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Strengthening of structures

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Presentation on theme: "Strengthening of structures"— Presentation transcript:

1 Strengthening of structures
Rak Repair Methods of Structures II (4 cr) Esko Sistonen

2 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.



5 f mm f mm

6 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

7 Repairing process of the parapet and slab of the balcony using self-compacting concrete (Batch 2, November 2004, outdoors condition) Moulding work Condition before casting Condition after repairing

8 Repairing process of the supporting column and slab of the balcony using self-compacting concrete (Batch 2, November 2004, outdoors condition) Moulding work Condition before casting Condition after repairing

9 Tensile strength results for drilled specimens from Batch 1, stored in laboratory condition
A) SCC, B) Old concrete

10 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)

11 The result of freeze-thaw test for drilled concrete samples
SCC layer Substrate concrete

12 Number of freezing and thawing cycles during July 2005 and April 2006

13 The relative humidity, temperature and water vapour content of the barrier layer between old concrete and the new 50 mm of SCC layer

14 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.

15 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.



18 Self-compacting concrete in the repair of pier

19 Self-compacting concrete in the repair of swimming hall structures

20 Drying shrinkage cracking
Strengthening / shotcrete Drying shrinkage cracking

21 Shotcreting stock

22 carbon fiber reinforced (CFRP) bar/laminate
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


24 Flexural strengthening
Shear strengthening Confining reinforcement

25 Strengthening foundations
Shotcreting Concrete casting


27 Piling Ref.

28 Temporary supports

29 Build in 1860’s

30 Column is hanged from the intermediate floor during mining
intermediate floor supported with steel columns WeeGee-house; Ref. Betoni 3/2006

31 WeeGee-house; Ref. Betoni 3/2006

32 Shotcreting Dry injection method Wet injection method

33 Strenghtening with shotcreting

34 Concrete injection Crack injection two component epoxies (<0.5 mm)
Cement glue (>0.5…1.0 mm) Mortar (>5 mm)

35 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)

36 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






42 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



45 encasing

46 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



49 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

50 Too low prestressed ridge beam in which hooks at the top surface are missing

51 Ref.:

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