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Loads and Load Combinations as per AS/NZS 1170.0 2002

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Designing Piperacks (pipe support structures) in compliance with Australian Standards involves determining appropriate loads and load combinations. These ensure structural safety and serviceability under expected operating conditions.

๐Ÿ“˜ Relevant Australian Standards

  • AS/NZS 1170 series โ€“ Structural design actions:
    • AS/NZS 1170.0 โ€“ General principles
    • AS/NZS 1170.1 โ€“ Dead and live loads
    • AS/NZS 1170.2 โ€“ Wind actions
    • AS/NZS 1170.4 โ€“ Earthquake actions
  • AS 4100 โ€“ Steel structures (for structural design)
  • AS 3990 โ€“ Mechanical equipment (can also be relevant)
  • Client/project-specific specs may also impose extra load combinations.

๐Ÿ”ฉ Typical Loads on Piperacks

1. Dead Load (G)

  • Self-weight of the steel structure.
  • Weight of empty pipes, cable trays, and other permanent components.
  • Pipe insulation or cladding if applicable.

2. Live Load (Q)

  • Maintenance access (personnel loads).
  • Temporary equipment.
  • Occasional loads (e.g., pipe replacement).

3. Pipe Contents Load (Fluid Load)

  • Internal fluid weight.
  • May be treated as a variable action depending on operation.

4. Thermal Loads

  • Axial expansion/contraction of pipes.
  • Induces force on pipe supports if restrained.

5. Wind Load (W)

  • As per AS/NZS 1170.2.
  • Acts on structure and exposed surfaces (pipes, trays, etc.)

6. Seismic Load (E)

  • As per AS/NZS 1170.4, especially in seismic-prone zones.

7. Equipment Loads

  • Point loads or distributed loads from mounted equipment (valves, actuators).

8. Imposed Deformations

  • Settlement or differential movement.
  • Movement of connected equipment.

โš–๏ธ Load Combinations (AS/NZS 1170.0:2002, Clause 4.2.1)

Ultimate Limit State (ULS)

Example combinations:

  1. G + Q
  2. G + ฮจ<sub>l</sub>ยทQ + W
  3. G + W
  4. G + E
  5. G + T (thermal) (if thermal loads induce significant restraint forces)

Note: Factors and ฮจ values depend on reliability class and action variability.

Serviceability Limit State (SLS)

Example combinations:

  1. G + Q
  2. G + W
  3. G + E
  4. G + T (thermal movements affecting deflection/expansion joints)

โœ… Example Ultimate Load Combination (from AS/NZS 1170.0)

For normal importance structure:

Comb 1 1.2G + 1.5Q + 0.9W
Comb 2 1.2G + 1.5W + 0.9Q
Comb 3 1.2G + 1.3E

Adjust the coefficients based on the reliability level (importance) of the piperack.

๐Ÿ“Œ Notes

  • Check for load cases with empty vs. full pipe conditions.
  • Consider thermal loads as primary actions when they govern.
  • Pipe supports may be designed for restrained or unrestrained thermal expansion.
  • For dynamic loads (e.g., surge or vibration), specialized analysis is required.

General ULS Combination Format (Clause 4.2.1)

For permanent actions (G), variable actions (Q), and exceptional actions (A):

โœ… Design action effect =

โˆ‘[G] + โˆ‘[ฯˆiยทQi] + โˆ‘[ฯˆEยทEi] + โˆ‘[ฯˆAยทAi]

But for ultimate limit state, the standard gives this general format:

๐Ÿ”ธ Most common ULS combinations:

For normal structural importance (Importance Level 2):

1.2G + 1.5Q
1.2G + 1.5W + ฯˆlยทQ
1.2G + 1.3E + ฯˆlยทQ

Letโ€™s break them down.

๐Ÿงฑ Detailed ULS Load Combinations for Piperacks

CombinationLoad CaseFormulaNotes
1Dead + Live1.2G + 1.5QMost basic combination.
2Dead + Wind1.2G + 1.5WWind governs in open or elevated areas.
3Dead + Wind + Live1.2G + 1.5W + 0.4QLive load has reduced factor when accompanying wind.
4Dead + Live + Wind (reverse)0.9G + 1.5W + 0.4QUse 0.9G when wind could uplift or reduce gravity effects.
5Dead + Seismic1.2G + 1.3EFor seismic zones (per AS/NZS 1170.4)
6Dead + Seismic + Live1.2G + 1.3E + 0.4QLive loads reduced due to improbability of concurrent peak.
7Dead + Thermal + Live1.2G + 1.5T + 0.4QThermal expansion restrained by structure.
8Accidental loads (if any)G + A or as specifiede.g., explosion, vehicle impact โ€” project-specific.

๐Ÿ“Œ Notes on Load Factors (per AS/NZS 1170.0)

ActionSymbolULS FactorSLS Factor
Dead LoadG1.2 or 0.91.0
Live LoadQ1.51.0
Wind LoadW1.51.0
Earthquake LoadE1.31.0
Thermal LoadT1.5 (if treated as action)1.0
  • Use 0.9G when dead load resists overturning or uplift.
  • Use 0.4Q as a companion load when it’s unlikely to occur at the same time as wind/seismic.

๐Ÿ’ก Piperack-Specific Considerations

  • For tall piperacks or racks with large-diameter pipes, wind often governs.
  • For hot process plants, thermal expansion may create significant axial loads and needs inclusion in design.
  • If piperack supports pipes with large slug flow (e.g., multiphase lines), account for dynamic surge โ€” typically treated as an accidental or transient action.
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