Fall-protection anchorage

The anchorage of a personal fall arrest system:

• the anchor device;
• the bolts that fix its post or bracket to the host;
• the host member in bending.

It is checked for two forces:

• ASCE/SEI 7-22 4.6.5: a live load of 3,100 lb for each attached line, in any direction, factored by the load combinations.
• OSHA: 29 CFR 1926.502(d)(15) for construction or 1910.140(c)(13) for general industry. Either 5,000 lb per person attached, or twice the system's maximum arrest force under a qualified person. ANSI/ASSP Z359.6 is offered as an option.

An end anchorage of a horizontal lifeline takes the line tension. Commentary C4.6.5 explains the link between the two: 1.6 × 3,100 lb = 4,960 lb, which matches OSHA's 5,000 lb.

Inputs of the fall-protection anchorage #

• OSHA standard: construction (1926.502) or general industry (1910.140).
• Persons attached: one line each (4.6.5).
• OSHA basis: one of
  • 5,000 lb per person;
  • qualified person, a safety factor of 2 on the maximum arrest force;
  • the ANSI/ASSP Z359.6 engineered system, 2 × the maximum arrest force.

  For the last two, enter the maximum arrest force from the system's manufacturer (OSHA limits it to 1,800 lb with a body harness).

• OSHA strength compared with: the available strength (φRn or Rn/Ω), as C4.6.5 relates the two rules. This is the default. The other choice is the nominal strength ("without failure"). This is your judgment.
• System: a single anchorage, or the end anchorage of a horizontal lifeline. For a lifeline, enter its span and the sag at arrest from the lifeline manufacturer. The arrest load acts at midspan and T = P / (2 sin θ).
• Anchor and connection:
  • The device's rated (ultimate) strength.
  • The attachment height e above the host.
  • The base bolts: count, grade, diameter, threads.
  • The lever arm from the compression edge to the tension bolts. Half the bolts are in tension.
• Host member: a simple span with the anchor at a distance a, its nominal flexural strength Mn (from its own calculation), and the dead load moment at the anchor.

Auto-design varies the bolt count (2 to 8) and diameter (1/2 to 1-1/4 in.) for the least bolt area. The persons, the arrest basis, the device, the height, the lever arm and the host are kept.

Checks performed #

The drawings show the anchor elevation and, for a lifeline, its schematic with the end tension.

Limitations #

• Written from knowledge. The OSHA sections and ANSI/ASSP Z359.6 are written from knowledge (to confirm against the code text). The regulations are free at osha.gov and are listed in research/DOCUMENTS_NEEDED.md. ASCE 7-22 4.6.5 and C4.6.5 are read.
• Not designed here. Prying of the base plate, the plate itself, welds, the post or bracket, fall clearance, swing fall and rescue.
• Host member. The host is checked in bending only, as a simple span. Lifeline hosts are designed in their own calculation.

Verification examples #

Verification status: 17 values compared in 3 examples (0 published, 3 hand calculations from the cited equations): 17 within tolerance, 0 recorded deviations. No published example: every value is a hand calculation. That checks the program against this reading of the code, not the reading itself. Code basis: the provisions it uses were read in the target edition.

No published worked example is on disk. Hand calculations check:

• The 4.6.5 and OSHA forces.
• The factored ASCE force.
• Bolt tension and shear with their AISC strengths, in LRFD and ASD.
• The host moments.
• The qualified-person force for two persons.
• The lifeline angle and tension.