A beam is a horizontal structural member that spans between supports and carries the loads above it — from slabs, walls and floors — transferring them to the columns or load-bearing walls. Beams work mainly in bending: the top fibres compress and the bottom fibres stretch, which is why reinforcement steel is concentrated near the bottom (and over supports in continuous beams).
In a framed house, beams tie the columns together and support the slab edges. Common types include the main beam (carrying other beams), secondary beam, and the plinth beam at foundation level. Beam sizes depend on span and load — a typical residential beam might be 230 mm wide by 300–450 mm deep.
Because beams are bending members with significant tension, their steel content is higher than slabs — around 120 kg per cubic metre as a planning estimate. Estimating a beam means its concrete volume (width × depth × length) plus the reinforcement from its bar bending schedule.