Building safe homes: How to carry out a structural audit

The recent building collapse in Thane has raised troubling questions about the safety of buildings. What does carrying out a structural audit really mean? And how do we keep our buildings structurally safe?

Built in 1964, a building close to the Thane station collapsed during the night of August 4, 2015. Two families and three generations were completely wiped out. Such stories jolt people and local governing bodies awake to the issue of maintenance of their dwellings. Maintenance of buildings and carrying out structural audit is similar to carrying out routine health check-ups. It is structural health monitoring and is a must, especially if the building is more than 30 years old. In the first of this two-part series, we shall understand what conducting a structural audit entails, as well as when and how to go about it. 

It is advisable to carry out a structural audit of your building every ten years or so. The Municipal Corporation of Greater Mumbai and recently even the Thane Municipal Corporation has mandated that buildings more than 30 years old should conduct a structural audit. A reputed agency or structural engineer who is registered and has a Structural License from MCGM or the Thane Municipal Corporation should be appointed to carry out the audit. An audit involves three stages – examination, evaluation and prescription. 

Examination
Once an agency has been appointed for the purpose of carrying out the audit, provide all prior information on renovations, repairs and history of the building to the engineer. Provide all architectural layouts and structural plans if available to the engineer. Most building societies do not have such plans. It is advisable to get such plans prepared with as much detail as possible from the engineer at the start of the audit and keep a copy at the society office. The examination stage should involve a detailed visual observation and light hammer tapping of all structural elements. The engineer should map visual observations such as cracking in members, concrete quality and spalling, dampness and leakages and observation of any exposed or corroded reinforcement on the developed drawings. The engineer should also note any settlement issues and foundation deterioration issues if visible. The complete building, including external façade, internal units, basement, terrace, water tanks etc that form an integral part of the building should be assessed.

Non-destructive testing (NDT) of a few structural members is recommended. NDT provides qualitative assessment in terms of the quality of concrete, strength of concrete and extent of deterioration of load carrying capacity due to corrosion and carbonation processes. It is necessary to carry out these tests on the concrete member rather than just the external plaster. It is advisable to allow the engineer to damage some external plaster so as to reach to the concrete. This helps in assessing the actual conditions of the structure. More information on the aspect of NDT can be found here.

In general, NDT tests include – Schmidth Hammer Test for strength of concrete, ultra-sonic pulse velocity for quality of concrete, core test for in-situ strength of concrete, carbonation test and EMF test to assess extent of corrosion of steel reinforcement.

Evaluation
Data from all the visual observations, test reports and preliminary information collected should be presented in the report with a detailed analysis and comment on the health of the structure. Based on the NDT tests performed, the audit report should contain a comment on the strength and quality of the concrete in the structural members. The evaluation should provide a clear picture of the current health of the structure, including the causes of any deterioration observed. It should comment on the current durability of the concrete and the expected service life of the structure. It should comment if excessive loading or change in use of building has been observed.

Prescription 
The purpose of a structural audit is also to understand the possible solutions for the damage that may have been observed in the building. The report should provide a brief recommendation on a possible retrofit and repair scheme if necessary. The eventual outcome of the audit should be an understanding on the future safety of the building based on current loading parameters and durability conditions. A report prescribing methods to achieve habitable and safe building is the desired outcome.

A timely structural audit aids in increasing the life of a structure as well as maintaining the value of the structure. It is a required maintenance tool for buildings. 

The author holds a PhD in Civil Engineering from Purdue University. She has taught at several Universities in the USA and currently is Principal Consultant at Renuka Consultants.