FIELD OBSERVATION of FIVE - Iowapublications.iowa.gov/16994/1/IADOT_hr104_Field...Composite...

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I I ·1

I I I I I I I 'I I I I I I

FIELD OBSERVATION of FIVE

LIGHTWEIGHT AGGREGATE

PRETENSIONED PRESTRESSED

CONCRETE BRIDGE BEAMS

Iowa Highway Research Board

· Project HR 104

Iowa State Highway Commission

Ames, Iowa

POR llTTIR HIGHWAYS

BEAM NO.

152

153

154

155

156

CORRECTION

HR-104, "Field Observations of Five Lightweight Aggregate Pretensioned Prestressed Concrete Bridge Beams."

Please replace Table #5, page 36 with the following.

(All Cambers are in inches)

CAMBER. PRIOR TO CAMBER AFTER INITIAL CAMBER SLAB PLACEMENT SLAB PLACEMEN'T' FINAL

PRED. MEAS. PRED. MEAS. PRED. MEAS. PRED. CAMBER

MEAS.

2.50 2.50 3.20 3.10 1. 20 1.05 0.70 + 0.25

2.50 2.50 3.20 3.15 1. 20 1. 05 0.70 + 0.40

2.50 2.50 3.20 3.00 1. 20 0. 70 0.70 + 0.20

2.50 2.50 3.20 3.00 1. 20 0.60 0.70 - 0.20

2.50 2.70 3.20 2.85 1. 20 0.65 0.70 + 0.10

a) as of January 14, 1969

b) Figure 16, page 26 shows how the beam has developed a negative camber.

(a)

(b)

I I I I I "Field

I I I I I I I I I I I I I I

Observation of Five Lightweight Aggregate Pretensioned Prestressed Concrete Bridge Beams

Final Report

By James A. Young

Research Department Iowa State Highway Commission

Ames, Iowa

Iowa Highway Research Board Project No. HR-104

•I!'

I I I I· I I I I I I I I I I I I I I I

Chapter

1 2

3

4

TABLE OF CONTENTS

List of Tables List of Figures

INTRODUCTION AND SCOPE EXPERIMENTAL PROCEDURES

2.1 Concrete Mix 2.2 Instrumentation 2 .3 Beams 2.4 Field Deflection Measurements

DISCUSSION OF RESULTS

3~1 Laboratory Tests 3.2 Camber Development

OBSERVATIONS ACKNOWLEDGEMENTS LIST OF REFERENCES APPENDIX

Page

ii iii

1 4

4 4 6

15

21

21 22

36 37 38 39

I I I I I I I I I I I I I I I I I I I

Table

1

2

3

4

5

LIST OF TABLES

CONCRETE MIX QUANTITIES FOR LIGHTWEIGHT CONCRETE BRIDGE BEAMS

STRENGTH AND AGE OF CYLINDERS FOR GROUP I BEAMS

STRENGTH AND AGE OF CYLINDERS FOR GROUP II BEAMS

COMPRESSIVE STRENGTHS FOR LIGHTWEIGHT CONCRETE CYLINDERS

COMPARISON OF PREDICTED AND MEASURED CAMBER AND DEFLECTION VALUES

ii

Page

5

8

8

21

36


Figure

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

LIST OF FIGURES

Comparison of Old and Proposed New Standard Crossing

Detail and Location of Brass Plates

Development of camber immediately after release in Beam number 152

Development of camber immediately after release in Beam number 153 ·




Development of camber in Beam number 155 for short intervals of time at release.

Beam layout on test bridge

Calculation of correction to be applied to compensate for the rotation of the beam ends during camber development.

Set-up during deck placement

Procedure in reading rods

Camber development with respect to time for Beam number 152



iii

Page

2

7

9

10

11

12

13

14

16

18

20

20

23

24

25


Figure

16 Camber development with respect to time for Beam number 155

17 Camber development with respect to time for Beam number 156

18 camber development for a typical beam

19 variation of camber in beam number 152 during the deck placement

20 Variation of camber in beam number 153 during the deck placement


22 Variation of camber in beam number 155 during the deck placement


iv

Page

26

27

28

29

30

31

32

33


CHAPTER I

INTRODUCTION AND SCOPE

1

The use of lightweight aggregates in pretensioned ·prestressed

concrete beams is becoming more advantageous as our design criteria

dictate longer span concrete bridges. Bridge ~earns of greater lengths

have been restricted from travel on many of our highways because the

weight of the combined beams and transporting vehicle was excessive,

making hauls of any distance prohibitive. This, along with the fact

that new safety requirements necessitate the use of longer spans in

grade separation structures over major highways, prompted the State

of Iowa to investigate the use of lightweight aggregate bridge beams.

Until recently, it was possible to use 67' bridge beams in the

two interior spans of a four span overhead crossing over interstate

highways in Iowa. The new safety standards require that any obstruc

tion such as columns or abutments be at least 30' beyond the out

side edge of the pavement. This requirement means that beams for

the two interior spans must be increased to at least 87' in length

on a right angle crossing. If it should develop that a skewed cross

ing would be necessary, the length of the beams could conceivably

be 90-95 feet in length. Figure I shows the relationship between

typical new and old overhead crossing standards.

A series of three projects was started to investigate the pos

sibility of using lightweight aggregate with natural sand fines in

pretensioned prestressed concrete bridge beams. These projects were

--------- ----------

~a~ I . I v; ! :------------~--~------

i I

I. ~ ;

-l~ I

i 24'5/ob I r G' i-___.------------:-___ '

'/v/1~'/- Cf. l·

---,,,===t===r---.:......- ~

' I 74 -o <t: to cf

I f---------------------------- 2 I G '- i

Standard at Present

3 9'-1

I I ....--~="==r===-----..___JJL..~-----:"=="'-'===~~----....jj !I

L __ B_Y_~:_G ___

88 '~-~::-1

-_4. ___ 8~7'G .j. •8'o ~ ~-

Proposed New Standard

Figure 1. Comparison of Old and Proposed New Standard Crossing


3

basically designed to investigate the feasibility of using light

weight aggregate bridge beams in the State of Iowa and to determine

the properties of the material which are ,essential for design pur

poses. The three projects, which were started at approximately the

same time are: "Creep and Shrinkage of Lightweight Aggregate Con

crietes;' "Time Dependent Camber and Deflection of Non-Composite and

Composite Lightweight Prestressed Beams," and "Field Observation of

Five Lightweight Aggregate Pretensioned Prestressed Concrete Bridge

Beams".

The first two are under the supervision of the. Civi~ Engineer

ing Department, at the University of Iowa, the third project is

the subject of this report.

The objective of this project .. is the collection of field

deflection measurements for five pretensioned prestressed light

weight aggregate concrete bridge beams fabricated by conventional

plant processes; also the comparison of the actual cambers and deflec

tions of the beams with that predicted from the design assumptions.

The test bridge is located on County Road "W" over Tipton

Creek in Hardin County, Iowa. The bridge was designed by Mr. P. F.

Barnard, Consulting Structural Engineer, Ames, Iowa and the beams

were fabricated by Prestressed Concrete of Iowa, Inc., Iowa Falls,

Iowa.

The Situation Plan and Superstructure Details of the test bridge

are shown on pages A-1 and A-2 respectively in the Appendix.


2.1 Concrete Mix

CHAPTER II

EXPERIMENTAL PROCEDURES

4

One of the essential parts of any project involving

concrete is the proper proportioning and mixing of the necessary

constituents.

Three possible sources of lightweight aggregate were suggested

for use on this project and they were tested by the Material Test

ing Laboratory at the Iowa Highway Commission. Aggregate A was

eliminated on the basis of a very low durability of its beam samples.

Aggregates B and C, using air dry aggregate, had durability factors

of 100 and 97 respectively. It was noted, that even though aggre

gates B and C had durabilities which were acceptable, the beam made

with aggregate B crumbled around the edges at one end. Based on

these results Aggregate C, known by the brand name Idealite, was

selected.

Table 1 shows the Mix Design Objectives, Ingredients and Pro

cedures for this project.

2.2 Instrumentation

A permanent set of reference points was established on

each beam at a distance of 22" from each end and at the midspan.

The distance of 22" was used so that the reference points on the

end would not be covered by the abutment diaphragms when the bridge

is complete. These reference points consisted of 3~" x2" brass

p;Lates cast to the bottom flange of the beam. A ~" diameter hole


TABLE I CONCRETE MIX QUANTITIES FOR LIGHTWEIGHT CONCRETE

' BRIDGE BEAMS

MIX DESIGN OBJECTIVES

Concrete Quantity l~ cu. yds.

Concrete Strength @ 28 days 5000 psi

Unit Weight, Maximum' Air-Dry (117) pcf

Air Entrainment (5+ 1) %

MIX INGREDIENTS

Cement (Type 1) 1058 lbs.

Natural Sand 2093 lbs.

Idealite Aggregates (60% of 3/4" to 5/16" and 1230 lbs. 40% of 5/16" to #8)

water 52.5 gal.

Darex'@ 7/8 oz. per sack of cement 9.75 oz.

Pozzolith 31.5 oz.

MIXING PROCEDURES

1. Proportion sand and Idealite.

2. Add 26 gallons of water.

3. Mix for approximately two minutes.

4. Proportion the cement.

5. Add six gallons of water.

' 6. Add Darex AEA in 3 gallons of water.

7. Add Pozzolith with remaining water while adjusting to 2~" slump.

5

I I

was tapped in the plate: the hole was used to receive a ~" SAE -

I fine thread bolt on which the level rod is seated when the camber

I readings are taken. Figure 2 shows the position of the plates

I I I I I I I I I I I I I I I

on the beam. A level rod (reading to 0.005') and a precise level

was used on all measurements. The camber and deflection are deter-

mined on the basis of relative displacement between the reference

points.

2.3 Beams

Five pretensioned prestressed concrete beams were cast I

'

in 2 groups; the first group of 3 was cast on April 15, 1968 and

steam cured for 40 hours; the second group of 2 was cast on April

19th, 1968 and cured 67 hours in steam. The beam detail and data

sheet is shown on page A-3 in the Appendi~.

Group I, consisting of beams numbered 152, 153, & 154 was to

have been released* on April 16th, however the cylinder strength

did not reach 4500 fc' and the beams were not.' released until the

17th of April. Table 2 shows the strength and age of the cylinders

at the time of testing.

*released - is defined as the time at which the pretensioned cables are cut and the stress is transferred from the prestressing steel to the concrete.

- - - - - - - - -:~

t ! t I I I

~--------,-,

l I : I

'

±'-<"om - ~"-' ,.

I !

;

: I

i ' l

y ----tb-----------~ i .__~i _________ __,il ~ ~

I 1.i

ffi

, - r-.. , JU 4: ,_ 8

87'-o

-..I!_ e--3 l 8 I

1-ft , ""'1' I ?J..

·r<-------1--

/ _1/<P f)Q/e fapped :!"or 1 ''""' rA f:, r-,n· ·"' i z ~.,,.I Ir.- I '-

fhread b o If.

Detail of Plate

- - - - - - - - -I I

I i

11 ti I ,

! I i '

I i \

i l I

4 I,_ 8

~I I

I

t i

_,,.If 3eanno \ J

' i I 3r :

"' ' r'' ass---+-· ·--1

<:

--::} !

r:b------- _____ L

" A

, '. _ ,__eve,1n9 __ _ rod

-__J ''<P 60 If ~--.J

Rod position on Reference Bolt

Figure 2, Detail and Location of Brass Plates

-


8

Table 2, STRENGTH AND AGE OF CYLINDERS FOR GROUP I BEAMS

Cylinder No. (a) Beam No. Age (Hours) Strength (psi)

152A 152 24 4310 152B 152 48.5 5160 153A 153 40.5 4460 153B 153 48.5 4480 154A 154 40.5 4420 154B 154 '48. 5 4950

(a) Note: All cylinders except 152A were tested at time of

release.

Group II, consisting of beams numbered 155 and 156, was cast

on the 19th, and released on the 22nd of April. At the time of

release, the test cylinders exhibited the strengths and ages as

shown in Table 3.

Table 3, STRENGTH AND AGE OF CYLINDERS FOR GROUP II BEAMS

Cylinder No.

155A 155B 156A 156B

Beam

155 155 156 156

Age (Hours)

67

67 67

Strength (psi)

5130

4350 4360

When the beams were released, readings were taken at short

intervals of time to show the development of camber with respect

to time. The graphs in figures 3-7 show the camber development

immediately after release. Figure 8 shows how the camber developed

in beam number 155 over very small increments of time immediately

after release. During the first minute and 45 seconds the beam

camber held at a constant value of about 0.10 inch. It would appear

that the bond and friction between the beam and steel pallet restrained '

-- -- 3. 0

1.0

w

- - - - - - - - - - - ---- - -

0

20 40 60 80

TIME, MINUTES

CAMBER vs

TIME BEAM NO. 152

100 120 140 160

-

- 1 - - - - - - - -· 3.0

0 0

1.00

20 40 60 80

TIME, MINUTES

- - -CAMBER

vs TIME

BEAM NO. 153

100 120

- -

140

- -

160

-

I-' 0

-

\fl

~ CJ z !·-!

l - - - - - - - -3. 00 ..

0

- - -CA.MEER

vs TIME

-BEAM NO. 154

- - - ...

G

2.00 1--~--::---------=-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~----i 0

0 G

1.00 ;..

I • . • I . ' 20 40 60 80 100 120 140 160

rrIME, MINUTES

-

- - - - - - - - -3. 00 ,.,.

2.00

0

(

l. 00 r-

I I

20 40 60 80

TIME, MINU'l'ES

-

I

100

- -CAMBER

vs TIME

-BEAM NO. 155

- I

120

- - - - --

..

I I

140 160

- , 3.00

1. 00

! I

- - - -

20 40

- - - -

60 80

TIME, MINUTES

- -CA!\IBER

vs TIME

-3EAt<i ~::c'. 1S".:

.100 120

- - - - -

140 160

.•

-

.. ~ li:i

~

l 3.00

~ u 1.00

- - - - - -

1.0

- -· - - - - -

2.0

TIME, MINUTES

CAMBER VS TIME IMMEDIATELY AFTER RELEASE

BEAM NO. 155

3.0

- - -

4.0


15

the beam from deflecting upwards during this interval of time.

Once the beam overcame the bond and friction deflection upwards

was rapid. The deflection proceeded to increase until it leveled

off at about 1.80 11 only 2 minutes after the bottom flange was

separated from the pallet.

During the 2 months immediately after casting, the beams

were stored outside. The temperature varied during this period

from a low of 30°F on the 24th of April to a high of 89°F on the

7th of June. Camber measurements were taken during the period of

22 April to 7 June at an average of once every 8 days.

On June 10th the girders were moved from their plant storage

location to the bridge site. A final set of readings was taken

after the beams were seated on the abutments and before any super

imposed load was applied. Figure 9 shows the beam layout on the

test bridge.

On June 21st the deck was placed on the bridge. As the deck

concrete placement progressed, deflection measurements were taken

at 30 minute intervals. The placement of the deck took approx

imately five hours without any major delays. Readings were taken

at 30 minute intervals over this entire period.

2.4 Field Deflection Measurements

The observation of the deflections of the center of the

beams is one of the prime objectives of this report.

-------------------cf: Pa,-, ~,:nq L.. ~·--'/

Vv' :. ·;...,U~ --, .,-1..,,1._~

3 1 ~eam 155 I

F ~I I I '

-" -· ., ! : ; r 8.eom "1s0 i

! -·

4-- -1- ..

' ()d --~ '"'- we; : I i

" I I r-8eam 4

15Z \

: i - " 1 ==r. ..

i

' I JI.

r 8eam /53 I i

.L... .. - . ~I-

L

3.eom tt

r 15 '+ I

\ !

.. ..:.+I· ~ Ii

~] i

Figure 9, Beam Layout on Test Bridge


17

While the beams were in the storage yard all camber measure

ments were made by placing a level rod on the reference bolts and

taking readings with a precise level. When the readings at each

point had been taken it then becomes necessary to convert the

displacement of the centerline to inches and add a correction

to compensate for rotation of the end bolts about a point on the

end of the beam. Figure 10 shows how the compensation is figured.

The calculation of the correction involved one assumption which ·

can be justified. rt was necessary to assume that when the cen

ter of the beam deflected vertically upward, the reference bolts

displaced vertically also, rather than on an arc about the rota-

tion point which is the neutral axis. The rotation about the

neutral axis, for a vertical deflection of 3.2" at the centerline,

0 amounts to an angle of 0 21'.

When the assumption of vertical displacement of the end bolts

is employed it is found the bolts will move vertically 0.13" when

a deflection of 3.2" is observed at the center. The horizontal

movement, X, would then be 0.0008 in, therefore, the assumption

of vertical displacement is justified.

After the beams had been set on ~he abutments readings were

taken on all reference points before any load was superimposed.

When formwork for the deck was completed it became very dif

ficult to read the rods by setting them on the top of the bolts.

At this time, a single hole was drilled in the rods at the top so


18

Figure 10

d ..

122" I : > .5Z2 ·I In calculating the additional vertical displacement due to

rotation, it is assumed that the bolt at the end moves vertically in direct proportion to the displacement at the centerline. The preceeding page served as a justification of this assumption.

The correction, y is given by:

y = 22 /),, 522

t1 = Camber

Li = y+d, where d is the rod reading

y = 0.0421 (y+d)

y = 0.0421 d 0.9579

y = 0.0440 d

l .6


19'

they could be bolted to the centerline of the five beams and

allowed to hang free for ease of reading. This method was

employed to check camber measurements during the entire period

of time the deck was being placed. Figures 11 and 12 show the

set up during the deck pour. Readings were taken at short inter

vals of time and periodic checks were made on the bolts ,at the

end of each beam to note the vertical displacement.at these points.


Figure 11 Set-up during deck placement

Figure12, Procedure in reading rods

20


21

CHAPTER III

DISCUSSION OF RESULTS

3;1 Laboratory Tests

In addition to the cylinders which were cast at the

time the beams were made, another series of cylinders were made

to study the strength development pattern of the lightweight con-

crete. The cylinders were cured exactly as the beams~ the first

set was cured for 40 hours in steam, the second set 67 hours in

steam. Table 4 shows the properties as they were determined.

It should be noted that the f 'c of the test cylinders cured for

67 hours averaged slightly less than that of the test cylinders

cured for 40 hours.

Table 4, Compressive Strengths of Lightweight Concrete Cylinders

a Date Cast Age f 'c E

(days) (psi) (psi xc106)

4/15/68(b) 7 5125 3.10 4/15/68 14 5560 3.23 4/15/68 28 5980 3.35 4/15/68 58 6360 3.46

4/19/68(c) 7 4915 3.04

4/19/68 14 5570 3.23 4/19/68 54 5925 3.34

a. Computed by E = 33 ~w3. f~1

where w has an average value of 120 lb/ft~ c

b. 40 hours steam cure.

c. 67 hours steam cure.


22

3.2 Camber Development

Figures 13 to 17 indicate the pattern of the camber

development from the time when the prestress was transferred to

the beams until about 200 days after the deck was placed. Figure 18

shows the development of camber in a typical beam. The deck was /·

1cast with normal weight sand and gravel concrete.

There was a slight difference in the camber development between

the two sets of beams. Group I, consisting of beams 152, 153, and

154, had developed a larger value of camber, prior to deck placement,

than the Group II beams. The beams in Group I were about 0.1" below

the value of 3.20" which had been predicted for them. The beams

in Group II had a value which was approximately 0.3" below the pre-

dieted value of 3.20". The design calculation for the beams and

the camber predictions are shown on pages A-4 and A-5 in the

Appendix.

During the time the deck was being placed continuous readings

were taken on the reference bolts as described in Chapter II, sec

tion 4. The graphs in figures 19 to 23 show how the camber of

the beam varied during the deck pour.

The pour started at the west end of the bridge and proceeded

east across the bridge. The initial set of readings was taken

with the finish machine "in place" on the west end of the bridge.

The apparent rebound near the end could be attributed to the

- - - - - - - - - - - - - - - -- - l -CAMBER DEVELOPMENT vs

3.00 TIME BEAM NO. 152

2.00

1.00

0

0

40 80 120 160 200 240 280 320

TIME, DAYS SINCE BEAM RELEASED

- 1 - - - -3.00

2.00

t.f}

rx:i ::r: 0 z H

.. ~ rx:i i:x:i ~ ~ 0

1. 00

40 80

- - - - -

120 160 200

- - -CAMBER DEVELOPMENT

vs TIME BEAM NO. 153

-

240 280


- - -

320

-----------------3.00

2.00

CJ)

~ () z H

.. 0:: rx:i IJ'.l :E: .:r: ()

1.00

40 80 120

0

160 200

CAMBER DEVELOPMENT vs

TIME BEAM NO. 154

0

240 280


320

-

. "' Ul

- 1 - - - - -3.00

2.00

CJ) µ::i :r: C) :z; H

.. p:: µ::i

~ .::i:; C)

1.00

40 80

-

120 0

- -

160

- - - - -CAMBER DEVELOPMENT

vs TIME BEAM NO. 155

240 200-e-~----

280

0 TIME, DAYS s"'INCE BEAM RELEASED

- - -

320

- -, I

3. 00:

2.00

-- _l. 00

I-' -....]

- --------------

0

CAMBER DEVELOPMENT vs

TIME BEAM NO. 156

-

--~----__,..__ _____ 0 __ ...._-:--------"""--'.::-------LO~·--------J.__ ______ ---1 ________ -L ________ ....L __ ~--~....I' ~ 120° 160 200 240 280 320 -...J 40 80


- -, 3.00

2.50

2.00

VJ r.::i p:; CJ z H

.. r:r: µ:i (:Q :E: ,:l; CJ

1. 00

. o. 7·J

f':j I-'·

l.Q s:: Ii CD

I-' ())

- - -DECK

PLACEMENT

3.20 -

0 0

N

- - - -

TI.ME

- - - -PREDICTED CAMBER

vs

-'rIME FOR A TYPICAL BEAM

- - -

0 l[) . 0

"' 00

-· -

(()

rz.1 ::r:: 0 z .H

3.00

2.00

1.00

---------------

~o t/JO 120 160

TIME,

CAMBER VS T!ME DURING DECK POUR

BEAM NO. 152

200 240

MINUTES

290 3i0

Figure :19.'.o

160

l'V l.D

- -3.00

2.00

U)

Iii :r: tJ z H

~

p::; Iii Ill ~ ~ tJ

1.00

---------------

40 2-0B'

TIME, MINUTES

CAMBER VS TIME DURING DECK POUR

BEAM NO. 153

Figure -20

w 0

- - , - - - -3.0

2.00

U)

i:z.l ::r:: () z H

.. o:; li:i

~ .:x; ()

1.0

- - - -

I-20

TIME, MINUTES

- - - - - -CAMBER VS TIME DURING DECK POUR

BEAM NO. 154

-280

Figure .21_

-

------------------'

3.00

2.00

120 160

TIME, MINUTES

CAMBER VS TIME DURING DECK POUR

BEAM NO. 155

200 320

Figure 22

360.

- - - - - - - - - -3.0

2.00

F6-0

TIME, MINUTES

- - - -

CAMBER vs TIME DURING DECK POUR

BEAM NO. 156

- - -

Figure 23 ·


34

finish machine being removed at about the 280 minute mark and the

last 2 readings on each beam taken without the finish machine on

the deck.

No cylinders for the Group II beams were broken at the 28

day mark, however we can get a comparison of the strengths and

calculated modulus of elasticity for Group I and Group II, at

58 and 54 days respectively. The 435 psi difference in f 'c and

6 0.12Xl0 psi difference in modulus of elasticity are not signif-

icant to where this data could be used to explain the difference

in camber between Group I and Group II.

A factor which would have caused a difference in the camber

was the different conditions under which the beams were cured.

The time spent in raising the steam to curing levels was different

for the two groups. It took nearly 4 hours to raise the steam on

Group I and only 2~ hours to raise the steam on Group II. Group I

was steam cured 40 hours while Group II was cured 67 hours. These

conditions could have had an effect on the creep characteristics

and could change the pattern of camber development completely.

There are many inherent factors in concrete, especially in

lightweight concrete, by which the camber is affected. Aggregate

type and shrinkage characteristics are just two more factors

which could affect the camber development.


35

The effect of the deck placement is to rapidly decrease the

camber under the action of the dead load (deck). Initially it

was estimated that 3.20" of camber would be in the beam at the

time the beams were to be set. It was predicted that the dead

load would cause the beams to deflect about 2.00" thus leaving

approximately 1. 20" of camber in the beam after the dead load

was applied. Creep and shrinkage will cause the beam to deflect

approximately 0.50" over a period of time.


36

Chapter IV

Observations

In looking at the results, it is evident that the work done

under Iowa Highway Research Board, Project HR-104 is consistent

1 with work done by others. Camber (inches) vs time (days after

release) has indicated that the results of this work are fairly

consistent with the predicted values.

The method of measuring camber that was used was rather sim-

ple yet it afforded very good results. The following table com-

pares the predicted results with the measured results of various

stages in the project development.

Table 5, COMPARISON OF PREDICTED AND MEASURED CAMBER AND DEFLECTION VALUES

Initial Final Slab D.L. Deflection after Camber Camber(a) Deflection Slab in Place

Beam No. Pred. Meas. Pred. Meas. Pred. Meas. Pred. Mea:s.

152 3.20 3.10 0.70 0.25 2.00 2.10 1. 20 1. 05 153 3.20 3.15 0.70 0.40 2.00 2.10 1.20 1. 05 154 3.20 3.00 0.70 0.20 2.00 2. 30 1. 20 0.70 155 3.20 3.00 0.70 0.20 2.00 2 .35 1. 20 0.60 156 3.20 2.85 0.70 0.10 2.00 2.25 1.20 0.65

.I a) as of January 14, 1969

The initial values of camber appeared to be slightly lower

than what was predicted. The dead load deflections were some-

what larger than the 2.00 inches which was initially calculated.

It appears the creep and shrinkage varied somewhat from their

predicted value of 0.5",


37

ACKNOWLEDGEMENTS

The author wishes to thank Mr. Charles Pestotnik, Bridge

Engineer, Iowa State Highway Commission, Mr. Henry Gee, Assistant

Bridge Engineer, Iowa State Highway Commission and Mr. James

Boehmler, Jr., President of Prestressed Concrete of Iowa, Inc.,

Iowa Falls, Iowa; without the aid of these men the preparation

of this report would have been very difficult.


38

REFERENCES

1. Furr and Sinno, "Creep in Prestressed Lightweight Concrete",

Texas Transportation Institute, October, 1967.


APPENDIX

39

- - -p-,0 ------·-··

J 1100 __ !_

I I '°'"

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HOLE 8-.J888 3TA. 1!i3'r8G B' er fsv£J'ACC EL. 1092.30

f o, I _t:-: 80(.JLOl:l:.S

I tJ ZlT"Z//VfrsT::JJ../~-

El '~"-s-Y;;;;f.E&-388;;-- ---srA. 15G~7Z tJ'LT.

I - ,l.i lLsvl(F.ACE £.l. IO'fZ.3S

II ~!l/ BR1P~£ l"L:Joe ro

. lei r-9.f~:'~r;. P:>zs I ~.,..._: 5orr SANDY sri.TY sf3? I "r-,t<i 5TJrF SAAIOY SIL"l"Y CU.Y

-~i~; <'15j -_; :;t:AVELLY SANO

f--1""1------

~·

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V£eY neM SA.VOY GLACIAL CLAY AAIO OCC. 80VL0£1!S

Bof of ?1hs

Sand Bonk.

SEC 18

-

1

'I'' i •' I I:

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HYDt:.AULIC DATA .O~AINAGE A£fA- !5'! :;q.M:ifS 1or..e0Lt..'.VC{ qo,;FLAT CfCI/. ~Ul;-IVAT.!D i07,~'IIT!/!Z£

4Et:.A OF :;Jl"ENIN(j- 5/!J SQ.FT. c. 518 ~ '" 3(;. • . 32 qD :;f.f00 C./:. S.

AV<1. VELOCtiY = 2400 ~SIB~ 4-G F/5.

(jl?AOF .!"~_!!l_'IZ.4 c;.r; Et.. 1092'.4!$ :;.c.!:J.E:. CL. 10'7;? . ...;

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10?~.

1080.

.)"i!:Ol.'./1'-fl!_Y ;/Ii..~ /08/.0

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GD./f:cAL Jlo.-.:s o.:s::;:.i.,::

THIS .!N.•.;.- /Sf)ESl<J!.·~=.:> .c-o.e_ r12a.;.; LOAD.:</<; PU.IS ,4N4LLJw.::vc~

sP%.:~;,-~~;,;i~_.s-?. ,,- .::-ae n;rur:.E :v.:-..:.c-·\·..; ~,· R . .::~a:.

OE Sl(/AJ: -4-~ S.1·10 . .''?GS. CONS;e:.;:·.-10N: srAA'DAi!,D :'."'~C/F/CATIONS OF n1£ IOW-4 STA;-.: #1.SkW.-iY -:;ofVIM:;r:cu.; SEe1cs OF 164 Al.JO CUZl!:.£NT APP:.. .·..is.:.z. LO:V_;cc'DINM 5L·.-·o.v ON t i?OAJWAY $."':£C/,,C!.. .:::.)l!SIQNS AND SVPF'!.EV1£'-'-4.L ;._·p.=_~· . .::'"'(._·.:-:-,'.JAIS CONC.CLrE Foe P.C£T£NS/ONED P'.<'ESTRE"S-SEO BE.AMS ro BC !IV A(COZDANCE NITH !OWA STATE" h'l(ji.WAY COMM!SS'ON SPEC/AL PeOV/S/ONS ,roe U<j.t!T WCl(jllT CONCl':CTE ee1.ove VN/TS, .f./o.:;z4, :JAT£D MA2"Cll G., /9h8.

ST.ANOAeo eFF.!"C~AICCs.· ALUM!t/Uf/ HANOKAIL DE"?"".AILS." SCAA'.::>AeD V/4--~4-G4 .o..;-;-c_;, AVGV.:T 19<;7, ££VIS£D /O-!O·G7,

EAeTfl WOJ?K' t!.F?IOG£ CONieAcroe ro MAJ:£ C!IANN£L CHA.Vtf£ AS INDICAT£C WASTINt; £..<C..4VA.-;;, M,.:,T£f!IAL Al.ONr; /jANKS A:S N£f:CT.€0 BY Tf./£ ENGIN££.C. f(E .;HAL!. .::..EA£ (fa,.!.\,\"£;. VNDEJ? s;.:.;2:;.: (APP. 2.!JO C,!,/. VDS C!.AS-- 10 Ctl-lNNEL EAC/J•') TO LINES ANOLEvns 5HOWN USIJ./G EXCAVATED MA:££1AL TO Bllll...D, SllAPE .4.'/D CO/Y/FAC-;-- '3£R!"iS AN:; e.:.~·J:..,:/Ll eE'flND AB:.Ji//,!'NT:. COST OFbU/LDING e£<M ... ~ AN.::-· ".AC,t",.::'"/LLING B~llJWO ABU714£NTS TO f5£ IN'CLU0£D INPE/C.£ BID ~ae ~LAS.:: /0 .CXCAi/AT/'::N. $£JOG£ CON71<:ACTOe ..'.'."HALL Wlr>£N Pe.!:SE"A"T /?0ADW.4Y Sl{OULC£.2$ AT 8elOS£. A.VO BACKF!l..L 8.Cl-llND WI.'.~:; TAP£e./NG S!/JUL0£1?. LIN£.S 11:-:; ,:;:;.eEsf.'JT Sh'ou:..DE<?S . .!.5?'.IT ZS' BACK or ENDS OF W!N(jS~VS!Al(i CLAS..S 24 £x:....·,,:.,,..;:--,0J.1 CSTAINEP W!TJ.//N 1$00 FT. OF S!i£J A.5 1>1££CT£f) BY T/.1£ £/.JG!N'CLC.

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e£MOVAI.. OF Pc~::.=vr ::ret1crue.L:

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All/MIA.'(,//vf ./;?,All. CONCl.?FT£ Aeurs

GENE!?AL D/?AVV!NG .STA;!ON JSG.;,-29 COU}.}T'r' Pl?OJECT

~ CONC BCAMS sv yo5 LBS UN FT ' UN n . LJ<ANN£L ; BOW*>'£'_ - 8'1>6' 5£'CT!ON ;7 J .:,1.1rE:R5TP/JCTl!R£ 5-Z!JbC SP[( 90 0 2Z4$i?,. !<:'/. C7 TIPTON TWP.

AJJVTMENTS 942 ffiS"'- .36..£>2S f(i5 - -~ -- ---- - ~e;; r~Z:o~ Cl?£.£K..

TOTAL 5 •184Z 3/"f27 1ti9(;7 ~ /o5 !15'74 /so- 4Q lf/MP.S(JM !IAJ:.:-IN COUNl"Y

.::'.A.ED/A' COUN-;-y LFM· 188(; (.2')--73-~2

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I I (Z" C.:.LAe) 480VE BOTTOM OF SLAB- TOP .i BOTTOl/f l?EINF. STEEL IS TO 8£.. 5UPPORTC.:J BY' MCrAt. BAe CNAres AT NOT MOE!E THAN .J!o N.ITCNAL.5 ! reANSVasLY t Lo,;qcvD1N.<LLY. I

/xG f/OTC..'f BARS" 6QCZ 72"<fr roP.f sorrou .5T,4<;q£2£/;>

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FILE NO i?3087

-

~ I w

- - - - - - -

:------------------·------

3EAM DATA -,- .'

:o-:-o. /n/.~ 10/ ~-,,..esf,,...e s s BG 7 I

I II

2 ¢

, No. of" ;fro /qn f sfrand..r 22 ! ' No or- def7ecfed sfrands 8

/n. 1 o' d:(/ec . .:.1on ~ir--_-... -o-~-·c_r--e-.i.-. -e-----------c-. -lj-.. -'---I-!-. -0-... -? -

;

I /3eam · 1.. • 1 vve10,11r :ans /{j. 35

:

- - - - - - - - - - -i '- 3

' ' r-----1

--r----+-- -0 0 -&' ~

-----, ----r lJ) .

----· _} __ _ ~i-~-

• :; J ~z

.__. -h

~

-.._ (). - I

8 t; I c J ... ,. ; .... z. cy-J

, __ l '3.

~--- ~--·-:-:·!-: -'-, ---1--r.> ..... ~ •.• ~ i _._._.a-•••-• c.r:_i l ~- ., .••. ·• ......... ---1---~l-

?' ' ' 1 r@ ? : ? :., -z _J - --- . . -'. ... ~ '-

~---L~_Z __ -~

_________ _z:-._~

Gross oeam c " I: ~·? s areQ __... I . i

---------·--------'

Tran-:;rormed .20,!09

4

6eam I ,+. }r)

(CV

8 " n = Lit ~ z;.47 :...;, = ;9"53 , /)

Transformed i20/0391i/ beam r @end .;.

0 Upper -!lgure /s t/1= beam camber af r::/eose. ~ower -... .. I-' I • • I ·' :-1qLJre is rne on:1c1.-:>area

I

beom camber :"usf 6erore ., slao LS placed.

" n = a r_; t. = 2 .:. 0 7 U. : I

IQ "9 .3 I c.

.. ... .. v...;t. of s/ab :... ewer Tlaur--e. I

cJef!echon due ro

L


DESIGN CAMBER AND DEFLECTION AT MIDSPAN

(1)

<; M1aspan

_f_________ . --·----·· r· ,. · N ·.~: ()_f 6m. -----------·-· _______ _

QJ ! I

,,.

---..-~~-i-------

I

GJ ~~~~~t-··· ~~:t~il~~;~-·- 3~:~:i. Midspan camber at release of prestress:

~. = (0.97 Pi) (L2 ) (Eel) (IB)

5 (MB) (L 2

)

48 (Eel) (IB)

~-,;.··

Pi = total initial prestressing force in lb.

0.97 Pi = assuming 3% loss of initial prestressing force due to stress relaxation in steel before release.

L = beam span length in inches.

Eel = 2.9lxl06 psi at f 'c = 4,500 psi

IB = average transformed I of beam in inch.4

~=moment at midspan (in-lb.) due to wt. of beam.

= ( 0 • 9 7 ) ( 8 6 7 I 0 0 0) ( 86X12 ) 2

.d. (2.9lxl06) (120,400) (0.0983xl4.33

+ 0.0267x6.2) 5 ---48

A-4

:,

(4,803,702) (86xl2) 2

(2.9lxl06 ) (120,400) = 2 ~ 5 i


(2) Midspan camber at time just before placing concrete slab:

5 48

0.82 Pi

(0.0983ec + 0.0267ee )

= assuming 18% loss of initial prestressing force due to stress relaxation in steel, and creep and shrinkage in concrete.

Ec2

= 3.06xl06 psi at f'c = 5,000 psi.

C = coefficient for creep effect = 1.8

[ (0.82) (867,000) (86xl2)2

= [(3.06xl06) (120,400) . (0.0983xl4.33

+ 0.0267x6.2) -~5-48

(4,803,702) (86xl2)2l =

( 3 • O 6x 1O6 ) ( 12 0, 4 0 O) J 1 • 8 II i 3.2

. (3) Midspan deflection due to weight of slab:

= 5 48

. (Ms) (L2)

(Ec2) (IB)

Ms = moment at midspan (in-lb) due to wt. of slab.

= 5 48

(6,789,528) (86xl2)2 (3 • 06xlo6 ) ( 120 I 400)

= II

2. 04i

(4) Midspan deflection due to creep and shrinkage in slab:

= 25% x 2~04 = 0~5~

A-5

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