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RE: Again on the HSS black book

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Title: RE: Again on the HSS black book

>How is section 9.2 of the [AISC HSS] specification to be applied?
>This merely gives the effective length of a weld made, I assume,
>in accordance with either Figure 2-7, 2-9 or 2-12 depending upon
>whether fillet, PJP or CJP welds are desired. Is this correct?

Yes, the limitation on effective weld length in HSS Specification Section 9.2 is simply to establish what segments of the weld can be considered to be effective in resisting load. It accounts for the relative flexibility of the wall of the HSS to which the branch member is welded. It's similar to the local flange bending criteria for wide-flange columns, except the most flexible location is at the center of the HSS face. Depending upon the actual detail and the angle of loading, the effectiveness of welds across the face of the HSS chord range from zero (for design purposes) to full.

>Given that and assuming fillet welds, what is the appropriate E width?
>Does this table imply that if I only need an E=0.7t that the minimum
>L requirements under the first column apply?

I think these are independent of each other as far as the strength of a given detail is concerned. That is, once you establish the effective length of the welding you have, you can calculate the strength based upon the effective length and the effective throat for the weld detail as given in the tables you cited.

On the other hand, if you are determining how much effective weld area you need to transfer a defined force, the two variable are a bit more related, since you will have to generate enough effective throat and length to produce the required effective area. But even in this case, the effective throat and effective length are not interdependent...they can be calculated independently of each other.

>There is also the question of which Resistance factor to use. Given that on
>the side welds of a rectangular to rectangular connection there is a shear
>component there is the question of what do we do? Since Le varies depending
>on the inclination of the tube, the portion of Le to which the shear
>component applies would vary. Or do we just use E and Le and phi = 0.9 and
>assume it is a straight tension connection with the adjustments to Le
>accounting for everything else?

The only difference for weld strength calculation in these kinds of HSS-to-HSS connections is the effective length provisions reflected in Section 9.2 of the HSS Specification. Once you know the effective length (and effective throat), you should apply the resistance factors and nominal strength values from the LRFD Specification. For example, phi = 0.75 and nominal strength equals 0.6Fexx for fillet welds from LRFD Specification Table J3.2. The design strength is then 0.75(0.6Fexx)(Le)(E).

Hope this helps.