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

The purpose of this study is to further 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 viable an alternative to welded shear studs in short span composite joists. The data and results obtained from 59 pushout tests performed on the 5/16 in. diameter Elco Grade 8 standoff screw are presented. The test parameters investigated in this study 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. Test results gathered in this study are used in conjunction with selected test data from research performed by Alander (1998). This combined test data is used in determining the validity of existing predictive equations for the shear strength of the 5/16 in. diameter Elco Grade 8 standoff screw. The influence of various independent variables on shear strength is investigated for all screw densities tested. The performance of the 5/16 in. diameter Elco Grade 8 standoff screw in solid slab applications is also investigated. Proposed predictive equations for the shear strength of the 5/16 in. diameter Elco Grade 8 standoff screw based on screw-related failure modes, concrete cone failures and longitudinal splitting, are presented. / Master of Science

The focus of this thesis was to capture and measure carbon dioxide concentrations upon exhalation to determine if an apnea event is occurring. Research in the fields of respiratory physiology and apnea built the foundation for the design of the standoff infant apnea monitor. The monitor is designed to track infant respiration using carbon dioxide and sound signatures of breath without touching the infant. Each detection system, audio and carbon dioxide, were designed separately and brought together for a final proof-of-concept device. The software was developed using LabView and run on a Netbook. Testing was conducted on healthy adults to fine tune the carbon dioxide sensor and measure its response during simulated apnea events. Overnight testing showed that the combined system detected fewer false alarms than either system alone. Infant testing was conducted to determine if the proof-of-concept standoff monitor could detect infant breath at specified distance. The results showed that both detection systems can detect infant breath consistently at distances less than one foot from the infant and poorly at distances exceeding one foot. Finally, conclusions were drawn and interpreted to aid in the design of future generations of the standoff infant apnea monitor. Other research avenues where this technology may be useful were also discussed.

The objective of the research reported herein is to present a comprehensive evaluation of all available experimental data from push-out tests utilizing the ELCO Grade 8 standoff screws. The goal is to develop a strength prediction equation and determine reliability parameters compatible with the Load Factor Resistance Design (LRFD) procedure that would allow the use of this shear connector in design of composite floor systems. The study considers results from push-out tests using this type of screw reported by Hankins et al. (1994), Alander et al. (1998), Webler et al. (2000), and Mujagic et al. (2000). Further, this study identifies the limitations in earlier approaches aimed at predicting the strength of standoff screws. An improved strength prediction model is developed that considers all applicable limit states and determines maximum strength of a connector. A reliability study was also conducted to derive strength reduction factors to be used in design. Parameters considered in the model include deck type and geometry, screw height, concrete compressive strength, top chord angle yield strength, and stand-off screw rupture strength. Results from strength prediction model were compared with results from composite joist tests. / Master of Science

The focus of this research is on the optical measurement of uranyl in a solid matrix using fluorescence spectroscopy. Nanoporous silica-based materials were used to extract uranyl from contaminated soil and to enhance the fluorescence intensity and lifetime. The fluorescence lifetime and intensity of uranyl ions adsorbed on porous silica-based materials of varying pore size was measured as a function of pH and in the presence of fluoride. The feasibility of uranyl fluorescence detection on the top of soil by silica gel is carried out by four types of natural soil. The results show that the uranyl fluorescence intensity can be enhanced by approximately two orders of magnitude by the silica nanoporous matrix from pH 4-12 with the greatest enhancement occurring from pH 4-7. The enhanced fluorescence lifetime can be used in time-gated measurements to help minimize the influence of background environmental fluorophores. The pH and the fluoride variation causes different uranyl speciation and results in a peak shift in the fluorescence spectrum. The mechanism of the uranyl ion on the silica nanoporous matrix was studied through 15 different silica materials with different water content ratios and various concentrations of uranium on different silica structures. The result shows that the particle size, pore size, water content and uranyl concentration on silica surfaces are all important factors for optimizing the fluorescence intensity. The spacing between silica materials, either the pore inside materials or the space between particles, causes the variety of uranyl distribution on the material surface and changes the fluorescence performance. Also, X-Ray Photoelectron Spectroscopy (XPS) is used to identify the possible uranyl surface species on silica. The fluorescence emission spectra from silica materials and the XPS results are consistent with the presence of two different uranyl compounds. The specific surface area of silica materials plays an important role on uranyl adsorption mechanism. To further enhance the sensitivity, an optical ball lens was used to preferentially direct the fluorescence signal toward the excitation source in standoff measurements. The application of the ball lens was found to increase the detection distance up to 14 times.

The effectiveness of removing anomalous material from cast-in-drilled-hole (CIDH) piles by water jetting was examined. The primary objectives of this research were to examine how reinforcing steel influences water jetting and to evaluate how jetting pressures and standoff distance from the material surface affect water jetting of concrete type materials and PVC tubing. The experimental work consisted of water blasting submerged test specimens using rotary jets, nozzles, pumping equipment, and testing procedures currently used in construction practice. The concrete test specimens were comprised of ring- and cylinder-shaped samples, containing materials with compressive strengths of approximately 160 and 3,600 psi. Typical PVC tubing used as inspection access holes for non-destructive testing in CIDH piles was utilized for tubing specimens. During testing, erosion depths were measured as a function of standoff distance and jetting pressure. Water jetted specimens containing reinforcing steel were cut apart after testing to permit inspection of the erosion cavity and eroded material surfaces behind the steel reinforcement. Reinforcing steel bars in CIDH piles do interfere with the jet path and will locally influence material erosion and water-jetting effectiveness. For a relatively weak material, water-jetting pressures between 10,000 and 11,000 psi produced erosion up to a radial distance of approximately 12 inches from the water jet. This erosion distance is less than half the typical maximum design spacing of PVC inspection access tubing installed in CIDH piles.

La spectrométrie laser d'absorption différentielle est une technique bien connue pour la détection à distance d'espèces chimiques dans l'atmosphère. À ce titre, la bande III qui s'étend entre 8 et 12 µm est une région particulièrement intéressante, car les bandes d'absorption de nombreuses espèces chimiques y sont intenses et se recouvrent peu entre elles. Afin de détecter ces espèces à distance dans la bande III, il est nécessaire de disposer de sources dont le rayonnement est fin spectralement, largement accordable, et énergétique. Les sources basées sur l'optique non linéaire du second ordre constituent la seule technologie capable de répondre à ces besoins. Dans ce travail de thèse, nous présenterons des résultats expérimentaux portant sur deux architectures de sources paramétriques permettant d'émettre un rayonnement dans la bande III adapté à la spectrométrie différentielle en configuration lidar. La première architecture consiste à émettre un faisceau directement dans la bande III grâce au pompage de cristaux non linéaire par des sources laser à 2 µm. La seconde architecture, consiste à amplifier les ondes signal et complémentaire issues d'un OPO à 2 µm, avant de les convertir dans la bande III par différence de fréquences. Ces sources sont basées sur l'association de technologies émergentes et sont susceptibles d'offrir des solutions viables au manque de sources émettant dans la bande III. / Laser spectrometry by differential absorption is a well-known technique for standoff detection of chemical species in the atmosphere. The longwave infrared region (LWIR), ranging from 8 to 12 µm is particularly interesting because the absorption bands of many chemical species are intense and non-overlapping. In order to detect those species in the LWIR, there is a need for sources that are spectrally narrow, widely tunable, and delivers high energies. The sources based on second order nonlinear optics are the only technology able to meet those requirements. In this work, we will present the experimental results on two parametric architectures that allows emission in the LWIR for lidar measurements. The first one consists in emitting a beam directly in the LWIR by pumping nonlinear crystals with 2 µm pump lasers. The second architecture consists in amplifying the signal and idler beams coming from a 2 µm OPO, before converting them into the LWIR by difference frequency generation. Those sources are based on the association of new technologies and have the potential to offer a viable solution to a lack of sources emitting in the LWIR.

Windows in building façade are vulnerable to blast pressures. When subjected to blast shock waves, glass windows may suffer failures, potentially causing serious injuries and casualties to the building occupants due to the flying glass shards and other projectiles. Protective films and laminated glass are widely used to protect windows against blast loads. These techniques have proven to reduce or prevent hazards associated with glass breakage. The use of steel or strengthened aluminum frames also reduce window blast hazards associated with frame failures. However, such measures are not always sufficient to mitigate the blast hazard if window retention anchors do not have sufficient resistance to blast pressures. Research on blast resistant windows is scarce in the literature. Therefore, a comprehensive research project was undertaken to address the behaviour, analysis, and design of window retention anchors. The research program consisted of combined experimental and analytical components. Three main phases were pursued, comprising of: i) Experimental research using a shock tube as blast simulator, ii) Numerical investigation based on three-dimensional finite element method (FEM) of analysis, and iii) Non-linear dynamic analysis of window systems based on a single-degree-of-freedom (SDOF) simplification. The experimental phase consisted of tests of 23 punched windows mounted on four different types of substrates consisting of structural steel, reinforced concrete, concrete block masonry, and stone masonry. The experimental parameters included window size and aspect ratio, glazing type, protective film thickness, substrate type, as well as the number and pattern of window retention anchors. Two levels of blast pressure-impulse combinations were used as per the recommendations of the U.S General Services Administration (GSA).The numerical phase involved FEM modelling and analysis of selected test windows. The FEM models were first validated against test results. The validated models were then employed to conduct an analytical parametric study. The parameters in this phase consisted of; substrate type, window frame rigidity, anchor fixity level in the substrate, window aspect ratio and size, anchor spacing, and blast pressure-impulse combination. The results demonstrated the significance of design parameters on window response, while also defining anchor force distribution along the window frame. A simplified SDOF method of analysis was developed for window systems, including the effects of anchor flexibility and substrate rigidity on non-linear response. The analysis approach includes the construction of window resistance functions in pre-break and post-break phases of response, where the latter stage of response is dominated by the membrane action of protective film. The analysis leads to the computation of anchor design forces, which have been validated against anchor shear and axial tension forces recorded experimentally. The SDOF analysis is recommended for use in designing blast-resistant window retention anchors on different substrates.

No description available.

This study consists of three self-standing parts, each dealing with a different aspect of design of composite steel-concrete flexural members. The first part deals with a new type of shear connection in composite joists. Composite steel-concrete flexural members have increasingly become popular in design and construction of floor systems, structural frames, and bridges. A particularly popular system features composite trusses (joists) that can span large lengths and provide empty web space for installation of typical utility conduits. One of the prominent problems with respect to composite joists has been the installation of welded shear connection due to demanding welding requirements and the need for significant welding equipment at the job site. This part of the study presents a new type of shear connection developed at Virginia Tech— standoff screws. Results of experimental and analytical research are presented, as well as the development of a recommended design methodology. The second part deals with reliability of composite beams. Constant research advances in the field of composite steel-concrete beam design have resulted in numerous enhancements and changes to the American design practice, embodied in the composite construction provisions of the AISC Specification (AISC 1999). Results of a comprehensive reliability study of composite beams are presented. The study considers specification changes since the original reliability study by Galambos et al. (1976), considers a larger database of experimental data, and analyses recent proposals for changes in design of shear connection. Comparison of three different design methods is presented based on a study of 15,064 composite beam cases. A method to consider effect of degree of shear connection on strength reduction factor is proposed. Finally, while basic analysis theories between the two are similar, requirements for determining the strength of composite beams in Eurocode 4 (CEN 1992) and 1999 AISC Specification (AISC 1999) differ in many respects. This is particularly true when considering the design of shear connections. This part of the dissertation explores those differences through a comparative step-by-step discussion of major design aspects, and accompanying numerical example. Several shortcomings of 1999 AISC Specification are identified and adjustments proposed. / Ph. D.