ABSTRACT
If a beam of symmetrical cross-section is subjected to a bending moment, then stresses due to bending action will occur. In pure or simple bending, the beam will bend into an arc of a circle. Due to couples, the upper layers of the beam will be in tension because their lengths have been increased, and the lower layers of the beam will be in compression, because their lengths have been decreased. Somewhere in between these two layers lies a layer whose length has not changed, so that its stress due to bending is zero. This layer is called the neutral layer and its intersection with the beam’s cross-section is called the neutral axis. The bending of beams is of much importance in designing buildings, bridges, ships, etc, and ensuring their safety under these loads.
In the case of the longitudinal strength of ships, due to sea waves, the maximum bending moments that occur along its length are due to either a big wave acting in the middle length of the ship, causing the vessel to hog, or alternatively, due to two big waves acting together at both the fore and aft ends of the ship at the same time, causing the vessel to sag at amidships. The transverse strength of ships is dependent on the buoyant forces acting upwards on the ship, and the self-weight of cargo, etc, acting downwards. In the case of bridges, bending stresses are caused by a number of different forces, including wind, snow, and the weight of automobiles and trains, together with the self-weight of the bridge. In the case of buildings, bending stresses can be caused by wind, snow, and the weight of the contents of the building, together with its self-weight.
