Struct Audit is a company dealing in structural audit of buildings in Mumbai.

1. Marketing presentation

2. • A pre-monsoon survey carried out by the BMC, has shown a rise in the number of
dilapidated buildings in Mumbai.
• According to the BMC, there are 1,236 dilapidated structures, mostly in south Mumbai
and parts of western suburbs. There is nearly a 29% rise as compared to last year of
959 buildings that were reported.
• Out of the total buildings, 840 are privately-owned, non-cessed buildings, while the
number of cessed structures included are 230.
• The list also has 166 buildings owned by the BMC. B (Dongri ward) has the highest number
of such buildings, that is 129, followed by P-North (Malad) 116 buildings, K-W (Andheri
West) 94 buildings, E (Byculla) 90 buildings, L (Kurla) 89 buildings.
• Source: http://www.dnaindia.com/mumbai/report-rise-in-dilapidated-structures-in-mumbai-by-29-bmc-1995773

3. • The dilapidated buildings have been classified as C1, C2, C3 and those that
are over 30 years old.
• Of the 32,429 dilapidated buildings in the city, 593 are in the C1 category,
which pertains to dilapidated or dangerous buildings.
• In the C1 category, 41 BMC buildings and 125 belonging to private persons
have already been vacated. Electricity and water supplies to 26 BMC
buildings and 85 private ones that have not been vacated have been
disconnected.
• The C2 category cover those that require major reconstruction, while the C3
category are those that require only minor repairs.
• There are only about 106 buildings in the C3 category.

4. • On March 16, the civic body had so far issued about 14,000 notices to
buildings— dilapidated and dangerous structures, structures that require
repair as well as those that have to go for compulsory structural audits.
• However, most residents are yet to act on them.
• According to records, as many as 817 buildings still require major
reconstruction
• Out of these 267 have been granted permission for repairs, but 650 of them
are yet to be repaired. On the other hand, several dilapidated buildings
that have been vacated are yet to be demolished.

5. • Only 927 private buildings among those that were issued
notices have undergone structural audit.
• The number of BMC/government buildings among them is not
available.
• Following the pre-monsoon survey of dilapidated buildings this
year, Mhada has notified eight buildings in the island city as
extremely dangerous. Of the eight buildings, three will be
demolished and the remaining five will be repaired.

6. • Taking serious note of dilapidated buildings in the city after the Kalwa
building collapse incident, civic commissioner Aseem Gupta has asked citizens
to carry out structural audit, failing which a penalty of Rs 25,000 will be
imposed.
• According to the government directives, all 30-year-old buildings should go
through structural audit and owners have to procure health card of the
structure. We request citizens to conduct structural audit of old buildings. If
they fail to do so, then they will be fined Rs 25,000
• The civic chief has directed his officers to initiate a survey and prepare a list
of old and dilapidated buildings that need to undergo structural audit.

7. • Structural Audit is an important tool for knowing the real status of the
old buildings. The Audit highlights & investigates all the risk areas,
critical areas and whether the building needs immediate attention.
• It should also cover the structural analysis of the existing frame and
pinpoint the weak structural areas for static, wind & earthquake
loads.
• If the building has changed the user, from residential to commercial or
industrial, this should bring out the impact of such a change.

8. The Purpose of Structural Audit is :
• To save LIFE & PROPERTY.
• To know the health of your building and to project the expected future life.
• Highlight the critical areas that need to be attended with immediate effect.
• To proactively assist the residents and the society to understand the
seriousness of the problems and the urgency required to attend the same.
• To comply with Municipal or any other statutory requirements.

9. • STEP 1: It is imperative that we must have Architectural and Structural plans
of the buildings, it will be helpful if we have detailed structural calculations
including assumptions for the structural design.
• The assumptions can also include the allowable live loads; Whether the
building is designed for residential, commercial, light industry or heavy
industry and whether any future provision for adding new floors is
considered?
• What type of Earthquake loads are considered?
• Which I.S. Code requirements have been met?

10. • If the Architectural plans and Structural plans are not available,
the same can be prepared by any Engineer by measuring the
size of the building & locating the position of the columns,
beams and size of all such structural elements.

11. Inspection of the building - A detailed inspection of the building can reveal the
following:
1. Any settlements in the foundations.
2. Visual cracks in columns, beams and slabs
3. Concrete disintegration and exposed steel reinforcements – photographs can
be helpful.
4. Slight tapping with hammer can reveal deterioration in concrete.
5. Extent of corrosion in reinforcement.
6. Status of Balconies – sagging, deflection, cracks?
7. Status of Architectural features viz. chhajjas, fins, canopies etc.
8. Cracks in walls indicating swelling in R.C.C. members or distress or deflection
or corrosion.

12. 9. Leakages from terrace & Toilet blocks.
10. Leakages & dampness in walls resulting into cracks and corrosion.
11. Changes carried out affecting structure.
• Toilet blocks - Added or changes made?
• Change of user – from Residential to Commercial to Industrial?
• Change of Partition Walls?
12. Status of lift and lift machine room – Type of Maintenance Contract,
renewal of license.
13. Status of electrical wiring from meter room to all the flats. Substation
status.
• Any explosion in the meter room, substation?

13. 14. Status of overhead & underground water tanks - capacity. Leakages, cracks &
frequency of cleaning, status of pumps.
15. Plinth protection in the compound including status of drainage, water pipes &
pumps. How much the Ground was flooded during recent monsoons?
16. External paint – When last painted and type of paint.
17. Status of repairs & last repaired. What was repaired? Who was the Agency? How
much was spent for repairs?
18. Are the Building plans available? When approved?
• Occupation Certificate available?
• Structural Plans available?
• Structural Stability Certificate available?
• Structural Calculations available?
19. Last Structural Audit prepared?

14. • It is important that various tests are carried out in the old buildings. This will
give an idea about the extent of corrosion, distress and loss of strength in
concrete & steel.
• Tests may include:
1. Concrete Core Cutting & Compression testing for columns, beams and
slabs for Strength Assessment of concrete.
2. Half Cell Potential test for determining the probability of corrosion in the
embedded steel.
3. Carbonation test for carbonation depth measurement for Steel.
4. Ultrasonic Pulse Velocity Test (UPV) for Strength Assessment of concrete.
This can be useful for simple foundations.
5. Integrity tests for pile foundations.

15. 1. No. of columns requiring immediate attention including treating rusted
steel, adding new steel, jacketing of columns etc. – Repairing foundations,
repairing balconies, chhajjas.
2. Attending of beams and slabs wherever required.
3. Attending water proofing of terrace, toilet blocks.
4. Attending cracks in external walls and providing good quality of paint.
5. The critical areas which are highlighted needs to be attended
immediately.

16. • Mumbai is located in Earthquake Zone III as per Indian Standard Codes.
• The Earthquake Code IS 1893-2002 provides rigorous analysis and designs
of building structures so that it can withstand the Earthquake forces.
• It may be possible to retrofit the old buildings, so that they do not collapse
during Earthquake; but may develop some cracks and allow enough time for
people to escape.
• Thus saving precious lives.

17. • Audit is a good thing, but in itself Audit is not sufficient. It is
important that the findings and/or recommendations of audits
are implemented satisfactorily, within a stipulated time limit and
are certified by Structural Engineers; Otherwise the Audit
findings will remain on paper.

18. Non Destructive Tests: The following NDT tests are required to be carried out on
structural elements. However, it is important that the testing scheme is prepared based
on preliminary survey of the building/structure :
• Core tests to determine the estimated equivalent in situ compressive strength & to
establish correlation between Rebound hammer test & in situ strength of concrete.
• Rebound Hammer test to estimate the in situ compressive strength of cover
• concrete.
• USPV test to assess the integrity of concrete.
• Carbonation test to assess the depth of carbonated concrete.
• Half cell potentiometer test to determine the probability of active corrosion.
• Cover test to assess the cover provided to RCC structural members.

20. Steps to the Core Tests:
1. The reinforcement is detected at planned location with the help of Rebar Locator called
Profometer to avoid cutting of reinforcement.
2. The Core cutting equipment is fixed at the planned location & core is extracted.
3. The Cores are transported to the laboratory & visual observations of cores are
recorded for interpretation purpose. Reinforcement bars, if encountered, are cut off.
4. The Cores are removed from water cut to the required L/D ratio of 2, wherever
possible, exactly perpendicular to the longitudinal axis.
5. Both the ends are prepared by grinding up to the tolerance limit as specified by
Clause 4:8 of BS 1881:Part 120: 1983 for flatness & parallelism.
6. A thin layer of plaster of Paris is applied to ends to ensure proper contact.
7. Now the cores are ready for compression testing.

21. Steps to carry out Rebound Hammer Test : This test is performed as per guidelines given by IS : 1331 (Part 2): 1992 & BS
1881: Part 202: 1986 to estimate the in situ strength of concrete based on the correlation established between in-situ
strength at the particular location & rebound numbers.
1. The plaster is removed at test locations.
2. For testing, smooth, clean, dry surface without any defect like Honeycombing cracks and hollow sound is selected.
3. The area of approx. 300 mm x 300 mm is rubbed with carborandum stone to remove loosely adhering scales, or remains
of plaster mortar, if any.
4. In this area 12 points at approximate 30 mm apart are selected in grids.
5. By holding the rebound hammer at right angles to surface of the concrete member, 12 readings are taken at selected
points.
6. Of these readings, abnormally high & abnormally low results are eliminated & average of the balance readings is
worked out.
7. Taking into consideration the factors influencing hardness of the concrete surface like moisture condition of the surface,
carbonation, test location within the member, direction of test etc. corrected rebound number is worked out.
8. The compressive strength of concrete against each rebound number is obtained from graph prepared on correlation
established between rebound numbers at core test locations & equivalent cube strength values.
9. The statistical analysis is carried out for this set of values of compressive strengths obtained by above method.

22. 1. The plaster is removed at test locations wherever required.
2. For testing, smooth, clean, dry surface without any defect like honey combing, cracks, and hollow
sound is selected.
3. The area of approx. 300 mm x 300 mm is rubbed with carbonation stone to remove loosely
adhering scales, or remains of plaster mortar, if any.
4. Two points are marked on opposite faces of the concrete members. (At exactly opposite
locations for direct transmission of ultrasonic pulses).
5. Grease is applied as a coupling medium to ensure proper contact of the transducers with
concrete surface so that ultrasonic pulse is transmitted through the medium without much
disturbance.
6. Now both the transducers are held at correct test locations by applying constant pressure &
ultrasonic pulses are transmitted through the concrete.
7. The machine displays the time taken to travel the known path in microseconds.
8. The velocity is calculated from the reading obtained against each known path.

23. • Following velocity criterion for concrete quality grading is given by IS 13311
(Part:1) 1992
Sr. No. Ultrasonic Pulse Velocity by Cross probing (Km/Sec.) Concrete Quality Grading
1. Above 4.5 Excellent
2. 3.5 to 4.5 Good
3. 3.0 to 3.5 Medium
4. Below 3.0 Doubtful

24. • The powder of concrete is obtained by drilling inside into
concrete at selected location.
• Then the collected powder is made moist & then phenolphthalein
indicator is dropped on it to check any colour change.
• If the colour changes to pink, indicates that concrete is not
affected by carbonation & if no colour change is observed,
indicates concrete is affected by carbonation

25. • The instrument used is PROFOMETER - 4, Rebar Locator Model S,
manufactured by M/s. PROCEQ SA, Switzerland, which is able to
perform following functions:
• To locate the bar accurately.
• To assess the clear cover to the bar.
• To calculate bar diameter of the selected bar.
• The instrument works on magnetic principle & has limitations of
spacing between bars to identify the bars individually.
• The limitation of rebar locator instrument to identify bars, its diameter
is that depth of rebar’s from concrete surface should be less than to
70 mm depth & spacing of bars should be more than 150 mm.

26. • The half-cell potentiometer consists of a rigid tube, which contains a copper rod
immersed in a copper sulphate solution.
• This is connected to a voltmeter and another live wire connection comes through
voltmeter to connect it to rebar. To start the experiment firstly the live wire is
connected to a rebar of the test specimen and the rigid tube is put on the surface of
concrete and the reading of voltmeter is taken.
• Reading gives the potential difference between the electrodes. From the value of the
potential difference, corrosion status inside the concrete can be predicted.
The possibility of active corrosion is found out according to guideline below
Sr. No. Half cell potential (mV) reading
Percentage chance of active
corrosion
1. < -350 90%
2. - 200 to - 350 50%
3. > -200 10%

27. • Chajjas are severely affected by corrosion.
• Severe corrosion cracks are developed in columns.
• Top level slab is severely affected by corrosion, cover of concrete has
spalled down and steel is exposed.
• Front side Chajja throughout the length of structure is severely affected by
corrosion.
• Top level beams are affected by corrosion.
• Almost 100% columns in the top floor have corrosion related distress.

28. 1. Polymer Modified Mortar Treatment
2. Jacketing to columns – Micro-concrete.
3. Recasting of Slabs/ Chajjas
4. Water proofing Treatment

29. • If your building is more than 15 years old, it is important that rigorous
audit is carried out every five years.
• This will be a continuous process as it is difficult to guarantee future
life of old buildings.
• However, regular Audits and implementing audit findings will avoid
sudden collapse of buildings. and save thousands of life. This process
will also increase the future life of buildings.

30. Prepared by Divyaank Sharma For Struct Audit