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Base - Isolation
Base Isolators
3- Earthquake Hinge
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Earthquake Hinge
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Carbon-fiber-reinforced polymer or
carbon-fiber-reinforced plastic
(CFRP or CRP)
Typical Properties High StrengthHigh
ModulusUltra-High Modulus
Density (g/cm3) 1.8 1.9 2.0 - 2.1
Young's Modulus (GPa) 230 370 520 - 620
Tensile Strength (GPa) 2.48 1.79 1.03 - 1.31
Tensile Elongation (%) 1.1 0.5 0.2
Table for carbon fibers
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FRP Sheet
FRP Plate
• FRP can be applied to strengthen:
1. Beams
2. Columns
3. Slabs of buildings and bridges
• It is possible to increase the strength of structuralmembers even after they have been severelydamaged due to loading conditions. In the case ofdamaged reinforced concrete members:
1. Repairing of the member by removing loose debrisand filling in cavities and cracks with mortar orepoxy resin.
2. Strengthening through the fibre sheets with epoxyresin then applying them to the cleaned andprepared surfaces of the member.
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Two techniques are typically adopted for thestrengthening of beams, relating to the strengthenhancement desired:
– Flexural strengthening
– Shear strengthening
• For the flexural strengthening of a beam,
FRP sheets or plates are applied to the tensionface of the member.
Principal tensile fibers are oriented in the beamlongitudinal axis, similar to its internal flexuralsteel reinforcement. This increases the beamstrength and deflection capacity, and its stiffness(load required to cause unit deflection).
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Beams
flexural strengthening of a beam
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• For the shear strengthening of a beam, the FRP is applied on the web orside faces of the member with fibers oriented transverse to the beamlongitudinal axis.
• This is necessary for resisting shear forces, in a similar manner as internalsteel stirrups, by bridging shear cracks that form under loading andrestricting their growth.
• The FRP can be applied in several configurations, this includes:1. Side bonding2. U-wraps or U-jackets3. Closed wraps or complete wraps.• Side bonding involves applying FRP to both sides of the beam only. It
provides the least amount of shear strengthening due to failures causedby debonding of the FRP from the concrete surface at the free edges.
• U-wraps, for which the FRP is applied continuously in a 'U' shape aroundthe sides and bottom (tension) face of the beam.
• closed wraps, If all faces of a beam are accessible, then the use of closedwraps is desirable to provide the most strength enhancement. Closedwrapping involves applying FRP around the entire perimeter of themember with an overlap of FRP.
• For all wrap configurations, the FRP can be applied along the length ofthe member as a continuous sheet or as discrete strips, having apredefined minimum width and spacing.
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Shear strengthening of a beam
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FRP is applied continuously
Side bonding involves applying FRP to both sides of the beam only
Carbon-fiber-reinforced polymer or carbon-fiber-reinforced plastic (CFRP or CRP or often simply carbon fiber)
Structural Defects – strengthening U-wraps or U-jackets
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Flexural and shear (U-wraps or U-jackets)strengthening of a beam
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Flexural and shear strengthening of a beam
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Flexural and shear strengthening of a beamaccording to bending moment diagram
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flexural strengthening of a beam
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21Shear strengthening of a beam, FRP is applied continuously
U-wraps or U-jackets
• Slabs may be strengthened by applying FRP strips at theirbottom (tension) face. This will result in better flexuralperformance, since the tensile resistance of the slabs issupplemented by the tensile strength of FRP. In the case ofbeams and slabs, the effectiveness of FRP strengtheningdepends on the performance of the resin chosen forbonding. This is particularly an issue for shear strengtheningusing side bonding or U-wraps.
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Slabs of buildings and bridges
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Slab opening
Anchorage for slab ConcreteRetrofitting
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• Columns are typically wrapped with FRParound their perimeter, as with closed orcomplete wrapping. This not only results inhigher shear resistance, but more crucial forcolumn design, it results in increasedcompressive strength under axial loading.The FRP wrap works by:
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Restraining the lateral expansion of thecolumn, which can enhance confinement in asimilar manner as spiral reinforcement doesfor the column core.
Closed wraps or complete wraps for columns
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Columns are typically wrapped with FRP
Closed wraps for columns
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Closed wraps for columns and shear strengthening of a beam
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5- Leakage of water
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Leakage of water
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Leakage of water
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6- Collapse
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Collapse
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Collapse
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Collapse
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Collapse
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Collapse
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Collapse
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7- Corrosion of reinforcement
Corrosion: Corrosion of reinforcing steel and other embedded metals is one of the leading causes of deterioration of concrete. When steel corrodes, the resulting rust occupies a greater volume than steel. The expansion creates tensile stresses in the concrete, which can eventually cause cracking and spalling.
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Corrosion of Steel Reinforcement
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Corrosion of Steel Reinforcement
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Corrosion of Steel Reinforcement
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Corrosion of Steel Reinforcement
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@Corrosion of Steel Reinforcement
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Corrosion of Steel Reinforcement
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Corrosion of Steel Reinforcement
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Column corner corrosion
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Mode of failure and corrosion
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Corrosion of reinforcement- Corrosion of steel reinforcement bar is anelectrochemical process that requires:
1- Oxidizing agent.
2- Moisture.
3- Electron flow.
The key to protecting steel from corrosion is to stop or reverse the chemicalreactions. This may be done by cutting off the supplies of oxygen ormoisture or by supplying excess electrons at the anodes to prevent theformation of the metal ions (cathodic protection). Cracks provide easyaccess for oxygen, moisture, and chlorides, and thus, minor splittingcracks can create a condition in which corrosion and cracking areaccelerated. The protection against corrosion-induced:
1. Use of concrete with low permeability.
2. Adequate cover.
3. In very severe exposure conditions, coated reinforcement.
4. Sealers or overlays on the concrete.
5. Corrosion-inhibiting admixtures.
6. Cathodic protection. 49
Mechanism of steel reinforcement corrosion
Anodic reaction Fe2 2Fe2+ +2e-
Cathodic reaction 4e- + O2 + 2H2O 4(OH)-
2Fe2+ +2 OH- Fe(OH)2 Ferrous hydroxide4 Fe(OH)2 + 2H2O + O2 4Fe(OH)3 Ferric Hydroxide
Normalmechanism of corrosion
Anode Cathode
Fe++ 2e-
2OH _Fe (OH)2
H2O + ½ O2
Ph. less than 10.5
Mechanism of steel reinforcement corrosion
passive film by Kerber el at.(1990):Hydrated Ferric oxide or Ferric oxide
passive film by Hanson at.(1984):Inner layer: Ferrous Oxide .Outer layer : Ferric Oxide
Concrete cover (PH value =12-13)
Marine Environment
Chloride Ions
Corrosion product ferrous hydroxide
Concrete cover (PH value =8-9(through carbonation)
Steel corrosion in marine environment concrete
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The corrosion of steel reinforced concrete member by the formation of electro-chemical cell results in cracking (characteristically parallel to the reinforcement), spalling or in delamination of concrete. This corrosion may occur due to chloride attack and carbonation.
Cases of steel corrosion in slabs
Delamination
53Sacrificial anode system in seawater
54Impressed-current cathodic-protection system in seawater
Supplying excess electrons at the anodes to prevent the formation of the metal ions (cathodic protection).
Improper casting
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Inadequate Concrete Cover
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8- Settlement of the foundation
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Settlement of the foundation
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Settlement of the foundation
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• What Causes A Concrete Floor Slab To Settle?• When a concrete floor settles, it can mean
serious damage. The causes of floor slab settlement are almost always due to the soils underneath being unable to support the weight of the concrete.
• The three most common causes of settling concrete floor slabs are as follows:
1- Drying/Shrinking Of Soils Under The Slab. 2- Washout Of Soil Underneath The Slab.3- Poor Compaction Of Foundation Fill Soils.
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Settlement
Causes of Settlement
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Drying/Shrinking Of Soils Under The Slab
Washout Of Soil Underneath The Slab
Poor Compaction Of Foundation Fill Soils
