IBC Wind Load Tables 1

[denoid]

For the Main Windforce Resisting System load table 1609.6.2.1(1), there are columns for "Horizontal Loads" and "Maximumn Horizontal Wall Loads". Footnote "b" for the "Horizontal Loads" refers one to Figure 1609.6(3), while footnote "d" for the "Maximum Horizontal Wall Loads" refers to Figure 1609.6(1).

Why do they have two ways of determinining horizontal loads? The "Maximum Horizontal Wall Loads" appear to always be less than the "Horizontal Loads" for the "Wall" category in the "End Zone" and "Interior Zone". Does that mean I just ignore the "Horizontal Loads" and go straight to the "Maximum Horizontal Wall Loads" every time? I don't get it!

 

[ERV]

denoid,

Section 1609.6.4 States (in part): All elements and connections of the MWFRS shall be designed for vertical and horizontal loads based on the combined leeward and windward wall pressures and roof pressures determined from table 1609.6.2.1(1). Pressures shall be applied in accordance with the loading diagrams shown in Figure 1609.6(3) (AND) to the end zone and interior zone as shown in Figure 1609.6(1). The building shall be desinged for all wind directions.....

As shown in IBC Figure 1609.6(3), the design wind pressures are assumed to act normal to the projected wall and roof areas. The values tabulated in IBC Table 1609.6.2.1(1) for the roof are composite pressures that include the internal pressures appropriate to an enclosed building condition. Values given for the walls represent the sum of the positive pressure on the windward face of the building and the negative (or suction) pressure on the leeward face and are applied to the windward projection of the building as shown. Internal pressures for the walls are not included since they cancel.

The location of end zones and interior zones for the main wind-force-resisting system are shown in Figure 1609.6(1) and shall be tabulated separately (MAXIMUM HORIZONTAL WALL LOADS).

IBC 2000 is based and ASCE 7-98, I prefer using ASCE 7-98 or 7-02, and I do not like using the simplified method. For lower buildings (10' to 20'), wind loads will come out much higher because wind pressures are taken at 30'.

 

[JAE]

There was some discussion of this on Eng-Tips some time ago and I ran a search for it but couln't find the thread. It is a bit weird to see the horizontal wall loads (both interior and end zone areas) given, and then the strange column at the right listing "Maximum" wind pressures for the walls. After a lot of posts, I thought we had it figured out but I can't seem to remember what we "all" decided was the correct interpretation.

Maybe someone else out there remembers that thread.

 

[haynewp]

thread507-25391

 

[denoid]

ERV, JAE, & haynewp:

Thanks for your help. I went back to thread507-25391 and read all of the responses. The response by DaveAtkins seemed to make the most sense to me. I guess for my overall lateral analyses, I'll be using the "Horizontal Loads" column, modified by exposure & height factors, if I continue to use the "simplified method".