Avhandling--Tekniska högskolan, Stockholm. / Extra t.p., with thesis statement, inserted. Includes bibliographical references (p. [124]).

Thesis (M.S.)--University of Missouri, School of Mines and Metallurgy, 1939. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed April 7, 2010) Includes bibliographical references (p. 57-58).

Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1899. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed November 20, 2008)

No description available.

Thesis (M.C.E.)--University of Delaware, 2006. / Principal faculty advisor: Michael J. Chajes, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

Gegenstand der vorliegenden Arbeit ist die Entwicklung einer optimalen Tragstruktur für Netzwerkbogenbrücken. Dabei wird die systematische Nutzung der Optimierungspotenziale dieses Brückentragwerkes an ausgewählten Tragwerkselementen erarbeitet. Es werden Lösungsvorschläge für die System- und Detailausbildung sowie Berechnungs- und Entwurfsgrundlagen entwickelt. Die Schwerpunkte der Arbeit bilden die Entwicklung von ermüdungssicheren Hängeranschlusskonstruktionen, statisch effizienten Hängernetzen sowie Bögen, die sich durch eine hohe Tragfähigkeit bei gleichzeitig geringem Materialverbrauch auszeichnen. Um eine ausreichende Ermüdungssicherheit der in dieser Hinsicht maßgebenden Hängeranschlusskonstruktionen zu gewährleisten, ist es notwendig, die risserzeugenden Spannungsspitzen zu minimieren und möglichst einen homogenen Spannungsverlauf über das gesamte Bauteil zu erzeugen. Mit Hilfe einer parametergestützten Gestaltoptimierung und anschließender Topologieanpassung wird zunächst eine optimale Lösung für die Hängeranschlusskonstruktion entworfen. Anschließend erfolgt die Entwicklung einer Bestimmungsgleichung für die Kerbwirkungszahl dieser Anschlusskonstruktion, welche die Anwendung des Kerbspannungskonzeptes für Hängeranschlüsse ermöglicht. Zur effizienten Nutzung der statischen Vorteile von Netzwerkbogenbrücken ist die Anordnung der Hänger von großer Bedeutung. Um die vorteilhafteste Hängeranordnung zu ermitteln, werden fünf mögliche Hängernetze mit variierenden Hängerneigungsparametern, Hängeranzahlen und Stützweiten hinsichtlich gezielt ausgewählter statischer Kriterien untersucht und bewertet. Daraus resultierend werden Empfehlungen formuliert, die dem Ingenieur die Wahl eines für entsprechende Rahmenbedingungen geeigneten Hängernetzes erleichtern. Auch die konstruktive Ausführung des Bogens sowie des oberen Windverbandes und das damit verbundene Tragverhalten sind beim Entwurf einer effizienten Netzwerkbogenbrücke von großer Bedeutung. Deswegen wird der Einfluss von Form, Geometrie und Steifigkeit des Bogens sowie von Ausführung und Konstruktion anderer Tragwerksteile auf die Bogenstabilität analysiert. Darauf aufbauend erfolgt die Optimierung dieser Konstruktionsparameter, um die Stahlmasse des Bogens ohne maßgebliche Reduzierung der Tragfähigkeit zu minimieren. Zusätzlich werden verschiedene Ersatzimperfektionen bezüglich ihrer Auswirkung auf die rechnerische Bogenstabilität untersucht und die maßgebenden Vorverformungen hinsichtlich ihrer Form und ihrer Größe herausgestellt. In ausgewählten Beispielen werden abschließend die entwickelten Lösungen mit Bauwerken aus der Praxis verglichen, um die Effizienz des optimierten Tragwerkes zu demonstrieren. / This work of research will tackle the development of an optimal structure for network arch bridges. The systematic employment of potentials to optimize these bridge structures will be examined for selected structural members. Suggestions for the construction of the bridge system and of selected details as well as basics for calculation and design will be developed. This paper will focuses mainly on the design of fatigue-proof hanger connections, statically efficient hanger networks as well as arches, which have a high load carrying capacity along with low material consumption. In order to provide sufficient security against fatigue failure for the decisive connections of the hanger bars, stress peaks that cause cracks have to be minimized and homogeneous stress distribution within the whole element has to be ensured. Initially, this paper will delineate an optimal solution for hanger connections by means of parameter-based shape optimization and subsequent topology adaptation. In the following, an analytic formula for the stress concentration factor of this connection will be developed in order to enable the application of the notch stress concept for hanger connections. To apply the static advantages of network arch bridges efficiently, the arrangement of the hangers is essential. In order to determine the most efficient hanger arrangement, five possible hanger arrangements with varying parameters (slope of the hangers, number of the hangers and span of the bridge) will be analyzed and evaluated with respect to systematically selected static criteria. On the basis of these investigations, recommendations for engineers how to choose an optimized hanger arrangement according to different geometrical bridge parameters will be made. Additionally, the constructive design of the arches and the upper wind bracing as well as the associated structural behavior are significant when an efficient network arch bridge is to be designed. For this reason, this paper will analyze the influence of the arch-shape, the arch-geometry and the arch-stiffness as well as the design and construction of other structural members on the stability of the arch. Based on these results, the constructive parameters will be optimized in order to reduce the steel weight of the arch without significantly reducing the load carrying capacity. Furthermore, the influence of different imperfections on the arch stability will be analyzed and the form and size of the decisive initial deflections emphasized. Finally, systematically selected examples will provide a comparison between the developed solutions and existing bridge structures in order to demonstrate the efficiency of the optimized structure.

The influence of the hanger configuration in the arch and deck bending moments under asymmetric loads is widely used nowadays for improved designs of arch bridges. In this work, by means of a parametric study, those hanger configurations that most efficiently increase both the natural frequencies and buckling factors are identified, simultaneously evaluating the dynamic and static performance of timber arch footbridges. A parametric FEM model allows to evaluate the performance of vertical, Nielsen, fan and network hanger configurations together with combinations of them among others for a three-hinge timber arch. The impact of other relevant design choices such as the number of hinges in the arch or the arch slenderness ratio is jointly addressed allowing for design recommendations. The results show a convergence of the natural frequencies regardless of the configuration of the hangers when increasing the number of them. Moreover, the performance of the studied hanger configurations is improved by introducing inclined hangers significantly increasing natural frequencies and buckling factors of the system. This highlights the importance of the stabilizing horizontal reaction appearing at the deck hanger anchor points and thereby improving the bending moment distribution at the arch. Furthermore, the analyses show that the combination of Nielsen and vertical hangers achieves both the largest natural frequency and buckling factor for a reasonable number of hangers. This contrasts with the low sensitivity of the static and dynamic performance that the vertical hanger configuration shows in relation to changes in the number of hangers, arch rise or arch stiffness among others. Additionally, an important consideration when designing three hinge arch bridges is found to be to prevent a local buckling mode from appearing at the crown of the arch. This can also be done by the right choice of the number and configuration of hangers, as has been shown in the thesis. The results produced in this work can be used to guide engineers towards designing arch bridges with higher static capacity and better dynamic performance while reducing at the same time the material consumption. Furthermore, the findings of the work open up the way towards optimization of arch bridge structures.

Gegenstand der vorliegenden Arbeit ist die Entwicklung einer optimalen Tragstruktur für Netzwerkbogenbrücken. Dabei wird die systematische Nutzung der Optimierungspotenziale dieses Brückentragwerkes an ausgewählten Tragwerkselementen erarbeitet. Es werden Lösungsvorschläge für die System- und Detailausbildung sowie Berechnungs- und Entwurfsgrundlagen entwickelt. Die Schwerpunkte der Arbeit bilden die Entwicklung von ermüdungssicheren Hängeranschlusskonstruktionen, statisch effizienten Hängernetzen sowie Bögen, die sich durch eine hohe Tragfähigkeit bei gleichzeitig geringem Materialverbrauch auszeichnen. Um eine ausreichende Ermüdungssicherheit der in dieser Hinsicht maßgebenden Hängeranschlusskonstruktionen zu gewährleisten, ist es notwendig, die risserzeugenden Spannungsspitzen zu minimieren und möglichst einen homogenen Spannungsverlauf über das gesamte Bauteil zu erzeugen. Mit Hilfe einer parametergestützten Gestaltoptimierung und anschließender Topologieanpassung wird zunächst eine optimale Lösung für die Hängeranschlusskonstruktion entworfen. Anschließend erfolgt die Entwicklung einer Bestimmungsgleichung für die Kerbwirkungszahl dieser Anschlusskonstruktion, welche die Anwendung des Kerbspannungskonzeptes für Hängeranschlüsse ermöglicht. Zur effizienten Nutzung der statischen Vorteile von Netzwerkbogenbrücken ist die Anordnung der Hänger von großer Bedeutung. Um die vorteilhafteste Hängeranordnung zu ermitteln, werden fünf mögliche Hängernetze mit variierenden Hängerneigungsparametern, Hängeranzahlen und Stützweiten hinsichtlich gezielt ausgewählter statischer Kriterien untersucht und bewertet. Daraus resultierend werden Empfehlungen formuliert, die dem Ingenieur die Wahl eines für entsprechende Rahmenbedingungen geeigneten Hängernetzes erleichtern. Auch die konstruktive Ausführung des Bogens sowie des oberen Windverbandes und das damit verbundene Tragverhalten sind beim Entwurf einer effizienten Netzwerkbogenbrücke von großer Bedeutung. Deswegen wird der Einfluss von Form, Geometrie und Steifigkeit des Bogens sowie von Ausführung und Konstruktion anderer Tragwerksteile auf die Bogenstabilität analysiert. Darauf aufbauend erfolgt die Optimierung dieser Konstruktionsparameter, um die Stahlmasse des Bogens ohne maßgebliche Reduzierung der Tragfähigkeit zu minimieren. Zusätzlich werden verschiedene Ersatzimperfektionen bezüglich ihrer Auswirkung auf die rechnerische Bogenstabilität untersucht und die maßgebenden Vorverformungen hinsichtlich ihrer Form und ihrer Größe herausgestellt. In ausgewählten Beispielen werden abschließend die entwickelten Lösungen mit Bauwerken aus der Praxis verglichen, um die Effizienz des optimierten Tragwerkes zu demonstrieren. / This work of research will tackle the development of an optimal structure for network arch bridges. The systematic employment of potentials to optimize these bridge structures will be examined for selected structural members. Suggestions for the construction of the bridge system and of selected details as well as basics for calculation and design will be developed. This paper will focuses mainly on the design of fatigue-proof hanger connections, statically efficient hanger networks as well as arches, which have a high load carrying capacity along with low material consumption. In order to provide sufficient security against fatigue failure for the decisive connections of the hanger bars, stress peaks that cause cracks have to be minimized and homogeneous stress distribution within the whole element has to be ensured. Initially, this paper will delineate an optimal solution for hanger connections by means of parameter-based shape optimization and subsequent topology adaptation. In the following, an analytic formula for the stress concentration factor of this connection will be developed in order to enable the application of the notch stress concept for hanger connections. To apply the static advantages of network arch bridges efficiently, the arrangement of the hangers is essential. In order to determine the most efficient hanger arrangement, five possible hanger arrangements with varying parameters (slope of the hangers, number of the hangers and span of the bridge) will be analyzed and evaluated with respect to systematically selected static criteria. On the basis of these investigations, recommendations for engineers how to choose an optimized hanger arrangement according to different geometrical bridge parameters will be made. Additionally, the constructive design of the arches and the upper wind bracing as well as the associated structural behavior are significant when an efficient network arch bridge is to be designed. For this reason, this paper will analyze the influence of the arch-shape, the arch-geometry and the arch-stiffness as well as the design and construction of other structural members on the stability of the arch. Based on these results, the constructive parameters will be optimized in order to reduce the steel weight of the arch without significantly reducing the load carrying capacity. Furthermore, the influence of different imperfections on the arch stability will be analyzed and the form and size of the decisive initial deflections emphasized. Finally, systematically selected examples will provide a comparison between the developed solutions and existing bridge structures in order to demonstrate the efficiency of the optimized structure.

This thesis reports on the application of ground penetrating radar (GPR) as a non-destructive technique for the monitoring of ring separation in brick masonry arch bridges. In addition, research is reported on the assessment of the clay capping layer often used in construction as a waterproof backing to arches. The thrust of the research is numerical modelling, verified by large laboratory experiments. Due to the heterogeneity of these structures, the resultant signals from the interaction between the GPR system and the bridge are often complex and hence, hard to interpret. This highlighted the need to create a GPR numerical model that would allow the study of the attributes of reflected signals from various targets within the structure of the bridge. The GPR numerical analysis was undertaken using the finite-difference time-domain (FDTD) method. Since micro regions in the bridge structure need to be modelled, the introduction of subgrids of supporting finer spatial resolution into the standard FDTD method was considered essential in order to economise on the required computational resources. In the main part of this thesis, it is demonstrated how realistic numerical modelling of GPR using the FDTD method could greatly benefit from the implementation of subgrids into the conventional FDTD mesh. This is particularly important when (a) parts of the computational domain need to be modelled in detail (i.e., ring separation between the mortar layers and the brick units, which is the case studied in this thesis); and also (b) when there are features or regions in the overall computational mesh with values of high relative permittivity supporting propagation of waves at very short wavelengths. A scheme is presented that simplifies the process of implementing these subgrids into the traditional FDTD method. This scheme is based on the combination of the standard FDTD method and the unconditionally stable alternating-direction implicit (ADI) FDTD technique. Given that ADI-FDTD is unconditionally stable, its time-step can be set to any value that facilitates the accurate calculation of the electromagnetic fields. By doing so, the two grids can efficiently communicate information across their boundary without requiring to use a time-interpolation scheme. The performance of ADI-FDTD subgrids when implemented into the traditional FDTD method is discussed herein. The developed algorithm can handle cases where the subgrid crosses dielectrically inhomogeneous and/or conductive media. In addition, results from the comparison between the proposed scheme and a commonly employed purely FDTD subgridding technique are presented. After determination of the optimum ADI-FDTD scheme, numerical experiments were conducted and calibrated using GPR laboratory experiments. Good correlations were obtained between the numerical experiments and the actual GPR experiments. It was shown both numerically and experimentally that significant mortar loss between the masonry arch rings can be detected. Dry hairline delaminations between the mortar and the brick masonry are difficult to detect using standard GPR procedures. However, hairline faults containing water produce distinct and detectable GPR responses. In addition, the clay layer was successfully identified and its thickness calculated to a satisfactory accuracy.

As timber structures become increasingly relevant and sought after – since they enable improvements in building time while reducing a structure’s life cycle impacts – streamlining their design can have meaningful economic and environmental implications. For timber footbridges, its design is frequently governed by serviceability criteria linked to excessive vibrations. To address this in design, it is necessary to correctly characterize the structure’s dynamic properties and understand what the leading parameters in its behaviour are. This thesis studied an existing timber arch footbridge, aiming to evaluate its dynamic behaviour both with experimental measurements and with theoretical models. The influence of temperature change over different seasons was considered, particularly around its effect on the asphalt layer – whose stiffness is highly correlated to temperature. The experimental results showed high correlation between temperature and natural frequencies: a variation of +21°C reduced the natural frequency for the 1st transverse mode of the deck by as much as 30.6% while the 1st vertical mode was reduced by 17.7% (variation of 0.029Hz/°C). The damping ratio was also measured, though a definitive correlation between its value and temperature was not identified. This change in behaviour cannot be explained by the influence of the asphalt layer alone however, as there is a high degree of uncertainty around many other components of the bridge and their interactions, such as the connections. Thus, to fully characterize the influence of each component with changing temperature, further experimental tests would have to be performed, or simpler structures with fewer connections should be considered. In designing a new structure, considering the asphalt layer as an added mass is a straightforward way to treat this material at the most critical condition (i.e. no contribution to stiffness). This strategy lead to sufficiently similar results between the computational model and the experimental results at warm temperatures. The asphalt stiffness could perhaps be considered for the 1st transverse mode of the deck, since it is in this mode that the asphalt layer plays its largest contribution.