Combination Method - CAESAR II - Help

CAESAR II Users Guide (2019 Service Pack 1)

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English
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CAESAR II
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CAESAR II Version
11.0 (2019)

Specifies the combination method to use only for combination cases (containing other load cases, such as L1 and L2).

Load case results are multiplied by any associated scale factors before performing the combination and comparison.

The available methods are:

Algebraic

Indicates a signed algebraic combination of displacement and force level. This method combines the displacement vectors and the force vectors algebraically and then calculates the stresses from the combined forces. Displacements are the algebraic combination of the displacement vectors. Forces are the algebraic combination of the force vectors. Stresses are not combined. Stresses are calculated from the algebraically combined forces. The Algebraic method would typically be used to calculate EXP code stresses.

The obsolete CAESAR II combination methods DS and FR used an Algebraic combination method. Therefore, load cases built in previous versions of CAESAR II using the DS and FR methods are converted to the Algebraic method. Also, new combination cases automatically default to this method, unless you change them.

Algebraic combinations can be built only from basic load cases. Basic load cases are non-combination load cases or other load cases built using the Algebraic combination method.

Scalar

Indicates a signed combination of displacement, force, and stress level. This method combines the displacement vectors, force vectors, and stress scalars. Displacements are the algebraic combination of the displacement vectors. Forces are the algebraic combination of the force vectors. Stresses are the scalar combination of the stress scalars.

The combination of displacements and forces are the same for ALG and Scalar methods. The combinations of stress levels are different between ALG and Scalar methods because the stresses are calculated from the combined forces in the ALG method and summed in the Scalar method.

For example:

Load Case 1: bending stress = 100 psi, due to X-moment
Load Case 2: bending stress - 100 psi, due to Z-moment

Algebraic (vectorial) sum = square root of (100*100 + 100*100) = 141.4 psi
Scalar sum = 100 + 100 = 200 psi

Scalar is typically used to sum (SUS + OCC) code stresses.

The obsolete CAESAR II combination methods ST used a Scalar combination method. Therefore, load cases built in previous versions of CAESAR II using the ST method are converted to the Scalar method.

For DNV, only Abs and Scalar are allowed.

SRSS

Indicates a combination of the square root of the sum of the squares of quantities, such as the displacements of the forces or the stresses. Displacements are the square root of the sum of the squares of the displacements of all cases included in the combination. Forces are the square root of the sum of the squares of the forces of all cases included in the combination. Stresses are the square root of the sum of the squares of the stresses of all cases included in the combination. This method is typically used to combine seismic directional components.

Abs

Indicates a combination of the absolute values of quantities, such as the displacements, the forces, or the stresses. Displacements are the sum of the absolute value of the displacements of all cases included in the combination. Forces are the sum of the absolute value of the forces of all cases included in the combination. Stresses are the sum of the absolute value of the stresses of all cases included in the combination. This method is typically used to combine SUS cases with OCC cases for occasional stress code check.

For flange checks that use the ABS load case combination method (specified in CAESAR II piping input), the software uses the following calculated (local) values:

  • The axial force and torsion, which is the absolute sum of these values from all load cases included the combination.

  • The bending moment, which is the sum of resultant bending moments from all load cases included in the combination.

The flange pressure, which is the maximum pressure defined in the load cases included in the combination.

For DNV, only Abs and Scalar are allowed.

MAX

Indicates a combination that reports the maximum displacement, the maximum force, and the maximum stress value of the cases combined. This method retains the original sign. Displacements are the displacements having the maximum absolute values of all the load cases included in the combination. Forces are the forces having the maximum absolute values of all the load cases included in the combination. Stresses are the stresses having the maximum absolute values of all the load cases included in the combination. This method is typically used to report the greatest restraint loads from among a selected set of load cases.

For flange checks that use the MAX load case combination method (specified in CAESAR II piping input), the software uses the following calculated (local) values:

  • The axial force and torsion, which is the maximum magnitude of these values from all load cases included the combination.

  • The bending moment, which is the maximum resultant bending moment from all load cases included in the combination.

The flange pressure, which is the maximum pressure defined in the load cases included in the combination.

MIN

Indicates a combination that reports the minimum displacement, the minimum force, and the minimum stress value of the cases combined. This method retains the original sign. Displacements are the displacements having the minimum absolute values of all the load cases included in the combination. Forces are the forces having the minimum absolute values of all the load cases included in the combination. Stresses are the stresses having the minimum absolute values of all the load cases included in the combination.

SIGNMAX

Indicates a combination that reports the maximum displacement, the maximum force, and the maximum stress value of the cases combined. The sign is considered in the comparison. Displacements are the maximum signed values of all the displacements from each case included in the combination. Forces are the maximum signed values of all the forces from each case included in the combination. Stresses are the maximum signed values of all the stresses from each case included in the combination. This method is typically used in conjunction with SignMin to report the envelope of restrain loads from among a selected set of load cases.

SIGNMIN

Indicates a combination that reports the minimum displacement, the minimum force, and the minimum stress value of the cases combined. The sign is considered in the comparison. Displacements are the minimum signed values of all the displacements from each case included in the combination. Forces are the minimum signed values of all the forces from each case included in the combination. Stresses are the minimum signed values of all the stresses from each case included in the combination. This method is typically used in conjunction with SignMax to report the envelope of restraint loads from among a selected set of load cases.