topic Re: Horizontal Rigid Links in Robot Structural Analysis Forum

Horizontal Rigid Links

crasmussenGKDV6 — Wed, 25 Oct 2017 18:49:32 GMT

I have custom aluminum beams that are connected to each other to form a solid pad for helicopters to land. I am trying to figure out how to spread the point loads for the helicopter across the whole pad. Can anyone help?

Thanks

Re: Horizontal Rigid Links

Rafacascudo — Wed, 25 Oct 2017 20:00:54 GMT

How is this connection between the beams? Where are the supports? Point loads?
Do you already have a model? Can you send it?

Re: Horizontal Rigid Links

Artur.Kosakowski — Thu, 26 Oct 2017 08:40:20 GMT

Hi @crasmussenGKDV6

First thing is to mesh the panel in case you used the cladding

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.

Re: Horizontal Rigid Links

crasmussenGKDV6 — Thu, 26 Oct 2017 11:01:28 GMT

Here is my model

Re: Horizontal Rigid Links

crasmussenGKDV6 — Thu, 26 Oct 2017 12:05:21 GMT

I am just trying to get the stress in the top layer of custom beams (helipad landing area). The structural steel is being designed by others so I am not worried about that steel only the landing area beams.

Re: Horizontal Rigid Links

Rafacascudo — Thu, 26 Oct 2017 15:55:43 GMT

All your rigid links are N/A . Where did they come from??

I think you should try loading just one pad beam with the helicopter point loads. The span is short and if the pad beam alone can withstand the full load ,then the pad is verified.

But before that , you need to correct the rigidlinks on the Top(pad) area. The nodes of the pad beam are as master to the main beams below. It shall be the contrary. The main beams nodes have to be the master ones.

If not ,you get the below moment diagrams for the pad beams(DL1).

Changing the master nodes to the main beam nodes and also releasing the 3 rotations on the rigid links , you get the typical moment diagram for a continuous beam.

Will this work for you??

PS the model you sent didn´t have the helicopter loads

Re: Horizontal Rigid Links

crasmussenGKDV6 — Thu, 26 Oct 2017 18:55:56 GMT

I am confused. The rigid links come from when I go to edit>correct drawing model. I links everything together except for the top beams connecting horizontally to each other. When they are built they are bolted together and sealed together so they cannot move or allow any liquids through them. I am trying to figure out how to prove that the loading will transfer between the beams.

Re: Horizontal Rigid Links

crasmussenGKDV6 — Thu, 26 Oct 2017 19:20:29 GMT

Also, their is a dead load for the helicopter of 11,000 lbs at two point loads 8 ft apart and a live load with the same configuration but the load is 27,500 lbs at 8 ft apart.

Re: Horizontal Rigid Links

Rafacascudo — Thu, 26 Oct 2017 21:21:40 GMT

I Never used "correct drawing model" . It links the bars that cross each other but are in different levels. But it isn´t able to set who is the master node or to evaluate if the connection is fully rigid or not .

For the horizontal link , I did 2 experiments. I took 5 consecutive pad beams and linked them to the main beams below the way I explained on my previous post.

Then I divided 3 central spans bar in 5 pieces. From the central pad beam nodes(masters) to the others I set a Uz only rigid link. Applied a 5tf point load on midspan .Better explained on the picture below.

So it was one central pad beam "commanding" the other 4 pad beams.

2nd experiment was linking the beams on pairs and applying the same 5tf load on central pad beam midspan. Also an Uz only link. Links have to have offset because a same node cannot belong to 2 distinct rigid links. I made it 2cm apart.

You can notice that total sum of bending moments for the 5 beams is around 1,30 tf.m. But the distribution among the beams is quite different.

I would choose the 2nd option(on pairs) as more realistic. But still a little hard to say if it is completely correct without knowing the conection details.

Probably a more exact solution would be modelling the pad beam as an orthotropic strip panel with adequate linear releases on the neighbour edges