Sign (C-45) · Lesson 1 of 7

Wind Inputs and Footing Load for a Sign (CBC 1609, 1605.2)

"Wind Inputs and Footing Load for a Sign (CBC 1609, 1605.2)" is lesson 1 of 7 in the Sign (C-45) Learning Hub. It opens with "Why Wind Governs, and What the CBC Gives You" 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 Wind Governs, and What the CBC Gives You
  2. Step 1: Risk Category and the Right Wind Map
  3. Step 2: Read V, and Convert Only When Required
  4. Step 3: Exposure Category
  5. Step 4: From Wind Force to Footing Load

The worked example in the course applies this lesson to a realistic job in 5 steps, from "Risk Category" through "Overturning moment at grade".

What you'll be able to do

  • Explain the main idea of "Wind Inputs and Footing Load for a Sign (CBC 1609, 1605.2)" in plain language you can use on the exam.
  • Apply this step with confidence: "Step 2: Read V, and Convert Only When Required".
  • Apply this step with confidence: "Step 3: Exposure Category".
  • Apply this step with confidence: "Step 4: From Wind Force to Footing Load".
  • Test yourself on the worked example and the quick-check quiz inside the classroom.
Wind Inputs for a Pylon Sign FootingOpen terrain, Exposure C5 ft widex 14 ft tallsolid faceW = 1,761 lbwindh = 7 ftgradeCBC Sec. 1609 and 1605.2 inputsRisk Category II (Table 1604.5)V from Figure 1609.3(2), 700-year MRIExposure C (Sec. 1609.4.3)W = 1,761 lb at h = 7 ft (from ASCE 7)Equation 16-2: D + L + 0.6WP = 0.6 x 1,761 = 1,057 lbM = 1,057 x 7 = 7,399 ft-lb at gradeP and h go to the pier equation(CBC Eq. 18-1, next lesson)Footing design load: P = 1,057 lb acting 7 ft above gradeCBC prints V, exposure and the 0.6W combination; the force W comes from ASCE 7 (Sec. 1609.1.1)The sign engineer or building official confirms the Risk Category and W for the actual site2025 CBC Sec. 1604.5, 1609.1.1, 1609.3, 1609.4.3, 1605.2 (Equation 16-2) - 5 ft x 14 ft pylon signCC
The diagram for this lesson, exactly as it appears in the Learning Hub.

The first steps of this lesson

Step 1: Why Wind Governs, and What the CBC Gives You

A sign face is a big flat sail standing on a small foundation, so wind - not the sign's weight - decides how deep and wide the pier must be. 2025 CBC Section 1609.1.1 says wind loads on every building or structure are determined in accordance with Chapters 26 to 30 of ASCE 7, and that wind is assumed to come from any horizontal direction, acting normal to the surface. The CBC itself prints the inputs a sign contractor must know: the Risk Category, the basic wind speed V, the exposure category and the load combination that turns wind into a footing load. This lesson uses those printed inputs; the wind force W itself comes from the sign engineer's ASCE 7 calculation (ASCE 7 is not reproduced in the California code book).

Step 2: Step 1: Risk Category and the Right Wind Map

2025 CBC Table 1604.5 sorts structures into Risk Categories I to IV. Category II is 'Buildings and other structures except those listed in Risk Categories I, III and IV', so an ordinary commercial sign normally falls in II (the engineer or building official confirms it). Section 1609.3 then sends you to one map: Figure 1609.3(1) for Risk Category I, 1609.3(2) for II, 1609.3(3) for III and 1609.3(4) for IV. Note 7 on each figure gives the return period: about 300 years for I, 700 for II, 1,700 for III and 3,000 for IV.

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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