CE2071 - REPAIRS AND REHABILITATION OF STRUCTURES

  

OBJECTIVETo  get  the  knowledge  on  quality  of  concrete, durability  aspects,  causes  of  deterioration, assessment  of  distressed  structures,  repairing  of structures and demolition procedures.

UNIT – IMAINTENANCE AND REPAIR STRATEGIES

 

Syllabus:Maintenance, repair and rehabilitation, Facets of  Maintenance,  importance  of  Maintenance various  aspects  of  Inspection,  Assessment procedure for evaluating a damaged structure, causes of deterioration

Definition:Maintenance of building is

defined as the work done to keep the civil engineering structures in working condition so as to enable them to carry out the functions for which they are constructed.

MAINTENANCE

Necessity of maintenanceThe maintenance of structures is done to meet the following objectives.

· Prevent damages and decay due to natural agencies and wear & tear - to keep them in good appearance and working condition.

· Repair defects occurred in structures and strengthen them, if necessary.

Maintenance work on dam structure

Classification of Maintenance Work:

· Preventive Maintenance· Remedial Maintenance· Routine Maintenance· Special Maintenance

Preventive Maintenance:-before the defects occurred or

damages developed

Remedial Maintenance:-after the defects or

damage occurs in the structures. It involves the following basic steps.• Finding the deterioration .• Determining the causes.• Evaluating the strength of the existing structures.• Evaluating the need of the structures.•Selecting and implementing the repair procedure

Routine Maintenance:• maintenance attended to the structure periodically.

• It depends upon specifications and materials of structures ,purpose , intensity and condition of use .

•It is done by the fund provided annually, which is normally 1.5% of the cost of construction.

•It includes the inspection, planning the programme and execute.

•It includes white washing, patching repair to plaster, replacement of fitting and fixtures, blinding of road surface.

Special Maintenance:• work not covered in routing programme or the annual repair

- is done under special condition • It may be done for strengthening and updating of the structure

- to meet the new condition of usage or to increase its serviceability.•It include particular or complete renewal, such as renewal of floors, roofs etc

Special Maintenance

Causes which necessitate the maintenance:

The causes which effects the service and durability of the structure are as follows:        · Atmospheric Agencies 1. Rain 2. Wind 3. Temperature.        · Normal wear and tear.        · Failure of structure.

Atmospheric Agencies1. Rain:

-important source of water which affects the structure in the following ways.

Physical:Dissolving and carrying away minerals as it

is universal solvent.

Expansion and contraction:- materials subjected to repetitive

expansion and contraction - while they become wet and dry and

develop the stresses.Expansion of water:- variation of temperature causes the

expansion and construction of absorbed water affects the micro structures of the materials.

Erosion:Abrasion of the structure materials is quite

evident effect of the water.

Spillway damage 

Chemical:Water contains acids and alkali and

other compound in dissolved form, acts over the material

-which is known as chemical weathering.

H2S corrosion on the concrete walls

2.Wind:which transports the abrasive materials and assists the physical weathering.

3.Temperature: The temperature variation may also change in the structure and chemical composition of the materials.

Normal wear and tear:During the use of structure it is subjected

to abrasion and there by it losses appearance and serviceability.

Concrete damage was found to be a serious threat to the structural integrity of spillway.

Failure of structure:

-behavior of structure not in agreement with expected condition of stability

-or lacking freedom from necessary repair or non- compliance with desired use of and occupancy of the completed structure.

The causes of failure may be broadly grouped as:         · Improper design.         · Defective construction.         · Improper use of structure         · Lack of maintenance.

Inspection of a Building:Inspection of a building and any other

civil engineering structure is routine duty of person in charge maintenance.

-It means keen, analytic and dynamic observation regarding •the change in condition of the structure

deterioration•reason and the causes, failure •concluding the remedies for the same.

The inspections should be made on the following points.• Condition of wall paint.• Condition of paint on wood- work.• Condition of flooring•  Roof leakage, leakage. if any• Dampness in wall or floors, if any• Condition of service fittings.• Drainage from terrace or pitched like

· Growth of vegetation, if any· Structural defects like

1. Crack2. Settlement3. Deflection (sagging)

CAUSES OF DETERIORATION

1. Local settlement of sub-grade. 2.  Movement of formwork. 3.  Vibrations 4.  Internal settlement of concrete suspension. 5.  Setting shrinkage.

6. Premature removal of forms. 7. Drying shrinkage8. Temperature stresses

This may be due to(i)Difference in temperature between

the inside and outside of the building.(ii)Variation in internal temperature of

the building structure.9. Absorption of moisture by concrete

10. Corrosion of reinforcementThis could be caused by(i)Entry of moisture through cracks or

pores(ii)Electrolytic action

11. Aggressive action of chemical12. Weathering action 13. Action of shockwaves 14. Erosion

15. Weathering action16. Action of shockwaves17. Erosion18. Poor design details at

(i) Re- entrant corners(ii) Changes in cross section (iii)Rigid joint precast elements (iv)Deflections

Poor design details leads to1. Leakage through joints2. Inadequate drainage3. Inefficient drainage slope4. Unanticipated shear stresses in piers, column

and abutments etc..,5. Incompatibility of materials of sections.6. Neglect in design7. Errors in design8. Errors in earlier repairs9. Overloading10. External influences such as(a) Earthquake

(b) Wind(c) Fire(e) Cyclone(f) Flash floors etc..,