Concrete Volume Beam

Concrete volume in a beam

A prismatic rectangular beam takes the most direct volume formula there is, V = L · b · h, where L is the beam length, b the width and h the total height. Take a beam of 6 m × 20 cm × 40 cm: V = 6 · 0.20 · 0.40 = 0.48 m³. Tack on 5–10% for losses from formwork leaks, the pump line and settlement. The cover (cobrimento) lives inside h and usually runs 2.5–4 cm; for beams in urban environments (aggressiveness class CAA II), NBR 6118 calls for 25 mm of nominal cover.

You name the concrete grade by its f_ck, the characteristic compressive strength at 28 days. Typical structural concrete sits between 20 to 50 MPa, and CAA III/IV exposure (industrial or marine) pushes you to higher-strength mixes of ≥ 30 MPa. That grade is what you quote when ordering from the batching plant by m³.

Applications

Estimate concrete consumption per beam for purchasing and budgeting. Add up the total m³ across the site, summing beams, columns and slabs. Proportion the mix design per m³ for cement, sand, gravel and water. Track waste as you go. And before you trust them, double-check the volumes that structural drawings or BIM quantity take-offs (Revit, ArchiCAD) hand you.

FAQ

Should I subtract the column intersection? For an accurate take-off, yes — remove the column volume from the beam length wherever the two meet. On a preliminary budget that overlap rarely tops 3%, so you can let it go.

Net or gross beam length? A quick estimate can run on the gross axis-to-axis structural length. When you need precision, switch to the clear span plus the penetration into the supports.

How much loss should I add? It depends on how the concrete arrives. Ready-mix from a batching plant runs 3–5%, mixing on site is more like 8–10%, and pumping up a tall building can cost up to 7% just in the line.