Let's consider a common structural component that an engineer would be called upon to design. We'll investigate some pipes that might be found in a manufacturing or process plant.
The pipes transmit fluid under pressure. There are also several loads that act on these pipes — loads from the weight of the pipes themselves, loads from the fluid contained in the pipes, and loads from other components connected to the pipes.
The pipes might be steel, copper, cast iron, or plastic. Each material has limits as to how much stress it can withstand. The engineer must design the pipes so that the stresses in the material remain within acceptable limits.