G = 0.85 for rigid structure Cp (refer to fig. 1-13) Gcpi = ± 0.18 for fully enclosed building.
Cp & Kz
Design Wind Pressure for Signs q h = wind pressure at top of sign G = wind gust coefficient A s = area of the face of sign C f = force coefficient affected by sign dimension and clear area ratio (for B/s = 4 see table 1-6). B=width of sign & s=height of sign & h=elevation from ground to top of sign. F = q h GC f A s
Snow Load Parameter that affects snow load: Roof geometry, Wind exposure, Location, Importance, Heated structure or not For roof slope < 5% then multiply snow load (p g ) by the following factors: p f = 0.7C e .C t .I.p g Where: C e = 0.8 in an unobstructed area & 1.2 if sheltered in a large city. C t = 1.2 for unheated structures & 1.0 for heated structures I = 0.8 for agriculture and storage facilities & 1.2 for hospitals Conditions: if p g ≤ 0.96 kN/m 2 then use the larger of p f = 0.7C e .C t .I.p g or p f = I.p g If p g > 0.96 kN/m 2 then use pf = I. 0.96 kN/m 2
Snow Loads on Roof
Earthquake Loads Caused by ground motion and lateral resistance of the structure Magnitude depends on: Ground acceleration Mass Stiffness of the structure
Earthquake Loads Two types of analysis: 1. Dynamic Analysis: Recommended for high rise and important structures Elaborate and requires the use of computers 2. Static Analysis Used for small structures Replaces dynamic loads by static loads to find base shear
Earthquake, Chile (2010)
Structural Design In construction error can happen due to: Variability in material property Accidental loading due to vibration or impact Material corrosion or decay Therefore safety factor must be introduced to design the methodology to account for uncertainties Two methods: 1. Working stress method Maximum allowable stress = elastic limit Loads are then multiplied by safety factor Load Combination: D 0.6 D + 0.6W 0.6 D + 0.7 E
Structural Design Two methods: 2. Stress Design or LRFD (Load and Resistance Factor Design) Maximum allowable stress = ultimate strength in concrete and plastic strength in steel Material safety factor and load safety factor are separated Load Combination: 1.4D 1.2D + 1.6L + 0.5S 1.2D + 1.5E + 0.5L
Earthquake, Wind, Snowloads Earthquake footage in Japan Earthquake - 2013 Fo Hurrican Katrina - 2007 AEGs
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