Report on the Repair of Earthquake Damaged R.C.C Structures

* REPAIR:- An action taken to address a damaged building component.

* STRUCTURAL REPAIR:- Repair that address damage to components to directly restore the structural properties.

* RESTORATION:- The repair of structural components intended to restore the seismic performance of a damaged building to a level equivalent to the pre-event condition of the building.

* UPGRAD:- The repair of structural components intended to improve the seismic performance of a damaged building to a level better then that of the pre-event building.

FAILURES OBSERVED IN RC FRAMED STRUCTURES DUE TO EARTHQUAKE

* Cracking of concrete surfaces

* Spall of plaster and concrete cover

* Column failure (Shear, Hinge formation, Splice )

* Beam failure (Shear, Flexure)

* Beam-column joint failure (Shear, Hinge formation)

* Slab failure

* Staircase (lack of connection to the diaphragm)

* Failure of Shear wall (Shear, Flexural)

CATAGORIS OF REPAIRS

Repairs for earthquake damaged concrete buildings fall in to three generic categories

* Cosmetic Repairs:- They are those repairs that improve the visual appearance of component damage. These repairs may also restore the non-structural properties of the component, such as weather protection. (e.g.:- routing, sealing, and painting of cracks in concrete)

* Structural repairs:- They address component damage directly, with the intent of restore structural properties. Examples include injection of cracks or the replacement of fractured reinforcing bars

CATAGORIS OF REPAIRS Cont….

* Structural Enhancement:- They are repairs that comprise supplemental addition, or removal and replacement of existing damaged components. They also include the addition of new components in the structure not necessarily at the site of existing damaged components. In this case, the intent is to replace structural properties of damaged components rather than to restore them. Examples include the application of concrete overlays to damaged elements.

COSMETIC REPAIRS

COSMETIC PATCHING:

* Cosmetic patch consists of applying a surface coating on the surface of the concrete or masonry wall to conceal the surface projection of cracks.

* Various materials can be used, choice depend on the functional and architectural requirements. Paints can be used to conceal fine cracks, Dry-wall taping compound can be used to fill cracks, Organic polymer materials can be used to fill cracks, Portland cement plaster can be applied, coatings and sealers can be used on exterior surface cracking.

COSMETIC REPAIRS Cont…

CRACK INJECTION METHOD:

* In good quality concrete, cracks as narrow as 0.075mm in vertical or horizontal plan can be sealed with epoxy compounds, pressure injection is required to sealing the cracks.

Procedure:

Before crack After sealing Pressure injection

was sealed the crack in progress

COSMETIC REPAIRS Cont…

ROUTING AND SEALING:

* This method is used on the cracks that are dormant and of no significance. The method involves enlarging the crack along its exposed face and sealing it with crack fillers.

* The method consists of preparing a groove on the surface that is sufficiently large to receive sealant having a minimum surface width of 6mm.The surface of the routed joint is to be cleaned and dried before placing the sealant.

Routing and Sealing

COSMETIC REPAIRS Cont…

STITCHING:

* This method is to be used when tensile strength is to be re-established across major cracks. It tends to stiffen the structure and stiffening may accentuate the overall structural restraint, causing a concrete to crack elsewhere. So, strengthening of adjacent section is also necessary.

* Stitching will not going to close a crack but, it prevents propagation

* The stitching procedure consists of drilling holes on both sides of the crack, cleaning the holes, and anchoring the legs of the staples in the holes, with either a non shrink grout or an epoxy resin-based bonding system.

Stitching with steel bars

COSMETIC REPAIRS Cont…

DRY PACKING:

* Dry packing is the hand placement of a low water content mortar followed by tamping or ramming of the mortar into place, producing intimate contact between the mortar and the existing concrete. Because of the low water-cement ratio of the material, there is little shrinkage, and the patch remains tight and can have good quality with respect to durability, strength, and water tightness.

* Dry pack can be used for filling narrow slots cut for the repair of dormant cracks. The use of dry pack is not advisable for filling or repairing active cracks.

COSMETIC REPAIRS Cont…

PROCEDURE:

* Before dry packing, the portion of crack should be widened to a slot about 25mm wide and 25mm deep. The slot should be undercut so that the base width is slightly greater than the surface width.

* To minimize shrinkage, the mortar should stand for 1/2 hour after mixing and then should be remixed prior to use. The mortar should be placed in layers about 10 mm thick.

* Each layer should be thoroughly compacted over the surface using a blunt stick or hammer, and each underlying layer should be scratched to facilitate bonding with the next layer. The repair should be cured by using either water or a curing compound.

Dry packing of crack

COSMETIC REPAIRS Cont…

GROUTING:

* Wide cracks, may be repaired by filling with Portland cement grout. This method can not structurally bond cracked sections.

PROCEDURE:

* Remove loose mortar and concrete. The cracks are flushed with water and then filled with pre-hydrated mortar. Injection holes are to be drilled, although not entering any air space. The holes are flushed with water. Grout is mixed and then pumped into the holes. Injection should start at the bottom and work upwards. Grout is injected at a port until grout flows from the adjacent holes.

COSMETIC REPAIRS Cont…

* However, the water-cement ratio should be kept as low as practical to maximize the strength and minimize shrinkage. After the crack is filled, the pressure should be maintained for several minutes to insure good penetration.

STRUCTURAL REPAIR

SPALL REPAIR:

* Spalls are small sections of element or wall that become loose or dislodged. The missing material is replaced with a suitable patch. The material used for the patch must have structural and thermal properties similar to the existing material. The materials and procedures for the patch will also depend on the size and location of the spall.

* Portland cement and latex-modified cement or epoxy and polyester mortar mix materials can be used

STRUCTURAL REPAIR Cont…

PROCEDURE:

* Remove all loose material with chipping hammers

* Remove concrete to provide sufficient clearance around the bar

* The perimeter of the spall to be cut to create an edge perpendicular to the original surface

* For large patches, new steel dowels should be set in to the substrate with epoxy.

* The mortar is applied with a trowel in lift.

* The surface is finished

* The patch is then cured

Spall Repair of Column

Spall Repair of Beam

STRUCTURAL REPAIR Cont…

REBAR REPLACEMENT:

* This method is used when the structural element is damaged and fractures have occurred in reinforcing bars, or where conventional lapped bar splices have failed. The method consist of replacing the bars. Mechanical connections can be used to connect or splice two pieces of reinforcing bar. Structure or element is to be supported carefully before removing damaged portion.

PROCEDURE:

* Support the structure with formwork

STRUCTURAL REPAIR Cont…

* Remove all loose material with chipping hammers

* Remove concrete to provide sufficient clearance around the bar

* Cut out the old steel

* The perimeter of the spall to be cut to create an edge perpendicular to the original surface

* Clean the surface

* New steel should be set in to the substrate with epoxy.

* The mortar is applied with a trowel in lift, or shotcrete is to be done for large scale work or dry packing can be done

* The surface is finished

* Required curing is to be done

Rebar Replacement of column

Rebar Replacement of Beam

Rebar Replacement of Beam

STRUCTURAL ENHANCEMENT

STRUCTURAL OVERLAY – CONCRETE AND STEEL:

* This method is used to improve the seismic performance of a damaged structure to a level better than that of the pre-event structure. Overlay can be of steel and concrete both.

* Overlay concrete is applied pneumatically or as cast in place layers. The concrete is reinforced and attached to the existing structure to enable the concrete to provide supplement strength.

* In steel overlay steel angles, plates and flats are used. They are welded as per technique adopted.

STRUCTURAL ENHANCEMENT Cont..

PROCEDURE:

* Prepare surface by removing loose or damaged materials

* The surface is to be chipped or scarified to avoid abrupt changes in dimension.

* Reinforcing steel is to be installed and securely anchored in to existing element using dowels set in epoxy.

* Before applying shotcrete, surface is to be pre-wetted

* Shotcrete the surface

* Shotcrete is applied in several passes, on vertical surface starting from base

* Finish the surface

* Cure the surface

Concrete Overlay on beam

Concrete Overlay on beam

Concrete overlay on beam and slab

Concrete overlay on column

Concrete overlay on column

Concrete overlay on shear wall

Concrete overlay on slab

Adding steel beams on each side of an existing concrete beam

Adding steel member on each side of an existing concrete beam

Adding steel member on an existing concrete beam

Adding steel member on each side of an existing concrete beam

Adding steel member on top and bottom of an existing concrete beam

Steel overlay on existing concrete column

Steel jacketing Steel cage technique Steel plates

using steel straps

Adding steel angle on each side of an existing concrete column

STRUCTURAL ENHANCEMENT Cont..

STRUCTURAL OVERLAY – COMPOSITE FIBERS:

* In this method thin glass or carbon fibres woven into a fabric sheet are applied to the surface of the element to enhance the stiffness and strength of the element. The fibres are generally applied to surface using an epoxy resin binder.

* The composite fibres are used as tension reinforcing for member

STRUCTURAL ENHANCEMENT Cont..

PROCEDURE:

* Prepare surface by removing loose or damaged materials

* Repair cracks and spalls

* Prepare surface by lightly sandblasting

* Apply a thin epoxy primer coat on the surface

STRUCTURAL ENHANCEMENT Cont..

* The composite fibres are saturated in epoxy and are pressed into the binder epoxy with a roller

* Number of layers and orientation of the layers depends on the design requirement

* The epoxy is then allowed to cure for at least 24hrs.

* Non structural coating is to be done (Paint, Plaster, etc.)

Composite fibre overlay on column

Composite fibre overlay

COMPARISON BETWEEN OVERLAYS

EFFECT OF REPAIR ON MEMBERS

EFFECT OF RETROFIT ON MEMBERS Cont…

CASE STUDY

CASE STUDY – 1

* Location: Ahmedabad

* Type of structure: R.C.C. Framed structure

* Floors: Parking + 10 stories + Pent house

DISTRESS:

� There were few cracks in beams and columns

� No distress was observed in the column

CASE STUDY – 1 Cont…

RESTORATION WORK:

* Appropriate design and execution of rehabilitation measures was done as per codes and established guideline

* Condition survey was done for the building and a retrofitting plan was laid-down for the structure.

* Cracks in beam and column were sealed with epoxy grout

* The beam-column joints in the structure were strengthened

Beam-Column Joint strengthening

CASE STUDY – 1 Cont…

* Sandwiching brick shear wall were formed by placing reinforcement on both faces of existing partition wall and shotcreting of 40mm

CASE STUDY – 1 Cont…

* The stub columns were supported by steel props, below the line of action of the stub-column, for realising the cantilever beam

CASE STUDY Cont…

CASE STUDY – 2

* Location: Ahmedabad

* Type of structure: R.C.C. Framed structure

* Floors: Block-A , G.F. + 4

Block-B, Basement + G.F. + 3

* Column nos. 32 (Section: 230mm x 450mm)

* Slab thickness: 150mm

* Lift wall: R.C.C

* Water tank: R.C.C (5500 lts.)

DISTRESS:

� Crushing of concrete and buckling of bars in columns

� Cracks perpendicular and along flight

� Separation of flight supporting beams and junctions

Plan

CASE STUDY – 1 Cont…

RESTORATION WORK:

* Repair of cracks

* Strengthening of staircase by

steel overlay

* Construction of plinth beams

* The columns in the structure

were strengthened by steel overlay

CASE STUDY Cont…

CASE STUDY – 3

* Location: Ahmedabad

* Type of structure: R.C.C. Framed structure

* Floors: Parking + 4 stories

DISTRESS:

� Concrete from the columns had been chipped-off

� Cracks in beams

RESTORATION WORK:

� Cracks were repaired by epoxy grout

� Repair of damaged columns by shotcreteing mortar on the columns of the ground and first-story

Repair work under progress of the damaged columns

Reinforcement was extended to the footing

Repair work under progress of the damaged columns

CASE STUDY Cont…

CASE STUDY – 4

* Location: Hyogoken, Japan, 1995

* Type of structure: R.C.C. Framed structure

DISTRESS:

* After the 1995 Hyogoken-Nanbu earthquake, design codes in Japan were modified. To meet the requirements of new design codes Improvement was required

RESTORATION WORK:

* Building structures were mainly retrofitted by FRP Overlay to meet the requirement of new design codes

Application of FRP sheets

FRP on Column FRP on Slab

Application of FRP sheets

Application of FRP sheets

REFRENCES

* Federal Emergency Management Agency, FEMA 308 / May 1999

* Federal Emergency Management Agency, FEMA 547 / May 1999

* Handbook on repair and rehabilitation of RCC Buildings Published by Director General (Works), C.P.W.D, G.O.I, Nirman Bhawan, 2002

* Assessment of Damage to Framed RCC Structures in Gujarat Earthquake and Retrofiting With Fiber Wrapping Techniques by B.V.Bhedasgaonkar, Pune.

* Repair and Strengthening Methods of Earthquake Damaged RC Structures by S. Pareek, Y. Hayashi and S. Sawada

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