Technical Manual

Inc.

p 207

APPENDIX 2H

DOCUMENTATION

Chapter 2

Helical Foundation Systems

ESR-3074

Most Widely Accepted and Trusted

Page 3 of 9

The ASD capacities of FSI helical foundation system

components are indicated in Tables 1, 2, 3, and 5. The

geotechnical analysis must address the suitability of the

helical foundation system for the specific project. It must

also address the center-to-center spacing of the helical

piles, considering both effects on the supported

foundation and structure and group effects on the pile-soil

capacity. The analysis must include estimates of the axial

tension and/or compression capacities of the helical piles,

whatever is relevant for the project, and the expected total

and differential foundation movements due to single pile

or pile group, as applicable.

A written report of the geotechnical investigation must

be submitted to the code official as one of the required

submittal documents, prescribed in Section 107 of the

2012 and 2009 IBC (Section 106 of the 2006 IBC), at the

time of the permit application. The geotechnical report

must include, but need not be limited to, the following

information:

1. A plot showing the location of the soil investigation.

2. A complete record of the soil boring and penetration

test logs and soil samples.

3. A record of soil profile.

4. Information on groundwater table, frost depth and

corrosion-related parameters, as described in Section

5.5 of this report.

5. Soil properties, including those affecting the design

such as support conditions for the piles.

6. Recommendations for design criteria, including but

not limited to mitigations of effects of differential

settlement and varying soil strength, and effects of

adjacent loads.

7. Field inspection and reporting procedures (to include

procedures for verification of the installed bearing

capacity when required).

8. Load test requirements.

9. Any questionable soil characteristics and special

design provisions, as necessary.

4.1.2 Bracket Capacity (P1):

Only the localized limit

state of concrete bearing strength in compression has

been evaluated for this evaluation report. All other limit

states related to the concrete foundation, such as those

limit states described in ACI 318 Appendix D, punching

(two-way) shear, beam (one-way) shear, and flexural

(bending) related limit states, have not been evaluated for

this evaluation report. The concrete foundation must be

designed and justified to the satisfaction of the code

official with due consideration to all applicable limit states,

and the direction and eccentricity of applied loads,

including reactions provided by the brackets acting on the

concrete foundation. (See Tables 1, 2 and 3.)

4.1.3 Shaft Capacity (P2):

The tops of shafts must be

braced as prescribed in Section 1810.2.2 of the 2012 and

2009 IBC (Section 1808.2.5 of the 2006 IBC). In

accordance with Section 1810.2.1 of the 2012 and 2009

IBC (Section 1808.2.9 of the 2006 IBC), any soil other

than fluid soil must be deemed to afford sufficient lateral

support to prevent buckling of systems that are braced.

When piles are standing in air, water or fluid soils, the

unbraced length is defined as the length of pile that is

standing in air, water or fluid soils plus an additional 5 feet

(1524 mm) when embedded into firm soil, or an additional

10 feet (3048 mm) when embedded into soft soil. Firm

soils are defined as any soil with a Standard Penetration

Test (SPT) blow count of five or greater. Soft soil is

defined as any soil with an SPT blow count greater than

zero and less than five. Fluid soil is defined as any soil

with an SPT blow count of zero [weight of hammer (WOH)

or weight of rods (WOR)]. The SPT blow counts must be

determined in accordance with ASTM D1586. For fully

braced conditions where the pile is installed in

accordance with Section 1810.2.2 of the 2012 and 2009

IBC (Section 1808.2.5 of the 2006 IBC) and piles do not

stand in air, water, or fluid soils, the allowable shaft

capacities must not exceed the maximum design loads

shown in Tables 1, 2 and 5. Shaft capacities of helical

foundation systems in air, water or fluid soils must be

determined by a registered design professional. The ASD

shaft tension capacities are shown in Tables 3 and 5, the

ASD shaft compression capacities are shown in Tables 1,

2 and 5, and the shaft torsional rating is shown in Table 5.

The elastic shortening/lengthening of the pile shaft will

be controlled by the applied loads and the mechanical

and geometrical properties of the 2

-inch-diameter

(73 mm) round structural tubing and the shaft coupling.

The shaft elastic shortening or lengthening can be

determined from the equation:

∆

shaft

P × L

A × E

(Eq. 1)

where:

∆

shaft

= change in shaft length due to elastic shortening

or lengthening (inches)

= applied axial compression or tension load (lbf)

= pile shaft length (inches)

= shaft cross-sectional area (in

) (see Table 4)

= shaft steel modulus of elasticity (psi) (see

Table 4)

4.1.4 Helix Plate Capacity (P3):

The allowable axial

compression and tension load capacities (P3) for each

individual helical plate diameter (8, 10, 12 or 14 inches) is

55 kips (244.6 kN). (See Tables 1, 2, 3 and 5.) For helical

piles with more than one helix, the allowable helix

capacity (P3) for the helical foundation system may be

taken as the sum of the allowable capacity of each

individual helix.

4.1.5 Soil Capacity (P4):

The allowable axial

compressive or tensile soil capacity (P4) can be

estimated by a registered design professional in

accordance with a site-specific geotechnical report, as

described in Section 4.1.1, combined with the individual

helix bearing method (Method 1), or from field loading

tests conducted under the supervision of a registered

design professional (Method 2). For either Method 1 or

Method 2, the predicted axial load capacities must be

confirmed during the site-specific production installation,

such that the axial load capacities predicted by the torque

correlation method are equal to or greater than those

predicted by Method 1 or 2, described above.

With the individual helix bearing method, the total

nominal axial load capacity of the helical pile is

determined as the sum of the individual areas of the

helical bearing plates times the ultimate bearing

capacities of the soil or rock comprising the respective

bearing strata for the plates.

The design allowable axial load must be determined

by dividing the total ultimate axial load capacity predicted

by either Method 1 or 2, above, by a safety factor of at

least 2.0.

With the torque correlation method, the total ultimate

and allowable axial load capacities are predicted as

follows: