The U.S. military requires the ability to rapidly deploy troops, equipment, and materials anywhere in the world. Recent operations have brought attention to the need to utilize austere, unsurfaced, and sometimes sub-standard airfields within a theater of interest. These airfields may require additional taxiways and aprons. One option for the rapid construction of such is airfield matting systems. The focus of the work for this thesis was commercially available airfield matting systems to support large military transport aircraft, such as the C 17. Several test sections with differing strength soils were built with chosen mats tested in an elimination method, using a load cart that simulates contingency loading of one main gear of the C 17. Matting systems were evaluated based on logistical and assembly requirements, and deformation and damage sustained during traffic. A modeling effort was performed to investigate the potential of a simple model to predict the response of these matting systems under full-scale testing.

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No description available.

Cold-formed steel roof truss systems that use complex stiffener patterns in existing hat shape members for both top and bottom chord elements are a growing trend in the North American steel framing industry. When designing cold-formed steel sections, a structural engineer typically tries to improve the local buckling behavior of the cold-formed steel elements. The complex hat shape has proved to limit the negative influence of local buckling, however, distortional buckling can be the controlling mode of failure in the design of chord members with intermediate unbraced lengths. The chord member may be subjected to both bending and compression because of the continuity of the top and bottom chords. These members are not typically braced between panel points in a truss. Current 2001 North American Specifications (NAS 2001) do not provide an explicit check for distortional buckling. This dissertation focuses on the behavior of complex hat shape members commonly used for both the top and bottom chord elements of a cold-formed steel truss. The results of flexural tests of complex hat shape members are described. In addition, stub column tests of nested C-sections used as web members and full scale cold-formed steel roof truss tests are reported. Numerical analyses using finite strip and finite element procedures were developed for the complex hat shape chord member in bending to compare with experimental results. Both elastic buckling and inelastic postbuckling finite element analyses were performed. A parametric study was also conducted to investigate the factors that affect the ultimate strength behavior of a particular complex hat shape. The experimental results and numerical analyses confirmed that modifications to the 2001 North American Specification are necessary to better predict the flexural strength of complex hat shape members, especially those members subjected to distortional buckling. Either finite strip or finite element analysis can be used to better predict the flexural strength of complex hat shape members. Better understanding of the flexural behavior of these complex hat shapes is necessary to obtain efficient, safe design of a truss system. The results of these analyses will be presented in the dissertation. / Ph. D.

Orthotropic steel deck has been widely used over the decades especially on long-span bridges due to its light weight and fast construction. However fatigue cracking problems on the welds have been observed in many countries. Rib-to-deck welds need special care since they are directly under wheel loads, which cause large local stress variations and stress reversals. Currently the only requirement by AASHTO bridge code is that the rib-to-deck welds need to be fabricated as one-sided partial penetration welds with minimum penetration of 80% into the rib wall thickness. However considering the thin rib plate thickness, it is very difficult to achieve this penetration without a "melt-through" or "blow-through" defect. Large cost has been caused for the repair. However recent research has found that the fatigue performance of the rib-to-deck weld is not directly related to its penetration. Other factors contribute to the fatigue performance as well. Therefore, alternative requirements which are more cost-effective and rational are desired. The objective of this research is to provide recommendations to the design and fabrication of rib-to-deck welds by investigating their fatigue performance with different weld dimensions, penetrations, and welding processes. Fatigue tests were performed to 95 full-scale single-rib deck segments in 8 specimen series fabricated with different welding processes and root gap openness. Specimens were tested under cyclic loads till failure. Three failure modes were observed on both weld toes and the weld root. Test results showed that the fatigue performance was more affected by other factors such as failure mode, R-ratio and root gap openness, rather than the weld penetration. The failure cycles were recorded for the following S-N curve analysis. Finite element analysis was performed to determine the stress state on the fatigue cracking locations. Special considerations were made for the application of hot-spot stress methodology, which post-processes the FEA results to calculate the stress values at cracking locations with the structural configuration taken into account. The hot-spot stress range values were derived and adjusted accounting for the fabrication and test error. Hot-spot S-N curves were established for each specimen series. Statistical analyses were performed to study in depth the effect of weld dimensions and test scenarios. Multiple linear regression (MLR) was performed to investigate the effects of different weld dimensions; and multi-way analysis of covariance (Multi-way ANCOVA) for the effects of specimen series, failure mode, R-ratio and weld root gap. It was found that the weld toe size was more relevant to the fatigue performance, other than the weld penetration. The failure mode and R-ratio were very influential on the fatigue performance. Recommendations to the weld geometry were proposed based on the MLR model fitting. S-N data were re-categorized based on ANCOVA results and the lower-bound S-N curve was established. AASHTO C curve was recommended for the deck design. / Master of Science

Les inclusions souples, telles que les colonnes ballastées, sont constituées de matériaux granulaires purement frottants et réalisées à partir de différentes méthodes, afin d’entraîner des améliorations des performances du sol (réduction des tassements, augmentation de la capacité portante, etc.). Dès leur origine, fin des années 1950, ces colonnes ont été employées en maillages réguliers sous des ouvrages de grandes dimensions (remblais, réservoirs, dallages…) apportant des surcharges uniformément réparties. Depuis plusieurs années, les colonnes sont souvent mises en œuvre de manière isolée ou en groupe d’éléments limités (2 à 6 unités) et coiffées par une semelle rigide. Il est donc important de prévoir le comportement mécanique de ces inclusions sous des semelles rigides compte tenu de leur application à de nombreuses structures (logements, bâtiments industriels…). L’objectif principal du travail présenté ici est : (1) d’analyser et de quantifier l’amélioration du sol obtenue par la mise en place des colonnes ballastées, dans un sol argileux, sous semelles rigides et (2) de développer une méthodologie numérique permettant de valider les résultats d’essais en grandeur réelle. Pour atteindre ces objectifs, une importante campagne d’essais en grandeur réelle a été élaborée puis mise en œuvre. Il s’agit d’une campagne de sondages de pénétration statique réalisés avant et après la mise en place des colonnes (isolées ou en groupe de 3 de 1,8 m d’entre-axe), ainsi que d’essais de chargement comparatifs en grandeur réelle pendant 77 jours, de semelles (1,2 x 1,2 x 0,5 m) sur une colonne ballastée et sur le sol naturel, et de semelles (2,3 x 2,5 x 0,5 m) sur trois colonnes et sur le sol naturel. Une importante instrumentation du sol et des colonnes (inclinomètres, sondes de pression interstitielle, capteurs de pression totale verticale) a été mise en place avant la réalisation des colonnes afin de déterminer l’amélioration du sol et le comportement à la rupture de ces inclusions. Puis, les résultats expérimentaux (déplacements horizontaux et verticaux, et contraintes totales verticales) ont été confrontés aux résultats de modélisations numériques en 2 (PLAXIS 2D V8) et 3D (FLAC 3D). Ont notamment été étudiés en 2D les outils numériques permettant de simuler le processus de mise en œuvre d’une colonne par refoulement latéral du sol / Flexible inclusions, such as stone columns, are made up of purely frictional granular material and are constructed using a variety of methods, in order to improve the soil (settlement reduction, increase in bearing capacity…). At their beginning, end of the 1950’s, stone columns were placed in a regular mesh under great structures (embankments, tanks, slabs…) bringing uniformly distributed loads. Since several years, these columns are often constructed as isolated elements or in groups of a certain number (generally 2 to 6) on top of which is placed a rigid footing. It is thus important to predict the stone column’s mechanical behavior under rigid footings knowing that they can be used under a broad variety of structures (accomodation, industrial buildings…). The main purpose of the work presented in this thesis is to: (1) analyse and quantify the soil’s improvement thanks to the construction of stone columns, in a clayey soil, under rigid footings and (2) to develop a numerical methodology allowing us to validate full scale experimental results. In order to achieve this, an important full scale load test campaign was first conceived and then set up. Cone penetration tests were carried out before and after stone column construction (in isolated elements or in groups of three columns located at the corners of a 1,8 m faced triangle). Another part of this campaign deals with comparative full scale load tests carried out during 77 days: two rigid footings of 1.2 x 1.2 x 0.5 m, one on the natural soil and one placed on top of a stone column, and two rigid footings of 2.3 x 2.5 x 0.5 m, one on the natural soil and the other one placed on three stone columns. An important soil and column monitoring (inclinometers, pore pressure cells, total vertical load pressure cells) was set up before column construction in order to measure the soil’s improvement and the column’s failure behavior. The the experimental results (lateral and vertical displacements, and total vertical pressures) were compared to numerical ones in 2 (PLAXIS 2D V8) and 3D (FLAC 3D). In 2D, part of the work was focused on simulating the installation process of a stone column by lateral displacement of the soil

The lateral resistance of pile foundations is typically based on the performance of round piles even though other pile types are used. Due to lack of data there is a certain level of uncertainty when designing pile foundations other than round piles for lateral loading. Theoretical analyses have suggested that square sections will have more lateral resistance due to the increased side shear resistance, no test results have been available to substantiate the contention. Full-scale lateral load tests involving pile shapes such as circular, circular wrapped with high density polyethylene sheeting, square, H, and circular with a corrugated metal sleeve have been performed considering the influence of soil-pile interaction on lateral load resistance. The load test results, which can be summarized as a p-y curve, show higher soil resistance from the H and square sections after accounting for differences in the moment of inertia for the different pile sections. The increased soil resistance can generally be accounted for using a p-multiplier approach with a value of approximately 1.25 for square or 1.2 for H piles relative to circular piles. It has been determined that high density polyethylene sheeting provides little if any reduction in the lateral resistance when wrapped around a circular pile. Circular piles with a corrugated metal sleeve respond to lateral loading with higher values of lateral resistance than independent circular piles in the same soil.

In SKB’s Äspö Hard Rock Laboratory (HRL) a full scale test of a concrete plug,part of a sealing structure for the depository of spent nuclear fuel, has been carriedout. The aim of this thesis is to evaluate the behavior of the concrete plug and howit corresponds to assumptions made during the design. The concrete plug is domeshaped, un-reinforced and casted in situ with low-pH concrete. It will be exposed tohigh water and swelling pressures and designed for a life span of 100 years. Duringthe first years it shall also prevent water leakage from the inside of the depositiontunnel. Before the pressure is applied, the concrete plug is assumed to de-bond fromthe rock due to autogenous and cooling shrinkage. The gap between the concrete androck is then grouted during cooling and the concrete plug will hence be prestressedwhen the cooling is stopped. The concrete plug is analyzed with the measurement data from the full scale testwith comparisons to results from finite element simulations. The performed measurementsinclude form pressure, internal strain and temperature, concrete plugdisplacements in the tunnel alignment, displacements relative to the rock and ambienttemperatures. Two assumptions have been made during the evaluation; fullbond to the rock or no bond to the rock. The results are also compared to twosimilar experiment that were previously performed. The results indicate that the concrete did de-bond from the rock before grouting tosome extent. It is plausible that a selective de-bonding was obtained. Due to highwater leakage, were cables for the measurement equipment are drawn out from theconcrete plug, the concrete plug was not exposed to the planed maximum pressureload. Results indicate that a water pressure is acting on the concrete plug frominside the rock slot which was not assumed during the design. / I SKB:s Äspölaboratoriet har ett fullskaleförsök på en betongplugg, del av ett pluggsystemför förvaret av kärnavfall, utförts. Syftet med denna uppsats var attutvärdera betongpluggens beteende under fullskaleförsöket och hur det förhållersig till gjorda antaganden under dess utformning. Betongpluggen är kupolformad,oarmerad och platsgjuten med låg-pH-betong. Höga vatten- och svälltryck kommerverka på betongpluggen som är utformad för en livstid på 100 år. Under deförsta åren ska den även motverka läckage från insidan av deponeringstunneln. Innantrycklasten läggs på är det antaget att betongpluggen släpper från berget till följd avautogen krympning och kylning. Utrymmet mellan betongen och berget injekterasoch betongpluggen kommer således vara förspänd efter att kylningen upphört. Betongpluggen är analyserad med mätdata från fullskaleförsöket som jämförts medresultat från finita element analyser. Mätningarna inkluderar formtryck, inre töjningaroch temperaturer, deformationer i tunnelriktningen, deformationer relativt bergetoch lufttemperatur utanför betongpluggen. Två antaganden har gjorts under utvärderingen;att betongen är fast i berget eller att den är fri från berget. Resultaten jämförsäven med två liknande fullskaleförsök som utförts tidigare. Resultaten tyder på att betongpluggen till viss del släppt från berget innan injekteringen.Det är troligt att den släppt på vissa ställen och på andra inte. På grundav för högt vattenläckage där de ingjutna mätinstrumentens kabelgenomföring utförts,kunde inte betongpluggen belastas till det maximala tryck som var planerat.Resultaten tyder på att ett vattentryck verkar på betongpluggen mellan berget ochbetongen vilket inte var antaget under konstruktionen.

The lateral resistance of pile foundations has typically been based on the resistance of circular pipe piles. In addition, most instrumented lateral load tests and cases history have involved circular piles. However, piles used in engineering practice may also be non-circular cross-section piles such as square and H piles. Some researchers have theorized that the lateral resistance of square piles will be higher than that of circular piles (Reese and Van Impe, 2001; Briaud et al, 1983; Smith, 1987) for various reasons, but there is not test data to support this claims. To provide basic comparative performance data, lateral load tests were performed on piles with circular, square and H sections. To facilitate comparisons, all the tests piles were approximately 12 inches in width or diameter and were made of steel. The square and circular pipe sections had comparable moments of inertia; however, the H pile was loaded about the weak axis, as is often the case of piles supporting integral abutments, and had a much lower moment of inertia. The granular fill around the pile was compacted to approximately 95% of the standard Proctor maximum density and would be typical of fill for a bridge abutment. Lateral load was applied with a free-head condition at a height of 1 ft above the ground surface. To define the load-deflection response, load was applied incrementally to produce deflection increments of about 0.25 inches up to a maximum deflection of about 3 inches. Although the square and pipe pile sections had nearly the same moment of inertia, the square pile provided lateral resistance that was 20 to 30% higher for a given deflection. The lateral resistance of the H pile was smaller than the other two pile shapes but higher than what it is expected based on the moment of inertia. Back analysis with the computer program LPILE indicates that the pile shape was influencing the lateral resistance. Increasing the effective width to account for the shape effect as suggested by Reese and Van Impe (2001) was insufficient to account for the increased resistance. To provide agreement with the measured response, p-multipliers of 1.2 and 1.35 were required for the square pile and H piles, respectively. The analyses suggest that the increased resistance for the square and H pile sections was a result of increases in both the side shear and normal stress components of resistance. Using the back-calculated p-multipliers provided very good agreement between the measured and computed load-deflection curves and the bending moment versus depth curves.

Assessing existing bridges is an important task in the sustainable management ofinfrastructure. In practice, structural bridge assessments are usually conducted usingtraditional and standardised methods, despite knowledge that these methods oftenprovide conservative estimates. In addition, more advanced methods are available, suchas nonlinear finite element (FE) analysis, that are used for research purposes and cansimulate the structural behaviour of bridges more accurately. Therefore, it would beuseful to develop practical and reliable procedures for refined assessments using theseadvanced techniques.Focusing on the ultimate load-carrying capacity of existing concrete bridges, this thesispresents a procedure for structural assessments. The fundamental idea is to improve theassessment successively, as necessary to predict bridges’ structural behaviour adequately.The procedure involves a multi-level assessment strategy with four levels of structuralanalysis, and an integrated framework for safety verification. At the initial level (Level 1)of the multi-level strategy, traditional standardised methods are used, no failures arecovered implicitly in the structural analysis and action effects are verified using localresistances calculated using analytical models. In the subsequent enhanced levels (Levels2 – 4), nonlinear FE analysis is used for stepwise integration of the verification of flexural,shear-related and anchorage failures into the structural analysis. The framework for safetyverifications includes partial safety factor (PSF), global resistance safety factor (GRSF) andfull probabilistic methods. Within each of these groups, verifications of desired safetymargins can be conducted with varying degrees of complexity.To demonstrate and evaluate the proposed structural assessment procedure, comparativestudies have been carried out, based on full-scale tests of a prestressed concrete bridge.This was the Kiruna Bridge, located in the northernmost city in Sweden, which was duefor demolition as part of a city transformation project, necessitated by large grounddeformations caused by the large nearby mine. Thus, it was available for destructiveexperimental investigation within the doctoral project presented in this thesis. The bridgehad five continuous spans, was 121.5 m long and consisted of three parallel girders with a connecting slab at the top. Both the girders and slab were tested to failure to investigatetheir structural behaviour and load-carrying capacity. Non-destructive and destructivetests were also applied to determine the residual prestress forces in the bridge girders andinvestigate the in situ applicability of methods developed for this purpose. The so-calledsaw-cut method and decompression-load method were used after refinement to enabletheir application to structures of such complexity. The variation of the experimentallydetermined residual prestress forces was remarkably high, depending on the sectioninvestigated. There were also high degrees of uncertainty in estimated values, and thusare only regarded as indications of the residual prestress force.Level 1 analysis of the multi-level assessment strategy consistently underestimatedcapacity, relative to the test results, and did not provide accurate predictions of the shearrelatedfailure observed in the test. With linear FE analysis and local resistance modelsdefined by the European standard, Eurocode 2, the load-carrying capacity wasunderestimated by 32 % for the bridge girder and 55 % for the bridge deck slab. At theenhanced level of structural analysis (Level 3), nonlinear FE analyses predicted thecapacities with less than 2 % deviation from the test results and correctly predicted thefailure mode. However, for existing bridges there are many uncertainties, for instance,the FE simulations were sensitive to the level of residual prestressing, boundaryconditions and assumed material parameters. To accurately take these aspects intoaccount, bridge-specific information is crucial.The complete structural assessment procedure, combining the multi-level strategy andsafety verification framework, was evaluated in a case study. Experiences from theprevious comparative studies were used in an assessment of the Kiruna Bridge followingthe Swedish assessment code. The initial assessment at Level 1 of the multi-level strategyand safety verification, using the PSF method, indicated that the shear capacity of one ofthe girders was critical. The most adverse load case (a combination of permanent loads,prestressing and variable traffic loads) was further investigated through enhancedstructural analyses implicitly accounting for flexural and shear-related failures (Level 3).Nonlinear FE analysis and safety evaluation using the PSF method, several variants of theGRSF method and the full probabilistic analysis for resistance indicated that the permittedaxle load for the critical classification vehicle could be 5.6 – 6.5 times higher than thelimit obtained from the initial assessment at Level 1. However, the study also indicatedthat the model uncertainty was not fully considered in these values. The modeluncertainty was shown to have strong effects on the safety verification and (thus)permissible axle loads. The case study also highlighted the need for a strategy forsuccessively improving structural analysis to improve understanding of bridges’ structuralbehaviour. The refined analysis indicated a complex failure mode, with yielding of thestirrups in the bridge girders and transverse flexural reinforcement in the bridge deck slab,but with a final shear failure of the slab. It would be impossible to capture suchcomplexity in a traditional standardised assessment, which (as mentioned) indicated thatthe shear capacity of the girder limited permissible axle loads. However, nonlinear FEanalyses are computationally demanding, and numerous modelling choices are required.Besides a strategy for rationally improving the analysis and helping analysts to focus oncritical aspects, detailed guidelines for nonlinear FE analysis should be applied to reduce the analyst-dependent variability of results and (thus) the model uncertainty. Clearly, toensure the validity of bridge assessment methods under in situ conditions, theirevaluations should include in situ tests. This thesis presents outcomes of such tests, therebyhighlighting important aspects for future improvements in the assessment of existingbridges.