Bearing Capacity for Strip Footing Calculator

Bearing Capacity Formula:

\[ q_{strip} = (C \times N_c) + (\sigma' \times N_q) + (0.5 \times \gamma \times B \times N_\gamma) \]

Cohesion (C):

Bearing Capacity Factor (N_c):

Effective Surcharge (σ'):

Bearing Capacity Factor (N_q):

Unit Weight of Soil (γ):

N/m³

Width of Footing (B):

Bearing Capacity Factor (N_γ):

Bearing Capacity (q_strip): Pa

1. What is Bearing Capacity for Strip Footing?

Definition: The bearing capacity of a strip footing is the maximum load per unit area that the soil can support without experiencing shear failure.

Purpose: This calculation is essential for designing foundations that are safe and stable under expected loads.

2. How Does the Calculator Work?

The calculator uses Terzaghi's bearing capacity formula:

\[ q_{strip} = (C \times N_c) + (\sigma' \times N_q) + (0.5 \times \gamma \times B \times N_\gamma) \]

Where:

\( q_{strip} \) — Ultimate bearing capacity (Pa)
\( C \) — Cohesion of soil (Pa)
\( N_c \) — Bearing capacity factor for cohesion
\( \sigma' \) — Effective surcharge at footing base (Pa)
\( N_q \) — Bearing capacity factor for surcharge
\( \gamma \) — Unit weight of soil (N/m³)
\( B \) — Width of footing (m)
\( N_\gamma \) — Bearing capacity factor for unit weight

3. Importance of Bearing Capacity Calculation

Details: Proper calculation ensures foundation stability, prevents settlement issues, and guarantees structural safety.

4. Using the Calculator

Tips: Enter all required parameters. The bearing capacity factors (N_c, N_q, N_γ) have ±5% uncertainty.

5. Frequently Asked Questions (FAQ)

Q1: What are typical values for N_c, N_q, N_γ?
A: For φ=0° (clay): N_c=5.14, N_q=1.0, N_γ=0.0. These vary with soil friction angle.

Q2: How do I determine soil cohesion?
A: Cohesion is obtained from laboratory tests like unconfined compression test or field vane shear test.

Q3: What is effective surcharge?
A: It's the vertical stress at footing base level from soil or other loads above the footing.

Q4: When is the third term (0.5γBN_γ) significant?
A: For cohesionless soils (sand) where N_γ can be substantial.

Q5: What safety factors should I apply?
A: Typical factors range from 2.5-3.5 depending on soil conditions and importance of structure.