TEST and DESIGN: PROCEDURES and CRITERIAS
All tests are performed in conformance with ASTM Standard E488-Standard Test Methods for Anchors in Concrete. Published loads are average ultimate (failure)
loads based on actual testing done in base materials listed in individual anchor sections.
Allowable Load Capacities
The allowable load that can be applied to an anchor is calculated upon applying a safety factor to the average ultimate load capacity obtained from testing.
One purpose of a safety factor is to allow for variation between the field and the testing conditions in the laboratory. Examples of these variations
include differences in the type and strength of base material, the setting method used, and long term performance factors. The standard established by the
industry is to reduce the ultimate load capacity by a minimum safety factor of 4 to calculate the allowable working load. Critical applications such as
overheard applications or dynamic loading may require safety factors of 10 or higher. The allowable loads are recommendations, however, local building codes
should be consulted to determine the required safety factors. Depth of Embedment
The depth of embedment published for each anchor in the load capacity charts is critical to achieving the expected load capacities. This depth is measured from
the surface of the base material to the bottom of the anchor. For mechanical expansion anchors, this would be the depth measured to the bottom of the anchor
prior to actuation. For each anchor type, a minimum embedment depth is specified. This depth is typically the minimum required for proper anchor installation
and reliable functioning. Attempting to install an anchor at less than the minimum required may over stress the base material causing it to fail when the anchor
is expanded. In some masonry materials, the minimum depth may be increased depending upon the anchor style as noted in the load tables.
Load capacities for some anchor types will increase with deeper embedment. As the embedment depth is increased, the load capacity will increase up to a
transition point. This point is usually the maximum embedment depth listed. At this point, mechanical anchors may experience material failure or localized
failure of the base material around the expansion mechanism.
Base Material Strength
The strength of base materials in which anchors may be installed varies widely and is a key factor in the performance of an anchor. Cobra publishes average
ultimate load capacities for anchors installed in concrete and masonry units along with other appropriate base materials depending upon the product. For
masonry unit base materials, the published load capacities should be used as a guide since the consistency of these materials varies widely. Job site tests
are recommended for critical applications in these materials.
Base Material Thickness
The minimum recommended thickness of solid concrete or masonry base material, BMT, when using a mechanical anchor is 125% of the embedment to be used.