Treatise on Condition Surveys for Concrete and Masonry Structures

Condition assessments of structures are performed for various purposes and for various causes. Consultants who are involved in repairs/retrofitting of structures should possess knowledge and experience of different causes that lead to deterioration of structures as well as expertise in analyzing the evidences collected through visual inspection as well as instrumentation. Strict quality control and good construction practices are also key factors that contribute to durable structures.

The quality of construction in our country has not risen to such a level for categorizing it as good, leave excellent. In such a situation, the potential of repairs and rehabilitation field is immense for the next at least 50 year. Concentrated R&D efforts in the field of repairs and rehabilitation supported by Government, is a need of the hour in order to develop controlled and organized restoration system across the country. Some initiative is needed from Government to attract good and intelligent manpower to the field of R&D and repairs to promote this field, looking at the potential.

Chetan R Raikar, Structwel Designers & Consultants Pvt. Ltd., Mumbai

Introduction

Condition assessment/survey of Civil Engineering structures needs great amount of knowledge and experience of practically all the aspects of construction namely structural design, material behavior, construction techniques, failure assessment etc. Condition assessment can be for many purposes. To enlist a few:

1) Assessing life expectancy
2) Insurance purpose
3) Pre-repair / restoration effort
4) Assessing age related damage
5) Assessing the damage caused by Calamities like earthquake / fire / flood / blast etc
6) Assessment of structural stability of buildings in the vicinity of infrastructure construction in metros
7) Early age damage due to design deficiency

Condition assessment can also be carried out to plan a maintenance strategy particularly for industrial plants.

Knowledge of why structures fail is as important as to know why they don't. A Consultant hence must be a combination of a structural engineer, a material scientist, a construction expert, a testing expert. Teams can be / shall be formed involving team members possessing various skills mentioned above.

Purpose of Condition Assessment

Remnant Life Assessment
All components of a structure do not fail simultaneously and have different life expectancy. Similarly, all plants in a big industrial plant like Refinery do not have same number of years of trouble free life though they are all in the same environment. This fact must be clearly understood before taking up life expectancy evaluation and maintenance manual preparation for various structures in an industrial plant. We have recently completed similar exercise for a large refinery complex in Gujarat. This gave a clear advice to client in depreciating their structures and preparing for repairs / reconstruction. Various structures were assessed and maintenance manual was prepared expecting different damage to various structures depending on the micro environment each structure was subjected to. For example: Sulphur pit (as in Fig.1) has much lesser life expectancy compared to a pipe rack though both are situated in the same industrial plant.


Condition assessment of power station for remnant life assessment is yet another interesting engineering exercise. Condition assessments of roads and highways whether rigid or flexible have far too many bureaucratic / political interventions. This is probably the reason of early failures or extremely poor riding quality of our roads.

Fire / blast damage


Fire damage / blast damage is yet another engineering challenge in case of assessing the residual strength of damaged material / structural members. Various construction materials like concrete, reinforcement, stone, wood etc behave differently at different temperature and duration of fire. Taj Mahal hotel (as in Fig.2) was restored / conserved by us after the 26/11 carnage which had all the above mentioned materials subjected to blast / fire. Use of microscopic test like petrography, endoscopy and other advanced tests like TGA, XRD are extremely useful while carrying out condition assessment of affected structure.

Corrosion damage
Corrosion assessment is a type of damage which is prominent along the 2000 km coastal line that our country has (as in Fig.3). Industrial structures exposed to corrosive chemicals like Naphtha, Ammonia etc also are subjected to extreme corrosion (as in Fig.4). Assessing corrosion damage in structures is a great challenge since the non destructive testing that can be deployed to assess the percentage corrosion of re-bars has high level of inaccuracy and low level of dependency in the field. Though this equipment is reasonably accurate for R&D purpose in the lab environment, the same has limitations due to high degree of variation of the condition from site to site. To assess the load carrying capacity of structural members affected by corrosion is a bigger challenge hence it is also not easy to repair corrosion damaged re bars in the field to full satisfaction of the structural members.

Earthquake damage
Earthquake damage (Fig.5 and Fig.6) assessment is a combination of structural damage and material damage. Ability to assess the stability of structures immediately post earthquake is extremely necessary while getting involved in condition assessment of earthquake damaged structures. It is noted that many consultants tend to "over specify" strengthening measures to an earthquake damaged structure. This may be due to either the fear of limitations of their assessment or due to improper understanding of the standard. Earthquake damage assessment of load bearing structures requires great degree of understanding of load bearing structures and experience in similar capacity under expert.


Early age damage due to Design Deficiency and Original Construction Deficiency (OCDs)
Unfortunately, majority of the construction in our country is carried out without involvement of a competent structural engineer / architect. Engineered projects are being discussed and debated in technical seminars and the standards are being evolved for betterment each day. Most of the ground storey construction in 3rd tier cities, towns and villages does not have engineering support. Soil investigation is carried out only in 1% of the construction projects. This percentage may be debatable but the author wants to express that soil investigation is carried out in minuscule number of projects across the country.

Strict quality control and good engineering practices are not followed in most of the small and medium sized projects including infrastructure projects. This gives birth to a defective structure which requires investigation during early age of its service life for structural stability. Leakage in the structure is almost from the first day. Settlement cracks and other structural defects are noticed very soon after the structure is put to use.

Invariably, structural drawings of even these recently constructed structures are unavailable with the owners. This proves as a major hurdle in the assessment of distress observed in the structure. Architectural drawings can always be prepared by physically measuring the structure during any part of its service life but preparation of structural drawings particularly for RCC framed structures and pre- stressed concrete structures is extremely difficult during the service life. Preparation of structural drawings of foundations is nearing impossible task and the cost/inconvenience makes it unviable. Ironically, architectural / interior drawings of most of the structures are invariably available, probably due to FSI regulations and other statutory compliances.

Many structures need investigation due to improper / inadequate structural designing. Competitive designs provided by Contractor as a part of "design and build" is a typical example where several statutory regulations are flouted due to the desire of maximizing the profit. Case studies like collapse investigations of ESRs and retaining walls in infrastructure projects are good examples of failures which are related to lacunae in the systems. Staff housing in several mega industrial projects is yet another area which does not receive as much importance as their counter parts in the industrial plant. Several staff housing projects show distress in the form of settlement, early corrosion, leakages and extensive cracking etc due to original poor construction and deficient design.

Age related damage
Construction chemicals and other SCMs (supplement cementitious material) are being used in our country for more than 3 decades now, unfortunately, only in very few projects. The quality of concrete across the country still varies from "poor" to "medium" in most projects. Only in very few projects, it falls in the category "good" to "excellent." Most of the projects hence show age related damage during early part of service life which may vary from 5 years to 20 years depending on the quality of original construction, the environment in which the structure is situated, maintenance etc. Most structures situated in coastal area need major repairs after 10 years of service life. Unfortunately, this is an accepted norm across the industry and very few engineers strive to construct structures which can provide a trouble free service life of minimum 25 to 30 years.

Poor quality honey combed concrete with cold joints has become an accepted feature. The same is repaired immediately post stripping of shuttering but in the most unengineered way. This gives rise to early age corrosion of reinforcement and reduces the serviceable life of the structure substantially. Construction of brick work, plaster, waterproofing and other finishing items like tiling etc needs a much desired improvement in quality. It starts with training the young engineers and architects in their colleges about good engineering practices of construction that must be followed during construction. Much emphasis is given to construction of quality concrete. The quality assurance efforts are reduced apparently as soon as the RCC construction is over and finishing items are left to the discretion and competency of the construction workmen. Very few contracting companies conduct organized training to their workmen for construction techniques and most of the work force that arrives on site across the country is a self- trained (wrongly in most cases), self-proclaimed carpenters / fitters/masons.

All the factors mentioned above lead to poorer quality construction resulting in early age related damage.

Infra projects in densely populated metros
There is a definite need of ensuring the safety and comfort of citizens occupying the structures in the vicinity of infrastructural work under construction in densely populated city / Metros. In structural works like flyovers, Metros, storm water drains needing deep drilling / excavation etc need to be constructed very close to the existing structures. This requires careful assessment of structural stability of the existing structures which are subjected to vibrations due to excavation / piling/ heavy equipment movements deployed in infrastructure construction projects. Developed countries like Singapore have strict norms of dust and noise control for infrastructure projects in construction in cities. Though we are far away from graduating to such stringent norms for the comfort and health of our citizens, we must ensure safety of occupants of old dilapidated structures in vicinity of infrastructure constructions. This is something similar to environmental impact assessment (EIA carried out for mega projects in CRZ and other virgin lands across the country). We have carried out similar assessment for Metro construction and blast excavation up to 70m meters below ground for sewage pumping stations. The Terms of Reference of these assignments had to be evolved in consultation with the Contractor and statutory authority. This needs further evolution so that our investigation and distress assessment is comparable to international standards.

Load bearing structures
Condition assessment of load bearing structures cannot be properly done by most of the engineers as structural designing and assessment of load bearing structures is not taught any more in the colleges. Design of structures using timber / cast iron/ stone as a structural material is long forgotten by most of the engineering colleges. Since load bearing construction is no more popular in majority of the parts of the country, the same is not taught in detail in the colleges. We can't forget that our country with rich heritage has more than 10 Lakh odd old structures constructed using stone, wood, cast iron and are load bearing predominantly. Each part of the country has vernacular style of construction of low height local structures. Some large sized states like Maharashtra have different stones used in different areas within the state itself.

Importance of Accurate Assessment of Condition of Structures

Accurate assessment of the condition of structures has extreme importance in structures like hospitals, schools, bridges which are needed immediately after a calamity like earthquake. This does not mean that the other structures like industrial plants or low rise residential buildings are of any lesser importance to the owner.

Condition assessment of structures of national importance like dams, roads, military installations, bridges etc. require a different level of sensitivity and maturity. It is not easy to accurately specify the load carrying capacity or rating of an existing bridge. Consultants often tend to make an error in judgment either on the positive or on the negative side. A bridge collapse in Southern Gujarat a few years back is an example of misplaced confidence.

There is a great need of retrofitting of most of the structures constructed in last 100 years across the country for improving their earthquake resistance. Many of us are staying in houses which are not designed as per the current earthquake standards. Assessment of all the existing structures to a great level of accuracy is therefore extremely necessary.

"Just the right" is the only way to retrofit a structure. Many structures after the recent earthquake of Gujarat were subjected to retrofitting. In most cases, it was either ineffective / incorrect way of retrofitting that was deployed.

In fire damage assessment, the apparent damage to the structure is always much higher compared to the actual damage. Consultants are seen investigating fire damaged structures using NDTs like Ultrasonic and Schmidt Rebound Hammer only. This is highly inadequate and misleading. It is also important to understand that different areas of structures would be subjected to different temperatures during fire and hence would have different degree of damage. It may happen that two columns in the symmetrically opposite corners of the same room may have completely different degrees of damage in an incidence of fire. This generally is not the case in case of an earthquake. Accuracy of assessment hence plays an extremely important role in case of fire damaged structures.

Sequence of Activities in Condition Survey

Visual Survey
Vision is most important sense that needs to be used by an assessor while performing condition assessment of a structure. Other senses like sound, touch, taste etc. would be secondary. Sufficient light is a main requisite, and tools like binocular, hand held lens, crack width measuring instrument, light hammer etc form the basic kit for the team carrying out the visual survey. Visual survey forms the basis of determination of quantity and locations of non destructive tests along with types of tests on various components of structures.

It is extremely essential that first round of visual survey is carried out by most of the team members together along with the most experienced persons in the consultancy team planned to be deployed for the project. A group discussion carried out by the team on site helps substantially in arriving at the broad strategy for investigation and repairs.

Visual survey also helps in deciding the location and number of samples of different construction material to be collected from the site for detailed laboratory analysis.

Non Destructive Testing
Several Non Destructive Testing instruments rather most of the non destructive testing instruments that are available across the World are available today with many laboratories in the country. Truthful and judicious deployment of these techniques is necessary in carrying out correct assessment of material strength of the structure under investigation.

Interpretation of Non-destructive testing results again requires considerable level of experience and knowledge of various fields of civil engineering like material science, structural engineering etc. This is not possessed by most laboratories that do not have structural engineers in house. Their interpretation is limited to that extent that it becomes stereo type. Their reports if compared over a period of time will be of "copy - paste" type. It is important to understand that NDT and its inference plays a pivotal role in any investigation and a consultant can easily get misled by improper NDT / interpretation.

Structural Assessment
It poses a big challenge to an investigation consultant when the client announces that the structural drawings of the structures under investigation are not available. Considerable effort in the form of NDT needs to be deployed in preparing as built structural drawings. It is necessary to carry out structural designing of the structure prior to recommending reconstruction/ repairs.

As mentioned earlier, designing of load bearing structures using materials like timber, stone, cast iron etc is no more taught in Engineering colleges. Not many structural engineers across the country possess this knowledge, hence. Ability to suggest the retrofitting measures for load bearing structures is way beyond the capability of most of the structural engineers across the country due to this limitation of theirs.

Analysis of the data collected
An assessment team collects data in various forms like visual survey and distress mapping drawings, non destructive testing and inference, structural analysis and short comings etc. The leader of the investigation team has to be knowledgeable and matured enough to carry out a well balanced evaluation of the data to arrive at technically balanced recommendations. It requires great deal of confidence in certifying or otherwise, stability of a structure. This confidence is gained out of several areas of condition assessment of various types of structures. There are very few organizations across the country that possesses this confidence.

Status of R&D Efforts

Though there are several R&D laboratories across the country in civil engineering, very few of these R&D Labs are in private sector which cater to construction industry. Several applied research programs are being carried out individually by the R&D Laboratories spread across the length and width of the country. To the best of the knowledge of the author not many fundamental research programs are being taken up by these laboratories. Also, the common compendium of the R&D works of these laboratories is neither printed nor available on any website. The R&D efforts across the country are hence being carried out in a non coordinated way and we are probably lacking 2-3 decades behind the developed countries in R&D efforts related to construction industry.

Sand dredging is viewed as a major environmental hazard and is banned indiscriminately by the government. This has affected the construction industry severely and consultants / contractors are wandering around in search of a solution. There is immediate need to identify alternatives to sand that are available across the country and are cost effective. Likewise, there are several R&D efforts which are needed to be taken up in investigation and repairs field. To name a few:-

a) Use of organic admixtures in concrete / plastering/ water- proofing. These chemicals have been used for several centuries in our country but no authentic data seems to be available anywhere. They do not find place in DSR of the PWDs which is a major reference document for construction throughout the country.

b) Locally manufactured Non- destructive Testing and other quality control equipment is yet another need of the construction industry. India is a country which is capable of making its own satellite and light combat aircrafts. We sure have the in house capability of developing indigenous NDT equipments and other simple QC / QA equipments. Organized R&D effort supported by the government is an urgent need of construction industry.

c) Structures are being repaired / conserved / retrofitted without proper guidelines and specifications for the last 3-4 decades. Proper specifications and standards are needed to be developed in areas like corrosion repairs, investigation of earthquake, fire and blast damaged structures etc.

Future of the Field of Investigative Consultancy in India

The quality of majority of the structures being constructed is far from acceptable standards. The field of repairs/restoration / conservation / retrofitting has a great potential for the next 50 years at least. There is a tremendous shortage of intelligent technical manpower in civil engineering due to development of other options of engineering like IT / Computer Science etc. Civil Engineering unfortunately is the last priority for most of the engineering aspirants. R&D or repairs is yet again the last priority for most of the civil engineering graduates / post graduates.

The author therefore recommends the following to the construction industry:-

a) Immediately organize competitions for the best R&D programme and innovation in Civil engineering sectors.

b) Increase the salary and other benefits for engineering graduates / PGs who desire to go for R&D / repairs.

c) Encourage more R&D labs in private sector across the country and organize technical get-together at various levels in R&D institutions.

The situation of repairs, restoration, retrofitting industry is not good as regards availability of good quality manpower.

Our country is in an expansion spree in the field of infrastructure construction. There is tremendous shortage of experienced manpower and material in this field. I believe the next generations of civil engineers in our country will have large number of infrastructural projects waiting for repairs, restoration if not constructed well now.

Acknowledgment

This article has been reproduced from the proceeding of 'National Conference on Repair & Rehabilitation of Concrete Structures' organized by ICI western U.P Gaziabad, IA Sructural Engg, and Association of Structural Rehabilitation, with the kind permission of the organisers.