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Shallow Podium Anchorage Example

Anchorage Calculation Using Anchor Reinforcement

This example presents the anchorage solution in tension for a CIP anchor bolt in cracked concrete under seismic loading conditions in a reinforced concrete podium slab using anchor reinforcement. It is based on test results using flat bearing plates in which the full bearing surface is situated at the effective embedment depth. Other bearing surface geometries are not compatible with these test results. The calculation follows ACI 318-14 for the design of an anchor in tension, with AISC 360-16 used for the anchor allowable tensile steel strength. The witnessed testing conducted by Simpson Strong-Tie was used to validate ACI 318-14, Chapter 17 design concepts for anchor reinforcement and the need to design the structural slab to meet amplified 17.2.3.4.3 (a) anchor forces for use in SDC C–F. The design strength is based upon the ACI 318-14, Chapter 17 failure modes of tensile steel strength, concrete breakout strength, anchor pullout, concrete side-face blowout and anchor reinforcement strength. Additional failure modes observed in the testing validated greater capacities when anchor reinforcement is used, and those empirical findings are considered for that limit state. See strongtie.com for detailed calculations for all solutions shown on Simpson Strong-Tie website design tables.

Code Information
2015 International Building Code® (IBC)
ACI 318-14, Chapter 17 (Tension)
AISC 360-16
SDC C through F, seismic

Material Properties

Shallow Podium Anchorage Design Example Material Properties

Dimensions

Slab thickness: t = 12 in.
Initial anchor: hef = 9.39 in.
hef x 1.5 = 14.09 in.

where hef is based on Simpson Strong-Tie ABL height, heavy hex nut height and plate thickness.

Anchor reinforcement
Bottom cover: 0.75 in.

Per ACI 318-14, 17.4.2.8:
Project the failure surface, c, outward 1.5hef from the effective perimeter of the plate.

Shallow Podium Anchorage Design Example Dimensions
Shallow Podium Anchorage Design Example Initial Anchor

Tension Design Calculations (ACI 318-14) — Used for 17.2.3.4.3 "Ductility" Tensile Requirements for SDC C–F

17.4.1 — Steel Strength for Anchor in Tension
Shallow Podium Anchorage Design Example 17.4.1
17.4.2 — Concrete Breakout Strength of Anchor Only in Tension
Shallow Podium Anchorage Design Example 17.4.3
17.4.3 — Anchor Pullout Strength (Initial Abrg for Plate Bearing for Pullout)
Shallow Podium Anchorage Design Example 17.4.3
17.4.4 — Concrete Side-Face Blowout Strength
Shallow Podium Anchorage Design Example 17.4.4
17.2.3.4.3(a) — Ductility Check (Required for SDC C–F)
Shallow Podium Anchorage Design Example 17.2.3.4.3(a)

Anchor Reinforcement Estimate by Applying Sections 17.3.2.1 and 17.4.2.9

Shallow Podium Anchorage Design Example 17.3.2.1 and 17.4.2.9

Determine Anchorage System Capacity When Anchor Reinforcement Is Added

Testing performed by Simpson Strong-Tie indicates that when anchor reinforcement (A.R.) is added to these shallow slabs, ultimate capacity is a combination of A.R. resistance acting simultaneously with concrete breakout resistance.

Design Approach Using Empirical Data per Test Output

Using the test results, the % contribution to the measured peak capacity of both the inner concrete cone and the Anchor Reinforcement (A.R.) were determined. Both of these contributions are dependent on slab thickness.

  • Inner Concrete Cone Contribution:
    For inner concrete cone, that percentage contribution is based on a comparison of the Normalized Breakout Capacity vs. the Calculated Uncracked Breakout Capacity.
  • Anchor Reinforcement Contribution:
    For anchor reinforcement contribution, that percentage is based on a comparison of the Maximum Possible A.R. Contribution vs. Measured A.R. Contribution.

Determine Design Limit for Anchor Reinforcement (A.R.) + Inner Concrete Cone

  • Inner Concrete Cone Contribution:
    Based on testing, 41% of the contribution is coming from the inner concrete cone.
  • Anchor Reinforcement Contribution:
    Based on testing, 100% of the anchor reinforcement is contributing.
Contributions of Cone and Anchor Reinforcement Based on Empirical Findings
Contributions of Cone and Anchor Reinforcement Based on Empirical Findings

Vertical Block Shear Limit State Consideration for Shallow Slabs

Testing indicates that an additional failure mode is possible with a shallow embedment when resisting the breakout area with anchor reinforcement. A vertical "block shear" can form at the outer edges of the bearing plate. This "block shear" is separate from pullout and is dependent on embedment depth, bearing surface area and concrete strength. Size bearing plate so that "block shear" is not the design limit state.

Block Shear at Anchor Bearing Plate
Block Shear at Anchor Bearing Plate

LRFD Design Strength Capacity Summary

LRFD Design Strength Capacity Summary
LRFD Limit
LRFD Limit
LRFD limits 1–5 consider ACI 318 strength level values

Governing LRFD capacity = 54,517 lb.      1. Anchor tension controls at LRFD

Anchor Reinforcement Layout Summary

Anchor Reinforcement Layout Summary
SR_ATS-SA_InstLA_Ill_Instld_Anchordetail2SA1_CY.ai
Anchor Reinforcement Detail: 2/SA1