Page 317 - Bridge and Highway Structure Rehabilitation and Repair

292 SECTION 2 STRENGTHENING AND REPAIR WORK

7.3.10 Performing a Comparative Study for Selection
1. Replacement costs: Major reconstruction or replacement should be the last resort for a variety
of reasons. A new bridge is likely to cost millions of dollars. At any given time, a highway
agency may be looking at thousands of bridges for reconstruction. Extended budgets are
generally met by taxpayers, for example, through an increased tax on gasoline.
2. Accelerated schedule: A rehabilitation project takes less construction time than replace-
ment.
3. Administrative and environmental impacts: In addition to the administrative efforts in re-
solving right-of-way legal issues, relocation of utilities and obtaining environmental permits
can prevent the start of a new project for quite some time. Rehabilitation projects involve
fewer social and environmental impacts than replacement projects. Hence, project delivery
and procedural requirements are expedited with rehabilitation.
4. Redundancy: In a non-redundant structure, a failure of one principal load carrying member
would result in probable collapse. The possibility of adding redundancy favors replace-
ment.
Two girder bridges with welded construction have a greater risk of failure than trusses.
Concrete arches and concrete rigid frames are difficult and expensive to rehabilitate because

of their monolithic type of construction.
5. Foundation costs: For scour critical bridges, deep foundations are preferred. The type of
soil and scour depth will determine the type of foundation. If there are no serious scour
problems, rehabilitation should be preferred.

Table 7.5 The feasibility of rehabilitation versus replacement.
Task Purpose Method
1. Collect detailed structure To collect suffi cient data to assess the Perform an in-depth inspection in accordance with
condition data. viability of the work alternates. The data the requirements of the specifi cations for in-depth
should be detailed enough to allow the inspection. This activity could include taking cores of
completion of a level 1 load rating. existing concrete elements.
2. Assess the condition of the To determine whether a deck can be Perform a deck evaluation in accordance with the
structural deck. rehabilitated or must be replaced. current deck evaluation manual. The decision to
rehabilitate or replace a deck can signifi cantly impact
associated rehabilitative work, design criteria, and the
resulting costs. It is therefore imperative to accurately
defi ne the condition of the structural deck.
3. Assess the structural To assure serviceability of the structure Perform a level 1 load rating. The level 1 load rating will
integrity. during construction and to defi ne the provide a base structural capacity for the bridge from
extent of rehabilitative work required. which the necessity and potential for improvement can
be judged.
4. Assess the structure’s To identify impact to project scope Evaluate the structure and its details using the
vulnerabilities. and cost to address the structure’s procedures provided in the Bridge Safety Assurance
vulnerabilities prior to design approval. Policy.
5. Assess the feasibility Refi ne project cost and further assess Update project costs and schedule based on more
of rehabilitation versus the alternate’s cost effectiveness and detailed information. Perform rehabilitation versus
replacement. technical feasibility. replacement evaluation. This evaluation provides
direction concerning reasonable costs of various
alternates and technical considerations that correspond
to feasibility.