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64 Results and Bidding 12.1 Summary and Reporting of Evaluation Results One of the defining principles of the Recommended Prac- tice is to promote transparency in the design and selection of drainage pipe systems. Transparency in the process is achieved by presentation of technical and policy evaluations in a sys- tematic and clear manner across the full range of available pipe systems. The output from the evaluations performed as part of the Recommended Practice consists of a large amount of data and the summary and reporting of this information is best managed through a systematic process. It is proposed that the pipe system evaluation results be presented via a graphically coded matrix to allow the design engineer, technical reviewers, and other users of the Recommended Practice (bidders, contract managers, estimators, agency engineers, and construction inspectors) to conduct a visual review of the results. Transparency and data organization are achieved in the Recommended Practice through the use of the results matrix, which provides a clear and systematic process for recording the adequacy of each pipe system considered versus the vari- ous technical and policy criteria. The matrix approach provides a means to conduct a rapid evaluation and check of results through visual recognition and review of patterns within the matrix results. Adjacent rows contain similar pipe systems, and adjacent columns contain similar sizes such that continuous zones of pass and fail for the various technical and final criteria should be apparent in the final results matrices. The final results from the application of the Recommended Practice can be converted into a streamlined tender code for bidding purposes, as detailed in Section 11 of the Recommended Practice. In addition to the results matrices that depict the end result of the three technical evaluations and overall final and policy evaluation, it is important that calculations and other back-up design and decision information relied on are recorded and stored for future reference in line with other document control standards for engineering designs. The Recommended Practice does not specifically recommend the level or manner in which back-up information is stored, but rather recommends storage and record keeping in line with existing agency standards and protocols. The main purpose of providing good documentation is to define the design procedure that was used and to show how the final design and decisions were determined. Documentation should be viewed as the record of reasonable and prudent design analysis based on the best available technology. 12.2 Incorporation of Alternatives into Bid Documents Each agency typically has a detailed and multi-faceted sys- tem for bidding highway projects that involves cooperation and coordination amongst multiple agency departments and often coordination with multiple national review and funding agencies. As such, the Recommended Practice is intended to maintain flexibility for each adopting agency to develop the optimum manner for integration of results from the Recom- mended Practice into bid and tender documents. 12.2.1 Tender Code The result of the Recommended Practice is a complete list of technically acceptable pipe system alternatives for a specific drainage application. To facilitate management of long lists of alternative pipe type data, the information can be summarized into a concise alphanumeric code format suitable for use by designers, consultants, estimators, contractors, pipe suppliers, and project managers. This code is termed the tender code. While it is not necessary to use the code with the Recommended Practice, it may be a helpful option for some user agencies. The tender code is divided into three main parts: a minimum pipe diameter for smooth pipe (generic Manningâs n of 0.012), C H A P T E R 1 2
65 a minimum pipe diameter for corrugated pipe (generic Man- ningâs n of 0.024), and a material code. The use of these generic Manningâs n numbers is recommended; however, other Man- ningâs n values could be used. An example tender code is shown in Figure 28. 188.8.131.52 Diameter for Baseline Smooth Pipe The first element of the code is a three digit number specify- ing the minimum equivalent circular diameter for the baseline smooth circular pipe case using a Manningâs n of 0.012. 184.108.40.206 Diameter for Baseline Corrugated Pipe The second element of the code is a three digit number specifying the minimum equivalent circular diameter for the baseline corrugated circular pipe case using a Manningâs n of 0.024. 220.127.116.11 Material Code The material code is a nine digit code that specifies what materials are allowed. Each digit position represents a different pipe material. The value in each position specifies a particular class of pipe, wall thickness, or stiffness rating. Figure 29 below shows all the options for the material code portion of the tender code. The material code is interpreted in the following way: â¢ A zero in any position indicates that a particular pipe material is not technically suitable or allowed across all pipe system combinations evaluated for that pipe material type. â¢ An âXâ in any position indicates that that pipe material type was not evaluated during the performance of the Recom- mended Practice. â¢ The minimum class technically suitable across the range of installation conditions is always specified, with higher classes being allowed. For example, if a Class 2 pipe is spec- ified as the minimum, a Class 3 pipe would also be deemed acceptable. â¢ To streamline the tender code into a manageable length, only the minimum pipe class is listed for each pipe material type. Because of this presentational efficiency, bidders will need to confirm the installation requirements to use the minimum listed pipe class, and may want to bid the system with a higher class pipe that may have less stringent instal- lation requirements. â¢ The 1st digit represents concrete pipe. Five classes of reinforced concrete pipe can be specified with the numbers 1 through 5. Unreinforced concrete can be specified using the letter âUâ and the need for a special design is indicated with the letter âS.â â¢ The 2nd digit represents HDPE pipe. Three different wall profiles are allowed: profile, corrugated, and solid wall. Profile wall pipe is specified using one of six ring stiffness Figure 28. Format of a tender code. Figure 29. Material code summary.
66 constants (RSC). Corrugated wall pipe is specified using one of three profile shapes defined in AASHTO M294 as Type C, Type D, and Type S. Solid wall pipe is specified using one of twelve dimension ratios (DRs). A minimum DR is specified. A letter is used to represent each pipe option as shown in Figure 29. For example, a âDâ would indicate that a profile wall pipe with a minimum RSC of 160 was being specified. A âWâ indicates that steel reinforced polyethylene is being specified. Note that the letter âOâ is not included in the code so as not to be confused with the number zero. Three different systems are used for specifying the dimen- sions of solid wall HDPE pipe. Any of these systems can be used with this code system. â¢ The 3rd digit represents PVC pipe. Profile wall pipe can be specified using the letter âAâ and solid wall pipe can be specified using the letters âBâ through âDâ corresponding to three different pipe stiffness classes. â¢ The 4th digit represents polypropylene (PP) pipe. This pipe is specified using one of three profile shapes, defined in AASHTO MP-21 as Type C, Type D, and Type S. Polypropylene pipe is currently not listed as an avail- able pipe type in the AASHTO LRFD Bridge Design Specifications. â¢ The 5th digit represents glass fiber reinforced pipe and can be specified in one of four pipe stiffness classes; 9, 18, 36, and 72 psi. â¢ The 6th, 7th, 8th, and 9th digits represent galvanized steel, polymer laminated steel, aluminized Type 2 steel, and alu- minum pipe, respectively. Each of these material options is specified by the minimum gage thickness of the wall. It is noted that to provide a code of realistic length for incor- poration and use in bid documents some details regarding the suitability of particular pipe system options such as installa- tion class, installation type, pipe lining, pipe roughness values, other than baseline smooth and corrugated are not uniquely identified in the code. Bidders will be required to refer to the final results matrix (or conduct independent evaluations) to determine which combinations of those factors are suitable for the given performance criteria. If bidders wish to use larger pipe systems than the minimum specified in the tender documents, it is recommended that a submittal process be used to evaluate these cases. 12.2.2 Tracking of Bid Results The Recommended Practice strongly recommends that agencies record and database bid results such that regular and systematic evaluations of bid results can be made that allow for evaluation of the impact of Recommended Practice implementation, and also to provide insight into bid trends to direct and guide policy updates as appropriate.