Utilizing the higher capacity steel in design can provide additional advantages to the concrete construction industry including a reduction of congestion, improved concrete placement, reduction in the required reinforcement and cross sections which would lead to savings in materials, shipping, and placement costs. Using high-strength reinforcement is expected to impact the design provisions of ACI 318 code and other related codes. The Applied Technology Council (ATC-115) report "Roadmap for the Use of High-Strength Reinforcement in Reinforced Concrete Design" has identified key design issues that are affected by the use of high-strength reinforcement. Also, ACI ITG-6, "Design Guide for the Use of ASTM A1035 Grade 100 Steel Bars for Structural Concrete" and NCHRP Report 679, "Design of Concrete Structures Using High-Strength Steel Reinforcement" have made progress towards identifying how code provisions in ACI 318 and AASHTO could be changed to incorporate high-strength reinforcement. The current research aims to provide a closer investigation of the behavior of beams reinforced with high-strength steel bars (including ASTM A615 Grade 100 and ASTM A1035 Grades 100 and 120) and high-strength concrete up to 12000 psi. Focus of the research is on key design issues including: ductility, stiffness, deflection, and cracking. The research includes an extensive review of current literature, an analytical study and conforming experimental tests, and is directed to provide a number of recommendations and design guidelines for design of beams reinforced with high-strength concrete and high-strength steel. Topics investigated include: strain limits (tension-controlled and compression-controlled, and minimum strain in steel); possible change for strength reduction factor equation for transition zone (Φ); evaluation of the minimum reinforcement ratio (þmin); recommendations regarding limiting the maximum stress for the high-strength reinforcement; and prediction of deflection and crack width at service load levels. Moreover, this research includes long-term deflection test of a beam made with high grade concrete and high-strength steel under sustained load for twelve months to evaluate the creep deflection and to insure the appropriateness of the current ACI 318 time-dependent factor, λ, which does not consider the yield strength of reinforcement and the concrete grade.

Z-pinning is a through-thickness reinforcement technology for polymer composite materials that has been developed and commercialised over the past fifteen years. The through-thickness reinforcement of composites with thin metallic or fibrous pins aids in suppressing delamination, improving impact damage tolerance and increasing joint strength. Z-pins are applied to the composite part during its manufacture. Pins are embedded within sheets of foam and placed over the unconsolidated part. Subsequently, the foam is compacted and the pins transferred into the part, which is usually an uncured prepreg. In this manner, large numbers of pins can be inserted quickly and easily. The pinned composite is then cured using conventional processes. The use of z-pins is currently limited to several high performance composite structures, most notably Formula One racing cars and F/A-18 E/F (Superhornet) fighter aircraft, although the technology has potential applications in a d iverse variety of aerospace and non-aerospace composite structures. A limited understanding of the mechanical performance of z-pinned parts under high load and fatigue loading conditions currently hinders the application of z-pinned composites. The aim of this PhD project is to investigate the mechanical properties, strengthening mechanics and failure mechanisms of z-pinned carbon/epoxy laminates and joints. The effect of z-pin reinforcement on the tensile and flexural properties of laminates under monotonic and fatigue loading is studied. The sensitivity of these properties to the volume content and diameter of the z-pins is systematically studied by experimentation and analytical modelling. This PhD also evaluates the efficacy of z-pins in improving the load-bearing properties of carbon/epoxy lap joints. Improvements to the room temperature and elevated temperature properties of z-pinned lap joints under monotonic and fatigue tensile loading were determined. The effect of strain rate on the load-bearing properties of z-pinned lap joints was also evaluated. A further aim of the PhD project was to assess the z-pin manufacturing process and the microstructural damage caused by that process. The outcome of this study augments the analysis of the me chanical properties of z-pinned laminates and joints.

Tests are performed on a flexure-pivot-pad tilting-pad bearing with a series integral squeeze film damper in load-between-pads configuration, with both active and locked damper. The damper effects are negated when locked, resulting in a flexure-pivot-pad bearing only. Experimental tests provide static performance data and dynamic stiffnesses from which rotordynamic coefficients are extracted. The following two excitation schemes are implemented: (1) multi-frequency, single direction excitation and (2) single-frequency, rotating load excitation (or "circular excitation"). The XLTRC2 Rotordynamics Software Suite provides stiffness and damping coefficient, eccentricity, and power loss predictions for the locked damper bearing. Test conditions include the rotor-speed range of 4000-12000 rpm and the unit-load range of 0-862 kPa (0-125 psi). Dynamic tests utilizing the multi-frequency excitation for the locked and active damper bearing configurations both show that the real portion of the dynamic stiffness is well modeled by a quadratic curve fit, and the imaginary portion representing the damping is a linear function of excitation frequency. This means that frequency independent coefficients can be obtained when an added mass term is included. While stiffness coefficients are lower for the active damper bearing, damping coefficients remain almost constant between the locked and active damper configurations. A simulation shows that, although the damping coefficients do not change significantly, the reduced stiffness provided by the damper results in greater effective damping. Static performance tests for the locked and active damper bearing indicate low cross-coupling, as shown by the eccentricity and low attitude angle measurements. Pad metal temperature measurements show a smaller temperature differential along the pad arcs for the active damper bearing, than observed for the locked damper case. Frictional power loss is estimated based on lubricant temperature rise and does not differ significantly for the two bearing configurations.

Reinforced concrete frame buildings are the most common type of constructions in Turkey which are exposed to various types of forces during their lifetime. Seismic performance of reinforced concrete frame buildings is dominated by columns which can be classified as primary members of these structures. When current codes are considered, all of them contain several provisions in order to implement reliable seismic performances of reinforced concrete columns. In order to evaluate the accuracy of these provisions, analytical and parametric studies are carried out for flexure critical reinforced concrete columns. In these studies, total numbers of 30 flexure critical columns are extracted from PEER database (2005) and analytically investigated. Once the seismic responses obtained from analytical investigations are close enough to experimental seismic responses, performance based displacement limits are pointed out according to TEC (2007), FEMA 356 (2000), Eurocode 8 (2003), and ASCE/SEI 41 Update (2009). In addition to this, total numbers of 144 flexure critical columns are generated in parametric studies to present the effects of various parameters such as column geometry, concrete strength, axial load ratio, transverse reinforcement ratio, and yielding strength of longitudinal reinforcement on performance based displacement limits. Performance based displacement limits proposed by TEC (2007), FEMA 356 (2000), Eurocode 8 (2003), and ASCE/SEI 41 Update (2009) are found very conservative compared to limits obtained from both experimental and analytical behavior. On the other hand, performance based displacement limits given in Eurocode 8 (2003) and ASCE/SEI 41 Update (2009) predict the experimental behavior more accurate than TEC (2007) and FEMA 356 (2000). Improvements on these limits are proposed.

This thesis presents the dynamic and static forced performance of a flexure-pivot tilting-pad bearing load between pad (LBP) configuration for different rotor speeds and bearing unit loadings. The bearing has the following design parameters: 4 pads with pad arc angle 72o and 50% pivot offset, pad axial length 0.0762 m (3 in), pad radial clearance 0.254 mm (0.010 in), bearing radial clearance 0.1905 mm (0.0075 in), preload 0.25 and shaft nominal diameter of 0.11684 m (4.600 in). The dynamic coefficients and the static performance parameters of the FPB have been compared with the theoretical predictions using the isothermal analysis from the rotordynamic software suite XLTRC2-XLTFPBrg. The bearing shows a small attitude angle, about 10o, which indicates small crosscoupling stiffnesses. The pad temperatures increase in the circumferential direction of rotation with speed and load. The pads maximum temperature was measured near the trailing edge. The dependency of the stiffness and damping coefficients on the excitation frequency has been studied. The frequency dependency in the dynamic coefficients was removed by introducing an added mass coefficient to the bearing model. The direct added mass coefficients were around 32 kg. The direct stiffness and damping coefficients increase with load, while increasing and decreasing with rotor speed, respectively. A small whirl frequency ratio (WFR) was found of about 0.15, and it decreases with load and increases with speed. A comparison between the dynamic stiffnesses using a Reynolds equation and the bulk-flow Navier-Stokes models with the experimental dynamic stiffnesses shows that the Reynolds model (even for laminar flows) is not adequate, and that the bulk-flow model should be used for rotordynamic coefficients prediction. The bulk-flow model in general predicts well the static performance parameters and the direct dynamic coefficients, and underpredicts the cross-coupled coefficients (overpredicts the stability).

The use of composite steel-concrete columns and beam-columns in many structural systems is increasing globally due to the intrinsic synergy when these materials are designed and detailed together properly. However, limited test data are available to justify the structural system response factors and comprehensive design equations in current design specifications. This research, through the testing of 18 full-scale, slender concrete-filled steel tube (CFT) beam-columns, attempts to address the latter need. The circular and rectangular CFT specimens tested for this research are by far the longest and the most slender full-scale CFT members tested worldwide. These CFT specimens were subjected to a complex load protocol that includes pure compression, uniaxial and biaxial bending combined with compression, pure torsion, and torsion combined with compression. In addition, data from the hydrostatic pressure on the steel tubes due to the fresh concrete at casting was evaluated. The single most important contribution of this research is the clarification of the interaction between strength and stability in slender composite concrete-filled columns and beam-columns. Parallel to the experimental study, advanced computational analyses were carried out to calibrate material and element models that characterize the salient features of the observed CFT response, such as steel local buckling and residual stresses, concrete confinement, stability effects, strength, and stiffness degradation, among others. Based on the observed behavior, simplified guidelines for the computation of the strength and stiffness parameters for CFT columns and beam-columns are proposed for design purposes.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2007. / Title from PDF title page (viewed Feb. 5, 2010). Additional advisors: Ashraf Al Hamdan, Wilbur A. Hitchcock, Jason T. Kirby, Talat Salama. Includes bibliographical references (p. 148-153).

Syfte – Syftet med examensarbetet är att minimera eller helt eliminera den utböjning som uppstår i Husqvarnas trimmer 536 LiR från handtag ner till motor och trimmerhuvud då en 5 kilos vikt hängs i handtaget. Metod – En konceptstudie har utförts på Husqvarnas trimmer 536 LiR för att undersöka och utvärdera hur problemet med trimmern ser ut i dagsläget och därifrån ta fram olika koncept för att minimera utböjningen. Arbetet har följt en Stage-Gate produktutvecklingsprocess med sju steg från att skriva kravspecifikation till att ta fram och testa prototyper. Koncept genererades med metoderna brainstorming och Reverse Engineering och sållades sedan med Pughs beslutsmatris. Finita elementmetoden användes för att utvärdera produkten och för att analysera vissa koncept. Avancerade prototyper skapades med selektiv lasersintring medan enklare modeller togs fram för hand. Prototyperna testades och jämfördes mot originalprodukten. Resultat – I detta arbete presenteras fem olika förslag för att minska utböjningen i trimmern; en förstyvning av plastkåporna på originalprodukten, tre tillbehör att fästa på den befintliga trimmern och ett förslag på materialbyte. Alla förslag gav positiva resultat med minskad utböjning, men Tillbehör 3 var det som visade sig minimera utböjningen mest och det enda som klarade av att möta syftet. Dock gav detta tillbehör för stort viktpåslag. Förstyvningen och materialbytet gav också bra resultat gällande utböjningen och ökade inte vikten för mycket. Implikationer – Om de förslag som presenteras här skulle implementeras och tas i produktion skulle det innebära vissa tillfälliga konsekvenser vid produktion av trimmern. Verktygen för plastdetaljerna skulle behöva ändras för förstyvningen och kanske också för materialbytet, medan det för de två första tillbehören skulle behöva tillverkas helt nya verktyg för formsprutning. För att implementera Tillbehör 3 skulle nya beräkningar behövas eftersom trimmerns egenfrekvens ändras. Det skulle dock vara billigare att tillverka detta tillbehör än de första två eftersom detta inte behöver formsprutas. Begränsningar – Flertalet av prototyperna framtagna i detta projekt är tillverkade med selektiv lasersintring och inte med formsprutning, som är tillverkningsmetoden för de nuvarande plastkåporna. Detta innebär att hållfasthetsegenskaperna inte är desamma som de skulle bli vid verklig produktion. Dessutom är materialen som används glasfiberfyllda, vilket innebär att hållfastheten kommer att påverkas ytterligare beroende på tillverkningsmetod. Glasfibrernas positioner och riktningar blir olika vid olika processer vilket ger upphov till olika egenskaper. / Purpose – The purpose of this thesis is to minimize or completely eliminate the flexure in Husqvarna’s brush cutter 536 LiR from the handle down to the engine and the blade when a weight of 5 kilogrammes is hanged from the handle. Method – A concept study has been made on Husqvarna’s brush cutter 536 LiR to examine and evaluate what the problem with the model is and from that to develop different concepts to minimize the flexure. The work has followed a Stage-Gate product development process with seven steps from defining the specification of requirements to developing and testing prototypes. Ideas of concepts were generated using the methods brainstorming and Reverse Engineering and were later sifted using Pugh’s matrix. Finite Element Analysis was used to evaluate the product and to analyse certain concepts. Advanced prototypes were created using selective laser-sintering whilst simpler models were created by hand. The prototypes were tested and compared to the original product. Findings – This project presents five different suggestions on how to minimize the flexure in the brush cutter; one stiffer version of the original plastic casings, three accessories to attach to the original product and a proposal for a change of material. All these suggestions gave positive results with a lesser flexure, but the third accessory, Tillbehör 3, was the one that showed the smallest flexure and the only one able to fulfil the purpose of the study. The weight of the accessory was, however, too big. The stiffer version of the original casings and the change of material also showed good results regarding flexure and did not increase the weight too much. Implications – If any of the proposals of this project were to be implemented in production, it would cause certain temporary consequences for the production of the brush cutter. The tools for the plastic components of the current brush cutter would need some changing in order to manufacture the stiffer version of the mouldings or to produce the different material, whilst for the first two accessories completely new tools for injection moulding would have to be developed. To implement the third accessory, new calculations would be needed since the eigenfrequency of the brush cutter would be changed. It would, however, be cheaper to produce this accessory compared to the first two, since the third one does not need to be manufactured using injection moulding. Limitations – Most of the prototypes in this work is manufactured using selective laser sintering and not injection moulding, which is the manufacturing method of the current plastic casings. This means that the properties of the materials will be different than they would be if they were manufactured for production. Furthermore the materials used in the casings of the brush cutter are filled to certain degree with glass fibres, meaning that the material properties will be even more different depending on manufacturing method. The position and direction of the glass fibres will be different depending on which process is used, giving different mechanical properties.

published_or_final_version / abstract / toc / Mechanical Engineering / Master / Master of Philosophy

Baigiamajame darbe analizuojamas sapropelio kaip rišiklio panaudojimas termoizoliacinių plokščių gamyboje. Kompozicines medžiagas užpildant spygliuočių medžių pjuvenomis. Šiems tyrimams buvo pasirinktas užpelkėjusio Dobilios ežero esančio Kauno rajone sapropelis. Buvo Pagaminta speciali forma bandiniams formuoti. Formuojami bandiniai turėjo skirtinga sapropelio kiekį 200g formavimo masėje. Pasirinktas sapropelio kiekis bandinyje kito nuo 20 iki 35%. Sapropelio ir pjuvenų mišinys formoje buvo slegiamas 0,5; 1,5; 2,5; 3,5; 4,5 MPa slėgiu. Buvo ištirtas šių bandinių atsparumas gniuždymui, atsparumas lenkimui bei nustatytas bandinių tankis ir šiluminis laidumas. Taip pat buvo nustatyta šiluminio laidžio koeficiento priklausomybė nuo sapropelio kiekio bandinyje. / This Master Thesis analyses the appliance of sapropel as a binder in a heat insulation plate production. As a rest composing material sawdust of conifer was used. For the research was chosen a silt of a waterlogged lake Dobilė, located in Kaunas region. Samples were formed with a specially for the research made form. Every sample had a different quantity of sapropel in a forming mass of 200g. A chosen quantity of sapropel in a sample variated from 20 to 35% percents. The mix of sapropel and sawdust in a form was pressed by 0.5, 1.5, 2.5, 3.5, 4.5 MPa pressure. During the research was analyzed sample resistance to compression and flexure, estimated sample density and thermal conductivity. Thermal conductivity dependence on the quantity of sapropel in a sample was estimated as well.