Cable assembly force and regulation distance

[ashaath2012]

• Dear Sir,
• I am wondering for long time how can i benefit from the assembly force or regulation distance in cables do i add the assembly force to the cable internal force for design or do i have to consider dilating the cable with the regulation distance on the actual construction site?
• What is the assemply load case, does it only account for the cable selfweight within the first case as the assebly force does not change when adding other loads to the first load case.
• In summary, What is the exact difinition of assembly force and regulation distance and how do they affect the design or the actual construction excution, where are they required as an input?

Thanks

Ahmed

[Artur.Kosakowski]

Please check:

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/cable-design/m-p/3226780/highlight/true#M137...

and

http://forums.autodesk.com/t5/Autodesk-Robot-Structural/c%C3%A2bles/m-p/3302449/highlight/true#M2328

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

[ashaath2012]

I have already seen these answers

[ashaath2012]

The assembly force is only a function of the change in cable length and cable selfweight and does not get affected by other loads defined in the starting case (assembly force case).

The assembly force is different from the internal force for the first case. Where do I have to use the assembly force and for what purpose. The same applied for the regulation ditance when a prestress force is defined, where does it apply.

Thanks

Ahmed

[Pawel.Pulak]

     The assembly force is only a function of the change in cable length and cable selfweight and does not get affected by other loads defined in the starting case (assembly force case).

The assembly force as calculated by Robot (for cable defined by elongation or length) is affected not only by selfweight of this cable but by all loads applied to it in assembling load case. It is calculated for the center of the cable.

    The assembly force is different from the internal force for the first case. Where do I have to use the assembly force and for what purpose.

Yes, the assembly force in the cable is different from the internal force in this cable in assembling load case because:

1/ the internal force in the cable is calculated considering possible displacements of the end nodes of the cable (because of deformations of the whole structure) - the assembly force is calculated assuming that displacements of the end nodes of the cable are zero

2/  the internal force in the cable is given it the direction tangent to the deflected shape of the cable, so for horizontal cables this force is maximum in the end nodes and minimum in the center - the assembly force is given only for the center of the cable.

The assembly force gives some estimation of force necessary to assembly the cable of specific length and with specific loads between nodes of not-deformed structure.

 The same applied for the regulation ditance when a prestress force is defined, where does it apply.

Regulation distance means how much longer (positive regulation) or shorter (negative regulation) should be the unloaded length of the cable in relation to the distance of its nodes to obtain in assembling load case prestress required in cable definition. So in short: regulation + distance_of_end_nodes = length_of_unloaded_cable.

Robot is searching for regulation of cables defined by force or stress in asembling  load case. For concesutive load cases cables are already "clamped" with regulation found in assembling load case.

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Regards,

[ashaath2012]

Thank you. Kindly further clarify below two items,

The cable Assembly force only changes when changing cable length and cable properties, it does not change when changing other loads in the first case even other elements selfweights. In other words, if cable length was not changed and cable weight was not considered in selfweight, assembly force=0 and if cable length and weight were fixed and other loads in the starting case changed, the assembly force remains unchanged. This is tested many times.

Do i have to add the initial assembly force reported in the stresses table to the maximum internl force of the cables for designing the cable section as i understood that the asembly force has to be applied initially to the cable on the construction site and internal forces are applied consequently.

Thanks

[Pawel.Pulak]

The cable Assembly force only changes when changing cable length and cable properties, it does not change when changing other loads in the first case even other elements selfweights. In other words, if cable length was not changed and cable weight was not considered in selfweight, assembly force=0 and if cable length and weight were fixed and other loads in the starting case changed, the assembly force remains unchanged. This is tested many times.

In the attached file I have contained 2 very simple test files, where the only difference is the load applied to cable in assembling load case. In the first model it is only selfweight, in the second model it is additionally vertical uniform load of -0.1 kN/m2. In the first model the assembly force in cable is 10.44 kN and in the second model it is 207.16 kN.

Do i have to add the initial assembly force reported in the stresses table to the maximum internl force of the cables for designing the cable section as i understood that the asembly force has to be applied initially to the cable on the construction site and internal forces are applied consequently.

No, there is no such need in general case but it also depends on the method of assembling the cable into the structure. If cable length is fixed before assembling and during assembling there is a situation when the distance between points connected by cable is longer than the same distance in working conditions (points of structure pulled by the cable) it may be necessary to check cable for such situation because it may be more dangerous than working conditions in the structure.

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Regards,

[ashaath2012]

I could not find the attachments.

Thanks

[Pawel.Pulak]

Sorry, when answering yesterday it was too late

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[ashaath2012]

A strange thing happened, i have run again several times your file with the selfweight only and the resulting assembly force was 207.16 instead of 10.44. So I tried to run again your othe file with the unifirm load applied and the result remained 207.16 which confirms my previous findings that assembly force does not change with loads added. What is wrong? May be settings?

Additionally, if i do not have to add assembly force to the internal forces to design the cable and the other related elements (supporting the cable) in the structure, why i have to worry about this assembly force at all? The allowance of the assembly force in the model as additional internal force in the cable will change all the forces and deflections in the structure. Kindly clarify this item as it is very important!!!

Thanks

[Pawel.Pulak]

Hello,

                A strange thing happened, i have run again several times your file with the selfweight only and the resulting assembly force was 207.16 instead of 10.44. So I tried to run again your othe file with the unifirm load applied and the result remained 207.16 which confirms my previous findings that assembly force does not change with loads added. What is wrong? May be settings?

It confirms again that I was too tired when answering yesterday evening

When fine-tuning the test files to show you the differences I have forgot to re-run analysis of the first file after some modifications - the status of results was "Out of date". After re-running analysis the assembly force in cable changes from 10.44 kN to 207.07 kN. But it is still different than 207.16 obtained for the second model, where the additional load of -0.1 kN/m is applied to the cable. The difference is not big because the cable is very short (assembled 'tightly") - relative elongation is -0.01 - it means that unloaded cable length is 1% shorter than the distance of end nodes, which is in these models 20 meters.

When using longer cable, with relative elongation -0.001, this difference is more visible: the assembly force of  20.57 kN for self-weight only and 26.27 kN when the additional load of -0.1 kN/m is applied to the cable.

Attached file with modified models.

   Additionally, if i do not have to add assembly force to the internal forces to design the cable and the other related elements (supporting the cable) in the structure, why i have to worry about this assembly force at all? The allowance of the assembly force in the model as additional internal force in the cable will change all the forces and deflections in the structure. Kindly clarify this item as it is very important!!!

The necessity to check the cable for the assembly force depends on the method of assembling. It may be necessary if the cable is not gradually pulled using some rack and then fixed but it has some predefined length and during assembling the end is fixed in some "lock". In such case tension force in the cable before assembling may by higher than in working conditions, when it is already assembled with the structure. See the drawing below:

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[ashaath2012]

That is okay, however, applying loads to cable end nodes (e.g. axial loads) in your test models do not change the assembly force, kindly clarify?

Kindly confirm the correctness of the following statement,  The assembly force is the force necessary to maintain the length of the cable = length between end nodes (if dL=0 condition is specified for cable) considering all the loads in the assembly load case, even correcting the cable sagging deflection due to its selfweight.

Thanks.

[Pawel.Pulak]

     That is okay, however, applying loads to cable end nodes (e.g. axial loads) in your test models do not change the assembly force, kindly clarify?

Yes.

    Kindly confirm the correctness of the following statement,  The assembly force is the force necessary to maintain the length of the cable = length between end nodes (if dL=0 condition is specified for cable) considering all the loads in the assembly load case, even correcting the cable sagging deflection due to its selfweight.

Yes, if you mean "length of the cable" as the distance of its ends.

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[ashaath2012]

Why does not the assembly force change when applying axial loads to the cable end nodes as the answer to this question will actually answer my concern that I have started this conversation for. In my model the loads at the asembly load case acting on the cable are axial at the end node. This is why I initially stated that the assembly force does not change when applying loads at the assembly load case as my loads are axial. Kindly clarify as this would end this discussion.

Thanks. 

[Pawel.Pulak]

The assembly force is calculated for cable "isolated" from the rest of the structure and that is why only the forces applied inside the cable and not to the end nodes are considered in it.

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[ashaath2012]

This mean that the assembly force is not included in the analysis model and has to be allowed for separately as decided by the designer based on the methodology of the assembly and type of the structure. Kindly confirm.
Thanks

[Pawel.Pulak · Accepted solution]

Yes, it is true. The assembly force parameter is related only to specific cable and loads applied along it and not to the whole analysis model of the structure.

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