SUNMONTUEWEDTHUFRISAT
Events for February 28, 2007
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NONLINEAR ANALYSIS OF COMPOSITE AND FUNCTIONALLY GRADED SHELL STRUCTURES
Wed, Feb 28, 2007 @ 10:30 AM - 11:30 AM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
JOINT SEMINAR FOR AME & CIVIL ENGINEERINGSPEAKER: J. N. Reddy,
Advanced Computational Mechanics Laboratory,
Texas A & M University, College Station, TX 77843-3123
jnreddy@tamu.eduABSTRACT
A tensor-based finite element formulation for the nonlinear analysis of laminated shell structures and through-thickness functionally graded shells will be discussed. A tensor-based finite element formulation is used to describe the deformation and 3-D constitutive laws of a shell in a natural and simple way by using curvilinear coordinates. In addition, a family of high-order elements with Lagrangian interpolations is used to avoid membrane and shear locking. A first-order shell theory with seven parameters is derived with exact nonlinear deformations and under the framework of the Lagrangian description. This approach takes into account thickness changes and, therefore, 3D constitutive equations are utilized. Numerical comparisons of the present results with those found in the literature for typical benchmark problems involving isotropic and laminated composite plates and shells as well as functionally graded plates and shells are found to be excellent and show the validity of the developed finite element model. Moreover, the simplicity of this approach makes it attractive for applications in contact mechanics and damage propagation in shells. A number of examples of applications to laminated composite shell structures are presented.Keywords: Finite element model, nonlinear shell theory, multilayered composites, functionally graded shells, numerical examples.Acknowledgement. The research results reported herein were obtained while the authors were supported by the Structural Dynamics Program of the Army Research Office (ARO) through Grant . 45508EG.References
1. R. A. Arciniega and J. N. Reddy, "Tensor-based Finite Element Formulation for Geometrically Nonlinear Analysis of Shell Structures," Computer Methods in Applied Mechanics and Engineering, Vol. 196, Nos. 4-6, pp. 1048-1073, 2007.
2. R. A. Arciniega and J. N. Reddy, "Large deformation analysis of functionally graded shells," International Journal of Solids and Structures, Vol. 44, pp. 2036-2052, 2007.
3. J.N. Reddy, Mechanics of Laminated Composite Plates and Shells: Theory and Analysis, 2nd edition, CRC Press, Boca Raton, Florida, 2004.
Location: Kaprielian Hall (KAP) - RIELLIAN HALL, 203
Audiences: Everyone Is Invited
Contact: Evangeline Reyes
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Earthquake Damage Detection in Two Buildings.....
Wed, Feb 28, 2007 @ 02:00 PM - 03:00 PM
Sonny Astani Department of Civil and Environmental Engineering
Conferences, Lectures, & Seminars
Earthquake Damage Detection in Two Buildings - Comparative Analysis of Several Structural Health Monitoring Methods Including a New Wave MethodSpeaker: Dr. Maria Todorovska,
Department of Civil and Environmental Engineering,
USCAbstract:The only true validation of real time structural health monitoring methods is in terms of sensory data recorded in instrumented structures during a damaging event. For civil structures, damaging events are e.g. earthquakes, explosions, blasts, etc. Due to the high cost of instrumentation and the low frequency of occurrence of such events, data in damaged civil structures are rare, but do exist, e.g. vibrational data recorded in buildings by seismic monitoring arrays during a damaging earthquake. Yet, the existing data are rarely used, and methods are usually tested only on numerically simulated data of response with postulated damage and assumed additive Gaussian noise. Results will be presented of a critical comparative analysis of several structural health monitoring methods applied to detecting damage in two instrumented buildings th the 1971 San Fernando and 1994 Northridge earthquakes, and for which records of 10 other earthquakes are also available.The first method is a new method, based on measuring wave travel times through the building using impulse response functions, applied to structural health monitoring for the first time in the presented work. This method is more reliable than monitoring changes in the apparent building frequencies, which are sensitive to the effects of soil-structure interaction and environmental factors, such as weather. Further, it is local and can detect the location of damage with relatively few sensors as compared to the methods based on detecting changes in curvature of the mode shapes of vibration, which require extensive instrumentation. Another relatively new method is based on detecting novelties in the recorded response using wavelets, previously tested on numerically simulated data but not conclusively on real data. This method is superior to all other methods in its resolution of the estimate of the time of the occurrence of damage. The analysis of this method also revealed that the noise in this method, consisting of high frequency pulses from the ground motion traveling through the building, contains useful information about the travel times through the building, and hence can also be used to infer about the changes of the state of health of the structure. The results by these two methods are compared with the distribution and degree of the observed damage, and with results of analyses based on other indicators of damage, such inter-story (dynamic) drifts estimated from the recorded accelerations, observed changes of the "instantaneous" apparent frequencies of vibration as functions of the amplitudes of response, estimated from the ridges and skeletons of the Gabor transform, and finally by analysis of simulated response using ETABS. The mutual consistency of the results by different analyses methods, and their consistency with the observed damage are discussed and several important conclusions are drawn.Location: KLaprielian Hall 203
Audiences: Everyone Is Invited
Contact: Evangeline Reyes
