01Loads & contact
Service loads act along the shorter dimension B. The additional moment M and horizontal force H are signed; the base moment is M + Hh. Vertical load and automatic weights are centred. Hydrostatic uplift is deducted from the total downward load to obtain V′.
e = |M + Hh| / V′
B′ = B − 2e · A′ = B′L
Full contact requires e ≤ B/6. Beyond the middle third, a triangular pressure block of width 3(B/2 − e) is used. At e ≥ B/2, compressive equilibrium is lost. Effective base pressures exclude pore-water pressure.
02Bearing capacity
General bearing equation with Vesic Nγ, GEO shape and load-inclination factors. Level ground and horizontal base are assumed. No depth enhancement is taken. Physical B/L is used for shape factors; B′ and A′ account for eccentric loading.
qᵤ = c Nc sc ic + q′ Nq sq iq
+ ½ γ′ B′ Nγ sγ iγ
qₐ = q′ + max(qᵤ − q′, 0) / FS
Compare V′/A′ with qₐ. The displayed safety factor is net resistance divided by net demand. Groundwater reduces overburden and the average effective unit weight over B′ below the base.
03Sliding & overturning
FSₛ = (V′ tan δ + ca Acontact) / |H|
FSₒ = (V′ B/2) / |M + Hh|
Automatic: ca = 0.5 Cu (undrained)
Automatic: δ = ⅔ φ′ (drained)
Automatic interface values update with the parent soil parameters. The adhesion estimate uses a reduction factor of 0.5 as an initial concrete/soil interface assumption; the friction reduction is an initial estimate, not a measured interface property. Drained automatic adhesion is zero. Turn off either automatic option to enter project-specific values.
Passive resistance is excluded. Undrained sliding uses adhesion only; δ is ignored. No horizontal force or overturning moment is displayed as “No demand”, not a finite safety factor. Overall acceptance also requires full base contact.
04Immediate settlement
sᵢ = qnet B (1 − ν²) I × adjustment / E
I = 2/π [asinh(r) + r asinh(1/r)]
r = L/B · qnet = V′/(BL) − q′
Elastic settlement at the centre of an equivalent flexible rectangle on a homogeneous half-space. E is entered in MPa and settlement is reported in mm. Only full-contact compressive loading is assessed. Footing rotation, heave, and differential settlement are excluded.
05Primary consolidation
Δσ′ = qnet BL / [(B + z)(L + z)]
s𝚌 = Hc/(1 + e₀) × [Cr log₁₀(σ′r/σ′₀)
+ Cc log₁₀(σ′f/σ′r)]
One layer is represented at its midpoint z below the base. σ′f = σ′₀ + Δσ′; σ′r = min(σ′f, σ′p). This handles normally consolidated, recompression, and yield-crossing cases. The result is final primary consolidation; creep and consolidation time are excluded.
06Use & references
Defaults are examples, not verified site properties or code-prescribed targets. Review soil parameters, drainage conditions, and load combinations with the project geotechnical engineer. The footing thickness input is used for weight only.
GEO Publication 1/2006 · Table 3.1, bearing factors and elastic foundation response.
FHWA GEC No. 6, Shallow Foundations · effective area, settlement and consolidation, Chapter 5.
USACE EM 1110-2-2502 (2022) · §6.7.5.4, undrained interface adhesion. The 0.5 reduction is adopted as a preliminary interface estimate, not a universal footing correlation.
Design and Behavior of Seamless Bridge-Pavement Systems · §3.3, an experimental concrete/aggregate interface with δ close to ⅔φ. Other interfaces require project-specific values.