AAI AAI Load Calculations & Structural Requirements 2 — Questions and Answers
Question 1: In seismic design categories C through F, what additional requirement applies to adhesive anchor installations?
- Only adhesives with seismic qualification testing (ICC-ES AC308) may be used (Correct answer)
- All adhesive anchors are prohibited in high seismic zones
- Standard static load adhesives are acceptable with a 50% reduction
- Seismic design only affects the anchor rod size, not the adhesive
Correct answer: Only adhesives with seismic qualification testing (ICC-ES AC308) may be used
IBC and ACI 318 require seismically qualified adhesives tested per AC308 in Seismic Design Categories C–F due to the cyclic and dynamic nature of earthquake loading.
Question 2: What does the phi (φ) factor in ACI 318 anchor design represent?
- A strength reduction factor that accounts for variability and uncertainty in capacity (Correct answer)
- The angle of the failure cone in degrees
- The ratio of shear to tension demand
- The adhesive cure temperature coefficient
Correct answer: A strength reduction factor that accounts for variability and uncertainty in capacity
The φ factor is a probabilistic strength reduction that ensures the design capacity (φNn) is less than the nominal capacity (Nn), accounting for material variability, workmanship, and model uncertainty.
Question 3: For combined tension and shear loading on an adhesive anchor, which interaction equation does ACI 318 require?
- (Nua/φNn)^(5/3) + (Vua/φVn)^(5/3) ≤ 1.0 (Correct answer)
- (Nua/φNn) + (Vua/φVn) ≤ 1.0
- Nua/φNn ≤ 0.5 and Vua/φVn ≤ 0.5
- Max(Nua/φNn, Vua/φVn) ≤ 1.0
Correct answer: (Nua/φNn)^(5/3) + (Vua/φVn)^(5/3) ≤ 1.0
ACI 318 uses a 5/3 power interaction equation for combined tension-shear, which is less conservative than a linear interaction when one load component is dominant.
Question 4: What is the 'critical edge distance' (cac) for an adhesive anchor, and why does it matter?
- The minimum edge distance to develop full characteristic bond strength without reduction (Correct answer)
- The maximum allowable distance from any edge for anchor placement
- The edge distance that triggers mandatory inspection
- The distance at which side-face blowout controls over cone breakout
Correct answer: The minimum edge distance to develop full characteristic bond strength without reduction
When the actual edge distance is less than cac, the characteristic bond strength must be reduced to account for reduced confinement near the concrete edge.
Question 5: How does the anchor installation condition (Category 1, 2, or 3) affect the anchor design in ACI 318?
- Higher installation category numbers reflect less controlled conditions and require lower φ factors (Correct answer)
- Installation categories only affect the inspection protocol, not design strength
- Category 3 allows the highest φ factors because it has stricter inspection
- Installation categories apply only to post-installed mechanical anchors
Correct answer: Higher installation category numbers reflect less controlled conditions and require lower φ factors
ACI 318 ties the φ (strength reduction) factor to installation and inspection conditions — Category 1 with continuous inspection permits higher φ values than Category 3 with no special inspection.
Question 6: What is the role of the anchor's effective embedment depth (hef) in the ACI 318 concrete cone breakout equation?
- hef raises the breakout capacity to the 1.5 power, making deeper embedment highly effective (Correct answer)
- hef is raised to the 0.5 power, so depth has diminishing returns on cone capacity
- hef is not used in cone breakout calculations, only in bond calculations
- hef is multiplied linearly by the concrete tensile strength to get capacity
Correct answer: hef raises the breakout capacity to the 1.5 power, making deeper embedment highly effective
The ACI 318 concrete cone breakout equation uses hef^1.5, meaning increasing embedment depth has a super-linear benefit on cone breakout capacity.
AAI AAI Load Calculations & Structural Requirements 2
In seismic design categories C through F, what additional requirement applies to adhesive anchor installations?