NoDigTech Sleeve Structural Strength Calculator

AWWA Manual 11 chapter 6

 qa = (1/FS){(32 * Rw * B' * E' * EI / D^3)^ 1/2}

 Symbol Explanation Value qa allowable buckling pressure (psi) FS design factor  = 2.5 for (h/D) >= 2 OR  = 3.0 for (h/D) < 2 h = height of ground surface above top of pipe (in) D = diameter of pipe (in) 2.5 Rw water  bouyancy factor = 1-0.33(hw/h),  0<=hw<=h hw = height of water surface above top of pipe (in) 0.67 (for hw = h) B' empirical coefficient of elastic support (dimensionless) = 1 / (1 + 4 e^(-0.065 H) ) where H  = height of fill above pipe (ft) H: D pipe diameter (in) E modulus of elasticity 3*10^7 for steel [psi] I transverse moment of inertia per unit length of pipe wall 1.t^3/12 t is the thickness of pipe wall [in] E' modulus of soil reaction lb/in^2 (psi) 2000

 The allowable buckling pressure must be greater or equal the real buckling pressure calculated form the water column, the dead and live loads above the pipe.
 qa1= Gamma w * hw + Wc / D + WL / D

 Symbol Explanation Value Gamma w specific weight of water 0.0361 lb/cu in hw height of backfill above conduit (ft) = H Wc vertical soil load on pipe per unit length (lb/ft) w * Hc * Bc w unit weight of fill (lb/cu ft) Hc height of fill above top of pipe (ft) Bc = D Diameter of pipe (ft) w: D pipe diameter WL live load on the conduit for a 10 ft height cover = 1100 psf = 7.6389 psi

 t: thickness of sleeve wall needed to withstand the load: t: thickness of sleeve wall needed for 100 yrs service life:

 Remarks: 5 psi ----> 11.53' of water load 11.53' is entered  for water load in the formula for 100 years service-life 0.01" was added to the calculated value  calculate requested t  compare thickness t requested with thickness tg (Gauge of metal sheet available in the market)

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