Page 52 - Bridge and Highway Structure Rehabilitation and Repair

CHAPTER 1 OVERVIEW OF BRIDGE ENGINEERING 27

3. National policy objectives as defined by FHWA are:
• To understand the functioning and decision-making consequences affecting transportation
systems
• To develop strategies in which bridge engineers more effectively contribute to transporta-
tion-policy decisions.
• To develop recommendations to AASHTO on oversize/overweight vehicles and the long-
term impact of construction on the environment
• To develop strategies to enhance public involvement of bridge engineers, including out-
reach to all stakeholders.

1.8.14 Implementing Diagnostic Design Procedures
1. Preliminary diagnostic design
The steps are:
• Preparing plans indicating type, size, and location (TS & L)

• Preparing plans indicating geometry, alignment, profile, span length, and beam spacing
• Preparing a report on accessibility to the site, estimates of cost, and material
availability.
2. Final Diagnostic Design
The steps are:

• Preparing plans, specifications, and estimates (PS & E)
• Adjusting maximum truck load: After rehabilitation, the number of fatigue cycles and fatigue
stress level are expected to be lower since the remaining useful life of the substructure is
reduced to less than the original estimated life of 75 years. A fatigue evaluation study needs
to be carried out for the remaining fatigue life for the level of live loads (Table 1.5).
• Posting the bridge for a lower live load.

1.8.15 Compliance with Codes and Standards
1. When a bridge is being considered for rehabilitation, it should be reviewed for compliance
with current standards. Existing vertical clearance, horizontal clearance, load capacity,
free board, seismic capacity, lane width, and shoulder width should be compared to current
standards.
2. Hydraulic and seismic history should also be reviewed. If the existing features are non-stan-
dard, consideration should be given to improving them under rehabilitation or by replacing
the bridge. If improvements cannot be made or the improvements that can be made will not

be up to current standards, a non-standard feature justification will be required. This should
be taken into account when making the rehabilitation versus replacement decision.

Table 1.5 Truck weight for fatigue evaluation.
S. No. Deck Function Deck Type Truck Type Remarks
1A Pedestrian use Timber H5
1B -do- Lightweight H5
1C -do- Normal concrete H5
2A Passenger cars only Lightweight H10
2B -do- Normal concrete H10
3A Full service Lightweight HS20 Place load restrictions
3B -do- Normal concrete HS20 -do-