SEISMIC PERFORMANCE AND RETROFIT OF MULTI-COLUMN BRIDGE BENTS
Author: McLean, D I Kuebler, S E Mealy, T E | Size: 2.23 MB | Format:PDF | Quality:Original preprint | Publisher: Washington State University, Pullman | Year: 1998 | pages: 58
This study investigated retrofitting measures for improving the seismic performance of existing multi-column bridge bents. Experimental tests were conducted on 1/4.5-scale footing and column assemblages which incorporated details that were selected to represent deficiencies present in older bridges. Various retrofit measures for the bents were evaluated. The specimens were subjected to increasing levels of cycled inelastic lateral displacements under constant axial load. Specimen performance was evaluated on the basis of load capacity, displacement ductility, strength degradation and hysteretic behavior. Tests on the as-built specimens resulted in severe cracking in the footings due to insufficient joint shear strength in the column/footing connections. However, due to structural redundancy, the bents continued to resist lateral loads until eventual bent failure occurred as a result of flexural hinge degradation in the columns. Measures developed previously for retrofitting single-column bent bridges were found to be effective in improving the performance of the footings and columns. When all substructure elements were retrofitted, a ductile bent response was obtained. Retrofitting only some of the substructure elements resulted in incremental improvements in performance according to the number of elements retrofitted. While extensive damage occurred in the unretrofitted elements, the damaged regions continued to transfer forces during testing, enabling a stable bent response until failure occurred within one or more of the retrofitted elements. The addition of a stiff link beam just above the footings was found to be effective in preventing damage in the footings during testing, and a reasonably ductile bent response was achieved. Because the link beam retrofit may not require retrofitting of the footings, this strategy may be a very cost-effective approach for retrofitting multi-column bents.
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FIELD AND LABORATORY PERFORMANCE EVALUATION OF SPREAD FOOTINGS
Author: Sargand, S M Hazen, G A | Size: 9.51 MB | Format:PDF | Quality:Original preprint | Publisher: Ohio University, Athens | Year: 1999 | pages: 358
The performance of five highway bridge structures, located in Ohio and supported by spread footings on cohesionless soils or cohesive soils, was monitored in the field throughout construction and under service conditions. The performance of these structures was also examined through centrifuge modeling in the laboratory. Factors used in evaluating these bridges were overall settlement, tilting of abutment walls/pier columns, and pressure distribution under the footings. Field and experimental measurements were then compared against estimates made by selected geotechnical methods. None of the spread footings in these five bridge structures experienced an average settlement of more than 2 in. (5 cm) prior to service load application. Contact pressure monitored at the footing/bearing soil interface in the field remained less than 40 psi (276 kPa) and was generally close to the theoretical estimate. Poorer agreement resulted between the measured and predicted abutment wall tilting. None of the six geotechnical methods for predicting settlement of footings on cohesionless soils was accurate in all cases. The method proposed by Hough appeared to be the best. Standard methods used to estimate immediate and time dependent consolidation settlements were reasonably accurate when compared to field data. Centrifuge testing techniques provided settlement results superior to those predicted by any of the six geotechnical methods. One limitation of centrifuge testing, however, is the simulation of complex subsurface conditions in the laboratory.
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PERFORMANCE OF GEOSYNTHETIC-REINFORCED WALLS SUPPORTING THE FOUNDERS/MEADOWS BRIDGE AND APPROACHING ROADWAY STRUCTURES
Author: Abu-Hejleh, N Zornberg, J G Wang, T McMullen, M Outcalt, W | Size: 5.78 MB | Format:PDF | Quality:Original preprint | Publisher: Colorado Department of Transportation | Year: 2001 | pages: 162
The Founders/Meadows structure is the first major bridge in the United States built on footings supported directly by geosynthetic-reinforced soil (GRS) walls, eliminating the traditional use of deep foundations altogether. The performance of the front GRS walls, which support the bridge structure and embankment behind the abutment wall, was investigated by collecting data for the movements of the wall facing, settlement of the bridge footing, distributions of the vertical earth pressures and geogrid tensile strains inside the front GRS walls, and lateral earth pressures against the wall facing. Monitoring data was collected during six construction stages and while the structure was in service. This report provides a summary and analysis of the collected data, assessment of the performance and design of the front wall, and recommendations for design and construction of future GRS abutments. Compaction operations created large loads in the reinforcements and against the wall facing during interim construction stages of the front wall. The front GRS walls showed excellent performance because: (i) the monitored movements were significantly smaller than those expected in design or allowed by performance requirements, (ii) post-construction movements and geogrid strains became negligible after an in-service period of 1 year, (iii) measured loads in the reinforcements, connections, and on the wall facing were less than or around 50% of those estimated in the design, (iv) there is not any potential for overturning the structure (due to the flexibility of GRS wall system, resulting in the reduction of loads developed behind and against the wall facing), and (v) the measured bearing pressures were well below the allowable soil bearing capacity. The design employs a high creep reduction factor for the geogrid reinforcements although little if any long-term creep was observed.
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EVALUATION OF FEM ENGINEERING PARAMETERS FROM INSITU TESTS
Author: Townsend, F C Anderson, J B Rahelison, L | Size: 7.34 MB | Format:PDF | Quality:Original preprint | Publisher: University of Florida, Gainesville | Year: 2001 | pages: 265
The purpose of this study was to take a critical look at insitu test methods (SPT, CPT, DMT, and PMT) as a means for developing finite element constitutive model input parameters. The first part of the research examined insitu test derived parameters with laboratory triaxial tests at three sites: Saunder's Creek, Archer Landfill, and SW Recreation Center. The triaxial tests on these sands were used to develop baseline input parameters. These parameters were verified by simulating the triaxial tests using two finite element codes. From these comparisons, the following conclusions were drawn: (1) FEM simulations of triaxial test stress-strain curves produced excellent results; (2) The hardening models (PLAXIS - Hardening Soil and PlasFEM - Sandler Dimaggio) simulated the nonlinear behavior better than the Mohr-Coulomb or Drucker-Prager models; (3) In general, E sub 50 triaxial test modulus values agreed with those estimated from DMT and PMT unloading tests; and (4) FEM simulations of field PMT curves using triaxial test based parameters were unsuccessful. The second phase of this study was to predict the deformations of a cantilevered sheet pile wall (unloading case), and the deformations of a 2-m diameter shallow footing (loading case). Conventional analysis methods were compared with FEM using insitu test derived input parameters. Conclusions were: (1) Conventional analyses (CWALSHT) under-predicted wall deformations unconservatively, while wall deflections were accurately predicted using the Hardening Soil Model with input parameters estimated from SPT correlations and "curved matched" PMT values; (2) Fundamentally, the stress history of a soil profile, i.e., OCR or preconsolidation pressure, must be known for any settlement prediction either using conventional or finite element methods; (3) Of the conventional methods for estimating settlements (CSANDSET), only the SPT based D'Appolonia, and Peck and Bazaraa methods provided reasonable estimates of the observed settlement; (4) The conventional DMT method, which correlates OCR values, slightly overestimated measured settlements; (5) None of the insitu test derived input parameters (SPT, CPT, DMT, and PMT) coupled with FEM Mohr-Coulomb or Hardening Soil models, accurately predicted the shallow footing settlements.
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Bearing Capacity Analysis and Design of Highway Base Materials Reinforced with Geofabrics
Author: Hopkins, Tommy C Sun, Liecheng Slepak, Mikhail E | Size: 2.97 MB | Format:PDF | Quality:Original preprint | Publisher: University of Kentucky, Lexington | Year: 2005 | pages: 119
The primary objective of this study was to develop and implement mathematical bearing capacity models originally proposed by Hopkins (1988, 1991) and Slepak and Hopkins (1993, 1995). These advanced models, which are based on limit equilibrium and are operated together, can be used to analyze the bearing capacity, or stability, of early construction of loads on a single layer of material, two-layered problems involving a layer of base aggregate and subgrade, and a foundation involving multiple layers of different materials, such as flexible asphalt pavement. A Prandlt-type shear surface is used in the model analyses of layered foundations. In this report, the models are extended to analyzing flexible pavements reinforced with tensile elements. Although the current model does not account for strain compatibility, the strength of the tensile elements may be input for assumed strain levels. Any number of tensile elements may be analyzed in a given problem. In the limit equilibrium approach, shear strengths, the angle of internal friction, phi, and cohesion, c, are entered for each layer of material. Triaxial testing of the asphalt material is performed in a manner that the shear strength parameters, phi and c, are developed as a function of temperature. Hence, if the temperature of the asphalt layer is known (or assumed) at a site, then values of phi and c may be calculated from the relationships between the shear strength parameters and temperature. Moreover, to facilitate and provide an efficient means of analyzing early construction cases and flexible pavements reinforced with geosynthetics, "Windows" software was developed. In the case of the asphalt layer, the entire layer is divided into finite layers because phi and c varies with depth of asphalt. When the surface temperature of the asphalt is known (or assumed), a temperature distribution model is used to estimate the temperature at any depth below the asphalt layer surface. Consequently, the shear strength parameters are known at any depth (of each finite layer) below the surface. To establish the validity and reasonableness of the newly developed limit equilibrium models, bearing capacity factors are derived from the limit equilibrium methods and compared to classical bearing capacity factors, N sub c and N sub q, developed by Prandlt and Reissner. Differences range from 1 to 10 and 1 to 3%, respectively. The Slepak-Hopkins model yields values of N sub y that are 12 to 38 larger than values published by Caquot and Kerisel. However, values of N sub y from the Slepak-Hopkins model are only 3 to 11% larger than backcalculated values obtained by Debeer and Ladanyi from experimental footing tests. The Slepak-Hopkins model was also used to analyzed 237 flexible pavement sections of the 1959-1960 AASHO Road Test. Factors of safety from the model analyses showed that very reasonable results were obtained and were in line with failures recorded at the test site. Finally, actual analyses of a stretch of roadway where failures occurred were analyzed. Three sections involved tensile elements.
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Development and Assessment of Transparent Soil and Particle Image Velocimetry in Dynamic Soil-Structure Interaction
Author: Zhao, Honghua | Size: 8.28 MB | Format:PDF | Quality:Original preprint | Publisher: Missouri University of Science and Technology, Rolla | Year: 2007 | pages: 153
This research combines Particle Image Velocimetry (PIV) and transparent soil to investigate the dynamic rigid block and soil interaction. In order to get a low viscosity pore fluid for the transparent soil, 12 different types of chemical solvents were tested and the two best-matching pore fluids were identified. Transparent soil was adopted in the research as a substitute for natural sand. To examine the dynamic properties of transparent soil, a series of resonant column tests were carried out on dry silica gel under different confining pressures. The test results show that transparent soil has a similar dynamic behavior as natural soil under low confining pressure. Hence, transparent soil can be used as an effective substitute for natural soil in the shake table test, in which the confining pressure is usually lower than 400 kPa. A neural network-based camera calibration algorithm was developed for the PIV technique. Its application was illustrated through a case study of a rectangular strip footing by modifying the MatPIV code. The neural network camera calibration model was also compared with the linear model and method. Three shake table tests were conducted in this research. The free-field motion shake table test clearly showed the amplification effects as the wave propagated upward from the bottom. Two shake table tests conducted on a small-scale rigid wood model investigated the interaction between the block and the soil under the input of 2-Hz, 0.25- inch and 2-Hz, 0.5-inch sinusoidal waves. The testing results from the shake table test showed that the rigid wood block failed by the bearing capacity type of failure. The larger amplitude of the input motion at the same frequency would more easily topple the rigid block. The shake table test has also showed the near-field and far-field effects due to the soil-structure interaction. The near-field soil motion was significantly influenced by the motion of the rigid block. The far-field soil motion was unaffected by the motion of the rigid block. This research shows that transparent soil combined with PIV can be a powerful tool for future research in the field of dynamic geomechanics.
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Development of a Stand-Alone Concrete Bridge Pier Protection System
Author: Rosenbaugh, Scott K | Size: 7.01 MB | Format:PDF | Quality:Original preprint | Publisher: University of Nebraska, Lincoln | Year: 2008 | pages: 130
In order to prevent vehicles from impacting bridge piers located in the medians of arterial roadways, roadside barriers are warranted. For instances where roadside space is limited, rigid concrete barriers are often used to shield the bridge piers. These concrete barriers need to be anchored so that they do not translate nor rotate during vehicle impacts. If the roadway slabs do not extend far enough into the median in order to provide adequate anchorage, a footing may be required. Therefore, a concrete barrier with a stand-alone concrete footing was designed, constructed, and crash tested. The objective of the study was to evaluate the safety performance of an 813-mm (32-in.) tall, vertical concrete parapet shielding a bridge pier according to the Test Level 3 (TL-3) criteria established by NCHRP Report No. 350. The barrier width and reinforcement were optimized to provide adequate strength at minimal construction costs. A distance of 425 mm (16.75 in.) between the barrier face and bridge pier was determined necessary to prevent critical vehicle snag. The footing was designed to carry the barrier overturning moment during severe impacts, and thus maintaining the offset distance to the front face of the bridge pier. One full-scale crash test was performed with a ¾-ton pickup truck. Following the successful redirection of the pickup, the safety performance of the stand-alone, vertical concrete barrier was determined to be acceptable according to the TL-3 evaluation criteria specified in NCHRP Report No. 350.
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Retrofit of Rectangular Bridge Columns Using CFRP Wrapping
Author: Endeshaw, Mesay A | Size: 2.19 MB | Format:PDF | Quality:Original preprint | Publisher: Washington State University, Pullman | Year: 2008 | pages: 75
This study investigated retrofitting measures for improving the seismic performance of rectangular columns in existing bridges. Experimental tests were conducted on 0.4-scale column specimens which incorporated details that were selected to represent deficiencies present in older bridges in Washington State. Two unretrofitted specimens were tested to examine the performance of the as-built columns incorporating lap splices at the base of the columns and deficient transverse reinforcement. Five columns were retrofitted with carbon fiber reinforced polymer (CFRP) composite wrapping and one specimen was retrofitted with a steel jacket. The specimens were subjected to increasing levels of cycled lateral displacements under constant axial load. Specimen performance was evaluated based on failure mode, displacement ductility capacity and hysteretic behavior. For retrofitting of rectangular columns, it is recommended that oval-shaped jackets be used whenever possible. Column specimens with oval-shaped jackets of steel and CFRP composite material performed similarly, both producing ductile column performance. Failure in these specimens was due to flexural hinging in the gap region between the footing and retrofit jacket, leading to eventual low-cycle fatigue fracture of the longitudinal reinforcement. Details and procedures for the design of oval-shaped steel jackets are provided in FHWA Seismic Retrofitting Manual for Highway Bridges (2006). Design guidelines for oval-shaped CFRP jackets are given in ACTT-95/08 (Seible et al., 1995). Oval-shaped jackets designed according to these recommendations can be expected to prevent slippage of lapped bars within the retrofitted region. Design guidelines for rectangular-shaped retrofitting using CFRP composite materials are proposed for application to columns with cross-section aspect ratios of 2 or less. While no slippage of the lap splice was observed, it is conservatively recommended that rectangular-shaped CFRP wrapping be used only for the situation where controlled debonding of the lap splice is acceptable.
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Coated Steel Rebar for Enhanced Concrete-Steel Bond Strength and Corrosion Resistance
Author: Chen, Genda | Size: 11.42 MB | Format:PDF | Quality:Original preprint | Publisher: Missouri University of Science and Technology, Rolla | Year: 2010 | pages: 229
This report summarizes the findings and recommendations on the use of enamel coating in reinforced concrete structures both for bond strength and corrosion resistance of steel rebar. Extensive laboratory tests were conducted to characterize the properties of one- and two-layer enamel coatings. Pseudostatic tests were performed with pullout, beam and column specimens to characterize mechanical properties and develop design equations for the development length of steel rebar in lap splice and anchorage areas. The splice length equation was validated with the testing of large-scale columns under cyclic loading. For corrosion properties, ponding, salt spray, accelerated corrosion, potentiodynamic and electrochemical impedance spectroscopy (EIS) tests were conducted to evaluate the corrosion resistance and performance of enamel-coated steel and rebar. Experimental procedures and observations from various laboratory tests are documented in detail. The corrosion performances of enamel and epoxy coatings were compared. It is concluded that a one-layer enamel coating doped with 50% calcium silicate has improved bond strengths with steel and concrete but its corrosion resistance is low due to porosity in the coating, allowing chloride ions to pass through. Based on limited laboratory tests, a two-layer enamel coating with an inner layer of pure enamel and an outer layer of enamel and calcium silicate mixture has been shown to be practical and effective for both corrosion resistance and bond strength. A coating factor of 0.85 is recommended to use with the current development length equations as specified in ACI318-08. The large-scale column tests indicated that the column-footing lap splice with enamel-coated dowel bars had higher load and energy dissipation capacities compared to uncoated dowel bars. When damaged unintentionally, chemically reactive enamel coatings limit corrosion to a very small area whereas epoxy coatings allow corrosion expansion in a wide area underneath the coating.
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This report describes a precast concrete bridge bent system that is suitable for high seismic zones. Lateral load tests on both the top (column-to-cap) and bottom (column-to-footing) connections of the system have demonstrated that the connections have strengths and ductilities similar to those of comparable cast-in-place connections. Additional tests on the bottom connection of the system are ongoing, and construction of a demonstration bridge project will begin later this year. The final development of this system is partially funded by the FHWA’s Highways for LIFE Technology Partnerships Program (DTFH61-09-00005).
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