Understanding Beam Design
Proper concrete beam sizing ensures structural integrity and load-bearing capacity.
- Load Calculations Dead load: self-weight + floor. Live load: occupancy based. Moment: wL²/8 simple span. Shear: wL/2. Impact factor: 1.15-1.3.
- Size Guidelines Depth: L/12 to L/15. Width: 0.3-0.5 × depth. Cover: 1.5" sides, 2" bottom. Minimum width: 8". Maximum spacing: 1.5 × depth.
- Reinforcement Ratios Tension steel: 0.5-2.5%. Compression steel: 0.2-1%. Stirrups: #3 at d/2. Development length: 40× bar diameter. Minimum 2 bars top and bottom.
- Material Properties Concrete: f'c = 3000-5000 psi. Steel: fy = 60,000 psi. Elastic modulus: 57,000√f'c. Bond strength: 400-800 psi. Shear strength: 2√f'c.
Construction Guide
Formwork Requirements
Sides: 3/4" plywood. Support: 2×4 at 16" O.C. Ties: 1/2" diameter. Chamfer: 3/4" typical. Deflection limit: L/360. Oil forms before pour.
Placement Details
Concrete: 4" slump max. Vibration: 10-15 seconds. Layer height: 18" max. Temperature: 40-90°F. Curing: 7 days minimum. Strip forms: 14 days.
Cost Analysis
Concrete: $150-300/yd³. Steel: $1.50-2.50/lb. Forms: $15-25/ft². Labor: $200-400/yd³. Engineering: $500-1000/design. Testing: $75-150/set.
Quality Control
Rebar inspection pre-pour. Concrete test every 50yd³. Slump: 3-5". Air: 4-6%. Strength test: 7 and 28 days. Monitor cracks and deflection.