Planning bonded anchors for steel column bases on concrete foundations

A mortar marketed as high strength is insufficient grounds for changing the anchor layout. Check the concrete, steel, edge distances and behaviour of the anchor group. Where grout is required beneath the base plate, follow the design for the grout material and sequence of work. Simply standing the column on nuts does not establish how the finished base will transfer its loads.

For an existing building, first confirm that the anchor positions fall within the foundation. A hard floor surface gives no indication of the footing dimensions, condition or concrete strength class. Map cracks, areas of missing concrete, reinforcement and old holes that could affect installation. The engineer responsible for the structure determines what investigations are needed.

Locate reinforcement and services before drilling. If the drill encounters a reinforcing bar or a hole is misplaced, stop work at that position and refer it to the designer. Cutting the bar or shifting the anchor even a few centimetres can take the connection outside its design or the limits of the system assessment. Resolve the obstruction while the base is accessible.

Use the mortar, rod, nuts and borehole preparation covered by the technical assessment and installation instructions. Check that the system covers the concrete type, hole conditions and loads in the project. Matching nominal diameters alone do not establish that components can be used together.

Record the specified drill diameter, embedment depth, cleaning method, tightening torque and curing conditions. Take them from the design and instructions for the exact combination being installed. Some values depend on temperature or drilling method. A blanket rule such as adding two millimetres to the rod diameter can give the wrong borehole size.

After drilling, inspect the borehole dimensions and condition. Dust left on the hole wall can reduce the bond. The system instructions specify the cleaning cycles and equipment, which may include brushes, compressed air or a drill bit with dust extraction. Omit a separate cleaning step only where the instructions explicitly allow this for the drilling method used.

Before injecting, check the mortar’s expiry date and storage history, as well as the temperatures of both cartridge and concrete. Follow the instructions for the initial quantity dispensed and for filling the hole. Deep holes may require specific injection accessories. Once the rod is in position, allow the specified curing time for the bond to develop.

Use the curing time specified for the mortar and site conditions, including temperature and borehole moisture. Keep the rods undisturbed and unloaded for the required period. Schedule the next operations around the conditions recorded at installation.

After curing, carry out the specified tightening and alignment procedure. Observe the design torque, since overtightening does not increase the design resistance. Inspect the individual fastenings and check the level and position of each column base. The structural engineer specifies any acceptance tests as part of verifying the designed connection.

Record the system, material batches, anchor positions and relevant installation conditions. Take photographs before and after placing the base plates. Include approved deviations and the agreed treatment of misplaced holes. These records allow a future engineer to assess alterations even if the original installers are unavailable.

Reassess structural loads if an overhead crane or mezzanine is added, or if the cladding changes. Check the entire connection for the revised loading. During routine maintenance, look for corrosion, damaged concrete and water collecting at the column bases. Detail the plinth so that the connection remains accessible for inspection.