AAI Anchor Spacing, Edge Distance & Embedment Depth 1 — Questions and Answers
Question 1: What is the primary reason minimum edge distance requirements exist for adhesive anchor installations?
- To reduce the amount of adhesive used
- To prevent concrete splitting or breakout failure near the edge (Correct answer)
- To allow easier access for drilling equipment
- To comply with aesthetic requirements on visible surfaces
Correct answer: To prevent concrete splitting or breakout failure near the edge
Minimum edge distances prevent concrete splitting and edge breakout failure modes that occur when anchors are placed too close to a free surface.
Question 2: The effective embedment depth (h_ef) of an adhesive anchor is measured from:
- The top of the base plate to the tip of the anchor rod
- The concrete surface to the tip of the adhesive-bonded portion of the anchor (Correct answer)
- The underside of the nut to the bottom of the drilled hole
- The concrete surface to the bottom of the drilled hole
Correct answer: The concrete surface to the tip of the adhesive-bonded portion of the anchor
Effective embedment depth (h_ef) is the depth of the bond zone, measured from the concrete surface to the bottom of the adhesive-bonded length of the anchor.
Question 3: When adhesive anchors are installed in a group, the minimum center-to-center spacing requirement is intended to prevent:
- Anchors from being installed in the same plane
- Overlapping bond stress zones that would reduce individual anchor capacity (Correct answer)
- Excessive adhesive consumption during installation
- Interference between drilling operations
Correct answer: Overlapping bond stress zones that would reduce individual anchor capacity
When anchor spacing is too small, the bond stress zones overlap, reducing the effective load transfer area and lowering the capacity of each anchor in the group.
Question 4: According to ACI 318, what term describes the minimum edge distance below which the anchor capacity must be reduced due to proximity to a free edge?
- Nominal edge distance
- Critical edge distance (c_ac) (Correct answer)
- Factored edge distance
- Design edge distance
Correct answer: Critical edge distance (c_ac)
The critical edge distance (c_ac) is the ACI 318 term for the minimum edge distance at which the full anchor capacity can be achieved without reduction.
Question 5: If an adhesive anchor is installed with an embedment depth less than the minimum specified in the MPII, the installer should:
- Fill the remaining hole with non-shrink grout and proceed
- Stop work and consult the engineer of record before proceeding (Correct answer)
- Add a longer anchor rod to compensate for the shallow embedment
- Apply additional adhesive at the surface to increase bond length
Correct answer: Stop work and consult the engineer of record before proceeding
Installing below the minimum specified embedment depth compromises structural integrity, requiring an engineer of record to evaluate and approve a corrective action.
Question 6: The minimum concrete member thickness for adhesive anchor installation is typically specified as a function of:
- The diameter of the anchor rod only
- The embedment depth and anchor diameter as specified in the MPII or evaluation report (Correct answer)
- The compressive strength of the concrete
- The type of adhesive system being used
Correct answer: The embedment depth and anchor diameter as specified in the MPII or evaluation report
Minimum member thickness is typically specified as a multiple of embedment depth (e.g., h_ef + some clearance) and anchor diameter per the product's evaluation report or MPII.
Question 7: When an adhesive anchor must be placed closer to an edge than the critical edge distance but farther than the minimum edge distance, the design approach is to:
- Use a larger diameter anchor rod to compensate
- Apply a reduction factor to the anchor's tensile and shear capacity (Correct answer)
- Increase the embedment depth proportionally to offset the reduced edge distance
- Install supplemental adhesive on the anchor rod threads
Correct answer: Apply a reduction factor to the anchor's tensile and shear capacity
When the edge distance falls between the minimum and critical values, ACI 318 requires applying edge distance modification factors that reduce the calculated anchor capacity.
AAI Anchor Spacing, Edge Distance & Embedment Depth 1
What is the primary reason minimum edge distance requirements exist for adhesive anchor installations?