Structural system options for large dome

[hoshang]

Hi
Please find the link below:

https://www.screencast.com/t/ho2aV9zaOwO

The structure is reinforced concrete columns, beams and slabs.
My thought is using columns with bracket on top for carrying the large dome (12.5m diameter). My second thought would be using composite structure.
What are your thoughts?
Your help is highly appreciated.

 

[hoshang]

Hi
Kootk, Ron247, dhengr, HotRod10, others
Are there any thoughts

 

[BridgeSmith]

I got nothin', except one tidbit from one of my structural design classes regarding a geodesic dome structure for an arena at my university - wood beams would perform better in a fire than steel, since the timbers were more stable against buckling at the temperature likely to be experienced in a fire in the building.

 

[dhengr]

Hoshang:
I think you mean 12.5m radius, or 25m dia., don’t you? And, it consists of reinforced concrete columns, beams and slabs which are all below the spring line elevation of the dome. I would think in terms of a ring beam at that elevation, which acts primarily as a tension ring and as a continuous beam on top of and btwn. the columns. The dome is built atop this ring beam, and there is probably some advantage to try to make the column spacing as equal as possible. Then, the dome can be structured a number of different ways; as a thin shell, as a shell with curved beam ribs from the columns to the top, etc. Look for a couple good structural design text books on plates and shells, and thin shells, and study them for general ideas. Talk with contractors who have done this type of work, and might be involved in this project, for their ideas, and to know what they can physically do in the way of various framing systems, and their equipment and experience.

 

[hoshang]

And, it consists of reinforced concrete columns, beams and slabs which are all below the spring line elevation of the dome. I would think in terms of a ring beam at that elevation, which acts primarily as a tension ring and as a continuous beam on top of and btwn. the columns. The dome is built atop this ring beam, and there is probably some advantage to try to make the column spacing as equal as possible.

Thanks
Yes, it consists of reinforced columns, beams and slabs which are all below the spring line elevation of the dome.
I know that a tension ring is needed as a continuous beam on top of and between the columns. My concern is with respect to the columns which will be offset from the tension ring. Please check the attached link in the original post, for which I suggested using brackets on top of columns.

 

[dhengr]

Hoshang:
I don’t know what the eccentricity btwn. the columns and the tension ring is, you don’t show that at all well. Maybe you can shape the column artistically/architecturally to provide your bracket, to accommodate that eccentricity, and/or have the column leaning in some amount, bottom to top, so its axis matches the reaction vector from the dome rib. That is, the thrust and the vertical reaction being some inclined reaction vector. Furthermore, the tension ring can be wider to accomplish some of this. But, that will induce torsion in the tension ring, or a large top bending moment in the column or some combination of the two. Maybe the dome ribs should just continue down to the foundations, and replace those particular columns, to more fully express the dome shape. Then, the rest of the structure, the four corners and the vestibule areas, can be a more standard structural system. Playing around with some preliminary analysis models should help you determine what might be practical/possible.

 

[CANPRO]

What are the architectural finishes? That might have an impact on how you build the dome.

I'm primarily a steel guy, so my first thought was how to do this in steel. See sketch below. The plan would be to span across the dome with (2) identical curved trusses - each of these trusses would support (2) smaller curved trusses (all curved trusses shown in green). If the dome is symmetrical, all of the infill between trusses would be identical. Fill in the corners will horizontally curved beams.

This option might not work based on architectural restrictions - but it would allow you to pre-fab the dome off-site. And erection of the steel structure would be much easier/safer than forming a concrete dome.

 

[hoshang]

Maybe you can shape the column artistically/architecturally to provide your bracket, to accommodate that eccentricity,

I'm not aware of bracket size allowed by ACI code (I mean how much the size of the bracket would be with respect to the size of the column).

Furthermore, the tension ring can be wider to accomplish some of this. But, that will induce torsion in the tension ring, or a large top bending moment in the column or some combination of the two.

Thanks for this suggestion.

 

[hoshang]

Hi all

How about using corbels?

 

[dhengr]

Hoshang:
Read my posts for a more complete/full meaning and with a little engineering imagination (read btwn. the lines a little, we are just brain-storming at this stage after all), and answer the questions so we get a better understanding of what you are trying to do. Show us a cross section through the bldg., with enough detail, proper proportions, sizes, dimensions, etc. so we can see what you think you are going to do. I have no idea what you think a bracket is, and I don’t think you are going to find a code paragraph which tells you what to do. The column and its top corbel (bracket?) could be an up-side-down ‘L’ shaped column, with some reasonably proportioned eccentricity (e = the length of the horiz. leg of the ‘L’ shape) as long as you have enough cross section and can get enough rebar in there to accommodate the loads, moments, shears, etc. And, the tension ring ties everything together, column to column. Alternatively, the inner shape of the column could just be a continuation of the arched shape of a dome rib, right down to the foundation, with the actual dome stopping at the tension ring elevation. This would bring the rib loads down to the foundation in a more direct load path and primarily as compression loads.

 

[hoshang]

The column and its top corbel (bracket?) could be an up-side-down ‘L’ shaped column, with some reasonably proportioned eccentricity (e = the length of the horiz. leg of the ‘L’ shape) as long as you have enough cross section and can get enough rebar in there to accommodate the loads, moments, shears, etc.
Thanks.
In my OP my thought was using STEEL BRACKETS. By corbels I meant using CONCRETE CORBELS.
How much proportioned eccentricity is reasonable for corbels?

 

[KootK]

Concrete corbels should work fine although;

1) They'll work better if the column faces are oriented tangentially to the dome tension ring and;

2) It would seem a lot more elegant and robust to land your tension ring over top of your columns somehow.

3) I feel like circular columns centered beneath a ring beam wider than the columns, is going to feel right for this.

All parts of this structure are imagined to be CIP concrete, right?

 

[hoshang]

3) I feel like circular columns centered beneath a ring beam wider than the columns, is going to feel right for this.

Thanks
I hope this could solve the case.

All parts of this structure are imagined to be CIP concrete, right?

If CIP concrete alone can solve the case, it would be preferred than using composite structure.