Hi I'm checking a base plate. My bolts are M20. As per AS 5100.6, minimum pitch is 2.5d=50mm. Even as per ACI, minimum spacing is 4d=80mm (untorqued), M20, 4.6/S. I provided 85mm and Profis gave a warning that its too less and minimum should be 90mm. I had to update it to 90mm then. Whats the reason behind this warning? can you share reference (code, clause) this is based on? In case of space constraint, as in if the base plate is on top of a barrier, and if we are not able to achieve such spacings as per profis, do we overlook such warnings?
Hi Sir,
Apologies for the delayed response.
The minimum spacing criteria (often denoted as s_min) for anchors is a parameter defined in the specific product approval (ETA/ESR or Hilti technical approval document) for each anchor type, variant, diameter, and base material. Let me pull up the general guidance on this.
The minimum anchor spacing (s_min) is defined as a geometric installation requirement specific to each anchor product, variant, and base material, and it is determined through qualification testing rather than a single universal formula [1][2].
Key points:
- Purpose: s_min ensures that two anchors can be installed at a given spacing close to an edge without inducing cracking in the concrete due to installation forces (e.g., tightening torque for mechanical anchors, or expansion pressure) [1][2].
- Source: The exact s_min value (along with the corresponding minimum edge distance c_min) is given in the product-specific ETA (European Technical Assessment) or approval document, and depends on:
- Relationship with edge distance: s_min and c_min are often interdependent — a reduced spacing may require a larger corresponding edge distance, and vice versa (shown as paired values in approval tables) [2].
- Distinct from critical spacing (s_cr,N): This is a different parameter used in design (concrete breakout calculations per EC2-4), representing the spacing beyond which anchors act independently without overlap of breakout cones (typically s_cr,N = 3·h_ef for standard anchors, as defined in the respective ETA) [3]. s_min is an installation/detailing limit, while s_cr,N is a design/resistance calculation parameter.
Since s_min varies by exact product, diameter, and base material, I'd recommend checking the specific ETA/approval document for your intended anchor, .
You may please email your design file to inallengineering@hilti.com if the issue is still unresolved.