1. ASSESSEMENT AND REHABILITATION OF STRUCTURES
Course Code: CIVL524
Dr. Aeid A. Abdulrazeg

2. Plate bonding using steel or fibre reinforced plastic

3. Introduction
A significant proportion of current expenditure in the world, relating to repair and maintenance of existing structures, is directed towards maintenance and upgrading of its concrete infrastructure.
The effects of environment (harsh climate, de-icing salts, seismic activity, etc. ), the increase in both traffic volume and truck weights, and changes in the design codes which necessitate a re-evaluation of older structures, are factors which contribute to the infrastructure becoming either structurally deficient or functionally obsolete.
Upgrading usually involves strengthening of existing members to carry higher ultimate loads and/or satisfy more stringent serviceability requirements. Provided, rapid, effective, and simple upgrading methods are available, strengthening of existing structures becomes both environmentally and also economically preferable to demolition and rebuilding.

5. Traditional Methods for Strengthening Solutions
Strengthening solutions of RC members can range from repair of damaged members so that their original load-carrying capacity is restored, to adding elements to increase their strength. All solutions are project-specific to a certain application but some general approaches are commonly utilized. The most traditional techniques for strengthening the RC structures are as follows:
Increase the reinforced concrete cross-section
Add prestressing to relieve the dead load
Use plate bonding to enhance tensile reinforcement of the RC elements
Add confining elements to improve behavior of the concrete in the compression members
Shear strengthening by installing external straps

6. With the development of strong epoxy adhesives back in the 1960's, bonding external steel or fibre reinforced plastic (FRP) plates to the tension side of reinforced concrete beams, Figure 1, It has proved very attractive for increasing the flexural strength of beams and/or slabs: such externally bonded plates supplement the area of internal tension reinforcement and are, indeed, more effective (in terms of bending resistance) than the reinforcing bars, because the plates are located at a maximum possible distance from the centroid of the concrete compressive stress block.

7. Advantages of external plate steel bonding technique
The external plate bonding technique offers certain advantages when compared with other strengthening techniques and has, indeed, been extensively used in practice for both buildings and bridges, in a large number of countries.
The work can be carried out relatively simply and quickly, even while the structure is still in use, and its application causes minimal changes in the member dimensions (including overhead clearance) and negligible increases in the self-weight.
It does not alter the configuration of the structure.
Plates bonded to the tension side of reinforced concrete beams can be used to improve performance under service loads, by, for example, reducing cracking or deflections, and increase ultimate load in flexure. The plated member can carry the live load or live and dead load if propping is used.

8. Disadvantages of external plate steel bonding technique
Traditional steel based reinforcement systems for concrete elements are facing with serious problems mainly caused by corrosion due to chemically aggressive environments and salts used in deicing procedures especially in case of bridge steel reinforced concrete girders. Also in some cases special applications require structural members with magnetic transparency. An alternative to this major problem has recently become the use of fibre reinforced polymer (FPR) composite bars as internal reinforcement.
Reinforced concrete beams and slabs strengthened by external plates are usually designed for flexure on the basis of conventional ultimate load procedures such as, for example, those recommended by the British Standard BS8110, assuming full bond between concrete and the plate up to ultimate load, and using the plane section bending assumption and a concrete stress block at failure

9. . However, as repeatedly reported in the literature, the designer should also check that premature anchorage failure (Figure 2) caused by peeling and debonding of the plate at its end, in a brittle fashion, does not occur prior to the beam achieving its full flexural strength

11. Steel Plate Dimensions
Some researchers adopted expressions to attain a desirable or rational design for externally bonded plates; these expressions can be arranged as follows:
The width of plate and therefore interface layer is limited by the size of concrete section and is recommended to be at most 20mm less than the concrete beam width , so that:
The thickness of the plate must be equal to / or less than the plate thickness at balance load conditions and the maximum plate thickness to ensure a ductile flexural failure

12. Two tentative design criteria are suggested to ensure the full flexural capacity of the beam and ductility at failure
c, cb: neutral axis distance from top fiber in general at balance load conditions respectively.
bc, bg, bp, bpmax: concrete, glue layer, plate and the maximum width of plate respectively.
tg, tp, tpb, tpmax: glue, plate, plate at balance cond. and the max. thickness of plate respectively.
ß1: factor depending on concrete compressive strength (0.65 – 0.85).

13. Analysis of Section
0.45fcu
Fst
Fsp

16. Analysis of Section
Fsc
Fst
Fsp