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Using non-linear analysis solver in GSA 1 Non-Linear & Form-Finding Analysis In GSA (Using GsRelax Solver)
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Using non-linear analysis solver in GSA 2 Programme Introduction Non-linear analysis Form-finding analysis
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Using non-linear analysis solver in GSA 3 Introduction
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Using non-linear analysis solver in GSA 4 What are we here for? Have you used GSA before? Have you used GsRelax before? What design work are you involved in relating to nonlinear analysis? What do you think you might use GsRelax for? What do you want to learn from this course?
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Using non-linear analysis solver in GSA 5 Sources of advice Thomas Li : Software Technology Group Sarah Kaethner: Structural development and support, AT&R Course notes and GSA manual on Intranet On-line help includes description of features and chapters on GsRelax analysis and theory GSA intranet site ‘Tension & Lightweight Structures’ on intranet
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Using non-linear analysis solver in GSA 6 What is GsRelax A non-linear structure analysis program embedded in Windows GSA as a Solver (previously called – Fablon) It uses a non-linear solution method called Dynamic Relaxation It specialises in doing: uGeometrically non-linear analysis uNon-linear buckling analysis uMaterial non-linear analysis uForm-finding analysis
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Using non-linear analysis solver in GSA 7 The model vibrates under the action of out of balance forces until it is in equilibrium Equilibrium position: No out of balance force (‘residual’ ) - system ‘converged’ Unbalanced position: There is an out of balance force (‘residual’) which will generate an acceleration F = ma oscillation The solution method: ‘Dynamic Relaxation’
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Using non-linear analysis solver in GSA 8 Dynamic relaxation is not a matrix method 1F = m To apply the equations of motion, each node needs a mass. This is calculated by GsRelax 2Damping To prevent continuous oscillation, GsRelax applies damping to the system. Equilibrium position: maximum speed, zero acceleration, Most unbalanced position: zero speed, acceleration in peak,
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Using non-linear analysis solver in GSA 9 Original position Balanced position Original position Balanced position Extremely Geometric nonlinearity
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Using non-linear analysis solver in GSA 10 Using non-linear analysis solver in GSA Advantages of using GsRelax Geometric non-linear effects are considered automatically, so it gives more accurate results Versatile in terms of structure types. No limitation on structure types to be analysed. For example, it can analyse: urigid structures uflexible structures ufabric structures ucable structures umechanisms
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Using non-linear analysis solver in GSA 11 Using non-linear analysis solver in GSA Non-linear behaviour Material nonlinearity Geometric nonlinearity Buckling
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Using non-linear analysis solver in GSA 12 Using non-linear analysis solver in GSA Material nonlinearity: Tension only and compression only (Tensegrity)
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Using non-linear analysis solver in GSA 13 Using non-linear analysis solver in GSA Material non-linearity: fabric panel, tension only: Stiffness from axial force, geometry & pre-stress Pre-stress in tension only elements to give initial stiffness (important for lightweight structures) The flat fabric panels resist load through deflections
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Using non-linear analysis solver in GSA 14 Using non-linear analysis solver in GSA Material nonlinearity: cable net, tension only: make use of the form to sustain loads, the cable net gets its stiffness from its FORM. Load is resisted through form, pre-stress, and deflections.
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Using non-linear analysis solver in GSA 15 Using non-linear analysis solver in GSA Material nonlinearity: fabric structure, tension only: Use anticlastic curvature to stabilise the shape of the model Pre-stress and deflection are needed to adjust the surface shape to take loads
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Using non-linear analysis solver in GSA 16 Using non-linear analysis solver in GSA Material nonlinearity: Un- grouted stone arch, compression only: Stone is modelled as Compression only elements. The joints only sustain compression force, when applied moment/force changes direction, the joints will ‘flip-flap’ to form new load paths.
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Using non-linear analysis solver in GSA 17 Using non-linear analysis solver in GSA Material nonlinearity: tension only cables with pre-stress to stabilise/stiff compression only stone arches
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Using non-linear analysis solver in GSA 18 Using non-linear analysis solver in GSA Material nonlinearity – compression only: load path changes with loads
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Using non-linear analysis solver in GSA 19 Using non-linear analysis solver in GSA Nonlinear analysis of flip flap joints Using compression only bar to simulate (use Tie element in GSA) It involve geometric nonlinearity - ‘large’ deformations
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Using non-linear analysis solver in GSA 20 Using non-linear analysis solver in GSA Geometric nonlinearity: Vertical loads on the cable trusses are resisted through the geometric stiffness of the cables due to their pre-stress.
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Using non-linear analysis solver in GSA 21 Using non-linear analysis solver in GSA Geometric nonlinearity: In order for the struts to rotate about their pin at the glass frame, The cables need to rotate about a separate pin point. This gives out of plane stiffness to the loading point.
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Using non-linear analysis solver in GSA 22 Using non-linear analysis solver in GSA Buckling: Bicycle wheel spokes reduce the effective length of the arch – very slender arches
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Using non-linear analysis solver in GSA 23 Using non-linear analysis solver in GSA Buckling: The cable net restrains the arch from buckling. The key is the relative stiffness
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Using non-linear analysis solver in GSA 24 Using non-linear analysis solver in GSA Summary: when to use GsRelax Large nonlinearity features Features specific to fabric and cable structures Material plastic behaviour and yielding Form-finding analysis features Search processes to investigate ‘ultimate’ capacity of models Search processes to isolate individual elements and their buckling behaviour and the degree of restraint offered by the rest of the model
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Using non-linear analysis solver in GSA 25 Using non-linear analysis solver in GSA www.oasys-software.com
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