A. In order to minimize changing the characteristics of the deck slab supports and/or unduly affecting maintenance and aesthetics, during the preparation of widening plans, adhere to the following criteria:
1.) The widened portion of a minor widening must match the existing structure. Refer to Chapter 4 for deck slab design.
2.) Avoid mixing concrete and steel beams in the same span.
3.) The use of beams of the same type as those in the existing structure is preferred; however, if the existing beams are cast-in-place concrete, detail the widened deck supported on prestressed beams.
4.) Provide the required vertical clearance on Interstate structures unless an exception is granted. To assist in meeting the minimum vertical clearance requirements on a widening, the standard beam depth may be decreased. Where the existing bridge does not satisfy current vertical clearance requirements and where the economics of doing so are justified, the superstructure must be elevated and/or the under passing roadway must be lowered as part of the widening project.
Commentary: The stated clearance criteria are particularly important for bridges that have a history of frequent superstructure collisions from over-height vehicles.
B. The transverse reinforcement in the new deck should be spaced to match the existing spacing. Different bar sizes may be used if necessary.
C. Voided-slab bridges require special attention. Contact the DSDE for guidance. The DSDE will coordinate with the SDO to establish recommendations and criteria for the widening of the particular structure.
D. For all widenings, confirm that the available existing bridge plans depict the actual field conditions. Notify FDOT’s Project Manager of any discrepancies which are critical to the continuation of the widening design.
Commentary: In general, confirming the agreement of existing plans with actual field conditions should be included as part of any new survey. A structural engineer must be involved in checking that the existing plans agree with actual field conditions for items such as:
Bridge location, pier location, skew angle, stationing.
Span lengths.
Number and type of beams.
Wing wall, pier, and abutment details.
Utilities supported on the bridge.
Finished grade elevations.
Vertical and horizontal clearances.
Other features critical to the widening.