Author: Dehler, William | Size: 15.79 MB | Format:PDF | Quality:Original preprint | Publisher: University of Minnesota, Twin Cities | Year: 2007 | pages: 116
The objective of this work was to show that cone penetration testing (CPT) can be used for pavement applications, specifically estimating resilient modulus and organic content. A series of undisturbed samples were obtained from borings directly adjacent to CPT soundings. These samples underwent both laboratory resilient modulus and bender element testing. A statistical analysis was then performed on these results in conjunction with the data obtained from the CPT soundings to determine the feasibility of developing correlations between field and laboratory measurements of moduli. A relationship was developed between Young’s modulus determined by bender element testing and that determined by resilient modulus testing. However, the correlation did not apply to the field-based seismic measurements of stiffness from the CPT soundings. The analysis presented with respect to the identification of highly organic soils via CPT testing shows that at this point the model identified using the discriminate analysis method is not currently sufficient to use in practice. The 10% increase in correctly classified soils, however, holds promise for the future, and the introduction of additional independent parameters within a significantly larger data set can be easily analyzed using the methods and tools presented here.
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Seismic Response of Telescopic Pipe Pin Connections
Author: Doyle, Kelly A | Size: 8.19 MB | Format:PDF | Quality:Original preprint | Publisher: University of Nevada | Year: 2008 | pages: 182
Two-way hinges are often used in reinforced concrete bridge columns to prevent excessive flexural stresses from entering the connection to the superstructure or the footing. A study was undertaken for Caltrans to understand the behavior of pipe pin connections to help develop a simple and reliable design method. Two 0.3 scale specimens were constructed and tested under cyclic loading to determine if the models behave in pure shear and to study the effect of rotation on the connection behavior and strength. Analytical studies of a simple method gave the foundation for the development of a design method. A sensitivity analysis of the equations revealed that using the ultimate stress of the pipe (rather than the yield stress) in calculations leads to a close estimate of the actual ultimate connection capacity. If yielding is to be avoided in the pin, however, the pipe yield stress should be used in the simple method.
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Seismic Behavior of Reinforced Concrete Bridge Columns at Sub-Freezing Temperatures
Author: Montejo, Luis A | Size: 12.00 MB | Format:PDF | Quality:Original preprint | Publisher: North Carolina State University, Raleigh | Year: 2008 | pages: 397
The final goal of this research was to develop recommendations for the future seismic design or assessment of reinforced concrete (RC) bridge bent structures in cold seismic regions. Ten large scale circular columns were constructed and tested under cyclic reversal of loads inside an environmental chamber in the North Carolina State University Constructed Facilities Laboratory (CFL). The columns were tested at freezing (-40°C, -40°F) and ambient (23°C, 74°F) temperatures. In order to characterize every aspect of the seismic response at low temperatures, the columns' design was governed by a desired behavior: shear dominated columns, flexural dominated columns and reinforced concrete filled steel tube columns. Results obtained show that RC members exposed to the combined effects of sub-freezing temperatures and cyclic loads undergo a gradual increase in strength and stiffness coupled with a reduction in displacement capacity. The experimental results were used to calibrate a fiber-based model and a series of static and inelastic analyses were performed to typical Alaska Department of Transportation and Public Facilities bent configurations. Based on the results obtained from the experimental tests, the non-linear simulations and a moment-curvature parametric analysis, a simple methodology was developed to account for the low temperature flexural overstrength and reduction in ductility capacity.
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Dynamic Response of Bridges to Near-Fault Forward Directivity Ground Motions
Author: Rodriguez-Marek, Adrian | Size: 2.82 MB | Format:PDF | Quality:Original preprint | Publisher: Washington State Transportation Center | Year: 2008 | pages: 84
Research over the last decade has shown that pulse-type earthquake ground motions that result from forward-directivity (FD) effects can result in significant damage to structures. Three typical post-1990 Washington State Department of Transportation (WSDOT) monolithic concrete bridges were chosen to investigate their nonlinear response to FD ground motions (FDGMs) and non-FDGMs. Results showed that significant seismic damage may occur if the structural response is in tune with the period of the velocity pulse of the FDGM. This velocity pulse is a result of fault propagation effects in the near-fault, and occurs when the direction of slip and rupture propagation coincide. The period of the velocity pulse is proportional to the magnitude of the earthquake. The severity of the demand is controlled by the ratio of the pulse period to bridge fundamental periods. As a consequence of this, damage in a bridge with moderate periods (T=0.1s to 1.0s) may be more significant in smaller magnitude earthquakes where the pulse period is closer to the fundamental period of the structure. This was the case for both the MDOF and SDOF analyses of all three bridges in this research. The results showed also that the occurrence of high PGA and/or PGV is only one of several conditions that can cause high demand on the bridges. Of the three bridges considered, all typical concrete overpasses ranging from 50 m to 91 m in length, all generally survived the earthquake motions with only minor damage to their columns. However, column flexural failure was predicted for one model when subjected to two of the forward directivity ground motions. SDOF bridge models for preliminary analyses were found to yield slightly unconservative base shears and displacements compared to that of the full bridge models under non-FDGM. For FDGM, the results of a simple SDOF bridge model ranged from very conservative to slightly unconservative. Therefore, nonlinear SDOF analyses are specifically not recommended in the case of FDGM since the results were not consistent. A more detailed MDOF model should be used to assess bridge seismic performance so that SSI and the interaction of the longitudinal and transverse responses of the bridges can be included, particularly if a performance based design or assessment of the bridge is required.
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Development of Guidelines for Incorporation of Vertical Ground Motion Effects in Seismic Design of Highway Bridges
Author: Kunnath, Sashi K | Size: 2.72 MB | Format:PDF | Quality:Original preprint | Publisher: California Department of Transportation | Year: 2008 | pages: 108
This report describes a study which was conducted in order to assess the current provisions in the California Department of Transportation's Standard Design Criteria 2006 (SDC-2006) for incorporating vertical effects of ground motions in seismic evaluation and design of ordinary highway bridges. A series of simulations was carried out on a range of typical bridge configurations for the purpose of isolating the effects of vertical motions. Results from the simulations reveal that vertical ground motions can have a significant effect on the axial force demand in columns, moment demands at the face of the bent cap, and moment demands at the middle of the span.
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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: 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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