Pipe Deflection by the Iowa Formula

Deflection of flexible pipes is not a design criterion in most specifications, because if pipes are properly installed with approved soil and compaction level, deflections will be within normal limits. However, the deflection for given loading and backfill conditions

Подпись: TABLE 5.26 Values of Bedding Constant K for Deflection Calculations for Flexible Pipe Bedding angle, ° K 0 0.110 30 0.108 45 0.105 60 0.102 90 0.096 120 0.090 180 0.083 Source: From A. P. Moser, Buried Pipe Design, McGraw-Hill, 2001, with permission.

can be approximated for a round pipe. The traditional method of predicting deflection is the Iowa formula introduced by M. G. Spangler and modified by R. K. Watkins:

Подпись: (5.55)DTKWr

AX = ______ _ c______________

Pipe Deflection by the Iowa Formula Подпись: total horizontal deflection, in (mm) deflection lag factor bedding constant vertical load on pipe, lb/in (kN/mm) mean radius of pipe, in (mm) modulus of elasticity of pipe material, lb/in2 (MPa) moment of inertia of pipe wall, in4/in (mm4/mm) modulus of soil reaction, lb/in2 (MPa)

EI + 0.061Er*

Values for the bedding constant may be found in Table 5.26. Because the bedding constant does not vary greatly and the bedding angle is generally not well known, it is often taken as 0.10. Values of the modulus of soil reaction are given in Table 5.27. As used in this table, the bedding material refers to the soil surrounding the pipe, not just the bedding layer on which the pipe rests. The deflection lag factor accounts for the tendency for deflections to increase over time, particularly if the soil is not well com­pacted or if the soil has a significant plastic content. The value of DL used ranges from 1.0 to 1.5. Generally, reverse curvature of a round flexible pipe occurs when the deflection reaches approximately 20 percent. Traditionally, a factor of safety of 4 is used, so deflections are limited to 5 percent.

Updated: 18 ноября, 2015 — 4:53 пп