Advanced Analysis Robot Structural Analysis [PDF]

Zitiervorschau

Advanced Analysis in Robot Structural Analysis 2015 Rafal Gaweda Autodesk Inc., Technical Support Senior Specialist

Join us on Twitter: #AU2014

Class summary This class is a presentation of the advanced analysis capabilities available in Robot Structural Analysis 2015 software and Robot Structural Analysis software cloud computations. We will discuss nonlinear calculations, various dynamic analyses, seismic analysis, transient analysis (time history), and the Direct Analysis Method. We will also explore the wind simulation engine. We will cover basic examples of correct workflows, calculation data setting, and results retrieval, and we will discuss tips and tricks.

Linear Analysis

Nonlinear Analysis

Nonlinear Analysis

Nonlinear Analysis – Calculation Algorithms

BFGS Algorithm Newton-Raphson Algorithm

Nonlinear analysis VS P-delta analysis

http://forums.autodesk.com/t5/robot-structural-analysis/non-linear-analysis-pdelta-analysis/m-p/3643010

Buckling Analysis

Buckling Analysis










As concerns calculating the buckling length using buckling analysis to use it later in steel design module it is possible but in most cases the calculated buckling lengths are not the values user expects. Buckling analysis calculates global buckling of the structure. Of course some modes (especially higher ones) correspond to local buckling of some parts of the structure (for instance columns). For each load case the basic results of this analysis are critical coefficients (eigenvalues) and eigenvectors for appropriate buckling modes. Each critical coefficient corresponds to the factor by which the loads of appropriate load case should be multiplied to obtain appropriate loss of stability (buckling mode). Basing on these coefficients and results of static analysis for appropriate load case (normal forces in different bars) critical forces for each load case, mode and bar can be calculated. Note that such critical forces are calculated for all bars (except of these which are under tension) disregarding the shape of buckling - these forces may concern bars for which buckling does not occur - in such case they have rather mathematical than physical meaning. Basing on critical forces and Euler's formula the buckling lengths for appropriate load case, buckling mode and bars are calculated. In steel design module user needs buckling length of bar which is a property of bar itself and does not depend on load case and mode. In such case buckling length from buckling analysis can be taken only for very simple models or when load is applied directly to considered member and the buckling mode has local character related to this considered member.

Buckling Analysis Modes

http://forums.autodesk.com/t5/robot-structural-analysis/buckling-analysis-visual-resultslook-not-correct/m-p/4404473#M16676

Modal Analysis

Load to Mass Conversion

Modal Analysis for nonlinear model In any case of non-linear properties (tension-only members, uplift supports, cables, elasto-plastic members, non-linear releases, non-linear hinges, etc.) such objects are resulting in non-linear behavior of the structure. In such case in general vibrations are non-linear – they are not harmonic. It is so because stiffness of the structure can be changing during vibrations. Dynamic modal analysis is a linear analysis assuming constant stiffness of the structure. In case of non-linear models the dynamic modal analysis is run for the linearized model, i.e. assuming constant stiffness resulting from static load case preceding given modal load case. It means that results of modal analysis can be different depending after which static load case the modal analysis load case is defined.

Modal Analysis Eigenvectors As concerns the values of eigenvectors itself they are unitless but of course the relation between translation and rotation components is kept to give the correct shape of the vibration modes. The rotation components are given as derivatives of translation components (like RY=dZ/dX) so they are also dimensionless. These derivatives correspond to tangents of appropriate angles.

http://forums.autodesk.com/t5/robot-structural-analysis/modal-analysis-outputs/m-p/4877418#M21562 http://forums.autodesk.com/t5/robot-structural-analysis/mode-shape-vectors/td-p/3431943

Modal Analysis comparison with SAP2000

http://forums.autodesk.com/t5/robot-structural-analysis/help-for-using-arsafor-structural-dynamic-purposes/m-p/5344813#M27356

Harmonic Analysis

Harmonic Analysis with added masses Additional masses should be added to preceding Modal case then then newly calculated natural frequency should be used in Harmonic case

https://screencast.autodesk.com/Main/Details/8dd9905f-359b-4686-b631-bc233c8addae

Harmonic Analysis – speed and acceleration of nodes Is it possible to get the speed of the nodes in a harmonic load calculation?.

It is not directly output in results of harmonic analysis but amplitudes of speed in harmonic analysis can be obtained from amplitudes of displacements (displayed in for instance Displacements table) . It is resulting from the first derivative of sinusoidal function. It is enough to multiply displacements by 2*Pi*f where f is the frequency of excitation. Analogously amplitudes of acceleration can be obtained multiplying displacements by (2*Pi*f)^2

Equivalent Lateral Force Method – Linear Seismic

Seismic Analysis

Nonlinear Seismic Analysis – why not 1. Stiffness matrix for modal analysis is taken from the last calculated case before modal case so some tension members "are not working" in this case and this state will be fixed for next modal case(s) 2. Modes should (may) activate \ deactivate some different tension bars depending on direction they are acting but this effect can not be considered due to point 1 3. Even if we calculate model after combining results for most tension bars it may appear that results are "not existing" because combining "not existing" results and some value results gives "not existing" finally 4. Spectral/seismic analysis is based on assumption of harmonic vibrations which is not true for nonlinear model. In such case you should use time history instead. One have to convert time - acceleration data into time - displacement data and finally apply them to the supports of your structure (to model movement of the ground).

Quadratic combination in nonlinear model To define quadratic combination in non-linear model is to: 1/ run analysis of non-linear model without any combinations, 2/ after completing analysis defining combination(s) without "Quadratic" attribute - in combinations dialogue or on Edit tab of the table of combinations, 3/ opening the table of combinations on Edit tab (if it was not done in step 2/), 4/ clicking right mouse button to open context menu, selecting "Table Columns...", activating "Quadratic combination" in the dialogue and accepting by selecting OK - additional column SQRT will be displayed in the table 5/ selecting YES in SQRT column for appropriate combination(s) Results for combinations with SQRT attribute set to YES will be calculated as SRSS quadratic combinations of appropriate results of combination components - see the attached screen capture made for simple example. Opening the Analysis Type window in above case will result in change of the status of results from "available" to "out of date" and results for combinations will become not available (N/A in table of results). Running analysis again in above case will result in loosing quadratic combination status in combinations it was defined in step 5/. Additional note: it is important to remember that in case of models containing cables assembling load case (case 1) is automatically considered in other load cases. In case of using the workaround described in steps 1/ to 5/ the assembling load case (usually by default self-weight) may be considered in combination several times from different combination components.

Seismic in nonlinear load combinations If one defines or modifies combinations using the table of combinations the status of results changes to "out of date" and results for new created or modified combinations can be not available (N/A). In such case it is necessary to re-run analysis. It can be avoided not using the table of combinations to define or modify them – defining or modifying combinations using Manual Combinations or (for instance change to quadratic combinations) using Analysis Type window. Such behavior results from non-standard operations on results made by Robot in such case. Because model is non-linear the superposition principle is not valid for it so theoretically all combinations should be iterated in nonlinear way. But modal and seismic analysis (using response spectra method) is performed for linearized model and results of seismic analysis are combined with results of static non-linear load cases without non-linear iterations. Of course performing seismic analysis for linearized model and then combining these results with non linearized (non-linear) results for static analysis is some approximation. The precise approach for non-linear model would be running seismic analysis using non-linear time history.

Eccentricity in seismic analysis The eccentricity doesn't result to the shifting of the seismic force. The mass matrix is shifted and not the point of application of the seismic force. The only case that there is no shifting of the mass matrix is when in the analysis type "modal with automatic definition of seismic cases" the option of "simplified approach" is chosen, where the pseudostatic horizontal forces are implemented in parallel with seismic moments.

Damping for seismic and spectral cases Damping defined in advanced parameters of Modal case

1. damping correction of elastic spectra in these seismic codes where it is possible - for instance in EN-1998-1-1 (Eurocode 8) 2.in calculation of complete quadratic combinations (CQC) and double sum method (2SM) combinations

Damping for seismic and spectral cases

Damping defined spectral analysis is It is used in spectrainaveraging not only not used directly in spectral in spectra defintion but also analysis when calculationsit can be treated using averaged spectra directlyasinsome identifier of various spectral load case spectra here. It is used when preparing spectra in case of spectra interpolation.

Seismic Analysis – comparison with RISA and SAP http://forums.autodesk.com/t5/robot-structural-analysis/robot-seismic-combinations-compare-torisa-and-sap2000/m-p/3426765

http://forums.autodesk.com/t5/robot-structural-analysis/response-spectrum-analysis-gettingwrong-results/td-p/3425595

http://forums.autodesk.com/t5/robot-structural-analysis/robot-seismic-combinations-compare-torisa-and-sap2000/td-p/3406133

Spectral Analysis Spectral analysis available in Robot concerns movement of soil and is related to seismic effects.

Seismic vs Spectral Analysis SEISMIC analysis: • Based on the chosen code, seismic analysis works out the response spectrum etc automatically based on the input parameters (region etc). • The user can set an expected base shear that Robot will limit seismic base shear to. • Eccentricity option is available within the seismic options (can leave eccentricity zero in the preceeding modal case) SPECTRAL method: • Correct response spectrum must be defined • Eccentricity should be defined in the preceding modal analysis; • Nneed to do an initial run, then go back and do a second iteration to apply scaling factors to limit my base shear to the expected value. http://forums.autodesk.com/t5/robot-structural-analysis/responce-spectrum/m-p/3723824

Time History Analysis

Time History Analysis examples http://forums.autodesk.com/t5/robot-structural-analysis/time-history-analysisfor-a-rotating-motor/m-p/3239198 http://forums.autodesk.com/t5/robot-structural-analysis/tutorial-or-exaple-formachine-foundation/td-p/3534506 http://forums.autodesk.com/t5/robot-structural-analysis/time-history-unitsand-methods/td-p/4821103

Time History Analysis as Seismic

Time History Analysis as Seismic How can I create THA function corresponding to my spectrum/ earthquake? The method of creating response spectrum compatible artificial ( synthetic ) accelerograms is described for instance in the "Response Spectrum Compatible Accelerograms" chapter of the "Dynamics of Structures" by Ray Clough, Joseph Penzien. Some topics related to proper selection of accelerograms are discussed in this paper: http://hal.archives-ouvertes.fr/docs/00/70/02/45/PDF/laurendeauetal2012.pdf The software generating artificial earthquake accelerograms: http://www.seismosoft.com/en/SeismoArtif.aspx http://roboting.wordpress.com/2011/03/06/generation-of-simulated-earthquakescompatible-with-prescribed-response-spectra-in-robot/

Blast or Impact as Time History Analysis

Impact as THA example http://forums.autodesk.com/t5/robot-structural-analysis/mass-velocity-loadsamp-dynamic-response/m-p/3630846#M7725

Blast as THA example http://forums.autodesk.com/t5/robot-structural-analysis/definition-of-blastaccidental-loads-in-robot/m-p/3755536#M10038

Moving load as Time History Analysis

Moving load as THA example http://forums.autodesk.com/t5/robot-structural-analysis/time-history-dynamicanalysis-for-a-moving-load/m-p/4816405#M20729

Footfall Analysis

Footfall Analysis - Verification Example http://forums.autodesk.com/t5/robot-structural-analysis/footfall-analysis/mp/3072674#M245

Footfall Analysis – Base acceleration Base acceleration is set only according to available codes, i.e. Concrete Centre (2006), SCI P354 Design of Floors for Vibration and AISC DG11: Floor Vibrations due to Human Activity. But in case of SCI P354 and AISC DG11 base acceleration is a constant value and response factor is proportional to 1/base acceleration so it is very easy to convert it to different base acceleration value. In case of Concrete Centre (2006) Design Guide it is more sophisticated because in case of resonant response the base acceleration is a function composed of 3 different branches for 4 Hz < fh < 8 Hz and moreover the overall response factor is calculated as SRSS of response factors for harmonics. But in this case it is possible to use detailed results for harmonics from Diagrams of Footfall analysis in RSA. This data can be output to for instance MS Excel to be processed using arbitrary base accelerations.

Direct Analysis Method

Direct Analysis Method Whitepaper

http://bimandbeam.typepad.com/files/direct-analysis-method-whitepaper.pdf

Wind Simulation Engine

Wind Simulation Engine

Wind Simulation Engine Autodesk Robot Structural Analysis Professional Wind Simulator Validation Brief Whitepaper http://bimandbeam.typepad.com/bim_beam/2014/06/autodesk-robot-structuralanalysis-professional-wind-simulator-validation-brief-whitepaper.html How to make a compatible analysis of wind loads with RSA and code requirements? http://forums.autodesk.com/t5/robot-structural-analysis/terrain-type-windsimulation/td-p/5238985

Advanced examples Tuned mass damper http://forums.autodesk.com/t5/robot-structural-analysis/tuned-mass-damper-tmd-creation-withrsa/td-p/3933423 How to simulate a closing gap between two shell elements http://forums.autodesk.com/t5/robot-structural-analysis/how-to-simulate-a-closing-gap-betweentwo-shell-elments/td-p/3253276 Nonlinear release http://forums.autodesk.com/t5/robot-structural-analysis/non-linear-release/td-p/3636110 Pushover example http://forums.autodesk.com/t5/robot-structural-analysis/push-over-analysis/td-p/3617552

Autodesk is a registered trademark of Autodesk, Inc., and/or its subsidiaries and/or affiliates in the USA and/or other countries. All other brand names, product names, or trademarks belong to their respective holders. Autodesk reserves the right to alter product and services offerings, and specifications and pricing at any time without notice, and is not responsible for typographical or graphical errors that may appear in this document. © 2013 Autodesk, Inc. All rights reserved.

Voice of Customer Be Heard and Win! Help shape the future Autodesk experience. IPad Mini Raffle!

Mandalay Bay, South Convention Center, Level 1

Stop by and register to participate

autode.sk/AU2014VOC 9 am - 6 pm, Dec. 2-4 #AU2014VOC

Autodesk is a registered trademark of Autodesk, Inc., and/or its subsidiaries and/or affiliates in the USA and/or other countries. All other brand names, product names, or trademarks belong to their respective holders. Autodesk reserves the right to alter product and services offerings, and specifications and pricing at any time without notice, and is not responsible for typographical or graphical errors that may appear in this document. © 2013 Autodesk, Inc. All rights reserved.

Students, educators, and schools now have

FREE access to Autodesk design software & apps. Download at www.autodesk.com/education

Earn your professional Autodesk Certification at AU Visit the AU Certification Lab