R-3 Repository :: Browsing by Author "Conte, Joel P."

Browsing by Author "Conte, Joel P."

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Analysis of nonlinear structural systems accounting for both system parameter uncertainty and excitation stochasticity
(1998) Vijalapura, Prashanth Kumar; Conte, Joel P.
Limiting ourselves to only loading and system parameter uncertainties, the dynamic loading to a structure can be modeled as a random function while the system or material parameters can be modeled as random fields. Through a process of discretization, these random functions and random fields can be lumped into a vector of random variables that completely describe the uncertainties in loading and material parameters. These uncertainties result in a finite probability of failure or of the structural system not performing as intended. A powerful method to compute the failure probability is via the time history of the mean rate of out-crossing the "safe domain" by the structural system. Computing the mean out-crossing rate at any instant of time amounts to solving iteratively a constrained optimization problem. Each iteration of the constrained optimization problem requires the gradients of the constraints with respect to the vector of uncertain parameters and hence the response sensitivities with respect to loading and material parameters since the constraints are constituted in terms of response quantities. (Abstract shortened by UMI.)
Analysis, design, and construction of a shaking table facility
(1997) Muhlenkamp, Matthew Joseph; Conte, Joel P.
Rice University's Department of Civil Engineering recently added an electro-hydraulic shaking table facility to their testing laboratory. The purpose of the shaking table is to evaluate the response of scaled model structures subjected to base excitation. Every component of the shaking table was carefully designed or sized to perform optimally at targeted levels. The performance curves for the shaking table which define the maximum load, velocity, and displacements that the table can attain were developed from the specifications of the hydraulic system. Interaction between the shaking table system and the foundation mass was analyzed. The dynamic characteristics of the slip plate and its interaction with model structures were studied to determine the optimum size of the slip plate. The transfer function between the command displacement signal sent to the table and the table displacement was developed analytically for the system, encompassing servovalve hydraulics and the PIDF control system.
Analytical modeling of a shaking table system
(1997) Trombetti, Tomaso; Conte, Joel P.
A complete mathematical model of the Rice University shaking table facility is developed. The analytical model, developed on the basis of previous work, is then fully developed in order to account for: Proportional, Integral, Derivative, Feed-Forward and delta-Pressure controls, for servovalve response delay, for flexibility of the foundation, for flexible MDOF test specimen. The mathematical model is then used in order to gain insight into the dynamic performance of the shaking table and its sensitivity to the various control gain parameters. Furthermore, the mathematical model is used to determine the influence of the dynamic properties of the test specimen on the shaking table performance. These analyses are fundamental in order to tune the shaking table and in order to understand the capacities and limits of the shaking table. Comparison with experimental results shows that the mathematical model developed can predict very accurately the actual table performance.
Cognac platform: Correlation of analytical predictions with field measurements of dynamic response
(1997) Couch, Andrew Travis; Conte, Joel P.
Utilizing simplified structural and hydrodynamic models, a parametric study is performed comparing response predictions for the Cognac deepwater platform as it is subjected to wave-and-current forces. Comparisons for the parametric study include: quasi-static versus dynamic response solutions, modal contributions to the response, impact of considering fluid-structure interaction, effects of using various empirically modified linear wave models or the Hybrid Wave Model, and correlation of the analytical response predictions with Cognac field measurements. The results of this study indicate that: (1) the dynamic response of Cognac is very moderate, (2) the dynamic response is dominated by the fundamental mode, (3) the inertia-dominated wave-and-current forces provide minimal response reductions from interaction effects, (4) of the considered wave stretching schemes, Wheeler stretching technique combined with linear wave theory produces platform response results which are closest to those obtained using the higher-order Hybrid Wave Model, and (5) the platform responses predicted using the Hybrid Wave Model are in better agreement with the measured responses for Cognac than the predictions based on the various stretched linear wave models.
Experimental/analytical approaches to modeling, calibrating and optimizing shaking table dynamics for structural dynamic applications
(1998) Trombetti, Tomaso; Conte, Joel P.; Durrani, Ahmad J.
This thesis presents an Experimental/Analytical approach to modeling and calibrating shaking tables for structural dynamic applications. This approach was successfully applied to the shaking table recently built in the structural laboratory of the Civil Engineering Department at Rice University. This shaking table is capable of reproducing model earthquake ground motions with a peak acceleration of 6 g's, a peak velocity of 40 inches per second, and a peak displacement of 3 inches, for a maximum payload of 1500 pounds. It has a frequency bandwidth of approximately 70 Hz and is designed to test structural specimens up to 1/5 scale. The rail/table system is mounted on a reaction mass of about 70,000 pounds consisting of three 12 ft x 12 ft x 1 ft reinforced concrete slabs, post-tensioned together and connected to the strong laboratory floor. The slip table is driven by a hydraulic actuator governed by a 407 MTS controller which employs a proportional-integral-derivative-feedforward-differential pressure algorithm to control the actuator displacement. Feedback signals are provided by two LVDT's (monitoring the slip table relative displacement and the servovalve main stage spool position) and by one differential pressure transducer (monitoring the actuator force). The dynamic actuator-foundation-specimen system is modeled and analyzed by combining linear control theory and linear structural dynamics. The analytical model developed accounts for the effects of actuator oil compressibility, oil leakage in the actuator, time delay in the response of the servovalve spool to a given electrical signal, foundation flexibility, and dynamic characteristics of multi-degree-of-freedom specimens. In order to study the actual dynamic behavior of the shaking table, the transfer function between target and actual table accelerations were identified using experimental results and spectral estimation techniques. The power spectral density of the system input and the cross power spectral density of the table input and output were estimated using the Bartlett's spectral estimation method. The experimentally-estimated table acceleration transfer functions obtained for different working conditions are correlated with their analytical counterparts. As a result of this comprehensive correlation study, a thorough understanding of the shaking table dynamics and its sensitivities to control and payload parameters is obtained. Moreover, the correlation study leads to a calibrated analytical model of the shaking table of high predictive ability. It is concluded that, in its present conditions, the Rice shaking table is able to reproduce, with a high degree of accuracy, model earthquake accelerations time histories in the frequency bandwidth from 0 to 75 Hz. Furthermore, the exhaustive analysis performed indicates that the table transfer function is not significantly affected by the presence of a large (in terms of weight) payload with a fundamental frequency up to 20 Hz. Payloads having a higher fundamental frequency do affect significantly the shaking table performance and require a modification of the table control gain setting that can be easily obtained using the predictive analytical model of the shaking table. The complete description of a structural dynamic experiment performed using the Rice shaking table facility is also reported herein. The object of this experimentation was twofold: (1) to verify the testing capability of the shaking table and, (2) to experimentally validate a simplified theory developed by the author, which predicts the maximum rotational response developed by seismic isolated building structures characterized by non-coincident centers of mass and rigidity, when subjected to strong earthquake ground motions.
Modeling, analysis, and comparative study of several seismic passive protective systems for structures
(1997) Wan, Yaming; Conte, Joel P.
This thesis is concerned with passive control systems for seismic protection of building structures, with special emphasis on elastomeric bearings, viscous dampers and tuned mass dampers. Both mathematical modeling and earthquake response analysis techniques are presented for this class of problems. Earthquake response simulations are carried out for a six-story L-shaped building equipped with these protective systems and subjected to three real earthquake ground excitations, namely the El Centro 1940, Orion Blvd 1971 and Capitola 1989 earthquake records. Both deterministic and stochastic earthquake ground excitations are considered. The performance and effectiveness of these passive protective systems are studied mainly in the time domain with some considerations of the frequency domain. Based on all analyses performed and for the particular building structure considered, it is found that base isolation is very effective in reducing the seismic structural response, especially if it exhibits a nonlinear hysteretic behavior, since in addition to decoupling the frame structure from the ground motion, it dissipates the earthquake input energy through hysteretic action. Tuned-mass damping is less effective than viscous damping in reducing the structural response to earthquake excitations. The results also show that the characteristics of the earthquake ground excitation represent a very important factor which influences the performance of the three passive earthquake protective systems studied herein, especially of the tuned-mass damper system.
Nonlinear geometric and material analysis of shell structures with particular emphasis on tubular joints
(1998) Kamal, Rajiv; Conte, Joel P.
Linear and nonlinear analysis of shell structures are performed using finite elements. Shell elements are formulated to capture the linear and nonlinear behavior of shell structures. Although general, the elements are specially suited for tubular joints. An automatic geometric modeling and mesh generation procedure for T, K and DT-joints is first developed. A set of shell elements are then developed and implemented in a general purpose, research oriented finite element analysis program (FEAP) to carry out linear, materially-nonlinear only, geometrically-nonlinear-only and geometric and material nonlinear analyses of thin shell structures with special emphasis on tubular joints which represent essential components of offshore platforms. A six-degree-of-freedom per node (including a true drilling degree of freedom) assembly allows easy modeling of complicated shell structures such as tubular joints or stiffened shells. The displacement interpolation is carefully chosen in order to avoid shear and membrane locking in linear and nonlinear problems. The curvature effects (initial curvature and changes in curvature due to large displacements and rotations) are incorporated by a simple modification of the flat linear shell element. This computationally very inexpensive modification increases the performance of the element by several folds. The total corotational formulation, a Lagrangian formulation, is used to treat geometric nonlinearity. Each point in the thickness of the shell is considered to be under plane stress conditions. Von Mises yield criterion with linear isotropic and kinematic hardening and the associated Prandtl-Reuss flow rule is used to model the plastic flow behavior of the shell material. The flow rule and hardening law are integrated using the return map algorithm. The robustness of the analysis tool developed is demonstrated by solving a range of linear and nonlinear problems of shell analysis. It is demonstrated through examples and comparison with known analytical or reliable numerical solutions that the elements developed are accurate in predicting both displacements and stresses. The ultimate test of the predictive ability of the analysis tool developed is performed by considering three well documented tubular joint examples (T-, K-, and DT-joints) for which experimental results in terms of load deflection curve are available. The prediction of the collapse load and load-deflection curve for the T-joint is in excellent agreement with the experimental results. This agreement between numerical and experimental results for both the K- and DT- joints is also very good considering the complexity of the actual joint structure. Finally, a parametric study of tubular T-joints is conducted to study the effects of the various geometric parameters on the collapse load.
Nonstationary ground motion model and applications to analysis and design of earthquake-resistant structures
(1996) Peng, Bor-Feng; Conte, Joel P.
To account for the uncertainties that are inherent in the definition of earthquake ground motions, this investigation is carried out in a probabilistic framework. A new, versatile, stochastic earthquake ground motion model is developed to represent the multifold characteristics of actual earthquake ground motions. This earthquake model is formulated in continuous-time and can also be extended in discrete-time; therefore, it is usable for both analytical random vibration and Monte Carlo simulation studies of structural response. An existing nonparametric adaptive method is extended to estimate the temporal variation of the intensity and frequency content of real earthquake ground motions. The nonlinear least square identification technique is used to calibrate the earthquake model against real earthquake records. Explicit closed-form solutions are derived for the time-varying power spectral density functions and nonstationary correlation functions of the response of linear elastic multi-degree-of-freedom systems subjected to this new earthquake excitation model. Monte Carlo simulation studies are conducted to gain insight into the effects of earthquake ground motion nonstationarities on linear and nonlinear structural response. The effects of the frequency nonstationarity of earthquake ground motions on the inelastic response and related damage of structures is examined. The long-term goal of this research is to improve the reliability of seismic codes for the design of safer and more economical structures.
Statistical system identification of structures using ARMA models
(1993) Kumar, Satyendra; Conte, Joel P.
The present study focuses on the estimation of the modal properties, i.e., natural modal frequencies, modal damping ratios, and mode shapes, of a structural system under ambient vibration based on the response data of the structure and the statistical properties of the stationary loading process. The corresponding input-output system is represented by a covariance-equivalent ARMA model which is univariate in the case of multiple input - single output and multivariate in the case of multiple input - multiple output. The mapping between the physical modal parameters and the ARMA parameters is established. Two different algorithms are used to estimate the covariance-equivalent ARMA models, namely the maximum-likelihood algorithm and a two-stage least-squares algorithm. An augmented system approach including both a fictitious "load" system and a structural system is formulated to account for the non-whiteness of most realistic loading processes. Examples of its application are provided for the cases of earthquake, wave, and wind excitations.
System identification of dynamic structural systems using continuous-time domain methods
(1994) Krishnan, Swaminathan; Conte, Joel P.
Structural system identification is the process of deducing the properties of a structural system from its measured response to ambient vibration by fitting a mathematical model. The objectives of this study are to: (1) investigate the use of existing system identification methods, and (2) develop new system identification methods, in order to evaluate both loading and structural modal parameters of ambient excited structures for which the load process is difficult to measure. An example is the case of offshore platforms subjected to sea waves. The study considers the inverse problem from the viewpoint of continuous-time linear dynamic systems. An existing structural identification technique defined for the deterministic case (when the loading is known) and based on sequences of modal minimizations (called modal sweeps) is formulated for the general case of multiple-input multiple-output (MIMO) systems. A global minimization technique based upon the Levenberg-Marquardt algorithm for nonlinear least-squares problems is developed for the same case. Both identification techniques are applied to a multi-degree-of-freedom (MDOF) shear building model and the results are shown to be consistent. Using the framework of random vibration theory, these techniques are then converted to the stochastic case, namely when the loading process is known only statistically. These identification methods, both individually and combined, were tested based on simulated cases of increasing complexity. The results obtained are promising and indicate that under certain conditions, both load and structural parameters can be estimated from the measured response and the statistical properties of the loading process. However, the load parameters are not as well estimated as the structural parameters, since the load process is further removed from the response process than the structural filter. Although a generic shear building model has been used throughout this study to simulate the dynamic response of real structures, the results obtained are believed to apply to linear multi-degree-of-freedom systems in general.

Browsing by Author "Conte, Joel P."

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