Keith D Hjelmstad | Arizona State University (original) (raw)

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Papers by Keith D Hjelmstad

Journal of Sound and Vibration, Dec 1, 1996

A damage detection and assessment algorithm is developed based on system identification using a f... more A damage detection and assessment algorithm is developed based on system identification using a finite element model and the measured modal response of a structure. The measurements are assumed to be sparse and polluted with noise. A change in an element constitutive property from a baseline value is taken as indicative of damage. An adaptive parameter grouping updating scheme is proposed to localize the damage zones in the structure and a Monte Carlo method is used with a data perturbation scheme to provide a statistical basis for assessing damage. Damage indices computed from the Monte Carlo sample of data perturbations are used to assess damage. The threshold values, which distinguish damage from measurement noise, are established through Monte Carlo simulation on the baseline structure. The proposed algorithm is applied to the problem of locating a crack in a cantilever beam. A Bernoulli-Euler beam model and a plane stress model are employed to illustrate the use of the method and compare the efficacy of the two models for crack detection.

Nasa Sti Recon Technical Report N, Jun 29, 1983

An eccentrically braced flame is a structural framing system in which the axial forces in the bra... more An eccentrically braced flame is a structural framing system in which the axial forces in the braving members are transferred either to other braces or to columns through shea and bending in short beam segments called active links. The active link acts as a fuse, dissipating large amounts of input energy upon lateral overloading of the structure and its behavior dominates the behavior of the structure. While experiments have demonstrated the good global behavior of the framing system, the inelastic behavior of the active links was not adequately evaluated, especially as regards the web buckling phenomenon. Furthermore, rigorous analytical tools for the inelastic analysis of the active link elements, and therefore eccentrically braced frames, appear to be lacking.

The Newmark Structural Engineering Laboratory (NSEL) of the Department of Civil and Environmental... more The Newmark Structural Engineering Laboratory (NSEL) of the Department of Civil and Environmental Engineering at the University of Illinois at Urbana-Champaign has a long history of excellence in research and education that has contributed greatly to the state-of-the-art in civil engineering. Completed in 1967 and extended in 1971, the structural testing area of the laboratory has a versatile strong-floor/wall and a three-story clear height that can be used to carry out a wide range of tests of building materials, models, and structural systems. The laboratory is Abstract Contact analysis is an important branch of solid mechanics. Numerical simulation using the finite element method has become the dominant approach recently because of the high nonlinearity of contact problems. In the traditional Lagrangian description for solid mechanics, the numerical nodes are attached to the material particles, making it impossible to maintain node-to-node contact due to independent deformation. Various node-to-segment or segment-to-segment treatments are proposed to discretize the contact interface. But some issues still exist. Specifically, mesh distortion or element entanglement may be present if deformation is large.

A general parametric form of a dynamic finite-element model of a linear elastic structure with sm... more A general parametric form of a dynamic finite-element model of a linear elastic structure with small deformations is presented, with the model consisting of a set of scalar parameters multiplying element kernel matrices. The parameters of the finite-element model can represent stiffness and inertia properties, as well as axial forces if linearized buckling is assumed. Optimization of an orthogonality-based objective

Journal of Structural Engineering-asce, 1986

Journal of Structural Engineering, 1983

Journal of Structural Engineering, 1986

Journal of Sound and Vibration, 1996

We examine the question of uniqueness of solution to the modal parameter problem by applying a le... more We examine the question of uniqueness of solution to the modal parameter problem by applying a least-squares output error estimator to a six-degree-of-freedom shear building using both a two-and a six-parameter model. Multiple solutions are located by initiating the iterative parameter estimation algorithm from random starting points. The case study provides tangible illustrations of the phenomena latent in modal parameter estimators and demonstrates several counter-intuitive results. The study of the twoparameter model allows us to show the connection between multiple solutions for noise-free data and solution clustering for noisy data. The results suggest a new definition of the best measurement set as being the one most likely to lead to the correct solution with the least sensitivity to noise. We conclude that modal parameter estimation from sparse measurements, albeit fraught with difficulties, can yield valuable results.

Journal of Engineering Mechanics, 1997

A damage detection and assessment algorithm is developed based on a parameter estimation with an ... more A damage detection and assessment algorithm is developed based on a parameter estimation with an adaptive parameter grouping scheme. Damage is characterized by a reduction in a constitutive property of a parameterized finite-element model between two ...

Journal of Engineering Mechanics, 1987

$Research paper thumbnail of Effect of moisture and temperature on the fracture morphology of dacite$

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1971

... point loaded to failure at 100 C. To maintain saturation at 100 C, the chamber was filled wit... more ... point loaded to failure at 100 C. To maintain saturation at 100 C, the chamber was filled with steam at 1 atm during the ... DOUGLAS and EL-SHAMY [20] studied the reaction of various glasses to aqueous solutions and concluded that certain alkalies are selectively leached from ...

2016 ASEE Annual Conference & Exposition Proceedings, 2000

[1992] Proceedings. 11th IAPR International Conference on Pattern Recognition, 1992

... Introduction Parameter estimation in structures is a useful founda-tion for methods of assess... more ... Introduction Parameter estimation in structures is a useful founda-tion for methods of assessing damage in structures, esti-mating remaining ... inspection, as well as ultrasonic, acoustic emission, mag-netic, electromagnetic, and electrical potential tests (Agbabian and Masri 1988 ...

Journal of Structural Engineering, 1988

An approach to estimating the limit and post-limit behavior of a framed structure from its geomet... more An approach to estimating the limit and post-limit behavior of a framed structure from its geometrically linear response is presented. The method follows from a particular restatement of the weak form of the nonlinear differential equations governing the response of the structure, and is based upon the observation that geometric effects are insensitive to redistribution of the moment field in planar framed structures. The formulation gives insight into the relationship between important observed phenomena and the complex nonlinear governing equations. A novel derivation of Home's method for estimating the nonlinear response of frames is presented and extended to the important case of nonproportional loads. The role of the linearized geometric stiffness matrix, and the buckling eigenvalues is clearly demonstrated. Several examples are given to evaluate the validity of the inherent assumptions and to demonstrate the effectiveness of the approach. 2

Journal of Structural Engineering, 1991

This paper suggests an optimization-based design methodology for improving the strength and the o... more This paper suggests an optimization-based design methodology for improving the strength and the overall stability characteristics of framed structures whose capacities are governed by limit-load behavior. Attention is focused on spaceframed structures under static loads, and represents a natural extension of the basic ideas presented in the companion paper. The optimization objective function is taken here to be a linear combination of the critical buckling eigenvalues of the structure. A constant volume constraint with bounds on the design variables is used in conjunction with an optimality-criterion approach for search. The present approach avoids the need to know the eigenvector that dominates the response as the structure passes a limit load. A novel approach to solving problems with multiple loading conditions is introduced wherein each eigenvalue in the objective is weighted in accordance with the participation of that mode in the loading. Several examples are given to demonstrate aspects of the behavior of the proposed design procedure. 2 Asst. Prof., Memphis State Univ., ( 3 > where L, = the length of member i; and its density is p,. The sum is taken over all members associated with group TO. 916 J. Struct. Eng. 1991.117:914-935. Downloaded from ascelibrary.org by University of Memphis on 02/08/13. Copyright ASCE. For personal use only; all rights reserved. 929 J. Struct. Eng. 1991.117:914-935. Downloaded from ascelibrary.org by University of Memphis on 02/08/13.

Journal of Engineering Mechanics, 2000

Constitutive equations based upon stress dependent moduli, like K-and Uzan-Witczak, are widely us... more Constitutive equations based upon stress dependent moduli, like K-and Uzan-Witczak, are widely used to characterize the resilient response of granular materials for the analysis and design of pavement systems. These constitutive models are motivated by the observation that the granular layers used in pavement structures shake down to (nonlinear) elastic response under construction loads and will, therefore, respond elastically under service loads typically felt by these systems. Due to their simplicity, their great success in organizing the response data from cyclic triaxial tests, and their success relative to competing material models in predicting the behavior observed in the field, these resilient modulus constitutive models have been implemented in many computer programs used by researchers and design engineers. This paper provides an analysis of the nonlinear solution algorithms that have been used in implementing these models in a conventional nonlinear 3D finite-element framework. The analysis shows that these conventional algorithms are destined to fail at higher load levels. The paper offers two competitive methods for global analysis with these models. A comparative study of eight possible implementations of the algorithms described in the paper is made through two simulation examples.

Journal of Engineering Mechanics, 2001

ABSTRACT