Inaug.-Diss.--Bern. / Bibliography: Foot-notes.

Thesis (Ph. D.)--University of Pennsylvania, 1924. / Bibliography: p. 49-52.

Inaug.-Diss.--Bern. / Description based on print version record. Bibliography: Foot-notes.

Buckle arrestors are devices placed along an offshore pipeline for the purpose of arresting an incoming propagating buckle. Typically, buckle arrestors locally increase the pipe’s bending rigidity in the hoop direction. Spiral buckle arrestors are rods closely wound around the pipe for a number of turns and then welded at the ends to secure it in place. Spiral buckle arrestor have some key advantages to other designs in that they provide limited resistance to axial bending of the pipeline, and they can be wound on a continuous line away from free ends. This thesis uses a combination of experiments and modeling to study the effectiveness of spiral buckle arrestors. A series of experiments are conducted using 1.25-inch diameter SS-304 tubes with diameter-to-thickness ratios of 19 and 25. Stainless steel rods of four diameters are wound on tubes for a chosen number of turns and secured in place. A propagating buckle is subsequently initiated in the tube, engages the arrestor quasi-statically, is temporarily arrested, and eventually crosses the arrestor at a pressure defined as the crossover pressure. The crossover pressure was found to depend on the tube D/t and mechanical properties; and the rod diameter, number of turns, and mechanical properties. Finite element models are developed that enable the simulation of rod winding, buckle propagation, and buckle crossover. Local collapse is induced by external pressure and is propagated quasi-statically until it engages the arrestor. The pressure is increased until the buckle crosses the arrestor. The model is shown to reproduce the experimental observations and a large number of the measured crossover pressures with sufficient accuracy. Additional simulations were performed varying the rod diameter, numbers of turns, and tube D/t in order to enrich the database developed. This database was subsequently used to develop an empirical design formula for the arresting efficiency based on key nondimensional parameters of the problem. As was the case for the slip-on buckle arrestor, the arresting efficiency is bounded by the confined propagation pressure of the pipe. / text

Abstract A small opencast coal mine has been developed over previous underground workings in the Malvern Hills, inland Canterbury, New Zealand. The coal measure strata dip at ~45° to the southeast, and consist of finely laminated mudrocks with multiple coal seams of varying thickness. Production is in the range 10,000 to 15,000 tonnes per annum from two principal seams with an aggregate thickness of ~4.5m. The open pit has been designed with footwall batters parallel to bedding, vertical bench separation of 15m, and the highwall formed to a nominal 4V:1H. Preliminary examination of the open pit mine site in 2003 indicated that footwall failures involved de-lamination due to drying out on exposure, and buckling and/or shearing along bedding surfaces. During mine development it became apparent that the batters formed easily where thin (less than 0.3m thick) coal seams were present in the sequence. In the 2004 campaign the pit floor was lowered, with a new batter and bench formed to expose the 3m thick Main Seam coal. The day after completion of this batter, a large buckle failure occurred involving the entire length of the pit (85m along strike), and a 2m thick intact slab with a total volume of ~3700m³ translated down dip 6.2m on the base of a thin coal seam to form a pronounced buckle at the toe. Even though footwall batters are cut to the angle of dip, which is entirely realistic geotechnically, the de-coupling and buckling that occurred compromised the safety and economics of the whole operation. Buckling failure in moderately dipping soft rock sequences has been identified in footwall slopes of coal mining operations. Models used in the literature to simulate similar footwall failures include: the Euler solution using column and beam buckling theory to calculate the kinematic feasibility of a slab-buckle, conceptual modelling using a base friction table, and numerical modelling using distinct element analysis. Back analysis of the Malvern Hills failure was necessary to investigate the controls on the footwall stability, and for future mine design. Engineering geological description of the pit and slab materials was done, and an engineering geological model created. Samples of the slab material and failure surface were collected by coring and trenching, with testing of these materials to establish the required parameters for use in the Euler solution. Back analysis using three different forms of the Euler solution provided unrealistic results that overestimated the overall length of a stable slope by more than 10 times. An engineering geology reassessment was undertaken, and a number of inadequacies in the Euler solution methodology were identified particularly in relation to pore pressure and elasticity considerations. Given that the Malvern Hills toe-buckle slab failure displays both elastic and plastic deformation components in the soft mudrocks, and the slab itself cannot be considered as homogenous, reservations must exist about conventional predictive analytical techniques for pit slope failures of this type. No further large scale slab-buckle failures have developed at the mine site, in part because of the slow rate of coal extraction, but precautionary drainage of the footwall slopes has been undertaken to improve overall batter stability. The location of the slab-buckle failure on a critically positioned pre-sheared thin coal seam with full hydrostatic head is considered the most probable cause, rather than inherent instability of the generic bench and batter arrangement adopted. The adoption of a precedent based engineering geology approach to future mine design is considered the most appropriate solution in the circumstances.

PURPOSE: To investigate relationships between preoperative and intraoperative characteristics with outcome variables in patients suffering from primary rhegmatogenous retinal detachment (RRD) or traction retinal detachment (TRD) complicated by serous choroidal detachment (CD). Choroidal detachment is a rare complication of retinal detachment and the current literature cites generally poor visual outcome variables. By investigating a retrospective case series, we hope to elucidate new relationships and embolden existing ones so that future physicians can make more educated decisions regarding the care for these complicated patients. METHODS: A retrospective case series analyzed 18 patient’s medical records (18 eyes) who had been diagnosed and surgically treated for RRD or TRD associated with a CD at the Longwood Medical Eye Center at Beth Israel Deaconess Medical Center. Patients with RDCD who had undergone 23-gauge pars plana vitrectomy with silicone oil tamponade were selected. Exclusionary criteria included ocular complications such as phthisis bulbi and open globe trauma. Patients experienced a variety of surgical procedures including by not limited to relaxing retinotomy (n=12 eyes), choroidal drainage (n=10 eyes), endoscopy-assisted PPV (n=10 eyes), and ERM peeling (n=8 eyes). Primary outcome variables tabulated were primary and final anatomic success, defined as successful reattachment of the retina to the underlying choroid, and final visual acuity. RESULTS: The mean age of the sample group was 69 with 8 patients (44%) diagnosed with preoperative hypotony (IOP <= 6 mmHg). A total of 12 patients were pseudophakic (67%). With a mean follow-up of 21.6 months, patients exhibited expected visual outcomes with 6 patients (33%) improving visual acuity and 7 patients (39%) decreasing visual acuity. Final anatomic success was seen in 17 cases (94%). A significant correlation was found between decreased number of previous surgeries and better visual outcomes (change in BCVA). Another significant relationship correlates choroidal drainage with worse visual outcomes (change in BCVA). Finally, patients who received ERM peeling had better rates of primary anatomic success. CONCLUSION: The advanced age of the sample lends itself to increased risk for cataracts and thus pseudophakia. In addition, high rates of diabetes and macular degeneration follow. The pathophysiology of RDCD in relation to the risk factors of hypotony and macular holes is possibly based on the Starling forces and favorable fluid transudation into the suprachoroidal space. Although the outcomes of this study were similar to previous literature, the visual outcomes are still poor at best. Reducing the number of previous, invasive, ocular surgeries was seen to be correlated with better visual outcomes. In addition, performing ERM peels is seen to be correlated with improved rates of primary anatomic success. More research is required on the etiology of the disease process and a case-controlled longitudinal study may be helpful in determining more relationships with outcome variables.

This thesis looks into current requirements of having fire extinguisher in a car in both the Czech Republic and other countries. At first, there is an evaluation of current ways of mounting fire extinguishers in cars, as well as evaluation of various requirements concering safety and ergonomy of mounting fire extinguisher in a car and also what are the hazards of having unattached fire extihnguisher in the passenger compartment. The objective of this thesis is to desing and test a fire extinguisher holder which would fullfil these requirements and which will not require changes in the body of the vehicle. The final part of this thesis deals with evaluating of possibilities of mounting this holder into several types of vehicles.

Different fracture modes have been observed in thin film structures. One common approach used in fracture analysis is based on the principle of linear elastic fracture mechanics (LEFM), which assumes pre-existing cracks and treats the materials as linear elastic except for the damage zone around the crack tip. Alternatively, a nonlinear cohesive zone model (CZM) can be used to simulate both nucleation and growth of cracks. In this dissertation, the approaches of LEFM and CZM are employed to study fracture and delamination of elastic thin films on compliant substrates under various loading conditions. First, compression-induced buckling of elastic thin films on elastic compliant substrates is studied by analytical and numerical methods. The critical condition for onset of buckling instability without and with a pre-existing delamination crack is predicted. By comparing the critical strains, a map for the initial buckling modes is constructed with respect to the film/substrate stiffness ratio and the interfacial defect size. For an elastic film on a highly compliant substrate, nonlinear post-buckling analysis is conducted to simulate concomitant wrinkling and buckle-delamination, with a long-range interaction between the two buckling modes through the compliant substrate. By using a layer of cohesive elements for the interface, progressive co-evolution of wrinkling and delamination is simulated. In particular, the effects of interfacial properties (strength and toughness) on the initiation and propagation of wrinkle-induced interfacial delamination are examined. Next, using a set of finite element models, the effects of interfacial delamination and substrate penetration on channel cracking of brittle thin films are analyzed. It is found that, depending on the elastic mismatch and the toughness of interface and substrate, a channel crack may grow with interfacial delamination and/or substrate cracking. By comparing the effective energy release rates, the competition between the two fracture modes is discussed. Cohesive zone modeling is then employed to simulate nucleation and growth of delamination and penetration from the root of a channel crack. By comparing the results from the approaches of LEFM and CZM, the characteristic fracture resistance from small-scale bridging to large-scale bridging is identified. Finally, to determine the nonlinear traction-separation relation for cohesive zone modeling of a bimaterial interface, a hybrid approach is developed by combining experimental measurements and finite element simulations. In particular, both analytical and numerical models for wedge-loaded double cantilever beam specimens are developed. A two-step fitting procedure is proposed to determine the interface toughness and strength based on the measurements of the steady-state crack length and the local crack opening displacements. / text

No description available.

I vissa takstolskonstruktioner kan det ibland uppstå stora tryckkrafter i diagonala reglar. I Sverige löser man oftast detta med hjälp av stagning tvärs diagonalen för att hindra utböjning i veka riktningen. Ibland när det är svårt att på plats trä in strävor på grund av utrymmesbrist och dylikt kan man spika eller skruva på en regel för att på så sätt förstärka den diagonala strävan. Detta examensarbete har undersökt två olika förstärkningsalternativ, rektangulärt- och T-tvärsnitt, med hjälp av reglar med dimension 45x95 mm2 vilka skruvas respektive spikas ihop. Detta har gjorts laborativt genom att trycka provkroppar i en provningsram och undersöka hur mycket den axiala kapaciteten ökar med förstärkning. De två olika förstärkningslösningarna bygger på att man på plats kan förstärka strävor med enkla medel. Testbitarna har levererats till Växjö universitet och är av oklassat virke. Provbitarnas E-modul har undersökts för att på teoretisk väg undersöka hur stor axialkraftskapacitet den primära strävan har utan förstärkning. Provkroppar tillverkades och konditionerades i klimatrum, med temperaturen 20°C och 65 % RF, i ca tre veckor före provtryckning. De laborativa värdena visar att den axiella kapaciteten ökar med 1,9 – 2,7 ggr för de rektangulära tvärsnitten och 2,5 – 4,0 ggr för T-tvärsnitten. Förstärkningsfaktorn är beroende av längd, förstärkningsalternativ och sammanfogning. Förstärkningseffektiviteten är högst för de längre strävorna. / In wooden roof trusses there sometimes may occur buckling in compressed web members. In most cases in Sweden this is solved by bracing between two webs to prevent buckling of the minor axis. Sometimes it is hard to brace between webs because of lack of space. Then it is possible to nail or screw a side member on the compressed web to increase the capacity. This diploma work has examined two different ways of bracing, rectangular cross section and T-bracing, with webs 45x95 mm2. Experimental tests have been made on compression webs and examine the bracing efficiency. It is important that the bracing alternatives are easy to use with simple tools. Ungraded lumber were delivered to Växjö University. The Youngs modulus of the test pieces has been examined so the critical buckling load of the main member without bracing could be calculated theoretically. The lumber was conditioned to equilibrium moisture content of approximately 12 percent in a room maintained at 65 percent relative humidity and 20°C in three weeks before testing the critical buckling load. The experimental results show that the critical buckling load increases with a factor of 1,9 – 2,7 for the rectangular cross sections and with a factor of 2,5 – 4,0 for the T-bracing. The bracing efficiency is dependent on length, bracing alternative and type of connectors.. The bracing efficiency increases for longer webs.