Buildings

Buildings

Fixed permanent structures, more or less enclosed and designed to use as housing or shelter or to serve the needs of commerce and industry.

Building materials

Iron and steel building components are noncombustible, and their strength-to-weight ratio of steel is also good. Steel is equally strong in tension and compression and possesses excellent ductility, a highly desirable quality in building design. Contemporary applications of structural steel in building construction generally utilize rolled shapes in the form of wide flange and I beams, pipes and tubes, channels, angles, and plates. There are fabricated and erected into frameworks of beams, girders, and columns. Floors are usually concrete slabs cast of corrugated metal deck or on removable wood forms. See Floor construction, Structural steel

Another important building material is concrete. The material is inherently weak in tension and must be reinforced by means of steel bars embedded in and bonded to the concrete matrix. This combination of nonhomogeneous materials, called reinforced concrete, is utilized in many areas of building construction, including foundations, walls, columns, beams, floors, and roofs. See Column, Concrete, Foundations, Reinforced concrete, Roof construction, Wall construction

In North America, where large softwood forests were plentiful, the milling of small-dimension lumber gave rise to the balloon frame house in the latter part of the nineteenth century. In this technique, closely spaced studs, joists, and rafters are fastened together with simple square cuts and nails. The balloon frame allowed relatively unskilled persons to erect simple frame houses. In the twentieth century, the balloon frame gave way to the platform frame, in which the studs were capped at each floor rather than running continuously for two stories.

Masonry is a widely used construction technique, and perhaps the oldest building material. The three most common masonry materials are stone (quarried from natural geologic formations), brick (manufactured from clay that is exposed to high temperature in kilns), and concrete masonry units (solid or hollow blocks manufactured from carefully controlled concrete mixes). These materials are used alone or in combination, with each unit separated from the adjacent one by a bed of mortar. See Brick, Mortar

The strength of a masonry wall depends greatly on the quality of construction. Since quality varies widely, it is desirable to introduce a relatively large factor of safety into the design. Masonry has been used in structural supporting walls built as high as 20 stories. See Masonry

New materials include high-strength alloys of steel as well as products developed for space programs that have very high strength-to-weight ratios. Other desirable properties involve increased strength as well as resistance to corrosion, high temperature from fires, and fatigue. Plastics are used in many building applications. However, these materials require improvements in strength and stiffness, long-term dimensional stability, resistance to high temperature and the degrading effects of ultraviolet radiation, and ease in being fastened and connected. Composite materials have been developed for application in buildings, and include sandwich panels in which the surfaces are bonded to a core. Combinations of steel and concrete, masonry and steel reinforcement or prestress, timber and concrete, and timber and steel are in use. Other novel materials include high-performance fabric for roof coverings, structural adhesives, carbon fiber, and glass-fiber products.

Skyscrapers

Skyscrapers were developed at the end of the nineteenth and early in the twentieth century to maximize the economic return on parcels of land in urban environments. Earlier heavy-masonry-bearing-wall buildings had walls up to 6 ft (2 m) thick at their base to support as much as 16 stories of load. These walls occupied valuable space that could otherwise be rented to tenants. This drawback provided stimulus to the development of the skeleton steel frame, in which the thin exterior cladding does not participate in the support of the building but functions as a weather enclosure and a visual expression. These external skins (curtain walls) are often constructed of light aluminum or steel supports infilled with glass or metal panels. Curtain walls may also be fabricated of masonry veneer or precast concrete panels. They are designed to resist water and wind pressure and infiltration, and they are attached to the building frame for their primary support.

The major structural problem that must be considered in the design of skyscrapers is the ability of the frame to resist lateral wind loads. The building must be strong enough to resist the applied forces and stiff enough to limit the lateral displacement. The simplest method of providing lateral rigidity is to ensure that the joints between girders and columns remain rigid, that is, their geometry remains unchanged. Rigid frame design is still the most economical method of framing buildings up to 20 stories tall. See Structural analysis

As buildings became taller than 20 stories, diagonal braces were introduced between the top of one column and the bottom of an adjacent one to form a truss type of framework. The diagonals were found to be very efficient for buildings up to about 60 stories. See Truss

Building services

In order for buildings to be fully functional, they must be able to provide adequate levels of comfort and service. There are many methods used to supply the services of heating and cooling. Heating may be provided by radiation, conduction, or convection. Electrical systems are installed throughout buildings to provide lighting as well as power to operate appliances and machinery. Signal systems for telephones, computers, and alarms are also commonly specified and built. Finally, there is plumbing service, which delivers hot and cold water and carries away wastewater as well as storm water into disposal systems such as sewers or septic systems. See Air conditioning, Sewage

Building safety

Buildings are designed to resist loads due to their own weight, to environmental phenomena, and from the occupants' usage. The self-weight of a building, called dead load, is relatively easy to calculate if the composition and thickness of all of the materials are known. Included in the dead load are the building frame, walls, floors, roof, ceilings, partitions, finishes, and service equipment—that is, everything that is fixed and immovable. Environmentally applied loads include rain, which may cause ponding, and snow and ice.

Another significant load to which buildings are subjected is the force of earthquakes. Seismic loads, unlike most other loads except for wind, are dynamic in character rather than static. Engineers have devised a number of methods by which buildings can resist significant seismic loads. One is to design a maximum of energy absorption into the building by providing ductility in the frame and its connections. A second method involves an attempt to separate the superstructure of the building from ground-induced vibration—a method called base isolation. In this system, shock-absorbent material is inserted between the foundation and the superstructure to prevent vibrations from traveling up into the building.

The danger of fire in buildings has several aspects. Of primary importance is the assurance that all occupants can exit safely and that firefighters can perform their work with minimal danger. The second consideration involves the protection of property, the building, and its contents. In the initial planning of a building, the location, number, and size of exits must be carefully considered in relation to the anticipated occupancy and the material of construction. Where it is not possible to provide sufficient access to exit doors at ground level, fire escapes (generally steel-bar platforms and stairs) are affixed to the sides of buildings.

Sophisticated fire detection systems can sense both smoke and heat. These sound audible alarms and directly contact municipal fire departments and building safety officers. In addition, the alarm may automatically shut down ventilation systems to prevent smoke from spreading, may cause elevators to return to the ground floor where they remain until the danger is passed, and may close fire doors and dampers to compartmentalize the spread of smoke or flames. Supplementing this passive detection are automatic sprinkler systems. See Fire technology

Building codes and environmental concerns

The process of building is often regulated by governmental authorities through the use of building codes that have the force of law. In the United States there is no national code; rather there are regional, state, or even city building codes. Codes establish classifications of buildings according to the proposed occupancy or use. Then, for any given type of construction (for example, wood, steel, or concrete), they establish minimum standards for exit and egress requirements, for height and area, and for fire resistance ratings. In addition, minimum loads are designated as well as requirements for natural light, ventilation, plumbing, and electrical servies. Local codes are written to regulate zoning, stipulating items such as building type, occupancy, size, height, setbacks from property lines, and historic considerations.

The process of building raises large numbers of environmental issues. In many cases the owner must prepare an official environmental impact statement that considers the potential effect of the proposed building on traffic, air quality, sun and shadow, wind patterns, archeology, wildlife, and wetlands, as well as demands on existing utilities and services.

One of the primary environmental concerns is energy conservation. In the initial design of a building, all systems are studied to obtain maximum efficiency. Heating and cooling are two of the largest consumers of energy, and a great deal of effort is directed toward minimizing energy consumption by techniques such as building orientation, sun shading, insulation, use of natural ventilation and outside air, recapture of waste heat, cogeneration (using waste heat to generate electricity), use of solar energy both actively and passively, and limiting heat generation from lighting. Efforts at reducing electric power consumption by designing more efficient lighting, power distribution, and machinery are also of high priority. Consumption of water and disposal of liquid and solid waste are additional concerns. See Cogeneration, Solar heating and cooling, Ventilation