Page 210 - Bridge and Highway Structure Rehabilitation and Repair

5

Load and

Resistance Factor

Rating and

Redesign

5.1 RATING AND REDESIGN METHODS

5.1.1 Rehabilitation, Replacement, and Widening of Structural Components
For rehabilitation of bridge components, rating is followed by redesign
or replacement design. Dead load analysis is straight forward. However, live
load analysis is complicated due to:
1. Moving loads
2. Dynamic impact factor Strengthening and Repair Work
3. Vibrations and variable defl ections
4. Live loads combined with environmental loads. Section 2

Both rating and design methods have undergone fundamental changes
with the application of more refined ultimate load theories. In this chapter, an

overview of the latest AASHTO recommended design methods are reviewed
and presented to assist inspection and design engineers. Salient features such
as many load combinations are explained in detail.
Limit state methods for rating (LRFR) and design (LRFD) are applied
for structural evaluation of capacity and for redesign of members. AASHTO
formulae are summarized for computation. Detailed load combinations for
strength, serviceability, and extreme load conditions are given in tabular
forms. In addition, construction load combinations and effects of non-sym-
metric pouring sequence on girder stress are developed and presented. Live

load deflection criteria as opposed to stress criteria are reviewed. Suggested
computer software for use is listed, as well.

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