Stochastic Response of Lifeline to Spatial Variation of Seismic Waves

The spatial variation of seismic waves has an important effect on the seismic response of structures of extended length. Based on data collected from the SMART-1 array, the spatial variation of seismic waves can be examined. The purpose of this paper is to examine the effect of the spatial variation of seismic waves on a spatially distributed system. With the consideration of the soil amplification ratio between two sites and spatial variation of seismic waves, a ground deformation spectrum is developed from stochastic point of view. This spectrum can provide information useful in predicting maximum ground deformation. The seismic response of a spatially distributed system, such as the effects of variation in soil stiffness on the dynamic response of pipelines are discussed

Densely distributed and real-time scour hole monitoring using piezoelectric rod sensors

This study aims to validate a piezoelectric driven-rod scour monitoring system that can sense changes in scour depth along the entire rod at its instrumented location. The proposed sensor is a polymeric slender rod with a thin strip of polyvinylidene fluoride that runs through its midline. Extraction of the fundamental frequency allows the direct calculation of the exposed length (or scour depth) of the slender rod undergoing fluid flow excitation. First, laboratory validation in dry conditions is presented. Second, hydrodynamic testing of the sensor system in a soil-bed flume is discussed. Each rod was installed using a three-dimensional-printed footing designed for ease of installation and stabilization during testing. The sensors were installed in a layout designed to capture symmetric scour conditions around a scaled pier. In order to analyze the system out of steady-state conditions, water velocity was increased in stages during testing to induce different degrees of scour. As ambient water flow excited the portion of the exposed rods, the embedded piezoelectric element outputted a time-varying voltage signal. Different methods were then employed to extract the fundamental frequency of each rod, and the results were compared. Further testing was also performed to characterize the relationship between frequency outputs and flow velocity, which were previously thought to be independent. In general, the proposed driven-rod scour monitoring system successfully captured changing frequencies under varied flow conditions

System identification & damage assessment of structures using optical tracker array data

Damage assessment of a steel structure involves acquiring and identifying dynamic characteristics of the structure and using these characteristics to evaluate behavior and performance. To ensure the objective assessment three major issues need to be developed: sensing system, system identification and feature extraction. In this study, a unsymmetrical 3-story steel structure (fabricated with one week column in the first floor) subjected to a series of earthquake excitations with increasing level of excitation back to back. In between the earthquake excitation white noise excitation was also applied. Both the traditional sensing system (accelerometer and LVDT) and the optical tracker system were implemented in the structure to collect the vibration-based responses. First, the traditional system identification using global response data is used (subspace identification) to extract system natural frequencies and mode shapes from different set of seismic responses. Besides, to evaluate whether optical tracker array data from local measurement could be used to identify deterioration or damaged-induced changes in damage assessment, principal component analysis was applied to extract the curvature ad the earthquake–induce local stress of the structural member. From which the local stress distribution from different seismic event can be estimated. The relationship among the local displacement profiles, stress distributions and the global dynamic characteristics of the structure are investigated. The results reveal that the local flexibility was an excellent objective for both local and global condition assessment. Finally, discussion on the identified global dynamic characteristics from global measurement in relating to the calculated structural integrity index using optical sensing array data and local element strain on the identification of damage severity are presented

A Probabilistic Risk Analysis for Taipei Seismic Hazards: An Application of HAZ-Taiwan with its Pre-processor and Post-processor

This paper employs probabilistic risk analysis to estimate exceedance probability curves, average annual loss (AAL) and probable maximum loss (PML) for seismic hazards. It utilizes and event-driven loss estimation model, HAZ-Taiwan, and develops its pre-processing and post-processing software modules. First, the pre-processingmodule establishes a set of hazard-consistent scenarios. Then, the HAZ-Taiwan modelextimates hazards, vulnerabilities and economic losses for each scenario. Finally, the aggregate and occurrence exceedance probability curves for losses and theirconfidence intervals are simulated using the Monte Carlo simulation in thepost-processing module. The methodology is then applied to analyze seismic risks in Taipei. It is found that the exceedance probability of an aggregate loss of NT$40.398 billion is 0.001. This amount of loss is approximately 2.78$37.41-43.12 billion. The average annual loss of buildings in Taipei is NT$1.06 billion r approximately 0.07% of the total stock.probabilistic risk analysis, Hazard analysis, vulnerability analysis, exceedance probability curve, HAZ-Taiwan

Graphene sensing meshes for densely distributed strain field monitoring

The objective of this study is to design and validate distributed strain field monitoring using a patterned nanocomposite “sensing mesh” that is coupled with an electrical impedance tomography (EIT) measurement strategy and algorithm. Although EIT has been used in other studies and in conjunction with a piezoresistive thin film for spatial damage detection, different strain components cannot be directly extracted from reconstructed EIT conductivity maps. Therefore, this study seeks to address this issue by patterning piezoresistive graphene-based thin films to form a mesh-like pattern. The high aspect ratio of each nanocomposite grid interconnect acts as a linear distributed strain sensor, capable of resolving strains along the entire length and direction of the element. This study first began with the design, fabrication, and characterization of the strain sensing response of a graphene-based thin film of high strain sensitivity. Second, the strain-sensitive film was spray-coated onto patterned polymer substrates to form the sensing meshes, which were then subjected to load tests. Upon validating distributed strain field monitoring through EIT, its applicability for field implementation and damage characterization was also demonstrated by instrumenting sensing meshes in the column of a seven-story reinforced-concrete building subjected to shaking table earthquake excitations. The large-scale shaking table test results successfully validated distributed damage detection

Time-predictable model application in probabilistic seismic hazard analysis of faults in Taiwan

Given the probability distribution function relating to the recurrence interval and the occurrence time of the previous occurrence of a fault, a time-dependent model of a particular fault for seismic hazard assessment was developed that takes into account the active fault rupture cyclic characteristics during a particular lifetime up to the present time. The Gutenberg and Richter (1944) exponential frequency-magnitude relation uses to describe the earthquake recurrence rate for a regional source. It is a reference for developing a composite procedure modelled the occurrence rate for the large earthquake of a fault when the activity information is shortage. The time-dependent model was used to describe the fault characteristic behavior. The seismic hazards contribution from all sources, including both time-dependent and time-independent models, were then added together to obtain the annual total lifetime hazard curves. The effects of time-dependent and time-independent models of fault [e.g., Brownian passage time (BPT) and Poisson, respectively] in hazard calculations are also discussed. The proposed fault model result shows that the seismic demands of near fault areas are lower than the current hazard estimation where the time-dependent model was used on those faults, particularly, the elapsed time since the last event of the faults (such as the Chelungpu fault) are short

Implementation of a closed-loop structural control system using wireless sensor networks

Wireless sensor networks have rapidly matured in recent years to offer data acquisition capabilities on par with those of traditional tethered data acquisition systems. Entire structural monitoring systems assembled from wireless sensors have proven to be low cost, easy to install, and accurate. However, the functionality of wireless sensors can be further extended to include actuation capabilities. Wireless sensors capable of actuating a structure could serve as building blocks of future generations of structural control systems. In this study, a wireless sensor prototype capable of data acquisition, computational analysis and actuation is proposed for use in a real-time structural control system. The performance of a wireless control system is illustrated using a full-scale structure controlled by a semi-active magnetorheological (MR) damper and a network of wireless sensors. One wireless sensor designated as a controller automates the task of collecting state data, calculating control forces, and issuing commands to the MR damper, all in real time. Additional wireless sensors are installed to measure the acceleration and velocity response of each system degree of freedom. Base motion is applied to the structure to simulate seismic excitations while the wireless control system mitigates inter-storey drift response of the structure. An optimal linear quadratic regulation solution is formulated for embedment within the computational cores of the wireless sensors. Copyright © 2007 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/60230/1/214_ftp.pd

Experimental verification of a wireless sensing and control system for structural control using MR dampers

The performance aspects of a wireless ‘active’ sensor, including the reliability of the wireless communication channel for real-time data delivery and its application to feedback structural control, are explored in this study. First, the control of magnetorheological (MR) dampers using wireless sensors is examined. Second, the application of the MR-damper to actively control a half-scale three-storey steel building excited at its base by shaking table is studied using a wireless control system assembled from wireless active sensors. With an MR damper installed on each floor (three dampers total), structural responses during seismic excitation are measured by the system's wireless active sensors and wirelessly communicated to each other; upon receipt of response data, the wireless sensor interfaced to each MR damper calculates a desired control action using an LQG controller implemented in the wireless sensor's computational core. In this system, the wireless active sensor is responsible for the reception of response data, determination of optimal control forces, and the issuing of command signals to the MR damper. Various control solutions are formulated in this study and embedded in the wireless control system including centralized and decentralized control algorithms. Copyright © 2007 John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/56121/1/682_ftp.pd

Anti-UVC Irradiation and Metal Chelation Properties of 6-Benzoyl-5,7-dihydroxy-4-phenyl-chromen-2-one: An Implications for Anti-Cataract Agent

Coumarin derivative 1, 5,7-dihydroxy-6-(3-methyl-1-butyryl)-4-phenyl-chromen- 2-one, has been reported to possess radical scavenging activity and DNA protection. We have synthesized a series of coumarins with structural modifications at positions C4, C5, C6 and C7 and evaluated them for their anti-UVC properties. Coumarin 7, 6-benzoyl-5,6-dihydroxy-4-phenyl-chromen-2-one, was found to have the most potent activity in protecting porcine γ-crystallin against UVC insults. Results of fluorescence assays indicated that compound 7 was capable of decreasing the loss of intensity while lens crystallins and DNA PUC19 were irradiated with UVC. Presence of compound 7 decreased hydroxyl radical levels determined by probe 1b and the free iron concentrations determined by Ferrozine reagent. The chelation assay showed that compound 7 was chelated to metal via 6-CO and 5-OH on the benzopyrone ring. The observed protective effects of compound 7 towards crystallins from insults of UVC and free radicals may be due to its iron-chelating activity and its peak absorption at 254 nm