Budapest University of Technology and EconomicsFaculty of Civil Engineering - Since 1782

High-strength steel materials (grades S500 - S960) gaining prominence in civil engineering, especially for large-span bridges. Their widespread application is restricted by the lack of design background, which needs improvement and further research work. The special features of the material properties and manufacturing technology of high-strength steel structures mean design procedures developed for conventional steel structures may be not applicable or too conservative for high-strength steel structures. From this point of view, the limit states that are likely the most critical for high strength steel structures include global buckling and local plate buckling. Within the current research program, the characteristics of the global and local stability of members under compression, bending and the combination of these two effects will be reviewed. Theoretical basis of the stability assessment methods for welded plated structures using high-strength steel will be studied and specified design methods are to be developed having general validity and proven theoretical bases. The focus of the study is directed at the range of structural systems commonly employed in the bridge design practice (compressed and bended columns with box- and I-sections). 

There are well-described differences in the material behaviour and manufacturing techniques between normal strength steel and high-strength steel such as (i) stress-strain characteristic, (ii) character of the yield plateau, (iii) residual stress distribution, (iv) magnitude of compressive residual stresses, and (v) welding properties and quality check methods. These differences cause, design theories developed for normal strength steel cannot be applied in the same form for high-strength steel structures. 

The planned result of the program is the development of well-established design methods for the implementation of high-strength steel into bridge design. The most decisive intention is to clarify theoretically how the above-mentioned differences affect the resistance for welded structural members having different cross-section shapes (welded box and I-sections) and failure modes. It is known that differences between normal and high-strength steel could affect the failure mode and resistance in the case of different stability phenomena differently (e.g. global member buckling, local plate buckling, shear buckling). For all the mentioned stability problems the research aim is to give answers how the specific differences can affect the buckling resistance. A comparative numerical study is planned to be executed on simple structural members to analyse the impact of high-strength steel specialties on (i) global member buckling, (ii) local plate buckling and (iii) shear buckling resistance. Comparative study will be made using welded box-section and I-section beams and columns. General design methodology and explanation are to be developed to establish the reason of differences and consequences on the load-carrying capacities coming from the aforementioned specialties.  

Research tasks and expected outputs:

    • literature overview on global member buckling, local plate buckling and shear buckling of high strength steel welded box and I-sections

    • creation of a database on experiments available in the literature

    • state-of-the-art report on the material and manufacturing specialties of high-strength steel structures,

    • characterisation of the resistance behaviour based on experimental database and theoretical background

    • execution of numerical research program to extend the previous investigations and to analyse the effect of different geometrical and material properties on the resistance, 

    • description of the resistance increasing effects of high-strength steel for member buckling, local plate bucking, and shear buckling based on the numerical results, 

    • enhanced design method development for welded box-section and I-section compression members.