190644870 caesar static load case editor
TRANSCRIPT
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CAESAR II STATIC LOAD CASE
EDITOR
Loren Brown
Senior Engineer/Developer
CADWorx & Analysis Solutions
Intergraph Process, Power, & Marine
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CONTACT US
Feedback: [email protected]
Suggestions: [email protected]
Technical Support:
mailto:[email protected]:[email protected]:[email protected]:[email protected]:[email protected]:[email protected] -
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TYPES OF LOADS
Primary LoadsForce driven, cause
catastrophic failure.
Weight, Pressure, Point Loads, Uniform Loads,
Hanger Loads, Wind and Wave loads.
Secondary LoadsStrain based, cause fatigue
failure.
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
OPEOperating
SUSSustained
EXPExpansion OCCOccasional
HYDHydrotest
HGRHanger Design FAT - Fatigue
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Load Case Definition
Operating case contains all loads in the
system.
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 from
previously defined primitive load cases.
Necessary for proper EXP and OCC code stress
definition.
Not used for restraint or equipment load
definition, 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 on
position 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 Nonlinear
Restraints
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Example 1: T1 (EXP)
This is how the line is modeled in
Caesar II. The gaps are equal on
both sides of the pipe. No loads are
yet applied.
The thermal forces have closed
the gap on the right side.
L3 = T1 (EXP)
Total Displacement for T1 (EXP) = 1 x Gap
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Example 2: L1L2 (EXP)
L2 = W+P1 (SUS) L1 = W+P1+T1 (OPE)
Weight has caused the pipe to close
the gap to the left. This can happen
when the pipe pivots about a
different restraint.
Operating conditions have caused
the pipe to close the gap to the
right, even against the weight force
trying to hold it on the left.
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Example 2 (cont)
If we subtract the displacements of the SUS
case from OPE we get:
Total Displacement for L1-L2 = 2 x Gap
In a linear system T1 (EXP) = L1L2 (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 offshore
codes):
Set up an OPE case that includes the occasional
load
Subtract the standard OPE case from the OPE that
includes 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 aseismic 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 casesand subtracts them.
Then computes forces, moments, and resultant stressfrom 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 4Restraint Loads
The algebraic difference between these two conditions will result in a positive
force on the restraint. This is an impossible condition. But the EXP code stress is
correctly 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 primitive
load cases. Dont report stress for the operating load
cases.
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 of
elasticity for stress computation.
You can reduce restraint loads by use of the
hot modulus of elasticity.
Create identical OPE cases, one with hot
modulus for restraint loads, and one with cold
modulus for use in the combination with SUS
for determining EXP stress.
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Using the Friction Multiplier
Friction Multiplier acts on the Mu value
entered on each restraint in the model.
Input 0.0 for no friction and 1.0 for full
friction.
Create identical load cases, but change the
value of Friction Multiplier on one of them.
Compare the results in the Restraint Summary
and report the worst-case results.