Bridges

The Department of Transport and Planning (DTP) in Victoria manages a large number of traffic signal poles across the Victorian road network. DTP’s stock includes structures of varying age designed and constructed to different standards and codes over the years, some of which are unknown. DTP has recorded a small number of failure cases of these structures in recent years due to different causes. This prompted an investigation to ensure the safety of road users.

One of the investigated failure modes was fatigue cracking of the anchor bolts. Whether or not these structures were designed for fatigue loading is unclear in the absence of detailed calculations or notes on the historic drawings. Light poles under a certain height were traditionally considered as non-fatigue sensitive structures. However, fatigue effects become more significant when the pole is fitted with traffic lanterns, especially if these are installed on a cantilevered mast arm. Current fatigue assessment codes include BTN 014 Road Sign and Lighting Structures (issued by DTP – Victoria), AS/NZS 5100.6, AASHTO LRFD Specifications for Structural Supports for Highway Signs (2015) and AS/NZS 1170.2 (for wind loading) in combination with AS/NZS 5100.6 or AASHTO LTS.

However, the current Australian fatigue provisions are intended to be applied to new designs. If applied to existing structures, they could lead to conservative results requiring un-necessary treatment / strengthening work in some cases. This paper describes different approaches used in the assessment of fatigue effects on these existing structures using international and local codes / guides and draws conclusions aimed at ensuring the safety of road users while avoiding un-necessary treatment costs.