IWB
Recent developments and open problems …
Recent developments and open problems
Universität Stuttgart
Institute of Construction Materials
in Fastening Technique
by
Rolf Eligehausen
Werner Fuchs
IWB
Recent developments and open problems …
Content
Introduction
Qualification and design of fasteners
Installation of fasteners
Universität Stuttgart
Institute of Construction Materials
Fasteners for statically indeterminate applications
Research projects
- Fire resistance of fasteners
- Seismic loading
- Post-installed rebars
Summary
IWB
Recent developments and open problems …
Universität Stuttgart
Institute of Construction Materials
Structural and nonstructural applications for fastenings
Hoehler, 2005
IWB
Recent developments and open problems …
Universität Stuttgart
Institute of Construction Materials
Requirements to ensure reliable fastenings
IWB
Recent developments and open problems …
Connection between
design guideline and qualification testing in Europe
EOTA
CEN TC 250
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ETAG
Technical Specification
„Design of fastenings for use
in concrete“
Application
CUAP
European
Technical Approval
(ETA)
Organization
Guideline
Standard or
Approval
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Recent developments and open problems …
Connection between
design guideline and qualification testing in USA
ACI
ICC
ACI
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AC 193
ACI 349
(nuclear)
ACI 318
(standard)
ACI 355.2
Application
AC 308
Evaluation
Report
IWB
Recent developments and open problems …
Borehole cleaning for chemical anchor installation
Required borehole cleaning: blowing and brushing
Actual borehole cleaning:
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Universität Stuttgart
no cleaning
30
3
2
33
brushing
37
1
00
20
20
40
40
brushing and blowing
60
60
80
80
100 [%]
100
Survey in Germany, 2007
IWB
Recent developments and open problems …
Improvement of installation quality
Possible approaches:
Improvement of the training of installers,
e.g. certified installer
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Institute of Construction Materials
proof loading on site
IWB
Recent developments and open problems …
Relation between anchor failure and system failure
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anchor failure
anchor failure
load transfer to
neighboring anchors !
falls down!
a) single use
b) multiple use
Rößle (2002)
IWB
Recent developments and open problems …
Fixture with double anchors
N
NC
N/2
N/2
N+NC
5.0 . d
2.5 d 2.5 d
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Institute of Construction Materials
hef
N
a = 2.5.d
s = 1 … 5 hef
a) intact state
2.5.d
b) failure of one anchor
Rößle (2002)
IWB
Recent developments and open problems …
Ultimate anchor load as a function of crack width
1.2
Pf = 10 -5
Universität Stuttgart
Nu,i(w)/N u,i(0) [-]
Institute of Construction Materials
1.0
0.8
0.6
0.4
0.2
0.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Crack width w [mm]
Rößle (2002)
IWB
Recent developments and open problems …
Multiple use system,
definition of n1 and n2
- example
B
A
B
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lateral view A
n1 = 3
bottom view B-B
n2 = 4
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Recent developments and open problems …
Definition of multiple use
according to the EC Member States
If no definition is given by a member state,
the following default values are valid:
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n1 ≥ 4, n2 ≥ 1, n3 ≤ 3 kN
n1 ≥ 3, n2 ≥ 1, n3 ≤ 2 kN
National values are defined by F and GB:
F:
n1 ≥ 3, n2 ≥ 1, n3 ≤ 4,5 kN
GB:
n1 ≥ 4, n2 ≥ 1, n3 ≤ 10 kN
n1 = 1, n2 ≥ 4, n3 ≤ 40 kN
n1 …
n2 …
n3 …
number of fixing points to fasten the fixture
number of anchors per fixing point
limitation of the design value of action NEd [kN] per fixing
point so, that excessive slip or anchor failure need not be
taken into account in the design of the fixture
IWB
Recent developments and open problems …
Fire – Steel failure
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Carbon steel
Stainless steel, grade 316
Steel stress as a function of time until failure
Reick (2001)
IWB
Recent developments and open problems …
Fire – Steel failure
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Carbon Steel
Steel stress at a function of time until failure
Reick (2001)
IWB
Recent developments and open problems …
Fire – Concrete cone failure
185
185
172.5
172.5
dA
dH
hef
t=160
(550)
1200
Heating
Cooling
Temperature [°C]
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1000
800
600
400
200
= Pull-out test
Z
Y
0
X
0 15 30 45 60 75 90 105 120 135 150 165 180
Time [min]
Ozbolt et. al (2004)
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Recent developments and open problems …
Fire – Concrete cone failure
2
Fire duration 90 Minutes
FE-Analysis
Experiments, Reick (2001)
Headed anchors
Undercut anchors
CEN TS (2005)
Relative resistance NU/NU,t=0
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1.8
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
NU,t=0=0.75⋅15.5⋅fcc0.5⋅hef1.5
0
0
20
40
60
80
100
120
140
160
180
Embedment depth [mm]
Ozbolt et. al (2004)
IWB
Recent developments and open problems …
Fire - design of fastenings
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N 0Rk ,c,fi(90)
h ef
=
⋅ N 0Rk ,c ≤ N 0Rk ,c
200
N 0Rk ,c,fi(120) = 0,8 ⋅ N 0Rk ,c,fi(90)
Concrete cone resistance - CEN-TS (2007)
IWB
Recent developments and open problems …
Actions on fasteners under seismic loading
Crack Width
1
time
2
Tension Shear
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Global Structure
time
time
Sub-structure
FASTENING
STRUCTURE
ENVIRONMENT
Hoehler (2006)
IWB
Recent developments and open problems …
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Institute of Construction Materials
Crack in a beam
caused by transverse motion of the structure
w ≤ 0,8mm
Hoehler (2006)
IWB
Recent developments and open problems …
ACI 355.2,
loading pattern for simulated seismic-tension test
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Load
N eq
Ni
Nm
10
30
100
Number of Cycles
IWB
Recent developments and open problems …
Universität Stuttgart
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Load-displacement curves,
monotonic and stepwise cyclic loading, w = 0,8mm
Hoehler (2006)
IWB
Recent developments and open problems …
Universität Stuttgart
Institute of Construction Materials
Load-displacement curves
monotonic loading, w=0,8mm and
crack cycling, w1=0,8mm, w2=0mm, n=10, Nw=0,4Nu,m
Hoehler (2006)
IWB
Recent developments and open problems …
Post-installed rebar connections in existing buildings
Post-installed
rebars
Existing Building
New building
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Existing
column
New
infilled
walls
9
lv
Adding new columns
Strengthening
columns
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Recent developments and open problems …
Rebar connections in new buildings
Formwork Joint
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Couplers
Flashing Boxes with Stirrups
Post-Installed Rebar Connection
IWB
Recent developments and open problems …
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Institute of Construction Materials
Rebar connections in existing buildings
Connections made by trained and certified installers
Silva (2005)
IWB
Recent developments and open problems …
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Load transfer mechanisms
rebar
concrete
cast-in-place
rebar
mortar
concrete
post-installed
IWB
Recent developments and open problems …
Comparison of splice lengths
EC 2
100
BS 8110
80
ACI 318
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ls / d s
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60
Manufacturer
40
20
0
4
8
12
16
20
Bar Diameter [mm]
24
28
32
Spieth (2002)
IWB
Recent developments and open problems …
Splices in bending elements
Load [kN]
30
Yield Strength
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25
20
Cast-in-place
15
10
Post-installed
5
0
0
10
20
30
40
50
60
Deflection [mm]
Spieth (2002)
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Recent developments and open problems …
Bond behavior – influence of injection system
Nut
14
Load cell
Hybrid
Average Bond Stress [N/mm²]
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12
Universität Stuttgart
Calotte
Epoxy
10
Threaded rod
Ram
Cast-in-place
Cement
8
Polyester
6
Coupling nut
LVDT
Steel Plate
4
Rebar
ds =20 mm
hef = 300 mm
C 20/25
2
Teflon
Test slab
0
0,0
1,0
2,0
Displacement [mm]
3,0
Spieth (2003)
IWB
Recent developments and open problems …
Failure mode splitting – influence of edge distance
16
Average Bond Stress [N/mm²]
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14
Large Concrete Cover
12
10
ds = 20 mm
hef = 200 mm
C 20/25
8
6
4
Concrete Cover c = 50 mm
2
Cast-in-place
Hybrid System
0
0
2
4
6
8
10
12
Displacement [mm]
Spieth (2002)
IWB
Recent developments and open problems …
Post-installed rebars – cyclic behaviour
2
τ [N/mm ]
16
1st cycle
10th cycle
monotonic
12
8
4
s [mm]
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0
-5
-4
-3
-2
-1
-4
0
1
0,8
2
3
4
5
-8
-12
-16
Post-Installed Bar
(Serie A)
Cycling of post-installed rebars
displacement s = 0,8 mm
Hofacker/Eligehausen (2001)
Cycling of cast-in-place rebars
displacement s = 1,02 mm
Eligehausen et al. (1983)
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Recent developments and open problems …
Failure mode pullout – influence of hole cleaning
14
Compressed Air / Machine Driven Wire Brush
Bond Stress [N/mm²]
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12
Compressed Air / Machine Driven Nylon Brush
10
8
6
4
Hand Brush / Hand Pump
Hybrid System
Wet Concrete C 20/25
ds = 20 mm
2
0
0
5
10
15
Displacement [mm]
20
25
Spieth (2003)
IWB
Recent developments and open problems …
Post-installed rebars – design concept
Design of post-installed rebar connections with suitable mortar
systems according to provisions for cast-in-place deformed rebars
given in standards for reinforced concrete (e.g. EN 1992, ACI 318)
Injection mortar must provide corrosion protection for rebars
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Restrictions:
Larger minimum concrete cover
(depending on drilling method)
Larger minimum clear bar spacing (depending on drilling method)
Limited design compression strength (depending on system)
Special requirements for fire safety (depending on system)
Installation by skilled (certified) workers!
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Recent developments and open problems …
Post-installed rebars – qualification of the mortar
Suitability should be checked according to EOTA TR 23
‘Assessment of post-installed rebar connections‘
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Institute of Construction Materials
Testing of injection mortar system according to
EN 1504-6 ‚Anchoring Products‘ (2006) is inappropriate,
because the
- required bond strength is much too low
- requirements on bond behavior under sustained load
are insufficient
- chemical resistance to alkalinity is not checked
- corrosion protection of the rebar by the mortar is not checked
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Recent developments and open problems …
Conclusions
Innovative fastening systems and new testing and
design provisions capture new fields of applications
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Education and training of the users should keep pace
with the innovation process
Open questions e.g. application of fasteners
in seismic zones will be solved in the near future