Structural Audit
We Are Licensed Structural Engineers And Carry Out Structural Audit As Per Prescribed Government Norms
The following NDT tests are required to be carried out on structural elements. However, the testing scheme must be prepared based on preliminary survey of the building/ structure
REBOUND HAMMER TEST
Ultrasonic Pulse Velocity
CORROSION TEST OF STEEL
CARBONATION TEST
CORE TEST
HALF-CELL POTENTIOMETER
OVERVIEW OF-'STRUCTURAL AUDIT', 'VISUAL INSPECTION', 'RELEVANCE & LIMITATIONS OF NDT'
Structural Audit is the term generally used for inspection and Assessment of any structure. Primarily Structural Audit consists of noting the status of building, studying the history, and existing drawings (if any), detailed Visual Inspection and carrying NDT, and finally reaching to the conclusion (leading to classification-as in the case of MCGM proforma B)of the building.
The principle objective of a Structural Audit is to check the health of the building ‘as on date'(real-time basis)and to suggest corrective measures if the building is found deficient in the process of Visual Inspection and/or indicative problems noted through ‘NDT’.
Frequencies of Audit -There are broadly THREE criteria for deciding audit requirements or frequency of audit
A. Ageing(different practices decided/followed by different authorities)-
1) As per model bylaws-Co-operative Housing Society Act, Maharashtra
i) Age of building-15-30 years in 5 years
ii) Age of building-30 years+-once in 3 years
2) As per the factory Inspector Act in 5 years
B Human Intervention-Prior to actual execution
a) Change of Use-Over loading
b) Modifications/Vertical extension-increasing number of stories
D. Accident-after the incidence but before reuse
a) Fire, Blast
b) Collapse of any kind during construction
Let's look into the procedure of Structural Audit
As discussed before, ‘Visual Inspection is the first step of carrying out any Structural Audit.
It is most important activity, and there is no alternative to Visual Inspection’.
Guidelines -ACl 201.1R-08is very good document and can be used as -Guide for Conducting a Visual Inspection of Concrete in Service.(This publication is more oriented towards pure concrete structures like Bridges, Dams, Water Tanks…etc. and may not be sufficient for structures like Residential Buildings, Commercial Buildings, Schools, Colleges, Hospitals etc. where multiple
construction materials-Concrete, Stone, Bricks, Wood, Tiles etc. are used)
Proforma B as developed by MCGM is also good for other civil items.
However, following the guide(or any prescriptive formats) does not eliminate the need for intelligent (experienced)observations and the use of Sound Engineering Judgment. (page no. ACl 201.1R-08)
Now let’s check the relevance of NDT
Visual inspection is one kind of NDT only. Like Doctors taking pulse or BP, Assessment Engineers undertake visual inspection as a first step. Like the Doctor recommends Pathological Tests, The assessment engineer should recommend the type of NDT(as location and number of tests)
The visual inspection results and NDT aid in Early detection of distress and deterioration (if any)
enabling Repair or Rehabilitation before replacement is necessary.
We can say Inspections are often supplemented with NDT, Destructive test, and other Investigations, especially when distress and deterioration is observed and also sometimes when distresses are not observed)and information regarding the INTERNAL CONDITION of the concrete is needed.
At the same time there are limitations to visual inspection and relevance of NDT begins.
Stage 1 - Structural Audit
This is a preliminary but important stage of assessment. The steps to be followed in this state shall be as under:
- Condition Survey of building Visual
- Study of Drawings whatever is available
- Study of the History of Construction & Rehabilitation
If the purpose is statutory compliance to undertake repair/rehabilitation work or to check the feasibility of a proposed modest alteration, it may not be necessary to proceed beyond this stage.
Stage 2 - Collecting Data for Structural Analysis
If the owner is contemplating construction of additional floors on his existing building or the building has been damaged in a fire or earthquake or if he wishes to undertake its seismic retrofitting, it would be necessary to continue further and collect data which would be necessary for an exhaustive assessment. This stage shall involve the following steps:
- Conducting Non-destructive and other tests to decide properties of Structural Materials
- Deciding actual Structural Framing and Member Sizes
- Deciding type and sizes of actual Foundations
- Conducting Soil Investigation
Collecting data about structural members and foundations can prove to be a big challenge, especially in absence of as built structural drawings.
Stage 3 - Structural Analysis, Capacity Checking & Strengthening
In this stage, using the data collected in the previous stage, the structural engineer will be able to conclude the strength and stability of the existing building with or without the proposed modifications. It must be noted that the reliability of the results of the structural analysis and capacity checking would largely depend on the authenticity of the data collected in Stage 2. The steps to be followed in this state shall be as under:
- Preparation of Structural Framing Drawings
- Deciding Loading &Performance Criteria
- 3D Modelling and Structural Analysis
- Checking of Member Capacities
- Conclusion on Strength, Stability & Strengthening if necessary.
Purpose of Structural Audit
The main purpose of Structural Audit is to answer the following questions:
- Can the building ensure satisfactory performance for its intended mode of use?· Are there areas where structural stability may be a concern?
- Is there a grave and immediate danger to the life and property of the owner/occupier?· What could be the probable causes for the bad condition of the building?
- Is there a need for urgent corrective action or rehabilitation? If yes, what would it be?· Is any further assessment necessary?
A good understanding of structural systems, load path and structural behaviour and good engineering judgment are the essential qualities of a good Structural Auditor. Therefore, Structural Audit should be trusted to a structural engineer who has the necessary expertise and experience in construction materials, structural design, construction practices and building maintenance. Regular Structural Audit, maintenance and rehabilitation is the key to enhance the useful life of a building
Broad Scope of Structural Audit
Structural Audit is a visual condition survey of an existing building and constitutes the first step of any assignment for structural assessment of a building. Its broad scope may be as under:
- Collection of data from the owner: Drawings, history of extensions, repairs etc.· External and internal survey of the building
- Understanding structural system and load path
- Recording general and critical observations (distress maps on floor plans) ·Recorelation and rationalization of observations
- Understanding nature and extent of structural distress
- Conducting non-destructive tests as may be found necessary by the Auditor) ·Understanding probable causes of distress observed
- Identifying loss of stability, settlement or risk to life, if any
- Providing recommendations for further action or remedial measures
- Classification of Building as per guidelines of MCGM
C1: Unsafe …needing evacuation and demolition
C2A: Partially unsafe…needing major structural repairs by partial evacuation
C2B: Requiring major
Statutory Provisions of Structural Audit
The current provision of Structural Audit has its origin in the amendment to the Mumbai Municipal Corporation Act, the Bombay Provincial Municipal Corporations Act,1949,the Chy of Nagpur Corporation Act,1948 and the Maharashtra Municipal Councils, Nagar Panchayats and Industrial Townships Act,1965 which was published in the Maharashtra Government Gazette on 14 January 2009.This had led to the insertion of new sections in the respective Acts under the subject “Structural Stability Certificate
Some salient features of Section 353B as per Mumbai Municipal Corporation Act as modified up to 8th December 2011 are as under.
- It is a mandatory provision which came into force with immediate effect.
- It mentions “Examination of the building by a Structural Engineer for fitness for human habitation” which can be construed as a “Condition Survey” While such an examination has later come to be known as “Structural Audit”, it was not termed so in the original provision.
- First Structural Audit to be done when the building is aged 30 years or older from the issue of Completion /Occupation certificate OR physical occupation of at least 50%of its built-up area, whichever is earlier (certificate to be submitted within 1 year).
- Subsequent Structural Audits to be done every 10 years thereafter.
- The “Structural Stability Certificate” mentioned in the provision is defined as the “Certificate of Fitness of the building for Human Habitation“.
- Structural Auditor must be registered with the Corporation.
- The Commissioner can direct the owner/occupier to carry out Structural Audit at his discretion.
- Corrective repairs to be carried out by the owner or occupier within 6 months from the date of Structural Audit Report. On failure, may be punished with a fine as provided in Section 471.
- If corrective repairs are not caried out by the owner/occupier, the Commissioner can carry out the same and recover the cost from the owner/occupier
Provisions in the other Acts are similar and the reader may look them up in the Act of his interest
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