Rotational Ductility for Shear Tabs

[bfollett21]

Hello Everyone,

I am evaluating RISA Connection as part of the process for a project on steel connections. My question is concerning the checks for Rotational Ductility for shear tabs. I have been trying to determine (from their Help topics and other research) how RISAConnection is determining tmax-weld and tmax-plate. The references to the AISC code (p. 9-14) are not very useful. I have also found a few articles concerning ductility for shear tees but it doesn't seem like any of the equations are equal to what RISA is showing. I have also determined that the tmax-weld is a relationship based solely on the thickness of the weld. Any help on this subject would be great. I have also attached a simple screenshot of the values for reference. Thanks.

Ben

 

[JoshPlumSE]

An excerpt from the RISAConnection help file section on Rotational Ductility is given below for your reference. I believe that should be sufficient to answer your question.
Shear Tab (Single-Plate) Connection

In order to ensure adequate rotational ductility in a shear tab shear connection the following three conditions must be satisfied:
•The plate must yield in flexure prior to any weld failure due to flexure
•The plate must yield in flexure prior to any bolt failure (including bolt bearing) due to flexure
•The plate must yield in flexure prior to rupturing in flexure

The plate's flexural yield capacity is a direct function of its thickness. If a plate is too thick then its flexural yield capacity can be greater than the other capacities listed above, resulting in a non-ductile failure due to flexure.

The program uses the Instantaneous Center of Rotation method to calculate the capacity of the welds and bolts due to a pure-moment load. The C' coefficient as defined in the AISC 14th Edition, Eqn 7-21 is used to determine the bolt shear and bolt bearing capacities. These capacities are then converted into a maximum allowed thickness per AISC 14th Edition, Eqn 10-3.

For reference see AISC 14th Edition Manual, Pages 9-14 and 10-104.

 

[JoshPlumSE]

Also, reference AISC equation 10-3 (which should be cited in the RISAConnection calculation itself) for the bolt failure.

Page 9-14 only refers to the general concept that the plate must yield prior to rupture, weld, or bolt failure.

 

[bfollett21]

JoshPlum,

Thanks for the response and the information. In theory that now make tons of sense. However, I would expect that setting the Shear Yield of the Plate equal to the Available Weld Strength would yield me a result (based on strength of material, weld and weld size) that is similar in nature to what I would find in RISA. For instance, for a shear tab with a 0.25" weld, the tmax-weld = 1.27". However, the attached equation yields a much smaller result (0.3712"). Do you see something that I am missing? I have included my equation in the attached PDF. Thanks for any assistance you may be able to provide.