SEMINAR ON

“REPAIR OF EARTHQUAKE DAMAGED RC COLUMN USING FRP WRAPS”

CONTENTSCONTENTS

1)1) INTRODUCTIONINTRODUCTION

2)2) EARTHQUAKEEARTHQUAKE

3)3) FRP WRAPSFRP WRAPS

4)4) EXPERIMENTAL CASE STUDYEXPERIMENTAL CASE STUDY

INTRODUCTIONINTRODUCTION

RESEARCH STUDY HAS SHOWN CLOSELYRESEARCH STUDY HAS SHOWN CLOSELY

SPACED TRANSVERSE REIFORCEMENT IN THE SPACED TRANSVERSE REIFORCEMENT IN THE PLASTIC HINGE ZONE OF A RC COLUMN PLASTIC HINGE ZONE OF A RC COLUMN INCREASES THE COMPRESSIVE STRENGTH AND INCREASES THE COMPRESSIVE STRENGTH AND

ULTIMATE COMPRESSIVE STRAIN.ULTIMATE COMPRESSIVE STRAIN.

EARTHQUAKE

EARTHQUAKE IS SUDDEN GRINDING SLIPPAGE BETWEEN TWO PARTS OF THE EARTH CRUST WHICH RELEASES ENERGY AND PROPOGATES MOTION IN THE SURROUNDING GROUND.

From Newton's first law of motion, though the base of the building moves with the ground, the roof stays in its original position. Where as walls and columns connected to it deforms.

This tendency of the roof to continue to be in its original position or in its previous position is known as inertia.

If the roof has a mass ‘m’ and a acceleration ‘a’, from the Newton’s law of motion, the inertia force

F1 = M x A It acts in the direction opposite to that of the acceleration.

Lateral strength/ductilityLateral strength/ductility

Horizontal shaking produces horizontal Horizontal shaking produces horizontal forces throughout the building that are forces throughout the building that are transferred through the floors to the vertical transferred through the floors to the vertical structure and down into the ground. The critical structure and down into the ground. The critical property in terms of preventing failure is the property in terms of preventing failure is the vertical structure’s ability to resist horizontal vertical structure’s ability to resist horizontal forces applied to each storey (i.e., its lateral forces applied to each storey (i.e., its lateral strength).strength).

Most of the retrofits are conventional construction Most of the retrofits are conventional construction techniques, and include:techniques, and include:

Anchoring masonry and other heavy components to Anchoring masonry and other heavy components to the building structure the building structure

Building new sub-systems such as shear walls, Building new sub-systems such as shear walls, bracing systems or additional foundation elements, bracing systems or additional foundation elements, and connecting them to the existing structure.and connecting them to the existing structure.

Strengthening of concrete members by providing Strengthening of concrete members by providing additional confinement to the core concrete by means additional confinement to the core concrete by means of external reinforcement by FRP WRAPS.of external reinforcement by FRP WRAPS.

Lateral support and anchorage added to masonry  walls

New shear walls or bracing

WHAT ARE FRP COMPOSITE WRAPSWHAT ARE FRP COMPOSITE WRAPS

FRP – Fiber Reinforced PlasticFRP – Fiber Reinforced Plastic

Fiber composites are constructed of filaments such as Fiber composites are constructed of filaments such as glass (GFRP), kevlar, carbon (CFRP)glass (GFRP), kevlar, carbon (CFRP)

FRP TECHNOLOGYFRP TECHNOLOGYCHARACTERISTICSCHARACTERISTICS

High StrengthHigh Strength

High Resistance to Corrosion and ChemicalHigh Resistance to Corrosion and Chemical

High Resistance to Elevated TemperatureHigh Resistance to Elevated Temperature

High Resistance to AbrasionHigh Resistance to Abrasion

ToughnessToughness

FatigueFatigue

Light WeightLight Weight

Glass Fiber Reinforced Plastic composite is Glass Fiber Reinforced Plastic composite is very strong in tensionvery strong in tension

ULTIMATE TENSILE STRENGTH = 3447 MPaULTIMATE TENSILE STRENGTH = 3447 MPa

MODULUS OF ELASTICITY = 72.4 GPaMODULUS OF ELASTICITY = 72.4 GPa

WHAT IS FRP COMPOSITESWHAT IS FRP COMPOSITESCOMPONENTSCOMPONENTS

Fiber ReinforcementFiber Reinforcement

Resin MatrixResin Matrix

***(Fiber-Matrix Interphases)******(Fiber-Matrix Interphases)***

FillersFillers

AdditivesAdditives

FRP TECHNOLOGYFRP TECHNOLOGYMECHANICAL PROPERTIESMECHANICAL PROPERTIES

Fiber TypesFiber Types

Fiber OrientationsFiber Orientations

Fiber ArchitectureFiber Architecture

Fiber Volume (30-70%)Fiber Volume (30-70%)

PREPARATION OF FRP FOR REPAIR TECHNIQUE

UNIDIRECTIONAL E-GLASS FABRIC POLYESTER RESIN MATRIX MYLAR SHEET CURING

FRP composite wraps, constructed from FRP composite wraps, constructed from high strength glass fibers are weaved to form a high strength glass fibers are weaved to form a fabric like material of specified width and fabric like material of specified width and length and are externally wrapped around the length and are externally wrapped around the damaged regions of columns in continuous damaged regions of columns in continuous rings as shown in the figure.rings as shown in the figure.

Retrofitted and Un-retrofitted Concrete Column

F R P Composite Straps for seismic repairs

The stress-strain curves throughout the entire range of loading up to failure were plotted for the specimens with different fiber volume ratios as shown in Figure. In this figure, Vf defines the ratio of volume of fibers over the total volume of the strap. The data for the stress-strain curves were obtained by of the three fiber volume ratios. The material properties determined averaging the test results from three iden tical specimens for each from the tests are summa rized in Table 1. Composite wraps with Vf = 50.2 percent were used in this study.

Measured Properties of FRP composite strapMeasured Properties of FRP composite strap

Fiber volume ratioFiber volume ratio V Vf f =25.4%=25.4% V Vf f =50.2%=50.2% V Vf f =74.0%=74.0%

Tensile Strength (MPa) 281Tensile Strength (MPa) 281 532 532 814 814

Tensile Modulus (MPa) 9074 17755Tensile Modulus (MPa) 9074 17755 29056 29056

Ultimate Strain 0.031 0.030 0.028Ultimate Strain 0.031 0.030 0.028

EXPERIMENTAL CASE STUDY

An effective technique for repairing earthquake-damaged columns with FRP composite wraps is presented. FRP composite wraps, constructed from high-strength glass fibers weaved to form a fabric-like material of specified width and length, are externally wrapped around the dam aged regions of columns in continuous rings, as shown in Figure. The desired confinement to the core concrete at the critical sections is achieved by hoop stresses developed in the composite wrap as a result of the dilation of the core con crete undergoing inelastic deformations.

TOTAL SPECIMEN HEIGHT = 2.41m (7’-11”)HEIGHT OF COLUMN = 1.892m (6’-0”)

FOOTING DIMENSION = 1070x914x381 mm

EXPERIMENTAL PROCEDURE AND REPAIR PROCEDURESEXPERIMENTAL PROCEDURE AND REPAIR PROCEDURES

Each column (C-l, C-2, R-l, and R-2) was first tested lat erally subjected to inelastic earthquake load reversals in a reaction frame, Hydraulic rams at the base of the specimens were used to apply a constant axial load of 445 KN (100 kips) to simulate the dead load. A typical loading sequence for one of the specimens (Column C 1) is shown in Figure .

Loading Pattern on the Specimen

The loading cycles were divided into two phases: load control and displacement control. Load control phase was used up to yielding of the longitudinal bars; beyond that point, a displacement control loading sequence was used. In Figure, u, defined as the displacement ductility factor, is the ratio of the applied displacement at the top of the column over the displacement at first yield.

Local Buckling of Longitudinal Steel Separation of the main bars from the column core concrete

Debonding of Starter BarSpalling and Crushing of Concrete in the Compression Zone

REPAIR OF ORIGINAL REPAIR OF ORIGINAL COLUMN WITH EXTERNAL COLUMN WITH EXTERNAL CONFINEMENT USING FRP CONFINEMENT USING FRP

WRAPSWRAPS

Strengthening of concrete members by providing additional confinement to the core concrete by means of external reinforcement by FRP COMPOSITE WRAPS.

MEASURED AND CALCULATED LATERAL STRENGTH OF COLUMNSMEASURED AND CALCULATED LATERAL STRENGTH OF COLUMNS

SpecimensSpecimens Calculated lateral Calculated lateral strength ( KN) strength ( KN) before repairbefore repair

Measured Measured Maximum load Maximum load (KN) after repair(KN) after repair

Increase in strengthIncrease in strength

C-1C-1 50.750.7 58.358.3 ControlControl

C-1/RC-1/R RepairedRepaired 72.572.5 24 %24 %

C-2C-2 50.750.7 71.671.6 ControlControl

C-2/RC-2/R RepairedRepaired 72.572.5 1%1%

R-1R-1 89.489.4 92.192.1 ControlControl

R-1/RR-1/R RepairedRepaired 128.5128.5 38%38%

R-2R-2 132.5132.5 161.5161.5 ControlControl

R-2/RR-2/R RepairedRepaired 211.3211.3 31%31%

Load V/S Displacement Graph for C-1 & C-1/R Column

Load V/S Displacement Graph for C-2 & C-2/R Column

STIFFNESSSTIFFNESS

For each cycle of loading Stiffness for Both positive and Negative directions are found

For each cycle, the overall stiffness for both positive and negative directions was defined. The estimated value of the stiffness was determined by dividing the maximum load reached within a cycle by the displacement at the peak of the load cycle in the direction considered. The final stiffness for each cycle was then calculated as the average of the stiffness for the positive and negative directions.

STIFFNESS STIFFNESS

FRP composite wraps are effective in restoring the flexural FRP composite wraps are effective in restoring the flexural strength and ductility capacity of earthquake-damaged strength and ductility capacity of earthquake-damaged concrete columns.concrete columns.

After repair with FRP wrap, columns with lapped starter bars After repair with FRP wrap, columns with lapped starter bars developed stable hysteresis loops up to the displacement developed stable hysteresis loops up to the displacement ductility of ductility of u = u = ± 4. In columns with continuous reinforce ± 4. In columns with continuous reinforce ment, the hysteresis loops were stable even up to ment, the hysteresis loops were stable even up to u u = 6 with out = 6 with out showing any sign of structural degradation.showing any sign of structural degradation.

In all repaired specimens, the rate of stiffness deteri oration In all repaired specimens, the rate of stiffness deteri oration under large reversed cyclic loading was lower than that of the under large reversed cyclic loading was lower than that of the corresponding original columns. However, the initial stiffness corresponding original columns. However, the initial stiffness of repaired columns was lower than that of the original of repaired columns was lower than that of the original columns.columns.

CONCLUSION

REFERENCES

• Saadatmanesh.H, M.R.Ehsani and Limin Jin “Seismic Retrofitting of RC Columns by COMPOSITE STRAPS”. Earthquake Engineering Research Institute Journal “SPECTRA” V.13, NO.2, 1977.

• Saadatmanesh.H, M.R.Ehsani and Limin Jin “Seismic Strengthening of Circular Bridge Piers with Fiber Composites”. ACI Structural Journal, V.93.No.6, Nov-Dec, 1996.

• Priestly.M.J.N. and Park.R., “Strength and Ductility of Reinforced Concrete Bridge Columns under Seismic Loading.” ACI Structural Journal, V.84,No.1, Jan-Feb, 1987.

• Saadatmanesh.H, M.R.Ehsani and Limin Jin “Repair of Earthquake Saadatmanesh.H, M.R.Ehsani and Limin Jin “Repair of Earthquake damaged RC columns with FRP wraps” ACI Structural Journal.94:2, damaged RC columns with FRP wraps” ACI Structural Journal.94:2, 1997.1997.

• Http://www.paper.edu.cnHttp://www.paper.edu.cn

• 11stst Conference on Application of FRP Composites in Construction Conference on Application of FRP Composites in Construction and Rehabilitation of Structures May 4, 2004, Tehran, Iran “and Rehabilitation of Structures May 4, 2004, Tehran, Iran “Behavior Behavior of High Strength Square Concrete Columns Strengthened with of High Strength Square Concrete Columns Strengthened with Carbon Fiber Reinforced Polymers (CFRP)”.Carbon Fiber Reinforced Polymers (CFRP)”.

• www.efunda.comwww.efunda.com

Construction and Building Materials 17 (2003) “Experimental study Construction and Building Materials 17 (2003) “Experimental study on seismic strengthening of RC columns with wrapped CFRP on seismic strengthening of RC columns with wrapped CFRP sheets”. sheets”.

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