Jerome J. Connor

Robust Flexible Capacitive Surface Sensor for Structural Health Monitoring Applications

Early detection of possible defects in civil infrastructure is vital to ensuring timely maintenance and extending structure life expectancy. The authors recently proposed a novel method for structural health monitoring based on soft capacitors. The sensor consisted of an off-the-shelf flexible capacitor that could be easily deployed over large surfaces, the main advantages being cost-effectiveness, easy installation, and allowing simple signal processing. In this paper, a capacitive sensor with tailored mechanical and electrical properties is presented, resulting in greatly improved robustness while retaining measurement sensitivity. The sensor is fabricated from a thermoplastic elastomer mixed with titanium dioxide and sandwiched between conductive composite electrodes. Experimental verifications conducted on wood and concrete specimens demonstrate the improved robustness, as well as the ability of the sensing method to diagnose and locate strain.

Structural analysis and design of deployable structures

Abstract Deployable-collapsable structures have many potential applications ranging from emergency shelters and facilities, through relocatable, semi-permanent structures, to space-station components. Their main advantages are the small volume they occupy during storage and transportation, and their fast and easy erection procedure. A new concept of self-stabilizing deployable structures featuring stable, stress-free states in both deployed and collapsed configuration shows even higher promise. During the deployment phase these structures exhibit a highly nonlinear behavior. A large displacements/small strains finite element formulation is used to trace the nonlinear load-displacement curve, and to obtain the maximum internal forces that occur in the members of the structure during deployment. The influence of various parameters that affect the behavior of the structures, such as geometric shape, dimensions of the members, cross-sectional properties and kinematic assumptions is being investigated.

ENGINEERING APPROXIMATIONS TO NONLINEAR DEEPWATER WAVES

Recent measurements of wave kinematic indicate that the horizontal wave velocity is smaller at the crest and higher (more negative) in the trough than predicted by the Stokes higher order theories which are normally used in a deterministic design process. This has led to postulation of engineering methods for description of wave kinematics1,2 A methodology has been developed to establish second order corrections to the engineeringmethods. The purpose is to find a description of the wave kinematics which predicts measured behaviour with good degree of accuracy. The methodology has been applied to the engineering methods proposed by Wheeler1 and Chakrabarti.2 The second order Chakrabarti approximation (the ‘alternative approximation’) demonstrates good agreement with measured wave kinematics.

Wavelet Network for Semi-Active Control

This paper proposes a wavelet neurocontroller capable of self-adaptation and self-organization for uncertain systems controlled with semiactive devices that are ideal candidates for control of large-scale civil structures. A condition on the sliding surface for cantilever-like structures is defined. The issue of applicability of the control solution to large-scale civil structures is made the central theme throughout the text, as this topic has not been extensively discussed in the literature. Stability and convergence of the proposed neurocontroller are assessed through various numerical simulations for harmonic, earthquake, and wind excitations. The simulations consist of semiactive dampers installed as a replacement for the current viscous damping system in an existing structure. The controller uses only localized measurements. Results show that the controller is stable for both active and semiactive control using limited measurements and that it is capable of outperforming passive control strategies for earthquake and wind loads. In the case of wind loads, the neurocontroller is found to also outperform a linear quadratic regulator (LQR) controller designed using full knowledge of the states and system dynamics.

Combining numerical analysis and engineering judgment to design deployable structures

Abstract Deployable structures are prefabricated space frames that can be stored and transported in a compact folded configuration and then deployed rapidly into a load bearing configuration. The structures are stable and stress-free in the folded and the deployed configuration, but exhibit a highly nonlinear behavior during deployment. Therefore, their design process should include simulation of their response in two phases: in the deployed configuration under service loads, and during deployment. The first phase involves linear analysis while the second one requires a geometrically nonlinear finite element formulation. Both simulations can be very demanding in terms of computer storage requirements as the number of degrees of freedom increases. In addition, the nonlinear analysis is quite expensive because of the large number of load steps that are necessary in order to trace the complete load-displacement path. This paper first describes a set of numerical models that were used to simulate the exact structural behavior using the finite element program ADINA. Then, some simplified analytical and numerical models are proposed that can be applied in the preliminary design stage, or even for final design, in order to obtain approximate but satisfactory results at a much lower cost.

Deployability Conditions for Curved and Flat, Polygonal and Trapezoidal Deployable Structures

Prefabricated, deployable space frames that exhibit self-standing and stress-free states in both the deployed and collapsed configurations are investigated in this paper. This type of deployable structures shows considerable advantages as compared to previous designs that either required external stabilizing or had members with residual stresses in the deployed configuration. Following previous developments for flat deployable structures consisting of units with regular-polygon planviews, this study deals with flat structures made of trapezoidals, and curved structures assembled from regular-polygonal units. First, the general geometric constraints and deployability conditions for these units are formulated, and a methodology for using these constraints as geometric design criteria is presented. Furthermore, additional conditions for the assemblage of single units into larger structures are given. Then, structural analysis issues for this type of structures are discussed. The necessity of nonlinear analysis during deployment is emphasized. Finally, the above geometric design procedures are demonstrated with specific examples.

Modeling, loading, and preliminary design considerations for tall guyed towers

Abstract The inherent nonlinearity in the structural behavior of guyed towers leads to difficulties in their structural analysis, and prevents the formulation of a general-purpose design methodology. As a result, simplifying analysis assumptions regarding the loading and the modeling of structural behavior have to be made, and approximate design methods are used, that are often unjustified, and can lead to disastrous failures. In this paper, the authors first summarize the results of an investigation they carried out on the collapse of a 1900 ft tall guyed tower under ice and wind loads. Based on this investigation, they then proceed to present some structural analysis recommendations relating to loading and modeling concerns. Special emphasis is placed on the importance of ice loading, and on the level of accuracy required in modeling the nonlinear response behavior. Finally, the conclusions drawn from this study are used to formulate preliminary design guidelines. This facilitates a systematic approach for the design of tall guyed towers.

A SYSTEMATIC DESIGN METHODOLOGY FOR DEPLOYABLE STRUCTURES

The deployable structures investigated in this paper are prefabricated space frames made of basic units consisting of two straight bars connected to each other by a pivot, the so called scissor-like-elements. They can be stored in a compact folded configuration, and can be easily deployed into large, load carrying forms by simple articulation. In order to avoid major disadvantages of previous designs, the structures examined here obey strict geometric rules so that they are self-standing and stress-free in both their folded and deployed configurations. During deployment however, geometric incompatibility between member lengths results in a geometrically nonlinear structural behaviour. The optimum design of such a structure has to provide a compromise between desired stiffness in the deployed configuration, and desired felxibility during deployment.

A framework for performance-based design

The international competitiveness of the US construction industry is linked to its strategic ability to design and build quality projects. This means delivering facilities that satisfy all the needs of the client. Correct decision-making during design and construction planning is the best means for assuring a quality project. Performance-based design is a framework that enables the project team to approach the project delivery process systematically and provides basic principles for evaluating and comparing alternative solutions. The principles of axiomatic design (as previously advanced by Suh) and the concept of an interface index are key elements of the framework. Axiomatic design provides an operational structure for the design process as well as a set of basic principles or axioms for guiding each decision-maker. The interface index complements the design axioms by quantifying the effort associated with integrating the contributions of multiple decision-makers into a total system. Elements of the framework are demonstrated through application to an actual facility.

Research on modeling shear transfer in reinforced concrete nuclear structures

This paper provides an overview of research in modeling the mechanisms of shear transfer in reinforced concrete nuclear structures. Bases for the development of analytical models are discussed. Preliminary analysis results are presented for the wall specimens to study the behavior of a containment wall portion under biaxial tension and tangential shear loading. Further research needs and interests are suggested for improved analysis capabilities and design.