Experiences of HSS structures in Scandinavia -HILONG Workshop-

Transcription

1 Experiences of HSS structures in Scandinavia -HILONG Workshop- Milan Veljkovic London, 30 th June,

2 Outline Material properties, steel grades, costs Design of Hybrid Beams in Pure Bending Engineering examples Conclusions (obstacles and solutions) 2

3 EN structural steel grades and costs *) Yield Strength [MPa] *) Prof. B. Johansson, LTU, Common grade in US and Sweden Highest grade in Eurocode Highest grade in Eurocode Non standard grade (700) 690 (900) As rolled Normalised Thermomechanically rolled Both exist Quenched tempered 3

4 Eurocode SS-EN (for now) to be in EN Hot-rolled structural steel Thermo-mechanically rolled steel for cold forming 4

5 SSAB steels (examples) S460 rolling direction S o to rolling dir. - Forming data - Stress-strain curves - Welding tests, details on welding consumables 5

6 Requirements for ductility EN ( S460) EN ( above S460 to S690/S700) 6

7 Material properties Exempels: Mild steel - S275 Mild steel - S355 HS Steel - S700 Nominal stress (MPa) S275 S355 S700 Min yield strength Nominal strain (%) Acc. to EN 10025, parts 2, 3, 4 and 6 Ultimate strain 7

8 Ductility Yield strength 0.2% [MPa] 8 Ratio of yield strength to tensile strength

9 Material properties (FEA-explicit) Stress (MPa) Engineering stress-strain True stress-strain S275 S355 S Strain (%) 9

10 Beam bending Simple span beam L = 7.0 m Load application (displ. control) Different cross-sections are assumed to achieve the same beam resistance: S275 S700 10

11 Comparison S275 vs. S700 beam 11

12 Hybrid girder S275/S700 vs. S355/S P pl,rd,s700 = 1022 kn P pl,rd,s700 = 1022 kn Force (kn) P pl,rd,s700+s275 = 867 kn Force (kn) P pl,rd,s700+s355 = 895 kn S275 S700 flanges: S700; web: S275 Initial stiffness P pl,rd,s275 = 401 kn Deflection (mm) S355 S700 flanges: S700; web: S355 Initial stiffness P pl,rd,s355 = 512 kn Deflection (mm) 12

13 Cross-section classification and type of analysis Cross-section class Global analysis Crosssection/member verifications Class 1 Class 2 Plastic Elastic Elastic Elastic Elastic Plastic Plastic Elastic Plastic Elastic S700 Class 3 Class 4 Elastic Elastic 13

14 - Design of hybrid girders - Bending resistance Section 1 &2 14

15 Design of hybrid girders - Bending resistance Section 3 &4 Classification acc. to f yf 15

16 Design of hybrid girders Serviceability requirements Reversible behaviour JCSR paper 2004 ±0.92 f yf ratio

17 - Design of hybrid girders - Bending resistance Lateral torsional buckling Flange induced buckling the same as for homogenious girders The web does not have any effect 17

18 Flange induced buckling (validation of Basler 1961) 18

19 Flange induced buckling, homogeneous vs. hybrid girders Force (kn) flanges & web: S255 flanges & web: S460 flange: S460; web: S255 Elastic bending stiffnes Deflection (mm) 19

20 Flange induced buckling verification with Hand calculation Mpl,Rd,S460 = 4201 knm Moment (knm) 4000 Mpl,Rd,S460+S255 = 3935 kn 3000 Mpl,Rd,S255 = 2365 kn 2000 flange & web: S flnge & web: S255 flange: S460; web: S Curvature (mrad)

21 Flange induced buckling ductility assessment 1.4 Non Dimensional Moment (M/M p ) flange & web: S460 flnge & web: S255 flange: S460; web: S Non Dimensional Curvature ( / p ) 21

22 - Design of hybrid girders - Shear resistance, patch loading EC3-1-5 formulae with different yield strength - Interaction V-M Class 3&4 as it is Class 1&2 neglect Practice in USA and Sweden 22

23 Hybrid girder example - Partial yielding in the web will occur but the girder will still show a repeatable behaviour. - If the yield strength of the flanges is not more than twice that of the web the yielding can be neglected in serviceability limit state. - Easy fabrication of hybrid girders is no problem; matching electrodes can be met up to S Hybrid girders are more economical; Limit f yfl <2 f yw for serviceability reasons, as shown in experimental verification 23

24 Engineering examples Composite bridge in Sweden with hybrid I-girders. Flanges S500 Web S355 24

25 Engineering examples -cost comparison- Composite bridge with 23 m simple span, width 7 m, *). *) Mittådalen bridge Steel designer: Scandiaconsult (Ramböll today), Luleå With S355 as reference the alternative S460+S690 gives: Cost for site welding -15 % Cost for painting -20 % Total cost -12% 25

26 Engineering examples -cost comparison- Web S355 Flanges S355 Costs 1.0 S355 S690-5% S355 S690-6% 26

27 Engineering examples Fast Bridge 48, patented, developed in last 1980 and beginning of 90-ies for the Swedish army *). Truss girders in 5 mm thick S1100. Span 48 m, designed for 65 t tank, deflection 0,65 m. S1100 has the same weight/strength ratio as advanced Al-alloys *) Steel Designer: Kockums AB, Karlskronavarvet and KTH, Stockholm 27

28 Engineering examples Launching beam for erecting the bridge in S1100. Carries one man as cantilever and the bridge sections as simply supported beam. The bridge is erected in 1 h 15 min. Cross section of launching beam. Note: the folds used to stiffen the web. 28

29 Conclusions: Why High Strength Steel? Reduced costs due to: Less material (but more expensive) Less welding (thinner plates) Less painting (smaller area) Lower transport costs Reduced weight allows higher payload. Reduced environmental impact due to less material for a given performance 29

30 Conclusions: Obstacles and possible solutions Too high deformations -» precamber, composite action, trusses, Local buckling -» Stiffening by cold formed folds, innovative cross-sections. Availability -» Increased use will increase production and availability. Fatigue -» Post-weld treatments, improved detailing. 30