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I I Project Approach Our overall concept layout is included in Figure J. Two overall concepts are presented: I) a mid-level speed design horizontal alignment (preferred) and 2) a low-speed design horizontal alignment. Each has its merits and can be further refined with direct input from the City. Our approach has been to illustrate both an intcrim design that is pedcstrian oriented and can be implemented quickly and an ultimate design that has more of a vehicular orientation and can be implcmented once existing physical constraints are eliminated. A preliminary profile based on County Public Works Department vertical clearance requirements is also included. I I Bridge Design The bridge will provide a clear width of 40 feet between curbs as stipulated by the City and will be designed to accommodate future traffic loads. Initially, to maintain an open feel, sidewalks and impact resistant barriers will not be includcd but added when the structure is converted to accommodate vehicular traffic. The gcometry of the crossing will playa major role in the determination of possible structure alternatives. The proposed bridge lies on a horizontal curve, and will have an overall span length betwecn 110 feet and 135 feet depending on roadway alignment. A shallow superstructure is required to minimize the vertical profile due to ADA demands and still provide enough under clearance to mcet maintenancc and environmental criteria. A structural form that can meet these geometric requirements and the aesthetic visions of the City is the goal of the Gannett Team. Multi tamily residences are adjacent to thc site and proper consideration must be given in the selection of the form, material, and appearance of the structure to be constructed. The local residents will be sensitive to what is built and will demand a structure that is as beautiful as it is functional. Much thought and imagination has been given to create a "plaza" feel on the bridge while balancing the budget concerns. Amenities such as alcoves, viewing platforms, aesthetic railings, and possibly even planters have been considered for this project. I I I I I The Gannett Team envisions four possible alternatives to meet the City's needs. They are as follows: I Alternative J: Post- Tensioned Box - The first option makes use of a post-tension concrete box superstructure resting on reinforced concrete abutments supported by drilled shafts. This structure type not only provides a clean, smooth look, but the inherent behavior properties of the section align with the demands of the site. A closed box section is ideal for resisting torsion forces generated due to curvature, and post tensioning provides sufficient strength with controllable section depths. Though the structure can bencfit from all these positive attributes, structure depth will still be an issue. Minimum vertical clearance above mean high water will be an issue to address with this structure typc and the GF Team is committed to work with the appropriate agencies. Proper measures, such as a more resistive concrete mix and coated reinforcing stcel can be taken to assure stmctural integrity at dccreased clearance levels. Since there will not be any exposed anchorages inside thc box, the minimum inner void height bascd on accessibility criteria may be relieved and a shallower section used. The use of a vertical curve to raise the alignment profile is anothcr option in handling depth issues. I' l~=-- - =---/ rJ \\LL- ~ol b;.. T'10 :Ek" P9~,T-T::N~,JC'r'E) ~ . tI~.. . f. w-:r.:rl> r:.,,~ 4~ W l I I I I The box section can be either pre-cast segmental or cast-in-place concrete. A pre-cast option would allow for quicker construction and more refined quality control opcrations, though the placement of segments may bc difficult for many local contractors due to special truss systems and gantries that may be required. Additionally, tendon layouts may become more complicated due to the several stages of stressing required to construct such a structure. A cast-in-place box would simplify the tendon patterns, but forming of the element would bring challenges of its own. Temporary easements in the canal would be required to permit temporary supports of thc form system, and constmction time would bc prolonged over the pre-cast counterpart. I I I The box superstructure would rest on two reinforccd concrete stub abutments supported on drilled shafts. Drilled shafts are recommended over driven piles due to noise considerations of the driving process, and would be less intmsive in terms of environmcntal impacts. Tie downs may be required to resist the coupled forces rcsulting from curvature, but these can easily be dealt with using the eorreet details. Form liners and other architectural treatments could be incorporated, adding character to the exposed surfaces of the abutments and increasing public appcal. Wing walls will I I