Closer Look at the M11 Harness

The AWWA M11 Harness provides a means of restraining non-restrained pipelines operating under pressure. In areas where gasketed joint pipe and non-self-restraining couplings are subject to thrust resulting from internal pressure, an option to mitigate the thrust is to harness across the joint. However, a closer look at M11 reveals deficiencies, including overstressed back ring and gusset plates, insufficient weld size, lack of weld access holes, inadequate load transfer between back ring and gussets, improper weld types and underestimate of strength, oversize holes too small for easy field assembly of tie rod and nuts without washers to spread load, and complex double-curved geometry of skewed gussets resulting in welding assembly issues. This paper addresses the deficiencies with current M11 harness and provides suggestions to improve the design and fabrication with the goal achieving structural code compliance and improved safety for water projects. Example calculations are provided.