Post-Installed Anchors | All You Need to Know
Post-installed anchors are critical components in modern construction and engineering, providing a reliable means of attaching structural and non-structural elements to existing concrete, masonry, or other base materials. These fasteners are installed after the base material has hardened, making them indispensable for retrofitting, renovation, and repair projects.
Post-installed anchors are versatile and reliable fastening solutions for a wide range of applications. Understanding their types, installation steps, corrosion resistance methods, anchors selection and governing standards is essential for ensuring their safe and effective use.
Applications
Post-installed anchors are used in a wide range of applications, including:
Structural Applications: Connecting steel beams, columns, and plates to concrete or masonry.
Non-Structural Applications: Installing handrails, HVAC equipment, electrical conduits, and signage.
Seismic Retrofitting: Strengthening existing structures to resist seismic forces.
Facade and Cladding Systems: Attaching exterior cladding or curtain walls to buildings.
Industrial and Infrastructure Projects: Securing machinery, pipelines, and bridges.
Types of Anchors
According to ACI 318-19; an Anchor is “A steel element either cast into concrete or post-installed into a hardened concrete member and used to transmit applied loads to the concrete.”, in which a Post-Installed Anchor is “Anchor installed in hardened concrete; adhesive, expansion, screw, and undercut anchors are examples of post-installed anchors.”
Post-installed anchors can be broadly categorized based on their load-transfer mechanism and installation method. The main types include:
Adhesive Anchors
Adhesive anchor is a post-installed anchor, inserted into hardened concrete with an anchor hole diameter not greater than 1.5 times the anchor diameter, that transfers loads to the concrete by bond between the anchor and the adhesive, and bond between the adhesive and the concrete. Anchors are supplied as a two-piece set, containing resin (in capsule or cartridge form) and a steel element. Adhesive anchors minimize the introduction of stresses in the substrate material, due to the absence of expansion forces.
Undercut Anchors
Undercut anchor is a post-installed anchor that develops its tensile strength from the mechanical interlock provided by undercutting of the concrete at the embedded end of the anchor. Undercutting is achieved with a special drill before installing the anchor or alternatively by the anchor itself during its installation.
Torque-Controlled Expansion Anchors
Applied loads are transferred to the substrate via friction between the anchor and the wall of the drilled hole. Friction is the result of expansion force, achieved by applying torque to the bolt or nut, thus drawing a cone component in to an expanding sleeve to create the anchorage.
Displacement Controlled Expansion Anchors
Applied loads are transferred to the substrate via friction between the anchor and the wall of the drilled hole. Friction is the result of expansion force, achieved by displacement of a wedge component, deforming the anchor body and creating the anchorage.
Concrete Screws
Concrete screw is a post-installed threaded, mechanical anchor inserted into hardened concrete that transfers loads to the concrete by engagement of the hardened threads of the screw with the grooves that the threads cut into the sidewall of a predrilled hole during anchor installation.
Installation Procedures
Proper installation is critical for the performance of post-installed anchors. The general installation steps include:
Preparation
Inspect the base material for cracks, voids, or other defects.
Mark the anchor locations according to the design drawings.
Drilling
Use a hammer drill or rotary hammer to create holes of the specified diameter and depth.
Clean the holes thoroughly using a brush, air blower, or vacuum to remove dust and debris.
Anchor Installation
Adhesive Anchors: Inject the adhesive (in capsule or cartridge form) into the hole, insert the anchor rod, and allow the adhesive to cure as per the manufacturer’s instructions.
Mechanical Anchors: Insert the anchor into the hole and tighten using a torque wrench to achieve the required expansion or undercut.
Concrete Screws: Drive the screw into the hole using a power tool or manual wrench.
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Verification
Perform pull-out tests or torque checks to verify the installation quality.
Inspect the installed anchors for proper alignment and load capacity.
Corrosion Resistance
Corrosion is chiefly fueled by the interaction of metal surfaces with moisture, oxygen, and other corrosive substances present in the geological environment. Corrosion resistance is critical for ensuring the long-term performance of post-installed anchors, especially in harsh environments.
Two basic corrosion types must be considered: atmospheric and galvanic corrosion.
Galvanic corrosion may occur when two dissimilar metals are in contact with each other. In the presence of an electrolyte (e.g. water) a galvanic cell is created, causing gradual corrosion of one of the metal elements.
Atmospheric corrosion is caused by the interaction of moisture or chemical compounds from the air with exposed metal. Corrosion rates depend on the concentration of chemical compounds in the air, as well as humidity levels.
Common methods of atmospheric corrosion resistance include:
Zinc plated steel: Offers additional protection against corrosion.
Hot-dip galvanized Steel: Provides a protective zinc coating for moderate environments.
Zinc flake coatings: Provide superior corrosion resistance compared to traditional galvanizing.
Stainless steel: Grades such as A2 (304) and A4 (316) offer excellent corrosion resistance.
According to ISO 12944-2:1998, below table shows the atmospheric corrosion categories differentiated depending on locality, as well as the prevailing conditions.
Anchors Selection
When selecting any anchor for a job, there are many factors to consider. When you install an anchor?into concrete, the goal is that the anchor will fulfill the required specs. To make sure that goal can be achieved, it is important to choose the option that is right for you. Factors to be considered include:
Anchor size: As the diameter?of the anchor increases, so does the load capacity.
Anchor length: The deeper the anchor is installed into the concrete, the higher the?load-bearing power is.?
Edge distance: The minimum allowable distance between the concrete edge and the closest anchor centerline. This is to avoid damage to the concrete during installation, usually given in the product datasheet.
Spacing: The minimum allowable spacings between the anchors. This is to avoid damage to the concrete during installation, measured centerline to centrerline, usually given in the product datasheet.
Concrete class and type: The concrete strength (i.e. grade) and whether it is considered as cracked (cracks may appear under service load no wider than 0,5mm) or non-cracked (no cracking is expected to occur under normal service conditions) concrete.
Loading criteria: The holding capacity of an anchor reduces with vibrating and shocking loads.
Surrounding environment: Invest in a?corrosion-resist option if there is a risk of corrosion occurring.
Main Codes and Standards
The design, testing, and installation of post-installed anchors and screws are governed by several international and regional codes and standards. Key standards include:
International Standards
ISO 898-1: Specifies mechanical properties of fasteners made of carbon steel and alloy steel.
ISO 17081: Provides guidelines for corrosion testing of anchors.
European Standards
EOTA EAD 330232-00-0601: Mechanical Fasteners for Use in Concrete
EOTA EAD 330499-00-0601: Bonded Fasteners for Use in Concrete
EN 1992-4 (Eurocode 2): Design of fastenings for use in concrete.
American Standards
ACI 318: Building Code Requirements for Structural Concrete (Chapter 17 covers anchorage to concrete).
ICC-ES AC193: Acceptance criteria for mechanical anchors in concrete.
ASTM E488: Standard test methods for strength of anchors in concrete.
References
Civil Engineer at INGENIEURGRUPPE BAUEN
3 周Very informative!