Bridges

Limiting carbon footprint by reducing the amount of construction materials is one of the main actions that contributes to sustainable construction practice. This applies to composite bridge superstructure designed to AS5100.6. The revised version of the Standard issued in 2017 allowed steel plate to AS 3597 with grade ranging from 500 to 700 (yield stress 500, 600, 620, 650 and 690 MPa) to be used, these are quenched and tempered plates manufactured in compliance with this Standard. This constituted a significant difference to the previous version of the Standard (2004) in which Cl 1.1.1 (Scope) limited its applicability to steel members for which the value of the yield stress (fy) does not exceed 450 MPa. Furthermore, the revised AS 5100.5 has extended its application to concrete characteristic compressive strength at 28 days up to 100 MPa. The first observation that can be made relating to bridge design is that lighter superstructure may now be able to be designed to AS/NZS 5100.6 (and AS 5100.5) implying significant material savings. However, some technical issues may limit the benefits of using high strength steel plate and concrete. This paper aims to provide design comparison between steel composite trough girders already designed and built using grade 350 steel plate and the same trough girders had they been designed using high strength steel plate (grade 700 to AS 3579) with yield strength of 690 MPa. Issues found such as deflection limits, fatigue stress compliance and plate elements slenderness are investigated and their effects compared. The paper also considers the use of hybrid steel sections and draws a conclusion on the pros and cons of using high strength steel grade.