Curved Concrete beam in elevation
Curved Concrete beam in elevation
(OP)
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.
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.






RE: Curved Concrete beam in elevation
Steel beam with timber framed cladding is always cheaper but not as durable, best to check with architect if this is acceptable.
Look up Roarks or similar for a formula on this, it can be designed with no horizontal restraint at the base.
RE: Curved Concrete beam in elevation
RE: Curved Concrete beam in elevation
RE: Curved Concrete beam in elevation
RE: Curved Concrete beam in elevation
Or you could design it as a three hinged arch and pour one half on top of the other, then raise both halves with a couple of cranes and connect all of the hinges.
A three hinged arch is statically determinate and easy to analyze. It requires horizontal reactions at the supports to support gravity load.
BA
RE: Curved Concrete beam in elevation
RE: Curved Concrete beam in elevation
A good reference book is " Reinforced Concrete Designer's Manual" by Reynolds & Steedman. An excellent book.
Lexim
RE: Curved Concrete beam in elevation
RE: Curved Concrete beam in elevation
RE: Curved Concrete beam in elevation
BA
RE: Curved Concrete beam in elevation
RE: Curved Concrete beam in elevation
I assumed from the title of the thread that we were dealing with an arch. The dimensions given, 35' span and 55' curve length seemed to be consistent with a circular arch. If that is not right, the OP should let us know.
It is not possible to help people who do not provide adequate information.
BA
RE: Curved Concrete beam in elevation
RE: Curved Concrete beam in elevation
KOTOR1 are you still there?
RE: Curved Concrete beam in elevation
We just got revised backgrounds from the architect and it seema a lot has changed since I was in Florida. The walls are now revised to ICF walls. The openings size has been increased to 40'(end to end) and now it is a elevated complete semi circular arch supported by 14' tall vertical piers/jambs. Originally, it was about 1' feet short of being a complete semi circle and it was directly supported on the foundation. The curve is in elevation. It looks like this (Elevation View)
/ \
/ \
I ^ I
I I I I
^ - is a semi circle.
The arch is now taking more load since the roof joists are now spaced at 30' (orignally it was 8'). The arch is at a non bearing side of a hip concrete tile roof w/ SIP panels as the roof. The architect wants to use Metwood as the joists. Has any one used this before?
So I can assume it be a straight beam (span = pi/2 * 40). I will look through Roark's book this weekend. I will try to get the other references mentioned also.
RE: Curved Concrete beam in elevation
If you have an end to end dimension 40', the span is 40', not pi/2 * 40. It is a simple beam, although the loading is not likely to be uniform.
Personally, I don't think that is the way to go, but let's not sweat it too much. The architect may change his mind again.
BA
RE: Curved Concrete beam in elevation
So I should design the beam as a simple span of 40'. Isnt the curved length its entire length (half a semi circle)?
RE: Curved Concrete beam in elevation
You can have a beam which undulates up and down, and, if the support is a hinge at one end and a roller at the other, the moment at any point will be precisely the same as a straight beam. That is a fact upon which you can always rely. So the moment at the midspan of your strange shaped beam will be wL2/8 if the load is uniform along the length of the beam. Moreover, that will be the maximum moment in the beam.
If you elect to use a hinge at each end, the structure becomes indeterminate to the first degree and you must consider conditions of compatibility.
If you use a fixed end at each support, the structure becomes indeterminate to the third degree and must be solved by one of the many techniques to which you have no doubt been exposed in your engineering education.
BA
RE: Curved Concrete beam in elevation
BAretired is of course correct in its statement concerning the maximum moment at midspan (oops...at the tip of the arch). However he perhaps didn't fully catch your description with the arch sitting onto two columns: this makes it necessary to consider the arch as pinned-sliding, unless the columns may be made really massive and quite short or you want to embark in calculating the behavior of the complete frame (columns+arch). So, for a vertical load that's uniform on the horizontal projection, the maximum moment is indeed wL2/8, L being the span column to column.
In the first site below you can find calculation sheets for circular arches under Beams -> Curved -> Arches -> Circular -> Pinne-h.slide , with various loading conditions.
prex
http://www.xcalcs.com : Online engineering calculations
http://www.megamag.it : Magnetic brakes for fun rides
http://www.levitans.com : Air bearing pads
RE: Curved Concrete beam in elevation
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.
RE: Curved Concrete beam in elevation
(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
RE: Curved Concrete beam in elevation
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.
RE: Curved Concrete beam in elevation
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
RE: Curved Concrete beam in elevation
RE: Curved Concrete beam in elevation
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.
RE: Curved Concrete beam in elevation