Abstract
Numerical simulations, irrespective of the discipline or application, are often plagued by arbitrary numerical and modeling choices. Arbitrary choices can originate from kinematic assumptions, for example the use of 1D beam, 2D shell, or 3D continuum elements, mesh discretization choices, boundary condition models, and the representation of contact and friction in the simulation. This works takes a step toward understanding the effect of arbitrary choices and model-form assumptions on the accuracy of numerical predictions. The application is the simulation of the first four resonant frequencies of a one-story aluminum portal frame structure under free-free boundary conditions. The main challenge of the portal frame structure resides in modeling joint connections, for which different modeling assumptions are available. To study this model-form uncertainty, and compare it to other types of uncertainty, two finite element models are developed using solid elements, and with differing representations of the beam-to-column and column-to-base plate connections: (1) contact stiffness coefficients or (2) tied nodes. Test-analysis correlation is performed by comparing the range of numerical predictions obtained from parametric studies of the joint modeling strategies to the range of experimentally obtained natural frequencies. The approach proposed is, first, to characterize the experimental variability of the joints by varying the bolt torque, method of bolt tightening, and the sequence in which the bolts are tightened. The second step is to convert what is learned from these experimental studies to models that bound the range of observed bolt behavior. We show that this approach, that combines small-scale experiments, sensitivity analysis studies, and bounding-case models, successfully produces bounds of numerical predictions that match those measured experimentally on the frame structure. (Approved for unlimited, public release, LA-UR-13-27561.)
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Acknowledgements
This work is performed under the auspices of the Los Alamos National Laboratory (LANL) as part of the Los Alamos Dynamics Summer School (LADSS). The authors are grateful to Dr. Charles Farrar, The Engineering Institute, for organizing the LADSS. The authors also wish to express their gratitude to Dr. Peter Avitabile, University of Massachusetts Lowell, for guidance in the experimental testing. The companies Simulia and Vibrant Technology, Inc., graciously contributed Abaqus and ME’Scope software licenses to the LADSS, without which this work would not have been possible. LANL is operated by the Los Alamos National Security, L.L.C., for the National Nuclear Security Administration of the U.S. Department of Energy under contract DE-AC52-06NA25396.
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Gonzales, L.M., Hall, T.M., Van Buren, K.L., Anton, S.R., Hemez, F.M. (2014). Quantification of Prediction Bounds Caused by Model Form Uncertainty. In: Atamturktur, H., Moaveni, B., Papadimitriou, C., Schoenherr, T. (eds) Model Validation and Uncertainty Quantification, Volume 3. Conference Proceedings of the Society for Experimental Mechanics Series. Springer, Cham. https://doi.org/10.1007/978-3-319-04552-8_6
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DOI: https://doi.org/10.1007/978-3-319-04552-8_6
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