{"id":19763,"date":"2025-12-15T14:28:14","date_gmt":"2025-12-15T13:28:14","guid":{"rendered":"https:\/\/www.darda.de\/?page_id=19763"},"modified":"2026-05-19T10:07:02","modified_gmt":"2026-05-19T08:07:02","slug":"anchor","status":"publish","type":"page","link":"https:\/\/www.darda.de\/en\/knowledge\/anchor","title":{"rendered":"Anchor"},"content":{"rendered":"
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Anchors – often also called concrete screws, screw dowels, or concrete screw anchors – are mechanical anchoring elements<\/strong> for fast, secure, and often repeatedly removable fixation in concrete and, with limitations, in dense natural stone. In the context of Darda GmbH they are typically used wherever temporary or permanent anchorage points are needed during concrete demolition and deconstruction<\/a><\/strong>, building gutting and concrete cutting<\/strong>, in rock demolition and tunnel construction<\/a><\/strong>, as well as in natural stone extraction<\/strong>. This includes auxiliary structures and anchorage points for positioning concrete demolition shears<\/em> or for brackets and shoring when working with hydraulic splitters<\/em>. In these applications, defined screw-in depths<\/em> and torque-controlled installation<\/em> enable precise positioning, reliable load transfer, and clean reversibility.<\/p>\n

Definition: What is meant by an anchor?<\/h2>\n

An anchor is an anchoring element screwed into a predrilled hole whose special thread cuts load-bearing thread grooves into the base material during installation. Loads are transferred by positive mechanical interlock directly into the concrete or dense stone. Anchors are usually made of steel (zinc-plated) or stainless steel, are available with various head shapes (hex head, countersunk head, internal thread), and cover tension and shear loads. Characteristic features are rapid installation, the option of removal by unscrewing, and, compared to bonded systems, the minimal curing time – in fact, none is required. Approvals and technical specifications define use in cracked or uncracked concrete, permissible load categories, and, where applicable, fire and seismic performance; this distinguishes screw anchors clearly from expansion and bonded systems.<\/p>\n

Design and operating principle of anchors<\/h2>\n

The load-bearing behavior is based on a cutting, partly saw-tooth-like thread that, when screwed into the predrilled hole, creates a form-fit engagement in the concrete. The screw-in depth<\/em> and the drill diameter<\/em> are central to this: they define the effective thread length and thus the load transfer. Depending on edge distance, member thickness, and concrete strength, the limit states of concrete failure (cone pull-out, edge spalling) and steel failure are designed. In cracked concrete, suitable anchors are used that are rated for crack widths within the approval. Under dynamic actions – for example, vibration excitation from demolition tools – adequate preload and controlled tightening torque are important to minimize embedment relaxation. Hole geometry, surface roughness, and cleanliness further influence performance; oversize or dusty holes reduce thread engagement and capacity.<\/p>\n

Types of anchors and suitable substrates<\/h2>\n

Anchors differ by head shape, material, thread geometry, and approval scope. In practice, three aspects are decisive: base material, corrosion exposure, and installation access. In Darda GmbH applications, concrete substrates dominate; for natural stone, a case-by-case assessment is required. Depending on the fixture, hex heads<\/strong> simplify torque application, countersunk heads<\/strong> allow flush finishes, and internal threads<\/strong> enable exchangeable studs or accessories. Stainless variants are preferred in moist or chemically aggressive environments and for longer exposure durations.<\/p>\n

Concrete and reinforced concrete<\/h3>\n

In uncracked and cracked concrete (e.g., C20\/25 to C50\/60), concrete screws are widely used. They are installed in pre-positioned installation and allow short edge distances and small center-to-center spacing – within the respective approval. For temporary auxiliary structures, such as brackets for positioning concrete demolition shears<\/strong> or anchorage points when working with hydraulic splitters<\/strong>, a removable fastening is often preferred. This is where the anchor plays to its strengths: quick to install, retightenable if needed, and removable with minimal residue. Where fixtures are exposed to moisture or de-icing salts, stainless steel increases durability and reduces maintenance.<\/p>\n

Rock and natural stone<\/h3>\n

In dense natural stone (e.g., granite, basalt), anchors can perform well provided the stone is sufficiently homogeneous and strong. However, variability in material properties is greater than in concrete. Prior to use – for example in rock excavation and tunnel construction<\/em> or natural stone extraction<\/em> – field tests<\/em> and anchor pull-out tests are advisable. In bedded or weathered rock, special caution is required. Alternative anchoring systems are evaluated for critical locations. Drilling technique is adapted to the substrate: reduced impact energy and sharp bits help avoid microcracking and preserve load capacity.<\/p>\n

Planning and design for use in deconstruction and extraction<\/h2>\n

The selection of an anchor depends on load level, load type (tension, shear, combined), substrate, boundary conditions (edge distances, member thickness), environmental influences, and installation conditions. In the Darda GmbH fields of work – whether concrete demolition and special demolition<\/strong> or building gutting and concrete cutting<\/strong> – additional temporary load cases and changing situations must be considered. Where access is limited, installation sequences and tool selection are coordinated to avoid rework and downtime.<\/p>\n