In a brand new foundation, four 1-1/4" diameter cast-in-place anchors were installed in a 16" square anchor pattern. This needs to be changed to a 12" square anchor pattern. The intention is to install four new 1-1/4" diameter stainless steel anchor rods with 24" embedment in the correct 12" square anchor pattern utilizing Hilti HIT HY 200 adhesive. The center-to-center spacing between the new and abandoned anchors would be about 2-3/4", or about 2.2 anchor diameters. Anchors would be loaded in occasional shear and moment caused by wind loads.
1. Can the new Hilti adhesive anchor be installed with the existing cast-in-place anchor abandoned nearby?
2. Would the new Hilti adhesive anchor have any reduction in capacity that would need to be considered?
3. Does Hilti have any other recommendations on this condition?
Hi Kyle,
Thank you for reaching out. Conditions where an adhesive anchor is to be installed near an abandoned cast-in-place anchor are ultimately outside of Hilti’s published test data, which lends the decision to engineering judgement by the Engineer of Record on the project. In general, installation wise, this would involve grinding the exposed portion of the old anchor down so that the anchor is receding below the base material's surface; this will allow a fixture to sit flush against the surface in that abandoned anchor's location. Afterwards, the new adhesive anchor would be installed.
It is likely the new anchor's performance will be influenced by the abandoned anchor; refer to the new anchor's supportive testing for spacing considerations to determine the influence that the abandoned anchor may have on the new anchor's capacity. One approach may be to consider the new anchor’s spacing requirements compared to the abandoned anchor spacing requirements then take the more limiting of the two.
When installing the new anchor, care must be taken so that the minimum edge distance for the new anchors (not the abandoned anchor) is not violated. Sometimes when the new anchor is installed there may be a desire to install closer to an edge. It would be critical to ensure the new edge distance is not violating the minimum values, and a new design may need to be performed based on the new geometry.
Ultimately, as the condition is outside of Hilti’s published testing, the approach is at the discretion of the Engineer of Record.
For additional questions, please reach out to hnatechnicalservices@hilti.com
Kind regards,
Sinan