Precast Solutions - March/April 2008 - (Page 20)

trench construction details of the structural design calculations. • The engineer must be able to mathematically approximate the load that will need to be accommodated by the pipe. • The engineer must understand the national specifications and the independent design method of the product to be used. • The engineer must understand long-term material properties and how to conservatively use the material properties and soil interaction to properly complete any structural design for any of the available pipe products. installation materials and backfill procedures for RCP installations. This conservative approach normally requires a very low percentage of support from the bedding and backfill. This flexibility for the designer to utilize available soil materials to the spring line of RCP allows for some real-world field and installation imperfections while still providing for proper structural system strength. The concrete pipe industry provides a variety of design aids posted on of the American Concrete Pipe Association’s Web site (www.concretepipe.org) to help the designer. HDPE pipe design requires knowledge of the material properties of plastics and the importance of the soil-pipe interaction to create the structural component of the Simply utilizing published fill height tables from material suppliers, product associations or DOT documents does not relieve a professional of his or her duty to ensure that the design is correct and structurally sound. Rigid pipe design requires an understanding of material properties of reinforced concrete. Reinforced concrete pipe (RCP) is a confirmed structural RCP is the only pipe product that utilizes local raw materials. It is manufactured and transported by people who most likely live and pay taxes in the community served by the concrete pipe facility. component when it arrives at the job site. Even though the full design strength of the installed system requires some level of support from the bedding and backfill, the majority of the system strength is in the pipe wall when it arrives on site. Most engineers specify conservative trench installed system. Most practicing civil engineers have not received any formal training on the material properties or behavioral properties of plastics. An article in the October 2007 issue of Modern Plastics Worldwide, “Long-term testing critical for material selection” by Chris O’Connor, stressed the need for engineers and designers to fully understand plastic properties. Most HDPE storm pipe producers provide one pipe stiffness and a limited selection of profile configurations for each of the different sizes of conduits they manufacture. Due to this lack of options for increased pipe wall strength, most installations require high-quality imported pipe embedment materials to be placed a minimum of 12 inches above the pipe combined with high strength in-situ trench walls to accommodate the design loads properly. If the field conditions or embedment materials vary from the design assumptions, then the anticipated structural strength can be compromised. Corrugated steel conduits also depend heavily on the soil and steel conduit interaction to obtain the structural component and load carrying capability of the installed system. In most CMP installations, a majority of the structural strength of the installed system is provided by the soil interaction component of the installation. Various wall thicknesses and corrugation patterns are available to help the designer accommodate more load in the pipe wall if required in project design requirements. All pipeline designs must also include a hydraulic analysis. Pipelines must be sized to meet postconstruction runoff. It is important to know that 20 PRECAST SOLUTIONS | MARCH/APRIL 2008 http://www.concretepipe.org http://www.concretepipe.org

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Precast Solutions - March/April 2008 Contents Smooth Move Riding the Waves Comparing RCP With Plastic Pipe Cost-Value Analysis of Storm Sewer Pipe Concrete Testing On a Grand Scale Building Confidence

Precast Solutions - March/April 2008

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