AAI Anchor Spacing, Edge Distance & Embedment Depth 2 — Questions and Answers
Question 1: When installing adhesive anchors at a corner where two free edges are present, the anchor capacity is affected because:
- The drilling equipment cannot be properly positioned at corners
- Both edge distances influence the concrete breakout capacity, resulting in greater reductions (Correct answer)
- Corner locations have higher concrete compressive strength due to formwork pressure
- Adhesive curing is slower at corners due to reduced heat dissipation
Correct answer: Both edge distances influence the concrete breakout capacity, resulting in greater reductions
At a corner, both edge distances independently trigger breakout capacity reductions, and the combined effect results in a larger overall reduction in anchor capacity than a single edge condition.
Question 2: The minimum spacing between adhesive anchors is most commonly expressed as a multiple of:
- The anchor rod diameter (d_a)
- The anchor hole diameter (d_o)
- The effective embedment depth (h_ef) (Correct answer)
- The concrete compressive strength (f'c)
Correct answer: The effective embedment depth (h_ef)
Minimum anchor spacing is typically expressed as a multiple of the effective embedment depth (h_ef) to ensure adequate separation of bond stress zones.
Question 3: Which primary U.S. code document governs the design requirements for post-installed adhesive anchor spacing and edge distances in concrete structures?
- ACI 530 — Building Code Requirements for Masonry Structures
- ACI 318 — Building Code Requirements for Structural Concrete, Chapter 17 (Correct answer)
- ASCE 7 — Minimum Design Loads for Buildings and Other Structures
- ASTM E488 — Standard Test Methods for Strength of Anchors in Concrete
Correct answer: ACI 318 — Building Code Requirements for Structural Concrete, Chapter 17
ACI 318 Chapter 17 (Anchoring to Concrete) is the governing U.S. code for post-installed anchor design, including spacing, edge distance, and embedment depth requirements.
Question 4: An installer notices that achieving the specified center-to-center spacing is impossible due to existing reinforcement. The correct action is to:
- Reduce the anchor diameter to fit between the rebar
- Notify the engineer of record and await revised instructions before drilling (Correct answer)
- Relocate all anchors to the opposite face of the member
- Increase the embedment depth to compensate for reduced spacing
Correct answer: Notify the engineer of record and await revised instructions before drilling
When specified spacing cannot be achieved due to field conditions, the installer must notify the engineer of record, who must evaluate whether revised anchor placement is acceptable.
Question 5: What effect does increasing the embedment depth of an adhesive anchor typically have on its tensile (pullout) capacity?
- Decreases capacity because deeper holes accumulate more debris
- Increases capacity because more bond area is available for load transfer (Correct answer)
- Has no effect since capacity is governed solely by anchor rod yield strength
- Decreases capacity because deeper adhesive columns are more prone to voids
Correct answer: Increases capacity because more bond area is available for load transfer
Greater embedment depth increases the bonded surface area between the adhesive and the concrete hole wall, directly increasing the tensile bond capacity of the anchor.
Question 6: The 'critical edge distance' (c_ac) specified for an adhesive anchor system is determined by:
- The local building official based on site-specific conditions
- Testing and product qualification per ICC-ES AC308 and published in the product evaluation report (Correct answer)
- The engineer of record on a project-by-project basis using ACI 318 equations
- OSHA field safety inspectors during installation inspections
Correct answer: Testing and product qualification per ICC-ES AC308 and published in the product evaluation report
The critical edge distance for a specific adhesive anchor product is established through testing under ICC-ES AC308 protocols and is published in the product's evaluation report (ESR).
Question 7: If an adhesive anchor group must resist combined tension and shear near a free edge, which interaction condition must the designer evaluate?
- Compression and torsion interaction at the anchor head
- Combined tension and shear interaction per ACI 318-14 Section 17.6 (Correct answer)
- Biaxial bending interaction per ACI 318 Chapter 10
- Punching shear interaction per ACI 318 Chapter 8
Correct answer: Combined tension and shear interaction per ACI 318-14 Section 17.6
ACI 318 Section 17.6 requires evaluation of the combined tension and shear interaction for anchors subjected to both loading types, using a trilinear or parabolic interaction equation.
AAI Anchor Spacing, Edge Distance & Embedment Depth 2
When installing adhesive anchors at a corner where two free edges are present, the anchor capacity is affected because: