This thesis utilized a linear analytical approach to explore the damage tolerance or residual strength as a function of increasing damage in traditional single and hybrid-grid IsoTruss® structures. Residual strength was studied for structures subjected to axial compression, torsion and flexural bending, independently. Carbon/epoxy material properties were applied in all load cases, and fiberglass/epoxy material properties were also applied in the flexural bending case. Prior to imposing damage conditions, the IsoTruss® structures were parametrically optimized to achieve the highest strength-to-weight ratios. Typical compression strut, driveshaft, and utility pole specifications governed the design strength dimensions and boundary conditions. Damage growth was achieved by removing members from IsoTruss® structures progressively about the circumference in a symmetrical manner. The sequence of member removal, beginning with primary or secondary members, was examined, and is described as primary and secondary analyses. ABAQUS finite element analysis was employed to quantify the residual strength of each IsoTruss® configuration. Reduction in residual strength trends are compared to net section strength, which assumes a linear relationship between damage size and residual strength. Results indicate that the 6-node IsoTruss® configuration is the most damage tolerant structure in the sense that the 6-node configuration deviates the least from the net section strength. As more nodes are added, IsoTruss® structures behave more like a composite tube, exhibiting a brittle behavior characterized by an increase in strength reduction for a given damage size. Bending results reveal that carbon fiber IsoTruss® structures are more damage tolerant under primary bending conditions than fiberglass poles. On the other hand, fiberglass IsoTruss® poles prove to be more damage tolerant under secondary bending conditions than carbon fiber structures. Most importantly, however, hybrid-grid IsoTruss® poles are definitively more optimal structures than single-grid poles in terms of both strength-to-weight ratio and damage tolerance. The results and conclusions from this thesis provide benchmark capacities for mechanically manufactured IsoTruss® structures. Also included in this thesis is documentation of a special program written to analyze IsoTruss® structures.

Assessment of post-liquefaction residual strength is needed for the development of empirically-based, predictive correlations for earthquake engineering design. Previous practice commonly assigned negligible strengths to liquefied materials for engineering analysis, producing overly-conservative designs. Increasingly available case history data, and improved analytical tools have allowed for more accurate and less overly-conservative estimation of soil residual strength, improving empirical predictive models. This study provides a new case history to the limited suite of (approximately 30) liquefaction failure case histories available for post-liquefaction in-situ strength predictive correlations. This case history documents the Las Palmas gold mine tailings dam failure, resulting from seismic-induced liquefaction during the moment magnitude 8.8 February 27, 2010 Maule, Chile earthquake; the sixth largest since 1900. Forensic analysis provides reasonably well-constrained values of 1) back-calculated representative post-liquefaction residual strength, 2) representative penetration resistance, and 3) representative vertical effective stress along the suspected liquefied failure surface. This study employs the incremental momentum method to incorporate momentum effects of a moving soil mass. The incremental momentum method requires a series of cross sections animating the geometry of failure progression from initiation to termination, converging on the observed final geometry. Using interpreted soil strength characteristics, an iterative procedure approximates the back-calculated value of post-liquefaction residual strength. Findings of this case history plot well with existing empirical deterministic regression charts and are in general agreement with previous, related efforts. Results yield representative, well-constrained values of: 1) post-liquefaction residual strength ≈ 173 psf, 2) penetration resistance of N1,60,CS ≈ 5 and N1,60 ≈ 2.5, and 3) vertical effective stress ≈ 4,300 lb/ft2, or ≈ 2.0 atm.

No description available.

Shotcrete or sprayed concrete has become an inevitable material for stabilising and supporting hard rock tunnels. To prevent rock block fallouts in the excavated tunnel, shotcrete is pneumatically projected under high pressure on the rock surface. This method has proven to reduce the construction time drastically, and the addition of fibres in the shotcrete material results in Fibre Reinforced Shotcrete (FRS). The fibres increased the strength of the parent matrix and made the reinforcement bar (mesh) placing procedure with its heavy labour work unnecessary. Even though FRS have been in use for many years, to design FRS lining there are currently no complete, widely used guidelines. Traditionally, the most frequently used testing was a traditional beam testing method which helps to determine the FRS mechanical properties. Previous studies prove that the result from beams often show a high scatter in the results. Another proposed standard testing method is the Round Determinate Panel method to determine the energy absorption capacity. This method has the potential to be a reliable test procedure with a repeatable and predictable crack pattern.In this project, an experimental investigation was carried out to understand the behaviour of macro fibres of steel, basalt and synthetic materials in FRS. The specimens were sprayed in situ and cast in laboratory, of which the in situ samples were assigned to different curing conditions. The test standard ASTM C-1550 was used to design the round panels and SS-EN 14488-3 for the beams. Each type of FRS specimen’s compressive strength was tested, evaluated and compared. The single fibre pullout strength was tested to determine the bond strength between shotcrete and fibres.The calculated results showed the coefficient of variation (COV) of energy absorption capacity from panels varied within 3 % – 13 % and the residual strength of beams within 12 % – 35 %. Irrespective of testing method, the Dramix 3D steel fibre and Minibars basalt fibre for the tested cases showed the lowest dispersion of result. Minibars showed a significant increase in compressive strength compared to the other fibres. Single fibre pullout testing concluded that the steel fibre had superior load capacity at the first crack. Minibars showed a strength close to that of steel fibres and a failure mode similar to that with synthetic fibres.

The purpose of this research is to evaluate and compare the structural performance of composite floor slabs reinforced with 6 x 6 W1.4/W1.4 welded wire fabric (WWF) and STRUX 90/40 synthetic macro fibers. Slabs were subjected to flexural strength tests and concentrated load tests while monitoring load, steel deck strains, and deflections. Test results obtained from this test program were also compared to results from a similar test program conducted in 2001. Tests were also performed to obtain the average residual-strength of the fiber-reinforced concrete using the ASTM C 1399 (2003) standard test. All slabs were loaded until a complete failure was observed. The observed failure loads were compared to failure loads calculated by design guides published by the American Society of Civil Engineers (ASCE) and the Steel Deck Institute (SDI). The flexural strength tests showed that composite slabs reinforced with synthetic macro fibers and WWF exhibited strength and behavior that was almost identical. The observed values of strength were also within the range that was predicted by ASCE prediction models. At a typical office design load of 70 psf, all slabs exhibited midspan deflections that were much smaller than those necessary for serviceability requirements. The concentrated load tests also showed that the observed strength of all composite slabs tested was above those values predicted by ASCE and SDI models. However, an effective comparison between the WWF-reinforced and synthetic macro fiber-reinforced slab was difficult due to a poor shear bond in the latter slab prior to testing. The results of the ASTM C 1399 test verified the ability of concrete reinforced with synthetic macro fibers to meet average residual-strength values recommended by the SDI. / Master of Science

Aluminum alloys have increasing applications in construction and transportation industries. Both 5xxx-series (Al-Mg) and 6xxx-series (Al-Mg) alloys are frequently used in marine construction because of their light weight, high strength, and corrosion resistance. One of the major concerns regarding the marine application of aluminum alloys is their mechanical performance in fire scenarios. The material strength may be degraded due to both thermal and mechanical damage during fire exposure. This work emphasizes the stress-induced mechanical (physical) damage and its impact on the residual (post-fire) performance of 5083-H116 and 6061-T651 aluminum alloy. Thermo-mechanical tests were performed at various temperatures and stresses to study the stress-induced damage at induced plastic creep strain levels. Unstressed thermally exposed and thermo-mechanically damaged samples were examined to separate the stress-induced microstructural damage. The stress-induced microstructural damage primarily manifests itself as dynamic recovery at low creep temperatures, while cavitation, dynamic recrystallization and dynamic precipitation (in Al6061) are the types of damage developed in the high creep strains at high exposure temperatures. Different creep mechanisms are also studied for both Al5083 and Al6061. The post-fire mechanical response at room temperature after thermo-mechanical damage was investigated with reference to the damaged microstructure present in the material. Residual material strengths based on deformed cross sectional area after the creep test were calculated to provide insight into how microstructural damage affects the post-fire material performance. The competing effects of strength degradation caused by cavitation and strengthening due to grain elongation and subgrain refinement were investigated. Engineering residual material strengths calculated based on the original cross sectional area prior to creep tests were also studied to provide guidance for structural design. / Ph. D.

[pt] O concreto é conhecido por ter um bom desempenho quando exposto a altas temperaturas pelo fato de apresentar baixa condutividade térmica, ser incombustível e não exalar gases tóxicos. Entretanto, devido à sua composição heterogênea, o concreto sofre alterações físicas, químicas e mecânicas que podem comprometer sua integridade estrutural. Em estruturas de concreto armado, deve-se ter atenção especial aos pilares, cuja capacidade portante é reduzida significativamente em altas temperaturas e seu colapso, de natureza brusca, pode resultar na instabilidade global da estrutura. As reduções nas propriedades mecânicas dos materiais aliadas a lascamentos, fissuras e deformações excessivas podem comprometer seu desempenho, tornando-se necessária a verificação da segurança em situações de incêndio. Com o objetivo de analisar a resistência residual de colunas de concreto armado submetidas a altas temperaturas, foram realizados ensaios de compressão em corpos-de-prova cilíndricos de concreto simples de 5x10 cm submetidos a diferentes temperaturas (200, 400, 600, 800 e 1000 graus Celsius) e de concreto armado de 15x30 cm com diferentes configurações de estribos e submetidos a distintos tempos de exposição (30, 60, 90 e 120 minutos). Em ambos os ensaios, os corpos-de-prova foram resfriados em temperatura ambiente. Os resultados do programa experimental comprovam a perda de resistência à compressão e seus valores foram comparados a modelos numéricos e ao Método da Isoterma de 500 graus Celsius constante na ABNT NBR 15200 de 2004 e no EUROCODE 2. / [en] Concrete is well-known for exhibiting good performance when exposed to elevated temperatures because its low thermal conductivity coefficient, noncombustible properties and reduced emission of toxic gases. However, due to its heterogeneous composition, concrete undergoes physical, chemical and mechanical alterations that can compromise its structural integrity. In reinforced concrete structures, special attention should be paid to the columns, in bearing capacity is reduced significantly at elevated temperatures and their collapse, naturally brittle, may result in overall instability of structure. Reductions in the mechanical properties of the steel and concrete combined with spalling, cracking and excessive deformation compromise its performance, making it necessary to verify the safety in fire situations. In order to analyze the residual strength of reinforced concrete columns submitted to elevated temperatures, compression tests were carried out on plain concrete cylindrical specimens of 5x10 cm exposed to different temperatures (200, 400, 600, 800 and 1000 degrees Celsius) and on reinforced concrete of 15x30 cm considering different stirrups configuration and exposure times (30, 60, 90 and 120 minutes). In both tests, the specimens were cooled to room temperature. The results of the experimental program demonstrate the loss of compression strength and their values were compared to those obtained numerical models and to the Isotherm Method of 500 degrees Celsius, recommended in ABNT NBR 15200 of 2004 and in EUROCODE 2.

Die Arbeit beschäftigt sich mit der Weiterentwicklung des verdämmten Druckversuches zur Bestimmung experimenteller Daten an verschiedenen Keramik- und Glassorten. Die untersuchten Materialien (Al2O3, TiB2, B4C, Floatglas, schweres Flintglas) lagen in Form von Fragmenten (Bruchstücken) vor und wurden aus realen Impaktexperimenten wiedergewonnen. Zusätzlich wurden thermisch vorgeschädigte Aluminiumoxidzylinder in die Betrachtungen einbezogen. Daten granulierter bzw. vorgeschädigter spröder Materialien sind von besonderem Interesse für Finite Element Rechnungen, um beispielsweise experimentell sehr aufwendige Beschußversuche rechnerisch zu simulieren.Als Untersuchungsmethode wurde der verdämmte Druckversuch verwendet und sowohl an quasistatische als auch an schlagdynamische Belastungsbedingungen angepaßt. Außerdem wurden die entwickelten Testaufbauten für sehr hohe hydrostatische Drücke optimiert. In den quasistatischen Experimenten konnten damit Drücke von 380 MPa bis 1960 MPa und in den dynamischen Versuchen von 495 MPa bis 2060 MPa erreicht werden. Im Ergebnis wurden mechanische Kennwerte der granulierten bzw. vorgeschädigten Materialien ermittelt (Restfestigkeit, Verdichtungsverhalten) und deren Schädigungsgrad vor und nach den Versuchen bestimmt (Rasterelektronenmikroskopie und Messung der spezifischen Oberfläche). Die vielversprechenden Resultate der verschiedenen Keramiken und Gläser wurden verglichen und die Materialien im Hinblick auf ihr Energieaufnahmevermögen unter schlagartiger Belastung bewertet.

The objective of this study is to develop test protocols for comparing the effectiveness of fiber-reinforced concrete (FRC) mixtures with high-performance steel fibers. Steel fibers can be added to fresh concrete to increase the tensile strength, ductility, and durability of concrete structures. In order to quantify steel fiber-reinforced concrete (SFRC) mixtures for field applications, a material test capable of predicting the performance of SFRC for field loading conditions is required. However, current test methods used to evaluate the structural properties of FRC (such as residual strength and toughness) are widely regarded as inadequate; a simple, accurate, and consistent test method is needed. It was determined that the Double-Punch Test (DPT), originally introduced by Chen in 1970 for plain concrete, could be extended to fiber-reinforced concrete to satisfy this industry need. In the DPT, a concrete cylinder is placed vertically between the loading platens of the test machine and compressed by two steel punches located concentrically on the top and bottom surfaces of the cylinder. It is hypothesized that the Double-Punch Test is capable of comparing future fiber-reinforcement design options for use in structural applications, and is suitable for evaluating FRC in general. The DPT Research and Testing Program was administered to produce sufficient within-laboratory data to make conclusions and recommendations regarding the simplicity, reliability, and reproducibility of the DPT for evaluating the performance of SFRC. Several variables (including fiber manufacturer, fiber content, and testing equipment) were evaluated to verify the relevance of the DPT for FRC. In this thesis, the results of 120 Double-Punch Tests are summarized and protocols for its effective application to fiber-reinforced concrete are recommended. Also, fundamental data is provided that indicates the DPT could be standardized by national and international agencies, such as the American Society of Testing and Materials (ASTM), as a method to evaluate the mechanical behavior of FRC. This project is sponsored by the Texas Department of Transportation (TxDOT) through TxDOT Project 6348, "Controlling Cracking in Prestressed Concrete Panels and Optimizing Bridge Deck Reinforcing Steel," which is aimed at improving bridge deck construction through developments in design details, durability, and quality control procedures. / text

Diplomová práce se zabývá návrhem metodiky výpočtu závislého šíření trhlin ve více konstrukčních částech s využitím programu AFGROW. Prezentována metodika, která také zahrnuje stanovení zbytkové pevnosti, byla aplikována v damage tolerance analýzách vybraných míst na konstrukci křídla L 410 NG.