Anchor Factors

[DCBII]

I have a question about anchors.

ASCE 7-05 says I need to design my anchors for overstrength (in my case 2.0)

ACI Appendix D Section D.3.3.3 says I need to decrease the design strength of my connection to 75% of its actual strength for cracked concrete in seismic applications.

App. D Section D.3.3.6 punishes me further for having any kind of brittle failure mechanism controlling the design, giving my only 40% of the actual strength.

By the time I add all these factors up I'm basically using 6.67 times the original load. I've heard that the 0.75 factor doesn't need to be used with the overstrength factor, but even if I pull the 0.75 out I'm still at 5 times the original load. My question is this: do I have to use all of these factors concurrently? It seems like all of these factors are trying to accomplish the same thing... ductility. Why am I being punished so many times for the same problem? I hate Appendix D.

 

[Lion06]

If you can, provide steel across the failure plane o tale the equites load.

If you can do that and have adequate development length on both sides then you don't have a ductile failure anymore. Unless, of course, you have blowout or pullout problems which are not common.

 

[DCBII]

These anchors will be post-installed into an existing mat foundation.

 

[sandman21]

No the .75 is used regardless; yes you need to use all the values concurrently.

What are you designing?

 

[DCBII]

AISC 341-05 Section 8.5 states:

"The special requirements of ACI 318, Appendix D, for 'regions of moderate or high seismic risk', or for structures assigned to intermediate or high seismic performeance or design categories need not be applied."

I'm assuming this refers to ACI 318, Appendix D, Section D.3.3 altogether. As I understand it (correct me if I'm wrong) because you are designing connections for the inelastic actions of attached members the seismic factors in ACI do not apply.

I'm not designing to AISC 341-05, but I was curious if anyone knew of any similar provisions when designing for overstrength (an amplified force caused by inelastic demand in other parts of the structure). In other words, does the overstrength factor get me out of the ACI factors the same way capacity design does?

 

[delagina]

I just use whatever hilti capacity i see in the table =)

 

[sandman21]

I had no idea that a steel code can override a concrete code. So ACI can override AISC SCBF hinge zone requirements? lol

Amplified forces are not caused by inelastic demand, it is used as a means to keep curtain items in the elastic range leading to desired failure modes. ACI has no load combination with amplified factor in them, check 9.2, the use of amplified factor comes from IBC or ASCE 7-05. If you are required to use the amplified seismic loads all the provisions of ACI apply, there is no exception in ACI appendix D

 

[JAE]

I hate Appendix D

You are not alone.