Moving Load optimization issues

Question:

Hi I am trying to use the moving load optimization tool but I am having problems.

When I define my optimization lane, lane width, anal, lane offset, margin, etc correctly and run the analysis,

I am finding my truck positions are not following these rules (vehicle distance is okay, but margin, lane width is not obeyed..)

Can you advise how I could correctly model this ? I would like to run two trucks on two lanes with each vehcile 600mm away from (margin) centerline of the roadway.


Thanks.


Answer:

Hello ,

Kindly refer the image below from our online help manual (Link).


Judging from the provided input, margin entered in lane is 600mm and in moving load optimization case, it is 1200mm.  If it is intended to run the vehicle with maximum distance of 600mm, then kindly provide margin in lane as 300mm and in moving load optimization case as 600mm.
Do let us know if further assistance would be required.

Regards,
Nandeep
Technical Manager, MIDAS


Margin and minimum vehicle distances are two different things..

I would like to keep margin at 600mm but have minimum distance between two vehicles at 1200mm.

So for example, for a 8.2m carriageway, I would like to have two 4.2m lanes with each vehicle 600 mm from its lane boundary, so that they keep a distance (margin) from the centerline of the bridge. Does Midas allow users to do that?

It seems when I run my model, either the Lane 1 and Lane 2 boundaries are overlapping as opposed to the diagram below or the lane boundary is extending past the carriageway.


My colleagues are having the same issues..


Thanks for your help in advance





Hello,

So, to summarize, you want the vehicle to move only in 4.2m width and do not want vehicle of lane 1 to more over lane 2 par.  So, the distance between the vehicles could be more than 1.2m as well.  In that case, I wouldn't recommend using moving load optimization.  Because in this case, the governing factor for distance between 2 vehicles is just margin and minimum transverse distance.  If it is intended to just move vehicle in a lane, then I'd recommend using the Transverse lane optimization option in traffic lane definition.  Definition of one such lane is shown below.  Other lane could be defined with eccentricity of 2.1m.

Kindly let us know if further assistance would be required.

Regards,
Nandeep
Technical Manager, MIDAS


Perfect this makes sense..

One final question while we are here: the moving load result gives you maximum envelope values and I saw in a video that there is a function to 'view by max',

but I can not find this tool. Can you advise how I can find this tool? I want to get load demands on other elements at one truck location rather than envelope values

Thanks





Hello,

To obtain the concurrent forces for moving load, first of all this option would have to be activated from under the Analysis control as shown in the image below.
Once this is done, just analyse the model.  To check the concurrent forces, go to Results. Result Tables> Beam> Forces.  Select the relevant load cases and click OK.  The values should be tabulated.  Once done, just right click on the table and the 'View By Max' should be visible.  Just select the relevant component and that's it!
Kindly let us know if further assistance would be required.

Regards,
Nandeep
Technical Manager, MIDAS


is this same thing as 'view by max item' ? I only have that function in my table results..

This function only reorganizes my values, instead of recalculating load demands for other elements for a given element.. if that makes sense..





Hello,

Sorry for misunderstanding the question.  Thats correct.  This will give you the concurrent forces of the selected element.  If it is required to check the forces in other elements, the only way to do it is by use of moving load tracer.  A process of how this could be done for checking uplift is shown below.

Activate the maximum displacement for the generated moving load
cases, to view the uplift. To know the corresponding vehicle position, Moving Load Tracer option can be used.


Go to Results > Deformations > ‘Deformed Shape…’



1. For the moving load combinations (max case) check the deformed shape in the direction of gravity (DZ) at the support locations.
2. Positive value of DZ implies there is an uplift at that support.
Alternatively, same could be checked by verifying the
Reactions at supports for moving load combination (min case).




To track vehicle position causing the maximum uplift at the particular node, Invoke
moving load tracer from

Results > Moving Load > Moving Trace



1. In the moving load tracer menu, select the appropriate moving load case (max)
2. Enter the Key node, node with the maximum uplift.

Follow the same steps for reactions as well, except that
only support nodes could be selected as Key node.

NOTE: It is recommended to check the uplift results for
moving load combinations along with permanent load.

Clicking on ‘Write Min/Max Load to File’ option, generates a .mct file. Running the .mct file using, Tools > MCT command shell, the said vehicle position is added as a static load case to existing static load cases.

Files:
2016_FAQ_Vol.1_image (1)[1].jpg
2016_FAQ_Vol.1_image (1)[2].jpg
2016_FAQ_Vol.1_image (1)[3].jpg
Vol.1_51_How to verify for the uplift due to moving load_And how to obtain the corresponding vehicle positioning.pdf


Regards,
Nandeep
Technical Manager, MIDAS


Thanks for your help..

I have one last question = is there a way to output 'total moment/shear on bridge' then? not total moment on individual girders



Hello,

Its apleasure to help.
In this case though, what the software can give is the magnitudes of moment and shear.  Not the moment/shear ratio.  Kindly let us know if further assistance would be required.

Regards,
Nandeep
Technical Manager, MIDAS
Creation date: 10/17/2018 9:55 PM (dklee@midasit.com)      Updated: 10/18/2018 7:26 AM (dklee@midasit.com)
Files   
Concrete Box girder -700-no skew-16m.mcb
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midas error.PNG