Civil MDC

Guide for Widening Highway Bridges (ACI 345.2R-13) 2

Guide for Widening Highway Bridges (ACI 345.2R-13)


Design and construction engineers should investigate several potential issues if a bridge is to be considered for widening. These include retention of bridge elements, traffic control, structural constraints, economy and feasibility, expected increase in traffic volume, life span, and construction limitations. Certain elementary procedures should be followed to study the feasibility of widening. These include:

a) Review the drawings and specifications of the original structure.

b) Review any revisions of engineering documents (for example, plans, specifications, and design calculations) that might have been approved during the original construction.

c) Thoroughly inspect the structure and note changes to in-place conditions, such as deterioration of structural members due to environmental factors (for example, deicing salts, weathering, and collision of heavy trucks).

d) Obtain additional subsurface information to accommo-date increased superstructure loads, including soil borings.

e) Review previous changes or upgrades to the structure.

f) Perform structural analysis with allowance for existing deterioration to confirm that the existing elements are adequate for increased loads (due to widening and compli-ance with current design standards). If the existing elements are part of the replacement, all possible geometric properties need to be considered.

One of the first considerations for widening a bridge is to determine whether to retain structurally adequate parts of the bridge deck. Entire bridge deck replacement should be considered if the bridge deck is severely deteriorated, the existing bridge deck will become less than a half of the new bridge deck width, or both (Seible et al. 1991; “Operation Bridgeguard” 1992). If the bridge deck, or a portion of it, is to be retained and connected to a new deck, the design should provide for bending moment and shear transfer through the longitudinal joint between the new and old portions of the bridge deck. The steel passing through the construction joint should be protected from possible increases in corrosion potential between the old and new concrete.

Another important matter is the consideration of whether substructures, such as footings, pier caps, and abutments, should be widened to accommodate widening a superstruc-ture. Potential interaction between the new substructure and the existing substructure should be considered. The design professional should be aware of possible problems that could occur when a bridge is widened on both sides. In most cases, the existing portion is trapped between new sections, making it difficult to replace the middle section

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