topic Re: Section properties tab doesn't appear in Structural Bridge Design Forum

Section properties tab doesn't appear

Anonymous — Thu, 04 Jun 2020 02:15:59 GMT

Hi,

I have modeled a single span half joint bridge. Since I am only interested in the reaction at the support therefore I am using Design section to assign section properties not Beam Design. Furthermore Beam Design section can't be used as the section changes as it approaches the supports. (at least that's what I think)

The issue here is that the structure section properties window doesn't seems to appear when I want to assign SS4 4- Edge Section, hence I can't change the section reference axis or click OK to finish selecting my member. ( model attached)

The other question that I have is, since this is a box section bridge , can I still use grillage and I wont have any issues with the transverse load distribution? or do I have to change it to FE model so that the slab is interconnect at multiple points to top flange of the box beam ?

Many Thanks

Salman

Re: Section properties tab doesn't appear

dave_geeves — Thu, 04 Jun 2020 11:57:40 GMT

Hi,

I have downloaded your model and had a quick look. I am not absolutely sure what you mean by the "Section Properties Tab does not appear" but I do experience a problem in displaying the section shape in the graphics window when assigning the section to the structure - so I assume that this is the problem you are experiencing. If not, please reply to this post with more description and possibly a screen capture to show the exact problem.

So, if it is the graphics problem I seemed to correct it by assigning the section (without it appearing in the graphics window) and then using the 3D elements view to see that the section is assigned correctly. When I then went back to the section assignment the graphics seemed to be there then. Hopefully the software developers will see this post and look to see what the issue is.

I don't understand the reason that you are not using a design beam rather than a section as they are intended to have changing sections along the span length - maybe I have misunderstood your comments.

With regard to your question about using a grillage for a box beam deck then you are quite right in questioning the suitability especially with regards to the transverse distribution of load. The section you have chosen is often used with solid infill between the boxes, together with the insitu slab, and with this type of construction the deck behaves more like a voided slab - so a grillage is fine with the transverse members having the properties of a top and bottom flange. If there is only a top slab acting transversely then a grillage becomes more difficult to represent the behaviour. However, it is still possible to use a grillage with some careful modelling techniques. One of these techniques is to introduce longitudinal rows of joints and members along the lines of the webs of the boxes, The members along these rows will have a nominal section (say 10mmx10mm) properties but the transvers beams will now have alternate single top slap/combined top and bottom slab.

I hope this has helped but please let me know how you get on. If this has answered your query then please mark my reply as a solution so that others may benefit.

Kind regards

Dave geeves

Re: Section properties tab doesn't appear

Anonymous — Thu, 04 Jun 2020 19:02:07 GMT

Hi Dave,

Thanks you for your prompt reply.

The first screenshot shows that when "SP2-2 Intermediate" is selected the "Structure Properties" window appears, However when "SP1 1-Edge Section" or "SP4-Edge Section" is selected the Structure properties window doesn't appear. Therefore it make is difficult to alter the section reference axis relative to centroid or the origin. (refer to screen shot 2) (I have also reattached the SBD model)

With regards to beam design over the design section, it is possible for the section to be changed as it approaches the support in the beam design. The section change is shown in the screenshot below.

If I am only interested in the maximum reaction as the support and prefer to use the section design would it cause any issue in the analysis ?( I.e issue in transverse distribution- because when the box section is defined the slab is not included )

This section have solid infill between the boxes and insitu slab. How can I assign the section properties to the transverse member, do I have to manually calculated the transverse torsional properties and halve it or is there away the SBD will can calculate section properties including the torsion.

Many thanks

Regards

salman

When SP2:2- Intermediate Section is selected , "Structure Properties Section" Window AppearsHowever when "SP1 :1Edge Section and SP5: 4-Edge Section" is selected the Structure Properties Window does'nt appear

Typical Bridge Cross sectionThe transverse torsional properties should be based on the top and bottom slab . The transverse section properties only should be based on the top slab only

The section is hollow box sectionThe section is becames solid as it approaches the supportThe section becames half thickness.( ie becames half joint)

Re: Section properties tab doesn't appear

dave_geeves — Fri, 05 Jun 2020 16:34:55 GMT

Hi,

Thanks for sending more detailed information. I see now what you mean about the section properties form not being visible. I cannot reproduce this problem in the current version (2020) of the program but I notice you are using a 2017 version so it may well have been fixed in later versions. I suspect that the form is being displayed behind the graphics window - which you have made full screen. Normally you can bring the section properties form to the front by just selecting the section again in the navigation window but obviously this does not work for you. Have you tried restoring the graphics window to a smaller size to see if you can get focus that way?

I also see now the details of the deck you are trying to model and it now makes sense. I would think that the grillage you have created is an acceptable way to proceed as the solid infill between the beams makes the deck more like a voided slab, even though the transvers reinforcement in the infill doesn't appear to be continuous. The torsion properties will be quite important to get the correct distribution of load to the supports and as you say the torsion stiffness should be calculated based upon only the top slab and bottom slab acting together (in both transverse and longitudinal directions) halved in each direction. These will have to be added manually using Advanced Beam Properties in the Section Property assignment navigation window, and this has been shown to be a good approximation to the global torsion behaviour.

Using design sections for your section properties is perfectly acceptable, especially as you are not using the results for beam design (or assessment), but the sections should have the insitu slab and infill components added to them (as separate components with different material properties) so that the composite section properties for bending are used. You can also create the transverse properties as design section (a different one for each different width) with two components, one for the top slab the other for the bottom slab/infill. Again the torsions will need modification.

I hope this has helped but please let me know how you got on and if this provides a solution for you please mark my post as a solution so that others may benefit. Thanks

Kind regards

Dave Geeves

Re: Section properties tab doesn't appear

Anonymous — Fri, 05 Jun 2020 21:43:10 GMT

Hi Dave,

Thank you very much.

I just would like to inform you that the form is not hidden behind the graphics window.

Many thanks, You have been always very helpful.

regards

Salman

Re: Section properties tab doesn't appear

Anonymous — Tue, 09 Jun 2020 15:36:54 GMT

Hi Dave,

Hope you can help me with these queries

If we are modelling composite section (i.e. steel beam and concrete deck) for the main longitudinal member and use the continuous slab to define the transverse properties, is correct for me to say that SBD will calculate automatically the longitudinal bending stiffness using the transformed composite section and the transverse bending stiffness is calculated using the slab thickness?
Is the torsion stiffness also calculated by SBD in the longitudinal direction using full torsional stiffness of the beam plus half torsional stiffness of the slab ( Jlong = JBeam + Jslab/2 ) and the torsional stiffness in the transverse direction would be just from the half of the torsional stiffness of the slab. Is all the above is done automatically without the users input other than assigning the geometry properties?
In the bridge that I am modelling, will SBD calculate the longitudinal bending stiffness of the section using the box section together with the slab and will it calculate the transverse bending based on the top slab only? If not, how should I adjust it manually? (For your information between the box sections there are slabs at the top and bottom, however at cantilever section and on top corbel there is only slab on the top.) I have used the “continuous slab” in SBD to assign slab in locations where I have only top slab. ( model attached)
With regards to the torsional stiffness will SBD calculate it automatically for the longitudinal member (i.e. in longitudinal direction SBD will calculate torsion stiffness using full torsional stiffness of the box section plus half torsional stiffness of the slab ( Jlong = JBeam + Jslab/2 )
In the transverse direction, I have some locations where there is slab on the top and other locations, I have slab both at top and bottom. How do I address the issue of torsion? And where the is only slab on the top and is assigned using continuous slab, will SBD automatic will halve it?
How do I change the section gross properties to the transformed section properties?
How do I assign the self-weight of the section after transforming the section as this will reduce the cross-section area?

Many thanks

Salman

Figure 1 :Shows composite section to be assigned to the longitudinal memberFigure 2: Transverse Section properties to be assigned using continuous slabFigure 3: Shows that the transverse member is assigned as with 2 nos of slab ( top and bottom)Figure 4: Shows main box section beamFigure 5: Shows location where there is only slab at the top ( ie at the corbel and the cantilever /edge beams)Figure 6: Why the "type : gross section is greyed-out and cant be changed to transformed section.