Supports

members used to support and fasten the load-bearing components of structures. Supports transmit stresses from one part to another part of the structure or from the structure to the foundation. The design of supports varies greatly; it depends on the magnitude and nature of the stresses being transmitted, on the dimensions and shape of the load-bearing members, on the materials used in construction, and on climatic conditions.

In residential, public and industrial buildings, walls, posts, stanchions, and columns serve as supports for beams and girders. Structural joints, such as those linking main and secondary girders, can also serve as supports. Most arches and frames are fastened directly to the foundations of buildings and structures. Abutments and piers serve as supports for the span structures of bridges.

In structural mechanics, supports are treated in the form of schematic abstracts derived from actual support structures. In the most frequently used coplanar truss systems, four basic support schemes are distinguished (see Figure 1). These types are based, respectively, on (1) the hinged movable bearing, (2) the hinged fixed bearing, (3) the limited-movement bearing, and (4) the rigid fixed bearing. The hinged movable bearing permits the attached system to rotate around a certain axis, and it also permits translatory motion in one direction. Supports of this type, such as the roller bearings used on bridges, consist of two support plates connected by a hinge. Rollers are located between one of the plates and the bearing surface (Figure 1, a). In such a support, the support reaction passes through the center of the hinge in a direction normal to the bearing surface.

Figure 1. Supports for coplanar truss system: (a) hinged movable bearing, (b) hinged fixed bearing, (c) limited-movement bearing, (d) fixed rigid bearing

The hinged fixed bearing permits only a rotary motion of the system with respect to the point on which the support rests. Bearings of this type do not use rollers (Figure 1, b). The support reaction passes through the center of the hinge and is determined by two components, one horizontal and the other vertical. The limited-movement bearing permits only a translatory motion of the attached system in one direction. Such a support is built with rollers located between the bar and the bearing surfaces (Figure 1, c). In this case the support reaction is in a direction that is normal to the bearing surface and that is determined by the normal force and the support moment. The rigid fixed bearing does not permit any motion of the system and forms a rigid connection between the attached system and the overall structure (Figure 1, d). Here the support reaction consists of horizontal and vertical components and a support moment.