Rigoberto Burgueño

Buckling-induced smart applications: recent advances and trends

A paradigm shift has emerged over the last decade pointing to an exciting research area dealing with the harnessing of elastic structural instabilities for ‘smart’ purposes in a variety of venues. Among the different types of unstable responses, buckling is a phenomenon that has been known for centuries, and yet it is generally avoided through special design modifications. Increasing interest in the design of smart devices and mechanical systems has identified buckling and postbuckling response as a favorable behavior. The objective of this topical review is to showcase the recent advances in buckling-induced smart applications and to explain why buckling responses have certain advantages and are especially suitable for these particular applications. Interesting prototypes in terms of structural forms and material uses associated with these applications are summarized. Finally, this review identifies potential research avenues and emerging trends for using buckling and other elastic instabilities for future innovations.

STRUCTURAL CHARACTERIZATION OF FIBER-REINFORCED COMPOSITE SHORT- AND MEDIUM-SPAN BRIDGE SYSTEMS

The paper describes the development of a new structural system for short and medium span bridges wherein use is made of both advanced composites and conventional materials such as concrete. The concept uses prefabricated composite tubes as girders which are then filled with concrete, after which a conventional precast or cast-in-place, or advanced composite, deck system is integrated to form the bridge superstructure. The paper presents experimental results of large-scale tests aimed towards the structural characterization of the girders, anchorages, and girder-deck assemblies for both serviceability and ultimate limit states.

Experimental dynamic characterization of an FRP composite bridge superstructure assembly

A system comprised of concrete filled, filament wound, circular carbon/epoxy girders and an E-glass/polyester deck, representative of a bridge section in the positive moment region was tested at large scale to assess the overall and component structural response. The system was characterized for stiffness and overall response under monotonic and cyclic fatigue loads. Forced vibration testing was conducted as part of a level I non-destructive evaluation (NDE) procedure at each of the test stages, including after failure. Experimental results from the tests were seen to correspond well with analytical results for mode shapes and frequencies obtained through an eigenvalue analysis of a plane-grillage finite element model. The test method was shown to be effective in indicating changes in response as a function of load level and damage accumulation, and is expected to have significant potential for eventual routine health monitoring and damage detection of such structural systems in the field.

Kings Stormwater Channel and I-5/Gilman Bridges, USA

Advanced composite materials, or fiber-reinforced polymer (FRP) composites, have found wide application in recent years in the rehabilitation of structures. Most of the primary structure applicatio...

A concept for energy harvesting from quasi-static structural deformations through axially loaded bilaterally constrained columns with multiple bifurcation points

A major obstacle limiting the development of deployable sensing and actuation solutions is the scarcity of power. Converted energy from ambient loading using piezoelectric scavengers is a possible solution. Most of the previously developed research focused on vibration-based piezoelectric harvesters which are typically characterized by a response with a narrow natural frequency range. Several techniques were used to improve their effectiveness. These methods focus only on the transducer?s properties and configurations, but do little to improve the stimuli from the source. In contrast, this work proposes to focus on the input deformations generated within the structure, and the induction of an amplified amplitude and up-converted frequency toward the harvesters? natural spectrum. This paper introduces the concept of using mechanically-equivalent energy converters and frequency modulators that can transform low-amplitude and low-rate service deformations into an amplified vibration input to the piezoelectric transducer. The introduced concept allows energy conversion within the unexplored quasi-static frequency range (?1?Hz). The post-buckling behavior of bilaterally constrained columns is used as the mechanism for frequency up-conversion. A bimorph cantilever polyvinylidene fluoride (PVDF) piezoelectric beam is used for energy conversion. Experimental prototypes were built and tested to validate the introduced concept and the levels of extractable power were evaluated for different cases under varying input frequencies. Finally, finite element simulations are reported to provide insight into the scalability and performance of the developed concept.

Structural Assessment and Damage Identification Algorithms Using Binary Data

One of the challenges in structural health monitoring (SHM) is the power required for sensors to collect and communicate data. Self-powered sensors are able to harvest power by from their environment, i.e., strain and vibration of the host structure. However, the harvested power with current technology is still limited and improving the system’s efficiency requires reducing the power budget. A way to minimize the communication power demand is to transmit the minimum amount of information, namely one bit. The binary signal can be generated at a sensor node according to a local rule based on physical measurements, but interpretation at the global level requires dealing with discrete binary (1 or 0) data, which implies system information with reduced resolution. This study presents an investigation on approaches for the interpretation of such kind of binary data for use in structural assessment and damage identification. Pattern recognition (PR) methods based on image data analysis were adapted for the study. The methods used were classifiers based on deviation of patterns with respect to each other, two-dimensional principal component analysis, and two-dimensional linear discriminant analysis. The PR methods and the performance of the interpretation algorithms were evaluated by using virtual data from finite element simulations on an aluminum plate. The ability for each of the PR methods to identify service demands, load variations and localized material degradation was evaluated. Results indicate that PR methods can be used as damage identification algorithms for binary data sets in novel wireless self-powered sensor networks.Copyright

Self-powered piezo-floating-gate smart-gauges based on quasi-static mechanical energy concentrators and triggers

Changes in physical processes like ambient temperature or pressure variations occur at frequencies that are significantly lower than 1 Hz. This poses a challenge for designing self-powered sensors that monitor these quasi-static physical processes and at the same time scavenge operational energy for sensing, computation, and storage from the signal being monitored. In this paper, we present a novel paradigm for designing a self-powered sensor/data logger that exploits the physics of negative-stiffness mechanical energy concentrators with the physics of our previously reported piezoelectricity driven impact ionized hot-electron injection (p-IHEI)-based sensors. The operational principle is based on the sudden transitions from unstable mode branch switching during the elastic postbuckling response of slender columns, which are used to generate high-frequency deformations as an input to the p-IHEI-based sensor. The experimental results demonstrate that the proposed self-powered sensor based on an integrated circuit fabricated in a 0.5-μm CMOS technology can count and record the number of quasi-static input events with frequencies spanning less than 1 Hz.

Characterization of Mechanically-Equivalent Amplifiers and Frequency Modulating Concepts for Energy Harvesting Devices

One of the major obstacles that are limiting the development of deployable integrated sensing and actuation solutions is the scarcity of power. Converted energy from ambient loading in civil and mechanical structures is typically used as an alternative solution. Although, piezoelectric vibration harvesters have been widely used, these elements exhibit a narrow natural frequency response range, thus considerably limiting the levels of harvestable power. Most of the previously used methods focus only on modifying the transducer’s properties and configurations. These techniques do little to modify the stimuli from the source. In contrast, this work proposes to focus on the input signal generated within the structure by inducing amplified response amplitude and a frequency up-conversion toward the harvesters’ natural response spectrum. This paper introduces the concept of using mechanically-equivalent frequency modulators that can transform the low-amplitude and low-rate service and ambient deformations into an amplified input to the piezoelectric transducer. The introduced methods will allow energy generation and conversion for loads within the unexplored quasi-static frequency range (<< 1 Hz). The post-buckling behavior of bilaterally restrained columns and bistable plates is used for frequency up-conversion. A bimorph cantilever PVDF piezoelectric beam, attached to the columns and plates, are used for energy conversion. Experimental prototypes were built and tested to validate the introduced concept. The levels of extractable power are evaluated for different cases under varying input frequencies. Finally, numerical simulations provide insight into the scalability and performance of the developed concepts.Copyright

Using Soft Computing to Analyze Inspection Results for Bridge Evaluation and Management

The national bridge inventory (NBI) system, a database of visual inspection records that tallies the condition of bridge elements, is used by transportation agencies to manage the rehabilitation of the aging U.S. highway infrastructure. However, further use of the database to forecast degradation, and thus improve maintenance strategies, is limited due to its complexity, nonlinear relationship, unbalanced inspection records, subjectivity, and missing data. In this study, soft computing methods were applied to develop damage prediction models for bridge abutment walls using the NBI database. The methods were multilayer perceptron network, radial basis function network, support vector machine, supervised self-organizing map, fuzzy neural network, and ensembles of neural networks. An ensemble of neural networks with a novel data organization scheme and voting process was the most efficient model, identifying damage with an accuracy of 86%. Bridge deterioration curves were derived using the prediction models and compared with inspection data. The results show that well developed damage prediction models can be an asset for efficient rehabilitation management of existing bridges as well as for the design of new ones.

Model Development for Dynamic Energy Conversion in Post-Buckled Multi-Stable Slender Columns

Broadband piezoelectric energy harvesting solutions from ambient loading have been extensively studied with the purpose of increasing the efficiency of vibration-based harvesters. Most of the previously developed methods focus on the transducer’s properties and configurations, and require vibration input excitations. In contrast, we have previously experimentally shown a mechanical energy concentrator system that exploits the quasi-static input deformations (strains) generated within the structure and induces an amplified amplitude and frequency up-converted response. The tested energy converting devices transform low-amplitude and low-rate service strains into an amplified vibration input to the piezoelectric transducer. The snap-through behavior of bilaterally constrained columns was used as the mechanism for energy concentration. This paper presents a theoretical model, based on energy method, for the post-buckling behavior of a bilaterally constrained slender column under quasi-static axial loadings. The total potential energy of the buckled elastic element is the sum of the potential energies due to bending, compression and external applied force. The transverse deflection is limited by the lateral constraints. Therefore a constrained minimization problem of the total potential energy is solved to determine the equilibrium configurations. Equilibrium transitions are correlated to the changes in the magnitude of the weight coefficients that define the contribution of buckling modes to the deflected shape. Transition states are defined in terms of the axial displacements, axial forces, column shape, and energies stored in the system.Copyright