strengthening of structures rak-43.3312 repair methods of structures ii (4 cr) esko sistonen
TRANSCRIPT
Strengthening of structures
Rak-43.3312 Repair Methods of Structures II (4 cr)
Esko Sistonen
Using Self-compacting concrete in repairing
• The usefulness of using self-compact concrete in repaired structure is investigated in balcony repairs.
• Frames work and concreting methods are examined in field tests.
• Concrete properties and resistance to frost are also investigated.
• Shrinkage and bond strength between old and new concrete are also measured.
f 4 @12 mm f 12 @15 mm
250 mm
25 mm
115 mm
150 mm
50 mm
250 mm
25 mm
115 mm
150 mm
50 mm
Repairing process of the supporting walls, parapet and slab of the balcony using self-compacting concrete. (Batch
1, October 2004, laboratory condition)
• Condition before casting • Moulding work
• Condition after repairing
Repairing process of the parapet and slab of the balcony using self-compacting concrete (Batch 2, November 2004,
outdoors condition)
• Condition before casting • Moulding work
• Condition after repairing
Repairing process of the supporting column and slab of the balcony using self-compacting concrete (Batch 2,
November 2004, outdoors condition)
• Condition before casting • Moulding work
• Condition after repairing
Tensile strength results for drilled specimens from Batch 1, stored in laboratory condition
A) SCC, B) Old concrete
Examples of surface cracks of self-compacting concrete cast in the laboratory conditions (Batch 1).
Drying shrinkage of SCC removes forces from the old layer to the old concrete and in that way strengthens the
structure (composite structure)
The result of freeze-thaw test for drilled concrete samples
SCC layer
Substrate concrete
Number of freezing and thawing cycles during July 2005 and April 2006
2429
77
0
20
40
60
80
100
The barrier layer of oldslab & SCC
The barrier layer of oldcolumn & SCC
Outdoors condition
Nu
mb
er o
f fr
eezi
ng-
thaw
ing
cycl
es d
uri
ng
(07
.200
5 -
04.2
006)
The freezing - thawing cycles are below 0 °C
The relative humidity, temperature and water vapour content of the barrier layer between old concrete and the new 50 mm
of SCC layer
Conclusion 1/2• An objective with the work was to find the minimum cover depth
of the self-compacting concrete (SCC) suitable for the repair method studied. This cover depth thickness was defined as 15 mm.
• Fresh and hardened concrete tests for the self-compacting concrete used showed that the concrete fulfilled the requirements for balcony repairing.
• The results of slab frost resistance tests show the scaling and flexural strength change of self-compacting concrete was very small after 300 cycles and the changes in ultrasound transmission time were small, so there is no sign of inner deterioration.
• Drying shrinkage of self-compacting concrete was higher than the theoretical shrinkage for the normal concrete because self-compacting concrete contained more fine aggregate. Using reinforcement mesh reduces the shrinkage of self-compacting concrete.
Conclusion 2/2• Surface cracks were observed in the concrete surface,
specially the area around the reinforcement mesh supports.• The bond between the old concrete, which has a lower
strength than the repairing self-compacting concrete, is poor specially, when casting concrete in the lower surface of concrete slab.
• The results of relative humidity and temperature monitoring and the number of freezing-thawing cycles for the repaired balcony show that the winter condition is severe for the frost resistance of concrete.
• Based on the laboratory results, air entrained self-compacting concrete; with 5% air content is suitable for the outdoor conditions in Finland and fulfilled the requirements for frost resistance of concrete.
Self-compacting concrete in the repair of pier
Self-compacting concrete in the repair of swimming hall structures
Strengthening / shotcrete
Drying shrinkage cracking
Shotcreting stock
The strengthening of reinforced concrete (RC) structures using advanced fibre-reinforced polymer (FRP) composites = non-metallic
• carbon fiber reinforced (CFRP) bar/laminate• Glass Fiber Reinforced Polymer (GFRP)
Rebar/laminate – The unclear alkali and salt-frost resistance of FRP – Good corrosion resistance and high tensile strength – Good fire resistance of CFRP – The epoxy matrix will soften at temperatures close
to its glass transition temperatures between 65 and 150 °C.
– the bending and shaping of FRP elements must to be done beforehand
http://www.trancels.com/ http://www.savcor.com.au/art/?p=services&s=ss
• Flexural strengthening• Shear strengthening• Confining reinforcement
Strengthening foundations
• Shotcreting• Concrete casting
Ref. www.lemcon.fi
Piling
Temporary supports
Build in1860’s
WeeGee-house; Ref. Betoni 3/2006
Column is hanged from the intermediate floor during mining
intermediate floor supported with steel columns
WeeGee-house; Ref. Betoni 3/2006
Shotcreting
Wet injection methodDry injection method
Strenghtening with shotcreting
Concrete injection
Crack injection
two component epoxies (<0.5 mm)Cement glue (>0.5…1.0 mm)Mortar (>5 mm)
Strengthening concrete structures
Old structure and the addition of a new concrete is made to work as well as possible.
The surface must be transferred the shear strength without the parts slipping in between.
- Roughening the surface of the joint
-Into concrete stages are made a hole with a spike (a recess)
Strengthening slabs
Strengthening the upper and underside of the slab
Shortening the span of the slab with new beam
Strengthening the slab with stressing method
Incresing punching shear capasity of the slab
Bolting through the slab
Strengthening hollow-core slabs
Strengthening beams
Compressed side of the beam is to be increased with the upper side casting
Tensile and/or shear reinforcement will be increased by casting a new beam around the old one
Tensile and/or shear capacity is to be increased by cluing steel sheets / carbon fiber reinforced laminates into a lower and/or side surface of the beam
Reinforced concrete beam is to be strengthened by a form steel
Concrete beam is to be substituted with steel beam
Steel profile is to be fixed into a concrete beam
Steel profile is to be wedged below the beam
Extra supporting of the beam
Beam is to be post-tensioned by external tendons or tended beam is to be casted around the old concrete beam
encasing
Strengthening the column
Entirely or partly encasing
Strengthening the column with the steel form
Increasing cross sectional surface with steel profiles
Substituting the concrete column with the steel column
Important factors in strengthening:
-good bonding between new and old concrete (roughening for instance by making a hole with a spike, or sand blasting
-The base concrete should not be too wet or dry
-New reinforcements should have adequate concrete cover
Too low prestressed ridge beam in which hooks at the top surface are missing
www.fise.fi
Ref.: www.norcure.com