What is a Load Case? - CAESAR II - Help

CAESAR II Users Guide (2019 Service Pack 1)

PPMProduct
CAESAR II
PPMCategory_custom
Help
Version_CAESAR
11.0 (2019)

In CAESAR II, a load case is a group of piping system loads that are analyzed together and occur at the same time. An example of a load case is an operating analysis composed of the thermal, deadweight, and pressure loads together. Another example is an as-installed analysis of deadweight loads alone.

A load case can also be composed of the combinations of the results of other load cases. For example, a load case can be the difference in displacements between the operating and installed cases.

No matter what the contents of the load case, it always produces a set of reports, which list restraint loads, displacements and rotations, internal forces, moments, and stresses. Because of piping code definitions for calculation methods and/or allowable stresses, CAESAR II also tags load cases with a stress type. For example, the combination mentioned previously might be tagged as an expansion stress case (EXP).

Piping System Loads

The piping system loads that compose the basic non-combination load sets relate to various input items found on the Classic Piping Input dialog box. The following tables list the individual load set designations, their names and the input items, which make them available for analysis.

Designation

Name

Input items which activate this load case

W

Deadweight

Pipe Weight, Insulation Weight, Refractory Weight, Cladding Weight, Fluid Weight, Rigid Weight

WNC

Weight No fluid Contents

Pipe Weight, Insulation Weight, Refractory Weight, Cladding Weight, Rigid Weight

WW

Water Weight

Pipe Weight, Insulation Weight, Refractory Weight, Cladding Weight, Water-filled Weight, Rigid Weight (usually used for Hydro Test)

T1

Thermal Set 1

Temperature #1

T2

Thermal Set 2

Temperature #2

T3

Thermal Set 3

Temperature #3

T9

Thermal Set 9

Temperature #9

P1

Pressure Set 1

Pressure #1

P2

Pressure Set 2

Pressure #2

P3

Pressure Set 3

Pressure #3

P9

Pressure Set 9

Pressure #9

HP

Hydrostatic Test Pressure

Hydro Pressure

D1

Displacements Set 1

Displacements (1st Vector)

D2

Displacements Set 2

Displacements (2nd Vector)

D3

Displacements Set 3

Displacements (3rd Vector)

D9

Displacement Set 9

Displacements (9th Vector)

F1

Force Set 1

Forces/Moments (1st Vector)

F2

Force Set 2

Forces/Moments (2nd Vector)

F3

Force Set 3

Forces/Moments (3rd Vector)

F9

Force Set 9

Forces/Moments (9th Vector)

WIN1

Wind Load 1

Wind Shape Factor

WIN2

Wind Load 2

Wind Shape Factor

WIN3

Wind Load 3

Wind Shape Factor

WIN4

Wind Load 4

Wind Shape Factor

WAV1

Wave Load 1

Wave Load On

WAV2

Wave Load 2

Wave Load On

WAV3

Wave Load 3

Wave Load On

WAV4

Wave Load 4

Wave Load On

U1

Uniform Loads

Uniform Loads (1st Vector)

U2

Uniform Loads

Uniform Loads (2nd Vector)

U3

Uniform Loads

Uniform Loads (3rd Vector)

CS

Cold Spring

Material # 18 or 19

H

Hanger Initial Loads

Hanger Design or Prespecified Hangers

Available piping system loads display on the left side of the Static Analysis dialog box.

Basic Load Cases

Load cases are comprised of one or more major load types as defined in the input. Major load cases are load cases that require a solution to the matrix equation [K]{x} = {f}.

For example:

  • W+T1+P1+F1 (OPE) is a major load case

  • W+P1+F1 (SUS) is a major load case

Basic load cases can consist of a single load, such as WNC for an as-installed weight analysis. A basic load can also include several loads added together, such as W+T1+P1+D1+F1 for an operating analysis. The stress type categories sustained (SUS), expansion (EXP), occasional (OCC), operating (OPE), and fatigue (FAT) are specified at the end of the load case definition. The definition of the two examples is: WNC (SUS) and W+T1+P1+D1+H (OPE). Enter each basic load case in this manner.

Load components, such as W, T1, D1, WIN1, can be preceded by scale factors such as 2.0, -0.5, and so forth. Likewise, you can precede references to previous load cases by scale factors when you build combination cases.

This provides you with several benefits.

  • If one loading is a multiple of the other (such as Safe Shutdown Earthquake being two times Operating Basis Earthquake) you must type only one loading in the Classic Piping Input dialog box. You can use this loading in a scaled or unscaled form in the Static Analysis - Load Case Editor dialog box.

  • If a loading can be directionally reversible, such as wind or earthquake, you must type only one loading in the Classic Piping Input dialog box. You can use this loading preceded by a + or a - to switch the direction.

  • Load Rating Design Factor (LRDF) methods can be implemented by scaling individual load components by their risk-dependent factors. For example:

    1.05W + 1.1T1+1.1D1+1.25 WIN1

You can select the stress type from the list on each line.

Combination Load Cases

You can combine the results of the basic load cases by using combination load cases. Always type these combinations after the last of the basic load cases. Designate combinations of basic load cases by using the prefix L1, L2, and so on.

Algebraic combination load cases are combinations of previously-solved major load cases. For example:

  • L1-L2 (EXP) is a combination case which combines the displacements, forces, and stresses using a combination method that you select.

  • L4+L6+L8 (OCC) is a combination case which combines the displacements, forces, and stresses using a combination method that you select.

The + and - signs are unary operators/sign of multiplier. If no value precedes the load for major load cases or the load case for combination cases, then the multiplier is +1.0 or -1.0. If a value precedes the load or the load case, then the multiplier is +value or -value.

You must specify the expected number of load cycles for all load cases with stress type fatigue (FAT).

The following family of load cases provides an example of algebraic combinations.

Load Case


Designation


Comments

1

W+T1+P1+H+0.67CS (OPE)

Hot operating. The 0.67scale factor takes credit only for 2/3 of the cold spring.

2

W1+P1+H+0.67CS(OPE)

Cold operating with cold spring included.

3

W1+P1+H(SUS)

Traditional sustained case.

4

WIN1(OCC)

Wind case. This will be manipulated later to represent average wind 1X, maximum wind 2X (in the positive and negative directions).

5

L1-L2(EXP)

Traditional cold to hot expansion case. Use L for load, rather than DS.

6

L1-L2(FAT)

Same case evaluated for fatigue at 10,000 cycles.

7

L1+L4(OPE)

Hot operating with average wind (in positive direction).

8

L1-L4(OPE)

Hot operating with average wind (in negative direction).

9

L1+2L4(OPE)

Hot operating with maximum wind (in positive direction).

10

L1-2L4(OPE)

Hot operating with maximum wind (in negative direction).

11

L2+L4(OPE)

Cold operating with average wind (in positive direction).

12

L2-L4(OPE)

Cold operating with average wind (in negative direction).

13

L2+2L4(OPE)

Cold operating with maximum wind (in positive direction).

14

L2-2L4(OPE)

Cold operating with maximum wind (in negative direction).

15

L3+L4(OCC)

Occasional stress case, sustained plus average wind.

16

L3+2L4(OCC)

Occasional stress case, sustained plus maximum wind.

17

L9+L10+L11+L12(OPE)

Maximum restraint load case. The combination option should be MAX.

CAESAR II permits the specification of up to 999 load cases for analysis. Copy the model to a new file to specify the additional load cases if more cases are required.