Offset length of beam in axis while taking for full self weight of beam along length of beam

[skellyRSA2023]

Hi, for a horizontal concrete beam supported on a vertical concrete column using a concrete corbel. I wanted to offset the beam to model the eccentricities of the beam supported on the column. Hence for this situation i have just used the offset command and offset the beam in the local x axis (along the beam length) by 350mm (ux = 350mm beginning and end ux = -350mm). This seems to work fine to show how the eccentricities affect the column moments top and bottom of the column, i.e moment applied to column would beam end reaction * eccentricity. However this all works fine for an applied load to the beam but the self weight of the beam is reduced based on the offset? For instance say I have 1m x 1m concrete simply supported beam 10m long and reduced. Self weight being 25kN/m. The end reaction of the self weight of beam is 10m x 25kN/m/2 = 125kN in reality, however in robot this reduces the beam self weight based on the eccentricity/offset applied, thus the end reaction for the self weight is 116.25kN not 125kN. I.e. robot is only taking for the self weight of a beam of 9.3m long not 10m. This may sound trivial but is there a way to offset the beam as discussed above but still allow for the full length if beam on the column in relation to self weight. Any thoughts or comments would be appreciated. 

S.  

[Rafacascudo · Accepted solution]

That's the way it is  ,and not only the SW is affected but also the stiffness of the members.

The workaround would be deleting the auto-generated SW record from the load table and creating custom SW entries " for selected members " on the Load types dialog window on the SW tab.

In the example you cited ,the factor would be 1/0,93

[skellyRSA2023]

Rafael, 

Thank you for the prompt reply. I think i would rather just take the self weight load as it is with the offset, as to just all self weights of beams based on offset length when you have many different column and corbel length would be to complicated and asking for trouble. As it doesn't affect the loading information very much but does seem strange that there is not an option to include the self weight area of the beam over the offset length, especially considering it still allows for the offset area when a Imposed UDL on the beam is applied. when you refer to stiffnesses etc. see below. i have modelled a simple beam column and slab frame and applied a 20kN/m2 live load in the direction of the 8m span as shown. beams are simple supported. the 2nd frame has offset applied to all beams of 350mm, hence span is taken as 7.3m rather than 8m. however on this basis i would have thought the bending moment in beam for live load would be either 532.9kNm or 640kNm for a 8m span, however it is shown at 584kNm? is there something i am missing here? could you maybe give me your opinion on it. i have also attached the simple model. 

S. 

[Rafacascudo · Accepted solution]

Cladding load distribution will also consider only the offset span which is 7,3m . So , if you look at View/Display/Loads/ and mark "Forces generated automatically" , you will see that the beam is loaded with a 87,67kN/m to compensate for the missing 700mm.

Then QL^2/8 will give the 584kN.m moment

[skellyRSA2023]

Rafael, 

i see so from what i can make out, 1. If the load is applied from a floor plate or a cladding i.e. accumulated load to a member then the total accumulated line load on beam from floor area would be applied to the central non-offset beam length.section. (Beam length - offset sections). 2. If a load such as a UDL is applied directly to a member then it is just based on the UDL applied over the length of the section (minus the offset sections at beam ends). The reason i have asked was basically to create an unbraced frame (cantilevered type columns) and try to obtain the correct column moment distributions. However thinking about i now, it would be best to create two models, the first model without the offsets just your stand and model which i would obtain my axial loads at base level and along with all other forces, then make a duplicate model file and apply the offsets to the beam members and then just obtain the column moments due to eccentricities from this model. 

Thanks for all your help. Appreciated.👍

s.