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minimum acceptable reliability level is reached considering preventive maintenance)

Its reliability would decline over time due to a natural aging process, fair wear and tear on the structure, or a gradual increase in the load on the structure and would not fall below an acceptable level during the life of the structure. In reality, structures deteriorate, and various maintenance or repair actions can improve the reliability. It may be preventive maintenance long before a deterioration becomes serious or some form of essential maintenance to prevent the structure from falling below a critical performance level (see Figure 36.14).

36.8.1 Preventive Maintenance

Preventive maintenance may delay the onset of deterioration. A fresh coat of paint will often prevent a steel beam from corroding or a wooden support from rotting. This type of maintenance may also relieve additional stresses on the structure by cleaning an expansion joint or lubricating a bearing. It is often a continuous program with a predictable cost, but the benefits can be difficult to quantify.

Frangopol (1998) and Frangopol et al. (2001b) defined the eight random variable models associated with every aspect of the preventive and essential maintenance processes. This model was successfully applied to individual and groups of bridges in the United Kingdom and the United States (Frangopol et al. 2001b; Frangopol 2003; Frangopol and Neves 2003; Neves and Frangopol 2004; Petcherdchoo et al. 2004). One example of application consisted of maintenance of 713 existing steel/concrete bridges constructed between 1955 and 1998 in the United Kingdom (Frangopol et al. 2001b). Table 36.7 describes all the random variables considered in this example, and Table 36.8 lists their values with

TABLE 36.8 Random Variable Parameters for Preventive Maintenance Based on Database of Existing Bridges

Failure mode

Shear parameters Bending parameters Random Distribution ___

Shear parameters Bending parameters Random Distribution ___

TABLE 36.8 Random Variable Parameters for Preventive Maintenance Based on Database of Existing Bridges

Failure mode

variable

type

(1)

(2)

(3)

(1)

(2)

(3)

bo

Lognormal

0 0

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