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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Evaluation Of The Orientation Of 90° And 180° Reinforcing Bar Hooks
Author: Podhorsky, Nichole Sneed, Lesley | Size: 5.83 MB | Format:PDF | Quality:Original preprint | Publisher: Missouri University of Science and Technology, Rolla | Year: 2012 | pages: 172
This report describes test results of a study initiated to evaluate the potential influence of hook tilt angle of standard reinforcing hooks on the bond strength of concrete. The topic of the evaluation of the orientation of 90 and 180 degree reinforcing bar hooks in concrete members was identified by the Concrete Reinforcing Steel Institute (CRSI) as high-priority for the reinforcing steel industry. In the test program conducted, a series of single bar and multiple bar specimens was designed and tested to examine bar behavior and potential group effects that may exist in wide flexural members with multiple bars, such as a slab or footing. Using beamend specimens, 90 and 180 degree standard reinforcing hooks were placed at varying angles to compare the angle of tilt and to compare the two hook types. Twelve single bar specimens and twelve multiple bar specimens, each containing either No. 5 or No. 8 standard reinforcing bars,were tested by axially loading the reinforcing bar(s) in tension. Measuring the bar displacement and strain at varying locations along the bar, load-displacement curves obtained were utilized in the analysis of hook tilt. Based on the results, design recommendations for tilted hooked bar anchorages were made. For No. 5 bars and smaller with concrete compressive strength, f’c, greater than 4500 psi, spacing between 0.5 and 2 times the hook length, A, and concrete cover equal to or exceeding the values used in this study, tilting reinforcing hooked bars from vertical at any angle did not compromise the structural integrity. For No. 5 bars and smaller with concrete compressive strength less than 4500 psi, spacing less than 0.5 times the hook length,A, or concrete cover less than the values used in this study, further study is needed. Additionally, further study is needed for bars larger than No. 5.
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dear all,
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Hello,
For the last few days, I had a few discussions with some of my friends and colleagues which regards the subject question: Should supervisors/mentors transfer their knowledge to their researchers?
I know that persons research is a research done by one individual, but supervisor is there to direct you through the right path. Wouldn't be easier, and thus more productive if he shares some of his own experience to you? Or maybe it isn't so good because it doesn't give you the full opportunity for your own deduction?
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Contents
1 Introduction
1.1 The phenomenon of fatigue
1.2 Basic tests
1.3 Terms and definitions
1.4 Fatigue strength of unwelded material
1.5 Methodological aspects and stress assessments
1.6 Nominal stress assessment for fatigue resistant joints
1.7 General references to relevant literature
2 Fatigue strength for infinite life of welded joints in
structural steel 36
2.1 Simply loaded joints 36
2.2 Multiply loaded joints 59
2.3 Influence of mean stress
3 Fatigue strength for finite life and service fatigue strength
of welded joints 66
3.1 Fatigue strength dependent on number of cycles 66
3.2 Load spectra 74
3.3 Fatigue strength with load spectra 82
3.4 Manufacturing measures for increasing fatigue strength
4 Fatigue strength of welded joints in high tensile steels and
aluminium alloys 98
4.1 Welded joints in high tensile steels 98
4.2 Welded joints in aluminium alloys
5 Fatigue strength of welded components, design 10 Structural stress, notch stress and stress intensity
improvements 105 approach for assessment of fatigue strength ofspot welded
5.1 General aspects and welded components in structural joints 299
steel engineering (bar structures) 105 10.1 Development status of local approaches 299
5.2 Welded components in shipbuilding (bar to plate 10.2 Basic loading modes at weld spot 300
structures) 127 10.3 Elementary mechanics of tensile shear and cross
5.3 Welded components in tank, boiler and pipeline tension loading 302
construction (circular shell and plate structures) 136 10.4 Structural stresses at weld spot 305
5.4 Appropriate design with regard to fatigue strength 150 10.5 Notch stresses at weld spot 308
10.6 Stress intensity factors at weld spot 311
6 Fatigue strength of spot, friction, flash butt and stud 10.7 Local stress parameters for common weld spot
welded joints 153 specimens 314
6.1 Spot welded joints 153 10.8 Assessment of load carrying capacity of weld spots in
6.2 Weldbonded joints 160 structural components 322
6.3 Friction welded and flash butt welded joints 161
10.9 Effect of residual stresses and hardness distribution 324
6.4 Stud welded joints 161
10.10 Large deflections and buckling 327
7 Design codes, assessment of nominal and structural stress 163 10.11 Crack initiation with local yielding and crack
7.1 Codes based on science, empirical knowledge and propagation 331
tradition 163 10.12 Local fatigue strength of weld spot 333
7.2 Dimensioning for fatigue in accordance with the 10.13 Combination of spot welding and bonding 341
7.3 Scoudrveesy, aosfsethsesmdeesnitgonfcnoodmesinal stress 116664 @ Corrosion and wear resistance of welded joints 343
7.4 Design loads, load spectra, loading classes 168 11.1 General aspects 343
7.5 Notch classes and quality of manufacture 172 11.2 Corrosion resistance 343
7.6 Permissible stress, safety factor, multiaxiality hypothesis 189 11.3 Wear resistance 347
7.7 Assessment of structural stress 200
12 Example for the development of a fatigue resistant welded
8 Notch stress approach for assessment orratigue strength of structure 349
seam welded joints 208 12.1 Introduction, general outline, requirements 349
8.1 General fundamentals of the method 208 12.2 Development procedure, numerical and experimental
8.2 Elastic notch effect of welded joints with regard to simulation 350
fatigue strength for infinite life 214
8.3 Elastic-plastic notch effect of welded joints with Bibliography 356
regard to fatigue strength for finite life and service
fatigue strength 262
Index 375
9 Fracture mechanics approach for assessment offatigue
strength ofseam welded joints 277
9.1 Principles of the approach 277
9.2 Crack propagation equations 279
9.3 Input parameters of the fracture mechanical strength
or life evaluation for welded joints 287
9.4 Application for assessment of fatigue strength for
finite and infinite life 293
9.5 Application for assessment of safety, residual life,
fitness-far-purpose and backtracing of failures 295
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