c. Concentrated loads. The formula to be used for calculating concentrated loads on rigid

and flexible conduits is a modified form of the Boussinesq equation developed by Holl, and is as

follows:

Wc

= CsPF/L

where:

Wc

=

vertical load on the conduit in kilograms per lineal meter (pounds per lineal foot)

Cs

=

surface load coefficient for buried conduits

P

=

concentrated load in kilograms (pounds)

F

=

impact factor, and

L

=

effective length of conduit in meters (feet).

An effective length of 0.914 meters (3 feet) will be used in all cases, except where pipe lengths

are less than 0.914 meters (3 feet), in which case the actual length of pipe will be used. The

load coefficient Cs is a function of conduit width Bc and effective length L, each divided by twice

the height of fill H. Determination of the load coefficient will be by the use of table 5-1, and

impact factor F will be selected from table 5-2. It will be noted from table 5-1 that the effect of a

concentrated or distributed load diminishes rapidly as the amount of cover over the sewer

increases.

Table 5-2. Impact factor (F) vs. height of Cover

Height of

Installation

Surface

Condition

Cover, m.

Taxiways, Aprons

(ft.)

Highways

Railways

Runways

Hardstands, Run-up Pads

0 to 0.35

1.50

1.75

1.00

1.50

(0 to 1)

0.35 to 0.65

1.35

*

1.00

**

(1 to 2)

0.65 to 1.00

1.15

*

1.00

**

(2 to 3)

Over 1.00 m

1.00

*

1.00

**

(Over 3 )

_______________________________________

Note that for a static load, F = 1.0

Source: Handbook of PVC Pipe-Design and Construction by Uni-Bell PVC Pipe Association,

Dallas, Texas, Copyright 1977,1979, p. 133.

5-3

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