The proper name for one of the two principal structural sides of a ladder is a:

The proper name for one of the two principal structural sides of a ladder is referred to as a beam. In ladder construction, the beams form the primary framework and provide the necessary strength and stability required to support the weight of firefighters and their equipment during operations. The beams run parallel to each other and are connected by the rungs, which allow personnel to climb the ladder safely.

Understanding the structure of a ladder is essential for effective use in firefighting. The beams are designed to bear load and maintain the integrity of the ladder when extended or when weight is applied while climbing. Recognizing terms like "beam" helps firefighters communicate effectively and ensure they are using the equipment correctly according to safety standards and best practices.