High strength steel local buckling and residual stresses

Sammanfattning: High strength steel provide designers with the possibility of creating more slender and weight efficient structures than would be possible if using steels with lower strength. To be able to do this, a structural designer needs updated and validated codes as aid in their work. This thesis addresses the behaviour of high strength steel with respect to local buckling and residual stresses. The thesis was aiming to determine if there exists any significant differences in the resistance to local plate buckling of high strength steel (fy > 460 MPa) compared to steels with lower strength. Furthermore, longitudinal residual stresses induced by welding were also considered on a basis of material strength. Experimental work considering these two issues was conducted concerning the three steel grades Domex 420, Weldox 700 and Weldox 1100. The investigation concerning the local buckling resistance comprises experiments on 48 welded box section specimens made of the three grades. Nominal plate slenderness values were altered between 0,7 and 1,5. Moreover, the experimental work was founded on plate theory with respect to local buckling and a survey of other conducted comparable experiments. The results from the tests and the literature survey were evaluated with respect to Eurocode 3. The gathered test results from literature and experiments showed that no significant difference between the local buckling resistance of different steel strengths could be concluded if compared to the Winter function. However, the Winter function was concluded to overestimate the resistance for more slender simply supported plates (plate slenderness > 0,9) with residual stresses (in as-welded condition). The residual stress state present in three box sectioned specimens made of the three grades was measured with the blind hole technique. Evaluation of the test results was made with respect to the steel strength and complemented with test results collected from a literature survey. The study showed that the tensile residual stresses induced by welding could not be directly correlated to the material strength. Results from measurements on high strength steel specimens showed that the longitudinal residual stresses was lower if made dimensionless with respect to the strength of the steel.