4.1 Structural elements
A building structure consisting of a steel frame work skeleton is made up of the following structural elements or members
Flexural members; beams or girders
Tension members
Compression members: columns, stanchions, struts
Torsional members
Elements of foundation structure
Some elements or members may be subjected to combined bending and axial loads. The members of steel frame are jointed together by riveted, bolted, pinned or welded connections or joints. No matter how complicated a structure may appear to be, it must consist of some combination of the basic members mentioned above. However, flexural members, (or beams) may, in some cases, appear as extremely heavy built-up girders and the compression members (or columns) and tension members (or ties) may be combined to form heavy trusses in an extensive frame work. The structural elements are made up of the following commonly used structural shapes and built-up sections as shown in Figure 4.1 below.
Angle section
T-section
Channel section
I-section
Z-section
Solid square section
Square tube
Circular section (solid)
Hollow circular section
Plate section
Compound and built-up sections
4.2 Beams and Girders
A beam is a structural member the primary function of which is to support loads normal to its axis. The word beam and the word girder are used more or less interchangeably. However, the word girder may mean either a built-up member (usually a heavy one) or a main beam (single rolled shaped or built-up) which supports other beams. In a beam, loads are resisted by bending and shear, but local stress conditions and deflection are also important considerations. Beams in structures may also be referred to by typical names that suggest their function in the structure as given below:
i) Girder :Usually indicate a major beam frequently at wide spacing that
supports small beams
ii) Joists : Closely spaced beams supporting the floors and roofs of buildings
iii) Purlins : Roof beams usually supported by trusses
iv) Rafters : Roof beams usually supported by purlins
v) Lintel : Beam over window or door openings that support the wall above
vi) Girts: :Horizontal wall beams used to support wall covering on the side of
an industrial building
Spandrel beam :Beam around the outside perimeter of a floor that support the exterior walls and the outside edge of the floor
4.3 Tension Members
A tension member is the one which is intended to resist axial tension. Tension members are also called ties or hangers. The cross-sectional arrangement of material in axially stressed tension members is structurally unimportant.
4.4 Compression members
Compression members also called columns, struts, posts or stanchions are intended primarily to resist compressive stress. The requirements for compression members are more demanding than those for tension members, since in this case the carrying capacity is a function of shape as well as of area and material properties. The buckling of the column in any possible direction becomes a governing criterion.