Gravity loads deflection issue

[Anonymous]

Attached is a modular building 6 Storeys high . The frames consist essentially of channels with joists in between . The model has been analysed for plain DL & LL only. 

I dont seem to understand why deflections increase once i duplicate the stories from level 1 to level 6 ?

Its all a steel portal frame essentially in action.- 

The deflections at top are going up to 37 mm while same storey at lower levels is around 25 mm. 

 

[Rafacascudo]

the graphic result shows the global resultant displacement. To have individual local bar deflection ,only through View/Tables

[Krzysztof_Wasik · Accepted solution]

Hi @Anonymous 

As far as I can see you present model displacement (there is no option for deflection presentation only). In my opinion displacement of top beams is bigger due to column vertical deformation (column shortening). Beams displacement (for corresponding beams) should increase on each (higher) level.

[Anonymous]

Thanks for the reply, appreciate it! Is there a way in ROBOT to disable this? The reason being all these stories are modular prefabricated . 

I expect same deflections at each floor even after being stacked.

[Anonymous]

thanks for the reply! I am essentially looking to compare deflections at each storey .

[Krzysztof_Wasik · Accepted solution]

Hi @Anonymous 

Column shortening will not give such big differences in deflection (so I missed main effect- column shortening has very small influence on deflections). I can see only your structure screenshot but symmetrically supported middle levels (1) , have similar displacement (at least those marked in scr1). Not symmetrically supported levels first one and the last one (2) have different displacement than the middle segments.

Probably differences will be reduced when you will use pinned column connections between levels. See pinned connection influence on simplified model displacement.

[Anonymous]

Thanks for explaining ! I think pinning the columns would actually help controlling these deflections as we go up the storeys.

Just to clarify all storeys are symmetrical with absolutely no change in layouts .

[Anonymous]

Hi , I did pin all the columns but the deflections go crazy .

The method i used is:

1. Select columns of each storey except the base.

2.Assign pin releases through Geometry > releases option.

I am new to ROBOT interface . Am i missing something on this?

[Krzysztof_Wasik]

Hi @Anonymous 

You probably defined too many releases. Try to define them at the bottom nodes of each segment columns only.