When the anchor bolts get too close together, they do not develop their full strength in the concrete foundation (ie: the "pull out" strength does not develop the full strength of the metal bolt section). A typical recommended minimum anchor bolt spacing is about 18".

When COMPRESS is in "Design" calculation mode and the available bolt area is insufficient for the loading specified, this input limits the number of bolts in the automatic routine that selects an acceptable bolt size and number of bolts combination. ie: The maximum number of bolts that could possibly be placed on the bolt circle is limited by the minimum spacing required between bolts.

Additionally, a message is reported in the Deficiencies Summary if the actual anchor bolt spacing is less than the minimum spacing specified.