7.8 Bridge Design
Bridge structures refer to all overpasses, underpasses, interchanges and stream crossing structures. Bridge structures include span structures and bridge-class culverts. The following subsections describe tasks associated with developing bridge layouts and the associated bridge details.
Culverts with a total span greater than or equal to 20 feet are considered bridge-class culverts and their design must follow span bridge guidelines.
7.8.1 Final Geotechnical Surveys
Geotechnical investigations are necessary to design for satisfactory long-term performance of structure foundations. For some projects, geotechnical data may have been collected during preliminary engineering. All required data to finish designs must be obtained prior to beginning detailed bridge design.
To make a single data collection effort, coordinate obtaining geotechnical data for designing and planning of the following elements:
- Bridges;
- Radio towers;
- Retaining walls;
- Sound walls;
- Illumination structures;
- Overhead sign and signal structures;
- Pavement structures;
- Embankments;
- Soil in proposed cut;
- Trench excavation protection (shoring); and
- Excavation and backfill for structures.
Considerations in obtaining final geotechnical surveys include:
- Gather and review the existing geotechnical data obtained in preliminary engineering or existing geotechnical data from as-built plans;
- Evaluate project for changes made after original geotechnical investigations were performed during preliminary engineering (e.g., added structures or changed structure limits); and
- Identify additional data required to finalize design and prepare a boring layout to provide to the geotechnical firm obtaining data. Review the locations with roadway designers and structural designers to ensure placement of holes that can be accessed without special equipment if possible.
7.8.2 Bridge Layouts and Details
7.8.2.1 Final Bridge Layouts
After the PBLR (see
) is approved, the bridge layout is finalized and detailed bridge design may commence.
Detailed design should not begin prior to approval of the PBLR.
7.8.2.2 Final Bridge Details
Bridge detail design includes determining superstructure and substructure of span bridges and culverts to handle design loads. Structure type is usually determined while preparing bridge layouts. Bridge details provide information for the contractor to build all structural elements.
Some things to consider when preparing final bridge details include:
- Continued coordination with the roadway and drainage design is needed to update the bridge structures to accommodate any changes in roadway or drainage design. Obtain updates to any of the following:
- Typical sections;
- Alignments;
- Superelevation and transition locations;
- Pedestrian features;
- Bicycle accommodations;
- Required clearances;
- Proposed utilities;
- Roadway lighting;
- Drainage conveyance method and hydraulic design;
- Construction staging;
- Resource agency commitments; and
- Information regarding special issues such as sound walls on bridges and overhead fiber optic and power line restrictions.
- BRG review of steel structures and spliced girders is required at each PS&E milestone (Initial/Detailed/Final);
- Bridge design and detailing also includes retaining/sound walls, bridge rails, structural pedestrian features, lateral restraint, fender systems, utility attachments, bridge illumination, landscape/aesthetic components and drainage systems.
7.8.3 District Review of Bridge Plans
Once bridge plans and details are prepared, the District is responsible for a final review to determine what changes are made to the initial bridge layout and to verify the quantities. Review any significant changes made to the initial layout with the BRG – Project Development section. The District is also responsible for incorporating the structural details into the Sealed plan set (e.g., updating the index of sheets and numbering the plan sheets).
7.8.4 Bridge Plan Sheets
Bridge plan sheets typically include:
- Bridge Hydraulic Data Sheet (see );
- Bridge Layout;
- Estimate & Quantities Sheet;
- Structural Details; and
- Bridge Standards.
|
|
|
|