An important problem confronting the designer of machines and structures which may be subjected to suddenly applied loads is the determination of the actual forces which the members must withstand. This investigation has been confined to a study of impact forces on beams in simple flexure. Margerum (American Society of Testing Materials, 1922) suggested a method whereby the maximum load might be found by obtaining indentations on a calibration bar attached to the moving head of the impact machine, and suggested using this in conjunction with an autographic stress strain diagram. Tests have been made upon both notched and unnotched bars, but the results were not satisfactory. It has been proposed that an accelerometer be designed with which the acceleration could be measured directly. After the acceleration is known the force producing the acceleration can be calculated. The acceleration of a point can be determined by a double differentiation of a space-time diagram. This method is being employed in this thesis. / M.S.

This paper presents the results of testing to determine the appropriateness of the seismic load duration factor and to investigate the possible effect of previous load history from cyclic loading on connection reserve capacity and ductility. The single shear nail and bolt connection types tested represent common connection geometries used in wood construction in the United States. The results of two methods of fully reversing cyclic loading of connections are presented. The first method was a load-controlled test with the applied cyclic loads acting at specified percentages above current nominal design values. The sets of specimens were then ramped to failure and the results were compared to a monotonic control set of specimens to determine if any reduction in connection capacity or ductility had occurred as a result of the cyclic loading. From the load-controlled cyclic testing, it was found that previous cyclic loading at load levels as high as twice current nominal design loads did not adversely affect connection capacity. The second cyclic loading method was a displacement-controlled test that involved successive phases at increasing displacement levels. Each phase consisted of a peak displacement, followed by a series of three decay cycles, then by a series of three cycles at the original peak displacement, the third of which is used to determine the stabilized system. The process is repeated at increasing incremental levels of displacement. The phased displacement stabilized load-displacement curve was fit to an equivalent energy elastic-plastic system for determination of connection parameters. Results from the two cyclic test methods, and from monotonic testing, indicate that the current load duration factor for wind and seismic loading is justified. / Master of Science / incomplete_metadata

Optimization of dynamic systems involving complex non-hermitian matrices is often computationally expensive. Major contributors to the computational expense are the sensitivity analysis and reanalysis of a modified design. The present work seeks to alleviate this computational burden by identifying efficient sensitivity analysis and approximate reanalysis methods. For the algebraic eigenvalue problem involving non-hermitian matrices, algorithms for sensitivity analysis and approximate reanalysis are classified, compared and evaluated for efficiency and accuracy. Proper eigenvector normalization is discussed. An improved method for calculating derivatives of eigenvectors is proposed based on a more rational normalization condition and taking advantage of matrix sparsity. Important numerical aspects of this method are also discussed. To alleviate the problem of reanalysis, various approximation methods for eigenvalues are proposed and evaluated. Linear and quadratic approximations are based directly on the Taylor series. Several approximation methods are developed based on the generalized Rayleigh quotient for the eigenvalue problem. Approximation methods based on trace theorem give high accuracy without needing any derivatives. Operation counts for the computation of the approximations are given. General recommendations are made for the selection of appropriate approximation technique as a function of the matrix size, number of design variables, number of eigenvalues of interest and the number of design points at which approximation is sought. / Ph. D.

Thesis (MScEng (Civil Engineering))--Stellenbosch University, 2008.

Thesis (MScEng)--Stellenbosch University, 2003. / Some digitised pages may appear illegible due to the condition of the original hard copy. / ENGLISH ABSTRACT: A critical evaluation of provisions for imposed loads in the South African Loading Code for design of structures, SABS 0160-1989 (SABS), by comparison with other codes was performed earlier. The evaluation revealed the SABS loading code to be generally non-conservative in its provisions for imposed loads for a range of general and specialist occupancy classes. The SABS provision for imposed loads for inaccessible roofs was found to be substantially non-conservative in comparison with the other codes. An investigation into the imposed load for inaccessible roofs is subsequently performed in order to establish a scientific rationale through which the codified design values may be measured effectively. Due to the lack of information and the large uncertainties involved in the imposed roof load, stochastic treatment of the loads is implemented. This is in line with the stochastic modelling of loads as implemented in general. The approach applied is to select a type of building that can be regarded as a generic example of buildings to which these loads apply, and to discretisize the load into the various sub-mechanisms that translate into the imposed roof load. The probabilistic models for the load mechanisms are then quantified, either through physical load surveys, or through conducting an expert survey for those variables which are not observable. The use of expert opinion as a resource for information is not readily accessible in terms of yielding scientifically defendable results. Therefore, the expert survey is performed as a calibrated experiment whereby weights were calculated for the individual experts' opinions and their opinions combined accordingly. The probabilistic models for the load mechanisms are then translated into load effects by taking into account the physical process resulting in the load effects. By applying these mechanisms in such a way as to maximise the said load effects, equivalent uniformly distributed loads (EUDL's) were calculated for each mechanism. The probabilistic models obtained in terms of the EUDL's pose an easily accessible format through which existing load models and codified provisions can be evaluated. These load models are then utilised to evaluate the SABS provisions in terms of the level of reliability catered for by SABS ultimate limit-state design criteria. It is concluded that the SABS conservatively provides for maintenance loads on the roof, while the reliability for construction loads is non-conservative for large tributary areas and highly non-conservative for small areas. The load models so obtained can further be applied for structural reliability assessment. / AFRIKAANSE OPSOMMING: "n Kritiese evaluasie van die voorskrifte vir opgelegde belastings in die Suid- Afrikaanse Selastingskode vir die ontwerp van strukture, SASS 0160-1989 (SASS) deur 'n vergelyking met ander kodes is vroeër uitgevoer. Die evaluasie het getoon dat die SASS in die algemeen onkonserwatief is in sy voorsiening vir opgelegde belastings oor 'n bereik van algemene en spesialis okkupasie tipes. Die SASS voorskrif vir opgelegde belastings vir ontoeganklike dakke is hoogs onkonserwatief in vergelyking met die ander kodes. 'n Ondersoek na die opgelegde belasting vir ontoeganklike dakke word gevolglik uitgevoer met die doelom 'n wetenskaplike rasionaal daar te stel waardeur die gekodifiseerde voorskrifte effektief gemeet kan word. As gevolg van die gebrek aan inligting en groot onsekerhede betrokke by die opgelegde dakbelasting word stogastiese modellering geimplimenteer. Die aanslag wat gevolg is, is om 'n tipe gebou te selekteer wat beskou kan word as verteenwoordigend van die geboue waarvoor hierdie belastings van toepassing is, en om die belasting te diskretiseer in die verskeie lasmeganismes wat die opgelegde dakbelasting voortbring. Die waarskynlikheidsmodelle vir die lasmeganismes word dan gekwantifiseer, óf deur fisiese opnames, óf deur die uitvoering van 'n ekspertopname vir daardie veranderlikes wat nie waarneembaar is nie. Die gebruik van ekspert opinie as "n bron van inligting is nie maklik toeganklik in terme daarvan om wetenskaplik verdedigbare resultate te lewer nie. Daarom is die ekspert-opname uitgevoer soos 'n gekalibreerde eksperiment waardeur relatiewe gewigte bereken word vir die individuele eksperts en hulopinies daarvolgens gekombineer word. Die waarskynlikheidsmodelle vir die lasmeganismes word dan omgeskakel in laseffekte deur in agneming van die fisiese proses wat die las-effek voortbring. Deur die lasmeganismes op só 'n manier toe te pas dat die betrokke las-effekte gemaksimeer word, word ekwivalent uniforme belastings (EUS's) bepaal. Die waarskynlikheidsmodelle in terme van EUS's bied "n maklik toeganklike formaat waardeur bestaande lasmodelle en gekodifiseerde voorskrifte evalueer kan word. Die lasmodelle word gevolglik gebruik om die SASS voorskrifte te evalueer in terme van die vlak van betroubaarheid wat gehandhaaf word deur SASS limiet-staat ontwerp kriteria. Dit is bepaal dat die SASS konserwatief voorsiening maak vir onderhoudslaste op die dak, maar onkonserwatief tot hoogs-onkonserwatief is vir konstruksie laste. Die bepaalde lasmodelle kan verder toegepas word in strukturele betroubaarheids analise.

Geotechnical engineers are commonly faced with the need to perform ground improvement techniques to achieve the necessary bearing capacity for a project. Some of the most common techniques involve the excavation and replenishment of problematic geomaterial with one of better quality. Common projects, such as road embankments and retaining walls, also require the selection of backfill material. The guidelines for selecting backfill material are typically limited to complying with certain gradation bands, relative densities and allowable fines content. Round-grained silica sand, and beach sand from Boca Raton, FL, were used to generate a total of 16 binary granular mixtures containing different amounts of finer material, for which a series of direct shear tests were conducted. Based on the experimental results, it may be possible to provide an alternative criteria for selecting backfill material based on granulometric parameters and the amount of finer material. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection

No description available.

La compréhension du comportement des matériaux minces sous différentes sollicitations est un enjeu en matière de sécurité. Les modèles de comportement mécanique et de rupture ont évolué pour prendre en compte l’état de contrainte et la vitesse de déformation qui peuvent avoir une influence majeure sur la réponse du matériau. L’identification de ces modèles passe par la caractérisation expérimentale du matériau. Les essais mécaniques représentent donc toujours une étape indispensable au développement des outils numériques. L’objectif de ces travaux est donc de contribuer à l’apport de techniques expérimentales de caractérisation des matériaux. L’ensemble des travaux est illustré par l’étude de deux matériaux : un alliage d’aluminium AA- 2024-T3 et un acier dual phase DP450. L’effet de la vitesse de déformation sur le comportement en traction équi-biaxiale, ainsi que la déformation à rupture en traction équi-biaxiale et en traction en déformation plane sont étudiés. Pour cela, le dépouillement de l’essai de gonflement hydraulique (bulge test) est amélioré et un nouveau dispositif est utilisé pour atteindre des vitesses de déformation intermédiaires de 100 s-1. L’essai de poinçonnement hémisphérique et un nouvel essai de poinçonnement pour la traction en déformation plane sont effectués jusqu’à des vitesses de déformation intermédiaires. L’effet du trajet de chargement sur la déformation à rupture est également étudié. Une méthode de traction uni-axiale sur éprouvettes de grandes dimensions est développée pour appliquer un premier chargement. Ensuite un second chargement en traction équi-biaxiale ou en traction en déformation plane est appliqué jusqu’à rupture. / The understanding of thin materials behavior under various stress state is a current issue for security matters. Constitutive models and failure models evolved to take into account stress state and strain rate effect on material behavior. Experimental characterization of materials is necessary to identify models. Mechanical tests are mandatory for the development of numerical tools. The aim of this thesis is the development of experimental techniques for material characterization. This work is performed on two materials, a AA-2024-T3 aluminum alloy and DP450 dual phase steel. Strain rate effect on the equi-biaxial tension behavior and the failure, and on the plane strain tension failure is studied. For this purpose, we improved the analysis of bulge test and a new device is proposed ion order to attain strain rates up to 100 s-1. Hemispheric punch test and a new punch test dedicated to plane strain tension are proposed at high strain rates. Effect of loading path on failure strain is also studied. A new device for uniaxial tension on large specimens is use to apply the first load, a second loading under equi-biaxial tension or plane strain tension is then applied up to failure.

Abstract not available

The transfer of air travelers with disabilities between a mobility aid and an aircraft seat is a major source of injury for both the travelers and the airline personnel assisting in the transfer. The risk to both parties might be reduced through the biomechanical study of the transfer task. Such study requires that the contact forces acting on the body of the rear transferor be known, including the contact force between the rear transferor and the seat-back. A seat-back mounted force plate was designed and constructed to accurately measure the magnitude and the center of pressure location of normal forces applied to the seat-back. This force plate collects data from four preloaded single component force transducers. The force transducers are mechanically isolated from shear forces to protect them from damage. Testing of the force plate found a normal force magnitude accuracy of 0.19 %FS over the 890 Newton (200 lbf) calibrated range. The force plate was shown to have a horizontal and vertical center of pressure location accuracy of 2.66 and 1.58 millimeters (0.105 and 0.062 inches) RMS respectively over its 343 by 293 millimeter (13.5 by 11.5 inches) measurement range. By measuring forces that may have otherwise been ignored, the seat-back mounted force plate can improve the quality of the biomechanical analysis of aircraft transfers. / Graduation date: 2005