Design Quality Improvement – Bulletin 01 4/29/19 Prepared by – Todd Sisti, PE
AUXILIARY PIPE SUPPORTS – CONSIDER THE COST ($)
Auxiliary Supports are sometimes referred to as Engineered Supports, or Special Supports. Regardless of what you call them, these supports are custom designed for a specific application. Sometimes they are used as a gang support to support many lines, and other times they are custom to support a special pipe stress need. Regardless of the need, the support designer should consider the cost of the design of the support and plan for economics in design.
First and foremost an Auxiliary Support must be designed to meet the need. However, a balance between design and cost must be considered for each given application. Too often designers focus on the design and ignore the cost of design. In todays’ business climate, Construction teams are looking for faster and cheaper ways of doing the work. Additionally, construction teams are finding it more difficult to get skilled work force such as iron workers and welders. As such, designs need to be more efficient and minimize welding and cutting of steel.
Recommendations in the design of Auxiliary Pipe Support:
Standardization of Steel Member sizes: There are many sizes and shapes of steel members. Standardizing on the member sizes will make procurement easier, will minimize potential for wrong sizes to be accidentally be used, and can simplify the joining details.
Standardize the base plates: Start with using the same thickness in base plate material and then standardize on length, width, number and size of bolt holes for a given range of supports. This will allow for mass production of base plates from one common steel sheet.
Proper Weld Symbols and Application: This is one of the most abused areas in support design. Support designers will often apply a fillet weld “all the way around” for a given connection point. Side welds or stitch welds can be used to reduce the amount of welding. With every weld, there are two end preparations to be made to the steel. Consider the use of bolted attachments or bending steel in lieu of welds.
Selection of proper type of Spring Hangers: Spring hangers have various type of connections and can be selected to reduce support components. Stress engineers may size a Spring, but the designer can help identify the installation. Spring cans can be purchased with guided load columns and may reduce or eliminate the need for a guide support.
Joining methods of steel: Consider the various construction methods of attaching support steel to the major building steel. Avoid transverse welds across horizontal building members as this will weaken building steel.
Case 1 – Field Goal Pipe Support: 4 different member sizes, 10 individual steel members, at least 10 material cuts, 16 preps, 8 welds. In addition, 2 members have to be coped to the pipe diameter. For the purpose of the guide, this could have been plate steel with a width greater than the insulation welded to the side of the pipe. Much cheaper and does the exact same thing.
Case 2 – Same Support: 1 member size, 1 steel member, 1 end cut, 2 end preps. In this case a guided load column was purchased with the spring hanger which greatly reduced the support detailing, construction labor, and material costs. The concrete base was extended a little taller to eliminate the bottom trunnion.