Songye Zhu

A shape memory alloy-based reusable hysteretic damper for seismic hazard mitigation

This paper presents a special shape memory alloy-based hysteretic damper with distinctive features such as tunable hysteretic behavior and ability to withstand several design level earthquakes. Superelastic nitinol stranded wires are used for energy dissipation in this damping device, termed a reusable hysteretic damper (RHD). By adjusting its design parameters, the hysteretic behavior of the RHD can be modified to best fit the needs for passive structural control applications. Adjustable design parameters of the RHD include the inclination angle of the nitinol wires, pretension level, and friction effect. A simulation-based parametric study was carried out to examine the effects of these design parameters of the RHD on its energy dissipating performance. The effectiveness of the RHD in passive seismic response control of civil engineering structures is examined through a nonlinear dynamic analysis of a three-story steel frame building with and without an RHD. The simulation results suggest that it can effectively reduce the structural response of building structures subjected to strong earthquakes. With proper design, an RHD can be reused for several strong earthquakes without the need for repair, due to the high fatigue life of nitinol wires.

A thermomechanical constitutive model for superelastic SMA wire with strain-rate dependence

The recent increased use of shape memory alloys (SMAs) for civil engineering applications manifests the need for a high-fidelity constitutive model which considers the materials strong dependence on the loading rate. This paper presents an improved thermomechanical constitutive model with strain-rate dependence for predicting the uniaxial superelastic behavior of shape memory alloys. The proposed constitutive model, which is formulated within a thermomechanical framework, is comprised of three principal parts: a mechanical law, an energy balance equation, and a transformation kinetics rule. The analytical derivation of the model and experimental test results for superelastic NiTi wires are described in this paper. The prediction made by this phenomenological model shows good agreement with experimental data for superelastic NiTi wires at various loading rates. Through a comparison with experimental results, the proposed constitutive model was evaluated for several key characteristics of superelastic behavior such as reduction of hysteresis area, increase of transformation plateau, and temperature change with strain rate. The proposed constitutive model offers a useful tool for the design and simulation of superelastic SMA-based devices in civil engineering applications.

Harvesting energy via electromagnetic damper: Application to bridge stay cables

Energy harvesting from ambient vibration is an emerging and promising solution to the power supply problem associated with autonomous sensors. This article proposes a novel strategy of harvesting damping energy from vibration control devices. A novel system, termed electromagnetic damper cum energy harvester, is employed to fulfill both vibration damping and energy harvesting functions. Electromagnetic damper cum energy harvester is essentially an electromagnetic device connected to a specially designed energy harvesting circuit, which is a buck–boost converter operating in a discontinuous conduction mode. The energy harvesting circuit can achieve satisfactory efficiency without any feedback loop. The effectiveness of the dual-function electromagnetic damper cum energy harvester is demonstrated through a numerical case study of bridge stay cables under wind excitations, in which the major parameters of electromagnetic damper cum energy harvester are determined through a simple design approach. Simulation results project average output power ranging from 82.5 to 2396.8 mW at a wind speed of 9–15 m/s, corresponding to an overall efficiency of 42.3%. The dual-function electromagnetic damper cum energy harvester also exhibits vibration control performance comparable to an optimally designed viscous fluid damper.

Integrated optimal placement of displacement transducers and strain gauges for better estimation of structural response

Although a variety of sensors provide more comprehensive information and advanced features of structures, their distinct properties and limitations considerably complicate the design procedure of multi type sensor systems. This paper is focused on the optimal design of integrated sensor systems with both strain gauges and displacement transducers. Unlike traditional sensor placement approaches, in which these two types of sensors are often designed separately to monitor structural deformations and displacements respectively, the integrated design procedure presented in this study treats the sensor system as a whole. The number and locations of strain gauges and displacement transducers are optimized simultaneously, and their measurement data are fused together to better predict the unobserved structural response. The theoretical criterion for the optimization procedure is first formulated based on the strain and displacement mode shapes extracted from finite element models. Then, the initial candidate sensor locations are reduced to a smaller optimal set with minimized prediction error of structural response. A two-dimensional cantilever beam is then analyzed as a numerical example to investigate the effectiveness and accuracy of the presented optimal sensor placement approach. The results indicate that the integrated sensor system provides better estimation of structural response than single-type sensor system.

Mechanical properties of superelastic Cu–Al–Be wires at cold temperatures for the seismic protection of bridges

This paper examines the suitability of superelastic copper–aluminum–beryllium (Cu–Al–Be) alloy wires for the seismic protection of bridges in cold regions. Experimental results for the mechanical properties of superelastic Cu–Al–Be alloy wires at a variety of temperatures and loading rates are presented. This research is motivated by the recent use of shape memory alloys for bridge restrainers subject to harsh winter conditions, especially in cold regions. Bridge restrainers made of superelastic Cu–Al–Be wire strands are expected to be used for protecting bridge decks from excessive displacement when subjected to strong earthquakes. Using a temperature chamber, superelastic Cu–Al–Be wires with a diameter of 1.4 mm were tested under uniaxial cyclic loading at various loading rates and cold temperatures. The test results from 23 to −50 °C demonstrate that Cu–Al–Be exhibits superelastic behavior at cold temperatures down to −85 °C. It is also found that with decreasing temperature the transformation plateau stress is reduced while its fatigue life increases under cyclic testing.

Multi-type Sensor Placement for Multi-Scale Response Reconstruction

Although various types of sensors are now available to monitor a structure, measurements are usually obtained in only a few locations numbering less than the total degrees of freedom (DOFs) of the structure. The lack of structural responses of the structure at all its critical areas may hamper the effectiveness of structural monitoring. Therefore, multi-scale response reconstruction at those key structural locations where sensors are not available is essential to fully achieving the structural monitoring objectives. This paper addresses a problem of placing multi-type sensors in a structure with the objective of best reconstruction of structural responses. The types of sensors include accelerometers, displacement and strain measurement sensors, all of which are widely used in civil engineering structures. The number and locations of the three types of sensors are determined aiming to best possibly reconstruct the strain, displacement and acceleration responses, in which the Kalman filter algorithm is employed. By minimizing the overall reconstruction error variance at the locations of interest and maintaining reconstruction errors to a desired target level, the initial set of candidate sensor locations is reduced to a smaller set. The key multi-scale structural responses are reconstructed from the fusion of limited multi-type sensor data information. A simply-supported overhanging steel beam is investigated as a sample case in numerical and experimental study to investigate the effectiveness and accuracy of the presented approach. The good response reconstruction results clearly demonstrate the effectiveness of the proposed optimal placement method for multi-type sensors.

Dynamic behavior of stay cables with passive negative stiffness dampers

This paper systematically investigates the dynamic behavior of stay cables with passive negative stiffness dampers (NSD) installed close to the cable end. A passive NSD is modeled as a combination of a negative stiffness spring and a viscous damper. Through both analytical and numerical approaches, parametric analysis of negative stiffness and viscous damping are conducted to systematically evaluate the vibration control performance of passive NSD on stay cables. Since negative stiffness is an unstable element, the boundary of passive negative stiffness for stay cables to maintain stability is also derived. Results reveal that the asymptotic approach is only applicable to passive dampers with positive or moderate negative stiffness, and loses its accuracy when a passive NSD possesses significant negative stiffness. It has been found that the performance of passive NSD can be much better than those of conventional viscous dampers. The superior control performance of passive NSD in cable vibration mitigation is validated through numerical simulations of a full-scale stay cable.

Damage Detection in Long Suspension Bridges Using Stress Influence Lines

AbstractNumerous long-span cable-supported bridges have been built throughout the world in recent years. These bridges begin to deteriorate once built and continuously accumulate damage during their long service life. The growing popularity of comprehensive structural health monitoring systems (SHMSs) in recently built long-span bridges has started a new trend of integrating SHMS and damage detection technology for real-time condition assessment of these bridges. This paper explores a novel damage detection technique based on stress influence lines (SILs) of bridge components and validates the efficacy of the technique through a case study of the Tsing Ma suspension bridge. A mathematical regularization method is first introduced to identify SILs based on the in situ measurement of train information and train-induced stress responses in local bridge components. Good agreement between the identified and baseline SILs demonstrates the effectiveness of the proposed identification method. Damage indexes based...

Incremental Dynamic Analysis of Highway Bridges with Novel Shape Memory Alloy Isolators

Base isolators are commonly used to protect highway bridges from severe seismic damage. A novel self-centering isolator based on superelastic shape memory alloy (SMA) has been proposed to be installed between the piers and decks of highway bridges. This paper systematically evaluates the seismic performance of SMA isolators via the incremental dynamic analysis (IDA) of a prototype highway bridge with SMA isolators. The multi-span reinforced concrete highway bridge and the corresponding SMA isolators are designed according to an ad hoc displacement-based design (DBD) approach. The seismic analyses are conducted under different seismic intensity levels using the computation program DRAIN2DX. IDA results indicate that the SMA isolators can effectively protect the superstructure of the highway bridge and minimize the post-earthquake residual deformation. The properly designed highway bridges with SMA isolators are subjected to limited damage under frequent and design basis earthquakes.

Structural health monitoring of wind turbine blade using fiber Bragg grating sensors and fiber optic rotary joint

Wind energy utilization as a reliable energy source has become a large industry in the last 20 years. Nowadays, wind turbines can generate megawatts of power and have rotor diameters that are on the order of 100 meters in diameter. One of the key components in a wind turbine is the blade which could be damaged by moisture absorption, fatigue, wind gusts or lighting strikes. The wind turbine blades should be routinely monitored to improve safety, minimize downtime, lower the risk of sudden breakdowns and associated huge maintenance and logistics costs, and provide reliable power generation. In this paper, a real-time wind turbine blade monitoring system using fiber Bragg grating (FBG) sensors with the fiber optic rotary joint (FORJ) is proposed, and applied to monitor the structural responses of a 600 W small scale wind turbine. The feasibility and effectiveness of the FORJ is validated by continuously transmitting the optical signals between the FBG interrogator at the stationary side and the FBG sensors on the rotating part. A comparison study between the measured data from the proposed system and those from an IMote2-based wireless strain measurement system is conducted.