IHRB Project TR-625 - 2014 Mid-Continent … 30 60 90 120 150 180 210 240 270 300 330 360 (µ ε)...

IHRB Project TR-625 Researchers:

Sri Sritharan Matt Rouse

Ebadollah Honarvar James Nervig Wenjun Hu

08/21/2014

2

Outline 3- Material Characterization

7-Long-term camber

predictions

6- Instantaneous

camber predictions

5- Long-term camber

measurements

4-Instantaneous

camber measurements

1- Problem Statement

2- Research Scope and Objectives

Problem Statement

3

Iowa Department of Transportation (Iowa DOT) currently uses the ConSpan program to predict the instantaneous camber with an assumption of elastic beam theory.

Long term camber is estimated using Martin’s multipliers (i.e.,1.80 for the deflection due to the effects of prestress and 1.85 for the self-weight deflection)

The current method frequently over-predicts the long-term camber of long beams in Iowa bridges, while underestimating the long-term camber of shorter PPCBs

Problem Statement

4

Overpredicting Camber: Ø  Build haunches along the entire

length of the girder Ø  Addditional nonprestressed

reinforcement (haunches exceeding four inches)

Underpredicting Camber: Ø  Flexural cracking in the top flange

Ø  Difficulty with field assembly

Ø  Delays in construction schedule

Ø  Serviceability problems with structures

Increase in the construction

costs

Research Scope and Objectives

5

Improve both short-term and long-term camber predictions, and minimize the error between the expected and actual camber of PPCBs especially at the time of erection.

Systematically, investigate the short-term and long-term material behavior, examine the camber measurement techniques, and quantify the camber from the time of construction of PPCBs until the completion of bridges.

The following objectives were used to achieve the project scope.

Research Scope and Objectives

6

1- Literature Review •  Recent completed work on this research topic by other DOTs

2- Historical Camber Data

•  Review existing recorded instantaneous and long-term camber data

3- Concrete Properties •  Compressive strength, modulus of elasticity,

creep and shrinkage

4- Camber Measurements

•  Various Iowa DOT PPCBs •  At transfer, storage at the precast plants, erection, and

before/after the deck pour

5- Scatter in Measured Data •  Potential sources of scatter in the measured data

•  Camber measurement techniques, bed deflection support condition, and temperature effect

6- New Measurement Approach •  Propose a new measurement technique

7- Instantaneous Camber Prediction •  Improve the estimation of instantaneous camber

8- Long-term Camber Prediction

•  Analytical models using Finite Element Analysis •  Long-term multipliers

Material Characterizations

7

Ø  4 HPC, and 3 NC concrete mixes for compressive strength, creep and shrinkage

Ø  Sealed and unsealed specimens

Compressive strength test of a cylindrical specimen

Sulfur-capped sealed and unsealed specimens


8

Ø  Environmentally controlled chamber with the temperature of 73.4°F ± 2.0 °F (23.0°C ± 1.1

°C) and relative humidity of 50 ± 4 %

Ø  A target stress of 2125 psi for creep test.

Loaded specimens for creep tests in the environmentally controlled chamber Details of a creep frame


9

Ø  Demountable mechanical (DEMEC) strain gage was used to measure the change of length

between two vertical gage points attached to the concrete cylinders.

Device and Measurement of strain by using the DEMEC gage


10

Shrinkage Behavior of a 4-ft Beam Section

Ø  Correlate the shrinkage behavior of actual beam and specimens in the laboratory.

Ø  BTB beam section with a length of 4 feet was cast and stored in the yard of a precast plant.

Debonded 4-ft BTB Beam section stored in precast plant A

0

100

200

300

400

500

600

700

0 30 60 90 120 150 180 210 240 270 300 330 360

Shri

nkag

e (µε)

Age of Concrete, days

Sealed Shrinkage Unsealed Shrinkage 4-ft Beam Section Average Shrinkage Adjusted Unsealed Shrinkage ACI Top flange shrinkage Web shrinkage Bottom flange shrinkage

Comparison of shrinkage strains measured from a 4-ft. full-scale beam section and standard cylindrical

specimens


11

Average creep coefficient:

φ(t) = 1.9 t↑0.48 /8+ t↑0.54  

Average shrinkage

strain: ɛ(t) = 480t↑0.60 /12+ t↑0.62  

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 50 100 150 200 250 300 350 400

Cre

ep C

oeffi

cien

t

Time (days)

Average Measured AASHTO LRFD 2010 HPC1 HPC2 HPC3 HPC4

-550

-450

-350

-250

-150

-50

0 50 100 150 200 250 300 350 400

Mic

rost

rain

(µε)

Time (days)

Average Measured AASHTO LRFD 2010 HPC1 HPC2 HPC3 HPC4

Instantaneous Camber Measurements

12

Cur

rent

Indu

stry

Pra

ctic

e

Measure camber while beam is on the precasting bed

Within three hours of the transfer of prestress

At midspan with a tape measure Measured to the nearest 1/8 in.


13

Historical Camber

y = -5E-07x - 0.0023 R² = 0.0007

-0.0120

-0.0100

-0.0080

-0.0060

-0.0040

-0.0020

0.0000

0.0020

0.0040

0.0060

0.0080

(Mea

sure

d C

ambe

r - P

redi

cted

Cam

ber)

/Len

gth

Variety of Bulb-T Beams Arranged in Increasing Length

BTD-29D BTC50 BTC55 SBT17M SBT24M BTC80 BTC85 BTD85 BTC90 SBT99 BTC100 BTC105 BTC110 BTD110 BTC115 BT120 BTC120 BTD120 SBT38M BT125 BTD125 BT130 SBT130 BTD130 BT135 SBT135 BTD135 BTE135 BT140 SBTD148.58

Average = -.002411 Standard Deviation = .00258


14

Historical camber values on 1300 beams has given the

following trends:

Instantaneous camber for certain types of beams is overpredicted and

other times underpredicted.

Larger scatter is observed in shorter beams than in longer beams.

Values decrease with greater length.

Overpredicted 75% of the time.


15

Mea

sure

men

t Tec

hniq

ues

A tape measure reading is taken at the midspan of the beam after release (recorded to the nearest 1/16 in.)

A rotary laser level is used to measure the beam from the top flange and the bed (accurate up to 1/16 in. at 100 ft).

String Potentiometers have been installed on multiple points along the beam and precasting bed to determine the camber and how the precasting bed is reacting (accurate up to 0.015 in.).


16

New measurement technique is recommended to take into account

the aforementioned factors

Factors misrepresenting the recorded camber

Bed Deflections

Inconsistent Top Flange

Surfaces Friction


17

-0.025

-0.020

-0.015

-0.010

-0.005

0.000

0.005

0.010

0.015

0.020

0 1000 2000 3000 4000 5000

Vert

ical

Dis

plac

emen

t (in

.)

Time (sec)

Bed at Midspan Bed at Left End Events

Rel

ease

Beg

ins

Rel

ease

Com

plet

e

Lifte

d B

eam

-0.080

-0.060

-0.040

-0.020

0.000

0.020

0.040

0 1000 2000 3000 4000 5000 6000 7000 8000

Vert

ical

Dis

plac

emen

t (in

.)

Time (sec)

Bed at End of Beam Bed at Midspan Events

Rele

ase

Begi

ns

Rele

ase

Com

plet

e

Beam

shift

s 2.2

5"

Bed Deflection

Ø  A Time vs. Displacement graph of the precasting beds shows that a downward deflection

can occur at the ends of the beam along with an upward deflection at the midspan.


18

Inconsistent Top Flange Surfaces

Ø  Due to uneven surface conditions along the top flange, the location where camber

measurements are taken at the jobsite can cause a discrepancy of up to 0.90 in.


19

Friction

Ø  Friction between the bed and beam inhibits camber at release. Lifting the beam after release

and then taking a measurement can cause an increase in the measured camber by an average

of 17%

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

5.00

Cam

ber

(in.)

Variety of Beams Arranged in Increasing Length

Effect of Friction on Camber Measurements

Before girder was lifted After girder was lifted


20

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

6000 6500 7000 7500 8000 8500 9000 9500 10000 10500

Vert

ical

Dis

plac

emen

t (in

.)

Time (seconds)

Top Flange at Midspan Events

Rel

ease

Com

plet

e

Lifte

d B

eam

Tota

l Inc

reas

e in

C

ambe

r due

to

Fric

tion.

Incr

ease

in C

ambe

r due

to

Bea

m E

nds

Ove

rcom

ing

Fric

tion.

In

crea

se in

Cam

ber d

ue

to

Lift/

Set o

f Bea

m.

Two components of Friction

Ø  Increase due to beam ends sliding towards each other (Time 6300-8600 seconds)

Ø  Increase in displacement when beam is lifted (Time 8600 seconds)


21

Rev

erse

Fri

ctio

n

“As the girder end is set on the bed, friction acts in the opposite direction to resist the weight of the girder pushing the girder end back outward.” (O’neill et al. 2012)

“The release cambers that might be obtained from a frictionless bed would be expected to lie somewhere between the initial on-bed release camber reading and the lift/set camber reading.” Ahlborn et al. (2000) used the average of the measured release camber and the lift/set camber as the assumed “true” release camber. Due to string potentiometer graphs, reverse friction, if any, is small in quantity.


22

PPCB with roller support under one end

Roller Support

Bea

m w

ith a

Rol

ler

Supp

ort

Beam 1-not lifted.

Beam 2-lifted and sat back down on the precasting bed.

Beam 3-a roller was placed under one end to simulate the effect of eliminating friction.


23 -0.1 0.0 0.1 0.1 0.2 0.2 0.3 0.3 0.4 0.4 0.5

4500 5000 5500 6000 6500 7000 7500

Vert

ical

Dis

plac

emen

t (in

.)

Time (sec)

Beam 1-No Lift or Roller Beam 2-Lifted Beam 3-Lifted with Roller

Rel

ease

Com

plet

e Lifting and setting the beam down eliminates

additional vertical displacement due to

friction

Rat

e of

Cam

ber

Gro

wth

Beam 1 has a larger rate of growth than Beam 2 and 3 (Friction is still present in Beam 1).

The beam with the frictionless roller (Beam 3) and beam that was lift/set (Beam 2) have the same rate of vertical growth.

Beam 3 is assumed to be frictionless (Increase in vertical displacement is due to creep and shrinkage).


24

Summary of Measurements Errors

Ø  The following errors with camber measurement were observed

Measured Value Error

Ave. (inches) Std. Dev. (inches) Ave. Std. Dev. Maximum Minimum

Friction* 0.392 0.294 17.60% 8.83% 38.43% 1.41%

Inconsistent Top Flange Surface along

the Length of the Beam

0.099 0.142 5.15% 24.55% 29.14% 0.00%

Inconsistent Top Flange due to Local

Surface Effects 0.113 0.119 6.84% 7.58% 66.02% 0.00 %

Bed Deflections 0.030 0.062 2.79% 8.21% 16.13% 0.00%


25

1- Place a 2x4 on the top flange of the PPCB at the ends and at midspan.

2- Cast concrete to the elevation of the 2x4 to ensure that flat surface will be produced at the measurement points.

3- Allow beam to cure using standard practice.

4- Remove the 2x4’s from the top flange.

5- After the beam has been released, precasters’ have one of the following options: (a) Lift/set the beam on the precasting bed. (b) Lift the beam and move it to the storage yard, placing it on temporary wooden supports.

Proposed Measurement Technique:


26

.

.

6- Measure the elevation of the beam with a rotary laser level, total station, or other survey equipment at the midspan and ends at the locations where the 2x4s were placed. At each location, take measurements at the center and towards the edges of the top flange.

7- If option 5b is used, determine the contribution in camber due to the reduced clear span and overhang caused by the temporary supports.

8- Take the average of the end elevation readings and subtract from average midspan camber elevation reading.

9- If option 5b is used, subtract the contribution in camber due to the temporary support placement from the camber value calculated in step 8.

Long-term Camber Measurements

27

Beam Type C 80 D 55 D 60 D 105 BTC 120 BTD 135 BTE 110 BTE 145 Overall Length (m) 24.7 17.1 18.6 32.3 37.0 41.6 33.9 44.6 Jacking Force (KN ) 4163 2268 2651 6058 9461 10217 5676 9843 Number of Straight Tendons 16 12 14 26 38 42 26 42 Number of Harped Tendons 6 0 0 6 12 42 4 10 Theoretical Instantaneous Camber (mm) 41.7 6.1 8.9 61.5 87.6 90.7 40.9 75.4 Theoretical Long-term Camber (mm) 73.7 10.7 15.7 108.5 154.2 159.3 71.9 132.3 Number of Measured Beams 4 12 12 12 3 8 9 6 Number of Beam Sets 1 4 4 4 1 4 3 2 Age at Last Measurement 117 202 158 173 75 65 446 253

Dat

a C

olle

ctio

n

The beams fabricated for five different bridges in Iowa were monitored periodically for camber measurements during storage as well as at erection.

These selected beams included different types of Iowa DOT PPCBs with various lengths and depths.

The rotary laser lever was used to measure long-term camber from the top flange of the beams.


28

Varying overhang lengths with an average measured overhang length of L/30

Inconsistent trends in data primarily due to temperature effect

0.000

0.010

0.020

0.030

0.040

0.050

0.060

0 20 40 60 80 100

Ove

rhan

g le

ngth

/ G

irde

r L

engt

h

Overhang Length (in.)

D 55 D 60 C 80 D 105 BTE110 BTC 120 BTD 135 BTE145 a = L/ 30

2.0

3.0

4.0

5.0

6.0

7.0

8.0

4/1/2012 7/10/2012 10/18/2012 1/26/2013 5/6/2013

Mea

sure

d C

ambe

r (in

.)

Date

BTE 145-1 BTE 145-2 BTE 145-3 BTE 145-4

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

6/20/2012 7/10/2012 7/30/2012 8/19/2012 9/8/2012 9/28/2012

Mea

sure

d C

ambe

r (in

.)

Date

BTD 135-1 BTD 135-2 BTD 135-3 BTD 135-4 BTD 135-5 BTD 135-6 BTD 135-7 BTD 135-8

Observations:


29

Dat

a C

olle

ctio

n to

Inve

stig

ate

Tem

pera

ture

Eff

ect

Twenty-two different PPCBs were instrumented with string potentiometers and thermocouples to measure thermal camber as a function of temperature over a short duration.

Measurements were conducted for four different seasons. Two instrumented beams to determine vertical temperature gradient distribution over the cross section depth. Temperature was measured at every quarter point of depth for two beams (BTE 145, BTE 155) throughout the day


30

Instrumented PPCBs in Summer

Instrumented PPCBs in Winter


31

Thermocouples every quarter point over beam depth

S t r i n g potentiometer

BTE 145 BTE 155

Observed Behavior

32

0

10

20

30

40

50

60

70

-10 0 10 20 30 40 50

Dis

tanc

e fr

om b

otto

m o

f bea

m

(in.)

Temperature (°F)

4/9/2014 13:40 4/9/2014 15:00 4/9/2014 18:00 4/9/2014 21:00 4/10/2014 0:00 4/10/2014 3:00 4/10/2014 6:00 4/10/2014 9:00 4/10/2014 12:00 AASHTO LRFD 2010

0

10

20

30

40

50

60

70

-10 0 10 20 30 40 50

Dis

tanc

e fr

om b

otto

m o

f bea

m

(in.)

Temperature (°F)

4/9/2014 13:40 4/9/2014 15:00 4/9/2014 18:00 4/9/2014 21:00 4/10/2014 0:00 4/10/2014 3:00 4/10/2014 6:00 4/10/2014 9:00 4/10/2014 12:00 AASHTO LRFD 2010

Vertical Temperature Distribution:

BTE 155 Beam

BTE 145 Beam

Observed Behavior

33

-15

0

15

30

45

60

-0.3

0

0.3

0.6

0.9

1.2

6/5/2013 8:09 6/5/2013 13:55 6/5/2013 19:40 6/6/2013 1:26 6/6/2013 7:12

Tem

pera

ture

Gra

dien

t (°F

)

The

rmal

Cam

ber

(in.)

Time

BTE 145-1 BTE 145-2 BTE 145-3 BTE 145-4 BTE 145-5 BTE 145-6 Temperature Gradient

Wind speed: 10 mph Maximum wind speed: 22 mph Average humidity: 69%

-20

-10

0

10

20

30

40

50

60

-0.4

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

7/18/2013 4:48 7/18/2013 12:57 7/18/2013 21:07 7/19/2013 5:16 7/19/2013 13:26

Tem

pera

ture

Gra

dien

t (°F

)

The

rmal

Cam

ber

(in.)

Time

BTC 115-1 BTC 115-2 BTC 115-3 BTD 115-1 BTD 115-2 BTD 115-3 Temperature Gradient

Wind speed: 8 mph Maximum wind speed: 18 mph Average humidity: 64 %

Thermal Camber and Temperature Gradient versus Time:

BTE 145 Beams in Summer (June)

BTC 115 Beams in Summer (July)

Observed Behavior

34

-15

0

15

30

45

60

-0.3

0

0.3

0.6

0.9

1.2

2/26/2014 7:12 2/26/2014 15:36 2/27/2014 0:00 2/27/2014 8:24 2/27/2014 16:48

Tem

pera

ture

Gra

dien

t (°F

)

The

rmal

Cam

ber

(in.)

Time

BTE 155-1 BTE 155-2 BTE 155-3 BTE 155-4 BTE 155-5 BTE 155-6 Temperature Gradient

Wind speed: 16 mph Maximum wind speed: 30 mph Average humidity: 73 %

-15

0

15

30

45

60

-0.3

0

0.3

0.6

0.9

1.2

4/9/2014 4:48 4/9/2014 14:24 4/10/2014 0:00 4/10/2014 9:36 4/10/2014 19:12

Tem

pera

ture

Gra

dien

t (°F

)

The

rmal

Cam

ber

(in.)

Time

BTE 155-1 BTE 155-2 Temperature Gradient


BTE 155 Beams in Winter (February)

BTE 155 Beams in Spring (April)

Observed Behavior

35

-15

0

15

30

45

60

-0.3

0

0.3

0.6

0.9

1.2

4/9/2014 6:57 4/9/2014 15:21 4/9/2014 23:45 4/10/2014 8:09 4/10/2014 16:33

Tem

pera

ture

Gra

dien

t (°F

)

The

rmal

Cam

ber

(in.)

Time

BTE 145-1 BTE 145-2 Temperature Gradient


BTE 145 Beams in Winter (February)

Instantaneous Camber Predictions

36

Use AASHTO LRFD 2010 Equation with

adjustment to estimated initial

compressive strength

Consider elastic shortening, seating

losses, and relaxation

Use AASHTO LRFD 2010

Equation

Use transformed

section

Factors Affecting Instantaneous Camber

Modulus of elasticity

Designed prestress

force Prestress

losses Sacrificial

prestressing strands

Transfer length

Section properties

Ø  Multiply Target Strength by 1.4 to calculate Eci When specified Target f'ci ≤ 6000 psi Ø  Multiply Target Strength by 1.1 to calculate Eci When specified Target f'ci > 6000 psi

Long-term Camber Predictions

37

0

1

2

3

4

5

6

7

8

9

0 1 2 3 4 5 6 7 8 9

Pred

icte

d C

ambe

r, in

.

Measured Camber, in.

Data Points 45 Degree +25% -25% 0

1

2

3

4

5

6

7

8

9

0 1 2 3 4 5 6 7 8 9

Pred

icte

d C

ambe

r, in

.

Measured Camber, in.

Data Points 45 Degree +25% -25%

Comparison of predicted camber and measured camber with overhang by using

Naaman’s Method

Comparison of predicted camber and measured camber without overhang by using Naaman’s

Method

Sim

plifi

ed

Ana

lysi

s Tadros’s Method

Naaman’s Method ( The most accurate method)

Incremental Method


38

Fini

te E

lem

ent A

naly

sis

(FE

A)

Various parameters that could potentially affect camber such as creep and shrinkage, changes in prestress, support condition, and temperature effect were incorporated into the finite element models.

Study the change in camber of PPCBs from release to the time of erection with and without girder overhang.


39

Finite Element Analysis (FEA) Ø  Beams were classified based on their estimated instantaneous camber into two groups as

follows :

0

0.5

1

1.5

2

2.5

3

3.5

4

0 20 40 60 80 100 120 140 160 180

Rel

ease

Cam

ber (

in.)

Overall Length (ft)

A B C D BTC BTD BTB BTE

Large Camber Beams

Small Camber Beams

Small camber beams: Instantaneous camber ≤ 1.5 in. Large camber beams: Instantaneous camber > 1.5 in.


40

0.0

0.4

0.8

1.2

1.6

2.0

2.3

2.7

3.1

0

10

20

30

40

50

60

70

80

0 100 200 300 400 500 600

Cam

ber (

in.)

Cam

ber (

mm

)

Time (days)

Camber-Without Overhang Camber-With Overhang

0.0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

3.1

3.5

0

10

20

30

40

50

60

70

80

90

0 100 200 300 400 500

Cam

ber (

in.)

Cam

ber (

mm

)

Time (days)

Adjusted Measured Camber Original Measured Camber

Support Conditions Ø  Eliminate the contribution of overhangs to camber (elastic and creep components).

Analytical camber curves for a BTE 110 Measured and adjusted data for a BTE 110


41

Thermal Camber

Ø  linear vertical temperature distribution over the cross section would create the maximum

thermal camber compared to the polynomial temperature distribution

y = 0.0319x - 1E-16 R² = 1

-0.1 0.0 0.1 0.2 0.2 0.3 0.4 0.5 0.5 0.6 0.7 0.8

0 2 4 6 8

10 12 14 16 18 20

0 5 10 15 20 25

Ther

mal

Cam

ber (

in.)

Ther

mal

Cam

ber (

mm

)

Temperature Gradient,ΔT (°C)

BTE 0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

0 5 10 15 20 25 30 35 40 45

Mea

sure

d / D

esig

n C

ambe

r

Temperature Gradient, ΔT (°F)

Average

The average temperature gradient with the minimum error is 15 °F (8.3 °C)


42

M = 1.145 t0.043 R² = 0.983

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

0 100 200 300 400 500 600

Mul

tiplie

r, M

Age (Day), t

Average BTE 110 Average BTC 120 Average BTD 135 Average BTE 145 Average D 105 Average C 80 Average of All Large Camber Beams Power (Average of All Large Camber Beams)

Ø  A set of multipliers without overhang (0-60 days; 60-180 days; and over 180 days) Ø  Temperature gradient multiplier, λT ( Use ΔT= 15°F) Ø  A set of multipliers with an average overhang length of L/30 (0-60 days; 60-180

days; and over 180 days) Ø  A Single multiplier (Average at-erection age: 120 days)

Multipliers as a function of time:

Ø  Multipliers were produced by comparing the instantaneous camber to long-term camber

predictions:


43

A representative of Results

0.00

0.25

0.50

0.75

1.00

0 50 100 150 200 250 300

Cam

ber (

in.)

Time (day)

Analytical Curve with ΔT= 0 °F Analytical Curve with ΔT= 15 °F Iowa DOT Long-term Camber Camber with Multipliers Camber with Multipliers ,ΔT= 15 °F Set 2 Average Data

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

0 50 100 150 200 250 300

Cam

ber (

in.)

Time (day)


D 105 Beams

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

0 50 100 150 200 250 300 350 400 450 500

Cam

ber (

in.)

Time (day)


BTE 110 Beams

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

0 50 100 150 200 250 300

Cam

ber (

in.)

Time (day)


BTE 145 Beams

D 55 Beams

Comparison of Different Long-term Camber Prediction Methods

44

Ø  Method 1, (M1): Multiplier Function with adjusted data for overhang Ø  Method 2, (M2): Set of multipliers- no overhang Ø  Method 3, (M3): Set of multipliers- with overhang Ø  Method 4, (M4): Single Multiplier-without overhang Ø  Method 5, (M5): Single Multiplier-with overhang Ø  Method 6, (M6): Current Iowa DOT approach

Long-term Camber Prediction Methods: 0.

22

-0.0

4

0.18

-0.0

8

0.19

-0.1

1 0.12

0.13

-0.1

7

0.44

0.46

0.54

0.60

0.72

0.78

0.58

0.77

0.71

-0.40

-0.20

0.00

0.20

0.40

0.60

0.80

1.00

M1, ΔT= 0°F

M1, ΔT= 15°F

M2, ΔT= 0°F

M2, ΔT= 15°F

M3, ΔT= 0°F

M3, ΔT= 15°F

M4 M5 M6

(Mea

sure

d C

ambe

r-Des

ign

Cam

ber)

(in.

)

Prediction Method

Average and Standard Deviation of Each Method

Average Standard Deviation

93

93

89

85

80

80

89

75 79

0 10 20 30 40 50 60 70 80 90

100

M1, ΔT= 0°F

M1, ΔT= 15°F

M2, ΔT= 0°F

M2, ΔT= 15°F

M3, ΔT= 0°F

M3, ΔT= 15°F

M4 M5 M6

-1''<

(Mea

sure

d C

ambe

r-Des

ign

Cam

ber)

(%)

< 1'

'

Prediction Method

Percentage of Data within ±1.0 in.

Assumption: No construction difficulties in the field if the difference between the measured and design camber is within ±1.0 in..

Conclusions

45

Modify the current instantaneous camber measurement techniques based on the new recommendations.

Store the beams without overhangs at the precaster’s yard.

Use the proposed equations to predict time-dependent behavior of HPC.

Assume an average temperature gradient of 15 °F (8.3 °C) for camber measurements/analysis.

FEA predicted long-term camber most accurately; however, a single multiplier with overhang adjustment can still significantly improve camber predictions compared to the current Iowa DOT approach.

Use different multipliers for small camber beams and large camber beams.

IHRB Project TR-625 - 2014 Mid-Continent … 30 60 90 120 150 180 210 240 270 300 330 360 (µ ε)...

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Transcript of IHRB Project TR-625 - 2014 Mid-Continent … 30 60 90 120 150 180 210 240 270 300 330 360 (µ ε)...