Reinforced Concrete Beam Calculator
Calculate Nominal Moment Capacity and Beam Weight
Calculation Results:
Total Steel Area (As): 0 mm²
Effective Depth (d): 0 mm
Nominal Moment Capacity (Mn): 0 kNm
Factored Capacity (φMn, φ=0.9): 0 kNm
Beam Self-Weight: 0 kN/m
Total Beam Weight: 0 kg
Understanding Reinforced Concrete Beam Analysis
This concrete beam calculator helps you determine the flexural strength (moment capacity) of a rectangular reinforced concrete section. Whether you are designing for a residential renovation or a commercial structure, understanding the interaction between concrete and steel is crucial for structural safety.
Key Parameters in the Calculation
- Effective Depth (d): This is the distance from the top compression fiber to the centroid of the tension reinforcement. It is critical because it defines the lever arm for the internal moment.
- Concrete Strength (f'c): The specified compressive strength of concrete. Standard mixes usually range from 20 MPa to 40 MPa for general construction.
- Steel Yield Strength (fy): The point at which the steel rebar begins to deform plastically. High-strength rebar (Grade 60 or 420 MPa) is the industry standard.
- Reinforcement Ratio (ρ): The ratio of steel area to concrete area (As / b*d). If this is too high, the beam may fail brittlely; if too low, it may not meet minimum safety standards.
Typical Example: Residential Lintel
Imagine a lintel spanning a 3-meter opening with a 200mm width and 400mm depth. If you use 2 bars of 16mm diameter (Grade 420 steel) and 25 MPa concrete:
- As: 2 * 201 mm² = 402 mm²
- d: 400mm – 40mm – 8mm (half bar dia) = ~352mm
- Nominal Capacity: Approximately 53 kNm.
Safety Considerations
Engineers apply a strength reduction factor (φ), typically 0.9 for flexure, to account for uncertainties in materials and workmanship. The factored load on the beam (from gravity, snow, or occupancy) must always be less than the factored capacity (φMn).