Unit III Building Materials Building materials

1.Building materials are used in two basic ways. In the first way they are used to support the loads on a building and in the second way they are used to divide the space in a building. Building components are made from building materials and the form of a component is related to the way in which it is used. We can see how this works by considering three different types of construction:

2. In one kind of construction, blocks of materials such as brick, stone, or concrete are put together to form solid walls. These materials are heavy, however, they can support the structural loads because they have the property of high compressive strength. Walls made up of blocks both support the building and divide the space in the building.

3.In another type of construction, sheet materials are used to form walls which act as both space-dividers and structural support. Timber, concrete and some plastics can be made into large rigid sheets and fixed together to form a building. These buildings are lighter and faster to construct than buildings made up of blocks.

4. Rod materials, on the other hand, can be used for structural sup­port but not for dividing spaces. Timber, steel and concrete can be formed into rods and used as columns. Rod materials with high tensile and compressive strength can be fixed together to form framed structures. The spaces between the rods can be filled with light sheet materials which act as space dividers but do not support structural loads.

Now say whether these statements are true or false. Correct the false statements.

1. Rod materials can be used for both dividing space and support­ing the building.

2. Concrete can be used as a block material, a sheet material and a rod material.

3. Steel is used for frame construction because it has high tensile strength and low compressive strength.

4. The sheet materials, which act as space dividers in a frame con­struction building, can be very light because they do not support structural loads.

5. Mass construction buildings are light whereas planar construc­tion buildings are heavy.

Сomposite

Solid material that results when two or more different substances, each with its own characteristics, are combined (physically, not chemically) to create a new substance whose properties are superior in a specific application to those of the original components. The term specifically refers to a structural material (such as plastic) within which a fibrous material (such as silicon carbide) is embedded. Glass-fiber-reinforced plastic is the best-known composite. Because of their stiffness, lightness, and heat resistance, composites are the materials of choice in numerous structural, reinforcing, and high-performance applications.

Building materials in the hot climate zones

Cane and leaves are available in the warm-humid zones and grass in the intermediate and subtropical

zones. Vine, bamboo and palm-fronds are used for buildings in the warm-humid zones. Because these

materials are light, do not store heat, and allow the free passage of air, they are frequently used for

making roofs. However, they have a relatively short life span because they deteriorate rapid­ly due to

termite attack. They are also highly combustible.

Both hardwoods and softwoods are found in most tropical and subtropical areas with the exception of the hot dry zones. On exter­nal woodwork preservative stains should be used rather than paints which tend to deteriorate fairly rapidly in the hot zones. Extremes of climatic conditions cause dimensional changes producing cracks, splits and warping. Wind-blown sand and grit gradually erode ex­posed timber. In warm-humid zones timber is liable to wet and dry rot and to attack by termites and beetles.

Earth is one of the most widely used traditional building materials in hot-dry lands. Earth is used not only for walls but also for roofs; mud brick vaults and domes are common in countries like Iran and Egypt. Because mud has less strength than most other construction materials, mud walls are built thicker. Partly due to the thickness of mud walls and partly due to its low thermal conductivity, rooms built of mud are much cooler in hot climates than those of any other material. Mud bricks are brittle and do not withstand tension well. For this reason the vault and the dome were evolved in the East. There is a high risk of termite damage in some areas. Walls exposed to weathering and rain require frequent repair work.

Concrete and reinforced concrete are widely used throughout the non-temperate zones. Cement is manufactured locally in many places. Sand is found almost everywhere but it may be contaminated with soluble salts. Suitable aggregate may be difficult to find. Con­crete is most frequently used for the structure, foundations and floor slabs of buildings. Care must be taken when using concrete for walls and roofs. Heat builds up on the exterior of concrete walls and roofs.

The single-storey structure

The single-storey structure consists of three frames. These frames are made up of steel stanchions and beams. The frames are placed between end walls and spaced at 3 metres centres. The stanchions carry the beams. These beams support the roof. The roof beams cantilever a short distance beyond the stanchions. This means that they extend over the profiled sheet steel cladding. The cladding can then be placed outside the line of the stanchions.

The beams are bolted to steel stanchion caps. The stanchion caps are welded to the top of each stanchion. The load on each beam is transmitted through these plates to the stanchions.

The upper face of the steel base plates and the ends of the stan­chions are machined flat. The bottom of each stanchion is welded to a base plate. Each base plate is fixed to a concrete column base by two holding-down bolts.

Steel angles are fixed across the ends of the beams and built into the brick walls. These angles tie the frames together and also pro­vide a place to fix the top of the cladding.