Which statement correctly summarizes the minimum MBS guidance for a two-rope anchorage system?

Which statement correctly summarizes the minimum MBS guidance for a two-rope anchorage system?

• A. It must be exactly 12 kN
• B. It must be the greater of 12 kN (2700 lbf) and twice the maximum arrest force of the backup system
• C. It must be twice the backup system's arrest force
• D. It must be at least 12 kN or 2700 lbf, or twice the maximum arrest force of the backup system, whichever is greater

Answer: (D)

In a two-rope anchorage, the anchor strength must cover both a fixed safety threshold and the potential load from the backup system during arrest. The standard baseline is 12 kN (2700 lbf). You also consider twice the maximum arrest force of the backup rope, since the backup can absorb a substantial portion of the arrest load and dynamic effects can amplify forces. The minimum MBS must be the larger of these two values, ensuring the anchor is strong enough for either scenario. If the backup’s maximum arrest force is low, the 12 kN baseline governs; if it’s high, the doubled ARF governs. Using the wording that states the minimum MBS is at least 12 kN (2700 lbf) or twice the backup ARF, whichever is greater, expresses this requirement clearly and precisely.

In a two-rope anchorage, the anchor strength must cover both a fixed safety threshold and the potential load from the backup system during arrest. The standard baseline is 12 kN (2700 lbf). You also consider twice the maximum arrest force of the backup rope, since the backup can absorb a substantial portion of the arrest load and dynamic effects can amplify forces. The minimum MBS must be the larger of these two values, ensuring the anchor is strong enough for either scenario. If the backup’s maximum arrest force is low, the 12 kN baseline governs; if it’s high, the doubled ARF governs. Using the wording that states the minimum MBS is at least 12 kN (2700 lbf) or twice the backup ARF, whichever is greater, expresses this requirement clearly and precisely.