UHPC and NSC columns.

Objectives

6

The experimental program consists of four large-scale UHPC columns tested

under combined axial and cyclic lateral loading at UNR

Experimental Program

7

• The specimens approx. 1/6 scale of typical California bridge column.

Elevation View

Plan View

1'-2"

5'

Loading2'

4'-10"

NSC6"

Side View

1'-2"

1'-4"

6'-8"

2'

Loading

2'

11"

Ø 10" UHPC

5'1'-2"

6"

2'

2'

4'-2"

5'

5'-6"

2'

Ø 1.5" holes

Column

2'

2'

1'-4"

Direction of

2'

Direction of6"1'-4" UHPC

5'

6"

2'

6'Ø 2.5" holes

≈1.5 m

≈250 mm

• Footing is capacity protected and consists of 2 parts (UHPC and NSC).

Experimental Program

8

Specimen Construction Stages: (a) Casting of NSC Footing; (b) Casting of UHPC Footing; (c) Casting of UHPC Column; (d) Casting of UHPC Column Head.

(a) (b) (c) (d)

Stages of Construction

9

Stages of Construction

10

• A commercial proprietary UHPC mix used Ductal® JS1000

• UHPC cylinders 3X6 tested in compression after surface preparation/grinding

Material Properties

Specimen S1 S2 S3 S4

Column Test day Strength (ksi) 29.64 31.17 33.28 30.95

11

• #5 Grade 60 rebars (ASTM A706) used

• #4 and #5 MMFX Grade 100 CHX9100 rebars (ASTM A1035) used

Material Properties

12

Material Properties

0

20

40

60

80

100

120

140

160

180

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14

Stre

ss (K

si)

Strain (in/in)

124

0

20

40

60

80

100

120

140

160

180

0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18

Stre

ss (K

si)

Strain (in/in)

128

#4 Rebars #5 Rebars

Diameter bar

Yield Strength (ksi)

Ultimate Strength (ksi)

Ultimate Strain (%)

#4 124 167 12.6#5 128 162 15.4

13

• Axial load 120 kips equivalent to 5% axial load index

Elevation View

Spreader Beam

4'-10"1'-2"

Ø 10" UHPC

2'

Side View

4"

9"

2'

5'-6"

6'-112"

5'

1.5" Grout Pad

5'

Column1'-4"

MTS-110 Kips Actuator

Mid. Stroke Length= 119"

Max. Stroke Length= 130"

Hollow Core Jack

714"Axial Load

9'-8"

2'

Spreader Beam

Ø 10" UHPC

Hollow Core Jack

Axial Load

1'-4"

1'-2"

2'

Act

uato

r Tot

al L

engt

h

Min. Stroke Length= 108"

6'-912"

2' 2'

1'-4"

Pre-stressing Rods

Lab Strong Floor

Column100 Kips CapacityR

eact

ion

Blo

cks

1'-2"

Test Setup

14

• Cyclic loading groups

Loading Protocol

0.01 in/sec 0.05 in/sec

15

DisplacementTransducers

R(1 to 5)

SE 5

4"

C02NE(1 to 5)

C04NE 3,NW 3

String Pots

NW(1 to 3)

Direction of

SE 2,SW 2

C10

2"NE 1,NW 1

C08

4'-2"

C06

NE 4

11"

5'-6"

SE(1 to 5)

LoadingSE 3,SW 3 C034"

NE 5

C01

1'-2"

C05

1'-4"

SW(1 to 3)

SE 1,SW 1

SE 4

5'

C074" NE 2,NW 2

C09

Strain gages Wire potentiometer dispLVDTs curvature(5 Levels)

Instrumentation Plan

16

Typical UHPC column test

Test Progression

17

• Mode of Failure was bar fracture (No cover spalling or bar buckling).

Results-Damage ProgressionSpecimen S1 (L=2.4%-Gr.60, T=1.1%-Gr.60 )

Concrete Crushing (2.76%)

Max Drift (10.83%)18

Strain history at 4” above column-footing face

0 20 40 60 80 100 120 140

-3

-2

-1

0

1

Stra

in [%

]

NW-1s t

rupture

0 20 40 60 80 100 120 140

-3

-2

-1

0

1

Stra

in [%

]

SE-2n d

rupture

0 20 40 60 80 100 120 140

-3

-2

-1

0

1

Stra

in [%

]

SW-3r d

rupture

0 20 40 60 80 100 120 140

Time [minutes]

-3

-2

-1

0

1

Stra

in [%

]

NE-4 t h rupture

Loading direction

NW1st rupture

Loading direction

SE2nd rupture

SW3rd rupture

NE4th rupture

North North

Drift= 7.72%

Drift= 10.83%Drift= 10.83%

Drift= 10.83%


19



Max Drift (10.83%)


20



Max Drift (7.72%)


21



Max Drift (7.72%)


22

-10 -5 0 5 10

Drift [%]

-25

-20

-15

-10

-5

0

5

10

15

20

25

Forc

e [k

ips]

16.1 kips

22 kips

10.8

3 %

Pmax = 16.1 kips

& 22 kips

Drift yield = 0.92 %

Drift rupture = 7.72 %

µΔ = 8.4

1st rebar yield

Max drift before 1st rupture

0.92

%

7.72

%

• Exceeds AASHTO Seismic Guide Specs displacement

ductility requirement of 5

(65 %)

Hysteretic ResponseSpecimen S1 (L=2.4%-Gr.60, T=1.1%-Gr.60 )

23

Loading directionNorth (push) South (pull)

10"

112"

22.9 kips

23.9 kips

10.8

3 %

Pmax = 22.9 kips

& 23.9 kips

Drift proof strain = 2.21%


1st rebar proof strain


2.21

%

7.72

%


24

-10 -5 0 5 10

Drift [%]

-25

-20

-15

-10

-5

0

5

10

15

20

25

Forc

e [k

ips]

20.2 kips

24.7 kips

7.72

%

Pmax = 20.2 kips

& 24.7 kips



1st rebar proof strain


1.39

%

7.20

%


25

19.6 kips

20 kips

7.72

%

Pmax = 19.6 kips

& 20 kips



1st rebar proof strainMax drift before 1st rupture

2.1%

7.72

%


26

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

0 2 4 6 8 10 12

K/Ko

Drift [%]

S 1

S 2

S 3

S 4

𝐾𝐾𝑜𝑜 =3 ∗ 𝐸𝐸𝑐𝑐𝐼𝐼𝑒𝑒𝑒𝑒𝑒𝑒

𝐿𝐿3

𝐸𝐸𝑐𝑐𝐼𝐼𝑒𝑒𝑒𝑒𝑒𝑒= 0.7 ∗ 𝐸𝐸𝑐𝑐𝐼𝐼𝑔𝑔

𝐸𝐸𝑐𝑐 = 46,200 𝑓𝑓𝑐𝑐′

𝐾𝐾𝑜𝑜 = 42 ⁄𝑘𝑘𝑘𝑘𝑘𝑘𝑘𝑘 𝑘𝑘𝑖𝑖.

Graybeal (2007)

50%

Stiffness DegradationFor S1 Spec.

27

Transverse reinforcement strains

Longitudinal reinforcementstrains

0 0.02 0.04 0.06 0.08 0.1

Strain [%]

-2

0

2

4

6

8

10

12

14

Dis

tanc

e fro

m C

olum

n Fo

otin

g In

terfa

ce [i

n.]

R-0.97%

R-1.93%

R-3.86%

R-5.52%

R-7.72%

R-10.83%

0 1 2 3 4 5

Strain [%]

-6

-4

-2

0

2

4

6

8

10

12

14

Dis

tanc

e fro

m C

olum

n Fo

otin

g In

terfa

ce [i

n.]

SE-0.97%

SE-1.93%

SE-3.86%

SE-5.52%

SE-7.72%

SE-10.83%

Yiel

d st

rain

StrainsSpecimen S1 (L=2.4%-Gr.60, T=1.1%-Gr.60 )

28

0 1 2 3 4 5

Strain [%]

-5

0

5

10

Dis

tanc

e fro

m C

olum

n Fo

otin

g In

terfa

ce [i

n.]

SW-0.97%

SW-1.93%

SW-3.86%

Transverse reinforcement strains

Longitudinal reinforcementstrains

Proo

f str

ain


0 0.02 0.04 0.06 0.08 0.1

Strain [%]

-2

0

2

4

6

8

10

12

14

Dis

tanc

e fro

m C

olum

n Fo

otin

g In

terfa

ce [i

n.]

R-0.97%

R-1.93%

R-3.86%

R-5.52%

R-7.72%

R-10.83%

29

0 2 4 6

Strain [%]

-5

0

5

10

SW-0.97%

SW-1.93%

SW-3.86%

Transverse reinforcement strainsLongitudinal reinforcement

strains

Proo

f str

ain


0 0.02 0.04 0.06 0.08 0.1

Strain [%]

-2

0

2

4

6

8

10

12

14

Dis

tanc

e fro

m C

olum

n Fo

otin

g In

terfa

ce [i

n.]

R-0.97%

R-1.93%

R-3.86%

R-5.52%

R-7.72%

Damaged strain

30

0 1 2 3 4 5

Strain [%]

-5

0

5

10

Dis

tanc

e fr

om C

olum

n F

ootin

g In

terf

ace

[in.]

NW-0.97%

NW-1.93%

NW-3.86%

0 0.02 0.04 0.06 0.08 0.1

Strain [%]

-2

0

2

4

6

8

10

12

14

Dist

ance

from

Col

umn

Foot

ing

Inte

rface

[in.

]

R-0.97%

R-1.93%

R-3.86%

R-5.52%

R-7.72%

Transverse reinforcement strainsLongitudinal reinforcement

strains

Proo

f str

ain


Damaged strain

31

UHPC column curvatures within plastic hinge region

Curvature Profiles

-0.03 -0.02 -0.01 0 0.01 0.02 0.03

Curvature [1/in]

0

2

4

6

8

10

12

14

16

18

20

Drift=2.76%

Drift=3.86%

Drift=5.52%

Drift=7.72%

Drift=10.83%

-0.03 -0.02 -0.01 0 0.01 0.02 0.03

Curvature [1/in]

0

2

4

6

8

10

12

14

16

18

20

Drift=2.76%

Drift=3.86%

Drift=5.52%

Drift=7.72%

-0.03 -0.02 -0.01 0 0.01 0.02 0.03

Curvature [1/in]

0

2

4

6

8

10

12

14

16

18

20

Drift=2.76%

Drift=3.86%

Drift=5.52%

Drift=7.72%

Specimen S1 Specimen S2 Specimen S3 Specimen S4

32

Moment-Curvature relationship

Mu = 933 k-in

& 1276 k-in

𝛷𝛷y = 0.00116 1/in

𝛷𝛷u = 0.025 1/in

µ𝛷𝛷= 15.4

Moment-Curvature ResponseSpecimen S1 (L=2.4%-Gr.60, T=1.1%-Gr.60 )

33


Mu = 1328 k-in

& 1386 k-in

𝛷𝛷proof = 0.0038 1/in

𝛷𝛷u = 0.020 1/in

Moment-CurvatureSpecimen S2 (L=2.4%-Gr.100, T=1.1%-Gr.60 )

-0.03 -0.02 -0.01 0 0.01 0.02 0.03

Curvature [1/in]

-1500

-1000

-500

0

500

1000

1500

Bend

ing

Mom

ent [

kips

.in]

34


Mu = 1172 k-in

& 1433 k-in


𝛷𝛷u = 0.017 1/in


-0.03 -0.02 -0.01 0 0.01 0.02 0.03

Curvature [1/in]

-1500

-1000

-500

0

500

1000

1500

Bend

ing

Mom

ent [

kips

.in]

35


Mu = 1137 k-in

& 1160 k-in


𝛷𝛷u = 0.017 1/in


-0.03 -0.02 -0.01 0 0.01 0.02 0.03

Curvature [1/in]

-1500

-1000

-500

0

500

1000

1500

Bend

ing

Mom

ent [

kips

.in]

36

• Similar column analytically investigated using

OpenSEES FEA model and Section Analysis (S0)

• 3-D two node fiber-section model.

• Nonlinear force-based element, forceBeamColumn,

with PDelta geometric stiffness matrix.

• Concrete01 and Steel02 material models.

NSC Column Model

37

0

2

4

6

8

10

12

14

16

18

20

0 2 4 6 8 10 12

Forc

e (K

ips)

Drift (%)

NSC Column UHPC Column

• Average backbone curves used for comparison.

(80 %)

(11 %)

NSC UHPC

10-in, 6#5-Gr.60, 5% axial load ratio

fc 5 ksi 30 ksi

Pmax (kips) 10.44 18.8

Drift yield-ideal 1.20 % 1.29 %

Drift max 9.62 % 10.84 %

µΔ 8.0 8.4

UHPC (S1) vs. NSC (S0) Columns

38

Pmax (kips)Ratio to S1 specimen

S0 10.44 55.5 %

S1 18.80 100 %

S2 23.40 125 %

S3 22.45 120 %

S4 19.75 105 %

Lateral Load Capacity

0

5

10

15

20

25

0 2 4 6 8 10 12

Forc

e (K

ips)

Drift (%)

S0 S1 S2 S3 S4

S1 vs S2 Gr. 100 vs Gr.60

S2 vs S3 50% less confinement

S2 vs S4 35% reduction in long. steel39

Drift Capacity• The bilinear elasto-plastic curve method.

(Valid only for columns reinforced with Gr. 60 rebars).

• Group II is compared to Group I with respect to their drift capacity.

• The drift capacity is lesser of ultimate drift and measured drift at 80% of

maximum lateral load capacity. 40

Driftmax(%)

Ratio to S1 specimen

S0 9.62 88.75%

S1 10.84 100%

S2 8.34 77%

S3 7.72 71.2%

S4 7.43 68.5%

Drift Capacity

0

5

10

15

20

25

0 2 4 6 8 10 12

Forc

e (K

ips)

Drift (%)

S0 S1 S2 S3 S4

41

S1 vs S2 Gr. 100 vs Gr.60

S2 vs S3 50% less confinement

S2 vs S4 35% reduction in long. steel

• The observed mode of failure for UHPC columns is tensile rupture oflongitudinal rebars without concrete spalling or reinforcement exposure.

• In all of the tested UHPC columns, no cracks were observed until thecolumns reached 1% drift ratio.

• UHPC column with Gr60 rebars showed adequate ductile behavior withdisplacement & curvature ductilities 8.4 and 15.4, respectively.

• Initial UHPC columns flexural stiffnesses (measured at 0.17% drift)ranged from 0.6 to 0.7 Eigorss then dropped to almost 50% at 2% drift.

• In all tested columns, measured strains of transverse reinforcementwithin the plastic hinge region were found to be smaller than 0.1% insignificant activation of confinement in UHPC columns

Concluding Remarks

42

• Using of UHPC of compressive strength of almost 6 times that of NSCleads to 80% increase in load capacity & 11% increase in drift capacity.

• Using Gr 100 rebars instead of Gr 60 rebars with same longitudinalreinforcement ratio led to 25% increase in lateral load capacity but 23%decrease in drift capacity.

• Decreasing transverse reinforcement ratio by half resulted in only 4%decrease in lateral load capacity and 8% decrease in drift capacity.

• Decreasing Gr 100 longitudinal reinforcement ratio by 35% resulted in15.5% decrease in load capacity and 11% decrease in drift capacity.

• Using longitudinal rft of 1.53% of Gr 100 rebars result in almost samelateral load capacity as column with 2.37% Gr 60 reinforcement, but30% decrease in maximum drift ratio.

Concluding Remarks

43

Further research questions need to be answered before implementation:

Design Philosophy

Inelastic seismic design what R factors to use for UHPCcolumns and what ductility/drift requirements?

Low-damage design use linear elastic design spectrum?

Compact cross-sections

Are there slenderness, buckling, or stability issues?

Pre-cast columns

ABC connections (pocket or grouted ducts connections)?

Square and rectangular columns?

What next?

44

This research along with future research can lead to future design guidelines

Thank You!

45

�Durable UHPC Columns with High-Strength Steel Slide Number 2Slide Number 3Slide Number 4Slide Number 5Slide Number 6Slide Number 7Slide Number 8Slide Number 9Slide Number 10Slide Number 11Slide Number 12Slide Number 13Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 19Slide Number 20Slide Number 21Slide Number 22Slide Number 23Slide Number 24Slide Number 25Slide Number 26Slide Number 27Slide Number 28Slide Number 29Slide Number 30Slide Number 31Slide Number 32Slide Number 33Slide Number 34Slide Number 35Slide Number 36Slide Number 37Slide Number 38Slide Number 39Slide Number 40Slide Number 41Slide Number 42Slide Number 43Slide Number 44Slide Number 45

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