Repairs to overcome low member strength
Need for Strengthening:
ü Load increases due to higher live loads, increased wheel loads, installations of heavy machinery or vibrations
ü Damage to structural parts due to aging of construction materials or fire damage, corrosion of the steel reinforcement, and impact of vehicles
ü Improvements insatiably for use due to limitation of deflections, reduction of stress in steel reinforcement and reduction of crack widths
ü Special Modification of structural system due to the elimination of walls/columns and openings cut through slabs.
ü Errors in planning or construction due to insufficient design dimensions and insufficient reinforcing steel.
Deflection due to strengthened in Flexural members
Many situations in which flexural members, and especially bridge girders, have been found to have less than their special attention was paid to the paid to the bond between the old concrete and the new anchor blocks. The existing concrete was cut back to the depth of the cover and roughened.
After the new block had been cast in-situ the contact surface was injected with low viscosity epoxy resin under pressure, the injection being monitored ultrasonically. Some of the new tendons were deflected at existing diaphragms, reinforced required.
Deflection due to Strengthening of slabs
The strengthening of slab is taken up only after the strengthening of beams is completed. A reinforced structural concrete topping over the existing slab can be used which provides a composite construction of old and new slabs, with additional depths to slab and beam.
To ensure a good bond between new and old concretes, mechanical anchorage consisting of steel bolts inserted in holes drilled into the slab at suitable intervals may be provided. The spaces surrounding the holes are filled with epoxy grout.
Deflection due to Strengthening of columns
Jacketing is the process of fastening a durable material over concrete and filling the gap with a grout that provides needed performance characteristics.
The column jacket can also be used for increasing the punching shear strength of column slab connections by using it as a column capital. When the jacket is provided around the periphery of the column, it is termed a collar. In most of the applications, the main function of the collar is to transfer vertical load to the column. Circular reinforcement can be used for load transfer. The practice of transferring load through dowel bars embedded into columns or shear keys has a disadvantage in that they require drilling of holes for dowels or cutting shear keys which are costly and time consuming, and can damage the existing column. Reinforcement encircling the column can be used to transfer the load through shear friction. The expansion of collar as it slides along the roughened surface causes the tensioning of circular reinforcement resulting in radial compression, which provide normal force needed for load transfer. The shear transfer strength is provided by both frictional resistance to sliding and dowel action of reinforcement crossing the crack.