Risa-3D Moving Loads on a Plates

[adycbrown]

I have a large top slab of a large 75'x15' box that I am trying to apply a HS-25 loading using the moving pattern loads. But apparently it requires a member underneath the pattern to follow. Is there a way to apply them to nodes or plates? or maybe a member have zero (or very little) strength. Tired that but unsure if the forces are getting transfered to the plates since the members still give forces in the results. any advise?

 

[JAE]

The way I would do it is to include a very (VERY) weak member in the line of the moving load. This could be a physical member attached to joints along its length.
The member stiffness should be set very small along with its modulus of elasticity E. Use a "general" material property that you invent.

After the analysis check to see what the sheas and moments in the beam are - should be small or negligent.

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[adycbrown]

I tired that but still seems to be high numbers in the members. See attached. The member material is HR7.

 

[JoshPlumSE]

The moving load is applied to the member, then the member transmits those shear forces into the plate elements which support it. So, the member carries the shear between plate joints.

You can check to see if the member picks up the internal plate joints by using the Color Coded plot option for the members and setting the basis for the color coding to "phys segment". That means wherever the member picks up an interior joint, you will see a color change.

Note: If the member isn't picking up your plate element joints, then you might have to move some of the joints so that they line up with the member or re-mesh your plates. Whatever you need to do to get those plate joints to fall in-line with the member.

 

[JAE]

OK - after reading this my statement about the member not taking force is wrong - the member must take force per Josh's post above.



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[adycbrown]

I re-meshed the slab so the member with no material strength and with the moving load was lined up with the mesh. Still saw forces up to 36k. I tried one long member from end to end and also multiple one plate length members end to end. Relatively the same results between the two.

 

[JAE]

But if you beef up the member the forces in the FE mesh should reduce, and if you use a "wet noodle" member the forces in the FE mesh should increase.

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[adycbrown]

Correct and they do, but not enough to be negligent unfortunately. It's hard to over look 30+ kip haha. I just went with doing a lot of different point load cases. Thank you for the help though!