topic Re: rsa 2020 moving loads in Robot Structural Analysis Forum

rsa 2020 moving loads

Anonymous — Mon, 04 Nov 2019 08:37:56 GMT

Hi,

I am trying to get my head round designing some moving loads over a RC cover, and I am getting some results that I am struggling to understand.

First of all, I am not sure why I am seeing the bending moment diagram under self-weight hogging instead of sagging.

Secondly, I am not sure why under the moving load cases it is not recognising the loads by no giving reactions and obviously no bending moments. However I can see the loads the applied.

Could you please advise and help with the modelling issues if any? I have attached the model.

Kind Regards,

Miguel

Re: rsa 2020 moving loads

Anonymous — Mon, 04 Nov 2019 09:40:48 GMT

I would also like to query about the panel calculation model. How is it possible that a one way slab as in the picture is not yielding moments under selfweight (450 mm thick slab).

Kind Regards,

Miguel

Re: rsa 2020 moving loads

Krzysztof_Wasik — Mon, 04 Nov 2019 10:31:11 GMT

Hi @Anonymous

While presenting bending moments (using intersection tool but as well for map presentation) choose MXX bending moment from Detailed tab instead of Reduced moment from Complex tab.

Reduced moment is calculated according to vonMises formula and has always positive value

see Complex results

Mxx selection gives expected sagging moment

Moving loads issue

While moving loads analysis I get non-zero results for both

complex moving load cases (2,3)

and moving loads positions defined as separate load cases (cases 15 to 40)

You can see non-zero values in result tables as well (see FZ reactions).

To answer your question about 0 results for moving load cases I need more explanation. In model I have downloaded from forum results seem to be calculated.

Re: rsa 2020 moving loads

Anonymous — Mon, 04 Nov 2019 10:42:44 GMT

Krzysztof, thank you for the quick response.

That's good to know, it was my understanding to use the tab complex to analyse stresses and bending moments. This is the first time I found an inverted shape of the BMD.

Regarding the moving loads, the real issue is not the non-zero results, but the expectation of finding much larger bending moments under axle loads of 200 kN and 120 kN as they move along/across the slab, as you can see in the load cases load representation these loads appear but the results do not seem to match.

Kind Regards,

Miguel

Re: rsa 2020 moving loads

Krzysztof_Wasik — Mon, 04 Nov 2019 10:49:32 GMT

Hi @Anonymous

After your model calculation and reduced Moment map display I am obtaining the following view.

I am not able to obtain results distribution presented in your screenshot

So please send me your file saved with incorrect moment distribution on the screen (as in your screenshot) for detailed verification.

I have additional suggestion to modify your model:

once you have supports pinned in RX direction and linear releases on panel 3 edges your model is instable in X direction. It can be observed looking at displacements after any FX load definition. Please update your supports to block RX rotation.
you have breaking forces in load cases 4 and 5 acting in Y direction while your supports in UY are elastic with small elasticity. It results in large displacements in UY direction (more than 2000 mm). I would update support parameters in UY direction as well.

If I have managed to answer your questions please accept my answer on forum as solution.

Re: rsa 2020 moving loads

Krzysztof_Wasik — Mon, 04 Nov 2019 11:04:05 GMT

Hi @Anonymous

Maybe your applied loads are smaller than expected

Actually you apply pressure 100 or 60 kN/m2 on area of 20x20cm which gives 4 kN or 2,4 kN of effective force in each load area.

So your maximal force from vehicle is 12.80 kN. If you would like to get 320 kN load from vehicle you should increase pressure 25 times

Re: rsa 2020 moving loads

Anonymous — Mon, 04 Nov 2019 11:24:52 GMT

Ok.

So, the second part of the query was that if I modeled the slab as one-way distribution, I was obtaining hardly any bending moment at all. I have removed the linear releases and still not getting satisfactory results. I am particularly interested in this query as it affects other models I have designed. I have attached the model.

Regarding the pressures from the moving loads, I now realise my mistake, it should have been modelled as concentrated forces. Thank you for clarifying this.

Re: rsa 2020 moving loads

Krzysztof_Wasik — Mon, 04 Nov 2019 11:55:08 GMT

Hi @Anonymous

One way deck slab calculation model defines load distribution method

In case of this model load is not applied to deck slab but is applied to supporting elements (in your cases to walls)

This calculation model was developed to simulate planar loads (for instance from wind) distribution on bar elements (purlins) not to calculate load distribution on bars manually.

In my opinion (when you want to calculate bending in deck slab) shall calculation model should be used.

To simulate one-way plate behavior (not load distribution) , orthotropic plate thickness can be used.

with reduced stiffness (Young modulus) in Y direction

Then Myy bending moment values will be almost 0.

See attached file