Time History Analysis results
By your picture ,it seems you are using bar offsets on the main girders to model them on their real position . In these cases , the bigger part of the additional moment is "hidden" on the couple formed by the girders and the slab normal forces . A smaller part is resisted by the slab itself .
If you want only the girder resisting almost all the load applied , delete the bar offsets .A small part of the acting forces will still be resisted by your slab.
If you want ALL the loads to be resisted only by the 2 girders ,then use cladding instead of a shell slab and make sure the concentrated loads are applied directly on the girder bars . Claddings can be very bad for distributing concentrated loads or distributed contour loads . Use them only when you have uniform distributed load on the whole cladding area.
Rafael Medeiros
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can you send the model? Zip and attach it
Rafael Medeiros
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You don´t need to send the file with THA results.
"Save as" "Robot - without results" with a different name for the file ( Bridge 1_NR ) .
File will be a lot smaller.
Rafael Medeiros
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Accepted solution
I am not an expert on dynamic analysis but I noticed a few things in your model.
1- THA uses modal analysis in its method to achive dynamic responses . They can be greater than those found in regular static analysis for the same loading. Your modal analysis only considers the generated self-weight as contributing mass. You should also include all the dead loads "attached " to the bridge . You can do that converting the corresponding dead load case to mass using the below tab on analysis type dialog window
2- The 10 modes you set to be found(and considered in THA) mobilized only around 55% of the bridge mass in the vertical direction. It is desirable that you have over 90% of mass to have reliable results. Also , there are 2 separate structures on your model. Avoid that when you have modal and THA analyses to be done.
3- So I deleted the isolated beam structure . Also deleted all the beam offsets. I Set the modal analysis to find 50 modes only in the Z direction(reached 96,29% of the mass contribution) . I also refined the mesh to 50cm size but that didn´t make a much difference comparing to 100cm size you used. Higher beam moment was at 4,75s .
For the static case of a 3205,8 Kn concentrated load at midspan ,overall bending modent found would be 40072,5 Kn.m which is exactly found on a test load case . Moments of 19865,19Kn.m for each beam and 342,17 for the slab which sums 40072,55Kn.m . See below
For the THA component at 4,75s(highest beam bending moment) Sum of the moments reach 39252,82Kn.m (2 x 19466,32 + 320,18) which is only 2% below the test static load case. see below
With 100 modes 98,05% of the mass is contributing and Sum of moments go up to 40006,19 kn.m .
Are you following any recomendations for your THA analysis ?
I cannot see how a single variable with time point load on midspan can simulate the passing of a train.
Test model without results attached
Rafael Medeiros
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