CHAPTER - 8

ENGINEERING DISCUSSIONS ON THE STRUCTURAL SPACES AND BUILT

FORMS OF KERALA TEMPLE áRIKOVILS.

8.1. General.

The temple ¿rikovils were/are built as per v¡stu principles, concepts and

canons. They endured for centuries. A study on the ¿rikovils for their structural

stability, sustainability, strength and durability from the point of view of their

structural spaces and forms is probably, a new endeavour. The word stability

from engineering point of view pertains to 'standing firm maintaining the

equilibrium condition for a prolonged period'. The word sustainability pertains

to 'standing to bear, to support and keep going for a long period. The durability

is the capacity of the structure to last long or endure. It should endure all

stresses, strains, moments, and fatigue and maintain stability and serviceability

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for the intended life period. The strength pertains to the safe resistance against

various forces and moments. It may be offered by the materials used in the

members of the structure, and the joints and connections in the structural

system. In the case of temples the life intended is 'kalp¡nta', a very long period of

life. The discussions are channelised under two main headings namely the

structural spaces and forms. The elements to be included for the study have

been mentioned in chapter VI. The discussions are made as brief as possible to

keep the main impacts intact. Rigorous calculations and analyses are purposely

avoided, which may be taken up for separate researches.

8.2. Structural Spaces of árikovils.

The structural spaces include the horizontal and vertical spaces. The

horizontal spaces include the plan shape, geometry and interior arrangements in

¿rikovils, the walls, corridors and the like. The vertical spaces include the three

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dimensional aspects of the elements like adhis¶¡na, walls, roof as spacial

structure, their connections, proportioning of the various elements and parts.

The basic structures in two dimensional and three dimensional aspects are

covered under the heading 'the structural spaces'. The engineering aspects are

discussed briefly in subsequent paragraphs.

8.3. árikovils as Structures.

A structure or structural system is built up of many components

(elements). The capacity of a structural system will depend on the capacities of

its components. The behaviour of the system depends on the performances of its

components. Civil engineering structures are invariably a kind of system. The

reliability of the structural system of the multiple components with multiple

failure modes is to be considered from the system point of view.414

414 Reliability Analysis and Design of Structures, R. Ranganathan, Tata MC Graw - Hill Publishing

Company Ltd, New Delhi, 1990, p.268.

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The ¿rikovils are built up of many components like the foundation on

which the basement, the wall, the body, the neck, the roof, the finale, namely the

six main parts as puruÀa. All elements have their functions, separate entity as

sub systems and function as a system. The system of ¿rikovils fits well as a civil

engineering structural system. The reliability of the structure depends on the

behaviour of the elements and the structure as a whole. Hence, the ¿rikovils

considered as structural systems can also be subjected to the structural analysis

using appropriate method(s) among many methods available. The canons and

concepts used in the planning and design of temples were based on thumb rules,

probably, based on the experiments and experience. The evolution of analysis

and designs had under gone transformations from thumb rule, working stress,

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ultimate load, limit state, finite element, plastic, probabilistic and experimental,

turning a full circle.

The main loads/forces for the analysis and design of a civil engineering

structure like building are the dead load, live load, wind load, snow load, seismic

load, soil pressure, erection loads, impact load, temperature effects separately or

in various combinations.415

All the loads/ forces given above are applicable to the ¿rikovils also. The

live load, constituent of the loads system, requires modifications as the live loads

mentioned in the code (IS. 875 of 1984) do not fit in the ¿rikovils category. The

live load (superimposed load) in ¿rikovil is very small, probably it can be limited

to repair and maintenance. In the various types of stresses applicable to the civil

415 Design of Steel Structures, Vol. I, Ram Chandra, Standard Book House, 1705. A, Nai Sarak,

New Delhi-6, 1989, pp.19-28.

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engineering structural systems like direct tensile and compressive stress, bearing

stress, bending stress, shear stress, temperature stress and certain combinations

of stresses are also applicable to the ¿rikovil structural system. The factor of

safety is defined as the factor by which the yield stress of a material is divided to

give the working stress in the material.416 In common terms it is the factor by

dividing the failure load with the allowable load. The factor of safety for the

elements of ¿rikovils, generally felt, is much higher compared to other types of

structures. Higher the factor of safety, heavier will be the sections of members.

The concept of factor of safety might have seen in-built in the design processes of

the ¿rikovils but may not be by this term, as the intended life of the structure

might be many centuries.

416 Ibid., pp.32-34.

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The basic methods adopted for the design of temple ¿rikovils are

generally the simple design, semi rigid design and rigid design. Less rigorous

and complicated designs are adopted. The supports are mostly simple supports,

continuos supports (like in the case of wall plates), semi-rigid supports (like in

the case of ceiling) and rigid (like in the case of wall plates at the corners).

Bending moments are minimised by providing corbels like potika over the pillars

supporting the beams. Bearing stresses are reduced by providing larger area by

means of oma at the bottom of pillars. Larger sections are provided where the

shear stresses are more near the supports by adding potikas or corbels.

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The conditions of equilibrium are satisfied as can be observed at every

mode of the ¿rikovils. The satisfaction of three force equations and three

moment equations establishes that the structure is in equilibrium.417

The six equations of equilibrium are:

Fx = 0 Mx = 0

Fy = 0 My = 0

Fz = 0 Mz = 0

In the cases of trusses (spacial structure) the planar trusses are in equilibrium

(statically determinate) if

2 j < m + r, the structure is statically in determinate

2 j = m + r, the structure is statically determinate.

2 j > m + r, the structure is unstable.

417 Basic Structural Analysis, C.S Reddy, Tata MC Grew-Hill Publishing Company Ltd, Asaf Ali Road,

New Delhi-2, 1989, pp. 13-14.

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The unstable conditions did not have occurred in ¿rikovils as evident

from the long life and remaining stable. The other conditions are pertaining to

the stability against over turning by ensuring sufficient restoring moments

against the overturning moments and also providing counter weights/anchorage

for overhanging members. Stability against sliding, lateral, sway due to wind

load and probable variations of dead loads and imposed loads (wind and seismic

loading shall be taken as imposed loads) are to be ensured. The stability of

¿rikovil is ensured by inherent design and construction. It will be discussed

more in details in this chapter.

The serviceability conditions on excessive deflection, cracking of flexural

and compression members leading to failures or unsightly appearances are also

to be met. Such undue deflections and cracks are seldom found in ¿rikovils.

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8.3.1 Contributions of the plan shapes and horizontal spaces

of ¿rikovils.

The aspect ratios (length - width ratio) is 1 for square, octagonal and

circular shapes. The aspect ratio of apsidal shape is 1.5. The aspect ratios

for rectangle and square with projecting mukhamandapas, however, do

not exceed 2. The munis like Garga and DakÀa preferred the length not

more than double the width.418 As per plates and grid theories the aspect

ratio of 2 or less ensures two way distribution of stresses.419 If any

element is plane, thin to act as plate, the stress distributions will be in

two directions, higher stresses in shorter direction. The example is two

way slabs.

418 ManuÀy¡layacandrika, Ch.4, Sl.9. 419 Theory of Plates and Grids, Timoshenko and D.H Young, M.C Graw-Hill International Edition,

New Delhi, 1956, Ch. Theory of Plates.

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The shapes of the structure influence the stresses due to wind

load. In all cases the calculated wind loads act normal to the surface to

which they apply and act at the projected area perpendicular to the

direction of the wind. National building code420 gives the pressure

coefficients for various shapes, length-width ratios and height-width

ratios. The aspect ratios and height-width ratios do play important roles

in deciding the pressure coefficients in addition to the shapes as it can be

seen from the tables given in the part 6, clause A of the National Building

Code, 2005.

The horizontal spaces in temple ¿rikovils in all shapes except

apsidal afford axial symmetries in X, Y and Z axes. It affords uniform

axial spaces and uniform loading about the axes, helping to maintain the

420 National Building Code of India, Bureau of Indian Standards, Manak Bhavan, Bahadur Shah

Zafar Marg, 2005, Part-6, Clause-4.

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equilibrium and stability. Apsidal shapes afford axial symmetry only in

Y direction. They are to be treated as special type of structures.

In storeyed ¿rikovil structures the plan shapes remaining the

same, the sizes (length, width and height) are reduced in proportion to

the lower storeys. This arrangement makes the structure heavier at lower

storeys and lighter at higher storeys. It acts more or less like a pyramid,

the most stable structure. However, it may not have the apex in

pyramidal form, as there may be a storey on top. This method of

reducing the plan sizes and heights at every storey coming one over the

other helps in bringing the centre of gravity lower which enhances the

stability. The dead weights are fully balanced by the axial symmetries.

The horizontal forces due to wind and seismic effects and the vertical

forces produce the resultant force, which invariably in temple ¿rikovils

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meet the bottom within the middle third causing practically no tension

in the masonry structure.

The outer walls of the ¿rikovils support the roof fully in case of

small temples without corridor inside. In case the ¿rikovils having

corridor, the load of the roof will be shared by the wall/pillars provided.

The outer walls and walls of antar¡las are invariably load bearing type

and have separate foundations. The wall thickness varies from 1/8 to

1/16th of the pr¡s¡da width or 1/6 to 1/11th of the height of the wall/pillar.

The minimum thickness adopted for small ¿rikovils ranges from 24 to 50

cm. In larger ¿rikovils it goes upto 120 cm. The garbhag¤has, if provided

separately with corridors around are almost independent structures

inside the ¿rikovils. Sometimes in small temples the walls of garbhag¤ha

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and outer walls of ¿rikovil merge each other by thicker walls.421 Case

studies have proved this aspect and also these thick walls support the

walls above the ground floor. (examples: áiva Temples at Tiruvannur and

Trikandiyur).

A workout sheet is attached at Annexture-2. The factors of safety

worked out for masonry walls (typical cases) are very high compared to

the contemporary situations. However, there were no methods of

rigorous analyses and designs available centuries ago when the old

¿rikovils were built. Sacrificial sections422 may be the main reason, which

can be attributed to higher sizes of sections. Sacrificial sections provide

lesser working stresses.

421 Tantrasamuccaya, (áilpabh¡ga), Ch.2. Sl.21-22. 422 Fire Technology, Chemistry and Combustine, Institution of Fire Engineers, 1974, Chapter 8-3,

Standard Design for Fire Safety.

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As per the Bureau of Indian standards, when the effective wall

height exceeds 12 times the wall thickness the slenderness effects shall be

considered as in the case of column.423 If the L/D ratio is less than 12, it

shall be considered to be short column and the effects of axial load shall

be predominant. As per the canons of v¡stuvidya, all walls come under

the category of short columns. Further, if the story height to the breadth

of the wall is 1.0 or 0.5 or less, the percentage increases in strength ranges

from 10 to 20%. The maximum height of the ¿rikovil does not exceed

twice its breadth of wall. Approximately the wall height will be the total

height less finale, roof, and basement, which will be less than the width of

the wall and hence rendering additional strength.

423 IS456 of 1978, Bureau of Indian standards, Manak Bhavan, Bahadur Shah Zafar Marg,

New Delhi-2, 1979, Section 31 (walls).

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The code of practice for structural safely of buildings (masonry

walls) considers the intermediary stiffening of walls while deciding the

slenderness ratio of walls.424 The National Building code of India425

states, "lateral supports are intended to limit the slenderness of a

masonry-element so as to prevent or reduce the possibility of buckling

due to vertical loads and to resist horizontal components of forces so as

to ensure stability of a structure against over turning". The lateral

support may be in the vertical or horizontal direction, the former

consisting of floor/roof bearing on the wall or properly anchored to the

same and latter consisting of cross walls, piers or buttresses.

In the case of ¿rikovils the lateral supports in the vertical

direction are attained through the floors / roofs bearing on the wall. In

424 IS1905 of 1969, Bureau of Indian Standards as referred in IS456 of 1978, Section 31. 425 National Building Code Indian, Bureau of Indian Standards, 2005, Part-6, Section-4.

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the horizontal direction the lateral supports are provided by the partial

pillars and wall decorations which protrude from the load bearing walls

outside. These wall decorations appear to be for beauty and aesthetics.

From structural point of view these provide lateral supports and

additional stiffness, stability and strength. The four main attributes to

perform well in earthquake conditions are simple and regular

configuration and adequate lateral strength, stiffness and ductility.426

The irregularities may be torsion irregularity, reentrant corners,

diaphram discontinuity, out of plane off sets, not symmetric about the

major octagonal axes, soft storeys and weak storeys. The temple ¿rikovil

designs ensure all the main four attributes and the irregularities are

reduced to the minimum and behave well in earthquake situations.

426 National Building Code Indian, Bureau of Indian Standards, 2005, Part-6, Section 5.4

285

The sizes of ¿rikovils vary from 3 kol pariÀa to 70 kol pariÀa and

the height from one storey to 12 storeys. All these sizes are based on

square shapes and appropriate yonis are worked out based on the

perimeters of the square shaped plans. There are 39 types in

alpapr¡s¡das, 60 pr¡s¡das in jatipr¡s¡das, 54 types in candapr¡s¡das and

48 types in vikalpapr¡s¡das and 38 types in ¡bhasapr¡s¡das. Such large

number of varieties can seldom be found in engineering affording such

wide range of flexibility in designs.

8.3.2 Properties of horizontal spaces.

The base measurements of ¿rikovils can be considered as the

width of the ¿rikovil known as pr¡s¡da dandu. The width taken from

ends of wall plates is considered as uttama, jagati to jagati as madhyama

and p¡duka to p¡duka as adhama. The uthama dandu is considered to

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be auspicious. The measurements of the other elements are in

proportion to the pr¡s¡da dandu. The garbhag¤ha is in proportion to the

pr¡s¡da dandu (inside and outside), the wall width, the door width and

height, the width of wall plate (this is another standard dandu), sop¡na

in proportion to the wall plate, width of bhittialank¡ras in proportions to

the wall plate. The members of ceiling and roofing are proportionate to

the wall plate. The positioning of door is in proportion to the wall

thickness, the height of the deity and pitÅa as per the door height

(proportion to the pr¡s¡da), width of antar¡la in proportion to the ¿rikovil

width divided into khandas and the like. The proportioning of the

elements ensure absolute integration, forward and rearward in the case

of ¿rikovils and ancillary constructions.

8.3.3 Vertical structural spaces.

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The textural works indicate the number of storeys upto 12 in

general and upto 16 storeys as special cases. Each storey above one

another reduces its size in plan and in the height making the ¿rikovil,

structure a pyramidal structure less the apex. The centre of gravity is

lowered. The centre of mass is also lowered. With the axial symmetries

added to the above the stability against overturning, sliding and any

horizontal thrust due to wind force or the shear thrust generated under

seismic conditions get enhanced by the attributes of the ¿rikovil

structure.

Brief discussions on the structural spaces in vertical direction

part by part are given in order to highlight the adaptability of temple

¿rikovils from engineering point of view.

288

The foundation is to be taken to a minimum depth equal to the

height of the owner, up to clear subsoil water level or up to hard soil

(rock).427 The site is selected by observations, analysis, testing and

assessing the buildability in suitable locations considered based on

scientific, geological, ecological, environmental and cultural aspects. The

condition that the foundation depth would be up to hard soil gives clear

indication that the foundation be found on hard soil in order to safely

distribute the load of the structure into the subsoil, prevent unequal

settlement and provide stability against sliding.428 The minimum depth

as the owner's height ensures anchoring the structure onto the ground

ensuring stability against sliding. V¡stuvidya is not against the methods

of soil investigations to be carried out to decide upon the various

427 National Building Code Indian, Bureau of Indian Standards, 2005, Ch.1, Sl.20. 428 A Text Book of Building Construction, S.P Arora and S.P Bindra, Dhanpath Rai Publication (P) Ltd,

Madras House, Danyaganj, New Delhi-2, Ch.7, pp.237-238.

289

characteristics of the soil both mechanical and engineering and decide

the depth, width and type of foundation. The soil investigations are

carried out to find out the density, moisture content, type of soil, bearing

capacity, shear strength, cohesive strength, angle of response of the soil

and the like.429 Though simple, the soil tests prescribed in v¡stu¿¡stra

aim to assess many of these characteristics.

The basement is the part above the foundation and below the

floor level. The basement has the functions of providing the wider base

over the foundation by giving offsets from the wall above, retaining the

filling in the basement, providing firm and level base for the wall,

preventing dampness in the floor, giving elevated look and taking

decorations intended. Except decorative function all other functions have

engineering base. The basements are basically of ®kavarga, dvivarga,

429 Ibid., Ch.6, pp.202-223.

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trivarga and pancavarga with variations of these. The case studies and

observations during site visits revealed that majority of basements of

temple ¿rikovils are of pancavarga type with certain modifications in

exceptional cases. In two ¿rikovils, upap¢tas are provided to add the

heights, provide decorations and add the grandeur. From engineering

point of view it can be considered as a broader base which reduces the

compressive stresses in the foundation. Each moulding in the basement

has vertical and horizontal offsets and provide broader base at bottom

transferring the load on a broader base. The construction of basement is

done mostly in granite. The stones are well dressed and laid in regular

courses ensuring the correct levels on each course. The stone masonry has

high crushing strength, excellent durability, least amenable to dampness,

retenability of shape, aesthetic look and retainability of colour, though

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costly.430 These characteristics make stones as excellent material from

engineering point of view for construction of basements of ¿rikovils. The

height of basement is proportional to the height of the ¿rikovil and

height of the wall. It ranges from 1 Hasta to 4 Hastas as per various texts.

In Kerala, as per site visits and observations, the height of basement is

found to vary from 72cm to 156cm. The horizontal offsets are found to

vary from 12cm to 48cm. The offsets are provided to match the yoni of the

¿rikovil's wall plates. In rare cases padmap¡dukas are provided. The

projection ranges from 12 to 24cm and the depth also varies from 12 to

24cm.

Vedika is an element above the basement and at the base of the

wall. It has decorative parts. The height ranges from 12cm for very small

¿rikovils to 48cm for big ¿rikovils. The projection ranges from 1½ to 9cm.

430 A Text Book of Building Construction, S.P Arora and S.P Bindra, Ch.8, pp.294-295.

292

The decorations are given for the vedika. It serves as a strong belt at the

bottom of the wall and above the plinth, a sort of plinth belt. The door

sill is at the top of the pati, the top most element of basements. The

vedika, the plinth belt, is continuous except at the door portions.

The wall height ranges from 2 Hastas to 4 Hastas for alpapr¡s¡da

at an increment of 4 Angulas for each pariÀa starting from 3 kol pariÀa

with small flexibility of increasing it.431 The height of basement is half of

the wall height with small allowances and sometimes taken to the nearest

appropriate p¡dayoni. The width of the wall may be either 1/8th of the

pr¡s¡da dandu, 1/5 or 1/7th of pr¡s¡da width or 1/6th to 1/11th of the wall

height.432 The smallest of 3 kol pariÀa ¿rikovil is 2 Hastas 18 Angulas. The

least height of wall is 2 Hastas. The least width works out to be 8.25

431 Tantrasamuccaya, (áilpabh¡ga), Ch.2. Sl.8-9. 432 Ibid., Ch.2, Sl.21,22.

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Angulas. In small ¿rikovils the minimum width observed is 24cm

(8 Angulas). In certain cases the exterior wall thickness was observed to

be as thick as 102cm for big ¿rikovil as load bearing walls. The minimum

width of basement of height upto 1.75 M is 30cm as per National Building

code of India433 in almost all cases is satisfied in the ¿rikovils. The height

of the door is more or less twice the width of the door or very near to it.

The positioning of the door is at the centre of the wall with a small shift

in clockwise direction. The opening should preferably be small and more

centrally located as per National Building code.434 The door openings in

¿rikovils are small and are more or less centrally located. From the

engineering consideration small sizes and central placing of doors are

ideal. The door is placed in such a way that the centre of the doorframe

433 National Building Code of India, 2005, Clause-4.2.2.6.

434 National Building Code of India, 2005, Part-7, Clause -7.5

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shall be at a line 7/12th part from inside and 5/12th part from outside of

the wall.435 It may appear to be eccentrically placed. It appears that there

is some reasoning behind it. The kÀudrothara (small wall plate) is placed

at the outer edge of the wall plate, which takes the load of the roofing

with an eccentricity. The wall load of the wall above the door acts

centrally but the roof load acts with an eccentricity creating moment

about the centre line. When the door's centre is shifted towards outside,

the eccentricity and moments caused thereby will be minimised. This can

be one of the engineering explanations to such eccentric placing of the

doors. The weight of the door shutters supported at bottom and top in

the traditional way may not be sufficient to counter the moment created

by the roof load acting away from the centre of the wall. This may be

435 Tantrasamuccaya, (áilpabh¡ga), Ch.3. Sl. 6.

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another explanation for placing the doorframe's centre with a shift

towards outside from the centre of the wall.

The maximum/height of the temple from the p¡duka to top of

finale is twice the width of pr¡s¡da436 (adbhuta type). The height of the

wall after reducing the roof, finale and base will be definitely less than 2

which confirms the requirements of the height to width ratio of 2 as per

National Building Code of India437 up to 4 storeys from the stability point

of view. The turavu in garbhag¤ha is given corbels indicating the

knowledge of the techniques in ancient times. The ceilings provided over

garbhag¤ha and the mukhamandapas provide. safely, heat proofing and

facilities for architectural features.

436 Tantrasamuccaya, (áilpabh¡ga, Ch2, Sl.7. 437 National Building Code of India, 2005, Part-A, Clause-4.2.2.

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The roof systems of the Kerala ¿rikovils with sloping roof suited

the climatic condition of Kerala. The timber structures consisting of the

wall plates, rafters, ridges, k£tas, v¡matas, collar pins and other elements

acting, as space frames are marvelous examples of structural

engineering. The roof systems are light, rigid, well connected, strong,

stable and represent the culture and typical architecture.

8.3.4 Structural forms

Most of the elements included in the structural forms apart from the

architectural and aesthetics aspects have certain engineering functions.

The bhittialank¡ras are progressive with the size of ¿rikovil starting from

bhittikal to more elaborate alank¡ras. The structural functions of these

are given below:

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(a) Bhittikals. These are provided at all four corners and two each

in each cardinal directions. As the size of the ¿rikovil increases

the number of bhittikals shall be increased to 16 and 24. These

bhittikals work as pilasters/buttresses to the walls and

strengthen the wall, lower the lateral slenderness ratio and

provide lateral stability.

(b) Ghanadv¡ra and torana. These are provided in the cardinal

directions except in the directions of the doors. The ghanadv¡ra

and torana though considered to be for decorative purpose

strengthen the wall.

(c) á¡la and K£ta. For big ¿rikovils k£tas at corners which project

up to the maximum of the wall thickness and width ranging

from 1/8th 1/9th or 1/10th of the width of the wall strengthen the

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wall by additional stiffness and lowering the stresses. Similarly,

the s¡las with width upto 1/8th of the pr¡s¡da width shall also

provide additional stiffness and lower the slenderness ratios and

stresses.

(d) Panjaras are provided in big temples between the bhittikals,

which provide additional stiffness and lateral stability to the

external walls.

(e) Valaru-kapotas. These elements provide additional bearing area

for accommodating the bearing plate and the beam of the ceiling.

(f) ViÀkhambhas. These are the struts either decorated or plain

made of timber with lower end supported by cornices from the

wall and supported at top by leveling plate connected to the

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rafters. These slanting struts provide supports to the overhangs

of rafters (eves' projection).

(g) N¡sikas. N¡sika means nose, the organ meant for breathing. This

alank¡ra provide magnificent look. It allows air to get in and get

out. From engineering point of view it reduces the wind pressure.

The alank¡ras appear to be for decoration and unique

architectural and aesthetic looks. They have in addition to these primary

roles, the secondary roles of providing additional stiffness, bearing area

and reducing slenderness ratios. The viÀkhambhas provide supports to

the roof elements and n¡sikas reduce the wind pressure.

8.3.5 Materials of construction.

In temple construction only time tested strong and durable

materials were used. Materials which corrode, subjected to fast

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deterioration due to vagaries of weather are avoided. The time tested

materials like granite, laterile, bricks, specially prepared lime mortar,

selected class of strong timber, tiles and copper plates were used. Certain

temples are renovated and constructed in the last four-five decades using

concrete and R.C.C.

8.4 Contributing factors towards Sustainability, Stability and Durability.

There are several contributing factors, which lead to the sustainability, stability

and durability of Kerala temple ¿rikovils. Some of the glaring factors are given

below:

(a) Length breadth ratio. The length breadth ratio of ¿rikovils does not

exceed 2:1. In most of the cases it is 1:1 (for square, circle and octagon).

The ratio of 2:1 or less affords two way distributions of stresses.

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(b) Reduction of plan sizes at successive storeys. Reduction of 1/7th or 1/8th at

successive higher storeys reduces the plan size. It reduces the weight at

higher storeys and affords heavier weight at bottom lowering the centre

of the mass. It provides larger base area at lower storeys which reduces

the stresses. At lower levels seismic effects are taken care of by increased

stiffness and dampening effect.

(c) Reduction of heights at successive storeys. The height of successive storeys

above the lower ones is reduced by 1/8th to 1/11th. Combined with

reduction of sizes at successive storeys it takes the form of a pyramidal

frustum. All walls above are supported properly at lower storeys. The

increased number of supports at lower levels will share the storey

moments. As per the analysis using Kanis method,438 for multi storeyed

438 Basic structural Analysis, C.S. Reddy, Tata MC Graw Hill Publishing Company Ltd.,

New Delhi, 1989, Ch. 13, p 407.

302

building frame with horizontal loading differs from that of a frame with

vertical loading. It is only by the fact that in performing the basic

operation for the determination of the translation moments, the sum of

the rotation moments of all the member ends of the storey must also

contain moment. Additional members at lower storeys share the joint

moment and carry over moment. The forces are mainly compression and

shear which avoids twisting moments about the axes.

(d) Axial symmetries. The axial symmetries in X, Y and Z orthogonal axes

afford uniform distribution of stresses, afford better stability and avoid

eccentric loading.

(e) Strengthening by wall decorations. The wall thickness varies from 1/8th to

1/16th of the pr¡sada width. It means that the lateral slenderness ratio

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does not exceed 16. NBC439 specifies the slenderness ratio not to exceed

26 to 30 depending on the thickness of load bearing wall. As per

IS456,440 the slenderness ratio of effective height to the thickness of wall

shall not exceed 30. For ¿rikovils it does not exceed 11. In addition to

these the wall decorations reduce these slenderness ratios rendering

them to very safe limit.

(f) Belts. The p¡duka at the base, vedika on top of the base, wall plate over

walls act as sort of belts/distribution bands, which avoid unequal

settlements.

(g) Strengthening of openings and corners. The sides of openings are

strengthened by bhittikals. The corners are strengthened by pillars /

k£tas.

439 National Building code of India, 2005, Part 6, Clause 4.2.2.2 440 IS 456 of 2000, Bureau of Indian standards, Manak Bhavan, Bahadur Shah Zafar Marg,

New Delhi, Clause 32.2.3.

304

(h) Connection/supports. Simple supports at ends avoid moments. Simple

supports for continuous beams afford reduction of moments in the

middle. The pin joints allow rotation and avoid moments.441 Most of the

supports of the elements of ¿rikovils are either simply supported or

continuously supported. The joints though not fully pin jointed, allow

certain rotation except in the case of joints of wall plates, which are

continuously supported.

(i) Chemistry inputs and structural engineering. The design of structures

requires the knowledge of the engineering, mechanical and chemical

properties of materials to be incorporated in the design. V¡stuvidya has

integrated the aspects appreciably well.

441 Engineering Mechanics, R.S. Kurmi, S.Chand and Company, Ram Nagar, New Delhi-55,

1996, Ch. 3.

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(j) Temperature effects. The main materials used in the temple

constructions were / are stones, bricks, wood and tiles. The linear

coefficients of expansion are 7,5,6 and 6 multiplied by 10-6 per decree of

temperature in Centigrade442 respectively. The coefficients of expansion

of concrete, steel and copper are 12,12 and 18 x 10-6 per degree centigrade.

By using conventional materials the expansion/contractions are

minimised. The differential expansions/contractions and the

development of differential temperature stresses are minimised and also

avoid cracks at the junctions of elements with the use of conventional

materials.

(k) Fire resistance. The bricks, stone and tiles are highly fire resistant

materials.443 Timbers, which are hard and dense, afford some time to be

442 SP:25 - 1984, Bureau of Indian Standards, Manak Bhavan, New Delhi-2, pp. 12 - 15. 443 Design Aids for fire Resistant Structure, Institution of Fire Engineers, pp. 25-27.

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fully burned due to the presence of charred surface at the burning

end.444 The timber sections are generally heavy in ¿rikovils - sacrificial

sections. Hence the ¿rikovil structures are fairly fire resistant as can be

deduced from the behaviour of main conventional materials.445

(l) Higher factors of safety. Higher the factor of safety lesser will be the

actual stress affording the elements structurally safer. However, it adds

cost.

(m) Stability against over turning/sliding. The increased area at the base and

higher mass at lower levels lowering the centre of mass afford better

stability against over turning. Taking the foundation sufficiently deep

into the sub soil and proper compaction and consolidation of the soil

below the foundation and the high mass afford better stability against

444 Ibid., p.90-91. 445 A Complete Guide to Fire and Buildings, Edited by Eric W.Merchant, M.T.P, England, Ch.11.

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sliding. The laws of friction states that that the frictional force is

proportional to the normal force.446

(n) Total quality control. Total quality control right from the selection of

material, stage by stage constructions, close supervision and ensuring top

class workmanship contribute substantially towards the strength and

durability of ¿rikovils.

(o) Integration of sub systems into the whole system. Each element

considered as sub system, is integrated into the whole ¿rikovils taken as

the whole system, making them sustainable and durable.

(p) Certain other factors brought out by engineers, v¡stu experts and tantris.

(all of them are valid in one way or other) are given below:

(i) Gradual constructions.

446 Engineering Mechanics, Prof.(Dr) E.M.S Nair, Educational Publications & Distribution, Ernakulam,

2003, p. 76 - 77.

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(ii) Accurate designs and constructions.

(iii) Frequent maintenance.

(iv) Use of preservatives.

(v) Strong foundations.

(vi) Proper proportioning of elements.

(vii) Protections provided by the pr¡k¡ras.

(viii) High quality control and workmanship.

8.5 Structural Characteristics of Apsidal árikovils.

There are certain structural characteristics peculiar to apsidal forms of

¿rikovils. The plan shape consists of a square with semicircle at the back with the

diameter same as the side of the square. The garbhag¤has are mostly of the

same shape of the ¿rikovil as apsidal shape. Few cases are observed with square

garbhag¤has. Small apsidal ¿rikovils do not have separate garbhag¤has. The

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outer wall of garbhag¤ha is considered as merged with the outer wall. Many of

the apsidal ¿rikovils have the corridors. The presence of corridor is not indicative

of higher storeys. Certain apsidal ¿rikovils have the higher storeys that are

supported on the thick walls which merge with the outer wall of garbhag¤ha and

the outer wall of the ¿rikovil. There are mukhamandapas in many temples which

are in front of the garbhag¤has but with in the ¿rikovils. The walls of

garbhag¤ha or corridor support the higher storeys. The doors are provided in

front in all cases. In some cases there are two or four doors in the cardinal

directions, but very few. Ghanadv¡ras are provided in all three cardinal

directions where the door openings do not exist. There are either ceilings or

turavu for garbhag¤has except in few cases. The plan shape of the higher storeys

are also apsidal. The case studies which covered about 70% of the apsidal

¿rikovils indicate that two ¿rikovils only are of mah¡pr¡s¡das and three storeyed

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and the rest are of alpapr¡s¡das. About 47% of apsidal ¿rikovils are of 5 or 7 kol

pariÀa. In the plan shape of apsidal ¿rikovils the axial symmetry is only about Y

axis. There are no symmetries about X and Z axis.

In the vertical spaces, as obtained from the case studies, out of 21 apsidal

¿rikovils, two of them are three storeyed, twelve of them are two storeyed and the

balance seven of them are single storeyed. Proper supports for the walls above

the ground floor have been found which distribute the load of higher storeys to

the lower storeys. The adhis¶¡na, vedika, walls up to roof have not much of

differences except that the back portions are semicircular having no sharp

corners at the back. The roof is spectacularly different from others in the

structural spaces. The space in vertical direction poses a semi circular cone at the

back and sloping triangular roof for the square portions. There are two main

k£tas, one at the centre of the diameter of the half circle and the other at the

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junction of hip rafters joining on the square portion. In certain cases, one more

k£ta at the centre of the two k£tas at junctions is seen provided. The number of

finale, hence found are minimum of one or two finale and maximum three.

Because of the curved surface, roofing with tiles is difficult. In some cases it has

been observed that the curved surface is divided into 8 or 12 segments to provide

the tiled roofing. Such segments are absent in the cases of copper sheeting or

RCC roofing.

As far as the decorations are concerned as part of the forms, there are not

much appreciable changes from other types of temples in apsidal forms. Yet,

there are few differences because of the curved face at the back. The forms which

include the elevations, from the rear and the sides are different from other types

of ¿rikovils. The apsidal forms present unique, spectacular and magnanimous

aesthetics, architectural form and structural form.

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8.6 Strengthening of árikovils Against Seismic Effects.

árikovils of ancient days with stood the natural calamities for centuries.

It would be a matter of academic and of engineering interest to verify the

structures of temple ¿rikovils from the effects of earthquakes.

The quasi resonance during earthquake i.e. the coincidence of the

predominant period of vibrations of the soil layers and fundamental period of

structure causes severe damage to the building. The predominant period of

ground vibration is the fundamental period of soil layers of the soil at that site.

Smaller periods are noted for firmer or rocky and larger for soft soils. Generally,

firm soils are more suitable for earthquake resistance for all types of buildings.447

The basic design concepts are:

447 National Convention for Civil Engineers, Institution of Engineers (India), Cochin Local Centre, 2005,

Proceedings, Article by Dr. (Prof.) R.P.R Nair, pp.18-19.

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(a) Selection of sound structural configurations with well defined lateral load

resisting system.

(b) Avoid discontinuities and irregularities in plan and elevation.

(c) The principle of symmetry and regularity can minimise substantial

increases in forces in members due to torsion.

(d) Availability of direct local path for transfer of forces from super structure

to the soil medium through strong foundation.

(e) Strong column - weak beam is a good design concept.

The ¿rikovils are provided with strong foundations and taken to the hard

soil. The induced ground failure and effect on structures due to liquefaction in

hard soils and rocks during earth quack conditions will be much less compared

to softer soils. The ¿rikovil designs take into considerations of avoiding

irregularities in plan and elevation. Axial symmetries are ensured in all

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orthogonal axes. The load transfer to the soil through strong foundation and the

principle of strong columns and weak beam - in many cases they are strong walls

and weak beams - are ensured in ¿rikovil designs to be safe in earthquake

resistance.

Temple ¿rikovils are generally found built with masonry foundations,

basements and walls. There are few principles448 to be adopted in the masonry

constructions to be safe under seismic conditions. In general, long unsupported

walls are unsafe. Box type enclosures are satisfactory. The walls are well

connected. Buttresses will strengthen long walls. Horizontal bands improve

earthquake resistance. Slenderness ratios in lateral and vertical direction shall

be within limits. Vertical strengthening at corners, jambs and horizontal

strengthening at openings.

448 All India Seminar on National Building Code of India, 2005, Cochin Local Centre Proceedings

of the seminar, Article by Dr. (Prof.) R.P.R Nair, pp.79-82.

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It is interesting to note that all these principles are well incorporated in

the design and construction of temple ¿rikovils. The strengthening measures as

above have been discussed in NBC.449 Workman-ship of very high standard in

temple constructions has a considerable impact on the strength of masonry.450

The criteria for earthquake resistance designs are described (most of them are

covered above) in IS code.451

8.7 Inferences

The main inferences are under:

(a) The structural spaces both horizontal and vertical through the regular

shapes, spaces, proper proportioning, strengthening sequential supports,

axial symmetries strong base and foundations contribute substantially

449 National Building code of India, 2005, Part 6, Section 4, Clause 8.5. 450 Ibid., Part 6, Section 4, Clause 6.3. 451 IS Code., 1893-2000; Part.1.

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towards the sustainability strength, stability and durability of temple

¿rikovils.

(b) Selection and use of time tested strong and durable materials, gradual

constructions, high quality control, constructional details to resist

natural calamities, use of preservatives, timely repairs and proper up

keep put together help in the sustainability and durability of temple

¿rikovils.

(c) The elements of the forms through appear to be creating uniqueness by

variations have unity in diversity, these elements in several cases help as

secondary structural members which provide strength, stability and

sustainability to ¿rikovils.

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(d) The concepts and principles of design and construction to resist the wind

load and seismic effects are inherent in designs and construction of the

¿rikovils.

(e) The apsidal ¿rikovils have all of the above features except in the case of

symmetries.

(f) There appears to have in-built system approaches and integration of all

elements (sub system) in the integrated whole (the system) and pre-

engineering the whole programmes of planning, design constructions

and maintenance of the ¿rikovils.

(g) It appears that v¡stu experts are amenable to the adoption of new

technology methodologies, practices, management and methods within

the framework of the v¡stu concept, canons, principles and practices.