Catenaries

Catenaries derive their strength from their form, and carry transverse forces in pure tension by deflecting (just as a tightrope will sag when someone walks on it). They are almost always cable or fabric structures. A fabric structure acts as a catenary in two directions.

Structural engineering theory (The Fourth Term)

Figure of a bolt in shear. Top figure illustrates single shear, bottom figure illustrates double shear.

Structural engineering depends upon a detailed knowledge of loads, physics and materials to understand and predict how structures support and resist self-weight and imposed loads. To apply the knowledge successfully a structural engineer will need a detailed knowledge of mathematics and of relevant empirical and theoretical design codes. He will also need to know about the corrosion resistance of the materials and structures, especially when those structures are exposed to the external environment. The criteria which govern the design of a structure are either serviceability (criteria which define whether the structure is able to adequately fulfill its function) or strength (criteria which define whether a structure is able to safely support and resist its design loads). A structural engineer designs a structure to have sufficient strength and stiffness to meet these criteria.

Loads imposed on structures are supported by means of forces transmitted through structural elements. These forces can manifest themselves as:

tension (axial force)

compression (axial force)

shear

bending, or flexure (a bending moment is a force multiplied by a distance, or lever arm, hence producing a turning effect or torque)

Loads

Some Structural loads on structures can be classified as live (imposed) loads, dead loads, earthquake (seismic) loads, wind loads, soil pressure loads, fluid pressure loads, impact loads, and vibratory loads. Live loads are transitory or temporary loads, and are relatively unpredictable in magnitude. They may include the weight of a building's occupants and furniture, and temporary loads the structure is subjected to during construction. Dead loads are permanent, and may include the weight of the structure itself and all major permanent components. Dead load may also include the weight of the structure itself supported in a way it wouldn't normally be supported, for example during construction.