16 Pole.xls

EMBEDDED POLE

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AN EXAMPLE OF THE SHOOTING METHOD

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351020302.xls

ENGINEERING with the SPREADSHEET Copyright 2006 American Society of Civil Engineers A

Christy

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POLE FOUNDATION -- LATERAL BEARING TYPE FOUNDATION This template uses the "shooting method" of converging two equations which depend upon each other for values. P h q b

0.5 4.0 266 1.00

k ft psf/ft ft 12"

Applied lateral force, kips distance from ground surface to P, ft allowable soil-brg UBC Table 18-I-A / IBC Table 1804.2 / psf/ft diameter or diagonal dimension of a 0.71' square post, ft

Constrained S3=q*d d² = 4.25 * P * 1000 * h /(S 3 * b) d² = 4.25 * P * 1000 * h /(q * d * b) d³ = 4.25 * P * 1000 * h /(q * b) d = (4.25 * P * 1000 * h /(q * b))⅓

0.510 k at 4.0 ft

row 20

b width

1.00 ft

q soil 266 psf d

3.19 ft

0.376 k 0.093 cy

Unconstrained at Top S1 445 A 3 du 5.02 converge 100.0

psf ft ft %

0.591 k 0.146 cy

(4.25 * P * 1000 * h /(q * b)) ⅓ (4.25 * 0.5 * 1000 * 4.0 /(266 * 1.00))^(1/3) weight (1.00 /2)² * π * 3.19 * 0.150 concrete (1.00 /2)² * π * 3.19 /27

Constrained 0.00 ft embed Unconstrained 5.02 ft embed Figure 16-1 POLE FOUNDATION ELEVATION

q * d_est / 3 2.34 * P * 1000 /(S 1 * b) A /2 * (1 + (1+ 4.36 * h /A)1/2 ) the difference in d_u for the last 2 iterative calculations = 0.00 ft 100 - 0.00 weight (1.00 /2)² * π * 5.02 * 0.150 concrete (1.00 /2)² * π * 5.02 /27

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NOTES See UBC 1806.7.2.1 equation 6-1 NonConstrained, 6-2 Constrained / IBC 1805.7.2.1 equations 18-1, 2, and 3 / and Table 18-I-A / IBC 1804.2 / Allowable Foundation and Lateral Pressure for typical allowable lateral pressures. The solution for this answer is iterative. Typically -- vary the estimated depth d_est to be greater than the required depth for constrained or unconstrained conditions. If you have a maximum depth which must not be exceeded, vary the width b.

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Width b is the diameter of a round post or the diagonal dimension of a square post (or footing). Hence, b for a 3'-0" round footing is 3.0 but for a 3'-0" square footing b is (3^2+3^2)^0.5 = 4.24' P * h = moment to overturn the foundation UBC 1806.7.2.1 d / IBC Table 1804.2 footnote d / states that allowable stresses and soil-bearing values may be increased 33% when combining vertical loads with wind/earthquake loads or when lateral loads are acting alone. Footnote 3 in Table 18-I-A / IBC 1804.3.1 / allows a 100% lateral bearing increase for poles not adversely affected by a 1/2" lateral translation at the top of the footing. Use judgement when increasing the 2x multiplier by another 33%. Depth d_est is the depth of embedment in the earth not to exceed 12 ft when computing lateral pressures

S_1 or S_3.

UBC Table 18-I-A note 3 / IBC 1804.3.1 / limits lateral bearing value increase to 15 x designated value. Current designated value = 266 psf/ft. Max value = 3990 psf. However, depth "d" used for computing lateral pressure is limited to 12'. Hence, lateral pressure is limited to 3192 psf.

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EMBEDDED POLE

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16

AN EXAMPLE OF THE SHOOTING METHOD

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C

D

6:21 04/09/17

351020302.xls

ENGINEERING with the SPREADSHEET Copyright 2006 American Society of Civil Engineers A

Christy

E

F

G

H

I

J

K

L

M

N

THE SHOOTING METHOD ITERATIVE CALCULATIONS FOR UNCONSTRAINED FOOTING d_est 5.00 ft ESTIMATED embedment, 5.00 ft. for pressure 443.33 2.69 5.03

445.70 2.68 5.01

444.89 2.68 5.01

444.36 2.69 5.02

444.82 2.68 5.02

444.84 2.68 5.02

444.68 2.68 5.02

444.73 2.68 5.02

$q*MINA(D_EST,12) /3 266 * MINA(5.00, 12) /3

$q * MINA(A91, 12) /3 266 * MINA(5.03, 12) /3

2.34 * $P * 1000 /(A89 * $B) 2.34 * 0.51 * 1000 /(443.33 * 1.00)

2.34 * $P * 1000 /(B89 * $B) 2.34 * 0.51 * 1000 /(445.70 * 1.00)

A90 /2 * (1 + (1+ 4.36 * $H /A90)^0.5 ) 2.69 /2 * (1 + (1 + 4.36 * 4.00 /2.69)^0.5 )

B90 /2 * (1 + (1+ 4.36 * $H /B90)^0.5 ) 2.68 /2 * (1 + (1 + 4.36 * 4.00 /2.68)^0.5 )

444.77 445 445 445 2.68 2.7 2.7 2.7 5.02 5.0 5.0 5.0

$q * MINA( (A91 + B91) /2, 12) /3 266 * MINA( (5.03 + 5.01) /2, 12) /3

445 2.7 5.0

444.74 2.68 5.02 0.00 row 80

in this row, a new depth of embedment is calculated

No convergence factor is applied to the math in these equations. Other equation sets require some sort of adjustment/convergence factor to achieve convergence.

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The notes below the inputs are not meant to represent the code. You will want to edit them to reflect your understanding of the code and soils engineering. They are included in the printout as an aid to the building department in reviewing these calculations. Also, the code can be complicated at times and these notes help to bring all of the design issues together in one place. Otherwise, some of the fine but important points may be forgotten such as the 12' embedment limit.

WORKSHEET Values for a lamp pole: Weights lamps 90 brackets 42 spar 100 pole 558 sum

790

row 100 h 2 0 1.33 30

cg 32.33 31.33 30.665 15

33.33 M seismic 0.5

Seismic 2910 1316 3067 8370 15662 7831 lb-ft

area 3 1 5 15

cg 32.33 31.33 30.665 15

M wind 18

Wind 97 31 153 225 506.645 9120 lb-ft row 110

relative P relative h

282.08 k 32.33 ft

wind

row 120

row 130