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High-strength steel materials (grades S500 - S960) gaining prominence in civil engineering, especially for large-span bridges. The application of hybrid girders combining low- and high-strength steel materials is an effective and economical method for producing steel bridges. The hybrid girders generally consist of webs comprised of low-strength steel and flanges made of high-strength steel. In Europe apart from some minor practical applications and research results in Sweden, these structure types are completely new solutions in bridges, and the theoretical background of their stability design is missing from the current European standardized design provisions. The aim of the research is to determine the theoretical background of the stability design for this girder type and to develop the design theories for application purposes supported by own laboratory test results. Economical design of hybrid girders requires the consideration of partial plasticity at the ultimate limit state design, which is currently not allowed for bridges. Computational design approaches, however, can provide efficient solutions to overcome on these limitations, but their application needs improvement of the current design approach.
In Europe, the application of hybrid girders is novel; therefore, the first task is a throughout study of the international literature of these hybrid girders. Laboratory tests are planned to determine the resistance of hybrid I-girders subjected to bending moment and interaction of bending moment and shear force, which are the primary external forces for bridges. Laboratory tests will be executed on large-scale test specimens (at least 14 specimens with loading span of 4-8 m) loaded by static load. Two different failure modes will be studied during the test program, (i) progressive plastic flow, and (ii) stability limit state. Theoretical bases for the design of hybrid girders are completely different for these two failure modes, therefore, they should be considered separately. Load-carrying capacities, stress distributions and plastic mechanisms will be measured and evaluated during the tests. These are primary inputs for the design theory development. Based on the laboratory tests executed numerical model will be developed and validated. Results of the numerical model will be used to determine the elastic and plastic stress distribution with the entire girder during loading. Based on the stress distribution and nonlinear behaviour the structural response of the specimens can be evaluated and additional limit states specific for hybrid girders can be developed. Based on the validated numerical model a numerical parametric study is to be executed analysing wide range of different bridge girder geometries. Within the numerical parametric study different steel grades for the web and flange plates should be applied. Different yield strength ratios will be investigated and its effect on the resistance is to be evaluated. Special focus will be given to the maximum plastic elongations within the plates with the lower yield strength, which can give limitation in the design theory. Based on the numerical parametric study the elastic, plastic and partially plastic limit states are to be determined for all analysed girder geometries and the relevant resistance levels are assigned. The final research aim is the development of improved design theory for hybrid girders using plastic, partially plastic and elastic limit states
• state-of-the art report gathering previous design theories and research results on hybrid steel girders and their application for bridges,
• experimental results determining the load-carrying capacity, stress distribution and plastic behaviour of hybrid girders,
• comparison of the test results with theoretical design methodologies,
• numerical parametric study to investigate the elastic, plastic and partially plastic limit states,
• improved design theory for hybrid girders used for bridges.
A téma meghatározó irodalma:
1. R.W. Frost, C.G. Schilling: Behavior of hybrid beams subjected to static loads, Journal of the Structural Division, 90(3) (1964), pp. 55-88.
2. H.S. Lew, A.A. Toprac: Static tests on hybrid plate girders, Austin: Center for Highway Research, The University of Texas; 1967.
3. M. Veljkovic, B. Johansson: Design of hybrid steel girders, Journal of Constructional Steel Research 60 (2004), pp. 535-547.
4. C.S. Wang, L. Duan, M. Wei, L. Liu, J. Hu: Bending behavior of hybrid high performance steel beams, Advanced Materials Research, 163-167 (2011), pp. 492-495.
5. M. Shokouhian, Y. Shi: Investigation of ductility in hybrid and high strength steel beams, International Journal of Steel Structures, 14(2) (2014), pp. 265-279.
6. C.S. Wang, L. Duan, Y.F. Chen, S.C. Wang: Flexural behavior and ductility of hybrid high performance steel I-girders, Journal of Constructional Steel Research, 125 (2016), pp. 1-14.
7. A.S. Kulkarni, L.M. Gupta: Experimental Investigation on Flexural Response of Hybrid Steel Plate Girder, KSCE Journal of Civil Engineering 22(7) (2018), pp. 2502-2518.
8. R. Lalthazuala, K.D. Singh: Structural performance of hybrid stainless steel plate girders under shear, Thin-Walled Structures 143 (2019), 106214.
9. R.R. Khartode, A.A. Godase, G. Narule, D. Ahiwale: A parametric study of hybrid steel plate girder, GIS SCIENCE JOURNAL 7(11) (2020), pp. 1045-1058.
A téma hazai és nemzetközi folyóiratai:
1. Journal of Constructional Steel Research
2. Thin-Walled Structures
3. Engineering Structures
A témavezető utóbbi tíz évben megjelent 5 legfontosabb publikációja:
1. B. Somodi, B. Kövesdi: Residual stress measurements on cold-formed HSS hollow section columns, Journal of Constructional Steel Research 128 (2017) 706-720.
2. B. Somodi, B. Kövesdi: Flexural buckling resistance of cold-formed HSS hollow section members, Journal of Constructional Steel Research 128 (2017) 179-192.
3. B. Somodi, B. Kövesdi: Residual stress measurements on welded square box-sections using steel grades of S235-S960, Thin-Walled Structures 123 (2018) 142-154.
4. B. Somodi, D. Kollár, B. Kövesdi, J. Néző, L. Dunai: Residual stresses in high-strength steel welded square box sections, Proceedings of the Institution of Civil Engineers – Structures and Buildings 170(11) (2017) 804-812.
5. B. Kövesdi, B. Somodi: Comparison of Safety Factor Evaluation Methods for Flexural Buckling of HSS Welded Box Section Columns, Structures 15 (2018) 43-55.
A témavezető fenti folyóiratokban megjelent 5 közleménye:
1. B. Somodi, B. Kövesdi: Flexural buckling resistance of welded HSS box section members, Thin-Walled Structures 119 (2017) 266-281.
2. B. Kövesdi, B. Somodi: Buckling resistance of HSS box-section columns, Part I: Stochastic numerical study, Journal of Constructional Steel Research 140 (2018) 1-10.
3. B. Kövesdi, B. Somodi: Buckling resistance of HSS box-section columns, Part II: Analytical study, Journal of Constructional Steel Research 140 (2018) 25-33.
4. B. Somodi, B. Kövesdi, T. Hornyák: Partial factor for local buckling of welded box sections, Structures 30 (2021) 440-454.
5. T. Hornyák, B. Somodi, B. Kövesdi: Vizsgálatok az esztétikusabb, könnyedebb szerkezetek érdekében: EN 1993-1-5 szabvány lemezhorpadási ellenállásának megbízhatósági analízise, Fémszerkezetek: Tervezés, gyártás, építés 2018/2 (2018) 30-35.