Introduction to Structural Analysis
FORMS OF STRUCTURES
Any civil engineering structure is conceived keeping in mind its intended use, the materials available, cost and aesthetic considerations. The structural analyst encounters a great variety of structures and these are briefly reviewed here.
One of the simplest structures is a simply supported beam, supported on a pin at one end and a roller at the other (Fig. 1.1a). Such a beam, it may be recalled from the fundamentals of strength of materials, is quite stable and statically determinate, and transmits the external loads to the supports mainly through shear and moment. The other types of beams which are more complicated from the point of view of analysis are those with fixed ends and those that are continuous over supports (Figs. 1.1b and c). As we shall see later, such beams are statically indeterminate and cannot be solved using equations of static equilibrium alone.
For longer spans, a truss may be employed in place of a beam. Unlike a beam in which the loads are resisted by shear and moment, the truss members transmit the load primarily by axial forces in the members. The structural action of a truss may be compared with that of a simply supported beam.
For a truss under vertical loading, the top chord members of the truss are subjected to axial compressive forces and the bottom chord members to axial tensile forces. Under similar conditions, the top fibres of a beam are subjected to compressive stresses and the bottom fibres to tensile stresses.