It can be stated with pride that construction and maintenance technologies in ancient India were developed to a high extent. Structure in sound condition built 500 to 600 years back are commonly found spread all over India.
However, it is also a matter of regret that a large number of structures built after 1947 have been giving substantial problems and some of the failures like that of Mandovi Bridge in Goa are worth quoting which happened to be within two decades of construction.
It is, therefore, a high time that engineers, both designers, constructors and maintenance engineers came together to have correct strategy in order that lessons are learnt and progress is made.
Early construction technology was based upon simple, natural structural materials like clay, stone etc.. These materials have been performing admirably well. The construction process was based on experience and emperical knowledge. The margins for structural safety were variable and often rather large. The acretetion of knowledge was slow and new materials of construction were few and far between.
In the 20th century even an ordinary person aspired to get a comfortable giving accomodation. To attain this goal it was essential to reduce costs.This could be achieved by refining design process, reducing the unnecessarily heavy sections of structural materials and bringing down the safety factor. This period also witnessed evolution of new material like steel etc.. which are comparitively unstable when compared to store, clay etc... hybrid forms of construction started coming in combining the traditional type of construction and the new materials together. This could mean that the construction suffered from deficiencies of knowledge. and unstableness as experience of durability of new materials was necessarily limited.
Currently, expectations of standards of comfort and environmental performance are increasing. The services to be provided in building have increased to a large extent. New materials based on new metals, new alloys, petro-chemicals have started coming. many of these are stated to be wonder materials even though no-long term experience is available.
Environment of buildings is changing fast. pollution, which is man-made, is taking a heavy toll of buildings. Pollution levels are increasing everyday in most of the cities and new pollutants are coming up with the manufacture of new materials. these environmental conditions are producing unhealthy buildings.
Levels of ordinary skills are on the decline. the level of th eskills required for new materials are not matching with the skills available. many times a good laboratory product fails at site because of such difference of skills.
All this has complicated the job of maintenance engineers. Amaintenance engineer is expected to not only maintain the present level of comfort etc.. but also to improve upon it and in many cases to rectify defects of design and construction. Unfortunately, there is not much of data available, nor the subject has received much of importance in the teaching institutions so far.
Building deterioration manifests itself in a variety of ways right from a total collapse of structure, extensive cracking which makes the structure unavailable or unfit for human habitation to many types of cracking which are not structurally unsound but aesthetically upleasing.
There are many reasons for such a deterioration which can be enumerated as follows:
a) Structural form and deficiency.
b) External forces.
c) Internal Forces.
d) Role of substructure.
e) Instability in fabric and cladding.
f) Instability in materials.
g) Dimensional instability moisture.
h) Instability due to thermal movements.
i) Instability of coatings.
j) Instability due to living beings.
These factors of deterioration are discussed in depth in paragraphs to come.
a) Structural Form and deficiency:
The anture of response of the structure will depend on the form of laoding, particularly, the direction and maginitude of the force. it is also very much dependent of the structural form.
In the traditional form of construction, due to limitations of the strength of constructional materials, the spans of spaces were limited which resulted in a well tied structure. Hence, deterioration due to form of the structure was few and far between. With modetn high strength materials of construction, the inhibititions of spans have been less, thus,more artistic building form have resulted which are many times unstable due to the structural form itself.
Generally creation of modern buildings relies more heavily on connections, often between materials with fundamentally different characteristics. These joints are the areas of concentrated stresss. many times the flow of stresses around the joint is not worked out properly by the designer and even if the designer has worked it out in his drawings the construction, the engineer is unable to get constructed.
The design and construction philosophy of the pre-second World War era was soft form of construction which was oriented towards allowing accomodating and concealing movements within the construction. The structure would undergo large amount of distortion without losing the structural stability.
In comparision, the modern structures where large modules of construction exist, where large range of materials with variable dimensional stability exist, the range of physical movements increase rapidly. The number of joints are now less with large spans of construction. Flexibility of traditional structure has been replaced with regidity.
Classical example of this type of failure is the famous "Roman Point failure" Here a relatively minor gas explosion on 5th of 22nd storey system built block blew a load bearing member out and there was a progressive failure of the building due to lack of redundancy in fixtures.
The form of structural design should have a correlation with the working tolerence and quality of construction force. For example, use of transfer girders or trusses to get column- free space on the ground or intermediate floor presupposes that these transfer girders are exactly plumb and in a straight line. The stability of all joints depends on the truss or girder being plumb and in a line. But is the construction force capable of doing it? The construction labour may consider that out of plumbness of 3-4mm as negligible and this small assumption can throw all the design calculations out of gear due to very heavy secondary stresses involved. Design assumptions about quality of site installations are far too optimistic and inspections by qualified personnal are fewer and there is always some dead line to be attained, whereby unacceptable work gets accepted.
With the movement towards slim and tall structural elements there is a corresponding increase in slenderness ratio. The modern design criteria for brick work for laod bearing walls has been developed around concepts of required thickness in relation to height and length. however, the quality of plumbness and quality of joijnts in the brickwork is expected to be excellent which unfortunately it is not.
Even in a framed construction, whether of steel or in RCC, the plumb is difficult to check, and hence, it is not checked. Corkscrew type of external columns is a common sight.
All this causes problems of stress concentration and attendant attemp by the structure to releive and re distribute stresses by cracking. But this cracking allows entry of Co2 leading to early carbonation of RCC and entry of water leading to corrosions. The structure therefore, suffers from less durability.
The older structural forms were rectangles,squares etc...The cantilever concepts were limited due to poor strength of materials. now the structural designers try toinitiate in RCC etc.. the artistic buildings of fancy shapes, large cantilevers etc.. unbalanced spans of structures with noticeable large differences of defections either due to loading or through thermal changes. All these acrobatics of designs result in cracking in places with attendant problems in maintenance.