Shear strength of fiber reinforced concrete beams was studied in this research project. Three types of fibers were examined: hooked-end steel fiber, crimped-steel fiber, and crimped-monofilament polypropylene fibers. The experimental program included five beam specimens. Two of the beams were control specimens in which one was reinforced with minimum shear reinforcement according to ACI 318, while the other one did not have any shear reinforcement. Each one of the other three specimens was reinforced with one of the above mentioned fibers by 1% volumetric ratio. In addition to the beam specimens, three prisms were also made for each type fiber to determine their toughness. The aim of this research was to investigate the following questions for medium-high concrete strength 1) to evaluate the effectiveness of each type of fibers on the shear strength, 2) to investigate the shear strength, toughness, crack patterns and near ultimate load crack width of each beam, and 3) to determine if using 1% volumetric ratio of fibers as shear reinforcement in beams would provide adequate strength and stiffness properties comparable to reinforcing steel used as minimum shear reinforcement. The results showed that all three types of fibers increased the shear capacity of the beam specimens more than the beam reinforced with minimum shear reinforcement. Moreover, some of the fibers used could shift the type of failure from a pure shear failure to a combined flexural-shear or pure flexural failure.

Shear links are used as fuse elements in lateral load resisting systems to provide ductility and dissipate seismic energy. These links have traditionally been employed in eccentrically braced frames, but have more recently been suggested for use in the innovative linked column frame system (LCF). Current design specifications for shear links require intermediate web stiffeners to provide out-of-plane web stability so ductility requirements can be achieved. This research focused on moving from discrete transverse web stiffening to continuously stiffened webs in built up shear links. Built up links were designed to yield in shear when subjected to severe cyclic loading, however the webs of the links were designed using two metal sheets joined by an elastic core. These composite "sandwich" webs allowed for an increase in web thickness (and inherent flexural rigidity) without increasing the shear strength of the links. Numerical and experimental investigations were conducted to assess the performance of composite sandwich links subjected to severe loading. Numerical results showed improved web behavior in sandwich links in which the core material was assigned an elastic modulus greater than 5000psi. Due to fabrication limitations, experimental specimens were fabricated with a core material elastic modulus of 1000psi. These specimens did not perform as well as unstiffened base case links in terms global hysteretic behavior or ductility.

There are presently many solutions to dealing with aging or deteriorated structures. Depending on the state of the structure, it may need to be completely over-hauled, demolished and replaced, or only specific components may need rehabilitation. In the case of bridges, rehabilitation and maintenance of the decks are critical needs for infrastructure management. Viable rehabilitation options include replacement of decks with aluminum extrusions, hybrid composite and sandwich systems, precast reinforced concrete systems, or the use of pultruded fiber-reinforced polymer (FRP) shapes. Previous research using pultruded glass fiber-reinforced polymer (GFRP) decks, focused on behaviour under various strength and serviceability loading conditions. Failure modes observed were specific to delamination of the flexural cross sections, local crushing under loading pads, web buckling and lip separation. However certain failure mechanisms observed from in-situ installations differ from these laboratory results, including behaviour of the connectors or system of connection, as well as the effect of cyclic and torsional loads on the connection. This thesis investigates the role of mechanical and non-mechanical connectors in the composite action and failure mechanisms in a pultruded GFRP deck system. There are many interfaces including top panel to I-beam, deck panel to girder, and panel to panel, but this work focuses on investigating the top panel connection. This is achieved through comparative component level shear, uplift, and flexure testing to characterize failure and determine connector capacity. Additionally, a connection of this GFRP deck system to a concrete girder is investigated during the system-level test. Results show that an epoxy non-mechanical connection may be better than mechanical options in ensuring composite behaviour of the system.

Hollow fiber membranes offer the opportunity to dramatically reduce the energy required to perform gas separations in the chemical industry. The membranes are fabricated from highly non-Newtonian precursor materials, including concentrated polymer solutions that sometimes also contain dispersed particles. These materials are susceptible to shear-induced microstructural changes during processing, which can affect the characteristics of the resulting membrane. This thesis explores several shear-related effects using materials and flow conditions that are relevant for fiber spinning. The findings are discussed as they relate to membrane processing, and also from the standpoint of enhancing our fundamental understanding of the underlying phenomena. First, the effect of shear on polymeric dope solutions was investigated. Shear-induced demixing—a phenomenon not previously studied in membrane materials—was found to occur in membrane dopes. Phase separation experiments also showed that shear-induced demixing promotes macrovoid formation. The demixing process was found to depend not only on the instantaneous shear conditions, but also on the shear history of the solution. This suggests that low-shear flow processes that occur in the upstream tubing and channels used for fiber spinning can affect macrovoid formation. The effect of viscoelastic media on dispersed particles was also explored. Shear-small-angle light scattering results showed that particles suspended in membrane dope solutions formed aggregated, vorticity-oriented structures when shear rates in the shear-thinning regime of the polymer solution were applied. Shear rates well below the shear-thinning regime did not produce any structure. In fact, the application of a Newtonian shear rate to a sample already containing the vorticity structure caused the sample to return to isotropy. Measurements using a highly elastic, constant-viscosity Boger fluid showed that strong normal forces alone are not sufficient to form the vorticity structures, but that shear thinning is also required. Lastly, a study was conducted examining cross-stream migration of particles dispersed in viscoelastic media. Fluids exhibiting varying degrees of shear thinning and normal forces were found to have different effects on the particle distribution along the shear gradient axis in Poiseuille flow. Shear thinning was found to promote migration toward the channel center, while normal stresses tended to cause migration toward the channel walls. In addition to hollow fiber spinning, many other industrially relevant applications involve polymer solutions and suspensions of particles in viscoelastic media. Often, the properties and performance of the material depend strongly on the internal microstructure. The results from the research described in this thesis can be used to guide the design of materials and processing conditions, so that the desired microstructural characteristics can be achieved.

This report details the design and construction of an AASHTO Type IV prestressed girder and a PCI BT-56 prestressed girder. It also details the shear testing and shear performance of the BT-56 girder. The results are compared with results from previous research dating back to 1986. Finally, all research was compared with the AASHTO Standard (2002), AASHTO LRFD (1998) and AASHTO LRFD (2004) Specifications to examine thier overall accuracy in predicting shear strengths.

Pipe jacking, has seen a rise in popularity, particularly in urban areas where infrastructure does not permit cut-and-cover methods. As pipe jacking has becomes more commonplace, engineers are pushing the limits of the technology more and more by designing longer drives in more difficult ground conditions. Lubrication is essential to reduce the frictional resistance generated at the pipe-soil interface. Even though lubrication is widely utilized, there is not a clear understanding of the conditions required to obtain the full benefit of lubrication. This dissertation focuses on bentonite slurry characteristics and interface behavior under different lubricating conditions with the goal to further the understanding of the mechanisms responsible for the large friction reductions observed in the field. An interface shear device capable of measuring interface behavior on pipe surfaces was used to perform tests under two lubricating conditions. Pipes were sheared against a mixture of sand and slurry and the effect of the slurry was quantified. In another series of tests, slurry was injected at the pipe-soil interface. An axisymmetric interface shear device was developed to further investigate the lubrication mechanism associated with injection of slurry into sand. The device was designed to inject slurry through injection ports built into a shaft displaced within a sealed sand-filled chamber. A series of tests were performed on dry sand as well as sand where water or slurry was injected during shearing. The effect of sand type and viscosity are also investigated. Findings from the experimental studies are related back to full-scale behavior with the objective of assessing the lubrication methods and their effectiveness. A rational procedure for predicting non-lubricated and lubricated jacking forces is proposed to optimize design and serve as a framework for evaluating jacking forces in the field.

Cell adhesion plays an important role in inflammation and immunological responses. Adhesion molecules (e.g., selectins and integrins) are key modulators in mediating these cellular responses, such as leukocyte trafficking under shear stress. In this thesis, we use a bio-membrane force probe (BFP) to study force regulation on kinetics and conformations of selectin and LFA-1 integrin. A new BFP was built up, and a new assay, using thermal fluctuation of the BFP, was developed and used to monitoring selectins and their ligands association and dissociations. The new BFP was also used to investigate the force and force history dependence of selectin-ligand interactions. We found tri-phasic transition of force-dependent off-rates and force-history dependence of selectin/ligaind interactions. The BFP was also used to characterize force-dependent lifetimes of the LFA-1-ICAM-1 interaction. We found that LFA-1/ICAM-1 bonds behaved as catch bond and that LFA-1-ICAM-1's catch bonds were abolished blocking the downward movement of αA domain α7 helix. Finally, the BFP was applied to dynamically probe the global conformational changes of LFA-1 and to characterize force-regulated transitions among different conformational states on a living cell. We observed dynamic transitions of LFA-1 between extended and bent conformations on living cells. The observed average distance change of LFA-1's extensions was about 18nm, while that of the bending was only about 14nm. We also found that forces could facilitate extension but they slow down the bending of LFA-1. The observed transition time of extension was less than 0.1s, while that of contraction was longer than 0.2s. Our observations here are the first in-situ evidence to demonstrate how integrins dynamically transit different conformations and how force regulates these transitions.

Ultra-High Performance Concrete (UHPC) is a new class of concrete characterized by no coarse aggregate, steel fiber reinforcement, low w/c, low permeability, compressive strength exceeding 29,000 psi (200 MPa), tensile strength ranging from 1,200 to 2,500 psi (8 to 17 MPa), and very high toughness. These properties make prestressed precast UHPC bridge girders a very attractive replacement material for steel bridge girders, particularly when site demands require a comparable beam depth to steel and a 100+ year life span is desired. In order to efficiently utilize UHPC in bridge construction, it is necessary to create new design recommendations for its use. The interface between precast UHPC girder and cast-in-place concrete decks must be characterized in order to safely use composite design methods with this new material. Due to the lack of reinforcing bars, all shear forces in UHPC girders have to be carried by the concrete and steel fibers. Current U.S. codes do not consider fiber reinforcement in calculating shear capacity. Fiber contribution must be accurately accounted for in shear equations in order to use UHPC. Casting of UHPC may cause fibers to orient in the direction of casting. If fibers are preferentially oriented, physical properties of the concrete may also become anisotropic, which must be considered in design. The current research provides new understanding of shear and shear friction phenomena in UHPC including: *Current AASHTO codes provide a non-conservative estimate of interface shear performance of smooth UHPC interfaces with and without interface steel. *Fluted interfaces can be created by impressing formliners into the surface of plastic UHPC. AASHTO and ACI codes for roughened interfaces are conservative for design of fluted UHPC interfaces. *A new equation for the calculation of shear capacity of UHPC girders is presented which takes into account the contribution of steel fiber reinforcement. *Fibers are shown to preferentially align in the direction of casting, which significantly affects compressive behavior of the UHPC.

Particulate materials are ubiquitous in the natural environment and have served throughout human history as one of the basic materials for developing civilizations. In terms of human activity, the handling of particulate materials consumes approximately 10% of all the energy produced on earth. Advances in the study and understanding of particulate materials can thus be expected to have a major impact on society. Geotechnical engineers have a long history of studying particulate materials since the fundamental building blocks of the profession include sands, silts, clays, gravels and ores, all of which are in one form or another particulates. The interface between particulates and other engineered materials is very important in determining the overall behavior of many geotechnical systems. Laboratory experimental studies into interface shear behavior has until now, been largely confined to systems involving uniformly graded sands comprised of a single particle size. This study addresses these potential shortcomings by investigating the behavior of binary particle mixtures in contact with surfaces. The binary nature of the mixtures gives rise to a changing fabric state which in turn can affect the shear strength of the mixture. Accordingly, packing limit states and the shear strength of binary mixtures were investigated across a range of mixtures, varying in particle size ratio and the proportion of fine particles to provide a reference. Binary mixtures in contact with smooth surfaces were investigated from both a global shear response and a contact mechanics perspective. A model was developed that allowed for the prediction of an interface friction coefficient based on fundamental material properties, particle and mixture parameters. Surface roughness changes as a result of shearing were also examined. The interface shear behavior with rough interfaces was examined in the context of the relative roughness between particles and surface features. The interpretation of traditional measures of relative roughness suffer from the need for a definitive average particle size, which is ambiguous in the case of non-uniform mixtures. Measures of an applicable average particle size for binary mixtures were evaluated.

During high flow rates, the acceleration of flow and turbulence around bridge foundations lead to scouring, defined as the removal of bed sediments. Due to the interparticle physico-chemical forces of clay particles, erodibility and transport mechanisms for fine sediments are different from those for coarse sediments, and the capability to predict the erosion resistance of fine sediments is still in question. In this study, silt-clay soil mixtures with different kaolin contents were prepared by mixing ground silica and Georgia kaolin with tap water. Geotechnical tests were carried out to obtain the physical properties of the specimens. The critical shear stress and yield stress of the soil mixtures were determined through hydraulic flume experiments and rheometer tests, respectively. Particle associations of the soil specimens were observed using the technique of scanning electron microscopy (SEM). From the laboratory work and data analysis, relationships among the critical shear stress, yield stress, and the soil physical properties were developed from multiple regression analysis. Specifically, values of the critical shear stress, yield stress, and their dimensionless form can be predicted by the soil properties including bulk density, clay content, and water content. Finally, a single relationship is obtained to predict the Shields parameter as a function of the corresponding dimensionless yield stress in this study. The results can be used to provide a methodology for engineering applications requiring the value of critical shear stress such as estimating fine sediment bed stability and assessing the erosion risk of river beds in proximity to bridge foundations and other flow obstructions.