Resources

This Technical advice note outlines a proposed amendment to Bridge manual clause 4.2.1(f) and systems approved for use in the interim.

Concerns have been raised over the difficulty or impracticability of Charpy V-notch testing of reinforcement mechanical couplers and anchors, as currently required in the Bridge manual, and whether this test method provides a good correlation with brittle fracture resistance. An alternative method employing high speed tensile testing is therefore being investigated to consider its appropriateness and reliability.

Possible additional requirements are being considered for other tests detailed in clause 4.2.1(f) to ensure that the full range of scenarios that may arise in practice are adequately catered for. Consequently revisions to Bridge manual clause 4.2.1(f) are in preparation.

In the interim until such time as the Bridge manual revised clause 4.2.1(f) requirements are promulgated, the three systems outlined below may be used on NZ Transport Agency projects subject to their use meeting the conditions specified herein. Other systems may also be accepted for use on a case by case basis subject to their meeting the existing requirements of Bridge manual clause 4.2.1(f) as modified herein.

Interim use of Reidbar™ Steel Couplers and Flange Nuts

ReidBar™ Steel Couplers and Flange Nuts may continue to be used on Agency projects subject to continuing compliance with the current requirements of Bridge manual clause 4.2.1(f).

Interim use of Ancon^® BT Couplers and Anchors, and IMBMS Iron Man Couplers and Anchorages

Ancon^® BT and IMBMS Iron Man Couplers and Anchorages may be used on Agency projects subject to continuing compliance with the current requirements of Bridge manual clause 4.2.1(f), excluding the requirement for Charpy V-notch testing for brittle fracture resistance and, on the basis of testing undertaken to date, the following:

• The coupled or anchored bars at their location of coupling or mechanical anchorage shall not be subjected to stresses under ultimate limit state non-seismic load combinations, or stresses due to the maximum considered earthquake (ie 1.5 x ULS) in combination with appropriate non-seismic loadings, determined by elastic analysis, in excess of the higher of:
  • 460MPa, or
  • 80% of the ultimate tensile stress of the reinforcement bars for specific tested batches of reinforcement bars that are to be used on the project at locations where coupling or mechanical anchoring of the bars is required.

(Non-seismic loadings to be considered in combination with MCE seismic loading are given in load combination 3A of the Bridge manual table 3.2. Capacity reduction factors are not applicable to the elastic analysis.)

• The couplers and anchors shall not be located in or immediately adjacent to ductile and limited ductile plastic regions.
• The couplers and anchors shall be subjected to batch testing comprising satisfactory tensile testing of the reinforcement/coupler or reinforcement/anchor system for each reinforcement diameter, from each combination of batch (heat of run) of couplers / anchors and of reinforcement that is to be used on the project.

Each tensile test shall comprise 5 pieces of randomly selected couplers/anchors and reinforcement samples from the diameter of bar to be used from that combination of batches (heat of runs) of couplers/anchors and reinforcing. The tensile test shall determine the capacity of the coupled/anchored bar system and during the test the following shall be noted, the yield strength, the tensile capacity, the failure location and the failure mode of the reinforcement/coupler system.

Combinations of couplers or anchors and reinforcement, making up systems, from each batch will be deemed suitable for use if from the results from test samples, for all bars and couplers/anchorages tested:

• the yield strength based on the cross-sectional area of the bar, f_y, is found to be greater than 500MPa
• the ultimate tensile capacity based on the cross-sectional area of the bar lies within the range specified by AS/NZS 4671, ie for Grade 500E reinforcement bars lies within the range 1.15f_y ≤ bar UTS ≤ 1.4f_y
• the failure mechanism is ductile with ductility not significantly reduced as compared with that of the parent bar; and
• the point of failure is found to be located more than two bar diameters away from the end of the coupler or anchor and away from any cold worked zone.

A summary of the results shall be forwarded to the Transport Agency project manager (or their agent) prior to the couplers or anchors being cast into concrete.

Please note that the above has been written for use with grade 500E reinforcement. Grade 300E reinforcement may be used with appropriate modification of the above and the agreement of the Transport Agency’s National Structures Manager.

Use of other reinforcement coupler and anchorage systems

Subject to acceptance by the Transport Agency’s National Structures Manager, on a case by case basis, reinforcement coupler and anchorage systems other than Reidbar™ Steel, Ancon® BT or IMBMS Iron Man may be used on Transport Agency projects where:

• compliance with the current requirements of Bridge manual clause 4.2.1(f), excluding the requirement for Charpy V-notch testing for brittle fracture resistance can be demonstrated; and
• the limitations on stress applied to the coupler or anchorage and the requirement for batch testing specified above for the Ancon^® BT and IMBMS Iron Man systems are applied unless satisfactory evidence of brittle fracture resistance can be provided to the Agency project manager (or their agent). 

Application

The requirements of this Technical advice note apply with immediate effect and until they are revoked, either by issue of a further technical advice note or promulgation of a revised Bridge manual clause 4.2.1(f).

Further information

For further information contact the Highways and Network Operations Structures team at bridgemanual@nzta.govt.nz.

Neil Cree