Post installed anchors

Definition

Post installed anchors are anchors that are installed into predrilled holes in existing concrete or masonry structures. They are important in structural connections and should be appropriately selected and installed as per the manufacturer’s specifications. These anchors can be used in various applications e.g. attaching fixtures or supporting loads.

The two types of primary post installed anchors are:

• mechanical anchors, which expand to grip the substrate material, figure 1, and
• chemical anchors, which rely on bonding agents, figure 2.

Specifying the appropriate type of anchor for the specific application and material is key. This will ensure the safety and integrity of the structure.

Safety Issues

Incorrectly specified or incorrectly installed post-installed anchors pose significant health and safety risks. The most immediate risk is structural failure, which can lead to the collapse of elements they support, potentially causing serious injuries or fatalities.

The hazard of structural failure related to the use of chemical and mechanical post installed anchors can be caused by:

• not having the anchor designed and specified by a competent person;
• carrying out changes on site without consulting the competent person, such as, a design engineer);
• not installing anchors as specified by the design engineer and/or manufacturer’s specifications; and
• incorrect preparation of drilled holes prior to chemical anchor placement.

Where post installed anchors are installed incorrectly, the risk of structural failure is increased.

Specifications and selection

The specification and selection of post installed anchors relies on:

• the basic type of fixing, such as stud, bolt or, reinforcing bars;
• the substrate material the anchor is fixed to, including cracked or uncracked concrete, masonry or blockwork,;
• the substrate material’s strength, and thickness;
• the environment; and
• the capacity requirements to best meet design load cases.

In structural applications the specification of post installed anchors should only be done by qualified structural design engineers or other suitably skilled persons in the design of anchors.

Structural applications include, but are not limited to:

• fixings for any structural steelwork or timber;
• fixings for cranes bases;
• fixings for elements that transfer or support loads (dead, live and wind loads etc).;
• fixings for guard railing; and
• anchorage systems for fall arrest systems.

In all other applications guidance can be sought by the post installed anchor manufacture or supplier.

When specifying a post installed anchor, the suitably qualified person, such as a structural design engineer, should provide the following information:

• anchor diameter and grade;
• type of anchor fixing (Mechanical or Chemical);
• substrate Material strength requirements;
• minimum anchor embedment into the concrete;
• minimum edge distances of anchors; and
• minimum and maximum spacing of anchors, where multiple anchors are used.

The manufacturer’s installation instructions should be consulted for a complete list of items to be included in the specification of post installed anchors.

Installation

Proper installation of post installed anchors is important for overall effectiveness and safety. Installation should comply with the manufacturer's specifications. This includes, but is not limited to:

• precise drilling;
• thorough cleaning of holes before inserting chemical anchors;
• thorough inspection of any defects in the substrate following drilling and cleaning of holes; and
• ensuring adherence to specified dimensions and depths.

Once installed, testing, ongoing inspection and maintenance should be conducted as per the manufacturer's specifications.