Steel Bridge - Can someone check my model please?

[ddavies.231016]

I have recently ventured into the world of Robot and would like some pointers. I have modeled a steel bridge using CHS sections which has an imposed live load of 5kN/m2 and the self weight of the steel. The results however do not seem right, apparently the maximum bending moment is 40 something kNm which seems very low. I am guessing that either my loading is wrong or the model is somehow. Can anybody shed some light on it for me?

Couple of questions:

1. When I loaded my model in via autocad as a DXF the connection points all had nodes. Do I have to specify that these are pinned supports or does Robot assume they are fixed automatically?

2. To imposed the 5kN/m2 UDL on the structure I created a polygon contour and then made it into a panel with a thickness of 8mm S275 steel. Will this automatically distribute the planar load onto the adjoining members? I have a feeling this is where the error is??

As I mentioned, this is all new to me so any pointers/tips would be appreciated3D_Grillage 2.zip

Many thanks

Dave

[teixeirahnuno421232]

Could you please post your model?

[pawel.pulak]

I have recently ventured into the world of Robot and would like some pointers. I have modeled a steel bridge using CHS sections which has an imposed live load of 5kN/m2 and the self weight of the steel. The results however do not seem right, apparently the maximum bending moment is 40 something kNm which seems very low. I am guessing that either my loading is wrong or the model is somehow. Can anybody shed some light on it for me?

Couple of questions:

1. When I loaded my model in via autocad as a DXF the connection points all had nodes. Do I have to specify that these are pinned supports or does Robot assume they are fixed automatically?

2. To imposed the 5kN/m2 UDL on the structure I created a polygon contour and then made it into a panel with a thickness of 8mm S275 steel. Will this automatically distribute the planar load onto the adjoining members? I have a feeling this is where the error is??

Dave,
explanations to your questions:
1. If the structure type is not 2D or 3D truss then by default all connections of bars are fixed. If some of connections should be pinned then releases should be defined for such bars or some bars should be declared as "truss bars"

2. For the panels you defined you have assigned "Shell" calculation model. It means that FE mesh was generated on them with the stiffness of finite elements corresponding to 8mm S275 steel deck. It means it means the load was not only distributed to adjoining members but the composite action of deck and these members was considered.
If you only want to distribute the load from the deck to supporting members not considering the stiffness of the deck itself then you can use different panel calculation model - like "Deck slab (two-way)" shown below with the tributary areas:
bridge1.png
It is also possible to use the panel calculation model with one-way distribution of loads (to for instance secondary beam).

I am not sure how and where have you checked the values of moments. If you mean the total value in the midspan of the bridge, then in case of arch bridge it should be the sum considering not only the moments in members but also the pairs of normal forces in the deck and in arcs. See some screen captures below.
bridge3.png bridge2.png
If you mean something else please give more details.
I have also attached your model with the panel calculation model replaced as above.

Regards,

[jclcereno433416]

Tried looking at your model and it does not pose any errors for me. the results seems desirable