US Army Corps

of Engineers

Construction Engineering

Research Laboratories

USACERL Special Report 99/01

October 1998

Shear Strengthening of

Reinforced Concrete Beams Using

Fiber-Reinforced Polymer Wraps

Pamalee A. Brady and Orange S. Marshall

Studies have shown that fiberreinforced polymer (FRP) wraps

can improve the capacity of

rectangular beam sections. This

technology has potential

application to highway bridges

that may have less shear

capacity than flexural capacity or

require added load capacity to

handle current traffic demands.

Compared with steel repair

materials FRP offers several

benefits, such as corrosion

resistance and field-workability.

Several studies have

investigated the use of externally bonded FRP

sheets to improve strength and stiffness of reinforced concrete (R/C) beams, but most have

addressed flexural strength, not shear.

The objective of the current study was to test

the effectiveness of FRP wraps in repairing fullscale prestressed high-strength concrete joists

fabricated with insufficient shear reinforcement.

Four prestressed high-strength concrete teebeams (joists) with integral web openings were

tested. Two of the joists were repaired or

upgraded with FRP wraps to improve shear

performance and two were used as control

specimens. Performance criteria were

specified, and standard structural engineering

practice for shear design was employed to

Approved for public release; distribution is unlimited.

determine wrap thickness. The results of the

tests indicate that significant increases in the

shear strength of R/C beams with insufficient

shear capacity can be achieved by proper

application of FRP wraps.

19990203 077

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REFERENCE: USACERL Special Report 99/01, Shear Strengthening ofReinforced Concrete Beams

Using Fiber-ReinforcedPolymer Wraps

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1. AGENCY USE ONLY (Leave Blank) 2. REPORT DATE

October 1998

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Final

4. TITLE AND SUBTITLE

Shear Strengthening ofReinforced Concrete Beams Using Fiber-Reinforced Polymer

Wraps

5. FUNDING NUMBERS

CPAR

LW4

6. AUTHOR(S)

Pamalee A. Brady and Orange S. Marshall

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

U.S. Army Construction Engineering Research Laboratories (USACERL)

P.O. Box 9005

Champaign, IL 61826-9005

8. PERFORMING ORGANIZATION

REPORT NUMBER

SR 99/01

9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES)

Headquarters, U.S. Army Corps ofEngineers

ATTN: CEMP-CE

20 Massachusetts Ave. NW

Washington, DC 20314-1000

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Copies are available from the National Technical Information Service, 5285 Port Royal Road, Springfield, VA 22161.

12a. DISTRIBUTION / AVAILABILITY STATEMENT

Approved for public release; distribution is unlimited.

12b. DISTRIBUTION CODE

13. ABSTRACT (Maximum 200 words)

Studies have shown that fiber-reinforced polymer (FRP) wraps can improve the capacity ofrectangular beam sections. This

technology has potential application to highway bridges that may have less shear capacity than flexural capacity or require

added load capacity to handle current traffic demands. Compared with steel repair materials FRP offers several benefits,

such as corrosion resistance and field-workability. Several studies have investigated the use of externally bonded FRP

sheets to improve strength and stiffness ofreinforced concrete (R/C) beams, but most have addressed flexural strength, not

shear.

The objective ofthe current study was to test the effectiveness ofFRP wraps in repairing full-scale prestressed

high-strength concrete joists fabricated with insufficient shear reinforcement. Four prestressed high-strength concrete

tee-beams (joists) with integral web openings were tested. Two ofthe joists were repaired or upgraded with FRP wraps to

improve shear performance and two were used as control specimens. Performance criteria were specified, and standard

structural engineering practice for shear design was employed to determine wrap thickness. The results ofthe tests indicate

that significant increases in the shear strength ofR/C beams with insufficient shear capacity can be achieved by proper

application of FRP wraps.

14. SUBJECT TERMS

concrete structural engineering

fiber-reinforced polymer (FRP)

composite materials

15. NUMBER OF PAGES

78

16. PRICE CODE

17. SECURITY CLASSIFICATION

OF REPORT

Unclassified

18. SECURITY CLASSIFICATION

OF THIS PAGE

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OF ABSTRACT

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ABSTRACT

SAR

NSN 7540-01-280-5500 Standard Form 298 (Rev. 2-89)

Prescribed by ANSI Std 239-18

298-102
USACERL SR 99/01

Foreword

This study was conducted for Headquarters, U.S. Army Corps of Engineers under Construction Productivity Advancement Research (CPAR) Work Unit LW4,

"Repair Upgrade of Concrete CE Structures Using FRP Composites." The technical monitors were M.K. Lee (CECW-EG), D. Chen (CEMP-ET), and C. Harris

(CEMP-CE).

The work was performed by the Materials Science and Technology Division (FLM) of the Facilities Technology Laboratory (FL), U.S. Army Construction Engineering Research Laboratories (CERL). The CERL Principal Investigator was

Orange P. Marshall, CECER-FL-M. Dr. Ilker R. Adiguzel is Acting Chief,

CECER-FL-M, and L. Michael Golish is Acting Operations Chief, CECER-FL.

The CERL technical editor was Gordon L. Cohen, Technical Information Team.

The Director of CERL is Dr. Michael J. O'Connor.
USACERLSR 99/01

Contents

SF298 1

Foreword 2

1 Introduction 7

Background 7

Objective 9

Approach 9

Mode of Technology Transfer 9

Units of Weight and Measure 10

2 Fiber-Reinforced Composites 11

3 Experimental Program 14

Test Specimens 14

Materials 15

Fabrication 16

Instrumentation and Data Recording 18

Test Procedure 19

Experimental Results 19

Load and Deflection 19

Strains 21

Cracking and Failure Mechanism 22

Experimental Test Conclusions 23

4 Design Procedure for Hybrid Joists 25

Overview 25

Design Criteria and Assumptions 25

Design Procedure 25

Define Loading 25

Define Capacity of Existing Beam Section 26

Determine Load Requirement for Upgrade/Repair 27

Determine FRP Properties 27

Determine Configuration and Calculate Thickness of FRP 28

Check Stresses 29

Check Deflections 29
USACERL SR 99/01

Determine Failure Mode 30

Detailing 30

Design Example 30

Assumptions 30

FRP Properties 30

5 Conclusions and Recommendations 33

References 35

Figures and Tables 36

Distribution
USACERLSR 99/01

List of Figures and Tables

Figures

1 Joist configuration 36

2 Joist prestressing tendon profile 36

3 HJ-3 and HJ-4 web reinforcement 37

4 FRP joist repair. 37

5 High-performance concrete strength versus time 38

6 Prestressing tendon stress versus strain 38

7 Prestressing and casting of hybrid joists 39

8 Completed hybrid joist construction 39

9 FRP application 40

10 Gap in FRP upgrade of HJ-3 40

11 Epoxy injection of voids 41

12 Internal strain gage layout for HJ-3, HJ-4, HJ-6, and HJ-7 41

13 External strain gage layout on HJ-3 42

14 External strain gage layout on HJ-4 42

15 LVDT locations on test specimens 43

16 Potentiometer locations on test specimens 43

17 Block diagram of data recording system 44

18 Test setup 44

19 Load versus deflection for HJ-3, HJ-4, HJ-6, and HJ-7 45

20 Load versus deflection cycles for HJ-4 46

21 Deflected shape for HJ-3 46

22 Deflected shape for HJ-4 before repair (top) and after FRP repair (bottom) 47

23 Deflected shape of HJ-6 47

24 Deflected shape for HJ-7 48

25 Strain distribution for HJ-3 49

26 Strain distribution for HJ-4 50

27 Strain distribution for HJ-6 51

28 Strain distribution for HJ-7 52

29 Strain distribution along strand length of HJ-3 53
USACERL SR 99/01

30 Strain distribution along strand length of HJ-4 54

31 Strain distribution along strand length of HJ-6 55

32 Strain distribution along strand length of HJ-7 56

33 HJ-3 upgrade FRP strains 57

34 HJ-4 repair FRP strains 58

35 Crack patterns for HJ-6 .....59

36 Failure of HJ-6 59

37 Crack patterns for HJ-7 60

38 Crack patterns for HJ-3 61

39 Failure of HJ-3 62

40 Crack Patterns of HJ-4 prior to FRP repair. 63

41 Crack patterns for HJ-4 64

42 Shear repair design procedure 65

43 Simply supported beam 65

44 Shear diagram 66

45 FRP wrap repair. 66

Tables

1 Hybrid Joists Tested 67

2 Epoxy Material Properties 67

3 Yarn Properties 67

4 Fabric Properties 67

5 Composite Laminate Specification 68

6 Composite Material Properties 68

7 Casting and Release Dates for Each Hybrid Joist Web 68

8 Instrumentation for HJ-3 Upgraded With FRP 69

9 Instrumentation for HJ-4 Without FRP Repair 71

10 Instrumentation for HJ-4 With FRP Repair 73

11 Principal Experimental Test Results for Hybrid Joists 75

12 Camber and Deflection for Hybrid Joists (in.) 75
USACERL SR 99/01

1 Introduction

Background

Previous studies of rectangular beams have shown that fiber-reinforced polymer

(FRP) wraps of the full cross section improve the capacity of the section. The

challenge of applying an FRP wrap to a beam with slab and the benefits of such

an upgrade have not been assessed. This technology has potential application to

highway bridges constructed in accordance with American Concrete Institute

(ACI) codes of the 1950s and 1960s where these bridges may have less shear capacity than flexural capacity, or where added load capacity is required. A proven

repair method for this reinforced concrete (R/C) application may provide a costeffective solution for military installations and Corps of Engineers civil works

facilities, as well as civilian departments oftransportation.

Shear repair of reinforced concrete beams using externally bonded materials is

not a new concept. For many years, sheets of steel were applied to the tensile

face of damaged beams. The steel was effective in increasing both the shear and

flexural capacities of the member, but there have been two major disadvantages

to this method. First, bonding the steel to the beam is quite difficult in the field

due to its bulk. Second, the new plate is susceptible to corrosion, which can

cause loss ofthe adhesive bond.

An innovative method of beam shear repair involves the use of FRP externally

bonded to the faces of the member where shear capacity is deficient. Several

schemes are available: FRP plates bonded to the sides, strips of FRP material

bonded to the sides, or a jacket (wrap) placed along the shear span. FRP addresses the traditional material weaknesses of steel discussed above: it is not

susceptible to corrosion and is relatively conducive to field prepping and hand

lay-up. There have been several studies investigating the use of externally

bonded FRP sheets to improve strength and stiffness of R/C beams, but most of

these have dealt with improving beam flexural strength. Only a few studies

have specifically addressed shear.

Al-Sulaimani et al. (1994) tested simply supported R/C beams with fiberglass in

all three configurations (plates, strips, and wrap) under four-point loading. The

specimens were 6 in. x 6 in. in cross section and 49.2 in. in length. Compression
USACERL SR 99/01

and tension reinforcement as well as web stirrups were present. These beams

were pre-damaged before retrofit and were designed to fail in shear (the stirrups

served mostly to confine the flexural reinforcement). The researchers determined that fiberglass plates and strips bonded to the sides of the beams produced a modest (25-30%) increase in shear capacity. This repair technique, however, did not provide enough of an improvement to prevent a shear mode of

failure. Also, the fiberglass plates and strips peeled off. Beams fitted with a fiberglass wrap, however, nearly doubled the beams' shear capacity, and this increase was sufficient to produce a flexural (i.e., not shear) mode offailure.

Chajes et al. (May 1995) investigated R/C beams with aramid, glass, and graphite wraps loaded in four-point bending. These specimens were structural tees in

cross section having a 7.5 in. depth, 5.5 in. wide flange, 2.5 in. thick web, and 48

in. length. These beams were completely lacking in shear reinforcement but contained enough flexural reinforcement (only tension steel) such that a shear failure would occur. While all beams experienced an increase in ultimate capacity

they still failed in shear. The glass and graphite wraps were torn along the diagonal crack. The aramid wrap allowed the failed beams to carry some load,

however. It is important to note that the purpose of this experimentation was

not to force flexural failure, but to determine the effectiveness of the system to

increase shear capacity in specimens that were designed to fail in shear. Therefore, the FRP wrap was shown to be effective for shear repair. Chajes et al. published another paper (1995) where the beams were designed to fail in flexure.

The only shear reinforcement would be provided by the FRP wrap. In that experiment the beams developed sufficient shear capacity and failed in flexure, as

designed.

Based on the results of the studies cited above, it is known that composite wraps

are potentially very effective in shear rehabilitation of reinforced concrete. Both

research groups concluded that there was a need for full-scale testing of this

technology. In 1997 the U.S. Army Construction Engineering Research Laboratories (CERL) conducted such testing as part of a broader investigation of concrete repair technologies funded and executed under the Army Corps of Engineers Construction Productivity Advancement Research (CPAR) program. The

results of this testing were published as an appendix to the final CPAR report

(Marshall et al., February 1998), but they are presented here on their own to

reach engineers and materials scientists interested in the specific problem of

composite-based repair techniques to improve the shear performance of existing

R/C structures.
USACERL SR 99/01

Objective

The objective of this study was to test the effectiveness of FRP-based repair

techniques on full-scale prestressed high-strength concrete joists fabricated with

insufficient shear reinforcement.

Approach

Four prestressed high-strength concrete tee-beams (joists) with integral web

openings were tested. Two of the joists were used as control specimens. One

control joist had insufficient shear reinforcement and one was properly reinforced, designated HJ-6 and HJ-7, respectively. The other two joists were repaired (HJ-4) or upgraded (HJ-3) with FRP to improve their shear performance.

Performance criteria were specified for the two joists to be repaired. HJ-3 and

HJ-4 were wrapped on three sides, along the outer 8 ft of each end, with an FRP

composite system called TYFO S Fibrwrap . Standard structural engineering

practice for shear designs was used to determine the wrap thickness. Calculations were based on controlling shear crack widths to maintain aggregate interlock and proper shear transfer through the concrete.

Technical details about test specimen fabrication, repair material properties and

specifications, shear reinforcement techniques, and testing procedures are presented in Chapter 3.

Mode of Technology Transfer

A version of the material presented here was included as an appendix to CERL

Technical Report TR 98/47 (Marshall et al., February 1998); that report presented the current topic within a much broader concrete repair context.

A number of FRP composite systems are already on the market for the repair,

strengthening, or seismic upgrade of unreinforced or lightly reinforced masonry

structures, and new products are regularly becoming available. The FRP/URM

Project Team of the Composites Institute Market Development Alliance

(CI/MDA) is establishing a database of contacts for companies that market these

types of structural enhancement systems. For further information contact Manager, Market Development, Composites Institute, 600 Mamaroneck Ave.,

Harrison, NY 10528-1632 (914-381-1253, x256 voice; 914-381-1253 fax).
10 USACERL SR 99/01

Units of Weight and Measure

U.S. standard units of measure are used throughout this report. A table of conversion factors for Standard International (SI) units is provided below.

SI conversion factors

1 in. = 2.54 cm

1ft = 0.305 m

1yd = 0.9144 m

1 sq in. = 6.452 cm2

1 sqft = 0.093 m

2

1 sqyd = 0.836 m

2

1 cu in. = 16.39 cm3

1 cuft = 0.028 m

3

1 cuyd = 0.764 m

3

1 gal = 3.78 L

1 lb = 0.453 kg .

1 kip = 453 kg

1 psi = 6.89 kPa

°F = (°C x 1.8) + 32
USACERL SR 99/01 11

2 Fiber-Reinforced Composites

A composite is a combination of two or more materials (reinforcing elements, fillers, and matrix binder) with different form or composition which, when combined into a material system, exhibit properties which are a combination of its

individual components. The system constituents retain their distinct identities,

meaning they do not dissolve or merge completely into each other, but act in concert to provide an overall function. The matrix can be a ceramic, metal, or polymer. Fillers may be mineral or metallic powders. Reinforcing can be particles,

fibers, rods, or bars. For example, reinforced concrete is a composite consisting

ofsteel reinforcement, sand and gravel fillers, and a portland cement matrix.

Fiber-reinforced composites or fiber-reinforced polymers (FRP) consist primarily

of a typical reinforcement of glass, carbon or aramid fibers, and a polymer matrix. Fillers to modify the physical, mechanical, thermal, electrical, and other

properties or to lower the cost or density, may or may not be included. The

polymer matrix may be a thermoplastic, a thermoset, or an elastomer. A thermoplastic polymer, polyethylene, polyvinyl chloride, or polystyrene for example,

is one which becomes pliable or plastic when heated and then becomes hard

again when cooled. A thermoset polymer changes into a crosslinked, substantially infusible material when cured by heat or chemical reaction. Epoxy, polyester, and polyurethane are examples of thermosets. An elastomer is a rubber-like

polymer which recovers its original shape and size after removal of a deforming

force.

The key component of an FRP is the fibrous reinforcement; it is the primary load

bearing component. The matrix serves as the mechanism by which loads are

transferred within the member from one fiber to another. Each type of fiber has

certain advantages and disadvantages; reinforcement is selected on the basis of

its physical, mechanical, and thermal properties.

Modern glass fibers were first developed in the 1930s for military purposes.

Soon after, its primary commercial use was for the reinforcement of plastics. Eglass is the standard because of its electrical and mechanical properties. This

fiber has a tensile strength nearly double that ofsteel and has modified versions

that resist strong acids. An interesting characteristic of glass fibers is that they

are elastic — elongating until failure without yielding. After the load is released

the fiber returns to its original length.
12 USACERL SR 99/01

Carbon fibers are the most widely used variety of reinforcement having a very

wide range of physical properties. Their strength can vary from that of steel to

about four times that. What separates carbon fiber reinforced polymer (CFRP)

from the rest is its low weight. Its performance based on stiffness to density is

very high. It also has very good fatigue and damping characteristics. Manufactured carbon fibers can vary from the weakest of all fibers to among the strongest. Likewise, their price also varies from inexpensive for the weaker fibers to

expensive for the strongest fibers. The most commonly produced versions of

CFRP are the intermediate strength fibers. They have tensile strengths stronger

than glass and somewhat weaker than aramids.

Like carbon, aramid fibers are lightweight, have high tensile strengths, and good

damping and wear resistance. They also have excellent fiber toughness. A

popular version of the aramid fiber is marketed under the trademark Kevlar.

However, its drawbacks are low resistance to acid attack and high cost.

As the manufacture of FRP composites improve and their mechanical properties

are better understood, they are being used in a wider variety of applications.

Because of the ultra-conservative nature of the civil engineering community and

the relatively short history of FRP composites use, fiber-reinforced composites

are just beginning to be considered as a civil engineering material alternative to

steel and reinforced concrete. Although many factors, including material form,

will significantly influence any design, some general differences between metals

and composites may make the latter appear to be the more attractive choice. Differences between composites and metals are as follows:

• Unidirectional aramid and carbon fiber reinforced epoxies provide a specific

tensile strength (ratio ofmaterial strength to density) that is approximately

four to six times greater than that ofsteel or aluminum

• Unidirectional carbon fiber reinforced epoxies provide a specific modulus (ratio ofmaterial stiffness to density) that is approximately ZVi to 5 times

greater than that ofsteel or aluminum. Aramid falls between carbon and

glass fiber reinforced epoxies

• Comparing efficiently designed structural elements, the fatigue endurance

limit for aramid and carbon fiber reinforced epoxies may approach 60% ofthe

ultimate tensile strength. For aluminum and steel, this value is considerably

lower

• Because ofthe properties listed above, aramid, carbon, and hybrid fiber reinforced plastics can provide structures that are 25 to 45% lighter than aluminum structures designed to the same functional requirements. Impact energy values for aramid-epoxy composites are significantly higher than those

for carbon fibers and aerospace aluminum alloys
USACERL SR 99/01 13

• Fiber-reinforced polymers can be designed with excellent structural damping

features to provide lower vibration transmission than metals

• Fibrous composites are more versatile than metals and can be tailored to

meet performance needs and complex design requirements. Design requirements sometimes cannot be satisfied by metal alloys within the critical

weight limitations

• The properties mentioned above can be balanced with cost by hybridization

(mixing different fibers in a given composite to attain an optimum combination of properties)

• Corrosion and other attributes of fibrous composites will contribute to reduced lifecycle cost

• Composite parts can eliminate joints/fasteners, providing part simplification

and integrated design

FRP composites consist primarily of fiber reinforcement and a polymer. Fibers

that are typically used for civil and structural engineering applications are Eglass, carbon, and aramid; polymers are either polyester, vinyl ester, or epoxy. A

major reason these polymers are used is because they cure by chemical reaction

at ambient temperature. FRP composites may take several forms. The fibers

can be in a woven or stitched fabric, or unidirectional sheet, tow or yarn. The

composite may be a prepreg (fabric with uncured polymer infusion at the factory), preform (extruded, cast, or shaped at the factory), laminate plate,

rod/cable, or a hybrid of these. Various methods exist for applying composites to

a structural member. They include hand lay-up, filament winding, vacuum resin

transfer molding, and any compaction process. When preforms or laminate

plates are used for repair or upgrade, matrix binders or adhesives made of polyester, vinyl ester, epoxy, or polyurethane are used to bond them to the structural

members. Depending upon the composite specifications, additives, fillers, or

coatings may also be incorporated in the composite to provide UV and/or fire resistance and special moisture or chemical resistance.
14 USACERL SR 99/01

3 Experimental Program

Test Specimens

The hybrid joist design used in the experiments is intended to combine the benefits of prestressed concrete double tees and open-web steel joists but overcome

their shortcomings. The hybrid joist was envisioned for use in office construction. A length of 32 ft and a tributary width of 8 ft were chosen for the initial design. Loads of 50 psf office live load and 20 psfsuperimposed dead load were assumed. All loads were assumed to be uniformly applied along the joist length.

This resulted in a superimposed total uniform service load of 70 psf and an ultimate load of 113 psf.

The overall configuration of the joist is shown in Figure 1. The joist webs had a

constant thickness of 6 in. Joist web ends were 10 in. deep; the depth of all other

joist web elements was 6 in. Overall depth ofthe web was 24 in. Three openings

were located along the joist length. Prestressing tendons were located in the top

and bottom chords of the web. The prestressing tendon profile is shown in Figure 2. Six tendons were used, two straight and four draped. Figure 3 summarizes the web reinforcement of each of the beams. The cast-in-place concrete

flanges of HJ-3 and HJ-4 had a thickness of 4 in. and width of 6 ft. The flanges

ofjoists HJ-6 and HJ-7 were 4 ft wide. The slab was reinforced with welded wire

fabric (WWF), 4 X 4-W4.0 X W4.0, placed at a height of 2 in. Detailed descriptions of each joist design are provided in Saleh, Brady, Einea, Tadros, and Decker

(1997).

Four prestressed high-strength concrete tee-beams with integral web openings

were tested. Two joists were used as control specimens. One control joist had

insufficient shear reinforcement; one joist was properly reinforced, designated

HJ-6 and HJ-7 respectively. The other two joists were repaired, HJ-4, or upAll figures and tables are presented at the end of this report.
USACERL SR 99/01 15

graded, HJ-3, with FRP to improve their shear performance. Joist designations

are shown in Table 1.

Performance criteria were specified for the two joists to be repaired. It was required that their shear capacity be increased 15 kips over a length 3 ft-10 in.

from each end and 10 kips over the following 4 ft. The two repaired beams were

wrapped on three sides with Fyfe's TYFO S Fibrwrap along the outer 8 ft of

each end of HJ-3 and HJ-4, Figure 4. The FRP repair design was based on the

following material properties:

fsj = 12 ksi (conservative estimate of allowable jacket stress)

f. = 65 ksi (ultimate jacket stress, minimum)

E = 3250 ksi (modulus of elasticity ofjacket)

eai = 0.004 ( allowable jacket strain)

suj = 0.02 (ultimate jacket strain)

u . = 400 psi (allowable bond stress) aj *

tj = 0.051 in. (jacket thickness per layer)

Standard structural engineering practice for shear designs was used to determine the jacket thickness. Calculations were based on controlling shear crack

widths to maintain aggregate interlock and proper shear transfer through the

concrete. The allowable jacket strain, saj = 0.004, represents 20% of the ultimate

composite strain. The calculations resulted in the requirement for two layers of

SEH-51, with the main fiber strength vertical, over the extreme 4 ft. The next 4

ft required only one layer per the calculations, however, the Fyfe Co. recommended the use of a minimum oftwo layers (Gee 1996).

No additional anchorage system was used due to the potential interference with

the prestressing tendons ofthe existing joist.

Materials

1. Concrete. The concrete mix used in the hybrid joist specimen webs was a

high-performance concrete (HPC). It provided special performance requirements

including ease of placement and consolidation without compromising strength,

superior long-term mechanical properties, early high strength, volume stability,
16 USACERL SR 99/01

and long life in severe environments. The HPC concrete strength used was designed to have a strength of 12,000 psi at 28 days. Figure 5 shows the time versus strength curves for the concrete used in the webs. Ready-mixed concrete was

used in the slabs of all specimens. The mix was specified to be 5,000 psi and

consisted of Type I cement with a maximum aggregate size of 1.0 in. limestone.

The mix corresponded to dry weight proportions of 1.0:3.0:2.6 (cement : fine aggregate : coarse aggregate). On the day of testing all cylinders were also tested.

Compression tests were conducted in accordance with ANSI/ASTM C39-86.

2. Steel. The tendons used were manufactured by the American Spring Wire

Corporation (26300 Miles Rd., Cleveland, OH 44146). These tendons were 1/2 in.

diameter, 270 ksi, low relaxation. The stress-strain curve for these tendons is

shown in Figure 6. The shear reinforcement in the webs consisted of bar reinforcement, Grade 60. A welded wire fabric mesh, Grade 75, was used as reinforcement for the cast-in-place slab.

3. FRP. The FRP was specified as TYFO S Fibrwrap System and manufactured by Fyfe Co. L.L.C. of San Diego, CA The TYFO S epoxy is a twocomponent, solvent-free, moisture insensitive epoxy matrix material. It is a high

elongation material which gives optimum properties as a matrix for the TYFO

fiber system. The epoxy has no offensive odor and maintains its properties up to

140 °F. Table 2 lists the epoxy properties. The TYFO fiber system is a plain

weave, predominately warp unidirectional fabric comprised of a warp (0 degree

orientation) of E-glass roving and a weft (90 degree orientation) of aramid, Eglass, and Thermoplastic Adhesive. The ratio of warp fiber to weft fiber is 17.5

to 1 by weight. Table 3 lists the yarn properties and Table 4 the fabric properties. Two layers of the TYFO S Fibrwrap System were used. Table 5 lists the

composite laminate specifications and Table 6 the composite properties. The system has been tested and develops an allowable shear stress of greater than 350

psi without anchors.

Fabrication

The webs of the joists were prestressed and cast horizontally, i.e., on their sides

as shown in Figure 7. Hold-down devices were used at the draping points to position the tendons and resist the prestressing forces. The concrete mix was

placed in the forms and vibrated to ensure consolidation of the concrete. The

specimens were covered with wet burlap that was kept moist for the first 3 days.

The specimens cured at room temperature for 7 days. Cylinders measuring 4 in.

diameter by 8 in. tall were cast and cured with the joists under the same conditions. The concrete strength was monitored by compression testing of cylinders

to assess when the required release strength was achieved. When the strength
USACERL SR 99/01 17

reached 7000 psi the tendons were released by alternately torch cutting a tendon

on each face at the joist ends. Casting and release dates for each specimen are

shown in Table 7. The webs were then turned vertically and stored in the lab.

The webs were then positioned vertically upright and level. The slab forms were

then constructed around them. After concrete placement, the forms and test

cylinders were covered with wet burlap followed by plastic sheets. The burlap

was maintained moist for 4 days following casting. After 7 days the forms were

stripped. Figure 8 shows the final shape ofthe joists.

Prior to application of the composite overlay the joist surfaces were prepared.

This involved removing the paint on the outer 8 ft ofthe webs, rounding the corners at the bottom ofthe beam web to a minimum radius of 1.5 in., and removing

trowel marks and smoothing out rough areas using an electric grinder. Once

completed, creases in the web left by the concrete form lining were filled with a

rapid strength repair mortar. After the mortar was cured, the surface of the

beams was again ground and then cleaned using methyl ethyl ketone to remove

any excess dust. Cracks in the concrete of HJ-4 created during pre-loading were

ignored since they were less than 1/16 in. wide. The two part epoxy TYFO S

Tack Coat was mixed and troweled onto the surface of the beams where the repair/upgrade was to be applied.

While the tack coat began setting up, the reinforcing fabric was cut to the proper

length using scissors and infused with the TYFO S two part epoxy. This was

done by laying the fabric out flat and evenly spreading the resin on the fabric by

hand to saturate the fabric. The fabric was then laid up around the end of the

joist from just beneath the slab, around the web and up to the slab/web intersection again, Figure 9. The material was placed vertically (main fibers vertical) in

bands of 52 in. (1.2m) on the sides of the joist. Adjacent bands were placed with

a 4 in. butt splice. In regions oftaper, the bands were applied as four pieces, two

per side ensuring that main fibers remained vertical on joist faces. The material

was carried under the joist and the excess cut off.

Because of lack of Cab-O-Sil in the tack coat, the system applicators had great

difficulty getting the FRP system to adhere properly to the concrete prior to

curing. The cure time was also slow because of high humidity. Upon cure it was

noted that the FRP had slipped down on both HJ-3 and HJ-4. A gap, uncovered

by FRP, existed beneath the bottom ofthe slab on the web. In most locations the

gap was not significant; however, on the north end of HJ-3 the gap was observed

to be 1.25 in., Figure 10. After curing, voids between the composite and the joist

were filled with epoxy, Figure 11.
18 USACERL SR 99/01

Instrumentation and Data Recording

Test specimens HJ-3, HJ-4, HJ-6, and HJ-7 were instrumented with displacement potentiometers, strain gages, and linear variable displacement transducers. Tables 8 and 9 summarize the instrumentation plans for HJ-3 and HJ-4.

Figure 13 shows the layout of internal strain gages for HJ-3 and HJ-4. Internal

strain gages were located so as to measure strains in both prestressing tendons

and reinforcement. Once the composite was cured, strain gages were placed on

the external surface at the locations of the most dramatic shear cracks, other

previous shear failure areas, and at the FRP lap joints to monitor strain in the

composite. Gages were symmetrically placed at each end ofthe joists. Figure 13

shows the location of these gages for HJ-3 and Figure 14 shows the gage locations for HJ-4. LVDT locations were the same for all joists (Figure 15). Displacements were measured by potentiometers at the center of the joist, beneath

one web post and a distance 25% of the span length from a support along the inclined portion of the joist, Figure 16. All recorded potentiometer displacements

were absolute, measured with respect to the laboratory floor. Displacement

measurements were also taken manually on the west and east faces of the slab

at each joist end, and along the east slab face at the center and beneath each actuator.

Figure 17 is a functional block diagram of the instrumentation, data acquisition,

and test control systems used at CERL. All of the transducer output signals

were connected to a Hewlett Packard* Model 3052A data logging system. The

system was controlled by computer through an instrument controller interface

bus. The record channels were scanned at a predetermined sampling rate, and

the data were recorded in ASCII text files on the computer.

The loading system consisted of two CGS/Lawerence Model 307-50 electrohydraulic actuators (controlled by closed-loop servo controllers) and a function

generator. The actuators were operated in a displacement-control mode. In this

mode, the function generator supplies a slowly changing command signal to the

controllers. The controllers send a drive signal to each of the actuators, which

causes the actuators to move until the displacement measured by LVDTs located

inside each actuator is equal to the command signal. The actuators also include

load transducers that measure the applied load.

Hewlett Packard Co., 5301 Stevens Creek Blvd., Santa Clara, CA 95052-8059.
USACERLSR 99/01 19

Test Procedure

The test setup on the CERL Structural Load Floor is shown in Figure 18. Each

specimen was tested as a simply supported beam under two symmetrical point

loads with a clear span of m (31 ft) and a shear span of m (11 ft - 3 in.). Vertical

loads were applied by 50-kip hydraulic actuators suspended from a load frame.

The actuators were centered directly over the web posts of the specimens. In

testing at CERL the stroke of each actuator was calibrated to zero after making

contact with the specimen; a small pre-load was associated with this positioning.

Specimens were loaded at a constant rate to a specified stroke limit. The actuators were maintained at this stroke while the joist was inspected for cracks;

these were marked. Measured readings of deflections were taken at selected locations and the deflection data were checked. Stroke was then further applied to

the specimen until the stroke limit of the actuators was reached. The full stroke

(i.e., full load) was then removed from the specimen. Steel plates were added

between the actuator and the beam. The actuators were then moved into contact

with the specimen again; this was associated with a small pre-load. The test was

continued in the same manner until the specimen failed. Data were recorded

during loading and unloading cycles.

Of the two repaired specimens, HJ-4 was damaged to a predetermined level defined subsequent to testing the control beams, which were unrepaired. The

beam was then unloaded and repaired. HJ-3 was not loaded prior to upgrading

it with FRR After repair, the beams were loaded at a constant rate of 0.2

in./min. in increments of 1 in. At each displacement increment, measured readings of deflections were taken at selected locations and deflection data were

checked. Loading of HJ-4 continued until the bottom of the joist was VA in. from

the load floor. The joist was then unloaded. HJ-3 was loaded in the same manner as HJ-4. The joist was tested to failure.

Experimental Results

The measured load and deflection, strains in concrete, steel rebar and FRP, and

crack development and failure of each specimen are discussed. Results of the

two repaired beams are compared with two control beams.

Load and Deflection

Table 11 summarizes principal test results, including cracking load, location of

first crack, failure load, equivalent uniform superimposed (SI) load at failure for

the test configuration, and type of failure. All load values in the table represent
20 USACERL SR 99/01

the sum of the two actuator loads. The experimental cracking load was determined at the time the first crack was observed. Joist HJ-4 was loaded to a peak

of 55.2 kips. After the FRP repair, HJ-4 was reloaded to a peak of 56.6 kips, approximately 690% ofthe SI service load or 422% ofthe SI ultimate load. The upgraded joist HJ-3 was then tested, and failed at a load of 52.6 kips, 393% of the

ultimate SI design load. The two control joists, HJ-6 and HJ-7, failed at 48.7

kips and 65.0 kips respectively. HJ-6 failed at well below the anticipated capacity but still 363% of the ultimate SI service design load. The premature failure

was attributed to insufficient shear reinforcement.

Deflection parameters, including camber at tendon release and experimental deflections due to the applied loads are summarized in Table 12. For the 31 ft clear

span and 6 ft tributary width, the experimental deflections at the load equivalent to live load (LL), 3.5 kips, and the load equivalent to SI dead load (DL) + LL,

4.1 kips, are much lower than the ACI 318-95 limitations of L/360 (1.0 in.), and

L/240 (1.55 in.), respectively, for specimens HJ-3 and HJ-4. Similarly HJ-6, and

HJ-7 with 4 ft tributary widths deflected much less than the ACI limitations under loads of 2.3 kips and 4.0 kips for (LL) and (SIDL + LL), respectively. HJ-4

with the FRP repair permitted a midspan displacement of more than 11.3 in.

without failing. The test was stopped as there was a lack of space to further deflect the joist. HJ-3 was able to deflect 7.7 in. before failure was initiated.

The experimental load versus midspan deflection curves for joists HJ-3, HJ-4,

HJ-6, and HJ-7 are shown in Figure 19. Initial stiffness (below 0.2 psf) of all

specimens is similar. After this point the stiffnesses of HJ-3 and HJ-4 were less

than for either control joist. HJ-3 displayed more flexible response than the

damaged or repaired joist HJ-4. HJ-4 was not able to achieve the performance of

the control beam HJ-7 which had sufficient shear reinforcement. All joists were

able to achieve their peak load repeatedly for several loading/unloading cycles.

HJ-4 achieved the peak load for 5 cycles before the test was stopped. Its stiffness

did not change significantly from cycle to cycle, Figure 20.

Deflection profiles along the joist length were approximated using potentiometer

data as well as manual measurements from the joists' top flanges. A deflection

profile is shown for HJ-3 with respect to load increments of a single actuator in

Figure 21. Figure 22 shows deflection profiles for HJ-4 prior to repair and after

the joist was repaired with FRP. HJ-3 deflected more than either the original or

repaired HJ-4 for comparable load levels up to 25 kips. It also deflected much

more than HJ-6. Similar plots for the other tested joists are shown in Figures 23

and 24. HJ-4, while able to deflect significantly was not able to match the performance of HJ-7. The shapes of HJ-3 and HJ-4 are much like that ofthe control

joist, HJ-7. The shapes reflect the constant moment between load points and the
USACERL SR 99/01 21

marked stiffness variation along the specimen length. The increased curvature

with increasing load also reflects progressively greater cracking in the center

section of the joists. The deflected shape of HJ-6 emphasizes the effects of insufficient shear reinforcement in the joist's inability to benefit from the prestressing

and optimized shape.

Strains

Three types of strain readings were used in testing the family of hybrid joists:

internal strain of reinforcement and external strain on FRP surfaces — both

measured by strain gages — and displacement measured over a specified gage

length on concrete surfaces by LVDTs. For the latter measurements cracks may

have developed within the gage length, and the strain (displacement/displacement) may be greater than the maximum concrete strain range of

0.003 - 0.004 for compression or 0.0001 - 0.0002 for tension.

Strain distribution over section depth is shown in Figures 25 and 26 for three

critical sections of HJ-3 and HJ-4 with FRP repairs. The distribution was approximated from concrete strain measurements near the top of the section and

prestressing strand strains above and below the openings. Similar plots are

shown in Figures 27 and 28 for HJ-6 and HJ-7, respectively. Strain along

prestressing tendon length is shown in Figures 29 and 30 for HJ-3 and HJ-4 respectively. Figures 31 and 32 show strand strain measurements for HJ-6

through HJ-7.

Strains at the end and midspan of HJ-3 are similar in magnitude to those of HJ6. It is apparent from Figure 25 that the full prestressing capacity could not be

developed in these joists. This is further shown in Figure 29 where results of internal strain measurements along the strands for both top and bottom strands of

repaired joist HJ-3 are presented. Strains in tendons were greatest in the shear

span of this joist. In the constant moment region, strains are much less for both

top and bottom tendons. From the strut section strain distribution, we can see

that the neutral axis lies at a depth approximately 5 in. from the top of slab in

HJ-3. From Figures 29 and 31 it is apparent that failure occurred before the full

prestressing capacity could be developed in these joists.

Comparing Figures 26, 25, and 28, strain distribution in the repaired joist HJ-4

is quite different from that of either HJ-3 or HJ-7. The neutral axis indicated by

the midspan strain is located at the member midheight. Peak strains in top and

bottom prestressing strands of HJ-4 were greater than those in HJ-7, Figure 30

versus Figure 32. However, strain distribution over bottom tendon length is
22 USACERL SR 99/01

much more uniform in HJ-7 providing greater ultimate flexural capacity of this

section. HJ-4 did not approach the load capacity of HJ-7.

lb assess the stress in the strands, the strains shown must be added to the

strain due to prestressing and related to the elastic modulus of the material.

The strand was fully tensioned, so the effective strain due to the prestress is approximately 6705 micro strain [(fM/Es) = 0.75 (270) / (30,000) (106

) = 6750 micro

strain]. All strains were below the ultimate strand strain of 35,000 micro strain.

Again, the lack of strain developed in the strand indicates the poor performance

of HJ-6. During testing it was observed that the bottom chord of HJ-7 appeared

to arch upward between the struts; this may be related to the larger strains

shown at the struts than the midspan for some load levels.

Figures 33 and 34 show load versus strain in the FRP material for HJ-3 and HJ4 respectively. Strain gages along the beam web show elongation of transverse

FRP with increasing load. In HJ-4 FRP strains do not begin to increase appreciably until the actuator load is approximately 12 kips indicating the widening of

shear cracks in the concrete beneath the FRP and the developing shear resistance in the FRP. Strain in gages ES4 and ES5, closest to the beam center,

reached a peak value greater than 0.005 in./in. This is above the allowable

strain of 0.004 but much less than the ultimate strain of 0.02. The limited capacity of HJ-3 is shown by the much lower strain values of gages ES4 and ES5

than for HJ-4.

Cracking and Failure Mechanism

None of the joists cracked when the prestressing tendons were released. During

handling, specimen HJ-7 developed a crack across the slab through its depth

near the south strut. Cracks were marked on each of the joists throughout testing. Cracking and failure mechanisms resulting from testing of HJ-6 and HJ-7

were compared with those of the two hybrid joists upgraded or repaired with

FRP. Early in the test series, limited cracking occurred in the bottom chord of

HJ-6. As actuator stroke was increased, cracking in the shear spans became

evident but the cracks in the bottom chord did not develop further. In HJ-6 an

inclined crack developed near the support and progressed upward along the

web/slab interface (Figure 35). This crack progressed into the slab and failure

ultimately occurred in this North end ofthe joist (Figure 36).

Figure 37 shows crack development for HJ-7. Initial flexural cracks formed

along the bottom chord at midspan. Cracks were regularly spaced, and they became more numerous and closely spaced as the displacement was increased.

Near the end of testing, when the load was not increasing but the specimen was
USACERL SR 99/01 23

able to deflect significantly more, inclined cracks developed in the shear spans of

the members. No actual failure was observed in specimen HJ-7. The joist continued to deflect after reaching an ultimate load capacity.

Cracking in HJ-3 initiated as for HJ-7 with flexural cracks in the web bottom

chord. At an applied stroke of approximately 5 in. a crack began to develop

along the edge of the FRP at the intersection between the joist web and slab,

Figure 38(b). A gap of more than 1 in. of exposed concrete existed where the FRP

had slipped down from the web/slab interface. The horizontal crack began near

the point where the FRP lapped. As the horizontal crack progressed toward the

North end of the joist, cracks also developed in the bottom of the slab perpendicular to the joist span as well, Figure 38(a). These were associated with popping sounds as ifthe FRP were debonding from the joist. A vertical crack in the

FRP was observed at a distance approximately 6 in. from the north end of the

joist. This occurred at a stroke of approximately 7.5 in. A maximum deflection

of approximately 9 in. was achieved before complete collapse ofthe joist occurred

by fracture ofthe top slab at a distance of approximately 56.75 in. from the north

end. The FRP separated from the joist by buckling over the web depth at a distance approximately 41 in. from the joist north end. A third vertical break in the

FRP was observed at 25.5 in. from the end, Figure 39 (a). These cracks in the

FRP were accompanied by peeling of the top slab from the web at the construction joint, Figure 39 (b). Investigation of the failure revealed the concrete in the

area of the FRP repair had completely broken up. The total length of crumbled

concrete was approximately 50 in. Examination of the TYFO S Fibrwrap System showed it to be adhered to the perimeter concrete even at failure. Failure

was in the concrete. This was precipitated by the weakness created by the gap

in the FRP repair at the top ofthe web.

Initial testing of HJ-4 without FRP repair produced crack patterns similar to

those for HJ-6, Figure 40. After repair testing began again, existing cracks between struts increased in size and additional cracks were observed to develop

near the edge of the FRP repair area, Figure 41 (a) and (b). The test had to be

stopped when there was no further vertical space between the web bottom chord

and the floor for the joist to deflect. The joist did not fail. At the test conclusion,

the FRP repair showed no signs of damage. The beam exhibited ductile response

throughout the test.

Experimental Test Conclusions

HJ-4, while being damaged prior to application of the FRP repair, was able to

deflect as much as HJ-7. However HJ-4 with FRP repair was not able to achieve

the strength and stiffness levels of a properly reinforced specimen, HJ-7. The
24 USACERL SR 99/01

shear mode failure ofHJ-3 was initiated by a gap on the joist web where the FRP

had slipped during curing. Its performance was not improved over HJ-6.
USACERL SR 99/01 25

4 Design Procedure for Hybrid Joists

Overview

Based on standard structural engineering design principals and the experimental test results, a simple procedure was developed to design FRP composite system repairs for reinforced concrete joists deficient in shear capacity. This design

procedure is a step-by-step process wherein load demands are assessed for an

existing member cross-section, a repair is designed based on specified engineering properties of the FRP composite system to achieve the required capacity, and

stresses and deflections for the repaired joist are checked. Figure 31 shows the

flowchart for the joist design procedure.

Design Criteria and Assumptions

Design criteria are based on Building Code Requirements for Reinforced Concrete, ACI 318-95 (1995). Load and strength reduction factors as specified by the

code are used. Flexural strength is calculated using strain compatibility.

The International Conference of Building Officials has developed a draft document on the subject of "Acceptance Criteria for Concrete and Reinforced and Unreinforced Masonry Strengthening Using Fiber-reinforced Composite Systems"

(ICBO 1997). This document provides good guidance for the establishment of

minimum requirements for evaluating FRP systems for strengthening concrete

elements.

The joist is assumed to be uniformly loaded at all stages with a simple span and

roller supports.

Design Procedure

Define Loading

As stated above, uniform loading of the beam is assumed. Service loading is defined as the unfactored load. This will generally be a combination of the beam
26 USACERLSR 99/01

self-weight, superimposed dead load, and live load. Ultimate load is typically

defined as shown below:

Ultimate Load = 1.4 DL + 1.7 LL

where: DL is the sum ofthe self-weight and superimposed dead load and

LL is the live load

Calculate the service load for each loading stage. Calculate the ultimate loads

acting on the joist. Again, it must be noted that the CPAR test results do not

support the use of this type of hybrid joist where concentrated loads will be applied.

Define Capacity of Existing Beam Section

Flexural and shear capacity ofthe section should be computed without use of reduction factors based on the existing properties.

Flexural capacity is based on strain compatibility and equilibrium. A maximum

concrete compressive strain of 0.003 is being assumed. The ultimate moment

capacity, Mu is computed as:

M, = Af

\ 2

where: a =

Axfy

0.85/c b

and a = depth of equivalent rectangular stress block, in.

A = the area offlexural reinforcement, in.2

s

f = yield stress ofreinforcement, ksi

d = distance from extreme compression fiber to extreme tension steel, in.

f'c = compressive strength of concrete, ksi

b = section width, in.
USACERL SR 99/01 27

Shear capacity is a function of the concrete shear strength and shear reinforcement:

Vn=Vc+ Vx (ACI, 1995 Equation 11-2)

where Vc is nominal shear strength provided by concrete computed as:

Vc = 2yjfc'bwd (ACI, 1995 Equation 11-3)

for members subjected to shear and flexure only. Ifthe beam has been damaged

a conservative assumption ofthe concrete shear capacity is Vc = 0.

Vsis nominal shear strength provided by shear reinforcement and computed as:

= _Jy_ (ACI,1995 Equation 11-15)

where Av is the area ofshear reinforcement within a distance.

Determine Load Requirement for Upgrade/Repair

The degree of upgrade/repair required is represented by the difference between

the load demand and the existing section capacity. The ratio of shear capacity to

shear demand should exceed that of the flexural capacity to flexural demand.

This is to ensure that a shear failure mode, which can occur without warning

and may be catastrophic, does not occur. Rather a ductile mode of failure with

obvious signs of distress, as would occur in a flexural failure, is desirable. The

final shear capacity of the upgraded/repaired beam should be approximately 1.5

to 2.0 times the flexural capacity. The upgrade/repair demand will be represented as Vreq - required additional shear capacity.

Determine FRP Properties

Shear enhancement is provided by fiber-reinforced composite materials with fibers oriented essentially perpendicular to the member's axis. Fiber orientation

is critical when determining FRP properties. Important properties to define for

design are:

fsj , allowable FRP tensile stress

f., ultimate FRP tensile stress
28 USACERL SR 99/01

a , allowable bond stress

Ej, FRP modulus of elasticity

e , allowable FRP strain

e , ultimate FRP strain UJ>

ICBO limits allowable composite material stress, faj, to be 0.004 E} and less than

O.754.

Determine Configuration and Calculate Thickness of FRP

Research directed toward determining effective configurations of FRP shear repairs for beams by Al-Sulaimani et al. (1994) showed that the use of strips or

wings on the beam faces provided comparable increases in shear capacity. However, the mode offailure for these sections tested was still in shear. Shear repair

by a jacket on three sides performed better than repair by strips or wings. The

wings of the jacket were well anchored at the bottom of the beam so that no premature peeling failure occurred. Additionally the continuity provided by the geometry of the jacket minimized the effect of stress concentrations in the plates.

The beams repaired with FRP jacket exhibited a higher capacity than those of

the strip or wing upgrade and ultimately failed in flexure.

Ajacket configuration should, therefore, be assumed whenever possible. It is optimal to wrap the entire section in the FRP. If this is not possible the use of anchors should be considered so that bond is not the primary mechanism of force

transfer.

Assuming a layer thickness oftj.

F^=2fy/^sme

where H is the depth of the FRP and 9 is the angle of the fibers relative to the

member axis. This equation assumes a shear crack inclination of 45 degrees.

ICBO recommends the following equation:

Vreq=2.S6tjfaJHsm

2

e
USACERL SR 99/01 29

Check Stresses

Bond, flexural, and shear stresses should be checked for the upgraded/repaired

joist configuration.

Check stresses due to service loads.

Check stresses at ultimate loading using ACI 318-95 approximate equations or

the strain compatibility method:

Vu =V' c +Vs +Vp

where: Vu, Vcand Vs are defined above and Vp is computed as

VP =2FP=2 (Al-Sulaimani et al. 1994)

This equation assumes a full U-jacket is used, that shear distribution is uniform

over the depth ofjacket, with the absence of stress concentrations; therefore, the

ultimate stress ofthe material may be achieved.

Check bond shear stress. ICBO guidance requires that where the performance of

the composite material depends on bond, the bond strength of fiber-reinforced

composite material to concrete [u^ shall not be less than the characteristic flexural tension capacity ft

' of the concrete. Under ultimate flexural strength conditions, bond stress between fiber-reinforced composite material and concrete shall

not exceed:

uj = -^<0.75/,

ax

where x is the direction parallel to the fiber. This value should be evaluated at

sections where the rate of change in fiber net force, tff., is a maximum. This will

normally correspond to locations of maximum shear force.

Check Deflections

An estimate of the load deflection relationship should be checked using structural analysis methods. Deflection limits should be evaluated relative to ACI

code requirements.
30 USACERL SR 99/01

Determine Failure Mode

The member should be designed to fail by ductile flexural failure mode. For the

strengthening of existing reinforced concrete beams with FRP it is recommended

that the repair/upgrade be designed such that ultimate failure occurs by yielding

ofthe steel reinforcing bars before a compressive failure of the concrete. Yielding

ofthe steel bars should not occur before reaching the permitted service loads.

Detailing

For rectangular sections where shear enhancement provided by transverse fiberreinforced composite material, section corners must be rounded to a radius not

less than % in. (20mm) before placement ofthe composite material.

Design Example

Assumptions

The concrete weight is 150 pcf.

Concrete compressive strength is 4 ksi,

Steel reinforcement yield stress is 60 ksi.

Shear reinforcement consists of #3 U-stirrups at 6 in. o.e. over the length of the

beam.

FRP Properties

Beam is originally designed to carry 4 k/ft uniform load. Check shear capacity.

4x25

Vu = —^— = 50 kips

Shear at critical section (at distance d from end) by similar triangles:

50 x (12.5-1.5)

Vuatd= K— -=44 kips

vu<<t>vn
USACERL SR 99/01 31

where: (|>Vn = (|>Vc + <|>Vs

Vc = 2Vfc bwd = 2 V4ÖÖÖ (12X18) = 27.3 kips

AvFyd (0.22)(60)(18)

V = = = 39.6 kips

(|>Vn = (0.85X27.3+39.6) = 56.7 kips > 44 kips OK

bws (50)(12)(6)

Minimum: A = 50 =

V ** J = 0.06 in2

F 60000

Av (provided = 0.22 in2) > Av (required = 0.06 in2) OK

Now, suppose uniform load increases to 6.5 k/ft.

Vu at critical section = 71.5 kips

Shear deficiency = 71.5 - 56.7 = 14.8 kips (say 15 kips)

We need FRP wrap from end to point along beam where shear is less than 56.7

kips.

(56.7)(11)

x = ' = 8.72 feet (say 9 feet)

Requires FRP wrap from end to 9 feet

Using Fibrwrap Jacket and TYFO TC epoxy adhesive

Vreq<2tfjdcot45°

where: tj = 0.051 inches (jacket thickness)

f\ = 12 ksi (allowable jacket stress)

and assuming 45° crack inclination

number ofjackets = 2{l2)(l^m05l) = 0-68 (1 layer required)
32 USACERL SR 99/01

15

check bond stress: u = "77^777—7ZZ = 8 psi < 400 psi allowable OK

Compute material required assuming a U-shaped jacket wrap.

Surface area = 2ends(8"+8"+5")(48") = 2496sq.in x 2 layers —> 34.7 sq.ft

Surface area = 2ends(24"+24"+5")(48") = 14384sq.in x 2 layers —> 200 sq.ft
USACERL SR 99/01 33

5 Conclusions and Recommendations

The results of tests performed in this study indicate that significant increase in

shear strength can be achieved by the application of FRP to concrete beams deficient in shear capacity. When an FRP jacket is properly applied over the shear

span of the member the failure mode of a member may be altered from that of a

brittle shear failure to a ductile flexural failure mode. However, the repaired

joist was not able to achieve the strength and stiffness levels of a properly reinforced specimen.

The effectiveness of an FRP upgrade or repair requires careful preparation of

concrete surface, selection of a tough epoxy, and placement of the fabric. A gap

between the web and slab that was not covered by the FRP proved to initiate

failure in a joist upgraded with FRP. While the joist deflected significantly more

than a control beam that failed in shear the mode offailure was similarly sudden

and brittle. This joist's overall stiffness was not as great as for the two control

joists. Bond between the FRP and concrete was shown to be very good.

Connectivity between the joist web and slab were also shown to be very important as all test joists tended to separate along this interface after testing was

completed. Both joists that failed in shear failed along this interface. Insufficient shear reinforcement may also affect the quality of tendon anchorage, concrete confinement, and anchorage of the web to the cast-in-place slab. Proper

application of FRP can assist in providing the latter two of these requirements

but will not aid in anchoring prestressing tendons.

When designed or repaired with adequate shear reinforcement, the behavior of

the test joists was exceptional. Failure loads for specimens HJ-4 and HJ-7 were

very high compared with design service and ultimate loads. Failure was also

very ductile for these members, with deflection capacity extending well beyond

the point at which the ultimate load was reached. The hybrid joist behaved very

much like a traditional prestressed precast concrete beam except that the hybrid

system had the capability to carry 30% more load than the conventional

prestressed double tee before first cracks appeared.

Additional analytical and experimental studies should be undertaken to establish the benefits ofsupplemental anchorage for improving the bond ofthe FRP to

the reinforced concrete structural member. Construction methods for ensuring
34 USACERL SR 99/01

proper placement and curing of the FRP in the repair process should be refined.

In addition, the effects of environmental factors, e.g., temperature and moisture

on the epoxy joint, as well as the performance of upgraded beams under fatigue

loading should be examined.
USACERLSR 99/01 35

References

American Concrete Institute (ACI). (1995). "Building code requirements for reinforced concrete and

commentary." ACI 318-95, Detroit, Michigan.

Al-Sulaimani, G.J., A. Sharif, I.A., Basunbul, M.H. Baluch, and B.N. Ghaleb, "Shear Repair for

Reinforced Concrete by Fiberglass Plate Bonding," ACI Structural Journal, vol 91, no. 3, (JulyAugust 1994), pp 458-464.

Chajes, M.J., W.W. Finch, T.F Januszka, and TA. Thomson, "Bond and Force Transfer of Composite Material Plates Bonded to Concrete," ACI StructuralJournal, vol 93, no. 2, (March-April

1996), pp 208-217.

Chajes, M.J., T.F. Januszka, D.R. Mertz, TA. Thomson, and W.W. Finch, "Shear Strengthening of

Reinforced Concrete Beams Using Externally Applied Composite Fabrics," ACI Structural

Journal, vol 92, no. 3, (May-June 1995), pp 295-303.

Chajes, M.J., TA. Thomson, and B. Tarantino, "Reinforcement of Concrete Structures Using Externally Bonded Composite Materials," Non-Metallic Reinforcement for Concrete Structures

(Proceedings), (1995), E&FN Spon, London, pp 501-508.

Engineered Materials Handbook, Volume 1, "Composites," ASM International, Metals Park, OH,

(1987), p 36.

Gee, Duane J., Memorandum of 21 June 1996.

International Conference of Building Officials Evaluation Service, Inc., "Acceptance Criteria for

Concrete and Reinforced and Unreinforced Masonry Strengthening Using Fiber-reinforced

Composite Systems," AC125, (April 1997).

Norris, T, H. Saadatmanesh, and M.R. Ehsani, "Shear and Flexural Strengthening of R/C Beams

with Carbon Fiber Sheets," ASCE Journal ofStructural Engineering, vol 123, no. 7, (July

1997).

Saadatmanesh, H. and M.R. Ehsani, "Fiber Composite Plates Can Strengthen Beams," Concrete

International, vol 12, no. 3, (March 1990), pp 65-71.
36 USACERL SR 99/01

Figures and Tables

2'-0"

1'-0'

et do fit

Ifi»

i .... "... i

- e* f~~

—Jr-CJ TR=4» ' JL-^ '

|.3'-10" J.

6"T~~~- 1

fir

7-11" , 8'-6" .). 7-11" .|.3'-10" _j

Eleveti

-Precast or cast-in-place

Top

2-0"

rH

Bottom

w

4'-0' to 6'-0"

Complete Joist System, Cross

K

Section ASection BFigure 1. Joist configuration.

Elevation

2"<f "3"

>"3"

2'_oi!

5

I

O e

6"

-r3"

1/2"F-strand Typ.

all 2"

Section Section A-A

Figure 2. Joist prestressing tendon profile.
USACERL SR 99/01 37

4 § 10" = 3'-4" 4 § 12" = 4'-0"

Hoid down device

J 5"

Type 3 (# 4 stirrups)

3.5"

Type 1 (| 4 stirrups)

Jype

4.5"

Type 2 (f 4 stirrups)

Figure 3. HJ-3 and HJ-4 web reinforcement.

r a

J

Figure 4. FRP joist repair.
38 USACERL SR 99/01

a

on

B

CU

S12 16 20

Time (days)

10000

5000

0 I

f^t

i i i 1 1 !

24

- -Batch #1

-B-Batch #2

28

Figure 5. High-performance concrete strength versus time.

280

240

200

160

W3

35

120

80

40

0

0

t

c

E Strand size 1/2 in.

: 270 ksi

0.153 in2

ate stress 270 ksi

ihis ofelasticity 30,000 ks

E Grade

c Ultim

P > Modi i

%/

tiii . . i

000 0.002 0.004 0.006 0.008 0.010 0.012 0.014 0.016 0.018 0.020

Strain (in./in.)

Figure 6. Prestressing tendon stress versus strain.
USACERL SR 99/01 39

Figure 7. Prestressing and casting of hybrid joists.

Figure 8. Completed hybrid joist construction.
40

ÜSÄCERLSR 99/01

Figure 9. FRP application.

Figure 10. Gap in FRP upgrade of HJ-3.
USACERL SR 99/01 41

Figure 11. Epoxy injection of voids.

HJ-3

HJ~4

Plan view for the two joists

Note: Gaqes # 42, 43, 44, and 45 on the closed stirrups.

Figure 12. Internal strain gage layout for HJ-3, HJ-4, HJ-6, and HJ-7.
42 USACERLSR 99/01

Figure 13. External strain gage layout on HJ-3.

Figure 14. External strain gage layout on HJ-4.
USACERL SR 99/01 43

LVDT Locations

OH (op ol sluü

X

DIS

759 ZET T

fTiX

.mo nu

Vn

.018

DI6 bottom of web

Figure 15. LVDT locations on test specimens.

Potentiometer Locations

Ihiui-spon

I'otetitiununietei I'utenlionumulttr

'Quarter

S|»nn Polentionometer

\////?J//JS/////>J///>>///??///////V////////////))//////////////;///////))////J///////////////////

Figure 16. Potentiometer locations on test specimens.
44 USACERL SR 99/01

Double-Acting

Hollow Plunger Hydraulic Cylinders

Model RRH-6010

Absolute Displacement

Position Transducer

Model P-10A

Strain Gages

Measutcments Group Inc.

EA-06-125BT-120

Strain Gages

Texas Mesuremcnts Inc.

PL-60-11

Mcgadac Data Aeuisition

Model 3000 Multi-Channel

Personal Computer

Figure 17. Block diagram of data recording system.

Figure 18. Test setup.
USACERL SR 99/01 45

0.8

0.6

0.4

0.2

,./-/- \v y V 1

0.0

HJ-3

HJ-4 w/o FRP

HJ-7

-— HJ-6

HJ-4 w/ FRP repair

0 1 2 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 17 16

Displacement (in.)

Figure 19. Load versus deflection for HJ-3, HJ-4, HJ-6, and HJ-7.
46

USACERL SR 99/01

35

30

35

30

^

25

S 20

'S 15

o

10

5

0

4 6 8

Displacement (in.)

4 6 S

Displacement (in.)

Figure 20. Load versus deflection cycles for HJ-4.

HJ-4

10 12

Midspan

HJ-4 w/ FRP

12

0 24 48 72 96 120 144 168 192 216 240 264 288 312 336 360 384

Span Length (inches)

Figure 21. Deflected shape for HJ-3.
USACERL SR 99/01 47

o

-l

-2

-3

-4

-5

-6

-7

-8

-9

-10

-II

-12

2h8kips

HJ-4 w/o FRP

0 24 48 72 96 120 144 168 192 216 240 264 288 312 336 360 384

Span Length (inches)

HJ-4 w/ FRP

48 72 96 120 144 168 192 216 240 264 288 312 336 360 384

Span Length (inches)

Figure 22. Deflected shape for HJ-4 before repair (top) and after FRP repair (bottom).

-2

-3

-4

-5

-6

-7

-8

-9

-10

-11

-12

23.9 kips

HJ-6

24 48 72 96 120 144 168 192 216 240 264 288 312 336 360 384

Span Length (inches)

Figure 23. Deflected shape of HJ-6.
48 USACERL SR 99/01

0 24 48 72 96 120 144 168 192 216 240 264 288 312 336 360 384

Span Length (inches)

Figure 24. Deflected shape for HJ-7.
USACERL SR 99/01 49

0.010

0

2

^. 4 V)

<D 6

O

C 8

•^ 10 n

o 12

F 14

S 16

s

18

g

20

"K 22

D 24 -

26 -

28

5 kips

10 kips

15 kips

20 kips

25 kips

Strut

-0.006 -0.004 -0.002 0.000 0.002 0.004 0.006 0.008 0.010

Strain (in./in.)

Figure 25. Strain distribution for HJ-3.
50

USACERL SR 99/01

<D

x:ü

c

a.

o

E

M—e

<DÜ

c

CO

CO

ID

s:

o

_c

Q.

O

E

p

CO

03

.CÜ

_c

Q.

O

E

2H—

Q>

Ü

C

TO

-0.006

0

2

4 h

-0.004 -0.002 0.000 0.002 0.004 0.006 0.008 0.010

6

8

10

12

14

0

2

4 -

6

8

10

12

14

16

8 18

£

20

1 22

Q 24

26

28

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

5 kips

10 kips

15 kips

20 kips

25 kips

27 kips

End

IL'I

V

l\

II

5 kips

10 kips

15 kips

20 kips

25 kips

27 kips

<.

5 kips

10kips

15 kips

20 kips

25 kips

27 kips

-0.006 -0.004 -0.002 0.000 0.002 0.004 0.006 0.008 0.010

Strain (in./in.)

Figure 26. Strain distribution for HJ-4.
USACERL SR 99/01 51

"S- (0 -0.006 -0.004 -0.002 0.000 0.002 0.004 0.006 0.008 0.010

<D .CÜ

c

Q.

O

E

2

8

c

(0

b

2

4

6

8

10

12

14

0

2

^^ 4 OT

CD R

.c

ü

c 8

^^ 10

o.

**o 12

F 14

2 16

o

18

c

CD 20

CO 22

O 24

26

28

0

2

^_^ 4

c/>

CD fi .c

o

c 8

^^ 10

Q.

*-*O 12

F 14

2 16

CD

u

18

c

to 20

0) 22

a 24

26

28

-0.(

5 kips

10 kips

15 kips

20 kips

23.9 kips

5 kips

10 kips

15 kips

20 kips

23.9 kips

End

J

N

Midspan

\\

V,

006 -0.004 -0.002 0.000 0.002 0.004 0.006 0.008 0.010

Strain (in./in.)

Figure 27. Strain distribution for HJ-6.
52 USACERL SR 99/01

</>

a>

s:

o

c

a.

o

E

2* —

o

C

to

(0

a>

x:

o

c

o.

o

E

2M—

03Ü

C

to

CO

0)

x:

_c

Q.

O

E

2

0)

o

c

TO

Q

8

10

12

14

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

-0 006 -0 004 -0 002 0.000 0.002 0.004 0.006 0.008 0.010

0

2

4

6h

5 kips

10 kips

15 kips

20 kips

25 kips

29.5 kips

5 kips

10 kips

15 kips

20 kips

25 kips

29.5 kips

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

-0.006

5 kips

10 kips

15 kips

20 kips

25 kips

29.5 kips

-0.004 -0.002 0.000 0.002 0.004 0.006 0.008 0.010

Strain (in./in.)

Figure 28. Strain distribution for HJ-7.
USACERLSR 99/01 53

0.010

0.009

0.008

0.007

~ 0.006

c 0.005

jöfc 0.004 CO

0.003

0.002

0.001

0.000

0.010

0.009

0.008

0.007

~ 0.006

~ 0.005

rö

t: 0.004 CO

0.003

0.002 h

0.001

0.000

24 48 72 96 120 144 168 192

1 1 1 1 1 1 1

-

5 kips

10 kips

15 kips

20 kips

25 kips

Top Chord .

/ \

-

s

5 kips

10 kips

15 kips

20 kips

25 kips

Bottom Chord

\

\

\

24 48 72 96 120 144

Distance from end of beam (inches)

168 192

Figure 29. Strain distribution along strand length of HJ-3.
54

USACERL SR 99/01

0.010

c

c

TO

0.009 -

0.008

0.007

0.006

0.005

0.004

0.003

0.002

0.001

0.000

0.010

0.009

0.008

0.007

:g 0.006

c

^T 0.005

'S

i= 0.004

C/)

0.003

0.002

0.001

0.000

24 48 72 96 120 144 168 192

5 kips

10kips

15 kips

20 kips

25 kips

27 kips

Top Chord

/

/

y

— 5 kips

- •• 10 kips

•— 15 kips

- •20 kips

— 25 kips

-•- 27 kips

24 48 72 96 120 144

Distance from end of beam (inches)

168 192

Figure 30. Strain distribution along strand length of HJ-4.
USACERL SR 99/01 55

0.010

0.009

0.008

0.007

^ 0.006

'=- 0.005

_c

(ÖJ= 0.004 CO

0.003 -

0.002

0.001 h

0.000

0.010

0.009

0.008

0.007

£ 0.006

'•=- 0.005

c

s

CO

0.004

0.003

0.002

0.001

0.000

24 48 72 96 120 144 168 192

5 kips

10 kips

15 kips

20 kips

23.9 kips

Top Chord

5 kips

10 kips

15 kips

20 kips

23.9 kips

Bottom Chord -

24 48 72 96 120 144

Distance from end of beam (inches)

168 192

Figure 31. Strain distribution along strand length of HJ-6.
56

USACERL SR 99/01

c

c

CO

0.010

0.009

0.008

0.007

0.006

0.005

0.004

0.003

0.002

0.001

0.000

0.010

0.009

0.008

0.007

c 0.006

==- 0.005

c

24 48

—i—

72 96 120 144 168 192

5 kips

10 kips

15 kips

20 kips

25 kips

29.5 kips

Top Chord

CO

CO

0.004

0.003

0.002

0.001

0.000

Bottom Chord

5 kips

10 kips

15 kips

20 kips

25 kips

29.5 kips

/

"\

\

24 48 72 96 120 144

Distance from end of beam (inches)

168 192

Figure 32. Strain distribution along strand length of HJ-7.
USACERL SR 99/01 57

30

25

S 20

o

I?

<

15

10

0

-0.001

30

25

o.

S 20

15

10

0

-0.001

* I

0.000 0.001 0.002 0.003

Strain (in./in.)

0.004

ES1

ES2

ES3

ES4

0.005 0.006

ES8

ES7

ES6

ES5

0.000 0.001 0.002 0.003

Strain (in./in.)

0.004 0.005 0.006

Figure 33. HJ-3 upgrade FRP strains.
58

USACERL SR 99/01

30

25 -

o.

3. 20

o

H 15

so

>

<

10

0

-0.001

J.:' "•' •• ' .-'

0.000 0.001

-0.001 0.000 0.001

Figure 34. HJ-4 repair FRP strains.

-/y.y^

ES1

ES2

ES3

ES4

0.002 0.003

Strain (in./in.)

0.004 0.005

30 1 i

25 1

' /

I /

a.

Ä 20 - 1 :"

-o i ;

o

J

15 . J : ..-"

o

3 1 -

: y

o 1: /

t io - ;; /

>

< j:/

5

n

.•*?'<$ h

ES8

ES7

ES6

ES5

0.002 0.003

Strain (in./in.)

0.004

0.006

0.005 0.006
USACERL SR 99/01 59

Figure 35. Crack patterns for HJ-6.

Figure 36. Failure of HJ-6.
60

USACERL SR 99/01

Figure 37. Crack patterns for HJ-7.
USACERL SR 99/01 61

a. Cracks at slab/web interface and in slab at north end of HJ-3.

b. Detail of crack at frp edge at slab/web interface of HJ-3.

Figure 38. Crack patterns for HJ-3.
62 USACERL SR 99/01

a. Failure at north end of HJ-3

b. Detail of crack and separation at slab/web interface at failure of HJ-3.

Figure 39. Failure of HJ-3.
USACERL SR 99/01 63

South End North End

ä

-""Va&tZZZZ^XS*^

'i(> mi .*Mt*<.ll*M|ti,niOt f I 1/ ' I IS • I 1/ > 11/ > >l / I )ij • I 1/ s I s/ ;</ j

Looking West

Figure 40. Crack Patterns of HJ-4 prior to FRP repair.
64

USACERL SR 99/01

b. Cracks at south end of joist

Figure 41. Crack patterns for HJ-4.
USACERL SR 99/01 65

Design Procedure for Shear Repair for Reinforced Concrete Beam using FRP

Calculate applied service and ultimate loads

Calculate capacity of existing section

(based on the provided preliminary design table)

Calculate the internal forces due to

each case of loading using a frame

analysis program

^ t

<Check ultimate flexural strength

OK

allowable initial

stress at release

., OK

/allowable final

\stress at service

| OK

<C Check crack width limit

OK

<6heck deflection )>-

OK

No

No

£

use shear reinforcement

^Check vertical shear

j OK

End

Figure 42. Shear repair design procedure.

No

No

change the section

No

No

increase the concrete

strength or change the

section

wu = 4 k/ft

UlUUmiTTT

t

25 feet t

Figure 43. Simply supported beam.

• • m

12 in 1
66

USACERL SR 99/01

wu = 4 k/ft

\ 1 i U U 11 I I I I I

t

25 feet t

0 (kips)

Figure 44. Shear diagram.

Figure 45. FRP wrap repair.
USACERL SR 99/01 67

Table 1. Hybrid Joists Tested

Joist Designation Configuration Web Shear

Reinforcement

Slab Width

(ft)

HJ-3 Upgraded with FRP Figure 4.6 6

HJ-4 Tested, then repaired with FRP Figure 4.6 6

HJ-6 Insufficient shear reinforcement Figure 4.8 4

HJ-7 Proper shear reinforcement Figure 4.8 4

Table 2. Epoxy Material Properties

Property Average Minimum Test Method

-Tg @ 45% RH 120°F 100°F

-Tg @ 95% RH 110°F 95°F

-Tg 140OF Postcure (24 Hours) 180°F 140°F

Tensile Strength 10,100 psi 9,500 psi ASTM D 638 Type 1

Tensile Modulus 461,000 psi 425000 psi ASTM D 638 Type 1

Elongation Percent 5.00% 3.50% ASTM D 638 Type 1

Flexural Strength 11,500 psi 10,500 psi ASTM D. 790

| Flexural Modulus 400,000 psi 375,000 psi ASTM D 790

Hill-inn Rrhorllllo 70 hnnrc nnct r~,,m ot A A rfic

Table 3. Yarn Properties

Property E-glass Polyaramid Test Method

Yield/Denier 1200 and 250 ypp 2160 denier

Density (g/cc) 2.54 1.44 ASTM D 792

Tensile Strength (psi) 440,000 400,000 SIM 13*

Tensile Modulus (psi) 10,500,000 17,000,000 STM13

Elongation (%) 4.2 2.5 STM13

* Seguin Test Method - Hexel Manufacturing facility standard methods based on appropriate

Standardized testing procedure

Table 4. Fabric Properties

Property Average Value Minimum Value Test Method

Areal Weight (oz/sq. yd.) 27.2 24.4 STM18

Tensile Strength dry 1" strip

(Break Load lb.)

1800 1600 STM27

Air Permeability (cu. ft./min.) 22 20 STM26
68

USACERL SR 99/01

Table 5. Composite Laminate Specification

Ultimate Tensile Strength min. (primary

fiber direction)*

Property Value

65,000 psi

Elongation at break, min.

Tensile Modulus

Ultimate Tensile Strength min. (90

degrees to primary fiber direction)

2.00%

3.0x106psi

4,800 psi

ASTM Method

D3039

D3039

D3039

* Tensile retained 7 days @ 100% RH, 1,000 hours ozone, 1,000 hours alkali, 1,000 hours salt water,

and 1,000 hours at 140°F

Cured for 48 hours at 140T Using Hexcel Sample Preparation

Table 6. Composite Material Properties

Property

Tensile Strength at 0" (ksi)

Tensile Strength at 90° (ksi)

Elastic Modulus (ksi)

Ultimate Strain

Coefficient of Thermal Expansion

Value

65

6.0

3,250

0.02

4.3x10c

Test Method

ASTM D3039

ASTM D3039

ASTM D3039

Table 7. Casting and Release Dates for Each Hybrid Joist Web

Specimen

HJ-3

HJ-4

HJ-6

HJ-7

Casting Date

1/29/96

1/29/96

2/12/96

6/20/96

Release Date

2/5/96

2/5/96

2/16/96

6/24/96
USACERL SR 99/01

Table 8. Instrumentation for HJ-3 Upgraded With FRP

Hybrid Joist Test HJ-3 Date:

USA Construction Engineering Research Laboratories

Instrument

CeILN

Stroke_N

CelLS

Stroke_S

POT_N

POT_Mid

POT S

lnt_1

lnt_2

lnt_3

lnt_4

lnt_5

lnt_6

lnt_7

lnt_8

lnt_9

lnt_10

lnt_11

lnt_12

LVDT.1

LVDT_2

LVDT_3

LVDT_4

LVDT.5

LVDT_6

LVDT.7

LVDT.8

LVDT.9

LVDT.10

LVDT_11

LVDT_12

LVDTJ3

LVDT_14

LVDT_15

LVDTJ6

LVDT.17

LVDT_18

LVDT_19

LVDT.20

CERL

Name/

Cable #

P1

P2

P3

IS1/3

IS2/2

IS3/1

IS4/12

IS5/11

IS6/10

IS7/15

IS8/14

IS9/13

IS10/18

IS11/17

IS12/16

D1

D2

D3

D4

D5

D6

D7

D8

D9

D10

D11

D12

D13

D14

D15

D16

D17

D18

D19

D20

CIR

Name

N/A

N/A

N/A

N/A

N/A

N/A

N/A

Conversion

Factor

(per volt)

s19

s20

s21

s28

s26

s30

s31

s27

s33

s34

s35

s36

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

5.000 kips

0.300 inches

5.000 kips

0.300 inches

1.994 inches

1.996 inches

2.000 inches

0.00150 in/in

0.00150 in/in

0.00150 in/in

0.00150 in/in

0.00150 in/in

0.00150 in/in

0.00150 in/in

0.00150 in/in

0.00150 in/in

0.00150 in/in

0.00150 in/in

0.00150 in/in

0.00500 in.

0.00500 in.

0.00500 in.

0.00500 in.

0.00500 in.

0.00500 in.

0.00500 in.

0.00500 in.

0.00500 in.

0.00500 in.

0.00500 in.

0.00500 in.

0.00500 in.

0.00500 in.

0.00500 in.

0.00500 in.

0.00500 in.

0.00500 in.

0.00500 in.

0.00500 in.

Location

(X - Dir.)

(inO

141.000

141.000

250.000

250.000

141.000

192.000

278.000

40.000

40.000

40.000

141.000

119.000

141.000

163.000

119.000

163.000

192.000

192.000

192.000

75.500

74.000

73.000

145.000

143.000^

142.500

142.000

170.500

N/A

169.250

193.500

194.000

194.000

193.500

243.000

194.000

222.000

222.000

242.000

242.000

Location

(Y-Dir.)

(in)

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

1.000

3.000

12.250

1.000

3.500

11.000

22.750

1.000

N/A

22.750

1.000

3.000

22.500

N/A

N/A

N/A

2.250

22.500

10.000

22.000

August 12,1996

Champajgn, IL

Gage

Length

(in.)

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

7.205

6.417

4.134

6.220

7.480

2.677

2.756

7.520

N/A

5.630

5.276

5.433

5.039

5.197

2.677

6.850

2.677

4.803

3.268

2.480

Comments

Concentrated Load - 50 Kip Actuator

Concentrated Load - 50 Kip Actuator

Third span Deflection - Potentiometer

Midspan Deflection - Potentiometer

Quarter span Deflection -

Potentiometer

Placed by the CIR

Placed by the CIR

Placed by the CIR

Placed by the CIR

Placed by the CIR

Placed by the CIR

Placed by the CIR

Placed by the CIR

Placed by the CIR

Placed by the CIR

Placed by the CIR

Placed by the CIR

Measured from the Top of the Slab

Measured from the Bottom Face of the Slab

Measured from the Bottom Face of the Slab

Measured from the Top of the Slab

Measured from the Bottom Face of the Slab

Measured from the Bottom Face of the Slab

Measured from the Bottom Face of the Slab

Measured from the Top of the Slab

Not used for this test, Sensor moved to D7

Measured from the Bottom Face of the Slab

Measured from the Top of the Slab

Measured from the Bottom Face of the Slab

Measured from the Bottom Face of the Slab

Placed on top of Slab

Not used for this test

Placed on bottom side of Web

Measured from the Bottom Face of the Slab

Measured from the Bottom Face of the Slab

Measured from the Bottom Face of the Slab

Measured from the Bottom Face of the Slab
70

USACERL SR 99/01

Hybrid Joist Test HJ-3

USA Construction Engineering Research Laboratories

Instrument

CERL

Name/

Cable #

Ext. Str._1

Ext. Str._2

Ext. Str._3

Ext. Str._4

Ext. Str._5

Ext. Str._6

Ext. Str._7

Ext. Str._8

CIR

Name

ES1

ES2

ES3

ES4

ES5

ES6

ES7

ES8

Conversion

Factor

(per volt)

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

Location

(X - Dir.)

m

0.00150 in/in

0.00150 in/in

0.00150 in/in

0.00150 in/in

0.00150 in/in

0.00150 in/in

0.00150 in/in

0.00150 in/in

Date:

Location

(Y - Dir.)

M

August 12,1996

Champaign, IL

Gage

Length

(in.)

Comments

See Attached Figure for External

Strain Gage Locations

*" +X direction is defined as running north to south with north being 0. Measurements taken to the north face of the LVDT blocks.

»* +Y direction is defined as running up to down with 0 being the bottom face of the slab, except where noted that measurement

was taken from the top of the slab. Measurement was taken to the middle of the circular opening in the block.

IMPORTANT NOTE: Sensor for D7 was not working. Sensor from D9 was placed in location of D7.
USACERL SR 99/01 71

Table 9. Instrumentation for HJ-4 Without FRP Repair

Hybrid Joist Test HJ-4 Date: June 3,1996

USA Construction Engineering Research Laboratories (First Test without FRP)

CERL CIR Conversion Location Location Gage

Instrument Name/ Name Factor (X - Dir.) (Y - Dir.) Length Comments

Cable # (per volt) (in.) (in.) (in.)

CeILN N/A 5.000 kips 141.000 N/A N/A Concentrated Load - 50 Kip Actuator

Stroke_N N/A 0.300 inches 141.000 N/A N/A

CelLS N/A 5.000 kips 250.000 N/A N/A Concentrated Load - 50 Kip Actuator

Stroke_S N/A 0.300 inches 250.000 N/A N/A

POT_N P1 N/A 1.994 inches 141.000 N/A N/A Third span Deflection - Potentiometer

POT_Mid P2 N/A 1.996 inches 192.000 N/A N/A Midspan Deflection - Potentiometer

POT.S P3 N/A 2.000 inches 278.000 N/A N/A Quarter span Deflection -

Potentiometer

lnt_1 IS1/19 s19 0.00150 in/in 40.000 N/A N/A Placed by the CIR

lnt_2 IS2/16 s20 0.00150 in/in 40.000 N/A N/A Placed by the CIR

lnt_3 IS3/21 s21 0.00150 in/in 40.000 N/A N/A Placed by the CIR

lnt_4 IS4 / 28 s28 0.00150 in/in 141.000 N/A N/A Placed by the CIR

lnt_5 IS5/26 s26 0.00150 in/in 119.000 N/A N/A Placed by the CIR

lnt_6 IS6/30 s30 0.00150 in/in 141.000 N/A N/A Placed by the CIR

lnt_7 IS7/31 s31 0.00150 in/in 163.000 N/A N/A Placed by the CIR

lnt_8 IS8 / 27 s27 0.00150 in/in 119.000 N/A N/A Placed by the CIR

lnt_9 IS9/33 s33 0.00150 in/in 163.000 N/A N/A Placed by the CIR

lnt_10 IS10/34 s34 0.00150 in/in 192.000 N/A N/A Placed by the CIR

lnt_11 IS11 /35 s35 0.00150 in/in 192.000 N/A N/A Placed by the CIR

lnt_12 IS12/36 s36 0.00150 in/in 192.000 N/A N/A Placed by the CIR

LVDT_1 D1 N/A 0.00494 in. 72.750 1.000 7.205 Measured from the Top of the Slab

LVDT_2 D2 N/A 0.00497 in. 71.375 3.000 6.063 Measured from the Bottom Face of the

Slab

Measured from the Bottom Face of the

Slab

Measured from the Top of the Slab

LVDT.3 D3 N/A 0.00495 in. 69.125 12.250 2.913

LVDT.4 D4 N/A 0.00497 in. 145.125 1.000 5.748

LVDT.5 D5 N/A 0.00496 in. 143.375 3.500 5.197 Measured from the Bottom Face of the

Slab

Measured from the Bottom Face of the

Slab

Measured from the Bottom Face of the

Slab

Measured from the Top of the Slab

LVDT.6 D6 N/A 0.00496 in. 143.375 11.000 2.559

LVDT_7 D7 N/A 0.00496 in. 142.375 22.750 5.236

LVDT.8 D8 N/A 0.00495 in. 168.125 1.000 5.236

LVDT_9 D9 N/A 0.00496 in. 167.375 3.000 2.441 Measured from the Bottom Face of the

Slab

Measured from the Bottom Face of the

Slab

Measured from the Top of the Slab

LVDT_10 D10 N/A D.00499 in. 168.375 22.750 2.441

LVDT_11 D11 N/A D.00489 in. 195.000 1.000 B.417

LVDTJ2 D12 N/A D.00496 in. 193.875 3.000 7.283 Measured from the Bottom Face of the

Slab

Measured from the Bottom Face of the LVDT.13 013 M/A 100496 in. 195.500 22.500 5.197 I 1 Slab
72 USACERL SR 99/01

Hybrid Joist Test HJ-4

USA Construction Engineering Research Laboratories

Instrument

Date: June 3,1996

(First Test without FRP)

LVDTJ4

LVDTJ5

LVDTJ6

LVDT_17

LVDT.18

LVDTJ9

LVDT_20

CERL

Name/

Cable #

D14

D15

D16

D17

D18

D19

D20

CIR

Name

Conversion

Factor

(per volt)

N/A

N/A

N/A

N/A

N/A

N/A

N/A

0.00491 in.

0.00496 in.

0.00500 in.

0.00503 in.

0.00487

inches

0.00501 in.

0.00500 in.

Location

(X - Dir.)

m

194.750

N/A

195.250

220.000

220.375

244.000

244.125

Location

(Y - Dir.)

OIL)

N/A

N/A

N/A

2.250

22.500

10.000

22.000

Gage

Length

(inj

6.260

N/A

6.299

7.638

4.055

2.362

2.717

Comments

Placed on top of Slab

Not used for this test, Sensor moved to

D13

Placed on bottom side of Web

Measured from the Bottom Face of the

Slab

Measured from the Bottom Face of the

Slab

Measured from the Bottom Face of the

Slab

Measured from the Bottom Face of the

Slab

*** +X direction is defined as running north to south with north being 0. Measurements taken to the north face of the LVDT blocks.

"* +Y direction is defined as running up to down with 0 being the bottom face of the slab, except where noted that measurement

was taken from the top of the slab. Measurement was taken to the middle of the circular opening in the block.

IMPORTANT NOTES: Sensor for D15 was moved into the D13 position. D15 position was not used.
USACERL SR 99/01 73

Table 10. Instrumentation for HJ-4 With FRP Repair

Hybrid Joist Test HJ-4 (2nd Test with FRP)

USA Construction Engineering Research

Laboratories

Champaign, IL

Date: August 2

1996

CERL CIR Conversion Location Location Gage

Instrument Name Name Factor (X - Dir.) (Y - Dir.) Length Comments

/ Cable # (per volt) (in.) (in.) (in.)

CeILN N/A 5.000 kips 141.000 N/A N/A Concentrated Load - 50

Kip Actuator

Stroke_N N/A 0.300 inches 141.000 N/A N/A

CelLS N/A 5.000 kips 250.000 N/A N/A Concentrated Load 50

Kip Actuator

Stroke_S N/A 0.300 inches 250.000 N/A N/A

POT_N P1 N/A 2.000 inches 141.000 N/A N/A Third span Deflection -

Potentiometer

POT_Mid P2 N/A 2.000 inches 192.000 N/A N/A Midspan Deflection -

Potentiometer

POT.S P3 N/A 2.000 inches 278.000 N/A N/A Quarter span Deflection -

Potentiometer

lnt_1 IS1/19 S19 0.00150 in/in 40.000 N/A N/A Placed by the CIR

lnt_2 IS2/16 s20 0.00150 in/in 40.000 N/A N/A Placed by the CIR

lnt_3 IS3 / 21 s21 0.00150 in/in 40.000 N/A N/A Placed by the CIR

lnt_4 IS4/28 S28 0.00150 in/in 141.000 N/A N/A Placed by the CIR

lnt_5 IS5/26 S26 0.00150 in/in 119.000 N/A N/A Placed by the CIR

lnt_6 IS6/30 s30 0.00150 in/in 141.000 N/A N/A Placed by the CIR

lnt_7 IS7/31 s31 0.00150 in/in 163.000 N/A N/A Placed by the CIR

lnt_8 IS8/27 s27 0.00150 in/in 119.000 N/A N/A Placed by the CIR

lnt_9 IS9/33 s33 0.00150 in/in 163.000 N/A N/A Placed by the CIR

lnt_10 S10/34 s34 0.00150 in/in 192.000 N/A N/A Placed by the CIR

lnt_11 S11/35 s35 0.00150 in/in 192.000 N/A N/A Placed by the CIR

lnt_12 S12/36 s36 0.00150 in/in 192.000 N/A N/A Placed by the CIR

LVDT_1 D1 N/A 0.00500

nches

72.750 1.000 7.205 Measured from the Top of

the Slab

LVDT_2 D2 N/A 0.00500

nches

S9.000 3.000 6.000 Measured from the Bottom

Face of the Slab

LVDT.3 D3 N/A 3.00500

nches

38.500 12.000 3.125 Measured from the Bottom

Face of the Slab

LVDT.4 34 N/A 3.00500

nches

145.125 1.000 5.748 vleasured from the Top of

he Slab

LVDT 5 35 N/A 3.00500 43.375 3.500 5.197 vleasured from the Bottom

N/A |(

nches

3.00500 | 11.000 j

r

ace of the Slab

|LVDT_6 |[36 43.375 | 2.559 Measured from the Bottom
74

USACERL SR 99/01

Hybrid Joist Test HJ-4 (2nd Test with FRP)

USA Construction Engineering Research

Laboratories

Champaign, IL

Date: August 2

1996

CERL CIR Conversion Location Location Gage

Instrument Name Name Factor (X - Dir.) (Y - Dir.) Length Comments

' Cable # (per volt) (in.) (in.) (in.)

nches Face of the Slab

LVDTJ D7 N/A 0.00500 142.375 22.750 5.236 Measured from the Bottom

nches Face of the Slab

LVDT_8 D8 N/A 0.00500 168.125 1.000 5.236 Measured from the Top of

nches the Slab

LVDT_9 D9 N/A N/A N/A N/A N/A Not used for this test,

Sensor moved to D5

LVDTJ 0 D10 N/A 0.00500 168.375 22.750 2.441 Measured from the [Bottom

inches Face of the Slab

LVDTJ 1 D11 N/A 0.00500 195.000 1.000 6.417 Measured from the Top of

inches the Slab

LVDTJ 2 D12 N/A 0.00500 193.875 3.000 7.283 Measured from the Bottom

inches Face of the Slab

LVDT_13 D13 N/A 0.00500 195.500 22.500 5.197 Measured from the Bottom

inches Face of the Slab

LVDTJ 4 D14 N/A 0.00500 194.750 N/A 6.260 Placed on top of

inches Slab

LVDT 15 D15 N/A N/A N/A N/A N/A Not used for this test,

Sensor moved to D13

LVDTJ 6 D16 N/A 0.00500 195.250 N/A 6.299 Placed on bottom

inches side of Web

LVDTJ 7 D17 N/A - 0.00500 in. 220.000 2.250 7.638 Measured from the Bottom

Face of the Slab

LVDT_18 D18 N/A 0.00500 220.375 22.500 4.055 Measured from the Bottom

inches Face of the Slab

LVDT_19 D19 N/A - 0.00500 in. 244.000 10.000 2.362 Measured from the Bottom

Face of the Slab

LVDT_20 D20 N/A 0.00500 244.125 22.000 2.717 Measured from the Bottom

Ext. Str._1 ES1 N/A

inches

0.00150 in/in

(Face of the Slab

Ext. Str._2 ES2 N/A 0.00150 in/in

Ext. Str._3 ES3 N/A 0.00150 in/in See Attach 3d Figure for Externa Strain

Gage LOCEitions

Ext. Str._4 ES4 N/A 0.00150 in/in

Ext. Str.J5 ES5 N/A 0.00150 in/in

Ext. Str.JS ES6 N/A 0.00150 in/in

Ext. Str._7 ES7 N/A 0.00150 in/in
USACERL SR 99/01 75

Hybrid Joist Test

USA Construction Engineering Research

Laboratories

Champaign, IL

HJ-4 (2nd Test with FRP)

Date: August 2

1996

Instrument

Ext. Str._8

CERL

Name

/ Cable #

ES8

CIR

Name

N/A

Conversion

Factor

(per volt)

0.00150 in/in

Location

(X - Dir.)

(inj

Location

(Y - Dir.)

(!!!)

Gage

Length

(!O0

Comments

+X direction is defined as running north to south with north being 0. Measurements taken to the north face

of the LVDT blocks.

+Y direction is defined as running up to down with 0 being the bottom face of the slab, except where noted

that measurement was taken from the top of the slab. Measurement was taken to the middle of the circular

opening in the block.

IMPORTANT NOTES:

Sensor for D15 was moved into the D13 position. D15 position was not used.

Sensor for D9 was moved into the D5 position. D9 position was not used.

Table 11. Principal Experimental Test Results for Hybrid Joists

Joist

designation

Experimental

cracking

load*

(kips)

First Crack

Location

Applied

Failure

load*

(kips)

Total

Failure

Load

(kips)

Equivalent

Uniform

Load

(ksf)

Type of failure

HJ-3 midspan,

bottom chord

52.0 53.0 0.62 shear

HJ-4 midspan,

bottom chord

56.6 56.6** 0.67 no failure

HJ-6 11.7 midspan,

bottom chord

48.0 49.0 0.57 shear

HJ-7 31.5 midspan

bottom chord

64.0 65.0 0.76 flexure

* Sum of two actuators.

**No failure occurred.

Table 12. Camber and Deflection for Hybrid Joists (in.)

Joist

designation

Camber

at release

LL Deflection SIDL + LL

Deflection

Deflection at

peak load

Deflection at

failure

HJ-3 0.40 .09 .14 5.66 12.58

HJ-4 without

FRP

0.45 .10 .16 7.66 7.67*

HJ-4 with FRP

repair

NA .10 .16 8.62 10.06*

HJ-6 0.45 0.03 0.16 3.52 3.52

HJ-7 0.38 0.02 0.14 16.6 16.6

* Deflection at end Qf test; no fail ure occurred.
76

USACERL SR 99/01

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