Anchor

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Masonry anchor
Wall anchor on the gable side of a brick building in Stralsund
Removed old wall anchor with long iron band
Wall anchor in ornamental design

In the construction industry, an anchor is a component for the tensile-safe connection (anchoring) of components. Anchors are mainly made of steel, but can also be made of wood, reinforced or prestressed concrete or other tensile materials.

Anchors in civil engineering and geotechnical engineering are described under Anchors (geotechnical engineering) .

Wall anchor for stiffening walls

A wall anchor is a metal part in a wall or wall that mainly absorbs tensile forces from components that adjoin the wall and is therefore also called tie rods .

The actual anchor usually consists of a round or flat iron or a metal plate. This anchor is either mortared in a wall joint or it is visible on the side of the wall that is opposite the component to be anchored.

A further flat iron, a bolt, a rod iron or a threaded rod is usually used to connect the anchor rail to the component to be anchored.

Traditionally, the wooden beam ceilings and the roof structure of a building were connected to the masonry with beam anchors or head anchors in order to stiffen it if there were insufficient stabilizing transverse walls.

Often the outer end of the historical flat iron was forged into an eyelet, the eye. An anchor pin, which was built into the wall or attached to the brickwork outside, was inserted through this eyelet. A flat iron with a compression in the middle that prevented it from falling through the eyelet could serve as the anchor pin.

The anchor pins of the wall anchors visible on the facade were often artfully forged into decorative anchors on more elaborate buildings or designed as double pins to form a cross anchor . Occasionally they were shaped as numbers and letters that reveal the year of construction and the builder (with his initials ) or they were decorated with forged ornaments or rosettes .

Wall anchors have been known since ancient times and were used until the 20th century, for example to prevent a facade from tipping over from the building. Today freestanding walls by can ring beam or a post and beam system more resistant to bending of reinforced concrete, so that fewer connections to the structure of the building are needed than before.

Tie rods for arches and vaults

St-Philibert , Tournus , tie rods in the upper front church

Tie rods , tension straps or anchor beams are used to receive the thrust action of arches and vaults. Tie rods were also installed to temporarily secure vaults and then removed after all of the stiffening walls had been completed and the mortar had hardened (demonstrated in Chartres Cathedral and Westminster Abbey ). In other buildings, the tie rods to secure the vaults were left under construction. This was particularly common in brick buildings. Wooden beams were also used as tie rods in combination with flat iron and iron pins (see wall anchors).

The anchor beam of a roof truss secures the longitudinal walls against the shear of the roof rafters by connecting the two rafters (the rafter ) to form a force-fit triangle, the roof truss . In a purlin roof , the foot purlins on which the rafters rest are usually connected by the ceiling joists.

Gable anchor

If a gable wall is not secured against tilting by transverse walls, it must be connected with gable anchors in the collar beam position or the central and ridge purlins of the roof structure. Since the joist layer runs parallel to the gable, the gable anchor should be connected to at least two other joists in addition to the joist. The roof structure itself is stiffened in the longitudinal direction by headbands or wind panes .

Ring anchor

A ring anchor is a ring-shaped closed component made of wood, iron or reinforced concrete, which is intended to prevent the enclosed components from falling apart. In masonry construction, a ring anchor is usually embedded in the masonry in all outer walls below the ceiling level. Its actual shape therefore corresponds to the contour of the building and only actually describes a circular ring in domed buildings. Especially in the case of domes and cloister vaults, the (vault) thrust introduced into the surrounding walls can most easily be absorbed by a ring anchor. If ring anchors are assembled from individual components, they must be connected to one another in a tensile manner.

Historical examples

Ring anchor on the Carolingian octagon of Aachen Cathedral , which was subsequently attached to secure the outer walls against the shear forces of the dome

A famous example of such a construction is the dome of the Florence Cathedral . The same iron ring anchors can already be found on the Carolingian dome of Aachen Cathedral, probably from the time it was built (around 800). The shear forces of the vaults and roof trusses occurring at the choir polygons of Gothic churches can also be neutralized by ring anchors. This is especially necessary when the walls are weakened in their resistance by large glass surfaces, as has been the case since the High Gothic. Examples can be found in the choirs of the cathedral in Cologne and Aachen . Finally, the walls rising to great heights must also be secured with ring anchors in tower buildings, even in buildings with a square floor plan, but especially in octagonal towers with pointed spiers that exert diagonal forces. Prominent examples are the tower of the Freiburg Minster with several ring anchor systems and other similarly constructed examples (spiers of the Magdeburg Cathedral ). Often, ring anchors are also added in the monument preservation building activity to retrofit the building or installed as additional security when reconstructing historical stone domes, for example in the Dresden Frauenkirche . Ring anchors are also used to absorb the thrust from roof structures.

In conventionally built houses (stone on stone), the ring anchor consists of reinforcement bars that are cast into concrete to protect against corrosion. Ring anchors are used, for example, at the head of masonry walls, in buildings with more than two storeys and walls with many large wall openings and lengths of over 18 meters, if the subsoil conditions require it. Here, too, they ensure the pane effect of the wall by forming a tie in the masonry . The ring anchor is usually designed as a closed polygon , i. H. all around the building , either in the slab edge as reinforcement in the slab , or z. B. as an inserted sheet metal strip in masonry walls, hence the name "ring" anchor. The function of the ring anchors in structures without shear-resistant ceiling panels (e.g. with wooden beam ceilings) can also be performed by the ring beams, which then have to be dimensioned separately .

Strand anchor

Strand anchors are used in rock construction and in slope stabilization. They generally consist of a wire rope with seven strands (single cores) made of high-tensile steel . They are inserted into a borehole andfixedwith cement mortar or synthetic resin . The outer end is clamped at the mouth of the borehole with clamping devices and fixed with wedges and anchor plates. Alternatively, a rod anchor can be used.

Sheet pile anchors

Sheet pile wall anchors are used to anchor permanent or temporary (less than 2 years) sheet pile wall structures . Corrosion protection is important for permanent anchors. The anchors can be used horizontally as a "dead man" construction with an anchor wall or inclined as so-called grouted anchors. The anchor material in horizontally anchored structures is usually a round steel bar made of structural steel (S355). In the case of so-called inclined anchoring ( injection pile ), GEWI steel can also be used as an alternative .

Air layer anchor

Air-layer anchors serve to anchor the outer wall in double-shell outer walls and are now usually made of stainless steel. In the past, galvanized or simple steel was also used, or some bricks were walled across to bridge the air layer.

literature

Web links

Commons : Anchor  - collection of images, videos and audio files

Individual evidence

  1. Maren Lüpnitz: The medieval ring beam in the choir clerestory windows of Cologne Cathedral. In: Kölner Domblatt 62.1997, pp. 65–84. Dorothee Hugot: The renovation of the medieval ring anchor system in the choir hall by master builder Dr.-Ing. Leo Hugot and the associated opening of the two medieval windows. In: Reports of the Karlsverein for the restoration of the Aachen Cathedral , 1984, pp. 1–22.