A Damage Identification Procedure for Bridge Structures with Energy Dissipation Devices
Author: Bozorgzadeh, Azadeh | Size: 10.15 MB | Format:PDF | Quality:Original preprint | Publisher: University of California, San Diego | Year: 2008 | pages: 211
Bridge abutments are designed to provide resistance to deformation and earthquake-induced inertial forces from the bridge superstructure. The passive earth pressure of the abutments' structure backfill is an integral part of the force-resistance mechanism of bridge abutments in the longitudinal direction. Current design practices by the California Department of Transportation (Caltrans) do not take into account the structure backfill properties of bridge abutments. This report describes an experimental and analytical research program that investigated the role that soil properties, abutment geometry, and structure backfill have on the ultimate capacity and stiffness of bridge abutments. Specifically, it examined the effects of structure backfill properties, area of structure backfill, backfill height, and vertical wall movement. In addition, the report evaluates the current design procedures by Caltrans, and also proposes an improved soil spring model for predicting the stiffness and capacity of bridge abutments in longitudinal direction for cases where post-peak softening behavior is important in system modeling efforts.
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A Damage Identification Procedure for Bridge Structures with Energy Dissipation Devices
Author: Benzoni, Gianmario University of California, San Diego Amaddeo, Carmen DiCesare, Antonio Palermo, Gene | Size: 6.38 MB | Format:PDF | Quality:Original preprint | Publisher: University of California, San Diego | Year: 2008 | pages: 143
This report describes research which focused on developing an effective health monitoring approach for applications to bridges that are protected with the most common seismic response modification devices (SRMD). Emphasis is on those devices tested extensively in the full-scale range of dimension, displacement, velocity and applied load. Devices considered in the project included viscous dampers or energy dissipators. The research included the following tasks: 1) parametric analysis of the effects of damper characteristics; 2) laboratory test on a full scale viscous damper to artificially introduce increasing levels of response degradation; 3) selection of an existing methodology for the assessing existing bridge conditions; 4) validation of the modified methodology using finite element models of an existing isolated bridge; and, 5) validation of the overall procedure with records from a bridge with energy dissipators in new and damaged conditions.
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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. A re-centering ratio developed by Hieber (2005), which took into account the external axial load, initial prestress force, and the mild steel ratio, was used to predict these re-centering capabilities. 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 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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Author: Pang, Jason B K | Size: 7.77 MB | Format:PDF | Quality:Original preprint | Publisher: Washington State Transportation Center | Year: 2008 | pages: 255
The use of precast components in bridge bents can accelerate bridge construction, but their use in seismic systems is challenging. Such systems must have connections that are both easy to assemble on site, and have sufficient strength and ductility during earthquakes. A precast bridge bent beam-column connection that is suitable for rapid construction in seismic regions has been developed and tested. The connection features a small number of large (#18) vertical column bars grouted into large corrugated ducts embedded in the cap-beam. This combination provides speed and simplicity of erection, as well as generous construction tolerances. Lateral-load tests on the system showed that it has strength and ductility similar to those of a comparable cast-in-place connection, and that deliberate debonding of a short length of the bars has little effect on its seismic performance.
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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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