Curved Concrete beam in elevation

[KOTOR1]

I have to design a curved concrete beam in elevation for a retail building. The architect wants it to have a tunnel like feel when entering the building.

The length of the beam in plan is about 35' feet. The curved length of the beam is going to be about 55' long.
Are there any books or code references that I could refer to for concrete curved beams? I am guessing the curved beam would result in a horizontal force at its ends along with the vertical down force. I am having second thoughts about designing the beam, because I think the spans are too big

Would it be much easier,using HSS tubes forming the curve in lieu of the concrete and then infilling w/ wood/steel studs to give the curved appearance.

 

[hokie66]

prex,

It is only an arch if it acts like an arch. The shape does not determine whether it is an arch or a beam. Without horizontal thrust, it is not an arch, but rather a curved beam, as BA has described.

My earlier post erred in stating 55' as the beam span. It is of course 40', again per BA.

 

[BAretired]

I would try to avoid considering the 'arched beam' as a simple span beam because:

(a) the moments are high and will require a large section and lots of reinforcement.
(b) the bottom reinforcement will be curved and will tend to burst out of the concrete unless tied regularly with stirrups.
(c) the deflected shape will push the walls outward at the top.

Using a three-hinged arch with the legs extending down to the floor is better because:

(a) the moments are a fraction of the simple span moment.
(b) the tension reinforcement is on the top and will pull against concrete...no bursting tendency.
(c) the base connection will not move.



BA

 

[kslee1000]

BA:

I like the idea of 3 hinged arch, clean and simple for analysis, also less problem for structure supporting the arch. However, while it is quite easy to provide hinge in steel structure, how to achieve it in reinforced concrete?
Looks like some special device is required. Any experience on that? Just curious.

 

[BAretired]

kslee,

Actually, if it were my choice, I think I would prefer to use either steel or glulam for the arch.

If the architect insists upon concrete, I guess I would elect to cast each half in a precast plant providing steel hardware at all the hinge locations and weld plates where other members connected. Then you are dealing with steel to steel connections in the field.

BA

 

[kslee1000]

For arch structures, the lateral thrust can be taken out by grade beam tying the columns, or just a big mat stretched from one column to the other. The columns will have to be quite large & stiff though.

 

[KOTOR1]

Update:

I just looked at a new section I recieved from the architect today. Good, I am not the only one working on a Saturday.
Basically, the arch projects about 5' from the face of the building (in plan view) to form the tunnel feel. In elevation, the projection itself is also about 5' deep. He has provided me with steel columns to support the "projection". It looks like there are two steel arches one on top of the other (spaced 5' in elevation) and infilled with studs. It seems he wants to use 4x4 tube steel to form these arches. I am not so sure 4x4 tube steel can bent for that radius and it also requires to take the out of plane loading. I will take a look at it.

For the main arch at the building, I was planning to use a rectangular concrete opening (its elevation at the tip of the arch at the top). Then, dropping tube steel tangential to the arch on both sides and infilling with steel studs to give the arch feel. Does that seem feasible?

I will attach a sketch as soon as possible.

 

[hokie66]

Yes, I think we need the architect's elevation to advise you sensibly.