Structures Design Guidelines | Jan 2009
7 - Widening and Rehabilitation |

## 7.3 Analysis and Design

### 7.3.1 Aesthetics

A. Design widenings to match the aesthetic level of the existing bridge.

B. Additions to existing bridges should not be obvious “add-ons”.

C. Consider specifying a Class 5 Finish coating for the existing bridge.

### 7.3.2 Materials

Materials used in the construction of the widening should have the same thermal and elastic properties as those of the existing structure.

### 7.3.3 Load Distribution (01/05) 2005 Jan: Deleted use of “LRFD for the distribution of live load.”

A. Proportion the main load carrying members of the widening to provide longitudinal and transverse load distribution characteristics similar to the existing structure.

Commentary: Normally, this can be achieved by using the same cross-sections and member lengths as were used in the existing structure.

B. When determining the distribution of the dead load for the design of the widening, and when performing stress checks of the existing structure, consider the construction sequence and degree of interaction between the widening and the existing structure after completion.

### 7.3.4 Specifications

A. Design all widenings and rehabilitations in accordance with LRFD.

B. Review stresses in the main exterior member of the existing structure for construction conditions and the final condition; i.e., after attachment of the widened portion of the structure. When computations indicate overstresses in the exterior member of the existing structure, request a variation from the appropriate FDOT Structures Design Office.

### 7.3.5 Overlays (01/09) 2009 Jan: Revised to include provisions for original design, plan note, existing bridges and sloping overlays.

A. Generally, asphalt overlays on bridge decks should be removed except where the overlay is part of the original design. When an asphalt overlay is to be removed, add the following General Note to the plans:

“Use extreme care when removing asphalt from the existing bridge deck. Repair any damage at no cost to the Department.”

B. For existing bridges with water spread drainage issues that may require sloping overlays consult with the District Structures Design Engineer.

### 7.3.6 Substructure

As with any bridge structure, when selecting the foundation type for a widening, consider the recommendations of both the District Geotechnical Engineer and the District Drainage Engineer.

### 7.3.7 Other Special Considerations

A. When detailing connections and selecting or permitting construction methods, consider the amount of differential camber present prior to placing the new deck.

B. Avoid open or sealed longitudinal joints in the riding surface (safety hazards.)

C. Specify that live load vibrations from the existing structure be minimized or eliminated during deck pour and curing.

D. Refer to SDG Chapter 6
for bearing requirements.

E. Provide ample clearance between proposed driven piles and existing piles, utilities, or other obstructions. This is especially critical for battered piles.

F. Bearing fixity and expansion devices should be the same in both the widened and existing bridges.