Section 2: Primary Responsibilities of the Bridge Design Section
Anchor: #i999870Overview
The primary responsibilities of the Bridge Design Section are structural design and the preparation of working drawings or plans. These primary responsibilities involve a procedure that begins with a concept to construct a highway facility and concludes with the submission of finalized plans, specifications, and estimates (PS&E). The procedure includes many steps and it is important to know these steps to fully grasp the responsibilities of the Bridge Design Section. Generally, the procedure for preparation of plans by the Bridge Design Section is as follows.
Consultation. Consultation between the Bridge Design Section, bridge project development manager, and the district design engineer, district bridge engineer, and/or area engineer should precede determination of structure type and scheduling of the letting.
NOTE: This is a good time to make a preliminary decision about who will prepare the bridge plans.
Preliminary Bridge Layouts. The area engineer or the project’s designated consulting engineer prepare preliminary bridge layouts. These layouts are usually complete with geometric controls, type, size, length of spans, hydraulic data, required clearances, soil test boring data, classification of highway, and projected traffic. At this time, type of foundation should be proposed and conveyance of water through stream crossings and scour analysis should be addressed and coordinated with the Hydraulics Section.
NOTE: Area engineers and consulting engineers are encouraged to contact the Geotechnical Branch for advice if there is any question regarding the proper foundation.
The layouts are sent to the bridge project development manager who will forward them to the Design Division, the Federal Highway Administration (FHWA) on federal oversight projects, or other agencies that may exercise review authority.
Bridge Plan Preparation. When approval has been secured from all the appropriate agencies, timing for the plan work is re-negotiated with the district and the job of bridge plan preparation is given to the bridge design engineer or to the consultant.
The following steps apply to the Bridge Design Section, but the routine for consultants will be similar.
NOTE: If consultants are unsure about the current design or detailing standards for an item, they are encouraged to contact the director of the Bridge Design Section.
- The director of the Bridge Design Section assigns the work to a Design Group according to its particular expertise in that type of design, and primarily on its ability to complete the plans in the required length of time.
- The Design Group leader schedules engineering and detailing work for the job according to the target completion date and the Design Group’s other commitments.
- The Geotechnical Branch is contacted early if there is any doubt about the foundation type. When foundation loads have been determined, the Geotechnical Branch will be asked to establish founding elevations.
- When the plans are complete, the bridge project manager sends prints to the district.
- Reviewed prints are returned to the bridge project manager and the Design Group makes any revisions required by the district review.
- Originals, including all reproducible standard drawings are sent to the district.
- Project plans, specifications, and estimates are sent to the Design Division. Any revision required by the pre-letting review are made by the Design Group.
- After letting, optional designs for prestressed concrete
beams are submitted by the fabricator and checked early. Other shop
drawings follow.
NOTE: Consulting engineers should be aware that shop drawings require a significant amount of checking time. They should budget their labor accordingly.
- Occasionally, bridge members that were fabricated beyond specification tolerances are reviewed by the Bridge Design Section for structural adequacy when properly repaired. Also, occasionally, construction problems arise that require review for structural adequacy.
- When the project is finished, geometric calculations are discarded and design notes are assembled and filed.
Structural Design
Structural design involves selection of appropriate materials, systems, and details for the structure and performing calculations of stress and strain in each component caused by the prescribed loading. The following items give examples of potential areas of consideration.
Stream Crossings. Stream crossings carry highway traffic over creeks, rivers, bayous, channels, and bays. Hydraulic considerations are usually involved. Clearances for marine traffic may be required.
Grade Separation Structures. Grade separation structures occur where one roadway must cross over another. Clearance for the overpassed traffic is critical. Highway over highway separations are called overpasses if the project highway passes over; otherwise they are called underpasses.
Railroad Underpasses. Railroad underpasses are where a highway passes under an intersecting railroad. Design is under strict control by the railroad companies.
Miscellaneous Structures. Miscellaneous structures include sign bridges, illumination poles, traffic signal supports, pedestrian overpasses, utility bridges, movable bridges, fender systems, ferry boat landings, and radio towers.
Culverts and End Treatment. Culverts carry storm water under highways. The larger of these culverts are reinforced concrete boxes. Most culverts are constructed from standard drawings. Under some conditions Safety-End Treatment is required to protect errant vehicles. These conditions are outlined in the TxDOT Roadway Design Manual.
Retaining Walls. Some types of retaining walls require structural design. Mechanically stabilized earth (MSE) wall designs require mostly geotechnical considerations. Detailed plans for MSE walls are prepared by the successful wall supplier.
Geotechnical Design. A special group within the Bridge Technical Services Section performs geotechnical design.
Anchor: #i1000020Preparation and Approval of Working Drawings
Preparation and approval of working drawings involve assuring that the various requirements of the design are shown on plan-size (22 x 34 in.) or half-size (11 x 17 in.) drawings as completely and accurately as necessary to allow the structure to be built according to the design. Half-size sheets are preferred by the department. The use of full-size sheets is being phased out.
Bridge Plans. Drawings for construction projects must contain accurate quantities of the various items of work so that the contractor can be adequately reimbursed according to the unit bid prices.
Bridge Standards. Bridge standards are maintained by the Bridge Standards Branch of the Technical Services Section. Standard drawings contain often-used systems and details that can be used in bridge plans without modification. Standards are indexed on the main TxDOT website under Business/TxDOT CAD Standard Plan Files. (See http://www.dot.state.tx.us/business/disclaim.htm.) The website contains instructions about the use of the graphics files.
Preliminary Bridge Layouts. Preliminary bridge layouts are reviewed and approved by the Bridge Design Section. Layouts are initiated by the district, sometimes with assistance by a consulting engineer. See the Bridge Project Development Manual for the submittal process.
NOTE: For major structures, coordinate with the Bridge Design Section through the project development manager as early as possible.
PS&E. Plans, specifications, and estimates contain structural details prepared by the district, consulting engineers, or the Bridge Design Section. In any case a review is necessary to determine that the structure is safe and reasonably economical.
Shop Drawings. The Field Operations Section of the Bridge Division coordinates and checks shop drawings. The Bridge Design Section assists the Field Operations Section when necessary and will check shop drawings for structures that they have designed. Consultants must check their own shop plans.
The specifications and special provisions dictate shop drawing submittal requirements. The following is a partial list of items that require shop drawings:
- Various prestressed concrete beams
- Deck panels
- Preformed metal deck forms
- Structural steel
- Segmental prestressed concrete
- Retaining wall systems requiring shop drawings by specification
- Sound barrier walls
- Bearing pads and other structural bearings
- Various bridge joints (armor joints, sealed expansion joints, finger joints, etc.)
- Bridge protective assemblies
- Overhead sign bridges
- Concrete piling
- Prefabricated pedestrian bridges