Page 82 - Bridge and Highway Structure Rehabilitation and Repair

CHAPTER 2 DIAGNOSTIC DESIGN AND SELECTIVE RECONSTRUCTION 57

6. Bearing cleaning.
7. Bearing lubrication.
8. Deck drain/scupper cleaning.
Most overlays of asphalt and concrete are expected to provide nearly 20 years of satisfac-
tory service. Deck slabs are expected to provide 25 years of repair-free service using corrosion
protection strategies.

2.3.5 Progressive Design Phases
1. Routine design methods are basically applicable to new bridges, replacement bridges, and
for widening of existing bridges. For existing bridges with defi ciencies, diagnostic design
methods are required. For historic and older bridges preservation design is needed. The im-
portant phases in the life of a bridge are transformation from a new to an older bridge and
then perhaps to a historic bridge for the lucky ones. Others get unceremoniously demolished.
Only those structures which are well maintained and possess optimum proportion and reserve
of strength have withstood the test of time. For successful maintenance, any reconstruction
effort must be based on diagnostic design and planning, made possible through the skills of
trained personnel.
As bridges get older, deficiencies are likely to emerge sometimes under heavier loads than

expected. Old bridges still need to perform as well as any new bridge. This requires constant
maintenance by correcting any deficiencies, performing repairs, and replacing any defi cient

members. Once again there are legal requirements for following standard procedures for
maintenance as laid down by the highway agency, state, and federal agencies.
2. The structural health of every bridge may not be identical. Performance of each bridge

depends upon its age, traffic volume, geometry, span length, load intensity, type of mate-

rial, etc. Deficiencies may also arise from substandard design and lack of quality control in
construction. “Diagnosis” will be determined by inspection and structural health monitoring.
Hence, the type of diagnostic design will be different in each case and will aim to remove

the diagnosed deficiency. A repair or replacement strategy will be implemented depending
upon the condition of the bridge at any given time.
Methods of repairs, retrofits, and strengthening are discussed in Chapters 7 through 12.

3. Engineering tasks for rehabilitation start with “diagnostic” design. It is a specialized but
restricted application of “routine design.” Guidelines for diagnostic design are:
• It should meet FHWA criteria of highway for life.
• The bridge needs to be rated for live load used in the original design if known but checked
for new loads. It should be posted for a live load based on new design criteria. The subject

encompasses both field and office procedures. The AASHTO Manual of Condition Evalu-

ation of Bridges is applicable.
• Remaining useful life needs to be evaluated for economical justification of continued

use.
• Accuracy of design will be based on the accuracy of the inspection report. It requires
inspection to identify all the deficiencies and perform diagnosis and structural evalua-

tions. Correct diagnosis is the basis of the rehabilitation process. It is made possible by
inspection, monitoring, coding guide, load rating, analysis, and the applications of modern
practice for rehabilitation and repair. Types of reconstruction depend upon evaluation of
physical conditions and inspection-based diagnosis.
• Each diffi culty needs to be resolved. For example, future widening may not be easy for
through type girder bridges. Also, where the fascia girder is weaker than the interior girder,
replacement or strengthening of the fascia is required.