Sign (C-45) · Lesson 2 of 7

Pier Embedment Depth for a Pole or Pylon Sign

"Pier Embedment Depth for a Pole or Pylon Sign" is lesson 2 of 7 in the Sign (C-45) Learning Hub. It opens with "Why a Sign Pier Is Not Just a Hole Full of Concrete" and works through 5 short steps, then a worked example you can check yourself against.

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Steps in this lesson

  1. Why a Sign Pier Is Not Just a Hole Full of Concrete
  2. The Embedment Equation (CBC Equation 18-1)
  3. Find S1 from Table 1806.2 and the Isolated-Pole Rule
  4. Solve by Trial Depth
  5. Check the Result and Know the Limits

The worked example in the course applies this lesson to a realistic job in 5 steps, from "Soil value" through "Compare with the trial".

What you'll be able to do

  • Explain the main idea of "Pier Embedment Depth for a Pole or Pylon Sign" in plain language you can use on the exam.
  • Apply this step with confidence: "Find S1 from Table 1806.2 and the Isolated-Pole Rule".
  • Apply this step with confidence: "Solve by Trial Depth".
  • Apply this step with confidence: "Check the Result and Know the Limits".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Pier Embedment for a Pole or Pylon SignS1P = 1,057 lbh = 7 ftd = 5 ftb = 2.5 ft (30 in.)Class 4 soilCBC 1807.3.2.1, Eq. 18-1 (non-constrained)d = 0.5A {1 + [1 + (4.36 h / A)]^(1/2)}A = 2.34 P / (S1 b)P = 1,057 lb h = 7 ft b = 2.5 ftSoil: 150 psf/ft x 2 (isolated pole) = 300 psf/ftTry d = 5 ft: S1 = 300 x 5 / 3 = 500 psfA = 2.34 x 1,057 / (500 x 2.5) = 1.984.36 x 7 / 1.98 = 15.4d = 0.5(1.98){1 + (1 + 15.4)^(1/2)} = 5.0 ftComputed d = trial d, so the trial is valid.Try d = 4 ft instead: result 5.75 ft - tooshallow, so the trial must be raised.Minimum pier: 30 in. diameter x 5 ft deepS1 is taken at one-third of the embedment depth (d / 3 = 1.67 ft)2x lateral value allowed only if 1/2 in. movement at grade will not harm the sign (CBC 1806.3.4)CBC Sec. 1807.3.2.1 (Eq. 18-1), Table 1806.2 (Class 4 = 150 psf/ft), Sec. 1806.3.4 (isolated poles)CC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: Why a Sign Pier Is Not Just a Hole Full of Concrete

A pole or pylon sign has no wall, slab or roof to hold its top still, so the pier alone must stop it from rotating over under wind. 2025 CBC Section 1807.3 covers posts and poles embedded in earth or in concrete footings in earth, and Section 1807.3.2.1 is the 'nonconstrained' case: no rigid floor or pavement restrains the pole at the ground surface and no structural diaphragm restrains it above. The soil on the downwind side pushes back, and the deeper the pier, the more soil pushes back.

Step 2: The Embedment Equation (CBC Equation 18-1)

d = 0.5A {1 + [1 + (4.36h / A)]^(1/2)}, where A = 2.34P / (S1 b). P is the applied lateral force in pounds (the 0.6W load from the last lesson), h is the distance in feet from the ground surface to the point where P acts, b is the diameter of a round post or footing (or the diagonal of a square one) in feet, and S1 is the allowable lateral soil-bearing pressure from Section 1806.2 taken at one-third of the embedment depth, in psf. The result d is the embedment depth in feet, and the code counts no more than 12 ft of depth when computing lateral pressure.

The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.

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