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Analysis of Bearing Capacity of the Nails

For each nail the following bearing capacities are either computed or input:

where:

Rf

-

nailhead strength

Rt

-

nail strength against breaking

Tp

-

pull-out nail bearing capacity

The strength characteristics of a nail represent the basic parameters to compute the total bearing capacity of a nail.

The nail strength against breaking follows from:

where:

Rt

-

strength against breaking

ds

-

nail diameter

fy

-

strength of nail material

SFt

-

factor of safety against breaking

The pull-out nail bearing capacity is calculated by one of the following ways:

1. calculate from bond strength:

where:

Tp

-

pull-out nail bearing capacity [kN/m]

d

-

hole diameter

gs

-

bond strength, given either as a parameter of the nail or as soil parameter

SFe

-

factor of safety against pull-out

2. calculate from effective stress

where:

where:

Tp

-

pull-out nail bearing capacity [kN/m]

d

-

hole diameter

σz

-

vertical geostatic stress

φ

-

effective angle of internal friction of the soil

c

-

effective cohesion of the soil

SFe

-

factor of safety against pull-out

3. calculate according to HA 68/94

where:

Tp

-

pull-out nail bearing capacity [kN/m]

d

-

hole diameter

σn

-

average radial effective stress

φ

-

effective angle of internal friction of the soil

c

-

effective cohesion of the soil

SFe

-

factor of safety against pull-out

Average radial effective stress σn is calculated by the following formula:

where:

σz

-

vertical geostatic stress

where:

The nail head strength is evaluated by the formula:

where:

l

-

nail length

Smax

-

maximum spacing of nails in a structure

Rt

-

nail strength against breaking

Tp

-

pull-out nail bearing capacity

SFf

-

factor of safety of a nail head strength

If the nail is not anchored to the structure cover, it is possible to set the nail head strength to zero.

Literature:

FHWA0-IF-03-017

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