Temporary bridges are often desired to maintain traffic during bridge reconstruction projects and are also utilized on an emergency basis to accommodate structures that are taken out of service by unforeseen circumstances such as nature or vehicular collisions. From a national perspective, the design and construction criteria for temporary bridges are an inconsistent practice among agencies. Some agencies have special provisions covering this work, while other agencies have no such provisions. Design of temporary bridges in accordance with the current AASHTO LRFD Bridge Design Specification or alternative specifications may result in potential over/under design for the following areas:
- Satisfying the Fatigue Limit State, and specifying details with infinite fatigue life, or a specified number of cycles;
Satisfying the Extreme Event Limit State for seismic, wind, stream, and vessel impacts, where the bridge is not anticipated to be in service for a particular event recurrence interval;
Satisfying exterior beam, deck overhang, and parapet loading criteria;
Satisfying bridge width, striping, and end treatment criteria;
Long term creep or prestressing losses in concrete elements;
Design of foundations for contraction scour, local scour and long term scour, and required hydraulic opening for a given design flood event;
Live Load requirements, including special and routinely permitted vehicle classes;
Inspection frequency and coding requirements subject to NBI compliance;
Load rating requirements; and
Limited traffic for temporary bridges where certain vehicles are restricted from use.
It is also desirable to provide definitions and requirements to address the anticipated service durations for “temporary” and “interim” bridges - given that these durations may vary considerably, and may require the need for different structural and safety performance. The need to define requirements regarding single-use temporary bridges/components versus multiple deployment temporary bridges/components also exists.
Obtaining a national perspective of the current design and construction requirements used by agencies for the procurement of temporary bridges may lead to the development of a more consistent and unified set of performance based criteria. To achieve this goal, focused analytical studies of existing temporary bridge specifications along with comparisons to AASHTO LRFD Bridge Design Specifications, 17th Edition Standard Specifications, and the AASHTO Guide Design Specifications for Bridge Temporary Works will need to be performed.
The objective of this research is to develop proposed AASHTO guidelines for design and construction of temporary bridges. The proposed guidelines should provide more consistency in the reliability and performance of temporary bridges, and offer agencies with economically feasible options that will eliminate the concerns of under/over designed temporary structures.
Task 1. Conduct a literature review of relevant domestic and international research, specifications from agencies or manufacturers. This information shall be assembled from published and unpublished reports, contacts with academia, transportation agencies, industry organizations, and joint manufactures.
Task 2. Investigate the applicability of various AASHTO bridge design specifications for temporary bridges such as:
AASHTO LRFD Bridge Design Specification
AASHTO 17th Edition Standard Specifications for Bridge Design
AASHTO Guide Design Specifications for Bridge Temporary Works
AASHTO Manual for Bridge Evaluation
Task 3. Synthesize Tasks 1 and 2 and prepare an outline of the proposed guidelines, including discussion of the contents and intent.
Note: Submit a draft of the synthesis and detailed outline no later than 4 months after contract award. NCHRP approval will be required before proceeding with the remaining tasks.
Task 4. Develop design and construction requirements, identify materials and create definitions for the classes of temporary bridges based on anticipated service duration.
Task 5. Develop a draft of proposed AASHTO guidelines with commentary for design and construction of temporary bridges according to the approved outline. Submit the draft of the proposed guidelines no later than 4 months after the Task 3 approval.
Task 6. Revise the draft of recommended AASHTO guidelines submitted in Task 5 according to the NCHRP project panel comments.
Task 7. Present the recommended guidelines in AASHTO standard interim-revision format to the AASHTO Subcommittee on Bridges and Structures, Technical Committees: T-4 Construction.
Task 8. Submit a final report describing the entire research effort with the proposed guidelines. Following receipt of the draft final report, the remaining 2 months shall be for NCHRP review and comment and for research agency preparation of the revised final report.
STATUS: Research in progress.