<p>  </p> <p>In order to comprehend complex and abstract phenomena, students must partake in the process of learning by integrating complex and invisible components without ever physically encountering or manipulating such components. Prior knowledge and experiences will influence the way students assimilate and model new experiences and knowledge. If prior knowledge possesses a degree of non-normative conceptions, students' understanding of abstract phenomena may diverge dramatically from accepted scientific explanations. Embodied cognition proposes that learning about natural phenomena can develop from information gained via interactions between the body and the physical environment. Multimodal experiences can shape students' conceptual understanding of abstract phenomena.</p> <p>Incorporating technology tools to explore science concepts is a trend utilized to give high-quality education. The use of physical and virtual manipulation tools in science instruction has favored the improvement of modeling science phenomena in general. Visuohaptic simulations are also learning manipulatives that blend physical and virtual manipulation affordances as a unison experience. </p> <p>The current dissertation proposed the implementation of a learning experience where students engage in experimentation with a visuo-haptic simulation to explore and model reaction forces on truss structures. The study examined undergraduate students’ conceptual understanding, graphical representations, and the modeling refinement process of reaction forces on truss structures before, during, and after engaging with visuo-haptic simulation on truss structures using different modalities. A design-based research methodology was implemented to design, explore, and refine a learning experience with a visuo-haptic simulation of truss structures through two research phases. The learning experience occurred as a laboratory activity in a statics course at a Midwest university.</p> <p>The first phase of this dissertation investigated students' conceptual understanding and graphical representations of reactive forces on a complex truss structure by interacting with a visuo-haptic simulation of truss structures. Students participated in two treatment groups: visuo-haptic exposure and visual-only exposure. The results of the first phase suggested that students that engaged with the visuo-haptic simulation using different modalities improved their conceptual understanding of truss structures significantly. Moreover, students exposed to haptic feedback significantly improved their graphical representations on tasks where the haptic feedback was involved. </p> <p>The second phase of the current dissertation examined students’ developing models of reactive forces on a truss structure before, during, and after engaging with a visuo-haptic simulation of truss structures. Students participated in two sequential treatment groups: visual to visuo-haptic and haptic to visuo-haptic. The quantitative results suggest that both treatment groups performed significantly better in their model representations after being exposed to the learning experience but show no difference across treatment groups. The qualitative results suggest that the visual to visuo-haptic group interpreted their experiences much more coherently, leading to a more sophisticated version of their model of reaction forces on truss structures. </p>

Fibre composite materials are gaining recognition in civil engineering applications as a viable alternative to traditional materials. Their migration from customary automotive, marine, aerospace and military industries into civil engineering has continued to gain momentum over the last three decades as new civil engineering applications develop. The use of fibre composite materials in civil engineering has now evolved from non-structural applications, such as handrails and cladding, into primary structural applications such as building frames, bridge decks and concrete reinforcement. However, there are issues which are slowing the use of fibre composite materials into civil engineering. Issues include high costs, difficulties in realising potential benefits, general lack of civil engineers' familiarity with the material and relatively little standardisation in the composites industry. For composites to truly offer a viable alternative to traditional construction materials in the civil engineering marketplace, it is essential that these issues be addressed. It is proposed that this situation could be improved by demonstrating that potential benefits offered by composites can be achieved with familiar civil engineering forms. These forms must be well suited to fibre composite materials and be able to produce safe and predictable civil engineering structures with existing structural engineering methods. Of the numerous structural forms currently being investigated for civil engineering applications, the truss form appears particularly well suited to fibre composites. The truss is a familiar structural engineering form which possesses certain characteristics that make it well suited to fibre composite materials. In this research a novel monocoque fibre composite truss concept was developed into a working structure and investigated using analytical and experimental methods. To the best of the author's knowledge the research presented in this thesis represents the first doctoral research into a structure of this type. This thesis therefore presents the details of the development of the monocoque fibre composite (MFC) truss concept into a working structure. The developed MFC truss was used as the basis for a detailed investigation of the structural behaviour of the MFC truss elements and the truss as a whole. The static structural behaviour of the principal MFC truss elements (tension members, compression members and joints) was investigated experimentally and analytically. Physical testing required the design and fabrication of a number of novel test rigs. Well established engineering principles were used along with complex finite element models to predict the behaviour of the tested truss elements and trusses. Results of the theoretical analysis were compared with experimental results to determine how accurately their static structural behaviour could be predicted. It was found that the static structural behaviour of all three principal truss elements could be accurately predicted with existing engineering methods and finite element analysis. The knowledge gained from the investigation of the principal truss elements was then used in an investigation of the structural behaviour of the MFC truss. Three full-scale MFC trusses were fabricated in the form of conventional Pratt, Howe and Warren trusses and tested to destruction. The investigation included detailed finite element modelling of the full-scale trusses and the results were compared to the full-scale test results. Results of the investigation demonstrated that the familiar Pratt, Howe and Warren truss forms could be successfully manufactured with locally available fibre composite materials and existing manufacturing technology. The static structural behaviour of these fibre composite truss forms was accurately predicted with well established engineering principles and finite element analysis. A successful marriage between fibre composite materials and a civil engineering structure has been achieved. Monocoque fibre composite trusses have been developed in the familiar Pratt, Howe and Warren truss forms. These structures possess characteristics that make them well suited to applications as primary load bearing structures.

The goal of this thesis is the development of theoretical methods targeting the implementation of topology optimization in structural engineering applications. In civil engineering applications, structures are typically assemblies of many standardized components, such as bars, where the largest gains in efficiency can be made during the preliminary design of the overall structure. The work is aimed mainly at truss-like structures in civil engineering applications, however several of the developments are general enough to encompass continuum structures and other areas of engineering research too. The research aims to address the following challenges:<p>- Discrete variable optimization, generally necessary for truss problems in civil engineering, tends to be computationally very expensive,<p>- the gap between industrial applications in civil engineering and optimization research is quite large, meaning that the developed methods are currently not fully embraced in practice, and<p>- industrial applications demand robust and reliable solutions to the real-world problems faced by the civil engineering profession.<p><p>In order to face these challenges, the research is divided into several research papers, included as chapters in the thesis.<p>Discrete binary variables in structural topology optimization often lead to very large computational cost and sometimes even failure of algorithm convergence. A novel method was developed for improving the performance of topology optimization problems in truss-like structures with discrete design variables, using so-called Kinematic Stability Repair (KSR). Two typical examples of topology optimization problems with binary variables are bracing systems and steel grid shell structures. These important industrial applications of topology optimization are investigated in the thesis. A novel method is developed for topology optimization of grid shells whose global shape has been determined by form-finding. Furthermore a novel technique for façade bracing optimization is developed. In this application a multiobjective approach was used to give the designers freedom to make changes, as the design advanced at various stages of the design process. The application of the two methods to practical<p>engineering problems, inspired a theoretical development which has wide-reaching implications for discrete optimization: the pitfalls of symmetry reduction. A seemingly self-evident method of cardinality reduction makes use of geometric symmetry reduction in structures in order to reduce the problem size. It is shown in the research that this assumption is not valid for discrete variable problems. Despite intuition to the contrary, for symmetric problems, asymmetric solutions may be more optimal than their symmetric counterparts. In reality many uncertainties exist on geometry, loading and material properties in structural systems. This has an effect on the performance (robustness) of the non-ideal, realized structure. To address this, a general robust topology optimization framework for both continuum and truss-like structures, developing a novel analysis technique for truss structures under material uncertainties, is introduced. Next, this framework is extended to discrete variable, multiobjective optimization problems of truss structures, taking uncertainties on the material stiffness and the loading into account. Two papers corresponding to the two chapters were submitted to the journal Computers and Structures and Structural and Multidisciplinary Optimization. Finally, a concluding chapter summarizes the main findings of the research. A number of appendices are included at the end of the manuscript, clarifying several pertinent issues. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished