Caesar static Load Case Editor

8/13/2019 Caesar static Load Case Editor

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CAESAR II STATIC LOAD CASE

EDITOR

Loren Brown

Senior Engineer/Developer

CADWorx & Analysis SolutionsIntergraph Process, Power, & Marine


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CONTACT US

Feedback: [email protected]

Suggestions: [email protected]

Technical Support:

[email protected]
mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]


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TYPES OF LOADS

Primary Loads Force driven, causecatastrophic failure.

Weight, Pressure, Point Loads, Uniform Loads,Hanger Loads, Wind and Wave loads.

Secondary Loads Strain based, cause fatiguefailure.

Temperature, Displacements.


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AVAILABLE LOAD TYPES IN CAESAR II

W (Weight), WNC (Weight No Contents) WW (Water-filled Weight) P (Pressure), HP (Hydrotest Pressure) T (Temperature), D (Displacement) H (Hanger Pre-loads), F (Concentrated Loads) U (Uniform Loads) Win (Wind), Wav (Wave and Current) CS (Cut Short or Cut Long)


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Available Stress Types in CAESAR II

OPE Operating SUS Sustained

EXP Expansion OCC Occasional HYD Hydrotest HGR Hanger Design FAT - Fatigue


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Load Case Definition

Operating case contains all loads in thesystem.

L1 = W+P1+T1+H (OPE) this is called a basic load case Sustained Case contains only primary loads.

L2 = W+P1+H (SUS) another basic load case Expansion Case is the difference between the

operating and sustained cases. L3 = L1-L2 (EXP) this is called a combination load case


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Combination Load Cases

Used to add or subtract results frompreviously defined primitive load cases.

Necessary for proper EXP and OCC code stressdefinition.

Not used for restraint or equipment loaddefinition, nor for displacement reporting.


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Why subtract SUS from OPE?

Why not simply use L3 = T1 (EXP)? Because the restraint configuration may result in

an incorrect solution. Nonlinear restraints drive the restraint

configuration. Other loads in the system combine to change the

restraint configuration.


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Nonlinear Restraints

Stiffness of Restraint changes depending onposition of pipe or forces on restraint.

Examples: Uni-directional Restraints (+Y) Gaps in restraints Friction Large-rotation rods Bi-linear Restraints


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Force vs. Distance in NonlinearRestraints


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Example 1: T1 (EXP)

This is how the line is modeled inCaesar II. The gaps are equal onboth sides of the pipe. No loads areyet applied.

The thermal forces have closedthe gap on the right side.

L3 = T1 (EXP)

Total Displacement for T1 (EXP) = 1 x Gap


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Example 2: L1 L2 (EXP)L2 = W+P1 (SUS) L1 = W+P1+T1 (OPE)

Weight has caused the pipe to closethe gap to the left. This can happenwhen the pipe pivots about adifferent restraint.

Operating conditions have causedthe pipe to close the gap to theright, even against the weight forcetrying to hold it on the left.


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Example 2 (cont)

If we subtract the displacements of the SUScase from OPE we get:

Total Displacement for L1-L2 = 2 x Gap In a linear system T1 (EXP) = L1 L2 (EXP) In a nonlinear system this is not guaranteed. This represents the effect of temperature in the

presence of other loads. This is a displacement stress range, not starting

from the neutral position.


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Occasional Load Cases

For most piping codes (not the offshorecodes):

Set up an OPE case that includes the occasionalload

Subtract the standard OPE case from the OPE thatincludes the occasional load. We call this the

segregated occasional load case. Add the above load case results to the SUS load

case results for the code stress check


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Example 3: Occasional Load Cases Assume we have a uniform load representing a

seismic load, U1. L1 = W+P1+T1 (OPE) standard operating

L2 = W+P1 (SUS) L3 = W+P1+T1+U1 (OPE) operating with occasional load L4 = L1-L2 (EXP) L5 = L3-L1 (OCC)segregated occasional L6 = L2+L5 (OCC) *occasional code stress case

* use scalar combination method.


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Combination Methods Algebraic:

Used for subtracting two load cases. Takes the displacements from the referenced cases

and subtracts them. Then computes forces, moments, and resultant stress

from these displacements. Scalar:

Used for adding two load cases. Adds the stresses from the two referenced load cases. Unlike algebraic the stresses are not recomputed from

displacements.


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Notes on combination methods

Dont use algebraic for adding two load cases. You cant take credit for occasional loads acting

opposite to operating loads. Dont use scalar for subtracting two cases.

This results in a lower code stress than actual.


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Output Types

Displacement Usually reported only for basic load cases

Force Usually reported only for basic load cases

Stress Reported based on code requirements.


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Example 4 Restraint Loads

The algebraic difference between these two conditions will result in a positiveforce on the restraint. This is an impossible condition. But the EXP code stress iscorrectly computed for this condition.


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What to report

Suppress the HGR cases and the segregatedoccasional load cases.

Report displacement, force for all primitiveload cases.

Dont report stress for the operating loadcases.

This is not true for offshore codes, nor FRP codes,nor buried pipe codes. Report only stress for combination load cases.


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Using the Hot Modulus of Elasticity

It is required to use the cold modulus ofelasticity for stress computation.

You can reduce restraint loads by use of thehot modulus of elasticity.

Create identical OPE cases, one with hotmodulus for restraint loads, and one with coldmodulus for use in the combination with SUSfor determining EXP stress.


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Using the Friction Multiplier

Friction Multiplier acts on the Mu valueentered on each restraint in the model.

Input 0.0 for no friction and 1.0 for fullfriction.

Create identical load cases, but change thevalue of Friction Multiplier on one of them.

Compare the results in the Restraint Summaryand report the worst-case results.

Caesar static Load Case Editor

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