PGSplice Symmetric Analysis Results

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CSnee
PGSplice Symmetric Analysis Results
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Rick-

I removed the supports and things seem to be progressing well. I did notice a scenario where the program is crashing and was wondering if you could provide insight.

When I do an analysis and review the graphs my things seem ok. However, when I create a detailed report for "Moments, Shears, Stresses" the program instantly crashes. It seems like this step works during others Analysis runs. Is it hanging up on how I have my model? Would this affect the output?

Thanks

Rick Brice
Symmetric Results

For some reason the axial restraints on Span 2 are not being properly applied. Axial stress due to creep, shrinkage, and relaxation are not developing in Span 2 and this leads to the difference is stress.

However, most precast girder systems of this type don't have axial restraints at the abutments. If you change the boundary conditions at Abut 1 and 3 from Hinge to Roller, the axial restraint will be removed and axial forces will not develop due to creep, shrinkage, and relaxation. The symmetric results you are expecting will then result.

CSnee
Symmetric Results

Thanks again Rick,
I am also finding that the Service I stresses differ in my model from one interval to the next when no changes in loading occur, at least any changes that I am aware of. I took the same model as earlier and removed the applied point loads and expected that the Service I stresses from interval 10 to interval 13 to be the same. That is essentially just a time step where only Pre-tension losses occur. However, I found that the Service I stresses changed. The results of the Service I loads are just a function of applied loads, correct?

Thanks again for any assistance,

Christopher

Rick Brice
Symmetric Results

You can expect incremental stresses to occur during time-steps. These incremental stresses are due to creep and shrinkage of the concrete, and relaxation of the strands and tendons. The incremental change in force in strands and tendons are typically referred to as the pretension losses.

Creep, shrinkage, and relaxation cause a redistribution of the internal forces resulting in a change in stress in the girder concrete. Additionally, secondary forces due to creep, shrinkage, and relaxation develop when girder segments are restrained axially and restrained from end rotations.

Review the moment diagraphs for creep, shrinkage, and relaxation for time-step analysis intervals. You'll see the incremental forces. Also review the Time-Step Details Report to see how internal forces are redistributed and boundary condition restraints cause secondary effects.

This presentation should also help.
https://www.eiseverywhere.com/file_uploads/c1f1f833c7ff4c27d7f0f631b0c65...

Rick Brice
Symmetric Results

I've been looking at your model a little more closely and at first glance, in Analysis Intervals 10-14, it appears that your girder segments are not restrained at the intermediate piers. Thus, secondary effects due to creep, shrinkage, and relaxation should not happen.

However, upon closer inspection I see that the segments are supported at Pier 2 by both the pier and erection towers. Even though these are simple supports, they create a force couple which creates a rotational restraining moment. This is easily seen by looking at the shear diagram for Creep. This is the cause of the secondary effects.

You might consider removing the temporary erection towers from your model. Change the Pier 2 connection geometry so that the girder segments are supported at the correct location.

CSnee
Symmetric Results

Rick-

I removed the supports and things seem to be progressing well. I did notice a scenario where the program is crashing and was wondering if you could provide insight.

When I do an analysis and review the graphs my things seem ok. However, when I create a detailed report for "Moments, Shears, Stresses" the program instantly crashes. It seems like this step works during others Analysis runs. Is it hanging up on how I have my model? Would this affect the output?

Thanks

Rick Brice
I've created Details Reports

I've created Details Reports with the "Moment, Shears and Reactions" chapter and the "Stresses" chapter. I'm not getting any crashes.

I'm not sure exactly what steps you are taking to get a crash. Do you have a custom report?

Generally, the crashes have to due to the program improperly accessing memory. The analysis result should be fine.

Please provide more details on what steps you are taking just before the crash.

CSnee
Symmetric Results

I click on Reports-->Details Report-->Moment, Shears, Reaction (Checked Only).

That is when it runs for a second and says something about building model, then crashes. I am able to generate most of the others, haven't tried all of them.

You are able to get it to work fine though?

Rick Brice
I'm not experiencing any

I'm not experiencing any crashes. I'm using the latest version (BridgeLink 1.1.3 which has PGSplice 3.1.3). It looks like you are using PGSplice 3.1.2.

Try updating the software

CSnee
Symmetric Results

I'm trying to understand the Pier 2 connection I should consider. I not understanding the difference between the "Integral Closure Joint" and the "Continuous Closure Joint". I figured integral would prevent rotation at the cap and cause frame action in the bent. The inputs for this selection are the same as for "Continuous Closure Joint" though and the "Bearing Offset" input has me a bit confused as I will not have bearings. Does this geometry result in cap width?
Any guidance to help me understand how the program considers those two options would be appreciated.

Thanks for all the help,

Christopher

Rick Brice
Pier Connections

Integral/Continuous Closure Joints at a pier models two precast segments being joined at the pier with a cast in place joint. This is contrasted by a single segment that is supported by the pier and is continuous over the pier.

If your pier is modeled as an idealized support...
1) Integral completely restrains the support so there is no rotation
2) Continuous makes the segments continuous over the support, but has not rotational connection to the support.

If your pier is modeled as a physical support...
1) Integral makes a full moment connection between each span and the pier.
2) Continuous makes the girder continuous over the pier, but there is no moment connection with the pier.

The bearing locations define where the segments are supported prior to closure joint being cast and attaining enough strength to change the structural system from a series of independent precast segments to a continuous girder.

If your pier is modeled as a physical support, the bearing locations can be used in determining the cap width if the "Compute" options are used.

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