Structural health monitoring and bridge condition assessment

Thesis (Ph.D.) University of Alaska Fairbanks, 2016This research is mainly in the field of structural identification and model calibration, optimal sensor placement, and structural health monitoring application for large-scale structures. The ultimate goal of this study is to identify the structure behavior and evaluate the health condition by using structural health monitoring system. To achieve this goal, this research firstly established two fiber optic structural health monitoring systems for a two-span truss bridge and a five-span steel girder bridge. Secondly, this research examined the empirical mode decomposition (EMD) method’s application by using the portable accelerometer system for a long steel girder bridge, and identified the accelerometer number requirements for comprehensively record bridge modal frequencies and damping. Thirdly, it developed a multi-direction model updating method which can update the bridge model by using static and dynamic measurement. Finally, this research studied the optimal static strain sensor placement and established a new method for model parameter identification and damage detection.Chapter 1: Introduction -- Chapter 2: Structural Health Monitoring of the Klehini River Bridge -- Chapter 3: Ambient Loading and Modal Parameters for the Chulitna River Bridge -- Chapter 4: Multi-direction Bridge Model Updating using Static and Dynamic Measurement -- Chapter 5: Optimal Static Strain Sensor Placement for Bridge Model Parameter Identification by using Numerical Optimization Method -- Chapter 6: Conclusions and Future Work

Optimisation of rigidly jointed frames

2 volsAvailable from British Library Document Supply Centre- DSC:D67685/86 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Rationalization of trusses and yield-line patterns identified using layout optimization

To help engineers to design and analyse structures, various tools exist. However, many of them are complicated and difficult for engineers to master. In industry simple, accurate, and rapid tools are potentially very useful. The development of such tools has thus been the main focus of this thesis. One application is the design of lightweight truss structures. Although techniques have been available to identify efficient truss designs for more than half a century, these are not widely used in industry. A major problem is that the structures generated are often complex in form, so that manufacturing becomes problematic. To address this, the current research explores two rationalization techniques: (i) introducing joint lengths to control the number of joints that exist in the resulting structure; and (ii) utilising geometry optimization to adjust the locations of joints in a truss. The former involves a minor modification to the standard process such that it retains the linear nature of the original problem, while the latter solves a more challenging non-linear optimization problem that can simultaneously simplify (make less complicated) and improve (make lighter) a given truss layout. To ensure a rapid and reliable process for the latter, analytical expressions of functions and their derivatives are supplied to a general purpose non-linear optimizer and various practical issues are also considered. A number of benchmark problems are solved to show the efficacy of the two rationalization techniques. Another application is yield-line analysis of reinforced concrete slabs. Even in the modern computer age, with many engineering analysis procedures successfully computerized, a fully automated means of undertaking a yield-line analysis has been lacking, forcing engineers in industry to use hand-calculations in order to benefit from the power of the yield-line method. This thesis is therefore concerned with the development of techniques that automate this method. By utilising the novel discontinuity layout optimization (DLO) method, the process of yield-line analysis has been truly automated at last. In addition, motivated by the outcomes of the rationalization procedure developed for trusses, research has been conducted to rationalize yield-line patterns generated via DLO. Similar to the technique used in trusses, analytical expressions of functions and their derivatives are deduced and then supplied to a non-linear optimizer, leading to a rapid and reliable computational process. To make DLO and the rationalization ready for use in industry, various slab configurations found in practice are also considered, permitting challenging slab problems to be tackled using the method. A number of examples from the literature and industry are analysed to demonstrate the efficacy of DLO and the rationalization technique

Parametric design and optimization of arched trusses under vertical and horizontal multi-load cases

This dissertation faces the problem of the optimum design of steel truss arches subject to multiple load cases. Arches are one of the most ancient shape-resistant structures, widely used in both civil engineering and architecture. For instance, arches can be considered as purely compressed structures, provided that their “line of thrust” coincides with the centre line of the arch. The “line of thrust” is the locus of the points of application of the thrusts (internal forces or stress resultants) that must be contained within the cross-section of the arch in such a way that the arch transfers loads to the foundations through axial compressive stresses only. As a matter of fact, the more the “line of thrust” differs from the centre line of the arch, the larger the unfavourable bending moments that arise in the arch. This is the reason why it is fundamental to pay close attention to the choice of the shape for an arch in order to minimize (or avoid when it is possible) unfavourable bending effects. Several analytical, graphical and physical methods are provided to find the optimal shape of a monolithic (single rib) arch subjected to a certain load case (i.e. the “funicular curve” for that load). However, if multiple load cases must be considered, it is not possible to find a proper optimal shape for an arch with single rib. In this case, the choice of truss arches with at least two chords becomes indispensable. Indeed, it has been demonstrated that structural optimization of in-plane truss arches with two chords subjected to a single load case leads to optimal solutions in which upper and lower chords tend to coincide with each other and with the “funicular curve” (i.e. the “line of thrust”) for that load. In light of the above, simultaneous shape and size optimization of steel truss arches with two arched chords linked each other through a bracing system (with variable Pratt-type pattern) has been performed for multiple load cases and different structural boundary conditions. Truss arches are effectively used in arch bridges, especially when the arch span exceeds 200 meters (five out of the six steel arch bridges with a span over 500 m are truss arch bridges). For this purpose, a hybrid optimization routine integrating a parametric definition of the design problem, a metaheuristic optimization algorithm and a code for Finite Element Analysis (FEA) has been developed through a MATLAB program. The proposed optimization method allows to simultaneously optimize a larger set of design variables, notwithstanding their large number and various nature (topology, shape and size, as well as continuous and discrete variables, have been concurrently considered). Third-degree Rational Bézier Curves have been chosen to optimize the shape of the arch chords because they can represent a wide family of curves (including conic curves), depending on a small number of parameters. In so doing, in-plane truss arches with different span lengths and structural boundary conditions have been optimized for multiple load cases, only considering vertical loads (acting on the same plane as the arch), since in-plane arches are not suited to withstand out-of-plane loads. On the other hand, spatial arched trusses with two arched chords lying on different planes have been optimally designed for multiple loadings acting in different directions. In particular, a steel arched truss with a lower arched chord variably inclined in the 3D-space and a horizontal upper arched chord linked each other through a bracing system has been designed and optimized for three vertical load cases and a horizontal seismic action parallel to the upper chord plane. Thus, analysing the obtained results, useful suggestions for steel truss arch design have been deduced and presented in this dissertation

Structural optimization of 3D masonry buildings

In the design of buildings, structural analysis is traditionally performed after the aesthetic design has been determined and has little influence on the overall form. In contrast, this paper presents an approach to guide the form towards a shape that is more structurally sound. Our work is centered on the study of how variations of the geometry might improve structural stability. We define a new measure of structural soundness for masonry buildings as well as cables, and derive its closed-form derivative with respect to the displacement of all the vertices describing the geometry. We start with a gradient descent tool which displaces each vertex along the gradient. We then introduce displacement operators, imposing constraints such as the preservation of orientation or thickness; or setting additional objectives such as volume minimization.Shell Oil CompanyNatural Sciences and Engineering Research Council of Canada (PGS Program)Samsung Scholarship Foundatio