Visual Inspection & Capacity Assessment of Earthquake Damaged Reinforced Concrete Bridge Elements
Author: Veletzos, Marc J | Size: 34.19 MB | Format:PDF | Quality:Original preprint | Publisher: University of California, San Diego | Year: 2008 | pages: 350
Caltrans geotechnical engineers initiated a research project aimed at broadening their perspective from simple geotechnical site response analyses to a more comprehensive seismological approach. The project was centered on a series of seminars on seismological theory and analyses using a pair of stochastic numerical ground motion models that allowed uniform treatment of uncertainties in recognized earthquake source, path, and site effects. The project was not intended to produce a “report,” but seminar notes and a portion of the analyses have been scanned and compiled for archival and educational value. Seven sets of seminar notes and two application examples are presented. Two seminars provide an overview of site specific specification of ground motion from a seismological perspective. Another seminar provides background on seismological instrumentation and processing of strong-motion recordings. A pair of seminars addresses empirical attenuation models and outlines the variety of numerical ground motion modeling approaches. The final pair of seminars systematically explore source, path and site effects on ground motion and various strategies employed to capture these effects for purposes of prediction. The two application examples use the stochastic model to explore the impacts and uncertainties of geotechnical site effects within the context of the broader seismological problem.
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Evaluation and Implementation of an Improved Methodology for Earthquake Ground Response Analysis: Uniform Treatment of Uncertainties in Source, Path and Site Effects
Author: California Department of Transportation | Size: 18.53 MB | Format:PDF | Quality:Original preprint | Publisher: California Department of Transportation | Year: 2008 | pages: 552
Caltrans geotechnical engineers initiated a research project aimed at broadening their perspective from simple geotechnical site response analyses to a more comprehensive seismological approach. The project was centered on a series of seminars on seismological theory and analyses using a pair of stochastic numerical ground motion models that allowed uniform treatment of uncertainties in recognized earthquake source, path, and site effects. The project was not intended to produce a “report,” but seminar notes and a portion of the analyses have been scanned and compiled for archival and educational value. Seven sets of seminar notes and two application examples are presented. Two seminars provide an overview of site specific specification of ground motion from a seismological perspective. Another seminar provides background on seismological instrumentation and processing of strong-motion recordings. A pair of seminars addresses empirical attenuation models and outlines the variety of numerical ground motion modeling approaches. The final pair of seminars systematically explore source, path and site effects on ground motion and various strategies employed to capture these effects for purposes of prediction. The two application examples use the stochastic model to explore the impacts and uncertainties of geotechnical site effects within the context of the broader seismological problem.
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A pre-cast concrete bridge bent designed to re-center after an earthquake
Author: Cohagen, L Pang, J B Eberhard, M O Stanton, J F | Size: 2.97 MB | Format:PDF | Quality:Original preprint | Publisher: Washington State Department of Transportation | Year: 2008 | pages: 105
In this study the post-earthquake residual displacements of reinforced concrete bridge bents were investigated. The system had mild steel that was intended to dissipate energy and an unbonded, post-tensioned tendon that was supposed to remain elastic and re-center the column. The columns tested had different mild steel to prestress ratios, which affected their re-centering ability. Two 40 percent scale specimens with large-bar connection details and a central unbonded, post-tensioned tendon were tested by using pseudo-static loading. The large-bar system is a rapidly constructible precast system for use in seismic regions. The test columns had re-centering ratios of 1.6 and 1.2. A column with the same connection details but no prestress and a re-centering ratio of 0.9 was used as a reference. The displacement at zero force in the test was used as a proxy for the residual displacement after an earthquake. The tests showed that columns with a larger re-centering ratio did experience lower residual drifts, although this distinction only became clear for drift ratios that exceeded 2 percent. The tests also showed that increases in post-tensioning force led to slight increases in damage at high drift ratios.
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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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