01/09/2026
Understanding Primary and Secondary Beams on Site
It is very important to identify which beam is primary and which is secondary, and understand which one carries the other. Remember this basic rule:
The primary beam normally carries the secondary beam.
Knowing this will help you arrange reinforcement correctly on site. There is a big difference between:
• Understanding reinforcement from the structural drawing, and
• Knowing how to arrange it properly on site.
Unfortunately, many people make mistakes because they misinterpret the drawing or improvise without confirmation. Common errors include:
• Placing bottom bars (BB or B1) in the wrong position.
• Confusing bottom top bars (B2) with bottom bars (B1).
• Not knowing which reinforcement should come first when one beam connects into another.
Here are some important guidelines:
• The longer span beam usually rests on the shorter span beam, although this is not a universal rule. A shorter span can also rest on a longer one if the longer beam is designed as the primary beam. The key is to identify which beam is primary and which is secondary.
• The beam that carries another beam typically has more reinforcement, but do not assume, always confirm from the detailing.