No abstract

Particularly efficient steel components can be designed by performing a plastic global analysis of a structure made of high‐strength steel (HSS) as well. However, plastic design of HSS structures is not embodied in current standards, which is why a broad research study was carried out to address different aspects of the use of HSS for plastic design. This paper deals with verified numerical investigations of the rotation capacity of HSS I‐girders considering realistic true stress‐strain curves, local plastic instability and damage mechanics approaches to predict ductile crack initiation. Various influences on the rotation capacity of HSS beams were assessed by varying flange and web slenderness ratios, material characteristics, system dimensions, stiffness of lateral supports and loading conditions so that recommendations for the plastic design of HSS girders can be given. It is apparent that, apart from the slenderness of the flange and the material properties, the slenderness of the web is one of the main influencing characteristics. The results show that the plastic design of HSS structures is possible when limits for cross‐section class 1 are more severe for HSS grades over S460 up to S690 compared with the current limits in EN 1993‐1‐1.

In order to design efficient and highly utilised sections, the plastic/plastic design approach depicts a valuable tool. Concerning plastic design, Eurocode 3 requires only Class 1 cross‐sections and material grades up to S460, depicting conventional strength steels (CSS), to be used. High strength steels (HSS) with yield strengths up to 700 MPa are not considered appropriate for plastic design due to their lower ductility. However, the exclusion of HSS appears to be unnecessary in the light of recent test results. Experimental investigations on 20 homogeneous and hybrid high strength double symmetric I‐section beams have been conducted comprising various slenderness characteristics of flange and web and different span lengths. The results show that the rotation capacity value of R = 3, currently required by EC3 regulations, can actually be achieved by high strength steel beams depending on their cross‐sectional characteristics. Additionally, the experimental tests have been recalculated numerically. The material characteristics of the models have been defined by flow curves, which have firstly been calibrated on the basis of small‐scale tensile tests and furthermore slightly fitted to the full‐scale test results. Ductile material failure in terms of crack initiation and evolution is considered by incorporating a damage mechanics model. It can be shown that experimental and numerical results show very good accordance.