Structural Soundness Audit

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677International Journal of Earth Sciences and Engineering

ISSN 0974-5904, Volume 04, No 06 SPL, October 2011, pp. 677-680

#020410350 Copyright 2011 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved

Structural Soundness of Buildings

M. J. MonteiroStudent, M.E. (Structures),MIT College of Engg. Pune,-411038, [email protected]

N. J. PathakProfessor, Dept. of Applied Mechanics,MIT College of Engg. Pune ,-411038,[email protected]: This paper deals with methods of estimating the soundness of existing structures whose life has crossedthe age of 30 years. As we know concrete is widely used as a construction material because of its high strength-cost ratio

in many applications. Concrete constructions are generally expected to give trouble free service throughout its intended

design life. However, these expectations are not realized in many constructions because of structural deficiency, materialdeterioration, unanticipated over loadings or physical damage and thus Civil structures like buildings, dams, bridges etc

are subjected to continuous deterioration over the years. This extent of damage or deterioration greatly depends on the

quality of work at the construction stage. The deterioration of buildings can be a result of various factors including firedamage, frost action, chemical attack, corrosion of steel etc during the life span of the structure. The investigation of

soundness is thus essential for finding the present serviceability of the structure and its scope for future developments orfor the change in its utilization. Such an investigation can be carried out using the following methods: a) Visual

examination b) Non Destructive Testing c) Partial Destructive Testing. Soundness estimation becomes essential for

buildings hit by an earthquake, a bomb blast or any other calamity.

KEY WORDS: Concrete, soundness, deterioration, non destructive testing, structural audit.

INTRODUCTION

In India there are many old structures and some of them

are of great importance. The strength of these oldstructures reduces in the due course of time because of its

usage, input of poor quality construction materials,

environmental conditions, improper practice or poor

workmanship. Also several factors such as plasticdeformation, interaction with the environment, initial

design, construction flaws and natural disasters develop

distress in the structure which may result in developmentof cracks, corrosion in reinforcement, leakage and

seepage. The final soundness of a building can vary due

to numerous reasons and thus, only proper precautions at

the initial stage and good maintenance in the later lifespan of the structure can result in a technically sound

building.

To ensure if buildings are sound requires the activeparticipation of building safety and fire prevention

officials, architects, builders, engineers, and others in the

construction industry, as well as property owners.

Determining the root cause of the defect directly depends

on the areas of the building that have been affected.Defects in the foundation, floor, or wall can be the direct

result of soil issues, water issues, or even workmanshipissues. Earthquakes, tropical cyclones, and other natural

disasters can also damage the structure of the building and

cause it to collapse.

This paper deals with the study of the principal problemslike the degree of deterioration of the structural memberswhich is one of the governing factors for poor

performance of the structure, their likely causes, and

approaches to their remedies. If the further use of suchdeteriorated structures is continued it may endanger the

lives of the occupants and the surrounding habitation. As

demolition and re-construction of these structures maybe

a very costly affair and strengthening the existingstructure may be a favorable option. Faulty concrete

repair can worsen structural problems therefore remedial

work should only be undertaken by an expert

NEED TO EVALUATE SOUNDNESS OF EXISTING

STRUCTURES

It is generally carried out on existing structures for thefollowing reasons, for:

1. Assessing the load carrying capacity of building.2. Feasibility of change in occupancy.3. Feasibility for construction of additional floors.4. Assessment of earthquake resistance (As per

revised codal provisions) in old structures.

5. Feasibility for structural modifications.6. Feasibility for placing higher capacity

equipments on building.

7. Assessment of structural soundness periodically.

STRUCTURAL AUDIT OF BUILDINGSStructural Audit is essential as it refers to health check up

of building. Its basically for ensuring that the building

and its premises are safe and under no risks. As a building

gets older & older it shows signs of wear and tear due to

ageing, use, misuse or overuse, exposure to the

weathering/environment and structurally unplannedmodifications and additions , which do affect the health of

the building significantly. In the initial service life of any

structure, there are no problems that are faced by theowner but as soon as one monsoon season passes after

another the series of troubles never cease.

Conducting Structural Audit

Structural Audit is done by appointing an experienced andexpert Consulting Structural Engineer registered with the

Municipal Corporations or chartered Engineers. The

owner shall give his brief of use or operation in the.


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678 M. J. Monteiro, N. J. Pathak

International Journal of Earth Sciences and Engineering


Fig 1. External defects of building.

building and old data, drawings, details of modifications/

additions etc. to the structural consultant

A structural audit broadly consists of two types ofsurveys. The external survey covers building faces,

common areas (Fig 1) (stilts, staircase, terrace, projections

etc) and ancillary structures (pump room, compound wall,water tanks etc). The internal survey covers individually

owned units such as apartments, shops etc, (Fig 2)

However, sometimes some units are locked or

inaccessible. If the number of such flats is small (sayabout 10%), structural audit report can still be prepared

based on the observations in the flats that were surveyed.

Structural Audit of Buildings- A Norm

According to the model bye-law no. 77 for co-operativehousing societies, it is mandatory that if the age of a

building is 15 to 30 years, a structural audit must be

carried out once in five years and for buildings older than30 years it should be carried out once in three years. One

may, however, go for it even earlier if one suspects the

condition of the building to be bad. Perhaps monsoon/post monsoon is the best time to commission a structural

audit since the seepage is more evident at that time.

The certificate, issued by a structural engineer registeredwith BMC, will have to be submitted within a year after a

building completes 30 years. For any corrective repairs

suggested by the commissioner, the owner or occupants

will be asked to submit the structural stability certificates

again after a specific period suggested by him. If foundunsafe, he has been given the authority to issue a notice to

the owner to submit a structural stability certificate within

30 days from the date of notice. It will be binding onowners to carry out corrective repairs to the satisfaction of

the commissioner. If they fail to do so within six months,

they will have to shell out a fine of Rs 25,000.

Fig 2 Structurally damaged beam of apartment.

Cause of Concern

The cause of concern is not alone regarding, whether ornot the audit is done, the actual concern lies beyond the

audit report i.e. the part of implementing the various

renovations and strengthening techniques suggested by the

concerned authorities and the experts. Old buildings maynot reach the same standards as modern buildings in somerespects but they make up for that by having qualities that

many new buildings do not such as history, character, and

craftsmanship. But as a building starts to age, it startshowing different signs of distress. It is necessary to take

the required action in time so that the building is protected

from severe damage at a later stage. There are many

buildings which have collapsed in the past killing manyprecious/innocent lives.

Advantages of Structural Audit1. Condition of safety is known hence further use,

buy, sell etc. can be finalized.

2. Easier to convince the owner/user to get co-operation for repairs if any.3. Statutory report available for submission to

Corporation Factory Inspector etc.

4. Helps maintenance team / contractors to understandthe exact nature of distress before undertaking thestructural repairs.

5. Cost effective solutions can be worked out basedon report.

6. Important remedial and preventive measures can betaken.

RESIDUAL STRENGTH CALCULATION BY NON

DESTRUCTIVE TESTING

Rebound Hammer Test

When the plunger of rebound hammer is pressed against

the surface of concrete, a spring controlled mass with aconstant energy is made to hit concrete surface to rebound

back. The extent of rebound, which is a measure of surface

hardness, is measured on a graduated scale. This measuredvalue is designated as Rebound Number (a rebound index).

A concrete with low strength and low stiffness will absorb

more energy to yield in a lower rebound value (Table 1).


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679Structural Soundness Of Buildings

International Journal of Earth Sciences and EngineeringISSN 0974-5904, Volume 04, No 06 SPL, October 2011, pp. 677-680

Table 1 Quality of Concrete from Rebound Values

Comparative Hardness

Average Rebound Quality of Concrete

>40 Very Good

30-40 Good

20-30 Fair

4.0 km/s Very good to excellent

3.5-4.0 km/s

Good to very good, slight porosity

may exist

3.0- 3.5 km/sSatisfactory but loss of integrity issuspected


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680 M. J. Monteiro, N. J. Pathak

International Journal of Earth Sciences and Engineering


General Procedure for Carbonation Depth Measurement

The 1% phenolthalein solution is made by dissolving 1gm

of phenolthalein in 90 cc of ethanol. The solution is thenmade up to 100 cc by adding distilled water. On freshly

extracted cores the core is sprayed with phenolphthalein

solution, the depth of the uncoloured layer (the carbonated

layer) from the external surface is measured to the nearestmm at 4 or 8 positions, and the average taken.

Core Sampling and TestingWhile rebound hammer, Pullout and ultrasonic pulse

velocity tests give indirect evidence of concrete quality, a

more direct assessment on strength can be made by core

sampling and testing. Cores are usually cut by means of arotary cutting tool with diamond bits. In this manner, a

cylindrical specimen is obtained, usually with its ends

being uneven, parallel and square and sometimes withembedded pieces of reinforcement. The cores are visually

described and photographed, giving specific attention to

compaction, distribution of aggregate, presence of steel

etc. The core should then be soaked in water, capped with

molten sulphur to make its ends plane, parallel, at rightangle and then tested in compression in a moist condition

as per BS 1881: Part 4: 1970 or ASTM C 42-77.

CONCLUSIONS:

1. Leakage weakens your RCC frame, which is thebackbone of any building. One has to make sure the

waterproofing system is in place.2. It is advisable to monitor the building health

periodically by taking a professional opinion.3. Implementing the various renovations and

strengthening techniques suggested by the concerned

authorities and the experts should be done at the

earliest.

4. Problems like Sulphate Attack, Alkali AggregateReaction and Corrosion should be avoided at the

construction stage itself.5. Non-destructive testing should be carried out for

buildings found deteriorated and damaged over time.

ACKNOWLEDGMENTSI am really grateful to our college institution and our

faculty members and my guide Mrs. N. J. Pathak for

helping me complete my paper.

REFERENCES

[1] Cpwd - Handbook on Repair and Rehabilitationof R.C.C. Structures.

[2] Dr. Durgesh Rai (2004) IITK GSDMA Guidelines for Seismic Evaluation and Strengtheningof Existing Buildings.

[3] Indian Stan.dard: 456: 2000- Plain andReinforced Concrete Code of Practice (FourthRevision).

[4] Indian Standard: 13311:1992 (Part 1) NDTmethods of Test- Ultrasonic Pulse Velocity.

[5] Indian Standard: 13311:1992 (Part 2) NDTmethods of Test- Rebound Hammer.

[6] Indian Standard: 516: 1959- Method of test forstrength of concrete.

[7] International Atomic Energy Agency, Vienna(2002). Guidebook on Non-Destructive Testingof Concrete Structures.

[8] Nondestructive Test Methods for Evaluation ofConcrete in Structures- ACI 228.2R-98.

[9] SP: 16-Design Aids for Reinforced Concrete toIS: 456- 1978.

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Structural Soundness Audit