Construction Process

Introduction

Construction carries important place in human civilization. It shows us the progress made by man from time to time. The first structures made by human were simple huts, tents etc. Wood, stones and sand were the only material he used for that. Similarly, when human invented bridge, he might have just placed wooden logs in front of each other across a stream.

Over the years, man made tremendous progress and developed his constructional skills. Ancient architects constructed large structures with the help of stones and other earthen materials like lime stone (chuna). Ancient architectural style is different in different parts of the world. It was a result of geographical, climatic, historical diversities. The knowledge gained over 5000 years ago is still used in the construction field to construct big structures all over the world. Only change is in the material used. Today steel, cement etc materials are available and used everywhere.

Objective

In this lesson, we will study history of construction, different types of ancient structures. Then we will study different tools used in construction. We will learn about current construction methods like RCC structure. We will also learn about different types of brick works. We will study about Ferro-cement construction and methods to increase the strength of the construction.

History of construction

Construction has a long tradition of thousands of years. To become immortal in history, many kings got constructed huge structures. Egyptian pyramids, Roman temples, arches and domes, Ajanta-Ellora caves, are few examples of it. We still wonder how those people have built these huge structures. These structures are very precise and accurate from architectural point of view. While building those structures, those people must have thought about calamities like earthquakes might damage the structure and so made it prone to such things. We see these structures standing today is a result of their advance architectural knowledge as well as thinking much ahead of time.

Ancient Egyptian ArchitectureEgyptian Pyramids are considered the oldest man-made structure. These pyramids were built to bury Pharaohs and their queens approx. 5000 years ago. It is believed that 20,000 to 30,000 workers worked over 80 years to build the famous and tallest Pyramids at Giza.

Height of the tallest pyramid is approximately 250-300 feet. Lime stone found near the river Nile is used to construct the pyramids. Those architects showed their skill of building such huge, accurate geometrical structure. Pyramids are one of the Seven Wonders of the World.

Fig. 1 - Egyptian Pyramids of Giza

Ancient Roman ArchitectureWith the help of their forefathers who supplied Romans with a wealth of knowledge essential for future architectural solutions and influenced by Greek architecture, Romans created their own architectural style. They invented new material for their construction. We can see different types and styles in Roman architecture is a result of above factors as well as their advanced knowledge in building and engineering. Changing needs of growing population, social and cultural demands as well as to control and maintain the power, Roman Empire developed different structures such as long roads for faster travel across their empire, amphitheatres to fulfill social need, Triumphal arches to celebrate the victories of the Romans etc.

Fig. 2 – Roman Colosseum

Ancient Architecture in IndiaAncient Indian architecture represents diversity of Indian culture. It comprises of a wide range of geographically and historically spread structures. Among ancient structures, which are still standing, prominent are Temples, Viharas (residence of monk), Chaityas

(Worship places) Stupas etc. The diversity in the architectural style in different parts of India was a result of climatic, geographical, historical, racial diversities. Indian architecture is believed to be as old as human civilization. Harappan civilization is the oldest but very advanced civilization in India. Back then, they had well planned cities like Harappa and Mohenjo Daro, well built market place, different types of houses, private baths, very planned drainage system throughout the city etc.

Following are few names of the great ancient Indian structures still standing today: Ajanta-Ellora caves, Stupas in Bihar, Sun temple at Konark, Khajuraho group of monuments, Buddhist monuments at Sachi etc. Among these structures, Kailash Temple at Ellora Caves is considered as one of the most astonishing 'Structures' in the history of architecture. It is believed that the construction of it was started in the middle of 8 th

century (i.e. around the years 750-770) under the direction of King Krishna I. This temple is world’s largest and most magnificent structure carved from one piece of rock and the most extensive rock-cut projects ever undertaken. The temple complex has idol of Lord Shiva (which measures 109 feet wide and 164 feet long) which is in the main temple building, life-size elephants and other carved sculptures around the building. It is estimated that to carve the Kailash Temple, 200,000 tons of rock had to be removed by thousands of workers for over 150 years. Archaeologists estimate that it took thousands of skilled stone cutters seven to eight generations to construct the temple.

Fig. 3 - Kailash temple at Ellora caves

Over the years, man made tremendous progress in every aspect of life and field of engineering, architecture, construction etc. developed a lot. Many discoveries, inventions which were happening around that time influenced all these fields too. In the following sections, we will study progress in the field of architecture and construction and its journey until now.

We find columns placed close to each other in old temples. That is because stones are weak in tension. In stony roof and columns, pressure comes on the beams due to the weight of the roof and it bends at the center. Therefore limited distance was kept between two columns. When man learned to build arch by arranging the stones in a particular manner, ample progress was made in the construction process. By using this method,

Roman people showed their creativity in construction. Afterwards Arab used the same skill in the construction of the mosque. Arches in our temples and village gates were also constructed by this method. About 600 to 700 years ago, people started building elliptical arches instead of rounded one. In case of circular arches, pressure is equally distributed and hence we can keep more distance between the columns. In elliptical arches we can increase this distance further and can construct the stony concave roof.

Later in this journey, people realized that wood and steel can bear the tension and pressure easily. Therefore, use of wood and steel started in construction. Architects recognized importance of triangular frames in construction. Triangular frames are stronger than square or pentagon frames. Therefore architects started making the truss for the roof by joining different sized triangles for small houses. People started using roof tiles on this truss with the support of vertical and horizontal planks. Afterwards method of putting steel or cement sheets on the roof got developed.

Use of plumb, level tube and spirit level

In all construction methods, accurate measurement is most importance. It is necessary to maintain the right angle direction. Tools used for it are discussed in the following section.

a. Plumb – bob: A plumb is a weight, usually with a pointed tip at the bottom that is suspended from a string. It is used as a reference line for leveling vertical length. Refer Fig. 8(a). Mesons used this method to ensure that their constructions are perfectly upright

Fig. 8(a)

b. String Line: You must have seen meson using string for laying bricks of foundation. A line is described by two points, the start point and the end point, and the shortest distance between two points is a straight line. A mason uses a string line between two points (nails or line blocks etc.) and he pulls the line tight to get it the shortest distance, to make it straight, with no sag. He takes this string as a reference to complete his work.

c. Water tube: To check all points of wall are at same level, a simple water tube is used. It uses the simple principle of ‘water remains at the same level’.

d. Spirit level: It is used to check the horizontal level of construction. The bubble in

the tube should be at the center to make the level horizontal. Refer Fig 8(b).

Fig. 8(b)

Construction at present

Today we see many big structures, tall buildings, roads, bridges etc. are standing all over the world. Most of them fall under either of following category:

1. Wall bearing structures2. RCC structures

Wall bearing structures

In wall or load bearing construction, all the load of the roof and structure is carried by walls down to its foundation. (Refer Fig. 4). This type of construction may not use supporting column or wood pillar. The size of walls needs to be bigger to carry all the loads. Further there is limitation to construct long walls at a stretch. This is typically used in residential or 1 -2 storied buildings. This is economical than RCC structure or steel frame structures.

Fig. 4

Reinforced cement concrete (RCC)

Most of the tall building uses RCC techniques. In an RCC framed structure, the load is transferred from a slab to the beams then to the columns and further to lower columns

and finally to the foundation which in turn transfers it to the soil. The walls in such structures are constructed after the frame is ready.

Fig 5

Cement concrete is strong in compressive strength but weak in tensile strength. To increase tensile strength mild steel bars in cement concrete are used. (Refer Fig. 5). Steel bars used in cement concrete provide good strength to the structure. Usually steel bars are roughened or corrugated to further improve the bond or cohesion between the concrete and steel. Care must be taken that there should be no joints in steel bars used for RCC work. Therefore you might have observed that steel used for RCC work is long in length. If full length steel bars are not available, proper overlap should be given in steel bar and overlap should be staggered. A care must be taken that steel should not disturb during concreting. Steel rods should be properly bind and proper planks or plates are provided for walking. Curing of all concrete is done at least for 20 days.

Following are different names of the structural elements in a building as shown in the figure: Slab: A flat ceiling of a story is called a 'Slab'.Beam: The peripheral horizontal members supporting the slab are called

'Beams'. Plinth Beams: The beams at ground level or plinth level (the lowermost habitable

level) are called 'Plinth Beams'. Columns: The vertical members supporting the beams are called 'Columns'.

Foundation: The system below ground transferring the entire load of the structure to the soil is called 'Foundation'.

Cantilever: A slab or a beam supported only on one side and projecting horizontally on the other side is called a 'Cantilever' slab or beam e.g. balconies, lofts and canopies.    

Fig. 6

Steel Frame StructuresIn construction of big buildings, a steel frame is constructed as a skeleton of the building. All the load of roof and floor are transmitted to beams and girders. Walls in these structures do not carry load of the structures.

FoundationFoundation is in direct contact with soil and transmits load of complete structure to soil. If foundation is weak then there is danger that walls will collapse or tilt due to the load of the structure. Generally foundation is below the ground level. Depth of foundation depends on type of soil and its bearing capacity, depth of ground water table and the size of the structure. To allow removal of top loose soil and variation in ground level, the best recommended depth of foundation is from 1.00 meter to 1.5 meter from original ground level.   Following are different steps in Foundation Work:

1. Excavation of soil for foundation.2. Laying out cement concrete.3. Laying Brick work up to plinth level.4. Refilling of earth around the walls5. Refilling of earth in the building portion up to the required height according to

the plinth level.

Brick work

When arranging bricks, the manner in which the bricks overlap is called the bond. Brick work is done in any of the following type of bond:

a. Stretcher bond, also known as running bond, is the most common bond. Refer Fig. 7 (a). It is easy to lay. It is entirely composed of stretcher bricks, set in rows that are offset by half a brick as shown in the figure. Stretcher bond is generally used to build a single-brick wall.

Fig. 7(a)

b. English bond: fairly easy to lay and is the strongest bond for a one-brick-thick wall. Refer Fig. 7(b)

Fig. 7(b)

c. Header bond, also known as Spanish bond is a very common bond for bearing walls. Refer Fig. 7(c).

Fig. 7(c)

d. Flemish bond, also known as Dutch bond, historically has always been considered the most decorative bond. Ref Fig. 7(d)

Fig. 7(d)

e. Rat-trap bond is also known as Chinese bond.

In this type of bond, air cavity gets created between the bricks hence the name ‘Rat – trap bond’. It requires less number of bricks than a solid wall. Air cavity helps in keeping the building cool. Refer Fig. 7(e).

Fig. 7(e) Ferro cement construction

In Ferro cement construction, a frame of chicken-wire mesh is made. A mixture of cement, sand, and water is spread over the frame. Then the Ferro cement structure is allowed to cure for 28 days. Advantages of Ferro cement structures are as follows:

Despite of the small thickness, Ferro cement structures are strong. It is very economical. It requires less skill to manufacture. Safe in earthquakes.

Now a day other materials like fiber, bamboo etc are used in place of chicken- mesh to further reduce the cost.

Fig. 9

Structures for strength

In this section, we will discuss commonly used arrangements to get the proper strength for construction. We see that nature has given a specific skeleton to all animals. And

because of that they are able to carry their own weight and move around. In tree trunks fibers are connected to each other using lignin. This makes wood strong. Like always, man learned from nature and made use of such structures in constructing things. There are two different kinds of structure:

1 Skeleton type:Flexible limbs and other parts of animal body are supported by a bony skeleton. Similarly, man created a construction frame-work to support weak substances. E.g. Construction of trusses, beams, and columns of steel or wood, to support roof made of grass or mud-tiles, also steel frames filled with concrete become stronger than just concrete or just steel alone.

2 Fiber method:Fibers are often flexible but they are strong in tension. If fibers are combined together by an adhesive substance then it produces stronger material. If fiber is added to brittle substances then its brittleness decreases. For example:

Cement is brittle; to overcome that weakness asbestos is added to cement to make strong asbestos-cement sheets.

Plastic is breakable; if glass fiber is added to it then it turns into strong FRP. Cement Mortar is easily breakable; but if thin chicken-mesh is put into mortar

then it makes strong Ferro cement. Fiber is added to tar to make it durable roof-sheet.

It is not always necessary to use two or different materials to create strong objects. Strength can be obtained by arranging the same material in different ways. We can learn this from the following:

a. Geodesic Dome structure Architect “Buck Minster Fuller” had shown the method of constructing a geodesic dome structures. In which round building is constructed by connecting frames. In this type of construction, wall and roof are not separately constructed but both are combined in single round. In this way buildings can be constructed with large diameter without any column.

Fig. 10Advantages of geodesic structure are as follows: It provides the greatest strength for the least volume of weight. The geodesic dome can withstand winds of 210 mph, while at the same time it

is light and easily transportable. It can be put up in hours. A geodesic dome can withstand cyclones and earthquakes far better than

conventional buildings.

The geodesic dome is the only structure that actually gets stronger, lighter in density and cheaper per square foot with size.

Cost effective housing structures: Low cost housing does not mean inferior or low quality housing. Many organizations worked on cutting down construction cost by using alternatives to conventional methods and inputs. It is about the usage of local and indigenous building materials, local skills, energy saver and environment-friendly options. Famous architect Laurie Baker said “A cheaper house is not just for the poor. One can cut unnecessary expenditure even while building beautiful houses”.

Summary

Here is the summary of what we have learned in this chapter:

History of construction: Construction has a very long history. Researchers in this field have found some constructions as old as 5000 years. Egyptian architecture is considered the oldest architecture in the history of mankind. Apart from Egypt, one can find ancient masterpieces in Roman and Indian architecture.

We learned the importance of accurate measurement in construction field. Simple tools which can be used for it are: Plumb, Straight Line, Water Tube and Spirit Level.

We studied two common and widely used methods of constructions: Wall bearing and RCC.

Brick Work: There is a specific way to arrange the bricks while constructing a wall. It is called bond. We studied Stretcher, English, Header, Flemish, Rat-Trap bonds.

Ferro-Cement Construction: In this type of construction, a mixture of cement, sand and water is made and it is applied on a structure which is made of chicken-wire mesh. It is very economical and easy to construct.

To increase the strength of the structure different methods are used. One is Skeleton type; in which a skeleton or a frame is made to give support to weak parts of the structure, other one is Fiber method; in which fiber is combined with some adhesive substance to produce stronger material.

Activity

1. Observe different types of trusses used in your surroundings. Draw sketches of trusses used in old houses, poultry shed, tin roof shed, poly houses.

2. Visit nearby sites where you can find old constructions (at least 150-200 years old). Study architecture of such structures and write down your observations.