You are here:
Condition Assessment Modeling for Distribution Systems Using Shared Frailty Analysis
Citation:
Clark, R. M., J. Carson, R. C. Thurnau, R. Krishnan, AND S. Panguluri. Condition Assessment Modeling for Distribution Systems Using Shared Frailty Analysis. Journal AWWA. American Water Works Association, Denver, CO, 102(7):81-91, (2010).
Impact/Purpose:
To inform the public.
Description:
Condition Assessment (CA) modeling is drawing increasing interest as a methodology for managing drinking water infrastructure. This paper develops a Cox Proportional Hazard (PH)/shared frailty model and applies it to the problem of investment in the repair and replacement of drinking water distribution system components. It is applied to a pipe break data base collected by the Laramie Water Utility (located in Laramie, Wyoming (USA) to illustrate how such models can help managers understand the factors affecting the “survival” of drinking water pipe sections or entire pipe “runs.” Shared frailty represents unobserved external factors, known to be important, which vary randomly and which are more consistent among sections in the same pipe run than among sections in different pipe runs. Results from the model developed in this paper indicate that, on the average, metallic pipe has fewer beaks than Poly Vinyl Chloride (PVC) pipe but is more subject to undefined random factors. The Cox PH model is utilized to develop “expected” pipe-run break curves. The Inspection Value Method (IVM) incorporates the “expected” break curve to optimize repair, replacement and rehabilitation decisions for selected drinking water distribution system pipes.
