Width of Strip Footing given Net Ultimate Bearing Capacity Calculator

Formula Used:

\[ B = \frac{q_{nu} - (C \times N_c + \sigma_s \times (N_q - 1))}{0.5 \times \gamma \times N_\gamma} \]

Net Ultimate BC (q_nu):

Cohesion in Soil (C):

Bearing Capacity Factor (N_c):

Effective Surcharge (σ_s):

Bearing Capacity Factor (N_q):

Unit Weight of Soil (γ):

N/m³

Bearing Capacity Factor (N_γ):

Width of Footing (B):

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1. What is the Width of Strip Footing Formula?

The formula calculates the required width of a strip footing based on net ultimate bearing capacity, soil properties, and bearing capacity factors. It's derived from Terzaghi's bearing capacity theory and is essential for foundation design in geotechnical engineering.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ B = \frac{q_{nu} - (C \times N_c + \sigma_s \times (N_q - 1))}{0.5 \times \gamma \times N_\gamma} \]

Where:

\( B \) — Width of Footing (m)
\( q_{nu} \) — Net Ultimate Bearing Capacity (Pa)
\( C \) — Cohesion in Soil (Pa)
\( N_c \) — Bearing Capacity Factor dependent on Cohesion
\( \sigma_s \) — Effective Surcharge (Pa)
\( N_q \) — Bearing Capacity Factor dependent on Surcharge
\( \gamma \) — Unit Weight of Soil (N/m³)
\( N_\gamma \) — Bearing Capacity Factor dependent on Unit Weight

Explanation: The formula calculates the minimum width required for a strip footing to safely support the applied load without shear failure.

3. Importance of Footing Width Calculation

Details: Proper footing width calculation is crucial for structural stability, preventing settlement, and ensuring the foundation can distribute loads safely to the underlying soil without excessive deformation.

4. Using the Calculator

Tips: Enter all values in consistent units (Pa for pressure, N/m³ for unit weight). Ensure bearing capacity factors are appropriate for your soil conditions and foundation type.

5. Frequently Asked Questions (FAQ)

Q1: What are typical values for bearing capacity factors?
A: Bearing capacity factors vary with soil type and friction angle. Typical values range from 5-50 for Nc, 1-40 for Nq, and 0-40 for Nγ.

Q2: How does cohesion affect footing width?
A: Higher soil cohesion reduces the required footing width as cohesive soils have higher bearing capacity.

Q3: What is effective surcharge?
A: Effective surcharge refers to the vertical pressure from any additional load acting over the ground surface beyond the basic earth pressure.

Q4: When is this formula most applicable?
A: This formula is most accurate for strip footings on homogeneous soils where general shear failure is expected.

Q5: What safety factors should be applied?
A: Typical safety factors range from 2.5-3.5 for bearing capacity calculations, depending on soil conditions and importance of the structure.