Tat S. Fu

Monitoring civil structures with a wireless sensor network

Structural health monitoring (SHM) is an active area of research devoted to systems that can autonomously and proactively assess the structural integrity of bridges, buildings, and aerospace vehicles. Recent technological advances promise the eventual ability to cover a large civil structure with low-cost wireless sensors that can continuously monitor a buildings structural health, but researchers face several obstacles to reaching this goal, including high data-rate, data-fidelity, and time-synchronization requirements. This article describes two systems the authors recently deployed in real-world structures.

Structural damage detection and localization using NETSHM

Structural health monitoring (SHM) is an important application area for wireless sensor networks. SHM techniques attempt to autonomously detect and localize damage in large civil structures. Structural engineers often implement and test SHM algorithms in a higher level language such as C/Matlab. In this paper, we describe the design and evaluation of NETSHM, a sensor network system that allows structural engineers to program SHM applications in Mat-lab or C at a high level of abstraction. In particular, structural engineers do not have to understand the intricacies of wireless networking, or the details of sensor data acquisition. We have implemented a damage detection technique and a damage localization technique on a complete NETSHM prototype. Our experiments on small and medium-scale structures show that NETSHM is able to detect and localized damage perfectly with very few false-positives and no false negatives, and that it is robust even in realistic wireless environments

Distributed Mass Damper System for Integrating Structural and Environmental Controls in Buildings

The writers recently proposed a new type of mass damper system to integrate structural and environmental control systems for buildings. External shading fins are used as mass dampers such that they can (1) control building energy consumption by adjusting the fins and, thus, the amount of sunlight entering the building; and (2) control structural movements by dissipating energy with the dampers during strong motions. Because shading fins are placed along the height of the building, the mass dampers are distributed along the building height instead of concentrated in one or a few locations like traditional tuned mass dampers (TMDs). The distributed mass damper (DMD) system is formulated and simulated for earthquake motions. Optimization is performed on damper parameters (i.e., masses, stiffness, and damping coefficients) of the passive DMD system to minimize structural responses. A near-optimal DMD system outperforms a single TMD system. The movable shading fins are also briefly discussed; they show a subst...

Active Control for a Distributed Mass Damper System

AbstractRecent developments of a distributed mass damper (DMD) system integrate structural and environmental control systems for buildings. This system simultaneously improves building safety and sustainability by using external shading fins as mass dampers, controlling the amount of sunlight coming into the building for energy efficiency, and reducing structural movements during strong motions. Unlike traditional mass dampers, which are usually placed at the tops of structures, the shading fin mass dampers (SFMDs) are distributed throughout structures because fins are placed along the entire heights of buildings. A recent paper by the authors shows that the passive DMD system is as effective in response mitigation as a conventional tuned mass damper (TMD). In this paper, active control strategies for mass damper control are analyzed and simulated to show further response reductions. Nonpassive controls are of interest for the SFMD system because actuators are already needed to control the positions of th...

Control strategies for a distributed mass damper system

Recent developments of a distributed mass damper (DMD) system integrate structural and environmental control systems for buildings. External shading fins are used as mass dampers such that they can (i) control building energy consumption by adjusting the fins and, thus, the amount of sunlight coming into the building and (ii) control structural movements by dissipating energy with the dampers during strong motions due to wind or earthquakes. Shading fins are placed along the height of the building, distributing the mass along the building instead of being concentrated in a few locations like traditional tuned mass dampers (TMDs). This eliminates any large damper mass on the top of the building that can be a structural and architectural challenge to design. The DMD system is formulated, simulated and analyzed with passive, active and semiactive control strategies. The passive DMD is shown to be as effective in response mitigation as a conventional TMD; active and semiactive strategies give further improvements. The building energy consumption using the movable shading fins is also briefly presented in this paper.

Integrating Double-Skin Façades and Mass Dampers for Structural Safety and Energy Efficiency

AbstractA new integrated control system was recently proposed to combine double-skin facades and mass dampers in buildings to improve both building safety and energy efficiency. Double-skin facade systems protect and insulate buildings with two heavy glass layers between which air is allowed to flow for ventilation. By enabling movements in the outer facade skin, the authors proposed to (1) use them as mass dampers to reduce structural vibration and damage during earthquakes and wind storms and (2) adjust the gap size between the outer and inner skins to control the ventilation rate and improve energy efficiency. The synergy of the proposed system can lead to buildings that are structurally safe, energy efficient, and ultimately sustainable. In this paper, two structural control strategies—passive and active—are considered. The facade damper system was formulated first, and stochastic and historical earthquake responses were simulated. Then, the damper parameters (stiffness and damping coefficients) for p...

An Indoor Probabilistic Localization Method Using Prior Information

In this paper, we propose a new probabilistic method for determining the position of an unknown node in an indoor environment. Our analysis shows that using a small subset of sensors reduces the error in comparison to larger sets. The best subset of sensors is determined by matching the power received by all of the sensors and comparing it to prior measurements. We present experimental measurements made that show the efficacy of this approach and compare this method to previously published techniques. Our analysis shows that the new method, Prior Measurement Comparison (PMC), yields greater estimation accuracy resulting in lower error.

Using prior measurements to improve probabilistic-based indoor localization methods

In this paper, we enhance a probabilistic method for determining the position of an unknown node in an indoor environment. Previous work shows that using a small subset of sensors with a probabilistic localization technique reduces the error in comparison to a large set of sensors. Because probability based models rely on a prior distribution for the unknown node, we propose that reference measurements performed at the time of deployment are used to improve the distribution model. We show this new method reduces the estimated location error and increases the likelihood of selecting the correct room.

Double skin façades as mass dampers

An integrative system is proposed by investigating the utilization of double skin façades as mass dampers in buildings to improve both building safety and energy efficiency. Façade systems protect buildings and also significantly affect building energy usage. By enabling movements in double skin facades, the author proposed to use them as mass dampers that reduce structural vibration and damage during earthquakes and wind storms. The synergy of the proposed system can lead to buildings that are structurally safe, energy efficient, and ultimately sustainable. The preliminary results related to the structural control aspects of the proposed system are presented in this paper. The façade damper system is first formulated and earthquake responses are simulated. Then, the damper parameters (stiffness and damping coefficients) are optimized using a pattern search algorithm to minimize structural responses to stochastic and historical earthquake excitations. Five configurations with one-, two-, four-, five- and ten-dampers are optimized and analyzed. The optimized configurations can significantly reduce vibrations.

Analyzing Prerepair and Postrepair Vibration Data from the Sarah Mildred Long Bridge after Ship Collision

The Sarah Mildred Long Bridge, an 854-m (2,804-ft) double-deck truss bridge in Portsmouth, New Hampshire, was struck by a 144-m (473-ft) cargo ship on April 1, 2013. After days of visual inspection and assessment, it was found that the main damage, significant bending of a vertical and a diagonal truss member, required replacement of the impacted members. According to the New Hampshire Department of Transportation, the repair cost