Billboard Wind-Load Example - Part A скачать в хорошем качестве

Billboard Wind-Load Example - Part A

The subject of this example is a 50’ wide by 20’ high interstate billboard sign located in rural Nebraska on a site characterized by flat and open grasslands. The billboard is mounted on two 16” diameter steel posts, with the top of the sign reaching 80 feet above ground level. Part A of the billboard wind load example focuses on establishing the General Wind Load Criteria required to determine the design wind loads for a specific structure using the ASCE 7-22 standard. These steps include: 0:00: Introduction 1:35: Overview of ASCE 7 Wind Load Provisions 3:35: Flow Chart and Steps Required for Determination of Wind Loads, and Introduction of Wind Load Parameters 8:00: Summary of Force and Velocity Pressure Equations 9:40: Wind Speed Maps in ASCE 7 10:03: Risk Category Assignment: The structure is assigned to Risk Category I because, given its rural location, a failure would represent a low risk to human life. 10:33: Basic Wind Speed (V): Using ASCE 7-22 maps and the online ASCE Hazard Tool, the designer selects the maximum wind speed mapped for Nebraska for Risk Category I, which is 107 mph. 12:30: Ground Elevation Factor (Ke): Although Nebraska’s elevation varies, the factor is conservatively taken as 1.00 since the specific site elevation is unknown. 13:46: Topographic Factor (Kzt): Because the terrain is flat and open grasslands, the topographic factor is taken as 1.00, assuming no "wind speed-up" effects from hills or ridges. 14:13: Velocity Pressure Exposure Coefficient (Kz = Kh): The site is classified as Exposure C. By referring to ASCE 7-22 tables for an 80’ height in Exposure C, the coefficient is determined to be 1.21. 15:34: Design Velocity Pressure (qz=qh): Using the established parameters in the standard velocity pressure equation (qz=0.00256KzKztKeV2), the "raw power" of the wind at the top of the billboard is calculated to be 35.46psf. This calculated velocity pressure serves as the foundation for Part B, where force coefficients and actual wind forces for different loading cases are determined