Page 315 - Bridge and Highway Structure Rehabilitation and Repair

290 SECTION 2 STRENGTHENING AND REPAIR WORK

If sufficient thought goes into the planning of a new bridge, fewer problems will be en-
countered down the road. Proper investment at the construction stage will minimize subsequent
mainatenance, repair, and rehabilitation costs.
Total cost 3 Initial cost 4 Lifecycle cost (useful service life for old and new components)

Lifecycle cost 3 $ (Cost of routine inspections 4 Maintenance and retrofi ts)
4 $ (Repairs from extreme events 4 Cost of demolition)

Total cost is computed over the life of the bridge. Extreme events may or may not apply
within the life of the bridge. They may be unforeseen events and include accidents such as vehicle

and vessel collision, floods and scour, earthquakes, fires, bomb blasts, etc.
Life cycle costs are linked to the quality of planning. If the initial cost does not cover all the
structural requirements, the life cycle costs for repair and rehabilitation will be much higher.
Screening criteria is based on several practical considerations, such as the owner’s prefer-
ence, the local community’s preference, and using a merit-based point system.
A matrix based on a point system can be used (Table 7.4). The mark for each criterion will
be based on engineering judgment, experience, and intuition.
The following grading is suggested for each abutment or pier alternate:
Condition multiplier
Poor 3 1
Fair 3 2
Good 3 3
Very good 3 4
Excellent 3 5

A list of viable superstructure or substructure components is first prepared. Issues may be

addressed in the following order of importance and given highest to lowest marks:
1. Constructability: Ease of construction.
2. Cost: Initial cost.
3. Maintainability and lifecycle cost.
4. Performance: Safety and durability.
5. Compatibility with environment: No adverse impact on environment.
6. Aesthetics: Pleasant appearance.
7. Construction schedule: Minimum period of construction.
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An Excel spreadsheet may be used for this process.
Other things being equal, alternate 2 with a total of 229 points would be the selection. The
above method can be used, for example, to select a prestressed concrete girder compared to a

Table 7.4 Matrix point system for ranking hypothetical alternates using screening criterion.
Constructability Cost Maintainability Performance Compatibility Aesthetics Schedule Total
Grade point 10 9 9 8 7 6 5 —
Maximum multiplier 5 5 5 5 5 5 5
Maximum points 50 45 45 40 35 30 25 270
Alternate #
1 5 x 10 = 50 4 x 9 = 36 3 x 9 = 27 2 x 9 = 18 1 x 9 = 9 2 x 9 = 18 3 x 9 = 27 185
2 4 x 10 = 40 4 x 9 = 36 5 x 9 = 45 3 x 9 = 27 2 x 9 = 18 3 x 9 = 27 4 x 9 = 36 229
n 3 x 10 = 30 2 x 9 = 18 3 x 9 = 27 4 x 9 = 36 3 x 9 = 27 2 x 9 = 18 3 x 9 = 27 183