Structural systems

The structures of buildings are mostly skeleton frames of various types. New domestic housing in many parts of the world today is commonly made from timber-framed construction. Wood products, are becoming a bigger part of the construction industry. They may be used in both residential and commercial buildings as structural and aesthetic materials. In buildings made of other materials, wood is still found as a supporting material, especially in roof construction, in interior doors and their frames, and as exterior cladding.

Laminated veneer lumber functions as beams to provide support over large spans, such as removed support walls and places where dimensional lumber is not sufficient, and also in areas where a heavy load is bearing from a floor, wall or roof above on a short span. Wood I-joists are used for floor joists on upper floors. They are engineered for long spans and are doubled up in places where a wall will be aligned over them. Glued laminated beams are created by glueing the faces together to create beams. By glueing multiple, common sized pieces of lumber together act as one larger piece of lumber. Manufactured trusses are used in home construction as a pre-fabricated replacement for roof rafters and ceiling joists. It is seen as an easier installation and a better solution for supporting roofs as opposed to the use of lumber struts and purlins as bracing.

Steel is one of the major structural materials in buildings. It is a strong and stiff material. It can be quickly fabricated and erected. The lightest and most efficient structural shape is the bar (or open web) joist, a standard truss made with angles for the top and bottom chords, joined by welding to a web made of a continuous bent rod. It is used almost exclusively to support roofs and can span up to 45 metres. Where steel beams support concrete floor slabs poured onto a metal deck, they can be made to act compositely with the concrete.

Steel columns are joined to foundations with base plates welded to the columns and held by anchor bolts embedded in the concrete. The erection of steel frames at the building site can proceed very rapidly, because all the pieces can be handled by cranes and all the boiled connections can be made swiftly by workers with hand-held wrenches.

Reinforced concrete is also a major structural material in buildings. In-situ concrete is used for foundations and for struc­tural skeleton frames. The oldest framing system is the beam and girder system, whose form was derived from wood and steel construction: slabs rest on beams, beams rest on girders, and girders rest on columns in a regular pattern. This system needs much handmade timber formwork, and in economies where labour is expensive other systems are employed. The simplest and most economical floor system is the flat plate where a plain floor slab rests on columns spaced apart. If the span is larger, the increasing loud requires a local thickening of the slab around the columns. Concrete columns are of rectangular or circular profile and are cast in plywood or metal forms. The reinforcing steel never exceeds 8 percent of the cross-sectional area to guard against catastrophic brittle failure in case of accidental overloading.

Precast prestressed floor elements are made in a number of configurations. At the building site, precast members are joined together by a number of methods, including welding together metal connectors cast into them or pouring a layer of in situ concrete on top of floor members, bonding them together. Precast prestressed construction is widely used, and it is the dominant form of construction in Russia and Eastern Europe.