MOST EFFECTIVE CONCRETE HINGE
Hinges are provided to have little resistance to rotation with a mechanism to transmit safely the thrust and shear forces that comes from the member to be supported. In the analysis of hinged structures it is assumed that the bending moment at the hinge is zero. This can be achieved in providing entirely free to rotate condition. Such ideal hinges cannot be constructed, since friction or other inevitable restraining factors cannot be avoided.
Practically, it is aimed to ensure that the flexibility of the hinge be considerably greater than that of any other portion of the structure of which it is a part. This done to have negligible errors as a very small moment in the hinge is occurred as compared to the moments in the structure proper.
The use of hinges is not restricted to arches and equally useful in rigid frames, bridges as well as in buildings preferably for long-span single-story frames.
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| Mesnager Hinge:A Reinforced Concrete Hinge |
The most satisfactory hinges present in use are Mesnager hinge (developed by French engineer Mesnager). For members that do not produce very large thrust, this is the ideal one. This ensures greater freedom of rotation.
In order to obtain maximum flexibility in a Mesnager hinge, it has been recommended that the hinge opening h should at least be equal to the concrete thickness t. A value h=1.3t is recommended by some. However, hinges with small opening have been used successfully.For the same purpose of maximum flexibility, the crossed steel bars should not be too thick and short. On the other hand, if their diameter were too small in relation to their length, they would be likely to buckle. For this reason the slenderness ration L/r of the hinge bars should be between the limits of 20 and 40, L being the length of the inclined bar between concrete faces (i.e., h/cos Ѳ), and r the radius of gyration of the bar(i.e.,
D/4 for the round bars of the diameter D). The length of the
embedment of the hinge bars on either side of the hinge should be at least equal to the prescribed of dowels connecting Columns to footings.
D/4 for the round bars of the diameter D). The length of the
embedment of the hinge bars on either side of the hinge should be at least equal to the prescribed of dowels connecting Columns to footings.