In this study, the real time strain response of the Multiwalled Carbon Nanotube (MWCNT) film is studied at macroscale experimentally. The response of the MWCNT film to temperature changes is also presented in the study. The MWCNT film is attached to a brass specimen using vacuum bonding, and the brass specimen is subjected to tensile load and voltage output from MWCNT film is obtained using four-point probe and a sensitive voltage measurement device. Experimental results demonstrate a linear relationship between change in voltage across the film and change in strain in the brass specimen when subjected to tensile load. The MWCNT film also exhibited excellent reversible electromechanical characteristics when the specimen was unloaded. The response of the MWCNT film to temperature is also studied and it is observed that the resistance of the MWCNT film decreased upon heating. The MWCNT film exhibited a stable and linear voltage response to changes in temperature. The experimental results demonstrate the effectiveness of Multiwalled carbon nanotubes in strain sensing as well as the effect of temperature on the MWCNT film.
Carbon nanotubes change their electronic properties when subjected to strains. In this study, the strain sensing characteristic of carbon nanotubes is used to develop a carbon nanotube film sensor that can be used for strain sensing on the macro scale. The carbon nanotube film is isotropic due to randomly oriented bundles of single-wall carbon nanotubes (SWCNTs). Using experimental results it is shown that there is a nearly linear change in voltage across the film when it is subjected to tensile and compressive stresses. The change in voltage is measured by a movable four-point probe in contact with the film. Multidirectional and multiple location strains can be measured by the isotropic carbon nanotube film.
Summary A new passive seismic response control device has been developed, fabricated, and tested by the authors and shown to be capable of producing negative stiffness via a purely mechanical mechanism, thus representing a new generation of seismic protection devices. Although the concept of negative stiffness may appear to be a reversal on the desired relationship between the force and displacement in structures (the desired relationship being that the product of restoring force and displacement is nonnegative), when implemented in parallel with a structure having positive stiffness, the combined system appears to have substantially reduced stiffness while remaining stable. Thus, there is an ‘apparent weakening and softening’ of the structure that results in reduced forces and increased displacements (where the weakening and softening is of a non‐damaging nature in that it occurs in a seismic protection device rather than within the structural framing system). Any excessive displacement response can then be limited by incorporating a damping device in parallel with the negative stiffness device. The combination of negative stiffness and passive damping provides a large degree of control over the expected performance of the structure. In this paper, a numerical study is presented on the performance of a seismically isolated highway bridge model that is subjected to various strong earthquake ground motions. The Negative Stiffness Devices (NSDs) are described along with their hysteretic behavior as obtained from a series of cyclic tests wherein the tests were conducted using a modified design of the NSDs (modified for testing within the bridge model). Using the results from the cyclic tests, numerical simulations of the seismic response of the isolated bridge model were conducted for various configurations (with/without negative stiffness devices and/or viscous dampers). The results demonstrate that the addition of negative stiffness devices reduces the base shear substantially, while the deck displacement is limited to acceptable values. This assessment was conducted as part of a NEES (Network for Earthquake Engineering Simulation) project which included shaking table tests of a quarter‐scale highway bridge model. Copyright © 2014 John Wiley & Sons, Ltd.
The intrinsic low-dimensional structure, which is implicit in the large-scale data sets of structural seismic and typhoon responses, is exploited for efficient data compression. Such a low-dimensional structure, empirically, stems from few modes that are active in the structural dynamic responses. Originally, limited to the sensor and time-history dimension, the structural seismic and typhoon response data set generally does not have an explicit low-rank representation (e.g., by singular value decomposition or principal component analysis), which is critical in multi-channel data compression. By the proposed matrix reshape scheme, the low-rank structure of the large-scale data set stands out, regardless of the original data dimension. Examples demonstrate that the developed method can significantly compress the large-scale structural seismic and typhoon response data sets, which were recorded by the structural health monitoring system of the super high-rise Canton Tower. Copyright © 2015 John Wiley & Sons, Ltd.
This paper presents the fully base-isolated highway bridge benchmark problem. The highway bridge benchmark problem consists of two phases: (1) Phase I—the bridge deck being base isolated only at the abutments and the center bent being integral with the pier (without isolation), and (2) Phase II—the bridge deck being fully base isolated at both the bent/pier and abutment locations. In both phases of the highway bridge benchmark, the objective is to augment the performance of the isolation system using supplemental control strategies. The problem definition (Part I) as well as a sample controller (Part II) for Phase I of the study has been presented in the companion papers. The focus of this paper is to present the fully base-isolated highway bridge and sample Lyapunov semiactive controller (Part III). As-built structural designs of the 91/5 overcrossing in Orange county in Southern California are used to develop the finite-element model for this benchmark based on Phase I. The nonlinear analysis tool and the controller interface have been developed in MATLAB. The bridge is isolated using nonlinear elastomeric bearings with a lead core. Magneto-rheological (MR) dampers are used to control the seismic response of the bridge. The MR dampers are installed at the isolation level at 10 locations over the abutments and bent/pier locations, each location consisting of an orthogonal pair of dampers to control the responses in both directions. The outputs allowed in the benchmark problem definition are used to design the controller and the velocity and displacement measurements if required are obtained by integrating accelerations using a filter, which simulates integration. Detailed comparisons of benchmark performance indices for the fully base-isolated bridge with sample semiactive controllers and passive strategies are performed in comparison with the uncontrolled case, for a set of strong near-field earthquakes. The sample Lyapunov semiactive controller is shown to reduce the isolator and mid-span displacements. The modeling and sample control designs demonstrated in this paper can be used to form the basis for studying a wider variety of active and semiactive control strategies—to be developed by the participants in the benchmark study—for fully base-isolated highway bridges. Copyright © 2009 John Wiley & Sons, Ltd.
In-service cables of structures, such as those in cable-supported buildings and cable bridges (e.g., stay cables and suspenders), suffer from cumulative fatigue damage caused by dynamic loads (e.g., the cyclic traffic loads on cable bridges) and wind excitation (on the cable-supported buildings and bridges). Monitoring the time history of time-varying cable tension for assessing their fatigue damage is thus essential to diagnose their health condition and predict their future performance. Currently, embedded measurement devices such as anchor load cells, elastomagnetic (EM) sensors, and optical fiber Bragg grating (OFBG) sensors are able to directly record the time-varying cable tension time history; however, poor durability, high costs, and intensive labor of installation significantly hinder their applicability in practice. On the other hand, a vibration-based technique manifests itself as a convenient, cost-effective, and reliable approach to determine the cable tension, and is widely used; it is based on an established formula (taut-string theory) between the cable tension and its frequency, which can be identified through the measured cable vibration responses. Existing research based on this approach, nevertheless, assume that the cable tension is time-invariant over a long time segment; real-time (online) identification of the time-varying cable tension has not yet been addressed. This paper develops a new computational framework to identify the time-varying cable tension time history through an unsupervised learning algorithm termed complexity pursuit (CP), which is capable of online tracking of the time-varying cable frequency, using as little information as the measured cable accelerations from only two accelerometers. The CP learning rule is especially exploited; it is found that CP can blindly separate the constituent modal responses of the cable even within a dramatically short duration such that the time-varying cable frequency can be identified, thereby computing the time-varying cable tension according to the taut-string theory. A hybrid example combining the simulated and real-measured data from an actual cable-stayed bridge and a laboratory experimental study of a scaled stay cable demonstrates that the proposed CP-based method performs accurate real-time identification of the time-varying cable tension. The proposed method is shown to be straightforward and efficient, with the potential to be an automated, economic, and convenient approach for health monitoring and assessing in situ or new cables of cable-supported structures.
