Best Structural System for....?

[HassanZebari]

Hello Colleagues,

What is the best structural system for a two story (10m*15m) auditorium with no columns at the middle?

Edited?

It is a Reinforced Concrete auditoriums

 

[WARose]

You are likely talking about a steel or masonry LFRS with heavy roof trusses.

Something else to consider in the MTO (if the architect didn't) is the cost of acoustic paneling (if necessary). I've seen that sort of thing slip through the cracks before. (I.e. the architect thought it would be on your MTO and vice versa.)

 

[HassanZebari]

Hey WARose,

What about reinforced concrete??

 

[milkshakelake]

@HassanZebari Reinforced concrete needs to be really thick for long spans with no column. 10m isn't a crazy long span, but it doesn't seem economical with concrete. The concrete beams would have to be quite deep and long term deflection is a concern.

Trusses are more cost effective because the top/bottom chords increase the moment of inertia with very little material in the middle. Also saves a lot of 2 story high formwork.

 

[HassanZebari]

Hey milkshakelake,

I haven't seen a multistory truss building? Do you mean steel frame buildings?

 

[milkshakelake]

I'm specifically talking about open web steel trusses, not a steel truss like in a bridge. I've seen plenty of multistory buildings that use open web steel trusses as the floor system. As WARose mentioned, the lateral system could be steel or masonry (or concrete). The total height of a building using open web steel trusses is limited by code to about 5 stories where I practice.

I don't mean a structural steel frame. It could theoretically work though; you'd need about 425mm deep steel beams. Depending where you are and the material/labor costs, it may or may not be more cost effective than cast-in-place concrete. Another option is precast concrete planks but I don't think it would be cost effective for such a small area.

Lastly, another option is long-span decks, like Comslab. But it's highly unlikely that the product is available in your area since you're using the metric system.

Edit: Based on your comments, it seems like you're very set on concrete. If you size the beams properly, it should work. Just be prepared for a lot of formwork and concrete shop drawings because it's 2 stories high. Also use a heavier lateral system due to added seismic weight.

 

[MIStructE_IRE]

I’d probably go with composite cell beams for something like this.

I don’t think I’d give concrete much consideration at that span.

 

[dik]

I'd probably do it in steel with a beam breaking the 15m in two and OWSJ or beams spanning the 7.5m possibly using composite deck and topping. Depending on the FRR required, you can get 2 hours with restrained design using 3"+/- concrete and 3" composite deck that will span 10' (used to be F902 ULC). Only need to fire-spray the beams. Might be able to use W14x22 or something of that ilk.

Dik

 

[Lomarandil]

Another vote for something besides an cast-in-place RC ceiling if possible. Possible, but that span is long and the weight will hurt your lateral design. Everything else can be concrete.

Check for availability of precast prestressed concrete, OWSJs as mentioned before (or cold-formed steel trusses), or at the very least some sort of voided slab system to reduce weight.

What is above this auditorium space? Just a roof, or another story?

----
just call me Lo.

 

[milkshakelake]

Oops, I got the word "truss" stuck in my head. I meant open web steel joist.

 

[dik]

msl: we knew what you meant...

Dik

 

[dik]

Depending on the cladding, the project may be too small for precast...

Dik

 

[Wenzhen_luck]

I think an arc shape just like the base of the Eiffel Tower.

 

[SteynvW]

Also is the second floor flat or is it stepping for the seats?

 

[Wenzhen_luck]

I am not so sure, and you can do some calculation for example use the ansys software, for the material strength and structure etc. then decide the real shape .

 

[BWCSA]

Depends on what your criteria for 'best' structural system' are (price, construction time, special performance requirements ...). What's economical depends on what kind of building products are available in your market (and what kind of deals the general contractors have with these companies).

Where I operate prestressed and prefabricated concrete floor elements (prestressed hollow cores, TT-slabs) are kind of the default for all floors spanning between 7 and 15 meters with an ordinary live load and 'normal' (non-special) criteria with regards to deflection and vibrations. Hard to beat on both price and on-site construction time, but again this all depends on availability in your region/country. 10 meters is a modest span for a prestressed floor element, so could definitely work even if an auditorium would probably have a somewhat higher live load then, for example, an office building.

 

[KootK]

In some markets, concrete is the right answer almost regardless of the question being asked. Perhaps Iraq is such a market. With the spans being contemplated, and the right beam depths, you could certainly make a simple, reinforced concrete beam and slab system work. And that might be a nice, sturdy system to carry the stuff that is often suspended from auditorium ceilings. If the technologies are viable in your market, you might also consider:

1) Post-tensioned concrete beams.

2) Old school waffle slabs.

 

[HassanZebari]

Thanks everybody for your answers and suggestions.

The second floor is also flat. The main material used in my area is concrete so i was wondering if solid slab (slab with beams) or two way ribbed slab(waffle)are good options?

 

[r13]

Waffle slab is a good idea, in conjunction with a stiff edge beam to ensure two way action.

 

[Lomarandil]

Yes, then I'd go with the waffle slab. As KootK mentions with his "old-school" reference, rather than trying to locate metal pan forms, it may be easier to source a local material (often a hollow clay brick) that can form your voids and reduce the weight. These can be broken out or left in place after the pour.

----
just call me Lo.