ACI318-08 Appendix D, attachment ductile yielding 1

[fbmok]

I don't see the chance of D.3.3.4 will happen for most of post-installed anchors. Then the choice will be to use either D.3.3.5 or D.3.3.6. I'm a little bit confused about the attachment ductile yielding if I use D.3.3.5. What's the definition of that?

The attachment, not the anchor bolt, not the structure, will yield in ductile way at the force level of 0.75*phi*Nn & 0.75*phi*Vn? Could anyone please give me a example? How often do we use this kind of situation? For any kind of MEP seismic brace, can I assume D.3.3.5 will happen?

 

[ishvaaag]

I think 3.3.5 and 3.36 are in the intent of that either you warrant trough the attachment that the connection fails without destroying the anchor assembly itself or if you don't worry to prove it you stay limited to 0.4 (or 0.5) times the nominal strength of the assembly.

Hence, if you want to approach the nominal strength of an anchor assembly outside the scope of 3.3.4, you need to include a yield fuse between the connected part and the base anchor assembly.

For example, assuming you were only to transmit shear, you would include a receiving shear tab or weld where the weld or plate thickness itself lead to yield prior to overstraining the base anchor assembly over its nominal strength in shear.

If we were sayomg "prior to for every case overstraining", quite likely we would have to include a overstrength factor for the strength of the yield fuse, in more than retiring the fi factors.

 

[ishvaaag]

In the last paragraph, errata, "saying".

The intent of such paragraph is that the base assembly must be sized in that case for any forces (shear in the example) that could potentially be transmitted by the "fuse", overstrength of the same included.

 

[fbmok]

Thanks a lot ishvaaag. The yield fuse concept is really helpful.

 

[TXStructural]

D3.3.4 can happen in a properly designed anchor. The requirement is that a ductile portion of the anchor yield before a brittle/fracture failure mode is reached in the anchor. I think this will be even more common with the new adhesive anchor rules.