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University of StuttgartInstitute of Construction Materials

Behavior and Design of Post-Installed Rebar Connections

fib Task Group 4.5 „Bond Models“– 6th Meeting, October 15 - 16, 2004, Edinburgh, UK –

Isabelle SimonsInstitute of Construction Materials,University of Stuttgart, Germany


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Connecting new and existing buildings usingpost-installed rebars

Strengthening with post-installed rebar connections

New building

Existing BuildingPost-installedrebars

Adding new columns Thicken columns

Applications with Post-Installed Rebar Connections

Source: 1) (Hilti)

1)

1)


Cast-in-place Post-installedrebar mortar concreterebar concrete

Source: 1) Kunz, Cook, Fuchs, Spieth(1998)

1)

Load Transfer Mechanism


Experimental Studies – Influencing Parameters

Geometry • Embedment Depth (hef=10ds, hef>20ds)• Concrete Cover / Edge Distance• Bar Spacing• Bar Diameter• Drilling Diameter in Relation to Bar Diameter

Material • Mortar (Hybrid, Epoxy, Cement)• Concrete• Cracks in Concrete

Environment • Temperature / Fire• Chemical Influences• Freeze-Thaw Cycles

Application • Injection• Drilling• Installation at Extreme Temperatures• Curing Time

Load • Static• Fatigue Loading• Monotonic Loading• Cyclic Loading








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The influencing parameters were examined in the laboratory at the University of Stuttgart and are illustrated in the followingslides.

Is the cement system suitable for post-installed rebars?

The cement is delivered in a 25kg sack. Therefore the cement must be mixed on-site using a special mixerand the components must be carefully weighed!!

The following points must be taken into account according to themanufacturers instructions:

- the borehole must be cleaned- the borehole must be moist; watering at least 6h.- the mixture contains 12% water- the mixture must be agitated at least 5min.

Test Program – Cement System


Installation Procedure of Cement Systems

Mixing Pour Compaction Installation

Cleaning (hand) Cleaning (machine) Pre-wetting

The process excludes horizontal and over head installations!The installation process is time consuming and complex.


Experimental Results – Cement Systems – Cleaning Method

0

5

10

15

20

25

30

0 1 2 3 4 5 6 7 8 9 10Verschiebung v [mm]

Ver

bund

span

nung

τ [N

/mm

²]

Reinigung H1

Reinigung H2

Reinigung M1

Bohrlochbewäs. 6h cc , s

τu

τu

τu

Displacement [mm]

Bon

d St

ress

[N/m

m²]

3xblowing, 3xbrushing, 3xblowing (Machine)

1xblowing (Hand)

1xblowing, 1xbrushing, 1xblowing (Hand)

1. Cleaning2. Moisture 6h3. Installation

C20/25ds=20 mmhef=200 mm


Experimental Results – Cement Systems – Moisture

0

2

4

6

8

10

12

14

16

18

20

0 2 4 6 8 10

Verschiebung [mm]

Verb

unds

pann

ung

[N/m

m2 ]

Bef.: trocken

Bef.: ~ 6h

Bef.: ~24h

Displacement [mm]

Bon

d St

ress

[N/m

m²]

1. Cleaning (1xblowing (Hand))2. Moisture 6h3. Installation

dry concrete

6h

24h

Installation of rebars in dry concrete not realisable.

C20/25ds=20 mmhef=200 mm


0

2

4

6

8

10

12

14


Ver

bund

span

nung

τ [N

/mm

²]

tcure = 2h tcure = 6h tcure = 18h

Reinigung H1 13% H2O

Reibungsanteil

Haftanteil

Displacement [mm]

Bon

d St

ress

[N/m

m²]

Experimental Results – Cement Systems – Curing Time


Bond

Friction

The system is highly influenced by the curing time. Curing time according to manufacturers instructions is 3 h!!


0

2

4

6

8

10

12

14

16


Ver

bund

span

nung

τ [N

/mm

²]

12% H2O ; tcure = 20h 30min

13% H2O ; tcure = 18h 30min

Reinigung H1

Displacement [mm]

Bon

d St

ress

[N/m

m²]

Experimental Results – Cement Systems – Mixture Process

The amount of water in the mixture process influences thebond stress (and the mixture process).









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Montage

Post-installed rebars

1. Hairline

2. Drilling

3. Rebar Installation

4. Crack Opening

1.

2. 3. 4.

Experimental Investigations – Installation Cracked Concrete

3.


Experimental Investigations – Cracked Concrete

crack

crackconcrete

rebar

Crack

Destroys bondbetween

mortar and concrete

Reduction of bond strength (~50%)


Hydraulikzylinder

Kugelkalotte

Stahlplatte Teflon

Prüfkörper

Beton-würfel

Wegaufnehmer

Rissaufnehmer

Stahlkeil

Kraftmessdose

Hydraulikzylinder

Kugelkalotte

Stahlplatte Teflon

Prüfkörper

Beton-würfel

Wegaufnehmer

Rissaufnehmer

Stahlkeil

Kraftmessdose

Experimental Investigations – Cracked Concrete

CalloteLoad cell

Hydrauliccylinder

LVDT

Steel Plate

Concrete Block

Slab

wedge

Crack measurementdevice


Failure Mode Pullout – Influence of Cracked Concrete

0,00

0,25

0,50

0,75

1,00

1,25

0,0 0,2 0,4 0,6

M8M12M16

Rissbreite [mm]

Nu (gerissen) / Nu (ungerissen) [-]

0,00

0,25

0,50

0,75

1,00

1,25

0 0,2 0,4 0,6

hef = 100 mmhef = 200 mm

Rissbreite [mm]

ßw = 35 - 37 N/mm2

ds = 16 mm

Nu(gerissen) / Nu(ungerissen) [-]

Bonded anchorsMeszaros (2002)

Cast-in-placeEibl/Idda/Lucero-Climas (1997)

Crack Width [mm] Crack Width [mm]

Nu (cracked) / Nu (uncracked) [-] Nu (cracked) / Nu (uncracked) [-]


0

5

10

15

20

-0,1 0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9

Rissbreite w [mm]

Ver

bund

fest

igke

it τ u

[N/m

m²]

Pagel V2/10

fcc = 60,9 N/mm²

fcc = 37-39,3 N/mm²

Crack Width [mm]

Bon

d St

reng

th[N

/mm

²]

Experimental Results – Cement Systems - Cracked Concrete

3xblowing, 3xbrushing, 3xblowing


0

2

4

6

8

10

12

14

16

18

20


Ver

bund

span

nung

τ [N

/mm

²]

w = 0,0 mm

w = 0,1 mm

w = 0,3 mm

w = 0,5 mm

fcc = 37-39,3 N/mm² lv = 200 mm

Bon

d St

ress

[N/m

m²]

Reduction of bond strength ~50% independent of crack width(w=0,1mm; 0,3mm, 0,5 mm)

Displacement [mm]

Experimental Results – Cement Systems - Cracked Concrete




Material • Mortar (Hybrid, Epoxy, Cement)• Concrete• Cracks in Concrete (Hybrid, Epoxy)




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Suitability of Post-installed Rebar Systems

Bond behavior of post-installed rebars should be comparable to cast-in-place rebars taking into account influence of

- sensitivity to installation

- concrete cracking parallel to bars

- temperature

- durability of mortar

Mortar should ensure corrosion resistance of reinforcing bars

Suitability of post-installed rebar systems should be checkedby tests at independent institutes


Design Concept for Post-Installed Rebar Connections

Simplified Design Concept: Design according to the rules for cast-in-place deformed rebars based on standards for reinforced concrete(e.g. Eurocode 2)

Restrictions:

Larger minimum concrete cover (depending on drilling method)

Larger minimum clear bar spacing (depending on drilling method)

Special requirements for fire safety (depending on system)

Limited design compression strength (depending on system)

Installation by skilled (certified) workers


Summary

• With suitable injection systems the bond behavior of post-installedrebars is similar to cast-in-place rebars.

• Connections with post-installed rebars are allowed when they areallowed for straight cast-in-place rebars.

• With suitable injection systems the design of connections with post-installed rebars can be done as for deformed cast-in-place rebarsaccording to codes for reinforced concrete (e.g. EC 2).

• The suitability of an injection system should be checked by an independent institute.

• Test criteria and acceptance criteria are required

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