Civil & Environmental Engineering
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Item Stress-Controlled Versus Strain-Controlled Triaxial Testing of Sand(1994) Alqutri, Samir Ahmed; Goodings, Deborah J.; Civil Engineering; University of Maryland (College Park, Md); Digital Repository at the University of MarylandThe purpose of this research was to compare the strength characterizations of Mystic White Silica Sands using stress-controlled loading versus strain-controlled loading in a standard compression triaxial tests. To this end one hundred sixty-six tests were conducted involving two types of quartz sand, one fine MWSS45 and one medium coarse MWSS18 , tested at three low to intermediate confining stresses of 14 kN/m2, 28 kN/m2 and 55 kN/m2 with only one specimen diameter size of 71.1 mm. Of the one hundred sixty-six tests, eighty-six were stress-controlled tests and eighty were strain-controlled tests. All specimens were dry, but both loose and dense specimens were tested. The results were evaluated individually and as group. Comparison of the two types of loading tests were evaluated for repeatability, stress-strain characteristics and strength parameters. The plots show that stress-controlled loading in general gives more reproducible results with smoother. steeper stress-strain plot s and a larger average deviator stresses at failure than strain-controlled loading at all three levels of confining stresses for both sands. This results in somewhat larger values of Φ' . Stress-controlled specimens were stiffer and failed with a clear cut failure surface while strain-controlled specimens mostly barreled.Item FINITE ELEMENT ANALYSES OF PARTIALLY REINFORCED MASONRY SHEAR WALLS(1996) Love, Aaron Ray; Chang, Peter; Civil & Environmental Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Partially reinforced shear walls are used in regions of relatively low seismic risk. Nevertheless, these structures should be capable to resist some lateral motion. The purpose of this paper is to examine the behavior of in-plane cyclic load tests of typical partially-grouted masonry shear walls and the capability of FEM/I in simulating their response. FEM/I is a nonlinear finite element program originally developed for reinforced masonry shear walls with a uniform grid of orthogonal reinforcement at close spacing. FEM/I has successfully simulated the response of fully grouted uniformly distributed reinforced masonry walls [Ewing, 1987]. FEM/I uses a smeared property approach in which the reinforcing steel and masonry composite is modeled as a single material. The applicability of FEM/I to partially grouted partially reinforced masonry shear walls is measured by comparing FEM/I force-displacement cycles, peak lateral forces, strains, energy dissipation and crack patterns with those generated from the experimental tests conducted at the National Institute of Standards and Technology. Partially reinforced shear walls can be modeled in FEM/I by smearing the steel over the blocks which are grouted and reinforced. The ungrouted blocks can be modeled as reinforced blocks with a reinforcement ratio of zero. This approach was shown to be adequate when the displacements and cracks were small. As the cracks increase in size, the smeared property assumption can no longer adequately represent the wall• s geometry and it's property. The result is a poor prediction of both local and global behavior at large displacements. The ratio of the lateral loads at the first major event (FME) demonstrate a good relationship in the forces generated by FEM/I for each wall with the exception Wall I. Results from Walls 3, 5, 9 and 11 exhibit FEM/I was able to predict the lateral load adequately up to the FME. The ratio of the lateral load up to the FME ranges from 0.9 - 1.3. After the occurrence of the FME, FEM/I overpredicts the lateral load considerably. In each of the finite element analyses, FEM/I overestimated the peak strength of the masonry specimens. The FEM/I models for Wall 11 and Wall 3 produced the best prediction of the peak strength. The difference for these two walls in the FEM/I predicted maximum lateral load and experimental data were 31 o/o and 41 o/o, respectively. Individual force displacement cycles are plotted at the various stages in the displacement history. FEM/I performs fairly well in predicting the force displacement response of the experiment. Walls 3, 5, 9 and 11 exhibit a good force displacement relationship for the first half of their displacement history until the development of major cracks. Wall 7 corresponded well with the experiment during the initial stages (Cycles 1 -17) of its displacement history. FEM/I did not produce good results in representing the cracking pattern generated by the experimental study. The inability of modeling the crack pattern is also shown in the differences in the plots for the amount of energy dissipated. FEM/I did reasonably well in the prediction of yielding in the vertical reinforcement. Local stress and strain of masonry predicted by FEM/I did not match the experimental data.Item Stress Intensity Factors for Structural Steel I-beams(1996) Feng, Daqing; Albrecht, Pedro; Sanford, Robert J.; Civil and Environmental Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)The application of fracture mechanics to highway steel bridges has been hampered by a lack of stress intensity factor (SIF) solutions for cracks in I-beams. Previous work cannot provide satisfactory solutions. In this study, the finite element analysis method was used to develop accurate SIFs for two-tip and three-tip cracks in I-beams under tension or bending. Cracked I-beams were modeled with eight-node shell elements, with the web and flanges being fully joined along the junction lines. The region around the crack tips, singularity quarter-point elements were used. To ensure accurate and converging solutions, mesh patterns around the crack tips were studied. Also, different methods of extracting SIFs from FEA results were discussed based on benchmark problem studies. Governing parameters for cracked I-beams were determined. For two-tip web cracks, the SIFs are functions of applied stress, crack length, eccentricity, and flange-to-web cross-sectional area ratio. For three-tip cracks in web and flange, the SIFs are functions of applied stress, web and flange crack lengths, and flange-to-web cross-sectional area ratio. The flange-to-web area ratio describes the constraining effect of the flange on the web crack of a two-tip cracked I-beam; the interaction forces between web and flanges greatly affect SIFs for a three-tip cracked I-beam. The SIFs were calculated based on a total of 2,106 FEAs performed for a wide range of the parameters. The results were fitted with equations for ready use by practicing engineers. An example illustrates the calculation of SIFs for a three-tip crack in a composite steel-concrete beam of a steel bridge.Item Design of Rigid Overlays for Airfield Pavements(1987) Rollings, Raymond Sydney; Witczak, Matthew W.; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md)Existing rigid overlay pavement design methods are empirical and use a specified level of cracking as the defined failure condition. The existing empirical designs are based on tests run thirty years ago, and current analytical models provide greatly improved abilities to examine the overlay pavement structure. Emphasis by many agencies on life cycle cost analysis and more sophisticated maintenance and rehabilitation strategies require methods of predicting pavement performance rather than simply developing safe designs. A layered elastic analytical model was selected to evaluate stresses from applied loads in the pavement structure. Pavement performance was measured in terms of a Structural Condition Index which related the type, degree, and severity of pavement cracking and spalling on a scale of 0 to 100. Models were developed to represent the effect of cracking in base slabs under the overlay, to account for fatigue damage of previous traffic on the base pavement, and to account for the effects of substandard load transfer at slab joints. The predicted performance of overlays and pavements using this analysis was checked against the results of full-scale accelerated traffic tests conducted by the Corps of Engineers and against current overlay design methods and was found to provide reasonable agreement. This methodology using the layered elastic analytical model and analysis of fatigue and cracking in the base slab provides a method of predicting pavement and overlay deterioration in terms of a Structural Condition Index.