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#22-02 Interim technical standards for the design of timber bridges

Published: | Category: Technical advice note | Audiences: Road controlling authorities, Road traffic engineers & consultants, Roading contractors

This note provides guidance on the technical standards that can be used for the design of a broad spectrum of timber bridges, including glue-laminated bridges. These technical standards are interim until Waka Kotahi NZ Transport Agency standards and guidance are updated. The interim standards apply from the date of this notice.

Publication details

  • Author:
  • Published: 1 March 2022
  • Reference: 22-02
  • Contact: structures@nzta.govt.nz

Purpose

This note provides guidance on the technical standards that can be used for the design of a broad spectrum of timber bridges, including glue-laminated bridges. These technical standards are interim until Waka Kotahi NZ Transport Agency standards and guidance are updated. The interim standards apply from the date of this notice.

General information

Waka Kotahi is currently developing design guidance for the use of timber for bridge construction. This is primarily to contribute to the goals for reducing embodied carbon in transportation infrastructure.

The Bridge Manual currently provides limited technical standards for traditional timber bridges but is not comprehensive and does not cover modern glue-laminated timber bridges.

The processes and procedures outlined in this update must be followed by any person engaged by Waka Kotahi for the design of a timber bridge undertaken from now on.

Specific changes, technical requirements for timber bridges

The design of timber bridges on Waka Kotahi projects shall be carried out in accordance with the following technical standards and requirements.

The Bridge Manual will continue to apply to all relevant common aspects of bridge design independent of the bridges’ construction materials, particularly the bridge loading requirements.

Designers of simple timber bridges shall adhere to the requirements of standard NZS 3603:1993, including the design of glue laminated members. The designer must consider and decide whether Eurocode 5 is appropriate for additional checks to achieve a robust design. However, note that it is intended that NZS 3603:1993 will be superseded by the publication of AS NZS 1720.1, later in 2022. At that point a further technical note will be issued to ensure any change is clearly advised.

As an alternative, standard AS 1720.1 may also be used as the design standard for simple timber bridges and may be used to provide additional design guidance for design aspects not covered by NZS 3603:1993.

Designers of more complex timber bridges must use standard Eurocode 5, including parts BS EN 1995-1-1, BS EN 1995-1-2 and BS EN 1995-2, for their structural design work especially for the vibration and fatigue checks required. Beyond that, standard AS 5100.9 shall be used for the design of stress laminated timber (SLT) elements.

Alternative standards may be accepted with appropriate justification through the NZTA Technical Departures process. Such alternative standards may only be approved by the Chief Engineer.

Communication plan

Our target audience for this manual is generally internal project staff and those external consultants and/or contractors who may be engaged in bridge design for Waka Kotahi. As a result, our communications will mostly be focussed on our project teams. Advice of these changes will be promulgated by:

  • this note and any others advising any change of status of the standards
  • direct access via the website and intranet
  • opportunities for remote presentations
  • delivery of a presentation at the next Project Managers Forum.

Implementation

The implementation will be enabled by ensuring that the standards are accessible.

Given this update is technical, opportunities to provide for specific training to appropriate technical staff on the changes will be considered.

Document review

This technical advice note remains current after publication of amendment 4 to the Bridge manual 3rd edition. It will be withdrawn when a future amendment of the Bridge manual replacing these requirements is implemented. Cancellation will be confirmed at that time.

Publication details

Author: Waka Kotahi NZ Transport Agency
Published: January 2022
Version: 1
Location: https://www.nzta.govt.nz/roads-and-rail/highways-information-portal/technical-advice-note/

Further information

If you have any questions or feedback, please contact the Team Leader Structural Performance at structures@nzta.govt.nz

 

Signed:

Greg Haldane
Chair, Ratification Group

Vanessa Browne
Delegated Approver