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Dissertation
Behaviour and Design of Built-up Structural Elements : Composed of Thin-walled Cold-formed Steel Profiles
Authors: --- --- --- ---
Year: 2015 Publisher: Leuven KU Leuven. Arenberg doctoral school of science, engineering & technology

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This doctoral thesis addresses an increasing demand from the cold-formed steel production industry for more stable load-bearing elements. As buildings constructed entirely from cold-formed steel profiles and sheeting increase their spans, heights and bays, light steel frames not only become more impressive, but the applications of light-steel framing widen.The limited stability of standard cold-formed steel elements is resolved in the thesis by using primary load-bearing elements composed of multiple profiles. Built-up (composed) members:• are assembled from multiple, standard cold-formed steel profiles,• offer a number of benefits in terms of production, transportation, storage, flexibility in shape and arrangement, and overall cost,• can carry higher loads than the sum of what the constituents can take up when used separately.The thesis concerns built-up columns of intermediate and high slenderness; namely, these are elements that undergo all of the common types of buckling that occur in thin-walled structures — local, distortional and overall (flexural, torsional, andtorsional-flexural) buckling.Built-up sections are investigated due to their potential to achieve notably higher load-bearing capacity and avoid overall and distortional buckling occurrences that may compromise a structure’s integrity. Currently, no reliable design methods existfor such elements in structural design codes worldwide.The research aims to (1) understand the response of such members in terms of load-bearing capacity, stiffness, failure modes, scatter in capacity, and (2) recognise the design methods that are required. The focus of the doctoral studies is onmembers loaded in axial compression; however, the design under combined forces is also addressed.Experimental and numerical investigations are performed in order to study the behaviour of built-up columns and beams in weak-axis bending. Results are compared to analytical predictions based on existing design methods. Investigations concern a variety of cross-sections, some of which have been taken from design practice, while others are contrived and optimised within the doctoral programmewith the goal to reach considerably higher load-bearing capacity and better stability.Design partially or fully based on numerical analysis is considered and its advantages and disadvantages are presented.The manuscript documents the rather complex instability of built-up thin-walled systems, which was observed both experimentally and in numerical analysis. On many occasions, the presented failures comprise multiple, interacting or mixedbuckling modes, often combined with plastic yielding in the higher load stages.Based on the results from the various investigations presented in the manuscript, a design method is proposed which is an extension based on currently existing design techniques.A special emphasis is put on simplifying the design process. The goal is to eliminate ambiguities, avoid a lack of clarity and structure, and thus prevent mistakes in everyday design practice. This is in line with a contemporary tendency in coldformed steel design to simplify design methods and step away from overcomplicated, unclear methods.An indirect benefit of a simple and concise design method is the promotion of the structural system itself — a simple, clear and structured design technique will stimulate engineers to use light steel as a solution to their everyday design tasks.


Multi
Towards a 3D GIS based monitoring tool for Preventive Conservation Management of the World Heritage City of Cuenca
Authors: --- --- --- --- --- et al.
ISBN: 9789460188572 Year: 2014 Publisher: Leuven KU Leuven. Arenberg doctoral school of science, engineering & technology

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Multi
Interactions between Cement and Combined Concrete Admixtures. : The Influence on Cement Paste Rheology.
Authors: --- --- --- --- --- et al.
ISBN: 9789460188589 Year: 2014 Publisher: Leuven KU Leuven. Arenberg doctoral school of science, engineering & technology

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During the last decades, innovative concrete applications have been the result of technological developments as new processing techniques, the use of concrete admixtures and advanced materials. All these improvements increase the demand for better performing concrete with enhanced workability. However, the lack of reliable engineering tools in traditional concrete production methods has led to some inconsistent control of the workability. Therefore, todays research is increasingly investigating advanced models that capture the flow behavior of fresh concrete as accurately as possible. These models are continuously improving but generally keep facing problems which are linked to the agglomeration of the cement particles and to the implementation of combined concrete admixtures. The objective of this work is to investigate the rheological mechanism in cement paste for the combined use of superplasticizer, retarder and accelerator. In particular, an effect on the particle agglomeration is aimed for in order to contribute to a more fundamental understanding of the concretes flow behavior. Concerning the superplasticizer impact on cement paste, thermodynamic modelling and mineralogy studies led to the conclusion that the superplasticizer can change the hydrate morphology to such an extent that the interparticle contact forces are modified. The extra addition of retarder led to a densified polymer layer at the cement grain surface which contributed to the steric stabilization of the cement paste. An additional electrostatic effect and the induced changes in hydrate morphology are also demonstrated to contribute to the low paste viscosity. With the extra addition of a calcium salt accelerator to the cement paste, an interstitial structure was assumed to diminish the rheological effect of the polymer layer.All the developed conceptual mechanisms were implemented in a coherent agglomeration model, based on measurable parameters. In this model, the internal and external hydrates in a cement agglomerate were defined and quantified. Generally, the cumulative amount of hydrates within the agglomerates influenced the agglomerate stability and the amount of external hydrates determined the reagglomeration rate. For the superplasticizer only, a proportional relation was found between the change in agglomeration rate and the external agglomerate connectivity while, for the extra addition of retarder and accelerator, a reverse relation was found. The latter was attributed to a mechanical contribution of the interstitial volume. On the one hand, the retarder creates a source of slowly hydrating nuclei and particles in that volume and, on the other hand, these particles are expected to coagulate due to the accelerator addition. In the second case, the interstitial volume also delivered a contribution to the stress resistance of the cement paste at rest.This fundamental research combines dedicated analytical methods and conceptual models to improve the understanding of particle agglomeration and contributes to a more extensive insight into the concrete rheology.


Dissertation
Integrated Approach in Management of Coastal Cultural Heritage

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Humans have had a long history of interconnectedness with the sea and ocean due to the use of natural resources available in the coastal areas. These interactions have influenced the natural landscape and play a crucial role in the formation of coastal cultural heritage. Coastal cultural heritage, a continuum of land and sea, is an important part of our cultural resources in the coastal areas. Presently, coastal cultural heritage has not been well integrated into coastal management plans as a cultural resource. The qualitative and comparative analysis of coastal management experiences show that, despite the fact that holistic coastal management plans (such as integrated coastal zone management (ICZM)) have theoretically addressed the importance of cultural ecosystems, cultural resources have mostly been overlooked in these plans. Regulatory regimes and management strategies for land and sea are separate even though the line between the sea and land is arbitrary. Separation of regulatory regimes and management strategies for land and sea has hindered the ability to achieve an integrated approach for cultural heritage management in the coastal areas. This fact negatively affects the protection of coastal cultural heritage as an entity. To achieve an integrated management, the present research identifies two sub-problems. One problem is with justifying values within integrative dimensions and understanding the role of these dimensions as control groups. The second problem is ambiguity in defining the coastal cultural area. Acknowledging the similarities between natural resources and cultural resources, this study relied on learning from natural resource experiences and adapting social theories for re-evaluating and re-defining coastal cultural heritage. Combining the applications of integrated complexity theory, social-cultural memory and theory of middle-ground proved to offer a powerful system for evaluation and defining coastal cultural heritage. This dissertation offers two tools for the integrated management of coastal cultural heritage. One is an integrative evaluation system, and the other is a coastal cultural middle-ground model. The integrative evaluation tool provides a systematic method to address different concerns from natural, socio-economic, political and cultural dimensions. Nonetheless, designing and implementing such an integrated system for management of coastal cultural heritage may cause conflicts among different stakeholders. Therefore, in order to deal with these conflicts and promote a common understanding among different dimensions and disciplines, this dissertation adapted the theory of middle-ground. The aim was not only to mediate encounters among different stakeholders, but also to define an area of maximum cultural values for adaption of an integrated coastal management strategy. Adapting the theory of middle ground and taking into consideration and recognition the links and connections among people, their heritage, and the environment ultimately results in the formation of a definitive area of cultural values—or as it is called in this dissertation: coastal cultural middle ground. Delineating coastal cultural middle-ground highlights the importance of coastal cultural heritage as one entity in management schemes—not as separate entities on land and underwater. In order to examine the proposed tools, the Belgian coast has been chosen as the case study. In line with the current project in Belgium—the SEARCH (Archaeological Heritage in the North Sea) project— which aims to develop an efficient evaluation method and proposals for sustainable management of coastal cultural heritage in the Belgian Part of the North Sea, the proposed methods will be tested for the Belgian coastal cultural heritage. The objective of this case study is to create a methodology that leads to a comprehensive understanding of many aspects and issues related to the management of coastal cultural heritage in Belgium.


Multi
Sustainable Materialisation of Residues from Thermal Processes into Construction Materials : Construction materials from stainless steel slags

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The amount of slag generated is almost athird of the total stainless steel produced. Owing to its mineralogy, a large partof the slag is produced as fines, which has a very low valorisation potentialand has to be landfilled. The present work is aimed at exploring the potentialof these slags to produce construction materials of higher economic value.To address the issue, two valorisationroutes were applied: 1) alkali-activation initiating binding reactions in theslag by the addition of alkali hydroxides and silicates, 2) carbonation initiating hardening reaction in the slag by the formation of alkalicarbonates. Two stainless steel slags, continuous casting (CtCs) slag and Argonoxygen decarburisation (AOD) slag, were targeted for valorisation.Initiation of hardening reactions in theslag was found to occur only under a combined treatment of alkali (Na and K)hydroxides and high temperature (80 °C) which was provided by steam curing. However,only a moderate strength in the mortar specimens was observed under suchconditions along with appearance of efflorescence with NaOH for molaritiesabove 5 M. The problem of low strength and efflorescence in the mortar sampleswas eliminated by the introduction of silicates in the system along with thealkali hydroxides. The compressive strength of the slag mortars was found toincrease with the increase in the amount of silicates in the activatingsolution and with the increase of the curing temperature. The reaction productfrom the activation was found to be C-S-H as confirmed by thermogravimetric,QXRD, FTIR and 29Si NMR analysis.The slag was also found to develop strengthunder acceleration carbonation conditions which was provided under two environments:i) in a carbonation chamber, maintained at atmospheric pressure, 22 °C, 5 vol.%CO2 and 80% RH; and ii) in a carbonation reactor, where the CO2partial pressure (pCO2)and temperature could be further increased. It was found that in thecarbonation chamber the compressive strength of the samples and the CO2sequestration continued to increase up to 3 weeks whereas in the reactor theoptimum for strength and CO2 sequestration was found at 80 °C, 8 barpressure in 2.5 h. The major reaction product was found to be calcite indifferent morphologies.Three types of masonry blocks were preparedform the slag with the two valorisation routes: alkali-activated solid bricks,perforated carbonated bricks and alkali-activated aerated bricks. Thecarbonated bricks were found to have the best resistance to freeze-thaw,whereas the aerated bricks were found to have superior thermal resistivity values.The LCA showed that the environmental impact of the bricks is lower (negativefor carbonated bricks) than the conventional clay fired bricks and the impactof the aerated bricks was found to be similar to the conventional aeratedblocks available in the market. A SWOTanalysis highlighted the advantage of using these bricks in the form of lowerenergy requirement in its production, reduction of stress on the use of prime materialsand ease of metal recovery from the residual slag.The results of the dissertation show that thebinding potential of the stainless steel slags can be exploited as valorisedapplications in the construction industry by novel thermo-alkali activation andcarbonation processes.

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