Page 307 - Bridge and Highway Structure Rehabilitation and Repair

282 SECTION 2 STRENGTHENING AND REPAIR WORK

The salient features are selection of structural solutions, feasibility, methodology, planning,
alternatives analysis, stress and deformation analysis, detailed design, constructability issues,
economics, life cycle costs, and aesthetics. Case studies of successfully completed projects are
also examined.
7.1.2 Widening Practice

Requirements for preparing widening plans are shown in Figure 7.1.
An example of deck slab design based on the LRFD method is included in this chapter.
Guidelines for girder selection based on optimum considerations are also summarized in this
chapter. After selecting the girder type, the steps required for preliminary or advanced design
described in Chapters 5 and 6 should be followed. Although familiarity with hand calculations
is required, the designer should be familiar with the listed approved computer software and its
supporting manual, which will outline the applicable methods of analysis and design, in keeping
with AASHTO requirements.
The current design method is the LRFD method, while the one used for original design is

likely to be ASD or LFD. The truck live load intensity and deflection criteria would be different.
Comprehensive load combinations and applications of AASHTO LRFD methods described in
Chapters 5 and 6 are as important for widening as they are for replacement bridges.
1. In order to match the existing deck thickness and reinforcement area, live load capacity for
new design may be different due to differences between old and new regulations. Following
are some general guidelines:
The transverse reinforcement in the new deck should be spaced to match the existing
spacing. Different bar sizes may be used if necessary.
2. The new girders in the widened portion must match the existing span lengths.
3. Avoid mixing concrete and steel beams in the same span. The use of beams of the same type
as those used in the existing structure is preferred.
4. If the existing beams are cast-in-place concrete, detail the widened deck supported on precast
prestressed beams.

Utilities and R.O.W.

Keep Span as Before
Skew Angle the Same

Widen Wingwall

Figure 7.1 Steps for planning deck widening.