Panoramica di esempio

In this advanced example you will continue to investigate the behavior of the previous beam, ma ora in termini di analisi statica non lineare.

L'analisi statica lineare e di instabilità lineare eseguita in precedenza consente di analizzare e ottimizzare rapidamente la struttura. Tuttavia, a volte è necessario vedere il “quadro reale”.’ del fallimento. Guarda come è distribuita la plasticità negli elementi, quali sono i valori e come l'imperfezione geometrica influisce sull'instabilità.

In order to see this final picture of failure the nonlinear static analysis must be considered. This analysis considers external loads by portions (or steps), where the material and geometric nonlinearity considered to determine the stress-deformed shape at each step.

Step 1. Mesh Refinement

In the Mesh panel define the mesh size for all edges and openings 35 mm, making the global model mesh more coarse than it was previously. Then go to the Refinement tab. Define row in the table and the mesh refinement zone starting from (P1) 100 mm e fine (P2) a 850 mm dall'inizio della trave. The mesh size in this zone is 15 mm. Genera la mesh per il modello e osserva come viene creata la mesh più densa nel primo pannello web.

Step 2. Nonlinear Material Properties

In the Materials panel define plastic stress and strain properties of the materials. Beam parts are made of steel with yielding stress values of 230 MPa for the web and 245 MPa for other components.

Define a bi-linear diagram that includes two zones: linear and plastic. First set Modulus of Elasticity (E) per acciaio. In the second row of the table create ‘plastic’ zone with the same value of plastic stress Repeat this procedure for the other beam components like the flanges and stiffeners with the plastic stress of 245 MPa.

Step 3. Web Imperfections

Define imperfections to web panels 2 e 3. Define two rows and select web panels. Define the direction of imperfection and magnitude (P1) come 2 mm for the one panel and -2 mm for another panel. Click the Preview button to see how it affects on the FE model geometry during the analysis.

Step 4. Displacement Load

Remove previously defined forces from the stiffeners. Then in the Displacement Stiffeners panel apply a displacement load along the y-axis of 40 mm.

Step 5. Analisi non lineare

In the Analysis panel select the Geometry and Material Nonlinear Static Analysis Type. Fare clic sul pulsante Analisi.

Step 6. Risultati di spostamento

In the Result Step select the final step (1.0). Select the displacement component and include the deformed view with a scale of 1.

Step 7. Plasticity Results

Select Plate side view both and click Display to see the plastic strain contour plot. Qui, a value of zero means that the element has no plasticity. Define in the Limit Strain field 5% and click the Status button. Di conseguenza, you will see the safe and unsafe zones of the structure.

Step 8. Load-Displacement Plot

The last what will be investigate is the Load-Displacement Diagram. This diagram allows to see the critical failure force applied on the beam. Go to the Chart in the main menu. In Displacement Node you pick the node from witch the vertical deflection can be extracted. This is the middle of the beam and bottom point. Then for the Forces Nodes you pick nodes from where the total vertical reaction force is extracted. Here two options: 1 – all nodes of supports, 2 – nodes of displacement load. Then you select the direction of reaction acting and displacement (Ru and Uy). Define scaling factors and click Generate button. The obtained diagram is close to the received one from experimental test.

Calcolatore gratuito di travi