Multidisciplinary Approach to the Assessment of Seismic Performances and Rehabilitation of Bridges: Nonlinear Analyses, Probability Theory and Optimization Theory

AbstractThe paper presents a multidisciplinary approach to the assessment of seismic performances based on the Performance-Based Earthquake Engineering (PBEE), taking into account the multi-criteria optimization theory in analyzing the priority methods for bridge rehabilitation/strengthening. One bridge model was subjected to nonlinear static pushover analyses (NSPA), target displacement analyses using the spectrum capacity method (CSM), vulnerability analyses, and reliability analyses, while for a damaged bridge, in addition to be considered using the above methods, was also analyzed using the VIKOR method of multi-criteria optimization. Seismic performances were determined based on monitoring the system's plastification and analyzing the relevant parameters for the level of target displacement, such as target displacement, total shear force, spectral displacement, spectral acceleration, vibration period, damping and ductility. The phases of damage were considered using the probabilistic analysis of vulnerability and reliability: slight, moderate, extensive and complete, as a function of system ductility

Development of small-scale thermoacoustic engine and thermoacoustic cooling demonstrator

Thermoacoustics is a science and technology field that studies heat and sound interactions. Sound waves in any fluid consist of coupled pressure, motion, and temperature oscillations. When the sound travels through a narrow channel, an oscillating heat flow between the fluid and the channel's wall becomes significant. The present study deals with the effects of thermoacoustic cooling with closed and open ended tubes and also investigates the performance of a small-scale thermoacoustic heat engine. The first part of this document presents the design, construction, and testing of a miniature standing-wave thermoacoustic heat engine. The main objective was to build and test a miniature heat engine without moving parts. Recorded parameters included the temperature difference across the stack and the corresponding acoustic pressure amplitude of the sound produced by the engine. The system was also tested for different stack materials and tube lengths. The most efficient system is described in detail in this document. The critical temperature difference across the stack was measured to be approximately 350°C for the 5.8 cm engine and 250°C for the 9.3 cm engine. The average acoustic RMS pressure of the sound produced was about 2.7 Pa at 30 cm from the engine for both lengths and the frequency of the sound was about 1.4 kHz for the 5.8 cm engine and about 1 kHz for the 9.3 cm engine. The second part of this document presents the effects of thermoacoustic cooling with closed and open ended tubes. The position of the stack and sound frequencies were varied to establish the most effective configuration. For each configuration, the pressure amplitude inside the tube and the sound frequency were the controlled parameters, and the temperature difference across the stack was measured. The experimental results of the thermoacoustic cooling system are compared to the theoretical results. For the closed-end system the temperature of the top of the stack was higher than the bottom and for the open-end system the temperature of the top of the stack was lower than the bottom. The maximum temperature difference was about 32°C for the closed-end and 16°C for the open-end

Nonlinear dynamic and static analysis of I-5 Ravenna Bridge

The Washington State Department of Transportation (WSDOT) developed a bridge seismic retrofit program in 1990 in order to address seismic risk associated with state owned bridges. Of particular interest are bridges with multiple column bents and those founded on precast/prestressed hollow core concrete piles. A number of deficiencies in the seismic behavior of these piles were observed. They have minimal energy-absorbing hysteretic behavior, and failure in such piles is sudden and violent. Knowing the behavioral properties of prestressed hollow core piles, a typical bridge built on them was evaluated for seismic loading. The outcome for this task is knowledge of the failure mechanisms for this type of bridge, the forces required for various levels of failure, and a definition of the earthquake magnitude that will cause failure. Two types of analysis were performed: pushover analysis and nonlinear dynamic analysis. The same type of structural model was used for both. A three-dimensional "spine" model of the bridge was developed using SAP2000 (2007), including modeling of the bridge bearings, expansions joints, and soil-structure interaction. The dynamic nonlinear response of the bridge was investigated by using three ground motions with different return periods. The nonlinear static response of the bridge was investigated using different variants of capacity spectrum methods. Nonlinear static analysis provided poor results compared to nonlinear dynamic analysis, due to higher mode effects. Results of both nonlinear static and dynamic analysis showed that the piles fail in a brittle fashion under seismic loading. Using results from 3D finite element analysis of the piles and pile-crossbeam connection, a more advanced spine model was created. The pile-crossbeam connection improved the strength of the bridge. The effect of foundation soil flexibility was examined by running analysis on three different soil types and comparing the results. Dense sand proved to be the most conservative soil model. Also, the effects on the seismic demand due to period lengthening and damping increase produced by structural deterioration were evaluated