ce1035 – repair and rehablitation of structures

CE 2071– REPAIR AND REHABLITATION OF STRUCTURES

(FOR VIII – SEMESTER)

UNIT – I

MAINTENANCE AND REPAIR STRATEGIES

Compiled by,

R.SURYA M.E;

ASSISTANT PROFESSOR

DEPARTMENT OF CIVIL ENGINEERING

SRI VIDYA COLLEGE OF ENGINEERING & TECHNOLOGY

VIRUDHUNAGAR

www.Vidyarthiplus.com


UNIT – I

MAINTENANCE AND REPAIR STRATEGIES

Maintenance, repair and rehabilitation, Facts of Maintenance, importance of

maintenance, various aspects of Inspection, Assessment procedure for evaluating a

damaged structure, causes of deterioration.

MAINTENANCE.

Maintenance is preventive in nature. Activities include inspection and works,

necessary to fulfill the intended function or to sustain original standard of service.

TYPES OF MAINTENANCE

i. Daily Routine maintenance.

ii. Weekly Routine maintenance.

iii. Monthly Routine maintenance.

iv. Yearly Routine maintenance.

CLASSIFICATION OF MAINTENANCE:

1. PLANNED MAINTENANCE

It improves uptime and quality of output and reduces repair maintenance costs

through the continuous quality improvement of equipment operation.

Planned Maintenance provides guidelines for a total system of activities in which all

employees work to improve the quality of product output, increase production

uptime, reduce costs of operations and reduce the amount and complexity of

machinery required.

It includes scheduled and unscheduled maintenance programs with strategies for

responding to machinery and equipment failures.

Planned maintenance includes two main activities: A) PREVENTIVE MAINTENANCE

It is a schedule of planned maintenance actions aimed at the prevention of

breakdowns and failures.

The primary goal of preventive maintenance is to prevent the failure of equipment

before it actually occurs.

It is designed to preserve and enhance equipment reliability by replacing worn

components before they actually fail.

Preventive maintenance activities include equipment checks, partial or complete

overhauls at specified periods, oil changes, lubrication and so on. In addition,



workers can record equipment deterioration so they know to replace or repair worn

parts before they cause system failure.

Recent technological advances in tools for inspection and diagnosis have enabled

even more accurate and effective equipment maintenance.

The ideal preventive maintenance program would prevent all equipment failure

before it occurs.

B) CORRECTIVE MAINTENANCE:

Corrective maintenance consists of the action(s) taken to restore a failed system to

operational status.

This usually involves replacing or repairing the component that is responsible for

the failure of the overall system.

Corrective maintenance is performed at unpredictable intervals because a

component's failure time is not known a priori.

The objective of corrective maintenance is to restore the system to satisfactory

operation within the shortest possible time.

Corrective maintenance is typically carried out in three steps:

1. Diagnosis of the problem. The maintenance technician must take time to locate the

failed parts or otherwise satisfactorily assess the cause of the system failure.

2. Repair and/or replacement of faulty component(s). Once the cause of system failure

has been determined, action must be taken to address the cause, usually by

replacing or repairing the components that caused the system to fail.

3. Verification of the repair action. Once the components in question have been

repaired or replaced, the maintenance technician must verify that the system is

again successfully operating.

2. ROUTINE MAINTENANCE:

Routine maintenance is such activities as cleaning, dusting, lubricating, checkup of

important parts such as battery.

These activities are to be performed on a daily or weekly basis. Some of these form

part of scheduled maintenance.

Routine maintenance, normally does not involve any replacement of parts

3. SCHEDULED MAINTENANCE:



Scheduled maintenance is a maintenance activity undertaken on equipments as per

a plan of action, which gives the sequence in which various jobs would be attended.

The schedule gives the calendar day and time at which a particular job is

undertaken.

A maintenance schedule is prepared for a week. As the job content of maintenance

activity is variable, the schedule for the next day is usually firmed up at the end of

each day.

The scheduled maintenance activities may be preventive or break down in nature.

The maintenance schedule is prepared based on certain rules such as:

1. First come first served

2. Emergency priority job first

3. Shortest competition time job first.

4. Longest competition time job first

5. Random

4. PREDICTIVE MAINTENANCE:

Predictive maintenance allows plant management to control the machinery

and maintenance programs rather than vice versa.

In a plant using predictive maintenance, the overall machinery condition at

any time is known, and much more accurate planning is possible.

Predictive maintenance utilizes many different disciplines, by far the most

important of which is periodic vibration analysis.

It has been shown many times over that of all the non-destructive testing

that can be done on a machine; the vibration signature provides the most

information about its inner workings.

The resulting benefits of preventive maintenance are many. Some of them are listed

below:

Safety. Machinery that is not well maintained can become a safety hazard.

Preventive maintenance increases the margin of safety by keeping

equipment in top running condition.

Lower cost. A modern and cost-effective approach to preventive

maintenance shows that there is no maintenance cost optimum. However,

maintenance costs will decrease as the costs for production losses decreases.

No preventive maintenance action is performed unless it is less costly than

the resulting failure.



Reduction in failures and breakdowns. Preventive maintenance aims to

reduce or eliminate unplanned downtime, thereby increasing machine

efficiency. Downtime is also reduced when the preventive maintenance

process gives maintenance personnel sufficient warning so repairs can be

scheduled during normal outages.

Extension of equipment life. Equipment that is cared for will last longer

than equipment that is abused and neglected.

Improved trade-in/resale value of equipment. If the equipment is to be

sold or traded in, a preventive maintenance program will help keep the

machine in the best possible condition, thereby maximizing its used value.

Increased equipment reliability. By performing preventive maintenance

on equipment, a firm begins to build reliability into the equipment by

removing routine and avoidable breakdowns.

Increased plant productivity. Productivity is enhanced by the decrease in

unexpected machine breakdown. Also, forecast shutdown time can allow the

firm to utilize alternate routings and scheduling alternatives that will

minimize the negative effect of downtime.

Fewer surprises. Preventive maintenance enables users to avoid the

unexpected. Preventive maintenance does not guarantee elimination of all

unexpected downtime, but empirically it has proven to eliminate most

downtime caused by mechanical failure.

Reduced cycle time. If process equipment is incapable of running the

product, then the time it takes to move the product through the factory will

suffer. Taninecz found, from an Industry Week survey, that there is a strong

correlation between preventive maintenance and cycle-time reductions as

well as near-perfect on-time delivery rates. Also, approximately 35 percent of

the surveyed plants who widely adopted preventive maintenance achieved

on-time delivery rates of 98 percent, compared to only 19.5 percent for non-

adopters.

Increased service level for the customer and reduction in the number of

defective parts. These have a positive direct effect on stockouts, backlog,

and delivery time to the customer.



Reduced overall maintenance. By not allowing machinery to fall into a

state of disrepair, overall maintenance requirements are greatly decreased

FACETS OF MAINTENANCE:

The avoidance of accidents, which may harm people.

The continued operation of facility.

The protection of the capital investment in the asset.

IMPORTANCE OF MAINTENANCE.

It improves the life of structure.

Improved life period gives better return on investment.

Better appearance and aesthetically appearing.

Leads to quicker detection of defects and hence remedial measures.

Prevents major deterioration that leads to collapse.

Ensure safety occupants.

REPAIR.

Repair is the technical aspects of rehabilitation. It refers to the modification

of a structure, partly or wholly, which is damaged in appearance or serviceability.

REPAIR ASPECT OF MAINTENANCE.

Even though designers allow a large margin of safety in their designs, once

deterioration reaches a critical limit, immediate repair is needed to restore the level

of

performance to its intended level of service. In fact if the rehabilitation work is not

carried out in time, the structure may not be repairable to the required level of

service.

The execution of such a repair is an exacting, technical matter involving 5 basic

steps.

i. finding the deterioration

ii. determining the cause

iii. evaluating the strength of existing building or structure

iv. evaluating the need of repair

v. Selecting & implementing a repair procedure.

I)FINDING THE DETERIORATION

Before the repair can be effected, there must be a realization that something is



wrong, and the realization must come before it is too late to; make a repair, ie before

the

structure has collapsed

For eg:- timbers and timber piling can be damaged by insects or marine

organisms, virtually to the point of collapse, without exhibiting any external

evidence

which would be apparent except to a trained observed. Even a common defect like

corrosion of steel can be difficult to detect because if occurs, principally, in the most

inaccessible parts of the structure. The reason is simple. The accessible parts are

painted, but the inaccessible parts often are neglected.

The point to be made is that is that the engineer charged or interested in

maintenance must be trained, technically, in where to look, how to look & what to

look

for, before he can even be expected & realize that there is trouble knowing all these

requires a knowledge of various kinds & causes of deterioration & before checking

the

engineer must know all these.

II) DETERMINE THE CAUSE

To select the repair step, the cause has to be identified. In case of concrete the

specific cause might not be known due to several agents acting. What can be done is

to

Eliminate possibilities and design repair procedures for any of the remaining few. In

such cases the cost will go higher. But it should also be noted that the failure to

understand the cause of a defect fan lead to the selection of a repair procedure

which

would be harmful, rather than helpful.

For eg:- (racks in walls due the foundation settlements run diagonally)

(Cracks due to corrosion of reinforcement run straight & parallel at uniform

intervals &

show evidences of rust, staining)

A few tips are as follows

a. Inspect & observe the structure

b. Observe in bad & good weather



c. Compare with other constructions on the area or elsewhere & be patient

d. Study the problem & allow enough time to do the job

III) EVALUATE THE STRENGTH OF THE EXISTING STRUCTURE

This should be done to know whether it is safe to continue using the structure or

limit it to a less severe extend of usage if the structure has not completely

deteriorated

the adequacy of determination of strength becomes important for that the following

methods can be used

A) FIXED PERCENTAGE METHOD

It is to assume that all members which have lost less than some

predetermined % of their strength are still adequate and that all members

which have lost more than the strength are inadequate. It is usually from 15%

onwards higher values are applicable for piling % stiffness bearing plates etc

B) ANALYSIS OF THE ACTUAL STRESS CONDITION:

This method is to make detailed stress analysis of the structure, as it

stands including allowances for loss of section where it has occurred. This is

more difficult & expensive. Here also the first stop is to make preliminary

analysis by fixed percentage method and if it appears that major repairs will

be required, the strength is reevaluated based on detailed stress analysis,

considering all contributions to such strength.

C) LOAD TEST

Third step is load test. Load tests may be required by the local building

Offered, but they should only be performed where computation indicated that

there is reasonable margin of safety against collapse, lest the test bring the

Structure sown. Load test show strengths much greater than computed

Strengths when performed on actual structures. When performed on actual

Structures. In repair work every little bit of strength is important.

Accordingly the use of load test is recommended but with a full & clear

Understanding of their limitations and range of applicability.

IV) EVALUATE THE NEED OF REPAIR

When the cause of the deterioration has been determined and the strength of the

Existing structure has been checked, a decision must be made whether



a. To permit deterioration to continue

b. To make measures to preserve the structure in its present condition

c. Without strengthening

d. To strengthen the construction

e. If deterioration is exceptionally sever, to reconstruct or possibly abandon it.

These decisions are based on

safety

economy &

appearance subject to various principles different decision may

beappropriate for different elements of same structure

Case – a] Analysis show that structure still has adequate strength

If the appearance of the existing condition is objectionable – repair

Now

If appearance is not a problem then

Put the condition under observation to check if it is dormant or Progressive.

If dormant – no repair

If progressive – check the feasibility & relative economics of Permitting

deterioration to continue and performing a repair at some later Date & of making

the repair right away

Case – b] Analysis shows that the strength of the structure currently is or sowty will

be

in adequate

Either repair it or

Rebuild it or

Abandon it, partly or completely or

consider a change of use

V) SELECT & IMPLEMENT A REPAIR PROCEDURE:

Consider total cost

Do repair job in time

If defects are few & isolated repair on an individual basis.

Otherwise do in generalized manner

Ensure the repair prevents further development of defects

In case of lost strength, repairs should restore the strength



If appearance is a problem, the number of applicable types of repairs become

limited & the repairs must be covered

Repair works should not interface with facilities of the structure

Take care in addition of section to a member and in reattributing live loads and

other live load moments.

After selecting a suitable method of repairs, and after considering all the

ramifications of its application, the last step is to prepare plans & specification and

proceed with the work.

REHABILITATION.

Rehabilitation is the process of restoring the structure to service level, once it

had and now lost, strengthening consists in endowing the structure with a service

level, higher than that initially planned by modifying the structure not necessarily

damaged structure.

FACTORS TO BE CONSIDERED BY THE DESIGNER AT THE CONSTRUCTION SITE.

Minimum and maximum temperatures

Temperature cycles

Exposure to ultra violet radiation

Amount of moisture

Wet/dry cycles

Presence of aggressive chemicals

STAGES OF INSPECTION AND MAINTENANCE

Inspection

Analysis

Action Possibilities.

DETERIORATION a symptom of reduced quality or strength(or)

process of changing to an inferior state(or)

The process of becoming progressively worse.

CAUSES OF DETERIORATION 1. Deterioration due to corrosion 2. Environmental effects 3. Poor quality material used 4. Quality of supervision 5. Design and construction flaws

1.DETERIORATION OCCURS DUE TO CORROSION A.SPALLING OF CONCRETE COVER



Spalling concrete is concrete that has broken up, flaked, or become pitted. This is usually the result of a combination of poor installation and environmental factors that stress the concrete, causing it to become damaged. On a low level, it can be purely cosmetic in nature, but it can also result in structural damage, such as damage to reinforcing bars positioned inside the concrete. For this reason, it is important to address spalling when it first starts to appear.

The signs of spalling are easy to spot. The surface will become rough and flaky, and may pit. In some cases, chunks of concrete break loose from the installation. The concrete can also start to crack, especially if large chunks break off. It can be repaired by totally removing the damaged section of concrete and filling it in with cement.

The best time to address spalling is when concrete is first poured, by taking steps to prevent it from occurring in the first place. The concrete should be mixed with the right amount of water, and ideally the mix kept as dry as possible because a high water content can weaken the material.

It also needs time to cure properly and should be handled carefully during curing. Sealing the concrete can also protect it from the elements. There are a number of sealants available for concrete and they can also work with a decorative finish.

B.CRACKS PARALLEL TO THE REINFORCEMENT.

CONCRETE CRACKING DUE TO CORROSION OF REINFORCEMENT

The corrosion of steel reinforced concrete member by the formation of electro-chemical cell results in cracking (characteristically parallel to the reinforcement), spalling or in delamination of concrete.

This corrosion may occur due to chloride attack and carbonation.

MECHANISM OF CRACKING

The corrosion of steel results cracking and further deeper propagation of cracking in two successive steps. Firstly The production of corrosion occupies a volume several times larger than the original steel so that their formation results in cracking. This makes it easier for aggressive agents to ingress towards the steel, with a consequent increase in the rate of corrosion. Secondly The progress of corrosion at the anode reduce the cross-sectional area of steel,



http://www.wisegeek.com/what-is-spalling.htm

http://www.wisegeek.com/what-are-the-different-types-of-sealants.htm

thus reducing its load carrying capacity resulting increase in deflection encouraging cracks to be pronounced.

Location of appearance These are normally seen in columns and beams where environment is in favor of corrosion.

Cause of cracking Normally poor quality concrete is subjected to such types of cracking. Inadequate clear cover also makes easy intrusion of aggressive materials like chloride or results carbonation.

Remedy Good quality concrete adding suitable admixture depending on the environment surroundings of desired concrete member. Providing adequate clear cover also discourage cracking of this type. C.SWELLING OF CONCRETE



Swelling, turgescence or tumefaction is a transient abnormal enlargement of a body part or area not caused by cells. It is caused by accumulation of tissues. It can occur throughout the body (generalized), or a specific part or organ can be affected (localized).

Swelling is considered one of the five characteristics of inflammation; along with pain, heat, redness, and loss of function.

D.DISLOCATION INTERNAL CRACKING & REDUCTION IN AREA OF STEEL

REINFORCEMENT

CAUSES OF DETERIORATION 6. Deterioration due to corrosion

7. Environmental effects

8. Poor quality material used

9. Quality of supervision

10. Design and construction flaws

2.ENVIRONMENTAL EFFECTS: Micro-cracks present in the concrete are the sources of ingress of moistures atmospheric carbon di-oxide into the concrete which attack reinforcement and with various ingredients of concrete. In aggressive environme4nt concrete structure will be severely reduces.

Construction

Advice and guidance for preventing pollution, managing waste and resources sustainably on

construction, demolition and excavation sites. Good site layout, resource management, and taking sensible steps to minimise pollution can

greatly reduce the environmental impact of your site.

Pollution prevention

Every year we respond to 350 pollution incidents caused by construction. Individual

builders, small/medium enterprises and larger companies are all responsible for the impact

they have on the environment. Pollution during construction can be prevented by careful

planning and management of on-site activities.

Follow our guidance to help keep the environment clean and safe.

Construction, demolition and excavation waste

Around 20 million tonnes of construction, demolition and excavation (CD&E) waste was

sent to landfill in 2010. At the end of 2011 CD&E waste was the largest contributing waste

type in illegal waste sites.

Your Duty of Care is a legal requirement that applies to the use, treatment, disposal and

transportation of waste. Failure to comply with the law risks penalties in court and can lead

to serious impacts on the environment.



http://en.wikipedia.org/wiki/Inflammation

http://www.environment-agency.gov.uk/business/sectors/136250.aspx


Good site management and well managed waste handling makes good business sense,

reduces costs and enhances community relations.

Sustainable construction

Sustainable construction is about the better management of resources, reusing waste

materials where possible, and reducing your carbon footprint. It includes how

developments impact on and provide for the surrounding infrastructure and natural

environment as well as the fabric of buildings.

Good practice can help you achieve sustainability and reduce costs.

Planning

Local authorities consult the Environment Agency about planning applications.

We use evidence to assess the potential environmental risks associated with a particular

development. Whilst we provide evidence and comment on planning applications, we do

not have the power to grant or refuse permission for a development. This role rests with the

Local Planning Authority.

Often there is not enough information included in planning applications for us to determine

what impact the development will have on the environment. You can help speed up your

planning application by filling in a pre-application form.

Effect of selecting poor quality material for construction

Quality of materials, to be used in construction, should be ensured by means various tests as specified in the IS codes. Alkali-aggregate reaction and sulphate attack results in early deterioration. Clayey materials in the fine aggregates weaken the mortar aggregate bond and reduce the strength. Salinity causes corrosion of reinforcing bars as well as deterioration of concrete. DETERIORATION

a symptom of reduced quality or strength(or)

process of changing to an inferior state(or)

The process of becoming progressively worse.

CAUSES OF DETERIORATION 1. Deterioration due to corrosion 2. Environmental effects 3. Poor quality material used 4. Quality of supervision 5. Design and construction flaws

QUALITY OF SUPERVISION Construction work should be carried out as per the laid down specification. Adherence to specified water-cement ratio controls strength, permeability durability of concrete. Insufficient vibration may result in porous and honey combined concrete,

whereas excess vibration may cause segregation.




http://www.environment-agency.gov.uk/research/planning/default.aspx

DESIGN LEVEL FACTORS:

Concrete structures are an assembly of operating systems that experience temperature, air pressure and vapour pressure, gradients. Seasonal and diurnal fluctuations on outdoor conditions provide variability and direction of the gradients.These operating conditions can accelerate premature failure of the components in a repair. The relative severity of these factors will vary depending on the use and location of the structure; and the types of repair material used and so on. Predicting these fluctuations and accommodating them at a design stage is important. Allow for change in use in design:During the service life of a structure, its environment and occupancy may change. As a result, the structure will have to withstand stresses different from those for which it was originally intended. For e.g.:- Addition of roof garden to parking lot requires additional protection

against ponding of water on the roof of parking lot.



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