Overview
ISO 21725-2:2021 - Simplified design of prestressed concrete bridges - Part 2: Box-girder bridges provides a pragmatic, streamlined procedure for designing prestressed concrete box-girder road bridges within the limits defined in Clause 6.1. The document offers simplified rules intended as alternatives to more elaborate design codes, with primary applicability to bridges erected by the full staging method (FSM). It emphasizes structural integrity through continuity, redundancy, robust bearing and member detailing, and external protection against severe loads.
Key Topics and Technical Requirements
- Scope and limitations: Defines permitted use, maximum spans, heights, lane counts, width and skew limits - see Clause 6.1 for applicability conditions.
- Design approach: Simplified ultimate and serviceability limit state formats, with required factored loads and design strength criteria.
- Design documentation: Requirements for calculation reports, geotechnical reports, structural drawings and specifications.
- Actions (loads): Dead loads, live loads (design truck and lane loads), dynamic effects, longitudinal forces, wind, earth pressure, thermal effects, and detailed seismic provisions for different hazard zones.
- Jacking and post-tensioning: Procedures for jacking forces and anchorage design related to prestressing and post-tensioning.
- Structural analysis: Guidance on longitudinal and transverse analysis using empirical, approximate and refined methods; treatment of time-dependent concrete properties, secondary moments and frame analysis.
- Structural systems & layout: Superstructure, substructure and foundation guidance; layout and architectural guidance for box-girder bridges.
- Limit states and load combinations: Prescribed combinations for ultimate and serviceability limit states and recommended checks.
Practical Applications
- Use ISO 21725-2 when you need a reliable, efficient framework for designing prestressed concrete box-girder road bridges where simplified methods are acceptable and FSM erection is planned.
- Particularly useful for preliminary design, feasibility studies, routine road bridge projects, and as a harmonized reference for designers seeking time- and cost-efficient solutions while maintaining safety and durability.
- Supports consistent documentation and handover through required calculation and geotechnical reporting formats.
Who should use this standard
- Structural and bridge engineers designing prestressed concrete box-girder bridges
- Contractors and construction planners using the full staging method
- Bridge owners, road authorities and reviewers who evaluate simplified design submissions
- Engineering consultancies producing design documentation and specifications
Related standards
- Other parts of the ISO 21725 series (where applicable) and national or regional bridge design codes and standards for detailed or alternative design approaches.
Keywords: ISO 21725-2, prestressed concrete, box-girder bridges, simplified design, full staging method, bridge design standards, post-tensioning, limit states, structural analysis.