Belfry
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A bell cage is a traditionally elaborate carpentry structure for one or more free-swinging bells . The beams used are mainly made of oak , more rarely of coniferous wood. Since the middle of the 19th century, bell chairs have also been made of steel profile beams, especially for large bells. The required stability and the necessary space for the swinging movement of the bell must be observed.
construction
The bell hangs in the belfry on two supports with half bearings . There it is attached to its crown with iron bands on a supporting axis, the so-called bell yoke , which is wooden even in steel structures . The yoke lies with its ends on the support bearings. The bell cage must absorb the forces that occur when the bells swing and pass them on to the surrounding building.
Although the bars of a wooden belfry are mortised to one another, angles and tie rods are also used, which are ideally made of V2A steel to protect against rust, or at least are hot-dip galvanized .
In the case of bricked bell towers, the bell sound emits through sound openings to the outside.
Crank
The load on the chair and the building (tower) can be reduced by cranking the yoke. The bell does not swing around its crown, but around a lower axis closer to its center of gravity. However, this reduces the sound dynamics of the bells, so that when bells are hung cranked, one often has to accept severe sound losses.
Installation
Due to the irregular back and forth movement of the heavy bells and the associated horizontal forces, a church tower is stimulated to flexural vibrations. In the event of resonance , these vibrations can cause severe damage to the tower and the vault of the nave over time, also to severe cracks in the masonry and even to the tower becoming detached from the nave. Therefore, when installing the belfry in a bell tower, make sure that the chair does not come into contact with or even attach to the outer walls of the tower and ideally stands on its own foundation . If this is not possible, movements of the church tower from the vertical of 10 to 20 millimeters (but not for church towers made of masonry) are not uncommon.
Counter pendulum
With the additional installation of a counter pendulum system in the bell cage, these movements can be reduced to a measurable 0.2 to 0.5 millimeters, regardless of the age of the tower. Here, steel plates with exactly the bell weight are movably mounted to an existing bell. The bell and counterweights are connected to one another with belts or steel cables via large drive wheels. If the bell swings to the left, the counter pendulum moves to the right to the same extent. This minimizes the horizontal vibrations of the bell cage when the bell rings and their transmission to the masonry. However, it should be noted that the vertical forces are doubled, which can lead to static impairment in the long term, especially with wooden towers. The position of the counter pendulum is extremely important for long-term conservation. If they are to leave the bell cage free from constrained loads, they must be attached in the same horizontal plane as the bells. If they are installed above or below the ringing level, as is often the case for reasons of space, considerable additional forces are introduced into the bell cage, which must be checked for their long-term harmlessness to the construction.
Tyrolean bell chair
In the Austrian Brixental with its side valleys, in the Leukental , Alpbachtal and Zillertal , but also in the neighboring Pinzgau , the so-called Tyrolean bell chair can be found on many house roofs. While the bells hung here, with their pitch different from farm to farm, used to have the function of calling farmers, servants and maids to eat in the fields and in the forest, the small bell stalls with a round or square pointed roof are mostly used today only as an ornament of farms, country houses or garden sheds and shape the Tyrolean landscape.
See also
literature
- Böttcher, Detlef: Renovation of wood and stone structures: Findings, assessment, measures, conversions , Beuth Verlag, Berlin 2008, ISBN 978-3-410-21635-3
- Böttcher, Detlef: Preservation and reconstruction of historical structures - wood and stone structures , Ernst & Sohn Verlag, Berlin 2000, ISBN 978-3-433-01774-6
Web links
Individual evidence
- ↑ Sebastian Wamsiedler Bell Expert Advice & Research (accessed on April 5, 2014)