Corbel arch

As Kragbogen (English corbel arch ) or false Arc is in the architecture a design to bridge door or window openings in the masonry. He is regarded as a historical precursor of the real arc. Architecturally it is of no significance nowadays. It is found in old buildings, such as archways of the Maya, as well as the decay of ancient masonry under loss of stones.

While in a real bow only compressive forces occur, the building material of a Kragbogens must also absorb tensile forces. Since the strength of stone against tensile load is low, reach Kragbögen only low spans with large height. They also save a no material but are technically easier to build.

The distinction between true and false bow

When genuine bow ( arch ) the arch stones are arranged radially. When false bow ( Kragbogen ) the arch stones overlapping ( = cantilevered ) are arranged. When real bow is the keystone of the arch remaining stones is clamped under tension. When false arch the keystone is on the other arch blocks without tension.

Construction

In order to bridge distances which exceed the tensile strength of a single stone, ancient cultures put a Kragbogenkonstruktion. Instead of a bar, the tensile forces distributed over several stacked stones. Collared, they reduce the opening up so far until it can be closed by a final beam smaller wingspan. Unlike real arcs are Kragbögen uniformly stable during the construction phase and not rely on a scaffold. However, they need to final stabilization of a higher pressure from above and therefore a solid construction.

Figure 2: In masonry forms after removing the stones a Kragbogen.

Figure 3: The Kragbogen is by streamlining the verge of collapse.

The series of images above shows a wall (Fig. 1), are dissolved out of the three stones. The wall does not crash, but it will fall out three more stones that form a breakthrough in a triangular shape (Fig. 2): In the wall of a Kragbogen has formed. Its load capacity is extremely low, it stabilizes only on the weight of the surrounding rocks. The structure can streamline hardly without it collapses (Fig. 3, the Kragbogen is about to break-in).

In Figure 3, the final stone that bridges the opening is missing. Its function is performed by two stones, which are mutually tilted. They are the simplest form of a simple arc. So this picture shows a Kragbogen that is not completed by a bar, but a small arc.

Examples

The Maya in South America knew no genuine bow. The picture on the right is typical of the construction of door openings. The smoothed walls of the intrados extend at an acute angle up and find their financial statements in a laid flat stone slab. The material that is saved by the release of Stay archway in a wall must be coated to stabilize the Kragbogens in height. It is thus in contrast to the genuine bow saved any material.

Kragbögen can be found as a structural element in pre-historic stone buildings, for example in the Minoan civilization in Crete or in the Nuragern in Sardinia around 1500 BC, see picture on the left. They also arise unintentionally when from damaged masonry stones fall out; the remaining stones hold then by train and compression forces for a time against each other and form a false bow. From the wall in the picture to the right of the door lintel is broken out of wood, with him parts of the masonry. The Kragbogen stabilizes the opening of the ( geringe! ) tensile strength of the mortar. However, the blocks are too small to be held by the weight of the other shape.

Gallery

Kragbogen of Mycenaean " Treasury of Atreus "

Kragbogen the entrance to the royal palace of Ugarit

Arch of Kabah ( 800 )

Arc of Labná ( 800 )

Kragbögen the portals of the Quwwat -ul -Islam mosque in Delhi ( to 1195)

• Arch ( Architecture )