Structures are to be found in various shapes and sizes with various purposes and uses. These range from the human-made structures of bridges carrying traffic, buildings housing offices, airplanes carrying passengers, all the way down to the biologically made structures of cells and proteins carrying genetic information. Figure 1.1 shows some examples of human-made structures. Structural mechanics is concerned with the behavior of structures under the action of applied loads – their deformations and internal loads.

The primary function of any structure is to support and transfer externally applied loads. It is the task of structural analysis to determine two main quantities arising as the structure performs its role: internal loads (called stresses) and changes of shape (called deformations). It is necessary to determine the first in order to know whether the structure is capable of withstanding the applied loads because all materials can withstand only a finite level of stress. The second must be determined to ensure that excessive displacements do not occur – a building, blowing in the wind like a tree, would be very uncomfortable indeed even if it supported the loads and did not collapse.

Modern structural analysis is highly computer oriented. This book takes advantage of that to present QED, which is a learning environment that is simple to use but rich in depth. The QED program is a visual simulation tool for analysis.