What is the meaing of Minimum Bending Radius (Dynamic Conditions)?

Minimum Bending Radius (Dynamic Conditions)

The following formula can be used to determine the minimum values for the radii to which such cables may be bent while being pulled into an installation and while under tension. This value will largely depend on the tension the cable experiences as it exits the bend. The greater the exiting tension, the greater the minimum bending radius will be for the cable.

MBR = (Te ÷ SWBP) X 12 (in)

Where:

MBR = Minimum radius of bend (in)
Te = Tension as cable exits the bend (pounds x force)
SWBP = Maximum allowable Sidewall Bearing Pressure (pounds x force per foot of bend radius)

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MAXIMUM SIDEWALL PRESSURE AT BENDS

Sidewall pressure is caused by the tension in the cable acting horizontally and the weight of the cable
acting vertically.  Generally, the maximum sidewall pre
ssure should not exceed 300 lbs/foot of radius, i.e.,
the tension of a cable immediately as it leaves a bend must not be greater than 300 times the bend radius
(in feet).  Shown below are formulas to calculate the maximum allowable tension at a bend and the actual
sidewall pressure.
**
Bend radii for training cable into final position (no tension on the cable) are shown in Tables 2 & 3.  There
are no published limits for bend radii when pulling cable (when the cable is under tension), however
Superior-Essex recommends doubling the minimum bend radii shown on Tables 2 & 3 when pulling cable
through conduit.
Tb
m
= 300 x r
(Formula 4)
Where:Tb
m
= maximum allowable pulling tension at bend, lbs.
r = bend radius, feet
P = Tb / r
(Formula 5)
Where:P = actual sidewall pressure on cable, lbs./ft.
Tb = pulling tension at and of bend, lbs.
r = bend radius, feet
The  maximum  allowable  pulling  tension  at  bend  (Tb
m
)  is  the  limit  that  the  calculated  pulling  tension  (Tb)
should  be  compared  to.    If  Tb  is  greater  than  Tb
m
,  the  possibility  of  redesign  or  re-routing  should  be
considered.

Maximum allowable sidewall pressure

Sidewall pressure, P, is defined as the tension out of a bend expressed in newtons (pounds) divided by the radius of the bend expressed in millimeters (feet). The sidewall pressure on a cable can be calculated by thefollowing equations:

Single cable in conduit

P =To/r

Three cables in cradle configuration where the center cable presses hardest against the conduit

p=((3c-2)*To)/(3r)

Three cables in triangular configuration where the pressure is divided between the two bottom cables

P=c*To/2r

Four cables in diamond configuration where the bottom cable is subjected to the greatest crushing force


p=((3c-2)*To)/(3r)

where
P is the sidewall pressure, in newtons/millimeter (pounds/foot) of radius
To is the tension out of the bend, in newtons (pounds)
c is the weight correction factor (refer to J.3.1)
r is the inside radius of bend, in millimeters (feet)