topic Re: Comparing Section Properties and Modeling Integral Full Bridge With Section Eccentricity in Structural Bridge Design Forum

Comparing Section Properties and Modeling Integral Full Bridge With Section Eccentricity

maj.rentung — Wed, 07 Oct 2020 14:14:04 GMT

Hi,

a) Comparing Design Sections and Design Beams Module Section Properties

Usually, i always use values for section properties from “Design Sections” for my grillage model, and I think those are correct values because the values are easily proved by literature/books etc.

However, when using “Design Beams” module, i figure out the section properties wont give the same values as “Design Sections”. From my understanding , the section properties value should be same regardless what method we use. Im attaching both SBD files for your kind review.

b) Modeling Integral Full Bridge With Section Eccentricity

I found it is quite tricky to modeled fully integral bridge with eccentricity using SBD compared to other software like RM Bridge/Midas. With RM Bridge/Midas, I can set the section origin at top and can use rigid link to intergrade structure element.

Can you look into my model and advise whether the way i modeled my Fully Integral Bridge with section eccentricity is correct. Also attached the cad file for reference.

Your assistance is much appreciated

Thanks

Re: Comparing Section Properties and Modeling Integral Full Bridge With Section Eccentricity

dave_geeves — Wed, 07 Oct 2020 17:47:00 GMT

Hi,

Thanks for attaching your data files - it makes it so much easier to comment on.

I will look at this tomorrow (8/102020) as it is quite late here in the UK at the moment. I'll be in touch soon.

Kind regards

Dave Geeves

Re: Comparing Section Properties and Modeling Integral Full Bridge With Section Eccentricity

dave_geeves — Thu, 08 Oct 2020 18:25:54 GMT

Hi,

Question a)

I am looking at your file "Integral Bridge (2 Span) - As SUPERSUITE.sst" to look at the comparison of section properties. The design sections of the U12 composite girder have been created by defining the outer boundary of the complete composite section and then the inner boundary of the void. This may have been done by accident by using the join feature on the graphics toolbar. This means that the whole section is just one material (the grade 55 concrete) so will be essentially gross properties as there is only one material

When you have defined the design beams you have correctly defined the two separate components with different material properties so these will be transformed to the grade 55 concrete.

I regenerated the sections as transformed sections ant the two sets of section properties then agreed (to within 5 sig figures.

Question b)

With regards to using the member eccentricities to model the variation of the depth of the neutral axis between beam members then I believe that for this type of deck it is quite important to do this, especially with respect to transverse bending behaviour and torsional restraint as this is then modelled more accurately. You seem to have applied member eccentricities (Automatically using the origin as the member assignment reference) to only one model which the "Staged construction with eccentricities" model. I am very impressed with how you have created this model with the staged construction and with a quick inspection of the model, especially graphically,

it all seems to be ok. My only real comment is that I don't believe that the staged loading has been done the same way that I would do it and without detailed checks I'm not sure that it would give the same results. You seem to have applied the cumulative load at each stage together with the removal of the previous stage loading. It is really intended that the individual staged loading is applied at each appropriate stage and the program accumulates the effects from the analysis at each stage. This means you don't remove the previous stage loading. However, you do need to apply some form of loading at each stage, which may not be obvious at the last stage, so I normally apply a nominal point load at a supported joint (0.1kN) just to satisfy this condition.

I hope this has helped and if your query has been answered please mark my reply as a solution so that others may benefit. Thanks

Kind regards

Dave Geeves

Re: Comparing Section Properties and Modeling Integral Full Bridge With Section Eccentricity

dave_geeves — Wed, 14 Oct 2020 14:59:14 GMT

Hi,

I just wanted to check that my reply to your query at the beginning of this thread had answered your questions and if not, to find what other information you require.

I look forward to hearing from you

Kind regards

Dave Geeves