Bernt Johansson

Resistance of I-girders to concentrated loads

This paper presents the results from an experimental investigation including tests with welded girders and rolled beams subjected to three different cases of concentrated loads applied to the girder flanges. The welded girders were made from a high strength, quenched and tempered steel, while the rolled beams were of an ordinary steel grade. The results from the experimental investigation presented herein have been added to test results taken from the literature and used for a formulation of a design procedure for the resistance to concentrated loads. The suggested design procedure is unified for the three different load applications and also harmonized with the design procedures normally used for describing buckling problems in the steel codes. The design procedure is a further development of the design procedure for patch loading suggested in B. Johansson & O. Lagerqvist [J. Construct. Steel Res., 32 (1995) 69–105] and has in a simplfied form been suggested for use in Eurocode 3 Part 2 (Bridges), as well as in Eurocode 9.

Resistance of longitudinally stiffened I-girders subjected to concentrated loads

Abstract This paper presents a design procedure for the determination of the ultimate resistance of longitudinally stiffened girder webs to concentrated loads. The influence from the longitudinal stiffener is considered in the slenderness parameter λ , through the buckling coefficient k f . This procedure is harmonized with other design procedures currently used for describing buckling problems in steel structures. An expression is developed for the buckling coefficient based on finite element analysis. The interaction between the web plate with flanges and a longitudinal stiffener was considered in the analysis. The ultimate strength according to the design procedure presented herein and the results are compared with available experimental results. The interaction with bending is also investigated.

New design rules for plated structures in Eurocode 3

Abstract This paper gives an overview of Eurocode 3 Part 1.5 Design of Steel Structures. Supplementary rules for planar plated structures without transverse loading have been developed together with the Eurocode 3-2 Steel bridges. It covers stiffened and unstiffened plates in common steel bridges and similar structures. This paper presents the background and justification of some of the design rules with focus on the ultimate limit states. The design rules for buckling of stiffened plates loaded by direct stress are presented and explained. For shear resistance and patch loading the new rules are briefly derived and compared with the rules in Eurocode 3-1-1. Finally, the statistical calibration of the rules to tests is described.

Resistance of plate edges to concentrated forces

Abstract The prediction of the resistance of plate edges to concentrated loads has been dealt with in numerous studies of a more or less empirical nature. The normal approach is to use two criteria for the resistance, one based on yielding and one based on instability. This study aims at a procedure that is harmonized with those normally used for describing other buckling problems. It has been carried out as part of the work with drafting Eurocode 3 Part 2 and the paper is intended as a background document for the suggested design rules.

Design of hybrid steel girders

Abstract A hybrid steel girder is a welded girder with different steel grades in flanges and web. Usually, the flanges are made of high strength steel (HSS) like S690 and the web of a lower grade say S355 but combinations like S460 and S355 are also used. Such girders are more economical than homogenous girders. Hybrid girders have been used in the US since long but they are not commonly used in Europe. Some examples of the use of hybrid girders in Sweden are presented together with economic comparisons. Design rules for hybrid girders are presented together with justifications. Typically, hybrid girders are of cross-section class 4 according to Eurocode 3. The resistance in bending in ultimate limit state is influenced by the local yielding of the web, which limits the stresses in the web and affects the effective width of the web as well. Simplified formulae for the bending resistance are presented. For serviceability limit states, the local yielding of the web has to be accepted but the requirement of reversible behaviour will still be fulfilled. For the limit state of fatigue, Eurocode 3 states a restriction that the stress range should not exceed 1.5 times the yield strength. For hybrid girders, it is shown that this restriction applies to the yield strength of the flanges and that yielding of the web does not influence the fatigue strength.

Current design practice and research on stainless steel structures in Sweden

Abstract The current design practice in Sweden is using codes for structural steel also when working with stainless steel. For load cases governed by instability this may produce non-conservative errors amounting to 10% while it may greatly underestimate the ultimate resistance in cases when instability is not governing. Three ongoing research projects are briefly described, one on weldbonding, one on plastic forming and one on the behaviour of structural components. A part of the latter concerns fundamental work regarding the material behaviour which in general is described using too simple models. This is presented in some detail and its results will be used to provide improved finite element simulations.

Residual static resistance of welded stud shear connectors

Headed studs are widely used in composite bridges to provide longitudinal shear force transfer in the interface between concrete deck and steel beam. There is still no theoretical model available t ...

A new analytical model of inelastic local flange buckling

Abstract This paper deals with analytical modelling of inelastic local flange buckling of compressed I-beam flanges. A short discussion of the relevance of different constitutive models for the inelastic material behaviour is carried out. It is claimed that what is known as the ‘plastic buckling paradox’ is not at all a paradox but a result of improper use of plasticity theory. An analytical model for the inelastic local buckling of an I-beam flange is proposed. The model considers the buckling process as being composed of two parts. The first is associated with inelastic torsional buckling of a compressed flange and the second part corresponds to a yield line plate buckling configuration which includes the effect of stress redistribution due to large deformations. The transition between these phases is left out in the model. The model is capable of predicting approximately the force-deformation relation of a locally buckling stocky flange for different stress-strain relations. The model is evaluated against experiments and the agreement is found quite reasonable.

Tension flange instability of I-beams

Abstract The possible lateral–torsional instability of an I-beam with braced compression flange is studied. It is shown that taking the sagging prior to lateral–torsional buckling into account gives a finite critical moment. A solution for a uniform I-beam under uniform bending is presented. It is further shown that this solution can be approximated by a simple geometrical relation for the critical strain. This approximation is a lower bound also where the bending is causing inelastic deformations. For normal structures tension flange instability will not be a problem but it may be necessary to consider it for very high strength shallow beams or if plastic rotations occur in the sagging region.

Lateral-torsional buckling of continuous bridge girders

Abstract The resistance of bridge girders with respect to lateral-torsional buckling at support is strongly influenced by the moment gradient. In most design methods this influence is taken into account by the use of a correct critical bending moment in the slenderness parameter λ. This critical moment is influenced by the shape of the moment diagram as well as the distortion of the cross-section and the restraint from the web and stiffeners, if any. In this paper, a method for the calculation of the critical moment is presented. A further effect of the moment gradient is that the stresses due to lateral bending of the flange in connection with lateral-torsional buckling does not coincide with the maximum of stresses caused by bending in the vertical plane. This is taken into account by performing the check for lateral-torsional buckling in a design section at some distance from the support. A design procedure based on this concept has been introduced in Eurocode 3 Part 2: Steel Bridges.