Chance Technical Design Manual

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RS4500.337 LATERAL DEFLECTION ANALYSIS FOR SEISMIC DESIGN CATEGORIES D, E, & F: The free-headed pile lateral move ments at allowable loads (lateral only – no vertical) of Chance® Type RS4500.337 helical piles can be determined from the following table.

∆ = y t

P h = Allowable lateral load L = Pile length y t = Δ = Lateral drift of pile head H = Length from pile head to groundline D o = Depth along pile shaft to point of first zero-deflection point. (y t = 0), a.k.a. the flexural length of pile h = Depth along pile shaft to point of zero slope (S t = 0) M = Bending moment in pile shaft

P h H GROUND

D o

FIRST ZERO DEFLECTION POINT (y t =0) ZERO SLOPE POINT (S t = 0) (LOWER)

DRAWINGS & RATINGS

For lateral resistance in non-seismic areas, special analysis and tests of RS4500.337 helical piles indicate allowable lateral load with less than 1/2” lateral deflection in stiff, firm, and soft soils. Test and analysis data are listed in the table. Per AC358 1.4.7, the Shaft Flexural Length (D o ) is measured from the top of the pile down to the first point of zero lateral deflection in the soil. AC358 1.4.8 defines the Shaft Seismic Flexural Length (Seismic D o ) as 120% of the Shaft Flexural Length, which for RS4500.337 helical piles embedded in stiff, firm, and soft soils is 6.4 ft, 6.7 ft, and 10 ft respectively.

NON-SEISMIC LATERAL LOADING (SEISMIC DESIGN CATEGORIES A, B, AND C)

SEISMIC LATERAL LOADING (SEISMIC DESIGN CATEGORIES D, E, and F)

STORY DRIFT ( Δ )

DEPTH TO S t = 0 (h) (ft)

DEPTH TO y t = 0 (D o ) (ft)

SOIL TYPE

DRIFT AT PILE HEAD (y t ) (in)

LATERAL LOAD (P h ) (kip)

DEPTH TO SOIL (H) (ft)

(kip∙in)

AT PILE HEAD BENDING

ALLOWABLE

MOMENT IN PILE

Stiff Soil:

3.66 0.42

5.3

6.1

0.006h 67.2 3.66 0.97

1.1

6.4 7.2 0.011h 108.0

N = 9 to 20 Firm Soil: N = 5 to 8 Soft Soil: N = 1 to 4

2.36 0.42

5.6

7.1

0.005h 50.4 2.36 0.87

1.1

6.7

8.3 0.009h 76.8

0.78 0.42

8.3

10.1

0.003h 24.0 0.78 0.90 1.7 10.0 11.9 0.006h 37.2

All shaft, coupler, and bracket-tube shapes and materials have been checked for adequate ductility per AC358 3.14.3; AISC 341 Table D1.1 (including applicable footnotes); and IBC 1810.3.6.1. Lateral deflections during seismic loading should be checked against the ASCE-7 Table 12.12-1 (reproduced below) showing Allowable Story Drift values for various structure lateral load resistance system types that are presented as ratios of the story height in Seismic Design Categories D, E, and F. The story height (h) assumed for the helical pile is the depth from the pile top down to the point of zero pile slope-from-vertical in the soil (S t ). The Allowable Story Drift in the seismic loading table above must be less than or equal to the Allowable Story Drift in Table 12.12.1 in order to determine if RS4500.337 helical piles can be used in that Structure Type and Risk Category.

TABLE 12.12.1 ALLOWABLE STORY DRIFT, Δ

Structure

Risk Category

I or II

III

Structures, other than masonry shear walls, four stories or less above the base as defined in Section 11.2, with interior walls, partitions, ceilings, and exterior wall systems that have been designed to ac commodate the story drifts

0.025h

0.020h

0.015h

Masonry cantilever shear wall structures

0.010h

Other masonry shear wall structures

0.007h

All other structures

0.020h

0.015h

0.010h

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