Buried Steel Pipe Structural Design

Per the Specification for structural design of buried steel pipeline in water supply & drainage engineering. Loads, strength (NA case 1/2), stability, buoyancy and stiffness are each checked with an OK / fail verdict.

1 · Basic data — material properties

Steel modulus EpkN/m²

Side-fill modulus EnkN/m²

Soil reaction modulus EekN/m²

Subgrade coeff. ξ

Design strength fN/mm²

Thermal coeff. α1/°C

Soil unit weight rskN/m³

Steel unit weight rstkN/m³

Water unit weight rwkN/m³

Poisson steel νp

Poisson soil νs

Trench width Brm

1 · Basic data — geometry

Contact width am

Wheel spread bm

Member width b0m

Wall thickness tm

Inner diameter Dm

Ground elevationm

Pipe-centre elevationm

Moment of inertia Ipm⁴

External water levelm

Temp. diff ΔT°C

1 · Basic data — calculation coefficients

Bedding angle°

γG1

γG,sv

γGw

γ0

ψc

n (stability)

Kst

Kf (float)

Load inputs

Internal pressure FwkkN/m²

Vacuum pressure FvkkN/m²

Ground surcharge qmkkN/m²

ψq (surcharge)

Allowable ψ

Vehicle wheel load QvkkN

Dynamic factor μd

Wheel count n

Spread d1m

Spread d2m

Spread d3m

ψq (vehicle)

Computed geometry

Ed = ξ·Ee—kN/m²

Ee/En—

Br/d1—

Outer diameter D1—m

D0 = D + t—m

Computed radius r0—m

Reduced thickness t0—m

Cover depth Hs—m

2 · Load calculation

Self weight G1k—kN/m

Vertical soil pressure Fsv,k—kN/m

Internal water weight Gwk—kN/m

Design internal pressure Fwd,k—kN/m²

Vehicle load qvk—kN/m²

Groundwater buoyancy Ffw,k—kN/m²

3 · Strength calculation

Case 1 · Vehicle load

Axial force N—kN

Moment M—kN·m

Ring stress σθ—kN/m²

Reduced stress ησθ—N/mm²—

Case 2 · Ground surcharge

Axial force N—kN

Moment M—kN·m

Ring stress σθ—kN/m²

Reduced stress ησθ—N/mm²—

Longitudinal stress

σx (compression side)—N/mm²

σx (tension side)—N/mm²

Combined stress σ1—N/mm²

Combined stress σ2—N/mm²

Design value γ0σ—N/mm²—

4 · Stability check

Critical pressure Fcr,k—kN/m²

Case 1 · applied pressure—kN/m²—

Case 2 · applied pressure—kN/m²—

5 · Buoyancy (anti-float) check

Stabilising ΣFGK—kN/m

Buoyancy Ffw,k·D1—kN/m

Float factor kf——

6 · Stiffness (deflection) check

Allowable deflection ΨD0—mm

Deflection ωd,max (case 1)—mm—

Deflection ωd,max (case 2)—mm—

Loads per 埋地钢管: G1k = rst·π·D0·t; Fsv,k = rs·Hs·D1; Gwk = rw·π·D²/4; Fwd,k = 1.5·Fwk; buoyancy Ffw,k = rw·(WL − invert). Strength: N, M (case 1: vehicle, case 2: surcharge), ring stress σθ = N/(b0·t0) + 6M/(b0·t0²); ησθ ≤ f. Longitudinal & combined stresses with γ0σ ≤ f. Stability applied ≤ Fcr,k. Buoyancy kf = ΣFGK/(Ffw,k·D1) ≥ Kf. Stiffness ωd,max ≤ ΨD0 = 0.035·D0·1000. π uses the Excel rounded value 3.14.