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Concrete pavement monitoring with PPP-BOTDA distributed strain and crack sensors
Genda Chen,Yi Bao,Fujian Tang,Yizheng Chen,Weina Meng,Ying Huang 국제구조공학회 2016 Smart Structures and Systems, An International Jou Vol.18 No.3
In this study, the feasibility of using telecommunication single-mode optical fiber (SMF) as a distributed fiber optic strain and crack sensor was evaluated in concrete pavement monitoring. Tensile tests on various sensors indicated that the SMF-28e+ fiber revealed linear elastic behavior to rupture at approximately 26 N load and 2.6% strain. Six full-scale concrete panels were prepared and tested under truck and three-point loads to quantify the performance of sensors with pulse pre-pump Brillouin optical time domain analysis (PPP-BOTDA). The sensors were protected by precast mortar from brutal action during concrete casting. Once air-cured for 2 hours after initial setting, half a mortar cylinder of 12 mm in diameter ensured that the protected sensors remained functional during and after concrete casting. The strains measured from PPP-BOTDA with a sensitivity coefficient of 5.43 10-5 GHz/ were validated locally by commercial fiber Bragg grating (FBG) sensors. Unlike the point FBG sensors, the distributed PPP-BOTDA sensors can be utilized to effectively locate multiple cracks. Depending on their layout, the distributed sensors can provide one- or two-dimensional strain fields in pavement panels. The width of both micro and major cracks can be linearly related to the peak strain directly measured with the distributed fiber optic sensor.
Video Communication Optimization Using Distributed Edge Computing
Kouichi Genda,Mitsuru Abe,Shohei Kamamura 한국통신학회 2020 한국통신학회 APNOMS Vol.2020 No.09
We proposes a backbone network resource optimization algorithm for video communications that use edge computing. In the current video communication architecture, the key component of video communication, called the multi-point control unit (MCU), is deployed in the central cloud server, and its bandwidth consumption in the backbone network becomes enormous as the video resolution and the frequency of use increase. By implementing edge computing, the MCU can be deployed at the entrance node of the backbone network. This allows (i) a local loopback of video traffic at an edge, and (ii) traffic compression (e.g., thumbnailing) between edge nodes. Though these characteristics can reduce the resource consumption of the backbone network, the edge deployment and routing (EDR) problem, classified as NP-hard, should be solved to sufficiently reduce the bandwidth. To solve the NP-hard EDR problem within a feasible period, we propose a divide and merge algorithm based on the linear programming approach. With our algorithm, bandwidth consumption using edge computing is reduced by approximately 30% compared with the current video communication architecture in the world-wide network.
Soil-structure interaction effect on active control of multi-story buildings under earthquake loads
Chen, Genda,Chen, Chaoqiang,Cheng, Franklin Y. Techno-Press 2000 Structural Engineering and Mechanics, An Int'l Jou Vol.10 No.6
A direct output feedback control scheme was recently proposed by the authors for single-story building structures resting on flexible soil body. In this paper, the control scheme is extended to mitigate the seismic responses of multi-story buildings. Soil-structure interaction is taken into account in two parts: input at the soil-structure interface/foundation and control algorithm. The former reflects the effect on ground motions and is monitored in real time with accelerometers at foundation. The latter includes the effect on the dynamic characteristics of structures, which is formulated by modifying the classical linear quadratic regulator based on the fundamental mode shape of the soil-structure system. Numerical result on the study of a $\frac{1}{4}$-scale three-story structure, supported by a viscoelastic half-space of soil mass, have demonstrated that the proposed algorithm is robust and very effective in suppressing the earthquake-induced vibration in building structures even supported on a flexible soil mass. Parametric studies are performed to understand how soil damping and flexibility affect the effectiveness of active tendon control. The selection of weighting matrix and effect of soil property uncertainty are investigated in detail for practical applications.
Chen, Genda,Garrett, Gabriel T.,Chen, Chaoqiang,Cheng, Franklin Y. Techno-Press 2004 Structural Engineering and Mechanics, An Int'l Jou Vol.17 No.3
In this paper, the design, fabrication and characterization of a piezoelectric friction damper are presented. It was sized with the proposed practical procedure to minimize the story drift and floor acceleration of an existing 1/4-scale, three-story frame structure under both near-fault and far-field earthquakes. The design operation friction force in kip was numerically determined to range from 2.2 to 3.3 times the value of the peak ground acceleration in g (gravitational acceleration). Experimental results indicated that the load-displacement loop of the damper is nearly rectangular in shape and independent of the excitation frequency. The coefficient of friction of the damper is approximately 0.85 when the clamping force on the damper is above 400 lbs. It was found that the friction force variation of the damper generated by piezoelectric actuators with 1000 Volts is approximately 90% of the expected value. The properties of the damper are insensitive to its ambient temperature and remain almost the same after being tested for more than 12,000 cycles.
Functionally upgraded passive devices for seismic response reduction
Chen, Genda,Lu, Lyan-Ywan Techno-Press 2008 Smart Structures and Systems, An International Jou Vol.4 No.6
The research field of structural control has evolved from the development of passive devices since 1970s, through the intensive investigation on active systems in 1980s, to the recent studies of semi-active control systems in 1990s. Currently semi-active control is considered most promising in civil engineering applications. However, actual implementation of semi-active devices is still limited due mainly to their system maintenance and associated long-term reliability as a result of power requirement. In this paper, the concept of functionally upgraded passive devices is introduced to streamline some of the state-of-the-art researches and guide the development of new passive devices that can mimic the function of their corresponding semi-active control devices for various applications. The general characteristics of this special group of passive devices are discussed and representative examples are summarized. Their superior performances are illustrated with cyclic and shake table tests of two example devices: mass-variable tuned liquid damper and friction-pendulum bearing with a variable sliding surface curvature.
Chen, Genda,McDaniel, Ryan,Sun, Shishuang,Pommerenke, David,Drewniak, James Techno-Press 2005 Smart Structures and Systems, An International Jou Vol.1 No.2
A new design of distributed crack sensors based on the topological change of transmission line cables is presented for the condition assessment of reinforced concrete (RC) structures during and immediately after an earthquake event. This study is primarily focused on the performance of cable sensors under dynamic loading, particularly a feature that allows for some "memory" of the crack history of an RC member. This feature enables the post-earthquake condition assessment of structural members such as RC columns, in which the earthquake-induced cracks are closed immediately after an earthquake event due to gravity loads, and are visually undetectable. Factors affecting the onset of the feature were investigated experimentally with small-scale RC beams under cyclic loading. Test results indicated that both crack width and the number of loading cycles were instrumental in the onset of the memory feature of cable sensors. Practical issues related to dynamic acquisition with the sensors are discussed. The sensors were proven to be fatigue resistant from shake table tests of RC columns. The sensors continued to show useful performance after the columns can no longer support additional loads.