Strengthening Techninques

Prior to the repair of structural members, a structural analysis must be perform to determine if the members are overloaded or under designed for the service loads.

Interior Reinforcing:A common method of providing additional reinforcement across cracked surfaces is to install new dowels into holes drilled perpendicular to the crack surfaces. The entire length of the dowel is fixed into the concrete by use of bonding matrix.

Exterior Reinforcing

Steel elements may be placed on the exterior of an existing concrete member

The new reinforcement may be encased with shotcrete, mortar, plaster, or other product, or it may be left exposed and protected from corrosion with a coating

Placement of exterior reinforcement may be the most convenient method for repair and strengthening where obstructions limit access of equipment needed for placement of interior reinforcement.

Passive and Active Design

Passive strengthening

Attachment of Steel to Concrete

Exterior post-tensioning

Girders and slabs may be strengthened in both flexure and shear by addition of external tendons, rods, or bolts which are prestressed.

The use of high strength prestressing reinforcement effectively reduces the amount of reinforcement required in the repair and strengthening procedure.

The prestressing also provides beam camber which help to reduce deflection.

The addition of a single post-tensioning arrangement increase both shear and flexural strength.

Placement and stressing of prestressing strands and rods is often difficult in congested buildings and interior locations.

Externally Placed Post Tensioning

Summary of Techniques

Internally Placed Post Tensioning

Summary of Techniques

Jackets

Jacketing is the process whereby a section of an existing structural member is restored to original dimensions or increased in size by encasement in new portland cement or polymer-modified portland cement concrete.

A steel reinforcement cage is constructed around the damaged section onto which shotcrete or cast-in- place concrete is placed.

A variety of materials including conventional concrete and mortar, epoxy mortar, grout and latex-modified mortar and concrete have been used as encasement materials.

Techniques for filling the jacket include pumping,tremie or preplaced aggregate concrete.

Jacketing is particularly applicable in repair of deteriorated columns, piers, and piling where all or a portion of the section to be repaired is under water

Beam Overlay

Concrete Overlay and Section Enlargement

Overlay on Top of Slab

Concrete Overlay and Section Enlargement

Beam Overlay

Concrete Overlay and Section Enlargement

Combination Slab and Beam Overlay

Concrete Overlay and Section Enlargement

Soffit Slab Overlay

Concrete Overlay and Section Enlargement

Method A

Column compressive strengthening by section enlargement

Method B

Column compressive strengthening by section enlargement

Method C

Column compressive strengthening by section enlargement

Elevation view of Method A

Column compressive strengthening by section enlargement