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Previous research efforts have shown that fish and macroinvertebrates are responsive to fine sediment in streambeds. Excess fine sediment (<2mm in diameter) impairs over 40,000 miles of streams in the U.S., degrading habitat quality for many aquatic species. Embeddedness (emb, %), a measure of fine sediment in gravel bed streams, is negatively correlated with bankfull shear velocity (u*, m/s). This relationship can be modeled by emb = au*b, with baseline coefficient values of a = 10 and b = –1. The purpose of this thesis was to investigate the applicability of this relationship across the U.S., to begin to quantify the variation of embeddedness in time, and to determine the applicability of embeddedness as a habitat metric for lotic biota. The areas that were studied included Stroubles Creek at the Virginia Tech Stream Lab, the Upper Roanoke River Basin in southwest Virginia, and Level II and III ecoregions nationwide with the U.S. EPA National Rivers and Streams Assessment dataset. Nationally, measurements of embeddedness were higher than modeled in areas with higher sediment supply, and lower than modeled in regions with low fine sediment supply. By calculating shear velocity through remotely sensed channel geometry metrics, embeddedness may be predicted throughout a stream network. Various biotic metrics were found to be correlated to embeddedness, with regional variation. Burrowing macroinvertebrate taxa, which may use increased sand to escape predation, increased with increasing embeddedness while the number of Ephemeroptera, Plecoptera, Trichoptera (EPT) taxa, the number of lithophilic spawning fish, and the number of salmonid taxa decreased with increasing embeddedness. Highly embedded substrate is generally considered poor habitat, which was supported by a trend of decreasing intolerant fish taxa with increasing embeddedness. Richness (total number of taxa) did not show a significant correlation, indicating that embeddedness, and fine sediment in general, is not necessarily an impairment to all stream habitat, but is impactful for particular taxa. / Master of Science / Previous research has shown that fish and macroinvertebrates are responsive to fine sediment in streambeds. Excess fine sediment (sand, silt, and clay) impairs over 40,000 miles of streams in the U.S., degrading habitat quality for many aquatic species. Embeddedness (emb, %), a measure of fine sediment in gravel bed streams, decreases with increasing bankfull shear velocity (u*, m/s), a measure of a stream's ability to move a particular size of sediment. The purpose of this thesis was to investigate the relationship between embeddedness and shear velocity in varying areas, to begin to quantify the variation of embeddedness in time, and to determine the applicability of embeddedness as a habitat metric for stream biota. The areas that were studied included Stroubles Creek at the Virginia Tech Stream Lab, the Upper Roanoke River Basin in southwest Virginia, and Level II and III ecoregions nationwide with the U.S. EPA National Rivers and Streams Assessment dataset. Nationally, measurements of embeddedness were higher in areas that may have higher sediment supply, and lower in regions with low fine sediment supply. By calculating shear velocity with remotely available stream data, embeddedness may be predicted throughout a stream network and compared with biota in those locations. Various biotic metrics were found to be correlated to embeddedness, with regional variation. Burrowing macroinvertebrate taxa, which may use increased sand to escape predation, increased with increasing embeddedness while the number of Ephemeroptera, Plecoptera, Trichoptera (EPT) taxa, the number of lithophilic spawning fish, and the number of salmonid taxa decreased. Highly embedded substrate is generally considered poor habitat, which was supported by a trend of decreasing intolerant fish taxa with increasing embeddedness.

The purpose of this study is to evaluate the performance of the 5/16 in. diameter Elco Grade 8 standoff screw as a mechanical shear connector in composite joists. Standoff screws are being investigated as an alternative to welded shear studs in short span composite joists. The data and results obtained from 106 pushout tests performed on the Elco Grade 8 standoff screw are presented. The test parameters include: standoff screw height, quantity of standoff screws per deck rib, standoff screw position, slab depth, base angle thickness, deck type, and amount of transverse reinforcement. The test results from this study are compared to those obtained in previous research performed by Hankins (1994), and the applicability of Hankins' predictive equation for the shear strength of the Elco Grade 8 standoff screw is investigated. The influences of various test parameters on the shear strength of the standoff screw are evaluated and the effects of grouping the standoff screws in the deck ribs are examined. The performance of the standoff screw in solid slab applications is also investigated. Predictive equations for the shear strength of the Elco Grade 8 standoff screw, based on screw-related failure modes, concrete rib failures, and longitudinal splitting of solid concrete slabs, are presented. / Master of Science

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No / This paper presents a numerical investigation into the behaviour of headed shear stud in composite beams with profiled metal decking. A three-dimensional finite element model was developed using general purpose finite element program ABAQUS to study the behaviour of through-deck welded shear stud in the composite slabs with trapezoidal deck ribs oriented perpendicular to the beam. Both static and dynamic procedures were investigated using Drucker Prager model and Concrete Damaged Plasticity model respectively. In the dynamic procedure using ABAQUS/Explicit, the push test specimens were loaded slowly to eliminate significant inertia effects to obtain a static solution. The capacity of shear connector, load-slip behaviour and failure modes were predicted and validated against experimental results. The delamination of the profiled decking from concrete slab was captured in the numerical analysis which was observed in the experiments. ABAQUS/Explicit was found to be particularly suitable for modelling post-failure behaviour and the contact interaction between profiled decking and concrete slabs. It is concluded that this model represents the true behaviour of the headed shear stud in composite beams with profiled decking in terms of the shear connection capacity, load-slip behaviour and failure modes.

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<p>Better understanding of the structural behaviour of concrete and masonry structures is facilitated through experimental testing. Although some experimental testing of reinforced masonry (RM) rectangular walls is reported in literature, little experimental data is available on RM walls with flanges or with boundary element. Unlike those pertaining to rectangular walls, seismic design provisions of flanged and end-confined masonry walls are not available in North American masonry design codes.</p> <p>In the current study, the response of seven half scale fully grouted RM shear walls, all with the same length but different end configurations and aspect ratios is investigated. The goal of the study was to evaluate and document the enhanced ductile behaviour of rectangular RM shear walls when flanges and boundary elements are structurally connected at the wall ends. Another goal was to extract specific seismic performance parameters of reinforced concrete-block rectangular, flanged and end-confined shear walls based on quasi-static experimental results. Finally, nonlinear dynamic analysis was conducted on the test walls to quantify seismic force modification factors used in seismic design.</p> <p>High levels of ductility accompanied by relatively small strength degradation were observed in all walls in general with a significant increase in ductility and displacement capabilities for the flanged and end-confined walls compared to the rectangular ones. The drift levels attained at 20% strength degradation by the rectangular, the flanged, and the end-confined walls were 1.0%, 1.5%, and 2.2%, respectively. The ductility values of the flanged and end-confined walls were, respectively, 1.5 and 2.0 times that of their rectangular wall counterparts. In addition to the enhanced ductility, a saving of more than 40% in the amount of vertical reinforcement was achieved using the proposed alternative strategies while maintain the lateral resistance. The relationship between the energy dissipation and the ratio of the post-yield to the yield displacement was found to be almost linear for the test walls. Wall stiffnesses degraded rapidly to about 60% of their gross stiffness at very low drift levels (0.1 % drift). Measured compressive strain at the wall toes were almost double those specified in both North American codes. Extent of plasticity over the wall height was about 75% of the wall length. Equivalent plastic hinge lengths, needed in wall displacement predictions, using theoretical curvatures and experimental displacement ductilities varied between 17% and 40% of the wall length at ultimate load for all the tested walls. The test results indicated that higher seismic force modification factors should be assigned to the flanged and endconfined RM shear walls compared to values currently assigned to rectangular walls.</p> <p>The data presented in this study is expected to facilitate better understanding of RM wall behaviour under in-plane load to researchers, practicing engineers, and code developers. This study aimed at presenting the flanged and end-confined categories as cost-effective alternatives to enhance the seismic performance of midrise RM construction in North America.</p> / Thesis / Doctor of Philosophy (PhD)