PVC drainage connection approval memo, Apr 1985

NYC 9/11 Public Portal Document

Deflection is defined as the change in Although considered a conservative 1. Where live loads are not a factor or vertical inside diameter of a flexible approach, considerable variation in not involved in the total external load on conduit when subjected to a vertical predicted deflection will result depending the pipe, the chart can be used directly load. The amount of deflection that will upon the choice of empirical constants to determine the limit of the maximum occur in any flexible conduit is a fuik tion E', Kand Dl. long-term deflection of the PVC pipe. of three factors: 1. Pipe stiffness (F/Ay). £nipfrica1 methods of predicting Example: If a 24" Perma-Loc Series 10 2. Soil-sWness. ■ .deflection have evolved in recent years pipe is installed in Class IV material, 3. Load on the pipe. which eliminate the guesswork inherent having 85% compaction in the pipe zone In the Iowa method. When design is and with 12 feet of cower, will this It is important to recognize that flexible based on actual laboratory test and recommended maximum long-term conduits perform differently in the previous field measurements, it is deflection of 7V2% be met? ground than they do under laboratory unnecessary to know the actual load flat plate loading. The interaction of pipe acting on the pipe or the soil stiffness. Answer: Enter Figure 2 at 12 feet of stiffness and soil stiffness combine to Thus an installation can be designed cover, Class IV material at 85% give flexible conduits a high effective with a known factor of safety provided compaction, pipe will never deflect more strength when buried. ‘ enough empirtcal data is available. than 7%% (color code — green).

Methods for predicting pipe . To accommodate the problem of having ■2. Where live loads must be considered, deflection to establish data for the number of determine first the combined total The most commonly used approach in trench widths that are found in the field, external load on the pipe. Next predicting deflection has been the the prism load was chosen because it ' determ.iflfi..lb.a..fifluivalen prism load modified “Iowa Deflection Formula." repto'iprsts the maximum loading (without live load) for the particular pipe con(v*'^ii nrr T ftoabtepipe. Time lag to size involved using the table otprism M vtoiucj k.viu rcuudij. account for future settlement of the ■ loads. Read across to the left for the . • Ay K>Vc!' backfill can be included by choosing height of cover (ft) for the equivalent FT . ibl LL ’ long-term values of deflection. prism load. Using this height of cover with the bedding class and Proctor ■Where: Johns-Manville has developed through density, enter the maximum long-term Ay = Vertical deflection (inches) laboratory tests .and actual field data the- deflection chart, Figure 2, to determine Dl = Lag factor (1.5 maximum) maximum long-term deflection charts, the maximum long-term deflection limit. K = Bedding factor Figures 2 and 3, shown on page 7, These Wc = Earth load (Ib/in) efi’arts"eiriTimatethe guesswork in r - Mem! cd'bs' (-nt predicting deflection and give the design , E = Modulus of elasticity (Ib/in”) engineer a quick ready reference. Figure I = Moment of inertia** (in’) 2 IS for Perrna-Lov with a stiffness of 10 psi E' = Soil stiffness (Ib/in”) •' (Series 10), while Figure 3 is (or a ■ stiffnessaf 46 psi (Series 46). Tic; vaiues given for deflection limits are Uto ultimate ‘Distance from center of pipe to Beutral long-term deflection that will occur in a j 4 axis; r particular soil class having a given density “Calculate using standard strength of (compaction) in tne haunefting area of the material formulae. pipe zone for various heights of cover (feet).

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