In designing light-frame structures over concrete podium slabs, lateral loads from the structure above will produce large tensile overturning forces whose demands often far exceed the anchorage breakout capacities of these relatively thin slabs. The use of special detailing of anchor reinforcement will greatly increase the tensile capacities of the anchors.
The concept follows a code calculation procedure supported by this testing that indicates that when anchor reinforcement is added to these shallow slabs, ultimate capacity is a combination of anchor reinforcement resistance acting simultaneously with concrete breakout resistance. This combined limit state and the test results reported in the technical paper linked on this page below are only valid for anchor rods secured with flat bearing plates in which the full bearing surface is situated at the effective embedment depth.
Anchor reinforcement testing at Tye Gilb Laboratory for edge and away-from-edge conditions.
Selecting Your Anchor Solutions
Here are the recommended steps on how to specify a Shallow Podium Anchor and the accompanying anchor reinforcement.
- The designer should determine the following:
Select the appropriate anchor solution
- Uplift load designs from light frame superstructure
- Project concrete strength
- Slab thickness
- Anchor and/or tension load locations /key plan
- It is recommended to have a key plan with all tension load locations and values. This will help pin point the edge of slab, mid slab and slab step down locations.
- Is it a wind or seismic restraint?
Then from the design table:
- Scroll down to ‘Design Tables’ on this page.
- Based on thickness of concrete, and Wind or Seismic, choose the necessary design tables
- Select the necessary table that resembles the design condition (example: mid slab, 2.75” near edge, or 13” near edge)
- For Wind Designs, match the project demand loads with the tabulated Anchor Tension Capacity to select the appropriate Shallow Podium Anchor callout. This callout is noted under the column ‘DETAIL ON SHEET SA1’. Note, wind designs will be based on demand vs. capacity.
- For Seismic Designs, since the ductile anchor steel element must govern the design, the designer will base solutions on anchor diameter and strength and will use the Anchor Tension Capacities only as reference. Match the project anchor diameter and anchor strength to the proper detail under the column 'DETAIL ON SHEET SA1'.
- Go to sheet SA1 and find the proper anchor reinforcement detail as called out in the table.
- Download the details and include them in the construction documents.
- Coordinate the details and Shallow Podium Anchor callout on the construction documents.
- Specify this callout and detail on the construction documents.
- For seismic design per Notes for the Designer, footnote 7, the engineer of record will design the concrete slab based on 1.2 Nsa loads.
- Download sample calculations for reference on general ACI 318, Appendix D design procedure.
- Scroll to the bottom of the Design Tables for Notes for the Designer.
Typical Shallow Anchor Solutions Details
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