Preliminary estimate for concept-stage planning only. NOT a substitute for design by a licensed Professional Engineer (PE) / registered structural engineer. All structural designs must be independently verified and stamped per local code before construction.
Flexural Slab & Beam Rebar Sizing Calculator
Determine required flexural steel area (As), bar size spacing, and minimum reinforcement (As,min = 0.0018 bh) per ACI 318-19.
Section & Flexural Moment Inputs
Flexural Steel Sizing Results
As = 0.610 in²/ftReinforced Section & Strain Profile
Frequently Asked Questions (FAQ)
What is the minimum flexural steel ratio for one-way concrete slabs under ACI 318?
ACI 318-19 specifies a minimum temperature/shrinkage steel ratio of 0.0018 for Grade 60 rebar (As_min = 0.0018 × b × h).
How do you calculate effective depth 'd' of a reinforced concrete slab?
Effective depth d = Total Slab Thickness (h) - Concrete Cover - (Nominal Bar Diameter / 2).
What is standard clear concrete cover for interior vs exterior slabs?
Interior slabs require a minimum 3/4-inch (20mm) clear cover, while slabs cast against earth require 3 inches (75mm) of concrete cover.
How do you calculate required steel area As for bending moment Mu?
Required steel area is computed using As = Mu / (φ × fy × (d - a/2)), where a = As × fy / (0.85 × f'c × b).
What is the maximum allowed rebar spacing in a concrete slab?
ACI 318 limits maximum rebar spacing to 3 times total slab thickness (3h) or 18 inches (450 mm), whichever is smaller.
What is the difference between Grade 40, Grade 60, and Grade 80 slab rebar?
Grade 60 (yield strength 60,000 psi / 420 MPa) is the industry standard. Grade 80 permits smaller bar sizes, while Grade 40 is reserved for non-structural work.
Why is temperature and shrinkage reinforcement required in slabs?
As concrete cures and dries, it shrinks. Shrinkage steel distributes tensile stresses evenly across the slab to prevent wide surface cracks.
How does concrete compressive strength (f'c) impact slab moment capacity?
Higher concrete strength (e.g., 4,000 psi vs 3,000 psi) reduces compression block depth 'a', slightly increasing flexural lever arm (d - a/2) and moment capacity.
What is the minimum slab thickness required to prevent excessive deflection?
For simple span solid one-way slabs, ACI 318 Table 7.3.1.1 specifies a minimum thickness of L/20 unless detailed deflection calculations are performed.
How are welded wire reinforcement (WWR) mats specified for ground slabs?
WWR (e.g. 6x6-W2.9/W2.9) provides shrinkage control in ground-supported slabs, positioned in the upper third of the slab depth.