Response of Embedded Circular Flexible Foundations

The stiffness matrix approach to the solution of vertical vibrations of a circular flexible foundation embedded in a viscoelastic layered half-space have been described. Results of a parametric study, represented by displacement and soil reaction distributions and impedances, indicate a significantly different responses of flexible and rigid foundations. Important parameters are identified and include: the stiffness ratio, depth of embedment, soil stratification and loading distribution. Influence of each of the parameters is discussed

Use of Rayleigh Modes in Interpretation of SASW Test

The Spectral-Analysis-of-Surface-Waves (SASW) method is a seismic method for measuring in situ elastic moduli of layered systems, like soils or pavements. The inversion process associated with SASW can be an ambiguous task in certain cases, because a field dispersion curve needs to be matched with an unknown path through a family of theoretically defined curves for an assumed profile. A study of the influence of soil stratification on participation of higher Rayleigh modes in surface wave propagation included the evaluation of theoretical dispersion curves, modal shapes and rates of energy transmission in the horizontal direction. Wave propagation due to oscillations of a circular plate on the surface of layered systems was modelled and the resulting simulated dispersion curves compared with theoretical ones. The results indicate that higher Rayleigh modes can dominate wave propagation for all but a narrow range of low frequencies for profiles where softer layers are trapped between stiffer layers. Potential ways of identification of such situations are discussed and improvements of the inversion process suggested

Impact echo data from bridge deck testing: Visualization and interpretation

Accurate assessment of the condition of bridges leads to their economic management. Ultrasonic seismic methods can be successfully used for this purpose through evaluation of changes in material characteristics and detection of the development of defects and zones of deterioration. The impact echo (IE) method is of special benefit in evaluation of corrosion-induced deck delamination, due to the method's nondestructive nature, speed of evaluation, and ability to detect delaminated zones at various stages of deterioration: from initial to progressed and developed. The traditional approach in condition assessment of bridge decks by IE on the basis of review of individual test point records and a new automated approach based on three-dimensional (3-D) data visualization are presented. The developed 3-D visualization platform allows both the advanced presentation and interpretation of IE data. The data presentation is provided as 3-D translucent visualizations of reflectors in a bridge deck section and horizontal and vertical cross sections through all distinctive zones, including a zone of delamination. The associated interpretation platform allows both (a) the overall assessment of the condition of the deck, through cumulative distributions and histograms of reflection intensity, and (b) identification of deteriorated zones of the deck for repair or rehabilitation in an efficient and intuitive way. The visualization platform effectively enables an IE device to be used as a type of bridge deck sonar device

Robotic Platform Rabit for Condition Assessment of Concrete Bridge Decks Using Multiple NDE Technologies

Current assessment of concrete bridge decks relies on visual inspection and use of simple nondestructive and destructive evaluations. More advanced, but still manual nondestructive evaluation (NDE) technologies provide more comprehensive assessment. Still, due to a lower speed of data collection and still not automated data analysis and interpretation, they are not used on a regular basis. The development and implementation of a fully autonomous robotic system for condition assessment of concrete bridge decks using multiple nondestructive evaluation (NDE) technologies is described. The system named RABIT (Robotics Assisted Bridge Inspection Tool) resolves issues related to the speed of data collection and analysis. The system concentrates on the characterization of internal deterioration and damage, in particular three most common deterioration types in concrete bridge decks: rebar corrosion, delamination, and concrete degradation. For those purposes, RABIT implements four NDE technologies: electrical resistivity (ER), impact echo (IE), ultrasonic surface waves (USW) and ground-penetrating radar (GPR). Because the system utilizes multiple probes or large sensor arrays for the four NDE technologies, the spatial resolution of the results is significantly improved. The technologies are used in a complementary way to enhance the overall condition assessment and certainty regarding the detected deterioration. In addition, the system utilizes three high resolution cameras to image the surface of the deck for crack mapping and documentation of previous repairs, and to image larger areas of the bridge for inventory purposes. Finally, the robot’s data visualization platform facilitates an intuitive 3-dimensional presentation of the main three deterioration types and deck surface features

Shear Wave Velocity Profiling with Surface Wave Methods

Surface wave method was introduced as a tool to the geotechnical and infrastructure engineering fields in the early 1980\u27s. Since then, the method has been continuously modified and improved. The adoption of the method has accelerated in the last ten years because of the interest of the engineering community, and due to the development of affordable and portable hardware and software. Despite numerous studies that demonstrate its effectiveness in a wide spectrum of applications, the method has not been fully embraced by the engineering community mainly due to lack of standardization. The common attributes of different approaches in implementing the surface method from the point of view of the engineering applications are discussed, followed by the practical and theoretical strengths and limitations of alternative approaches. Different approaches should provide satisfactory results as long as the inherent limitations of each approach are matched with the requirements of the engineering objectives of a given project