Walter Pilkey

Nicholas Perrone

Thomas Geers

Kent Goering

Dedicated to Eugene Sevin

Since the events of September 11th, increased attention has been given to the effects of blast loading on structures. Bridges are especially important due to their potentially critical role in the economy and for emergency response. Prestressed concrete highway bridges are very common, representing 11 percent of state bridges nationwide. Yet, very little is known about how prestressed concrete bridges respond to blast loading.A finite element model of a precast, prestressed concrete girder was created and validated with two experimental blast tests. It was found that for an explosive event above or below the girder, numerical and empirical results were consistent.The girder model was expanded to a four-girder, simple-span bridge model. Three different scenarios were examined at the midspan of the bridge: a blast between two girders above the deck, a blast centered on a girder above the deck, and a blast beneath the deck. The two load cases from above resulted in highly localized damage with the possibility for other sections of the bridge to be immediately reopened after the event. Results for the load case from below indicate that the slab will be heavily damaged but the girders will remain intact.

William F. Cofer

Debra S. Matthews

David I. McLean

Effects of Blast Loading on Prestressed Girder Bridges

The objective of this paper is to develop a general design and analysis scheme for actively controlled piezoelectric smart structures. The scheme involves dynamic modeling of a smart structure, designing control laws and closed-loop simulation in a finite element environment. Based on the structure responses determined by finite element method, a modern system identification technique known as Observer/Kalman filter Identification (OKID) technique is used to determine the system Markov parameters. The Eigensystem Realization Algorithm (ERA) is then employed to develop an explicit state space model of the equivalent linear system for control law design. The Linear Quadratic Gaussian (LQG) control law design technique is employed to design a control law. By using ANSYS parametric design language (APDL), the control law is incorporated into the ANSYS finite element model to perform closed loop simulations. Therefore, the control law performance can be evaluated in the context of a finite element environment. Finally, numerical examples have demonstrated the validity and efficiency of the proposed design scheme. Without any further modifications, the design scheme can be readily applied to other complex smart structures.

Guang Meng

Lin Ye

Xing-jian Dong

Ke-xiang Wei

Closed Loop Finite Element Modeling of Piezoelectric Smart Structures

The probability of liquefaction in saturated sand deposits subjected to a train of shear stress pulses propagating from a point blast source applied at the boundary surface of the elastic medium is investigated. The load effect is evaluated in approximate closed form using three-dimensional tensorial mathematical physics in polar cylindrical coordinates. The adopted criterion of liquefaction has been experimentally verified both in the laboratory and in the field when continua of saturated sands were subjected to equivalent cyclic shear stress due to earthquake excitation. A first-order second-moment technique for the probabilistic assessment of the liquefaction potential in practical situations is developed and implemented in a computer program. Parametric studies are conducted to examine the sensitivity of results to the second-moment characterization of intervening key physical quantities.

Luis A. de B&#xe9;jar

Probability of Local Liquefaction of Saturated Sands in Half-Space Domains under a Train of Surface Point Explosions

A new method is presented for synthesizing the dynamic responses of a complex structure based upon the frequency response functions of the substructures. This method is shown to be superior to traditional methods for several reasons: (i) It can be applied to a generic class of systems. (ii) The analyst is spared the responsibilities of eliminating the coupling forces and rearranging the equations of motion. (iii) The coupling forces and the responses of the total system can be obtained simultaneously and efficiently.

C.Q. Liu

Xiaobo Liu

A New Method for Analysis of Complex Structures Based on FRF&#x2019;s of Substructures

Experiments have been conducted to benchmark DYSMAS computer code calculations for the dynamic interaction of water with cylindrical structures. Small explosive charges were suspended using hypodermic needle tubing inside Al tubes filled with distilled water. Pressures were measured during shock loading by tourmaline crystal, carbon resistor and ytterbium foil gages bonded to the tube using a variety of adhesives. Comparable calculated and measured pressures were obtained for the explosive charges used, with some gages surviving long enough to record results after cavitation with the tube wall.

G. Chambers

H. Sandusky

F. Zerilli

K. Rye

R. Tussing

Jerry Forbes

Pressure Measurements on a Deforming Surface in Response to an Underwater Explosion in a Water-Filled Aluminum Tube

The application of coupled Lagrangian&#x2014;Eulerian analysis to various types of underwater shock problems was investigated, with the verification and validation of this analysis approach in mind. Analyses were conducted for a simple TNT detonation problem and for the classical problems of an infinite cylindrical shell and a spherical shell loaded by a plane acoustic step wave. The advantages, disadvantages, and limitations of this approach are identified and discussed.

Young S. Shin

James E. Chisum

Modeling and Simulation of Underwater Shock Problems Using a Coupled Lagrangian&#x2014;Eulerian Analysis Approach

In hydraulic hybrid vehicles (HHV), vibration in dual-mode pump/motor units should be isolated from the chassis. A mixed mode magnetorheological (MR) fluid mount was adopted to isolate this vibration and was evaluated in a quarter car model. The MR fluid mount was designed to be able to operate in flow mode and squeeze mode independently and simultaneously. For HHVs, it is desirable to control force and displacement transmissibility. These simulation results presented a basis for designing an effective algorithm to control both the displacement transmissibility and force transmissibility. Moreover, a hierarchical controller for minimizing the two requirements for transmissibility was also constructed. At last, a fuzzy logic controller was devised to closely reproduce the effect of the hierarchical controller. The experiments were set up to facilitate the hardware-in-the-loop evaluation of the mount. Results from the experiments showed that the mixed mode MR fluid mount was able to achieve desired dynamic stiffness profile to minimize the dual-transmissibility criterion.

Shuo Wang

Mohammad Elahinia

The Nguyen

Displacement and Force Control of a Quarter Car Using a Mixed Mode MR Mount

The rotordynamic coefficients of fixed-pad thrust bearing are introduced and calculated by using the out-domain method, and a general analysis method is developed to investigate the coupled dynamics of a rotor equipped with journal and thrust bearings simultaneously. Considerations include the effects of static tilt parameters of the rotor on rotordynamic coefficients of thrust bearing and the action of thrust bearing on system dynamics. It is shown that thrust bearing changes the load distribution of journal bearings and the static deflection of the rotor and delays the instability of the system considerably in lateral shaft vibration.

Yu Lie

R.B. Bhat

Coupled Dynamics of a Rotor-Journal Bearing System Equipped with Thrust Bearings

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Shock and Vibration publishes papers on all aspects of shock and vibration, especially in relation to civil, mechanical and aerospace engineering applications, as well as transport, materials and geoscience.&nbsp;

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Chief Editor&nbsp;Dr Tai Thai&nbsp;is based at the University of Melbourne and his current research focuses on high strength materials for sustainable construction of buildings, bridges and other infrastructure.

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Shock and Vibration publishes papers on all aspects of shock and vibration, especially in relation to civil, mechanical and aerospace engineering applications, as well as transport, materials and geoscience. 

Shock and Vibration