Novel Optical Fiber Sensors for Monitoring Bridge Structural Integrity
Author: Feng, Maria Q | Size: 1.76 MB | Format:PDF | Quality:Unspecified | Publisher: National Technical Information Service | Year: 2009 | pages: 51
This Innovations Deserving Exploratory Analysis (IDEA) project successfully developed a novel sensor system based on innovative integration of fiber optics and Moire phenomena for measuring dynamic response of highway bridges to assess their structural integrity. The 18-month project was conducted in two phases. Work in the initial phase focused on the development of a prototype sensor system. Technical specifications of the proposed fiber optic accelerometer system were established, based on which a conceptual design of the system was developed. In the second phase, the system was extensively tested under a variety of dynamic excitations including earthquake inputs on seismic shaking tables. Furthermore, the sensors were tested at two highway bridge sites in California under traffic excitations, in collaboration with Caltrans. These tests demonstrated superior performance of the new fiber optic accelerometer system over its conventional electrical counterparts. Newport Sensors, Inc., has started to develop the fiber optic accelerometer system into commercial products.
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Determining the Effective System Damping of Highway Bridges
Author: Karim, Kazi Rezaul | Size: 0.98 MB | Format:PDF | Quality:Unspecified | Publisher: Missouri University of Science and Technology, Rolla | Year: 2009 | pages: 187
In this study, a damping-enhanced strengthening (DES) strategy was introduced to retrofit bridge structures for multiple performance objectives. The main objectives of this study are (1) to numerically demonstrate the effectiveness of the anchoring mechanism of a constrained damping layer in the proposed DES system, and (2) to evaluate the performances of a highway bridge retrofitted with a DES retrofit technique of viscoelastic (VE) damping and carbon-fiber-reinforced-polymer (CFRP) strengthening components that are nearly independent under weak earthquakes but strongly coupled under strong earthquakes. The effects of various constrained surface damping layers on the responses of simply-supported beams and cantilevered columns were first investigated analytically. An emphasis was then placed on the development of a finite element modeling technique to simulate the effect of a distributed VE damping layer on the responses of columns. Finally, the DES strategy was applied to retrofit the Old St. Francis River Bridge columns. Both operational and safety performance objectives of the bridge were evaluated with pushover analyses under earthquakes of various magnitudes. An anchored constrained damping layer was found several times more effective than a conventional constrained layer, particularly when covering 20-80% of the column height. To meet the two performance objectives, the Old St. Francis River Bridge columns must be wrapped with three plies of CFRP sheets and one VE layer. The new retrofit strategy is well suited in the context of next-generation performance-based seismic design and retrofit of highway bridges and other structures.
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Determining the Effective System Damping of Highway Bridges
Author: Feng, Maria Q | Size: 1.93 MB | Format:PDF | Quality:Unspecified | Publisher: University of California, Irvine | Year: 2009 | pages: 312
This project investigates four methods for modeling modal damping ratios of short-span and isolated concrete bridges subjected to strong ground motion, which can be used for bridge seismic analysis and design based on the response spectrum method. The four methods are: complex modal analysis (CMA), neglecting off-diagonal elements in damping matrix method (NODE), composite damping rule (CDR), and optimization in time domain and frequency domain (OPT) and applied to a short-span bridge and an isolated bridge. The results show that the NODE method is the most efficient and the conventional assumption of 5 percent modal damping ratio is too conservative for shortspan bridges when energy dissipation is significant at the bridge boundaries. From the analysis of isolated bridge case, the effective system damping is very close to the damping ratio of isolation bearing.
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Seismic Behavior of Circular Reinforced Concrete Bridge Columns under Combined Loading Including Torsion
Author: Shanmugam, Suriya Prakash | Size: 56.97 MB | Format:PDF | Quality:Unspecified | Publisher: University of Nevada | Year: 2009 | pages: 338
Reinforced concrete (RC) columns of skewed and curved bridges with unequal spans and column heights can be subjected to combined loading including axial, flexure, shear, and torsion loads during earthquakes. The combination of axial loads, shear force, and flexural and torsional moments can result in complex failure modes of RC bridge columns. This study carried out experimental and analytical studies to investigate the seismic performance of circular RC columns under combined loading including torsion. The main variables considered here were (i) the ratio of torsion-to-bending moment (T/M), (ii) the ratio of bending moment-to-shear (M/V) or shear span (H/D), and (iii) the level of detailing for high and moderate seismicity (high or low spiral ratio). In particular, the effects of the spiral reinforcement ratio and shear span on strength and ductility of circular RC columns under combined loading were addressed. In addition, the effects of torsional loading on the bending moment-curvature, ductility, and energy dissipation characteristics were also considered. The analytical investigation examined the development of existing models for flexure and pure torsion. Interaction diagrams between bending, shear and torsional loads were established from a semi-empirical approach. A damage-based design approach for circular RC columns under combined loads was proposed by decoupling damage index models for flexure and torsion. Experimental and analytical results showed that the progression of damage was amplified by an increase in torsional moment. An increase in the transverse spiral reinforcement ratio delayed the progression of damage and changed the torsional-dominated behavior to flexural-dominated behavior under combined flexural and torsional moments.
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Seismic Design of Pipe-Pin Connections in Concrete Bridges
Author: Zaghi, Arash E University of Nevada Saiidi, M Saiid University of Nevada, Reno | Size: 56.97 MB | Format:PDF | Quality:Unspecified | Publisher: University of Nevada | Year: 2010 | pages: 583
Telescopic pipe-pin two-way hinges are used in concrete bridges to eliminate moments while transferring shear and axial loads from integral bridge bent caps to reinforced concrete columns. The hinges consist of a steel pipe that is anchored in column with a protruded segment that extends into the bent cap. In the absence of experimental and analytical studies, design of pipe-pin hinges has been based on pure shear capacity of the steel pipe. The primary objective of this research was to investigate the seismic performance of the current detail of pipe-pin hinges and propose necessary modifications, and to develop a reliable design method for pipe-pin hinges that reflects their actual behavior. Comprehensive experimental and analytical studies of pipe-pin connections and their components including a shake table study of a two-column pier mode were conducted.
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Transportations Systems Modeling and Applications in Earthquake Engineering.
Author: Chang, L Elnashai, A S Spencer, B F Song, J Ouyang, Y | Size: 5.73 MB | Format:PDF | Quality:Unspecified | Publisher: University of Illinois, Urbana-Champaign | Year: 2010 | pages: 182
Transportation networks constitute one class of major civil infrastructure systems that is a critical backbone of modern society. Physical damage and functional loss to transportation infrastructure systems not only hinder everyday societal and commercial activities, but also impair post-disaster response and recovery, leading to substantial socio-economic consequences. Therefore, understanding and modeling the disastrous impact on the transportation infrastructures and the corresponding changes of travel patterns under extreme events are vital for stakeholders, emergency managers, and government agencies to mitigate, prepare for, respond to, and recover from the potential impact. This research is aimed at developing a systematic approach for risk modeling and disaster management of transportation systems in the context of earthquake engineering. First, by employing the performance metrics that are suited for immediate post-disaster response, this dissertation explores efficient methodologies to maximize the overall system functionality and the benefit of mitigation investment for transportation infrastructure systems. Furthermore, the regions potentially unreachable after a damaging earthquake are identified promptly by using network reachability algorithms that provide essential information for rapid emergency response decision- making. Lastly, an integrated simulation model of travel demand that accounts for damage of bridge and building structures, release of hazardous materials, and influences of emergency shelters and hospitals, is developed to approximate the 'abnormal' post-earthquake travel patterns and evaluate the functional loss of the transportation systems.
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Seismic Retrofit of Cruciform-Shaped Columns in the Aurora Avenue Bridge Using FRP Wrapping
Author: McLean, David I Washington State University, Pullman Walkenhauer, Brian J Washington State University | Size: 18.31 MB | Format:PDF | Quality:Unspecified | Publisher: Washington State University, Pullman | Year: 2010 | pages: 96
Experimental tests were conducted on seven 1/3-scale column specimens to evaluate the vulnerabilities of existing cruciform-shaped columns and to develop appropriate retrofit measures that address the identified vulnerabilities. The specimens represented both solid and split columns in the Aurora Avenue Bridge in Seattle, Washington. The as-built specimens failed at low ductility levels due to shear distress. Fiber reinforced polymer (FRP) jackets with FRP inserts to anchor the jackets in the column reentrant corners along with steel confinement collars to provide confinement in the hinging regions were used to retrofit the column specimens. The retrofitted specimens developed plastic hinging in the column, with enhanced strength, energy and ductility capacities. Guidelines were presented for designing the various components of the retrofit measures.
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Experimental Evaluation of P-Y Curves Considering Liquefaction Development
Author: Chang, Barbara University of California, San Diego Hutchinson, Tara C University of California, San Diego | Size: 10.08 MB | Format:PDF | Quality:Unspecified | Publisher: University of California, San Diego | Year: 2010 | pages: 98
This report presents details and findings of a test series conducted on a single pile embedded in homogeneous saturated Nevada sand, which was subjected to sequential dynamic shaking and lateral (inertial-equivalent) loading. This report documents the model test design and construction, details regarding the loading protocol, test observations and post test results. A key goal in the test program was to develop a data set capable of rendering insight into the characteristics of ’p-y’ resistance under developing liquefied soil conditions. While evidence in the literature indicates that this resistance is reduced as excess pore pressure increases, the shape and amplitude of how the reduced p-y curve develops during pore pressure build-up are needed for reliable design of pile foundations in areas prone to earthquake-induced soil liquefaction. Analyses of the experimental data show that mobilization of the partially liquefied soil was achieved during lateral loading. Additional data were evaluated including wave test measurements (hammer strikes to model), settlement, and acceleration measurements. Results presented focus importantly on the static p-y curves backcalculated from the bending moment distributions at the achieved excess pore pressures. A rich set of test data was produced from this testing series, which will be useful for model validation and subsequent design efforts.
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A special class of seismically isolated bridges shares a common feature in that both ends of the superstructure are restrained and isolators over the columns of bridge uncouple the superstructure from the ground motions. They are defined as partial isolation bridges. From measured acceleration responses, the effectiveness of full seismic isolation had been confirmed widely. However, the seismic isolation behavior in the partial isolation has not been widely observed. The effectiveness of partial isolation is evaluated in this study. The static design procedures for linear and nonlinear partially isolated bridges are developed. Results from the static analysis of linear and nonlinear partially isolated bridges, compared with conventional and fully isolated bridges, demonstrate that the effectiveness of nonlinear partial isolation is close to full isolation for reducing the yield force and displacement of the columns in some parameter ranges. However, increased displacement demands at the abutments are observed. Nonlinear time history analyses of the different bridge models under earthquake excitations are carried out to investigate the accuracy of the design procedure for nonlinear partial isolation. In addition, an example shows the application of nonlinear partial isolation to a practical bridge.
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Geophysical Testing of Rock and Its Relationships to Physical Properties
Author: Tran, Khiem T | Size: 6.27 MB | Format:PDF | Quality:Unspecified | Publisher: University of Florida, Gainesville | Year: 2011 | pages: 190
Testing techniques were designed to characterize spatial variability in geotechnical engineering physical parameters of rock formations. Standard methods using seismic waves, which are routinely used for shallow subsurface investigation, have limitations in characterizing challenging profiles at depth that include low-velocity layers and embedded cavities. This research focuses on overcoming these limitations by developing two new methods using both sensitive data and a global inversion scheme. The first method inverts combined surface and borehole travel times for a wave velocity profile. The technique is based on an extremely fast method to compute first-arrival times through the velocity models. The capability of this inversion technique is tested with both synthetic and real experimental data sets. The inversion results show that this technique successfully maps 2-D velocity profiles with high variation. The inverted wave velocities from real data appear to be consistent with cone penetration test (CPR), geotechnical borings, and standard penetration test (SPT) results. The second method inverts full waveforms for a wave velocity profile. The strength of this approach is the ability to generate all possible wave types and, thus, to simulate and accurately model complex seismic wave fields that are then compared with observed data to deduce complex subsurface properties. The capability of this inversion technique is also tested with both synthetic and real experimental data sets. The inversion results from synthetic data show the ability of detecting reverse models that are hardly detected by traditional inversion methods that use only the dispersion property of Rayleigh waves. The inversion results from the real data are generally consistent with crosshole, SPT N-value, and material log results. Employed for site characterization of deep foundation design, the techniques can provide credible information for material at the socket and partially detect anomalies near the socket. Lastly, based upon a laboratory testing program conducted on rock cores, it does appear that relationships between geophysical measurements and geotechnical engineering design parameters are credible, though significant scatter does exist in the data. It could be postulated that geophysical measurements should be capable of identifying large zones of poor quality rock, and the results can provide characterization of spatial variability in geotechnical engineering physical parameters useful in the design of deep foundations.
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