Parametric study on performance of bridge retrofitted by unseating prevention devices

Over the past decade, seismically induced damage to bridges has been widely reported following major earthquakes such as the 1994 Northridge, 1995 Kobe and 1999 Chi-Chi events. Since these earthquakes, restrainers and stoppers have been installed on bridges to prevent unseating and excessive displacements, respectively. Alternatively, column jacketing has also been proven to be effective. However, the enhanced shear strength may result in extra retrofitting works on the footing. For bridges damaged in the Chi-Chi earthquake, investigations revealed that most bridge columns experienced none-to-minor damage in the longitudinal direction. The reason for this unexpected performance was the construction practice of using a rubber bearing, which is an unbolted design that may slide under large lateral forces. In this paper, parametric studies on simply-supported bridges retrofitted by a restrainer or concrete shear key along the longitudinal and transverse axes were carried out. The research focuses on finding suitable combinations of the design force and gap spacing so the restrainer and concrete shear key can be used as an unseating prevention device, with respect to the allowable column damage in terms of displacement ductility under near-fault type earthquakes. A two-lane PCI-girder bridge was selected as the benchmark model. In the longitudinal direction, a total of nine combinations considering yielding strength and gap spacing for the restrainer were analyzed; while parameters for the concrete shear key were divided into three shear force levels and three gap spacings. In the transverse direction, a similar approach was adapted, except smaller gap spacing was used. For each of the above mentioned earthquakes, seven input ground motions were selected and their PGAs were adjusted to 0.36g and 0.45g as the Design earthquake and Maximum Considerable Earthquake, respectively. Based on the results of nonlinear time history analyses, proper parameters to design the restrainers and concrete shear keys are obtained. Responses obtained from numerical simulations under the Chi-Chi earthquake leaded to new implications to design those devices. Restrainer should not exceed its breaking strain and sufficient unseating length will be needed always. Concrete Shear key was determined by considering both displacement demand of the superstructure and displacement ductility of the column at the same time. Further study is needed to provide optimal design parameters for use in performance based bridge design.

EXPERT SYSTEM FOR COMPREHENSIVE ASSESSMENT TOBRIDGE SERVICE PROPERTY USING FUZZY THEORY

In this paper, based on consultation to tens of bridge exberts and a vast amount of investigation and study, experts knowledge on bridge assessment has been sorted out. A new concept Damage Value (DV) is put forward to measure bridge damage, and Fuzzy theory is used to create comprehensive Fuzzy system to assess bridge service property. The setup of an experts system for bridge assessment is tried as well. This system is programmed in Turbo C 2.0 and has been run successfully at IBM-PC (AT/XT).

Organic sensitizers with different thiophene units as conjugated bridges:molecular engineering and photovoltaics

Three structural modifications with incorporation of alkyl,alkoxy and vinyl bond into the skeleton of thiophene bridge in D-π-A featured organic sensitizers are specifically developed for insight into their influences on photophysical,electrochemical as well as photovoltaic properties in nanocrystalline TiO_2-based dye sensitized solar cells(DSSCs).The insertion of vinyl bond into the conjugation bridge leads to the molecular planar configuration,and the conjugation bridge of 3,4-ethylenedioxythiophene(EDOT)is prone to positively shift its highest occupied molecular orbital(HOMO).The electrochemical impedance spectroscopy(EIS)results indicate that the grafted long alkyl chain onto thiophene is favorable to suppress dye aggregation when adsorbed onto TiO_2film and modification on interface of TiO_2/dye/electrolyte,resulting in a relatively high open-circuit voltage(V_(oc)).Under optimized conditions,dye LS-4 bearing hexylthiophene as the conjugation bridge shows a relatively high overall conversion efficiency of5.45%,with a photocurrent of 11.61 mA cm^(-2),V_(oc)of 744 mV.

Novel organic dye sensitizers containing fluorenyl and biphenyl moieties for solar cells

Three novel triarylamine dyes（AFL1-AFL3） containing fluorenyl and the biphenyl moieties have been designed and synthesized for application in dye-sensitized solar cells.The light-harvesting capabilities and photovoltaic performance of these dyes were investigated systematically through comparison of different π-bridges.The dye with a furan linker exhibited a higher open-circuit voltage（VOC） and monochromatic incident photon-to-current conversion efficiency（IPCE） compared to thiophene and benzene linker.Thus,AFL3 containing a furan linker exhibited the maximum overall conversion efficiency of 5.81%（VOC = 760 mV,JSC = 11.36 mA cm^-2 and ff=0.68） under standard global AM 1.5 G solar condition.