In load-bearing-wall construction the walls transmit the load to the foundation. In skeleton construction, all loads are transmitted to the foundation by a rigidly constructed framework made up of beans, girders and columns. This skeleton carries the roof, walls, and floors, together with their loads. Load-bearing-wall construction is usually most economical for buildings less than four storeys high, but skeleton construction is better for taller buildings. All buildings in the skyscraper class are of skeleton construction. The first building to have skeleton construction was the 10- storey Home Insurance Building in Chicago. Completed in 1885, this building was the world's first skyscraper.
Many parts of a building have no structural function. Partition walls and curtain walls carry only their own weight and serve to divide the interior of a building or to keep out the elements. Other nonload-bearing parts include windows, doors, stairs, and lifts.
In one method of construction, called tilt-up construction, concrete wall panels are formed at ground level. Cranes or derricks then lift them into position. Lift-slab construction may be used for positioning roof and floor slabs. These slabs are formed with concrete at ground level, within the framework of the building. They are then lifted into place using hydraulic jacks.
Beams, girders, and columns support a building much like bones support the body. They form the skeleton of the superstructure, and bear the weight of the walls and each floor of the building. Beams and girders run horizontally. Girders are usually larger than beams. Closely spaced beams are called joists, especially in wooden buildings. Purlins are small beams that brace rafters or girders and help provide the structure to support roofs. Beams above window and door openings are called lintels. Slabs are beams whose width is greater than their depth.
Columns are heavy vertical supports that carry the load of beams and girders. Trusses consist of many wood or steel supports that are connected in triangular patterns. They provide the strength and rigidity to span large distances with relatively small amounts of material. Arches are curved supports that usually extend over openings.
Text 3. Prefabricated Construction
Prefabrication has become an important part of most types of building construction. Prefabricated sections of a building are produced in large quantities in a factory and then shipped to various construction sites. This procedure may allow work to continue despite poor weather conditions and should reduce any waste in time and material at the site. As a result, costs are lowered and construction time decreases.
Many types of building sections can be prefabricated. For example, entire walls may be prefabricated for a wooden-frame house. Huge wooden arches are prefabricated for use as supports in churches, gymnasiums, and other buildings.
Concrete beams, floors, roofs, and wall panels may be precast for many types of structures. Entire buildings may be constructed in a factory and then transported to the desired location.
Prefabricated structures are sometimes made by a process called modular construction, first used in Japan. Modular construction refers to the use of a standard measurement as the basis for all building materials. The size of the module may vary considerably from country to country. In the United States, the basic module is 10 centimetres. All building parts are designed so that each dimension equals this measurement. Modular parts are also used in buildings that are not prefabricated.
Text 4. Building Stone
Building stone ranks in importance with steel as a construction material. Stone is used for the foundations, walls, and steps of buildings, for the support of piers and bridges, and for finishing and decorating all types of structures. Crushed stone accounts for most building stone used in construction. Crushed stone is quarried stone crushed into small pieces suitable for such uses as the surfacing of roads and industrial construction.
Dimension stone is stone in natural blocks or slabs cut in definite shapes and sizes. Builders expect good dimension stone to last at least a hundred years. The best dimension stone has the fewest pores or air cells, making it able to resist the wearing effects of weather. Stone with large, open pores will chip off if water freezes and expands in the pores. Dimension stone includes granite, limestone, sandstone, marble and slate.
Granite is one of the strongest of all the building stones. However, it is difficult to cut and handle because it is extremely hard. It is used extensively in the construction of public buildings. Granite can be polished to a glossy finish, and is an excellent background for carvings and lettering.
Limestone is a hard and lasting building stone that can be cut easily and shaped with saws, planes, and even lathes. These buff or gray stones are sometimes placed over the rough stonework of a building to make an attractive surface. Limestone is also used to tile floors, and for sills, steps and trimming.
Marble is the most elegant building stone. Pure marble is white, streaked with veins of black, gray, green, pink, red, and yellow. Builders use marble to make monuments and tombstones, and to decorate stairways, hearths, floors, and panelling. Slate is fine-grained rock that can be split easily into thin slabs and used for roofing shingles and flagstone flooring.