Is there thrust in a reinforced concrete arch?
Is there thrust in a reinforced concrete arch?
(OP)
I am designing a reinforced concrete arch spanning 20 feet over a small creek. The creek is not 20 feet wide but the owner wants to be conservative.
I was wondering whether it is correct to assume that since I am designing for aashto loading of H20-44 shears and moments, do I need to worry about horizontal forces at the ends of the concrete arch? I am supporting the ends on 12 inch wide retaining walls with wing walls at each end. I would think that since the arch is designed to handle the moments and shears from the loading, I do not have any thrust. In other words, the arch is not handling the "thrust" like a true arch design, but rather it is designed as a reinforced concrete beam.
Is my assumption correct? Any help is greatly appreciated. Oh, and any recommendations for books on arch design would be nice too. Thanks in advance.
I was wondering whether it is correct to assume that since I am designing for aashto loading of H20-44 shears and moments, do I need to worry about horizontal forces at the ends of the concrete arch? I am supporting the ends on 12 inch wide retaining walls with wing walls at each end. I would think that since the arch is designed to handle the moments and shears from the loading, I do not have any thrust. In other words, the arch is not handling the "thrust" like a true arch design, but rather it is designed as a reinforced concrete beam.
Is my assumption correct? Any help is greatly appreciated. Oh, and any recommendations for books on arch design would be nice too. Thanks in advance.






RE: Is there thrust in a reinforced concrete arch?
RE: Is there thrust in a reinforced concrete arch?
RE: Is there thrust in a reinforced concrete arch?
RE: Is there thrust in a reinforced concrete arch?
You can design it as a curved beam and you will see lesser reactions at the springing level as compared to those of arch reactions. The distinction of a true arch and a beam is important here. While beam takes up all the load due to internal moments, arch will just transfer the whole load to support by compressive forces only (no moments), thus a thinner section.
RE: Is there thrust in a reinforced concrete arch?
If you put a sliding support at one end, the structure will definitely act as a beam as there can be no horizontal forces.
As an arch you would have to take account of the horizontal movement in the retaining walls due to the horizontal loading from the arch.
StephenA
RE: Is there thrust in a reinforced concrete arch?
RE: Is there thrust in a reinforced concrete arch?
RE: Is there thrust in a reinforced concrete arch?
To comment on KarlT's comment. The arch/ beam will act the way it wants to and a very curved beam will flex outwards under loading.
StephenA
RE: Is there thrust in a reinforced concrete arch?
RE: Is there thrust in a reinforced concrete arch?
The rise on this arch is about 24" with a span of 20'. Is there a "rule of thumb" on when one should consider large horizontal forces depending on the rise to span ratio?
I don't anticipate much shrinkage since the span is at about 20' and the minimum thickness at the peak is 12". Is this assumption wrong?
RE: Is there thrust in a reinforced concrete arch?
RE: Is there thrust in a reinforced concrete arch?
RE: Is there thrust in a reinforced concrete arch?
Technically, there is a difference when you call something a curved beam or an arch. Imagine you place a C shaped beam 90 degree rotated on a flat lubricated surface. Will it stand or flatten out? It depends on whether its rigid enough to take its own load or whatever load is applied to it on top.
antimatter,
You do not have to provide a real roller to achieve the sliding support. You can keep one end fixed and other end released by introducing a joint, tar felt or steel plate sliding supports. However, do not trust me over internet and go ahead with my advice as I don't understand the exact application. You have to act on your own and also design the beam correctly so that it acts in accordance with the assumptions.
RE: Is there thrust in a reinforced concrete arch?
For 20' span you will not need any kind of bearings. Provide pinned connections at both supports (you can use reinforced concrete joints), and let the wall of your abutment flex. You will have to compensate the movement of the structure with pressure relief joints at the ends of approach slabs.
RE: Is there thrust in a reinforced concrete arch?