ACI 318 Seismic anchorage requirements
ACI 318 Seismic anchorage requirements
(OP)
Hey Everyone - I've got a question relating to the requirements outlined in section D3.3.4.3 in ACI 318-11 (unsure of the section in chapter 17 of 318-14). I'm currently designing embeds with H.A.S. at a podium with 13 levels of a proprietary structural system on top of it comprised of a combination of HSS posts and light gauge framing. We've received overturning reactions from the manufacturer and we are in the process of resolving those forces through our embed plates into the podium. The building falls under seismic design category C. In section D3.3.4.3 there are (4) different options outlined to meet the anchorage requirements in a high seismic region. For those who are unfamiliar, option a requires the embed be designed for ductile yielding of the anchors, along with additional requirements to ensure ductility. Option d requires the overturning loads to be used in load combinations with the overstrength factor applied. We've run through these two options and have found some of the uplift forces are in excess of 300 kips, and our podium is only 24" thick, so it is not really feasible to go with either of these. I'd like to satisfy the requirements outlined in option c which states:
"The anchor group shall be designed for the maximum tension that can be transmitted to the anchors by a non-yielding attachment..."
The HSS post is directly welded to a base plate from their system, which in turn is welded to our embed plates. The way I read this option is that I can calculate the design strength of the fillet welds used to attach their post to their base plate (1.392dl * 1.5) and use this capacity as the load to design the embed with, given the welds are a non-ductile. Am I interpreting this section correctly? If so do I also need to divide the capacity by phi?
Sorry for the length of this question but there is very little literature on using this option online, in the commentary, or other references (NEHRP/FEMA docs). Any feedback is appreciated! Thanks.
"The anchor group shall be designed for the maximum tension that can be transmitted to the anchors by a non-yielding attachment..."
The HSS post is directly welded to a base plate from their system, which in turn is welded to our embed plates. The way I read this option is that I can calculate the design strength of the fillet welds used to attach their post to their base plate (1.392dl * 1.5) and use this capacity as the load to design the embed with, given the welds are a non-ductile. Am I interpreting this section correctly? If so do I also need to divide the capacity by phi?
Sorry for the length of this question but there is very little literature on using this option online, in the commentary, or other references (NEHRP/FEMA docs). Any feedback is appreciated! Thanks.






RE: ACI 318 Seismic anchorage requirements
In this case, maybe an approach worth investigating is to try to design the base plate or frame structure to hinge at a demand level that the podium can handle, then design the embeds for the reactions at that demand level. This would be the Option B approach in ACI 318-11. Again, the hinging mechanisms would have to be designed such that the frame structure maintains stability. The maximum ductility ratios would also need to be checked to ensure the hinge mechanisms are within the ductile capacity of the element.
RE: ACI 318 Seismic anchorage requirements
RE: ACI 318 Seismic anchorage requirements
RE: ACI 318 Seismic anchorage requirements
RE: ACI 318 Seismic anchorage requirements
RE: ACI 318 Seismic anchorage requirements
RE: ACI 318 Seismic anchorage requirements
RE: ACI 318 Seismic anchorage requirements
RE: ACI 318 Seismic anchorage requirements
RE: ACI 318 Seismic anchorage requirements
Doesn't sound like you have the option to take that approach in this case, since you have no control over the design of the proprietary framing system.