Analysis of Bearing Capacity of the Nails

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

where:	R_f	-	nailhead strength
	R_t	-	nail strength against breaking
	T_p	-	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:	R_t	-	strength against breaking
	d_s	-	nail diameter
	f_y	-	strength of nail material
	SF_t	-	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:	T_p	-	pull-out nail bearing capacity [kN/m]
	d	-	hole diameter
	g_s	-	bond strength, given either as a parameter of the nail or as soil parameter
	SF_e	-	factor of safety against pull-out

2. calculate from effective stress

where:

where:	T_p	-	pull-out nail bearing capacity [kN/m]
	d	-	hole diameter
	σ_z	-	vertical geostatic stress
	φ	-	effective angle of internal friction of the soil
	c	-	effective cohesion of the soil
	SF_e	-	factor of safety against pull-out

3. calculate according to HA 68/94

where:	T_p	-	pull-out nail bearing capacity [kN/m]
	d	-	hole diameter
	σ_n	-	average radial effective stress
	φ	-	effective angle of internal friction of the soil
	c	-	effective cohesion of the soil
	SF_e	-	factor of safety against pull-out

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

where:

σ_z

vertical geostatic stress

where:

The nail head strength is evaluated by the formula:

where:	l	-	nail length
	S_max	-	maximum spacing of nails in a structure
	R_t	-	nail strength against breaking
	T_p	-	pull-out nail bearing capacity
	SF_f	-	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

GEO5