Perhaps the two “main” forces engineers must design structures to endure are tension and compression. Tension is the force which causes a material to stretch, or be pulled. Compression is the force which causes a material to shorten, or be pushed.
A beam used in the construction of a structure will often experience both forces simultaneously. As shown in the Tension and Compression video, knowledge of where the beam experiences each force allows engineers to create more efficient beams, such as beams with circular holes in the middle.