3 Hinged Reinforced Concrete Arch
3 Hinged Reinforced Concrete Arch
(OP)
Good day, please I'm trying to design an open spandrel concrete arch of 12.8m span and 2.456m rise supporting a 588KN concentrated load at the crown. I have analyzed the structure to obtain
- Reaction = 820.59KN
- Horizontal Thrust = 766.12KN
- Max. Bending Moment = 342KNm2






RE: 3 Hinged Reinforced Concrete Arch
Dik
RE: 3 Hinged Reinforced Concrete Arch
Keep in mind that that your stirrups will need to restrain your concave side bars from straightening out and popping out of the concrete.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: 3 Hinged Reinforced Concrete Arch
RE: 3 Hinged Reinforced Concrete Arch
RE: 3 Hinged Reinforced Concrete Arch
If that is the case, then H = (294*6.4 + 526*6.4/2)/2.456 = 1451kN, considerably more than 766.12kN which you calculated. In fact, the horizontal reaction from the 588kN concentrated load alone would be PL/4h = 588*12.8/(4*2.456) = 766.12kN but the vertical reaction is only 294kN at each support.
Please clarify.
BA
RE: 3 Hinged Reinforced Concrete Arch
The horizontal thrust at the support = 766.12KN.
The last sentence in your post is actually the calculation.
Please help me out if I am missing something.
RE: 3 Hinged Reinforced Concrete Arch
If the arch is curved, its dead load will tend to reduce the bending moment under gravity load, but there may be other factors to be considered such as unbraced length and roof loading or perhaps wind and seismic loading. Is an "open spandrel arch" laterally braced between the two reactions? If so, where? Does it carry additional gravity load beside self weight? What concrete cross section are you considering? Shear, bending moment, axial force, buckling resistance and your calculation of reinforcement are all dependent on these factors.
How are you planning to resist the horizontal reaction of 766kN? A steel tie rod? I think you need to provide a little more information if you require a helpful response to your question.
BA
RE: 3 Hinged Reinforced Concrete Arch
A method for analyzing and designing major arches (made of reinforced concrete) is presented in the reference:
'Design of Concrete Structures 8th Ed'., by: George Winter & Arthur H. Nilson, New York: McGraw-Hill, 1972. pp. 431-464.
The method is based on classic engineering mechanics, and once the controlling forces have been obtained the cross section can be designed (as a short column) for those forces. One thing to note in this method is: there are no adjustments made in the load factors for the fact that the steel will have to be permanently bent for placement in the arch. It is highly recommended that the allowable stress of the steel (if you are using working stress design; which I have used for arches in the past.....even though it may be passe at this point) be reduced if the steel is permanently bent. AISI uses allowable load factors of 0.6 (for bending) and 0.55 (for compression). It should be sufficient (if not excessive) to superimpose these load factors upon the allowable stress of the steel to obtain a safe allowable stress for design.
The ties that are provided (since the cross section is designed as a column), may have to resist additional forces (other than shear) depending on the connection type to the support. (I.e. bursting & thrust forces.)
Like the others, I'm not sure why you would put in a hinge at the peak of the arch. Seems to me like you would just have it continue on.