Monthly Archives: February 2012

Pillar – stone by stone

Unlike single-stone pillars that demand time and money for making them, size-stone pillars are very easy to build and comparatively inexpensive.

Sturdy: Stone pillars are ideal for short spans that do not require RCC

Ask any architectural historian about the single-stone pillar and he/she will endorse its impressive image and instant attraction. The way antique markets get flooded by pillars from demolished buildings and regularly get sold proves their time-tested popularity.

Of course, stone pillars cannot be set in every building and are not affordable by all. Also, such pillars today are exclusive, expensive and require advanced procurement. For those who cannot afford them, but would still love to have them, pillars made of individual stones, called size stones, are a blessing. Unlike the single-stone pillars that demand time and money in making them, size-stone pillars are very easy to build and comparatively inexpensive. Any experienced stone mason can build them at site, along with the person who would dress them to size.

Merges or contrasts

Stone pillars are ideal for short spans that do not require RCC, and where the walls are already being built with natural materials such as stone, mud or brick. As a material, stone either merges or contrasts with the other natural materials, as such compliments any building. Depending upon the region of India, stones come in varied colours, textures and chemical compositions, wherein some varieties are best suited for pillars. The specific details of stone pillars may vary accordingly, but the basic approach is the same everywhere.

Dressing & bonding

All the visible surfaces of stone need to be dressed, by chipping off the unevenness. The degree of dressing, i.e. how smooth or rustic the surface should be, could be a decision left to the discretion of the owners. Comparatively richer mortar mixes, like in the range of 1:2 to 1:4, are required to ensure good bonding.

The size of stones varies between regions and quarries, where the pillar stones can be 6”x6”x6” cubes or 6” x 4”x 8” rectangular blocks. In the former, there would be four stones in each course, measuring up to a pillar 12”x12” size. The latter size will also have four pieces per course in a 12”x12” sized pillar, leaving a small void in the centre. This void could be filled with concrete and a reinforcement rod to take higher and non-axial loads.

Mason’s role

In case electrical conduits are to be encased within the pillar, it’s very easy, running the pipe in the centre. However, these smaller-sized stones are normally used for a 9”x9” pillar with only two stones per course. Not all masons are comfortable with smaller pillars, even if they are minimal load contexts, hence should be employed with due care.

The mason has to take extra precaution in building the pillar, ensuring the corner stones are mutually aligned creating the proper vertical corners and horizontal joints. For the stability of pillar, load from top is mandatory.

As such, until the roof is placed, it is common that the freshly built pillar appears weak. As such it is better not to check its strength by trying to push it!

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Just trust the stone pillars

If locally quarried, stone pillars consume the least energy, need zero life-cycle cost and also look elegant.

Have we observed one major difference between what we see along the street in older parts of the town and the newer parts? Within the line-up of buildings, traditional streets exhibit a variety of pillars, while the newer areas have more of walls and windows.

Pillars are seen in all possible masonry materials like brick, wood and stone, as could be locally available and often matching with the material used for the building. Though carved decorations were common in the bygone days, simple, plain pillars were also popular with the low-budget houses.

Huge loads

Let us remember, in those days, reinforced concrete columns were still unknown. However, the masonry pillars took huge loads of large havelis, shrines, palaces or pavilions. Structurally, pillars take axial load, i.e., the vertical load, from the superstructure in conjunction with the beam.

While the beam has to be singular and monolith across, lest it will crack at the centre, the pillar need not be so. Any material that can take compression can be piled one on another vertically to get the pillar effect. Even bags filled with sand can be placed on each other to get the pillar!

Popular

Historically, stone pillars appear to be among the most popular around the world, especially in localities where stone is available. The four major attractions of stone — beauty, dignity, durability and strength – made it a popular choice for a range of buildings, from choultries to temples.

The carved single piece pillars added to the public image of havelis and palaces, expressing the social status of the building owner. Often we see huge stone pillars in Indian temples supporting the massive towers, suggesting the strength of the pillar.

Back in usage

Curiously, single piece stone pillars are back in usage once again, in few cities where stone quarries are nearby. Once the building designs are finalised, the required pillar dimensions are provided to specially quarry it to order.

While the basic component of the pillar comprising the base piece, the main shaft and the top are maintained, carvings are kept to the minimal nowadays. Considering that the roof cannot be cast unless the pillar is in place, the project needs to be coordinated right from the designing stage itself.

Present-day buildings have a clear height close to 10′, but not all quarries can safely supply pillars of that height. In such cases, a short base platform needs to be built upon where the pillar could be rested.

To ensure no side buckling or slippage of parts happens due to unforeseen diagonal loads, and to tie the pillar to the beam on top, a small hole is drilled into the stone at every junction, holes on both sides are connected with iron rods and the holes filled with rich mortar, araldite or even molten lead.

If locally quarried, stone pillars consume the least energy, save time, need zero life-cycle cost, look elegant and are fully retrievable. It is possibly among the most eco-friendly options today.

Reinforced, but not concrete

Reinforced hollow brick pillar is a simple method to get the best of both strength and aesthetics!

Know this?: Verandahs and other small spaces do not require RCC columns

The way society forgets the past, often within one generation, is really strange. Between past practices, best practices and new practices, it is the past practices that possibly face the first blow from societal forgetfulness.

There was a time when concrete columns did not exist, and now we are going through a time where non-concrete columns are seemingly non-existent, as if they have vanished from our imaginations.

Elongated column

To state it simply, the wall is nothing but an elongated column and the column is an extremely short wall. Technically though, there are differences in the way they behave and transfer loads, which the structural engineers will consider before deigning them.

Most short span spaces such as verandahs, pavilions, sheds, and small rooms around 10 ft. span do not require RCC columns, but can be managed with columns erected using the same masonry material with which the building walls are built. In the case of higher loads, where we wish to reduce concrete, the brick column can be reinforced with structural steel.

While both the words ‘column’ and ‘pillar’ are found in common usage, the word ‘ column’ is more applicable to RCC while non-RCC ones like stone, wooden or brick ones are referred to as pillars.

Drawbacks

There are many examples and past attempts towards reinforced pillars using cement water pipes, hollow cement blocks and such others. They all require external plaster finish, may not have the minimum concrete volume to embed the steel or finally end up using high embodied energy materials like cement all over.

Alternatively, hollow clay blocks and jaali bricks are preferable, also due to the availability of internal perforations to run the steel through.

Steel rods

In the chosen hollow block, the number of voids and the distances are fixed; as such the numbers of steel rods have to be designed to take the roof, people and materials’ load from upper floors.

Every joint is to be used to have the steel tie called stirrups, placed within the mortar bed.

The rods are first erected from the ground up with some temporary support, each block is inserted from top down, stirrups either slipped down or freshly tied there, and voids and joint finished with mortar. Next, another block is inserted and so goes the process.

Ensuring the rods are held vertical, each block is filled with concrete made with 12 mm jelly. Blocks should be well soaked with water to reduce cement water absorption.

Placing details

The last course often does not match with the desired slab or beam bottom, where concrete packing or blocks cut thin can be considered. Each block has to be placed perfectly horizontal, within the margins of dimensional variations, otherwise joints will visibly appear angular.

Wiping the blocks regularly and externally covering the pillar with construction plastics during roof casting ensures least damage to the surface, later to be left exposed.

Reinforced hollow brick pillar is a simple method to get the best of both worlds – strength and aesthetics.

Where have the pillars gone?

The first human shelter would have been made of a thatch roof supported by four tree trunks cut to the required height, the earliest form of our modern RCC columns! 

Living patterns have no doubt changed, but the time-tested relevance of pillars has not

What are the important elements of a building? It is a question that anyone may answer: foundation, floor, walls, doors, windows and roof. The answer appears correct when we look at the buildings, each one covered by a wall. However, buildings did not begin this way. They began with pillars and roofs, and not with walls and windows. The first human shelter would have been made of a thatch roof supported by four tree trunks cut to the required height, the earliest form of our modern RCC columns!

The size of the covered area would have decided the materials, which together would have influenced the quantity of consumption and durability of the structure. Here we notice how construction systems, materials, costs and life cycle were the earliest determinants of architecture. They continue to be so.

Expansive with columns

During the development of design ideas and the changing notion of shelter, walls gained prominence, reducing columns to the back seat. While walls create a room space, the space is actually enclosed within but the spaces created by columnar constructions are visible and expansive, creating a sense of largeness. Columns not only support the roof, but also add beauty to the building, as in Chettinadu houses of Tamil Nadu or Theravadu homes of Kerala.

Traditionally many natural materials lent themselves to be used as pillars — stone, brick and wood being the most prominent. Invariably carved and decorative, these pillars would welcome any visitor home, being in the front of the building. The pillared verandahs cost little, but provide sheltered area for a range of activities. The internal court would have corner pillars, ensuring open planning for the rest of the home. Even a multi-storey palace or pilgrims’ choultry would have many pillars at each level, ably supporting the floors.

Living patterns have no doubt changed, but the time-tested relevance of pillars has not. Somewhere down the line, we seem to have forgotten how to use pillars. No wonder, today building elevations exhibit no pillars, but have a dozen of them within even a small house.

Ecological, economical

Replacing walls by pillars actually works to our ecological and economical advantage. Pillars reduce material consumption, as could be seen in the traditional courtyard homes with minimal walls. While allowing roof-level shelters, pillared structures do not stop air and light, as could be seen in any large temple complex. Goan ‘balcao,’ Kerala ‘mukha mantapam’ and rural Karnataka ‘jagali’ are all illustrations of simple shaded shelters created by rows of columns. Open sheds continue to dot our towns, housing anything from cars to cattle, besides being garden pavilions.

An ornately carved pillared construction could be costly, obsolete and near impossible now, yet a variety of material and design options continue to be available to us, for a judicious blend of walls and pillars.