A cosmetic treatment is not enough. To this effect, a general rehabilitation program and modern rehabilitation and retrofitting techniques are briefly described. Analytical aspects of the problem are also presented. In particular, simple mathematical models are described, which may help in locating the exact source of trouble. These models show that the distress in one location may come from a cause, which is located far away. In actual practice, the load transfer mechanism may be more complicated then these simple analytical models. This can be handled by using the advanced analytical technique such as the Finite Element Method.
It is suggested that the modern repair methods must be perfected in the laboratory before transfer of this technology for field application. A comprehensive research program must be initiated and a code of practice should be developed to facilitate proper execution with best results.
India has a huge spectrum of HBM like temples, forts, mosques and other similar structures. Large number of these were constructed several hundred years ago when the Indian Civilization was at its peak. Their architecture, design and construction at the time when computers, code of practice, design guidelines, research institutions and modern construction techniques did not exist makes one to realize the wisdom and expertise of our forefathers. These structures have survived for hundreds of years while most of the modern constructions need repair after couple of years of service. In addition, some of HBM have elaborate arrangement for rain water harvesting, which could be a lesson to all of us in the time of scarcity. The following reasons may be responsible for deterioration and degradation of HBM.
- Action of a natural disaster such as cyclone or earthquake
- Act of sabotage or a casual accident resulting in a fire
- Corrosive action of the contact materials
- Uncontrolled vegetation growth
- Natural deterioration due to aging and adverse environmental factors
- Vibrations due to heavier structural and land use
- Theft and vandalism
- National priorities
Forefathers WisdomThe construction materials like cement and concrete, and concept of putting steel reinforcement in the tension zones of a structure were, perhaps, not known at the time when some of the HBM were constructed. However, most of the existing HBM are symmetric in shape and their base is wider than the top. This shows, as described subsequently, that our forefathers had thorough knowledge of tension and compression. They devised efficient structural systems for the Available construction materials and technology so that the external loads could be safely transmitted to the foundations without causing tension anywhere in the structure.
where i = 1 and 2, respectively Where I [= DL3/12] is the moment of inertia of the cross section of the base about its neutral axis. Other symbols are identified in Figure 1. The development of tension amounts to uplifting of the base, which must be prevented at all costs. The condition given in
The vertical load W and lateral load P can be combined into an eccentric load W with eccentricity e, so that e = PH/W. The eccentricity is measured from the line of symmetry. This enables an alternative formulation of condition to prevent uplifting of an eccentrically loaded structure.
According to this the resultant of all forces acting on the structure must pass through the middle third region of the base. This may require enlargement of the base to accommodate uplifting caused by the lateral loading. This is a typical feature of most existing HBM, which gives a feeling that these kind of structural mechanics principles were known to the designers and builders of Indian HBM. Similarly, a symmetrical rectangular shape of HBM provides excellent resistance against torsion.
Consider the equilibrium of two building blocks resting over each other (Figure 2). The lateral load P will not initiate sliding if Equation 3 is satisfied.
Where µ is the coefficient of friction between the two surfaces and r is the material unit weight. Also, (X < B/2) will prevent toppling of the top block. A resultant force diagram can be constructed to study the equilibrium of several building blocks resting over each other (Figure 3). This information is readily available in the standard textbook on structural mechanics .
This kind of technology is extensively used in the Indian HBM. It appears very elementary in light of information available in the existing technical literature. However, it was known to our forefathers several thousand years ago. It is likely that our forefathers either did not document their technology or the related documents perished over a period of time. These concepts were rediscovered in the Western countries much later and are credited to others because these were properly documented. There is a story also that some rulers were so possessive of their monuments that they killed builders/craftsman after completion of a monument to prevent them from building a similar or better monument for another rival ruler.
Typical Damage ScenarioDamage in a typical HBM, which has existed for thousands of years, may take any of the following forms. It must be mentioned that most HBM have been neglected over a period of time so that damage keeps on accumulating.
- Loose building blocks, particularly in roof
- Seepage and leakage of water
- Corrosion and discoloring
Sources of DamageThe possible changes in structural system (or load transfer mechanism) of HBM over a period of time may be one or more of the following:
- Change in land use
- Change in eccentricity of loading
- Change in cross section of beams and columns on account of corrosion
- Change at interface of the building blocks–cracking and corrosion
- Change in foundation conditions– Differential settlement of foundation
- Seepage of water through cracks
- Action of bacteria, insects and rodents
- Plant growth
Change in ground water conditions and drainage conditions around the HBM could be a source to produce differential settlement. The plant seed blown either by wind or deposited in the bird droppings start to grow. The roots of these plant fracture HBM parts. Such sites could be ideal location for damage growth. As a first step towards the rehabilitation of any HBM, all plants must be effectively uprooted. Some other above mentioned points are elaborated in subsequently.
Effect of Change in Structural CharacteristicsThe structural characteristics such as joint rigidity and bearing capacity of ground may change with time. Such changes shall affect the integrity of HBM. Some examples are as follows.
Change in End StiffnessAnother example is given in Figure 5 in which fixed ends of the beam are losing fixity on account of deterioration in the material. A comparison of bending moment and deflection of simply supported and fixed ended beams under a uniform load of w per unit length shows that the deflection becomes five times while bending moment increases by a factor of 3. The additional deflection may bring the beam in contact with some other non-load bearing members and damage them by transfer of load. Again it may be noted that the damage in the beam or any other neighboring member is due to change in the rigidity of joints. These unrelated events cannot be diagnosed unless analytical models are prepared and analyzed. The above simple analytical models serve to illustrate the theme of this paper. However, these models may become fairly complicated in other real situations and one may have to use more sophisticated analytical tools like finite element analysis. It is not a bad idea at all to undertake preparation of finite element models of all HBMs and collect this information in a data base. As soon as a problem appears in a HBM, it could be immediately sorted out.
Member Size Reduction Due to CorrosionTable in Figure 5 shows that the deflection of a structural member depends upon modulus of elasticity (E) and moment of inertia (MI). Reduction in member size reduces MI, which increases deflection. Similarly, reduction in E also increases deflection. Reduction in EI changes distribution of BM in statically indeterminate structures. The consequence of change in BM appears in development of tensile stresses. On the other hand, due to excessive deflection, some load– bearing members come in contact with non–load bearing members and load transfer in unspecified directions takes place. This is clearly a sign of trouble.
Damage Due to Incoming Ground Vibrations and Control Vibration of ground due to movement of heavy vehicles and tourists in and around HBM can be a cause of distress. Trench construction around HBM could help in controlling such vibrations (Figure 6). These trenches can be scientifically designed and architects may locate these in an Aesthetically pleasing manner to blend with the surroundings. The length of Raleigh waves, which depends on the frequency of excitation, is the controlling factor in the design of these trenches. The design parameters in this case are the depth and distance of trench from the HBM. The presence of water table, if it is shallow, must be taken into account. These trenches may be filled with any soft material. Fly ash may be used to advantage.
Hilly Area HBM
It is well known that hills are in a state of fragile equilibrium, which can be disturbed by any unmindful and unplanned construction activity. Activities involving new construction require deforestation, apply extra load on slopes and tend to alter natural drainage pattern. In addition, greater number of visitors are generating big amount of waste which is usually dumped in to the valley. No proper waste management strategy appears to be implemented. A railway line from Kalka to Shimla in Himachal Pradesh was constructed during British rule. The railway passes through several tunnels which are now showing signs of distress.
Source of this distress lies in the construction activity around the tunnels. Effect of these development activities on the safety of tunnels has never been studied.
Source of damage in any hill area HBM can be easily traced to any other construction activity in the region. In such cases no amount of treatment of the shrine itself is going to help. The local administration and developmental agencies must not allow random construction activities. All development must be strictly controlled. If this does not happen now, the HBM may vanish Altogether in due course of time.
Rehabilitation ProgramIt is known that each of Indian HBM is a meticulously designed and skillfully constructed structure. An equally competent and compatible strategy is required for their preservation. It should commence with an analysis to arrive at the structural system and the mechanism of load transfer. A general rehabilitation program shown in Figure 7 may be adopted.
Modern Methods of Structural RepairTable 1 describes the modern methods of structural repair. Anyone or a combination of these may be found suitable in the repair or strengthening of HBM. The primary requirement is that the appearance of the HBM after repair must become compatible with the adjoining portions. These techniques are extensively used in the advanced countries for the seismic retrofitting of structures and a large number of publications covering analysis, design and construction aspects are readily available in the published literature (see bibliography at the end of paper). It is highly appropriate that laboratory studies on these be initiated in India to perfect usage of such technology before its transfer for field application. In addition, the exploration and treatment procedures for HBM foundations must also be perfected. Extremelyadvanced technology is now available  through which it is possible to look under HBM without excessive disturbance to the existing construction. Mathematical models of damage and repair should also be perfected .
A special requirement in connection with repair of HBM is that the repair method and material must not change the appearance of HBM. This requires more effort.
In the preservation of these HBM a scientific and holistic approach based on sound analytical models should be employed. This paper describes several reasons for distress in HBM and also presents analytical models to logically explain the observed behavior. In actual practice, the load transfer mechanism and the analytical model may be more complicated. For example, there may be variable cross section area. The secan be handled by using the advanced techniques such as the Finite Element Method. Proper development of understanding of the distress signs is of utmost importance. It is interesting to note that distress in HBM at a location may occur due to the cause located elsewhere.
The modern repair methods must be perfected in the laboratory before transfer of this technology for field application. A comprehensive research program must be initiated and it should be described in a code of practice to facilitate proper execution with best results. These HBM are reminders of civilization, which flourished in Indian subcontinent. These must be preserved at all cost.
- Marinos, P. G. and Koukis, G. C. (1988) Engineering geology of ancient works, monuments and historical sites. Proceedings of An International Conference, Vols. I – IV, Athens, Greece, Balkema Publication.
- Norris, C. H. and Wilbur, J. B. (1960) Elementary Structural Analysis. McGraw Hill Book Company, USA.
- Woods, R. D. (1968) Screening of surface waves in soils. Journal of Soil Mechanics and Foundation Engineering (ASCE), Vol. 94 (SM4), pp. 951 – 979.
- Harrison, H. B. (1973) Computer Methods in Structural Analysis. Prentice Hall of Australia.
- Kumar, P. et al (2001) Mathematical modeling of structural damage and repair. Proceedings Structural Engineering Convention-2001, Indian Institute of Technology, Roorkee, pp.888-898.
- P.C.Sharma Ferrocement Lining for water proofing Rehabilitation and Retrofitting of RCC and masonary structure (keynote Lecture) International workshop. Repair, Rehabilitation and Retroffing of concrete & masonary structures–Oct 2004, Gedu Bhutan.