to these loads. For any building design, both seismic and wind loads have to be checked to determine which one governs. It should be noted that even in cases where the seismic load controls the overall design of the lateral force – resisting system in a building, the wind load may still be critical for the uplift forces on the roof.
INTRODUCTION TO STRUCTURAL DESIGN LOAD FOUNDATION ENGINEERING Consolidation 6/12/2019 34 University of the Immaculate Conception Engineering and Architecture Program Buildings and their components are to be designed to withstand the code-specified wind loads. Calculating wind loads is important in design of the wind force-resisting system, including structural members, components, and cladding, against shear, sliding, overturning, and uplift actions. There are two types of systems in a building structure for which wind loads are calculated: a. the Main Wind Force – Resisting System (MWFRS): An assemblage of structural elements assigned to provide support and stability for the overall structure. The system generally receives wind loading from more than one surface. The MWFRS transfers safely to the ground the overall building lateral wind loads from the various levels of the building. Examples are shear walls, braced frames, moment frames, and roof and floor diaphragms, and these elements are usually parallel to the direction of the wind force. b. the Components and Cladding (C&C): Elements of the building envelope that do not qualify as part of the MWFRS . The components and cladding (C&C) are members that are loaded as individual components, with the wind load acting perpendicular to these elements. Examples include walls, cladding, roofs, uplift force on a column, and a roof deck fastener.
INTRODUCTION TO STRUCTURAL DESIGN LOAD FOUNDATION ENGINEERING Consolidation 6/12/2019 35 University of the Immaculate Conception Engineering and Architecture Program Irrespective of the procedure used to determine wind loads for buildings or structures, it is necessary to determine velocity pressure, q. Velocity pressure depends on wind speed, surrounding terrain including topography, and probabilities of directionality and occurrence of wind speed. In the Standard, the equation for velocity pressure q is given as ? = ?. ????? ? 𝐳 ? 𝐳𝐭 ? 𝐝 𝐕 ? 𝐥𝐛 𝐟𝐭 ? Where: q = effective velocity pressure to be used in the appropriate equations to evaluate wind pressures for MWFRS and C&C; q z at any height, z , above ground; q h is based on K h at mean roof height, h K z = exposure velocity pressure coefficient, which reflects change in wind speed with height and terrain roughness K zt = topographic factor that accounts for wind speed-up over hills and escarpments K d = directionality factor V = basic wind speed, which is the 3-s gust speed at 33 ft above ground for Exposure Category C and is associated with an annual probability appropriate for the risk category related to building use
INTRODUCTION TO STRUCTURAL DESIGN LOAD FOUNDATION ENGINEERING Consolidation 6/12/2019 36 University of the Immaculate Conception Engineering and Architecture Program
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