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Structural Audit

Scope of Structural Audit

  • A structural audit is the technical analysis of the building with a detailed inspection of the existing structure to determine its strength and stability. 

  • It is a significant part of the building repair works where the scope and scale of repairs are determined for the existing structure.  In Structural Audit, detailed observations are made through a qualified and experienced person and the necessary recommendations as per are provided based on the observations.

  • To verify the existing conditions of the structure, technical analyses are made through certain recommended Non-Destructive Tests are performed on the structural members.

  • The readings of the test and the detailed observations together bring the audit to a conclusion with the recommendations necessary to restrengthen the structure.

  • In recent times Government has amended the MMC Act, by inserting section 353-B which makes structural audit compulsory for all buildings.

  • A structural audit helps in improving the safety, efficiency and makes the building functional to its maximum level.

  • Through Structural Audit and regular maintenance of the building, it is possible to increase the property values.

METHODOLOGY

In order to carry out a structural audit old RCC building is selected of age around 50 years.

The steps involved in a structural audit carried out is as follows:

 

Step 1: Preparation of architectural and structural plan of the building. Architectural and structural plans are helpful in a structural calculation, identifying or highlighting critical areas in the building;

 

Step 2: Making the assumption of load based on the intended use of the building i.e whether it is commercial, residential. Finding which code requirement has been met.

 

Step 3: Preliminary inspection of the building:

 

This inspection involves

1. Visual inspection

2. Tapping observation

1. Visual Inspection

In this building is thoroughly inspected from flat to flat noting cracks, spells, crazing, seepage ect. Highlighting critical area of investigation and repair same is marked on the plan of the building.

2. Tapping Observation

During this observation some of the structural members area subjected to hammer tapping and tapping sound is noted i.e whether it is hollow or dence.

Step 4: Test recommendation after highlighting critical area in the building next step is to recommend the appropriate test to evaluate the structure which may include Non-destructive tests like
1. PROFOMETER TEST
2. REBOUND HAMMER TEST
3. ULTRASONIC-PULSE VELOCITY TEST
4. HALF CELL POTENTIAL METER TEST
5. CHEMICAL TESTS:

a. CHLORIDE CONTENT
b. SULPHATE CONTENT
c. PH VALUE


Step 5: ETABS modeling this step involves preparation of ETABS model of the building order to find response of the structure to gravity and earth quake loading. This step will give demand of the building to the loading.
 

Step 6: Finding actual capacity of the members andfinding Demand to capacity ratio for structural members.


Step 7: Recommendation of remedial or retrofitting methods for the suitable structural members.

RAPID VISUAL INSPECTION AND TAPPING OBSERVATION

1. Visual inspection: In this building is thoroughly inspected from flat to flat noting cracks, spells, crazing, seepage ect. Highlighting critical area of investigation and repair same is marked on the plan of the building.

2.Tapping observation: Column and beams of the building were subjected to tapping by the hammer .For some of the beams and column hollow sound was recorded. This hollow sound was due to loss of integrity between reinforced steel and surrounding concrete.

Selection of critical area for further Non-Destructive testing: Based on above observations flat no:2 of the ground floor was found most unsafe due to bad condition of structural elements such as beam, column and slab. Status of beams of this area is critical beams are sagging due to deflection and corrosion. There is bulging in column due to corrosion of reinforcement and disintegration of concrete has resulted in exposure of the reinforcement.

NON DESTRUCTIVE TESTIING

Non-destructive Testing method are the method of testings in which properties of material or condition of the material is determined without damaging or making changes in the object. This methods of testing allows to test the material or component without losing its usefulness.NDT method helps in testing integrity of concrete or structural members throughout its life span.
Once the NDT tests is performed it is possible to re-test the structure or the object.
NDT tests are applicable in testing the condition of the bridges, highways, building ect. NDT allows users to determine following properties of the object

  • Strength properties at the site

  • Durability

  • Density

  • Moisture content

  • Elastic properties

  • Extent of visible cracks

5.1 Classification of NDT Techniques.


1: Non Destructive Tests for Concrete

  • Rebound Hammer Test

  • Ultrasonic Pulse Velocity Test

2: Partially Destructive Tests for Concrete

  • Penetration Resistance Test (Windsor Probe)

  • Pull-out Test

  • Pull-off Test

  • Break-off Test

  • Core Cutting

3: Test for Hardened Concrete

  • Chemical Tests

  • Test for Determination Sulphate

  • Test for Determination Chloride

  • Test for Alkalinity

  • Carbonation Test

  • Tests for Absorption & Permeability

4: location of Reinforcement, size and corrosion

  • Rebar Locator & bar sizer

  • Corrosion mapping

  • Half-cell Potentiometer

  • Resistivity meter

5.2 Tests recommended for Structural audit of the building

1. Rebound Hammer: For determination of the compressive strength

of the concrete
2. Profometer test: Location of rebar and cover


5.3 Rebound Hammer
Application of rebound hammer test:

1. For determination of the compressive strength of the concrete
2. Determine uniformity of the concrete.
3. Determine the quality of the concrete.

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Method of testing:

1. Prepare the instrument for the test,remove the plunger from lock position by pushing the plunger on the surface and push it slowly against the surface.
2. Hold the plunger perpendicular to the testing surface.
3. As the body is pushed, the main spring connecting the hammer mass to the body is stretched. When the body is pushed to the limit, the latch is automatically released and the energy stored in the spring propels the hammer mass towards the plunger tip. The mass impacts the shoulder of the plunger rod and rebounds.
4. This rebound distance is measured on the graduated scale and is termed as rebound number. Major damage in RCC members are due to seepage of water in the members this need to be prevented by stoping the seepage of water into the members.


Seepage of water in members can be stopped by
a) Structural Repairs
b) External Plaster
c) Crack Filling/Joint Filling.
d) External Drain down take Plumbing
e) Terrace waterproofing by using non destructive method.
f) Dead wall / Internal Terrace parapet wall plaster repairs.

 


Rehabilitation of the RCC members
Propping the structure wherever necessary Removing loose/disintegrated concrete Cleaning the affected steel
Adding steel wherever necessary Applying Passivator coat to the steel
Applying Bond Coat and doing Polymer /MicroConcrete treatment depending on the requirements
Finishing with new plaster
Rehabilitation techniques recommended:
1. Polymer Modified Mortar Treatment
2. Jacketing to columns - Microconcrete.
3. Recasting of Slabs/ Chajjas
4. Water proofing Treatment

 

 

 

 


Conclusion:


For framed structure structural audit is necessary so that appropriate remedial measures can be recommended for all types of structural defects and damages .So that it continues to serve strength and serviceability requirement.
For any structure it is necessary to carry out structural audit at least once in the five years.
For structure older than 15 years structural audit should be carried out once in 3 years.
From above observation we conclude that even though heavy reinforcement is provided for the structural members and demand to capacity ratio is less than one for all structural members . Reinforcement provided is in very bad condition and lost its Strength due to corrosion .Due to corrosion there is reduction in the cross section of the reinforcement resulting on deflection under their own weight therefore unsafe to carry any further load.
It is observed that main cause of damage of the structural members is due to corrosion and ageing. Corrosion in structural members is observed due to dampness and leakage from the slabs,cracks in walls ect.
So the strength and serviceability of the building can be increased by taking necessary measures such as: Water proofing slabs and walls to stop seepage of water into structural members so as to avoid further corrosion. Providing polymer mortar treatment. Recasting of slab ect

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