ASCE7-05 Wind Load Fig 6-17 p65, External Pressure Coefficient Slope Line
ASCE7-05 Wind Load Fig 6-17 p65, External Pressure Coefficient Slope Line
(OP)
Hello Guys,
Can you guys help where can i find the equivalent equation of the line for the the external pressure coefficient in figure 6-17.
I really do not know how to determine the values of the pressure coefficient if my effective wind area is within that slope.
Thanks!
Can you guys help where can i find the equivalent equation of the line for the the external pressure coefficient in figure 6-17.
I really do not know how to determine the values of the pressure coefficient if my effective wind area is within that slope.
Thanks!






RE: ASCE7-05 Wind Load Fig 6-17 p65, External Pressure Coefficient Slope Line
To obtain your value for each of the areas, determine your tributary or influence area (effective wind area). Start at that value on the X axis and move up to the intersection of the appropriate line corresponding to the area of the building that is applicable. At the intersection of the line, turn horizontally and move to the left to get the appropriate GCp value. For example:
Consider that your effective wind area is 100 square feet and you want to know the uplift on the roof for area 2. Enter the graph at 100 square feet. Move up to the intersection of the 100 sf line and the sloped section of the "2" line. Turn left and go horizontally over the the Y-axis. Your horizontal line intersects the Y-axis at approximately -1.9.
A graphic example is attached
RE: ASCE7-05 Wind Load Fig 6-17 p65, External Pressure Coefficient Slope Line
result = (Value at 10sf)+((Value at 500 sqft)-(Value at 10 sqft))*(log10(act sf))-log10(10 sqft))/(log10(500 sq)-log10(10 sqft))
For line 3 at act sqft = 100, that would be (-3.2)+((-2.3)-(-3.2))*(log10(100)-log10(10))/(log10(500)-log19(10))
result = -3.2 + 0.9* (2-1)/(2.699-1.0) = -2.67
Line 4,5 suction will be the same process except use log10(20sqft) in lieu of log10(10).
This routine works for any line on a graph of this nature. If the x axis is normal scale rather than log10 scale, the process is the same except use the actual x values, not log10(x) values.
RE: ASCE7-05 Wind Load Fig 6-17 p65, External Pressure Coefficient Slope Line
RE: ASCE7-05 Wind Load Fig 6-17 p65, External Pressure Coefficient Slope Line
RE: ASCE7-05 Wind Load Fig 6-17 p65, External Pressure Coefficient Slope Line
RE: ASCE7-05 Wind Load Fig 6-17 p65, External Pressure Coefficient Slope Line
Further, not all jurisdications adopt the latest version of the code. It is getting better, but 20 years ago, it was not uncommon for a jurisdiction to be a couple of code versions behind.
ajh1..
RE: ASCE7-05 Wind Load Fig 6-17 p65, External Pressure Coefficient Slope Line
RE: ASCE7-05 Wind Load Fig 6-17 p65, External Pressure Coefficient Slope Line
RE: ASCE7-05 Wind Load Fig 6-17 p65, External Pressure Coefficient Slope Line
RE: ASCE7-05 Wind Load Fig 6-17 p65, External Pressure Coefficient Slope Line
Still I appreciate all your responses