ASCE 7-10, Wind Load: Simplified Design Wind Pressure, Ps

[SIZE=10.5pt]Hi Everybody![/SIZE]

[SIZE=10.5pt]I have a question about Chapter 28 (ASCE 7-10) and the simplified design wind pressure, Ps. I am having trouble understanding how to calculate Ps30 (Figure 28.6-1, pg 304).[/SIZE]

[SIZE=10.5pt]On page 303, there seems to be two cases: A and B, each case shows the difference sections that experience wind pressure (sections A-H). On the next page, pg 304, there are values for the horizontal (sections A-D), vertical pressures (section E-H), and overhangs.[/SIZE]

[SIZE=10.5pt]I have not been able to find a good example problem that explains step by step how to use this table...so here are my questions:[/SIZE]

[SIZE=10.5pt]When asked to calculate the simplified design wind pressure for a low rise building:[/SIZE]

[SIZE=10.5pt]1. Do I need to look at both cases, case A and B? or will the problem specify in what direction the wind is hitting the building?[/SIZE]

[SIZE=10.5pt]2. Do I need to use different values for case A vs case B? I only see one set of values on pg 304, I do not see one a set for when case A is applicable vs when case B is applicable. For instance, for case A, section A seems to be a different size from section A for case B. Do I use the same value listed under the Horizontal Pressure, A column for both cases?[/SIZE]

[SIZE=10.5pt]3. The value for Ps30, would it be the sum of all the pressures: horizontal, vertical, and overhangs, for a specific basic wind speed and roof angle? [/SIZE]

[SIZE=10.5pt]If someone has a good example problem, I would really appreciate it and you should share it![/SIZE]

[SIZE=10.5pt]Thank you so much for any help I can get on this.[/SIZE]

I suggest reading the notes for Figure 28.6-1 to gain a better understanding of wind design. In particular, note 2 specifies that both load cases need to be assessed for every corner (i.e. 8 total load cases) and refers the reader to Figure 28.4-1.

The pressure for each zone (A, B, C, etc) remains constant in all of the load cases, but is applied differently. For example, the pressure for zone A is applied over a distance of "2a" for Load Case A and over a distance of "a" for Load Case B.

Section 28.6.3 states, "For the horizontal pressures (Zones A, B, C, D) ps is the combination of the windward and leeward net pressures." Basically, figure out the pressure for each zone and add them together to obtain the total horizontal force. Word of caution, note 7 in Figure 28.6-1 states, "The total horizontal load shall not be less than that determined by assuming ps = 0 for zones B & D."

Last note - remember to check the minimum design wind loads in section 28.6.4.