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University of Sheffield, 7 th September 2009 Angus Ramsay & Edward Maunder.

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Presentation on theme: "University of Sheffield, 7 th September 2009 Angus Ramsay & Edward Maunder."— Presentation transcript:

1 University of Sheffield, 7 th September 2009 Angus Ramsay & Edward Maunder

2  Who are we?  Partners in RMA  Fellows of University of Exeter  What is our aim?  Safe structural analysis and design optimisation  How do we realise our aims?  EFE an Equilibrium Finite Element system

3  Displacement versus Equilibrium Formulation  Theoretical  Practical  EFE the Software  Features of the software  Live demonstration of software  Design Optimisation - a Bespoke Application  Recent Research at RMA  Plates – upper/lower bound limit analysis

4 Turner et al Constant strain triangle Fraeijs de Veubeke Equilibrium Formulation Teixeira de Freitas & Moitinho de Almeida Hybrid Formulation 1950196019701980199020002010 Ramsay Maunder RMA & EFE Robinson Equilibrium Models Heyman Master Safe Theorem

5 Discontinuous side displacements  = V v Semi-continuous statically admissible stress fields  = S s   Hybrid equilibrium element Conventional Displacement element


7  Sufficient elements to model geometry  hp-refinement – local and/or global  Point displacements/forces inadmissible  Modelled (more realistically) as line or patch loads

8 p=0, 4 elements p=1 p=2 100 elements 2500 elements


10 Error in Point Displacement EFE1.13% Abaqus (linear) 10.73% Abaqus (quadratic) 1.70%



13 Equilibrating boundary tractions Equilibrating model sectioning

14 Stress trajectories Thrust lines

15  Geometry based modelling  Properties, loads etc applied to geometry rather than mesh  Direct access to quantities of engineering interest  Numerical and graphical  Real-Time Analysis Capabilities  Changes to model parameters immediately prompts re- analysis and presentation of results  Design Optimisation Features  Model parameters form variables, structural response forms objectives and constraints

16  Written in Compaq Visual Fortran (F90 + IMSL)  the engineers programming language  Number of subroutines/functions > 4000  each routine approx single A4 page – verbose style  Number of calls per subroutine > 3  non-linear, good utilisation, potential for future development  Number of dialogs > 300  user-friendly  Basic graphics (not OpenGL or similar – yet!)  adequate for current demands

17 Demonstrate real-time capabilities post-processing features geometric optimisation Analyses elastic analysis upper-bound limit analysis Equal isotropic reinforcement top and bottom Simply Supported along three edges Corner column UDL

18 Demonstrate geometric variables design optimisation Analyses elastic analysis Axis of rotation Axis of symmetry Blade Load Angular velocity Geometric master variable Geometric slave variables Objective – minimise mass Constraint – burst speed margin

19 Geometry: Disc outer radius = 0.05m Disc axial extent = 0.005m Loading: Speed = 41,000 rev/min Number of blades = 21 Mass per blade = 1.03g Blade radius =.052m Material = Aluminium Alloy Results: Burst margin = 1.41 Fatigue life = 20,000 start-stop cycles

20 Flat slabs – assessment of ULS Johansen’s yield line & Hillerborg’s strip methods Limit analyses exploiting equilibrium models & finite elements Application to a typical flat slab and its column zones Future developments


22  EFE: Equilibrium Finite Elements  Morley constant moment element to hybrid equilibrium elements of general degree Morley general hybrid

23 RC flat slab – plan geometrical model in EFE designed by McAleer & Rushe Group with zones of reinforcement

24 principal moment vectors of a linear elastic reference solution: statically admissible – elements of degree 4 principal shears principal moments

25 elastic deflections Bending moments Transverse shear

26 basic mechanism based on rigid Morley elements contour lines of a collapse mechanism yield lines of a collapse mechanism

27 principal moment vectors recovered in Morley elements (an un-optimised “lower bound” solution)

28 M xx M yy M xy biconic yield surface for orthotropic reinforcement

29 closed star patch of elements formation of hyperstatic moment fields

30 moments direct from yield line analysis: upper bound = 27.05, “lower bound” = 9.22 optimised redistribution of moments based on biconic yield surfaces:  21.99

31  Refine the equilibrium elements for lower bound optimisation, include shear forces  Initiate lower bound optimisation from an equilibrated linear elastic reference solution & incorporate EC2 constraints e.g.  30% moment redistribution  Use NLP to exploit the quadratic nature of the yield constraints for moments  Extend the basis of hyperstatic moment fields  Incorporate shear into yield criteria  Incorporate flexible columns and membrane forces


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