ASCE 7-05 WIND DIAGRAMS

[LOKSTR]

It is a Low rise building

Main wind force resisting system consist of columns, VXB on outside grid in both directions and roof horizontal bracing.

The roof is made up of trusses and at the bottom chord level is the horizontal bracing acting as diaphragm.

There is "NO MOMENT CONNECTIONS" anywhere. The whole building is modeled in 3-D using S-Frame.

I am using Fig-6-10 of ASCE 7-05 only for getting force/reactions in VXB, Roof Horizontal bracing and columns at VXB locations.

I am confused between figure 6-10(MWFRS) and 6-11A(walls) & 6-11B(roof) as to which one to use for inputing in my 3-D model to get column and truss design forces for various load combinations.

My concerns are :

1. Do we use fig 6-10 only when we have "RIGID FRAME" type structure or can it be used for other cases also without rigid frames for modeling in 3-D.

2. The columns and truss has to be designed for forces based on individual tributary area based on coeff. from fig 6-11.
If I need to use these values, then for the columns it gives me max coeff. values(press. or suction) for ONE FACE ONLY. How do I enter in my model for both windward and leeward faces?

Am I thinking correctly or am I missing something?

Any clarification will be of great help.

Thanks,

 

[csd72]

The wind doesnt care if it is a braced frame or a rigid frame - the basic values are the same.

The only difference is in the relative areas that are supported by each element.

 

[OldPaperMaker]

LOKSTR,
Figure 6-10 is for the Main Wind Force Resisting System (MWFRS) and Figure 6-11A to D are for Components & Clading (C&C). Check section 6.2, Definations and Commentary Chapter C6.2 for clarification.

You might check section 6.4, Method 1-Simplified Procedure to see if your structure fits the conditions that let you use Figure 6-2.

 

[chichuck]

okstr,

YOu use Fig. 6-10 to calculate loads to input into your model, and then analyze it to get column loads (both uplift and compressive.) It doesn't matter if you have moment frames or not.

You do not have to design the truss and columns for the forces based on trib areas and coefficients from Fig 6-11. That may seem counterintuitive. The pressures you get on the wall & roof panels, girts & purlins, and all of their connections when using Fig 6-11 are higher than those you get when using Fig 6-10. This is so because when designing the panels, girts & connections, you are accounting for maximum pressures that can occur on these components, at any point in time. When yiou design the trusses and coumns, you take advantage of the fact that these maxima don't occur at all points at the same time: at a specific point in time, some locattions experience that max pressure, while many others do not. That's why the MWFRS coefficients & pressures are smaller than the components and cladding values.

Does this make sense?


regards,


chichuck