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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This report documents the findings and lessons learned from the February 27, 2010, M8.8 offshore Maule earthquake in Chile. Fewer than 0.15 percent of the bridges in Chile’s inventory, most built after 1995, collapsed or suffered damage that rendered them useless. Many spans of precast prestressed discontinuous girder bridges with continuous decks fell off their supports, probably due to significant in-plane rotation of the superstructure as a result of severe shaking. Lateral steel stoppers used to provide both vertical and lateral restraints on girders were largely unsuccessful due to their inadequate connection detail to cap beams and abutments. Reinforced concrete shear keys performed well as fuses limiting the transfer of excessive seismic loads from the superstructure to the foundation of bridges even though they could be optimized for maximum energy dissipation as part of the lateral restraint system at the bottom flange of girders. Vertical seismic bars were widely used to restrain the vertical motion of decks, and they also performed well. Bridge substructures (foundation, column, and cap beam) generally behaved satisfactorily except for two columns that suffered shear failure due to ground settlement and lateral spreading. All mechanically stabilized earth walls exceeded the expected performance.
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Effects of ground motion spatial variations and random site conditions on seismic responses of bridge structures
Author: Bi, K | Size: 1.92 MB | Format:PDF | Quality:Unspecified | Publisher: The University of Western Australia | Year: 2011 | pages: 204
The research carried out in this thesis concentrates on the modelling of spatial variation of seismic ground motions, and its effect on bridge structural responses. This effort brings together various aspects regarding the modelling of seismic ground motion spatial variations caused by incoherence effect, wave passage effect and local site effect, bridge structure modelling with soil-structure interaction (SSI) effect, and dynamic response modelling of pounding between different components of adjacent bridge structures. In the first part of this thesis (Chapters 2-4), a stochastic method is adopted and further developed to study the seismic responses of bridge structures located on a canyon site. In this approach, the spatially varying ground motions are modelled in two steps. Firstly, the base rock motions are assumed to have the same intensity and are modelled with a filtered Tajimi- Kanai power spectral density function and an empirical spatial ground motion coherency loss function. Then, power spectral density function of ground motion on surface of the canyon site is derived by considering the site amplification effect based on the one-dimensional seismic wave propagation theory. The influence of SSI is also examined (in Chapter 4) by modelling the soil surrounding the pile foundation as frequency-dependent springs and dashpots in the horizontal and rotational directions. A method is proposed to simulate the spatially varying earthquake ground motion time histories at a canyon site with different soil conditions. This method takes into consideration the local site effect on ground motion amplification and spatial variations.
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Seismic Behavior and Design of Segmental Precast Post-Tensioned Concrete Piers
Author: Dawood, Haitham ElGawady, Mohamed Washington State University, Pullman Cofer, William Washington State University, Pullman | Size: 7.37 MB | Format:PDF | Quality:Unspecified | Publisher: Transportation Northwest Regional Center | Year: 2011 | pages: 142
Segmental precast column construction is an economic environmental friendly solution to accelerate bridge construction in the United States. Also, concrete-filled fiber reinforced polymer tubes (CFFT) represents a potential economic solution for durability issues in the bridge industry. Combining the segmental precast and CFFT will result in a rapid durable construction system. The proposed research will build on recent work by the principal investigator (PI), where he experimentally investigated the seismic behavior of tens single-column and two-column bents constructed using precast post-tensioned CFFT. The columns were constructed by stacking precast CFFT segments one on top of the other and then post-tensioned using unbonded tendons. Two specimens had external energy dissipation devices and another two specimens had neoprene in the joints between the CFFT segments. The neoprene significantly reduced the seismic displacement demand. The columns re-centered upon the conclusion of the test resulting in minimal residual displacement, which represents, in the case of a real strong earthquake, a huge advantage since the post-earthquake repair measures will be minimal. 3-D finite element models were developed by the PI to predict the performance of the single-column under monotonic lateral loads. The main objective of this proposal is to improve and expand the capabilities of these finite element models to produce design recommendations. In particular, the models will be expanded to include dynamic loading, two-column bents, and the neoprene in the joints. Including dynamic loading in the model is essential to quantify the energy dissipation due to rocking of the columns segments. The output of this research will be recommendations on the optimum construction characteristics of the system including the segment height/column diameter ratio, neoprene thickness and hardness, external energy dissipater requirements, and post-tensioning force level. The proposed research will develop a durable environmental friendly rapid construction bridge system, which has low life-cycle costs, construction waste, noise, traffic disruption, and initial construction cost. In addition, the developed system will has high work zone safety, efficient use of construction material, a short construction time, and improved constructability. The proposed construction system will not have a leakage of wet concrete into waterways leading to pollution of water and harm migrating fish. Finally, when the proposed construction system is fully developed and implemented in construction, it will reduce the expense of bridge replacement, repair, and continuous operation interruption after earthquakes.
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