There is a lot of confusion regarding the purpose of prism testing and what prism tests are intended to simulate or replicate. Because masonry prisms are an assembly, they are often confused as being a small version of a full-scale masonry assembly. The actual purpose of a masonry prism is to test a masonry property, not the as-built masonry assembly, which in this case is either to document or verify the specified compressive strength of the masonry: f’m.
In design applications, this singular property (f’m) is used in a wide array of design checks and limits. Certainly the design axial strength of a masonry assembly is one attribute based on f’m, as is the stiffness of the masonry, the required lap splice length, the breakout strength of anchor bolts, masonry shear strength, and many, many other design properties. As such, the provisions of ASTM C1314 are not intended to predict how a masonry wall will perform in service, but to establish a material property that is used to design the entire masonry structure.
For the history buffs, years ago ASTM published and maintained ASTM E447 for the construction and testing of masonry prisms. ASTM E447 required that prisms be constructed in a manner that replicated as-built construction – i.e., running bond, face shell bedding of mortar, etc. This didn’t work for design application, so in adopting ASTM E447, building code and design standards modified ASTM E447 so that the resulting measured compressive strength could be used as a design property. These building code modifications eventually become what we recognize today as ASTM C1314.
Developed by Subcommittee: C15.04
Staff Manager: Krista Robbins
Date Initiated: 02-15-2022
Technical Contact: Jason Thompson
Ballot: C15.04 (22-01)
Status: Will Reballot Item
Ballot: C15.04 (22-02)
Status: Negative Votes Need Resolution