Structural Auditing

Mr. Avinash B. Kokare, Email: abkokare@coe.sveri.ac.in Assistant Professor, SVERI’s College of Engineering, Pandharpur

Why Structural Audit

With every passing year, your building combats a series of natural upheavals, facing the apathy of every season that goes by. Many buildings built during last 20 to 30 years in Mumbai are in severe structural distress. Leakages are a common sight during monsoons. To add to this, we keep hearing of sporadic incidents of building collapse, which have resulted in irreparable loses at times, both of men and material. And that’s when the concept of ‘structural audit’ became known and it was soon made mandatory to be followed. Structural Audit is an overall health and performance checkup of a building like a doctor examines a patient. It ensures that the building and its premises are safe and have no risk. It analyses and suggests appropriate repairs and retrofitting measures required for the buildings to perform better in its service life. Structural audit is done by an experienced and licensed structural consultant.

The various stages involved in Structural Auditing:

Stages for carrying out Condition Survey, largely depend on field conditions, user habits,  maintenance etc and have a direct relation with the pattern of distress, whether localised or spread  over. Condition Survey of a building/structure is generally undertaken in four different stages to identify the actual problem so as to ensure that a fruitful outcome is achieved with minimum efforts

at the least cost. The four stages of condition survey are:

• Preliminary Inspection,
  • Planning,
  • Visual Inspection,
  • Field and Laboratory testing 

Preliminary Inspection:

Basic Information Gathering:-A programme has to be evolved to obtain as much information as possible about the distressed structure at reasonable cost and in a reasonable time. Accordingly, the information required from the owner/client has to be listed out even though, many construction details and other related information may not be available with the owners/clients, yet as much as information and details as possible be gathered during the preliminary site visit. Before undertaking a condition survey of a building/structure, the following essential information is required and be obtained from the clients/owners:

• Period of construction;
  • Exposure conditions of structure;
    • Designed use vis-a-vis present use of structure;
    • Previous changes in use, if any;
    • Record of structural changes made, if any;
    • Record of first occurrence of deterioration, if any;
    • Details of repairs, if carried out in the past;
    • Reports of previous investigations/condition surveys, if any
    • Apparent cause of distress, as could be ascertained from the owner/client;
    • Photographs of distressed portions of structure.

Planning Stage

Planning stage involves preparation of field documents, grouping of structural members and classification of damage as under:

• Preparation of Field Documents
  • For condition survey, the following are required to be prepared
    • Survey objective;
    • Scope of work;
    • Method of survey;
    • The field and laboratory testing requirements and field equipment & tools required for the same;
    • List of tasks and their sequence for condition survey together with a work schedule;
    • Required number of  photo copy of available drawings;
    • Floor plans based on field measurements;
    • Work sheets and tables for recording in a logical manner all information, test results including field data gathered;
    • Previous Condition Survey results and Investigation Reports, if any;
    • Maintenance and repair records

 Visual Inspection:

• Visual examination of a structure is the most effective qualitative method of evaluation of structural soundness and identifying the typical distress symptoms together with the associated problems.
• This provides valuable information to an experienced engineer in regard to its workmanship, structural service ability and material deterioration mechanism.
• It is meant to give a quick scan of the structure to assess its state of general health.
• The record of visual inspection is an essential requirement for preparation of realistic bill of quantities of various repair items.
• Experienced engineers should carry out this work as this forms the basis for detailing out the plan of action to complete the diagnosis of problems and to quantify the extent of distress.
• Simple tools and Instruments like camera with flash, magnifying glass, binoculars, and gauge for crack width measurement, chisel and hammer are usually needed. Occasionally, alight platform/scaffold tower can be used for access to advantage.

NON DESTRUCTIVE EVALUATION TESTS:

The standard method of evaluating the quality of concrete in buildings or structures is to test specimens cast simultaneously for compressive, flexural and tensile strengths. The main disadvantages are that results are not obtained immediately; that concrete in specimens may differ from that in the actual structure as a result of different curing and compaction conditions; and that strength properties of a concrete specimen depend on its size and shape.

A number of non-destructive evaluation (NDE) tests for concrete members are available to determine in-situ strength and quality of concrete. Some of these tests are very useful in assessment of damage to RCC structures subjected to corrosion, chemical attack, and fire and due to other reasons. The term ‗non destructive is used to indicate that it does not impair the intended performance of the structural member being tested /investigated. The non-destructive evaluation have been broadly classified under two broad categories viz‗in-situ field test and

‗laboratory test- These tests have been put under five categories depending on the purpose of  test as under:

• In-situ Concrete Strength
• Chemical Attack
• Corrosion Activity
• Fire Damage
• Structural Integrity/Soundness

There are various NDT tests available for concrete structures, but based on its suitability and applications they are selected. These tests can be completely non-destructive, or partially destructive tests which may not have much effect on the strength and durability of concrete structure.The following methods are commonly used for NDT of concrete structures. The typical applications of those methods are briefed.

Rebound Hammer Test

Ultrasonic Pulse Velocity Test:

Half Cell Potentiometer Test:

References:

Pranjali V. Kulkarni, Sachin V. Admane, ‖Simplifying and Managing the Process of Structural Audit

Jedidi Malek, Machta Kaouther, ― Destructive and Non-destructive Testing of Concrete Structure

A.B. Mahadik, M.H Jaiswal,‖Structural Audit of Building