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73 CHAPTER 5 Element-Level Costs of Maintenance Actions Basic Computation qi = qi , post - qi , prior (Eq. 2) The NBMD system in its NBMD viewer application com- putes costs of maintenance actions that improve conditions of where bridge elements. These costs can be related to costs of Pontis qi Change in element quantity in condition state i actions. The NBMD implementation is valid for any condi- qi,post Element quantity in condition state i after the main- tion reporting system that yields element quantities in condi- tenance event tion states. qi,prior Element quantity in condition state i prior to the The unit costs of actions that improve bridge elements are maintenance event Values qi are computed for every element of the bridge. AllocatedCostelement Unit Costelement = (Eq. 1) Maintenance events that improve element conditions produce ImprovedQuantityelement positive changes to element quantities in better condition states and negative changes to quantities in poorer condition Allocated costs and improved quantities of elements are states. Improvements will be observed for some but usually determined by analysis of NBMD production data and asso- not all elements of the bridge. The total quantity (inventory) ciated NBMD element-level inspection data. The process has of each element is computed too, since maintenance events three steps: may alter element quantities or introduce new elements to bridges. 1. Identify a maintenance event and collect element-level condition data. 2. Identify elements that are the appropriate bridge compo- Identifying Elements nent and that show improvement to conditions after the maintenance event. Elements are included in a cost computation if element com- 3. Allocate maintenance costs to elements. ponent agrees with the component of maintenance actions and if elements show improvement. Maintenance Events and Element Condition Data Element Component and Maintenance Component For each maintenance event, element-level inspections before and after the event are identified in an NBMD Inspection_ All bridge elements and some maintenance actions are asso- Cross_Reference_Table. Inspection IDs are obtained from the ciated with specific components of bridges. Elements are kept cross reference table and element quantities are collected into in the cost computation if their component matches the action arrays. These are the element quantities for the single bridge (or component. Some components, such as Substructure, can culvert) in the maintenance event. Changes to element quanti- admit several elements at the same bridge. One component, ties, qi, are computed for each condition state. Bridge, admits all elements.