I've got a perfectly straight run of GRP/FRP pipe, anchored at both ends, modeled in Caesar v5.3. I'm analyzing in accordance with BS 7159.

I understand that stress ratios are calculated in the following manner (keeping in mind that compressive stress is induced from the opposing anchors, so sect.7.4 comes into play):

long: (axial + bending) <= 1.25 Sh
circ: [hoop - vh/a*(axial+bending)] <= Sh*Eh/Ea

where vh/a is Poisson ratio; Sh is axial allowable stress; Eh and Ea are moduli of elasticity, hoop and axial, respectively.

But why does Caesar alternate allowable stress (Sa) between each node? For example, Sa at node 10 is 1.25Sh but at node 20 it's Sh*Eh/Ea, and then at node 30 it's back to 1.25Sh.

Deepak:

For FRP piping codes (BS 7159, UKOOA and ISO 14692), there are two sets of code_stress/allowable:
1. Longitudinal stress and longitudinal allowable
2. Circumferential stress (hoop stress) and circumferential allowable.

CAESAR II calculates both sets and reports only one set with a larger code_stress/allowable ratio.

That is why you might see alternate code stress/allowable in stress report.

Makes sense. Thank you.

Follow-up questions:

1. Caesar automatically assumes 1.25xSh for compressive stress allowable for code BS 7159 but the code [para 7.4(g)] specifies that this allowable is only for unlined pipe. Can this allowable be manually changed to 1.0xSh for lined pipe?

2. Do the GRP/FRP material properties in the Configuration file get automatically overriden by material properties specified in Piping Input and Special Execution Paramaters?

1. I guess it depends on what you mean by "manual". Maybe I could re-analyze the system specifying 80% Sh and only check those points in compression. That would give me 1.0xSh. But I dont think that's what you want to hear.
2. Your point may be correct but I don't know if you are saying it correctly. FRP model data is established by the current configuration settings at the time you select material 20 (FRP). At this point - what you see is what you get. These data can then be changed in the piping input and Special Execution Paramters.

Dave,

1. I understand your workaround. But why does Caesar automatically assume that the pipe being analyzed is unlined? Seems like the less conservative approach.

2. Yup, that's what I meant. We're on the same page.

Thanks.

Hi,

According to the first point, can anyone explain why section 7.4 of the BS 7159 states:

For unlined GRP pipework the allowable compressive strain can be taken as 1.25 times the allowable strain from section 4.

Is this a conservative statement regarding lined piping (in which the allowable compressive stresses should be higher) or a uncomplete statement about lined piping?

When considering Euler's buckling theorem I would think that the critical buckling load should be applied to the total of the liner and the FRP instead of just the liner. Hence, a higher allowable compressive stress is achieved. Which would support the hypothesis of a higher allowable compressive stress for lined piping.

Considering the proposed solution by Dave Diehl, reducing the allowable stress to 80% might yield situations where the Hoop stress is higher then the compressive stress. These cases will not be shown by Caesar II since it only shows the most critical cases, right?

Can anyone make further suggestions on handling this matter?

Thanks in advance,

R. Fransen

I see I did not respond to your follow up question...
(and without reviewing the BS document)
Evaluating compressive longitudinal stress in these systems present many unanswered questions for FRP pipe (regardless of lining). As far as I know, the Code only provides this one compressive stress limit - please correct me if I am wrong. So that's all you get (allowable stress based on 1.25 times the allowable strain) out of CAESAR II.

Dear all:

Maybe ISO14692 can work on the problem of buckling evaluation, which includes relevant part dealing with pipe run imposed on pure moment and axial compressive loading respectively. I don't know wheher it can be applied to steel pipe or not. If ok, that's perfect. Why do not CII incorporate it into solver? For large bore pipe with thin wall, buckling is a necessary cocern .

Rds

Gino

Dear Deepak
you are user with BS7159 GRP
can you please send me a load case combination adopted for GRP pipe for BS7159?
And for BS7159 the SH is depending on diameter what you take for this input
Thanks

If this is available, I would very much like to receive the same thing. Big thank you ahead of time.

Hi Dave,
Im facing an issue with my GRP piping analysis.
The client has given the input data in the below given format.Im not able to co relate the values with the caesar input values as required.
The client has given
1. Hoop Tensile Strength (ASTM D2290, Uni‐Axial)=250 Mpa
2. Hoop Tensile Strength (ASTM D1599, Bi‐Axial) =200 Mpa
3. Axial Tensile Strength (ASTM D2015) = 85 Mpa
4. Hoop Tensile Modulus (Eht) =20000 Mpa
5. Hoop Flexural/Bending Modulus (Ehf) =23000 Mpa
6. Axial Tensile Modulus (Eat) =11000 Mpa
7. Axial Bending Modulus (Eab) =11000 Mpa
8. Ratio of Hoop Modulus to Axial Modulus (Eht/Eat) 1.818
9. Shear Modulus (G) = 11700 Mpa

Please advise me how to input the above values as per ISO 14692 in the al(0:1),al(2:1),al(1:1),hl(1:1) and hl(2:1) columns.
and also how do we calculate the allowable stress analytically so as to substantiate the caesar output values.

I believe you can help me out.

thank you
Jojo

CAESAR II requires long term, ideal hoop strength hl(2:1) and long term axial strength under no pressure al(0:1). Long term, ideal axial strength al(2:1) is half of hl(2:1).
My guess?
Do your ASTM specs work with short term or long term? If long term, then hl(2:1) is either 250 or 200 (without additional information, I would use 200). You do not have the (1:1) terms. I would say that your item 3 is your al(0:1) term. These values will be modified by your design factor (0.67) and other factors (A1, A2, A3) defined in your input.
The axial and hoop stress limits are dependent upon one another. As hoop stress increases, more of the available axial strength is dedicated to carry the increasing axial stress due to pressure. The available axial stress for loads other than pressure is shown below.

After posting this I see that you are referencing BS 7159. BS 7159 does not use those terms al(0:1), hl(2:1), etc. My comments are specific to ISO 14692.

Thank you Dave.
So can I use like as mentioned below
al(0:1) = 85 Mpa
hl(2:1) = 200 Mpa
al(2:1) = 100 Mpa
al(1:1) = 100 Mpa
hl(1:1) = 100 Mpa
also the Qs = 200 Mpa

Please advise me on the above inserts.
Also based on the link below
How do we calculate the allowable stress analytically so as to substantiate the Caesar output values.
AS per the Caesar Output report Im getting the below given values

Piping Code: ISO 14692 = ISO 14692 (2005)


CODE STRESS CHECK PASSED : LOADCASE 1 (OPE) W+T1+P1

Highest Stresses: ( KPa ) LOADCASE 1 (OPE) W+T1+P1
Ratio (%): 39.8 @Node 2691
OPE Stress: 33024.8 Allowable Stress: 83013.0
Axial Stress: 22829.9 @Node 835
Bending Stress: 13627.7 @Node 2691
Torsion Stress: 152.2 @Node 2505
Hoop Stress: 52422.1 @Node 2691
Max Stress Intensity: 47274.1 @Node 2405

CODE STRESS CHECK PASSED : LOADCASE 2 (OPE) W+T1+P2

Highest Stresses: ( KPa ) LOADCASE 2 (OPE) W+T1+P2
Ratio (%): 22.9 @Node 940
OPE Stress: 13797.0 Allowable Stress: 60374.5
Axial Stress: 11415.0 @Node 835
Bending Stress: 2382.0 @Node 940
Torsion Stress: 30.1 @Node 2040
Hoop Stress: 22829.9 @Node 835
Max Stress Intensity: 23636.9 @Node 925

CODE STRESS CHECK PASSED : LOADCASE 3 (SUS) W+P1

Highest Stresses: ( KPa ) LOADCASE 3 (SUS) W+P1
Ratio (%): 77.5 @Node 2691
Code Stress: 51931.9 Allowable Stress: 67000.0
Axial Stress: 22829.9 @Node 835
Bending Stress: 32534.7 @Node 2691
Torsion Stress: 377.8 @Node 2505
Hoop Stress: 71329.6 @Node 2691
Max Stress Intensity: 59546.3 @Node 2691

CODE STRESS CHECK PASSED : LOADCASE 4 (SUS) W+P2

Highest Stresses: ( KPa ) LOADCASE 4 (SUS) W+P2
Ratio (%): 38.8 @Node 2691
Code Stress: 25965.0 Allowable Stress: 67000.0
Axial Stress: 11415.0 @Node 835
Bending Stress: 16266.4 @Node 2691
Torsion Stress: 188.1 @Node 2505
Hoop Stress: 35663.8 @Node 2691
Max Stress Intensity: 29774.3 @Node 2691

From this results how do we substantiate the analytical calculations.

Please advise

I am in no position to approved or disapprove your data or model.

I do not believe you have any information to set al(1:1) and hl(1:1). I also question your value for Qs (Qs=hl(2:1)?).

The second illustration I provided gives you a means to calculate the axial allowable.

I am guessing your factors A1, A2, A3 all are set to 1.0.

Remember that CAESAR II is calculating two stresses and two allowable stresses and printing the single set that produces the largest (stress/allowable stress) ratio.

It appears to me that LC3 & LC4 are governed by hoop stress since your allowable is a nice, flat 67000. I would guess, then, that LC1 & LC2 are governed by the axial term since the allowables look interpolated.

Thank you Dave for the advise.
As per caesar help file it says that Qs= hl(2:1).whats wrong in assuming like this.
If we go for manual calculations to find this value for the different diameters available in loop, i will get more than 10 numbers of Qs values,so the above may be a practical assumption.
al(1:1) and hl(1:1) values is not mandatory also.

As per final study and understanding
the following values are inserted.

al(0:1) = 85/0.67 = 127 Mpa
hl(2:1) = 200/0.67 = 299 Mpa
al(2:1) = 149.5 Mpa
also the Qs = 299 Mpa
With this values I can plot the envelope and based on the output values generated from caesar, i can point the resulted values as well to complete the task.
Does it look logic ?
Following are the load case considered
L1 = WW+HP (Hyd)
L2= W+P1+T1 (OPE)
L3 = W+P2+ T1(Ope)
L4 = W+P1 (SUS)
L5 = W+P2 (SUS)
whether the Hydrotest case to be considered or not. it is found that the code stress is not processed for that case. What would be reason for that.
Please advise on this also.

Thank you and wish you a merry Christmas

Jojo

Thank you Dave for the advise.
As per caesar help file it says that Qs= hl(2:1).whats wrong in assuming like this.
If we go for manual calculations to find this value for the different diameters available in loop, i will get more than 10 numbers of Qs values,so the above may be a practical assumption.
al(1:1) and hl(1:1) values is not mandatory also.

As per final study and understanding
the following values are inserted.

al(0:1) = 85/0.67 = 127 Mpa
hl(2:1) = 200/0.67 = 299 Mpa
al(2:1) = 149.5 Mpa
also the Qs = 299 Mpa
With this values I can plot the envelope and based on the output values generated from caesar, i can point the resulted values as well to complete the task.
Does it look logic ?
Following are the load case considered
L1 = WW+HP (Hyd)
L2= W+P1+T1 (OPE)
L3 = W+P2+ T1(Ope)
L4 = W+P1 (SUS)
L5 = W+P2 (SUS)
whether the Hydrotest case to be considered or not. it is found that the code stress is not processed for that case. What would be reason for that.
Please advise on this also.

Thank you and wish you a merry Christmas

Jojo

Dear Dave,

http://65.57.255.42/ubbthreads/ubbthread...=true#Post37193

Can you just help me to understand the calculations of GRP calculations(attached link) using caesar manual in a simpler way.

thanks
Jojo