Browsing by Author "Puttonen, Jari, Prof., Aalto University, Department of Civil Engineering, Finland"

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  • Causality and Interpretation: Integrating the Technical and Social Aspects of Design
    (2019) Pikas, Ergo
     School of Engineering | Doctoral dissertation (monograph)
    A number of well-recognized problems, many arising from the inadequate organization of design processes, beset the building design and design management. Remedies have been attempted but no effective solutions have emerged. The root problem could be the prevailing view of incompatibility between the technical, subject to causality, and social, subject to interpretation, standpoints. A way to address this issue is to go back to first principles. Aristotle provided a first account of the productive act based on two strategies of inquiry: the method of analysis and rhetoric. The discovery of the dual nature of design theorizing by Aristotle gave rise to the hypothesis that a general solution might be provided by a new integrated design concept. The primary aim was thus defined as follows: to develop a comprehensive philosophical and conceptual framework as well as a design model integrating both technical and social phenomena and to use the resulting theory to develop better design and design management practices. To meet the research aim and select the research methodology, four main research questions were posed: (1) What are the key philosophical ideas relevant to the framing of design conceptualizations? (2) What are the fundamental concepts of ancient design theories (i.e., the method of analysis and rhetoric) in the ancient Greek context and in contemporary contexts? (3) What kind of new design model can be constructed based on these two strategies of inquiry? (4) How does the new model benefit design and design management practices? Design research methodology was adopted to answer the research questions. The answers to the questions were arrived at through arguments, findings, and constructions: (1) Concerning the philosophical framing, it is argued that pragmatism is more appropriate than positivism or constructivism, as it would permit the synthesis of the technical and social perspectives. (2) The two ancient strategies of inquiry, the method of analysis and rhetoric, help clarify fundamental design concepts. These strategies of inquiry need to be integrated for a more comprehensive conceptualization of designing. (3) For an understanding of the relationships between the fundamental concepts of designing, a new more comprehensive design model was constructed. The new model represents the structure of the design process. (4) With a view to the evaluation of the model and development of support for practice, three case study interventions were carried out. An initial implementation of the new model through instantiations in practice brought significant quantitative and qualitative improvements. Overall, three contributions to the body of design knowledge are made: the formalization of a new design process model; an elucidation of the intellectual history of the design discipline; and the clarification of core terms, concepts, and their relationships in the context of design.
  • Effect of the surface roughness of fibres on the bonding capacity of the interfacial zone between the fibres and cementitious matrix
    (2022) Antonova, Anna
     School of Engineering | Doctoral dissertation (article-based)
    As fibre-reinforced cementitious composites (FRCC) are multi-scale materials, their structural performance depends on the micro-scale properties of the fibre-matrix bond. However, the development and utilisation of FRCC are restricted due to the limited knowledge of the micro-scale phenomena that influence the bond between the fibres and the cementitious matrix and its response to loading. The focus of this research was the definition of the properties of the fibre surface and the cement paste surrounding it, which affect the formation and performance of the fibre-matrix bond. The examination involved analysing the effect of the surface roughness of steel fibres on the microstructure of the interfacial transition zone (ITZ) and the degradation of the fibre-matrix bond under repeated loading. The micro-scale properties were explored by employing a different approach to applying the existing experimental techniques to the FRCC. The utilisation of scanning electron microscopy (SEM) and phase-contrast micro-computed tomography (μCT) enabled the identification of the changes in the distributions of calcium hydroxide, calcium silicate hydrate, pores and unhydrated cement grains within the ITZ. The application of phase-contrast μCT allowed access to the three-dimensional microstructure of the cement paste around the fibre. The importance of the surface roughness of steel fibres for the packing of cementitious grains was examined by estimating the average height and wavelength of surface irregularities using an SEM image analysis and directly measuring the parameters using an atomic force microscope and stylus profilometer. The effect of the fibre surface roughness on its wettability was evaluated through contact angle goniometry. The decrease in the mobility of the water along the fibres that was observed with an increase in fibre surface roughness facilitated the reduction in the porosity near these fibres, which was confirmed using SEM. The resulting mechanical response of the bond between the cement paste and fibres with different types of surface roughness was examined under direct tension cycles with gradually increasing amplitudes. The outcomes of the fibre pull-out tests indicated that the detected micro-scale changes in the properties of the fibres and the cement paste surrounding them influenced the maximum capacity of the fibre-matrix bond and its deterioration. The development of the residual slip was identified from the beginning of loading with the three stages of evolution: deceleration, steady stage and acceleration. This study points out that the properties of the fibre surface and the cement paste surrounding it clearly affect the performance of the fibre-matrix bond by introducing novel insights about the fibre-matrix interaction that advance the development and modelling of FRCC.
  • Hygrothermal performance of wood-framed, mineral-wool-insulated walls and roofs with low thermal transmittance
    (2023) Viljanen, Klaus
     School of Engineering | Doctoral dissertation (article-based)
    Low thermal transmittance of external walls and roofs supports sustainability and energy savings, but the improved insulation efficiency may increase moisture problems in these building components. As the performance of the highly insulated (HI) building envelope subjected solely to water vapour diffusion has been found acceptable, this study analyses the consequences of built-in moisture, rain leakage and indoor air exfiltration for HI building envelopes and assesses the hygrothermal conditions and moisture safety of the ventilation cavities of HI walls and roofs. The extensive experiments of the thesis focused on mineral-wool-insulated wood-framed external walls and roofs with thermal transmittances of 0.12–0.13 W/(m2K) and 0.08 W/(m2K), respectively, and with wind barriers that had water vapour diffusion equivalent air layer thickness (sd) of 0.1–0.2 m. The experimental results received indicated that exfiltration is the most potential source of moisture to deteriorate the hygric performance of the wall studied. However, no connection was observed between the thermal transmittance and hygric performance of a wall that was subjected to air leakage. This also applied to the performance of the walls during the drying in the built-in moisture tests: all the walls dried to the state of equilibrium without significant risk of moisture problems. The HI walls had a slightly better tolerance to rain leakage than the baseline wall. The results of the wall experiments support the use of an insulating exterior sheathing in HI walls. Such a sheathing protects the wall against air exfiltration and decreases the level of relative humidity during the drying of the wall. The results indicated that a ratio of the thermal resistance of the exterior sheathing to that of the whole HI wall should be at least 10%. The measurements revealed that in the ventilation cavities of HI walls the hygrothermal conditions were the weakest at the bottom of the cavity. The performance of the cavities of the HI roofs studied was satisfactory at most, but in the future, the performance will deteriorate if climate changes as is predicted. Based on these results, it is recommended to use mould resistant materials in the cavity of HI walls and roofs, to use effective vapour barriers in HI roofs (sd at least 50 m), and to monitor the performance of the cavity of HI structures regularly. Based on the numerical analysis conducted, if necessary, the hygrothermal performance of HI roofs can be improved by using quintuple thermal resistance compared to the conventional level of the structural members above the ventilation cavity such as 0.13 (m2K)/W and by restricting the ventilation openings in windy regions so that the air change rate is about 20 1/h.
  • Improving building energy efficiency through novel hybrid models and control approaches including a data center case study
    (2016) Lu, Tao
     School of Engineering | Doctoral dissertation (article-based)
    The building sector consumes the most energy and emits the greatest quantity of greenhouse gases of any sector. Energy savings in this sector can make a major contribution to tackling the threat of climate change. Research has produced a variety of solutions, for example, net zero and positive-energy buildings. At the same time, both models and controls are being challenged by increasingly complex buildings equipped with advanced information and communications technologies (ICT). This dissertation addresses these challenges by proposing a multidisciplinary, wide-ranging modeling methodology that enables new strategies for saving building energy. The core methodology utilizes novel modeling approaches to improve predictive models and produce innovative energy solutions. Models are validated and investigated using a variety of buildings and controls. Data centers and demand controlled ventilation (DCV) are the focus because they represent both "multifunctional buildings" and general energy system controls. This dissertation makes the following seven original contributions: (1) The first systematic, complete case study of a data center in which infrastructure, energy and air management performance, and waste heat recovery systems were investigated, analyzed, and quantified using long-term power consumption data. (2) A novel and tuning-free DCV building control strategy that is far superior to proportional control and more competitive than proportional-integral-derivative (PID) control. (3) An artificial neural network (ANN) model for predicting the water evaporation rate in a swimming hall. (4) A new ANN model for estimating prediction intervals and accounts for the uncertainty of point estimation for indoor conditions in an office building. (5) A new Maximum Likelihood Estimation (MLE) model for predicting constant and time-varying air change rates and a coupled model for estimating the number of occupants in an office. (6) Discovery of a new physical law for run-around heat recovery systems that can be used to develop a simulation model to estimate the system performance for constant volume air (CAV) and DCV systems. This new law was verified in different sites. (7) A new hybrid numerical-ANN model for building performance simulation. The hybrid model can improve not only the model accuracy but also the generalizability of ANN. The results demonstrate the applicability of the modeling techniques and the models, and significant energy savings in buildings. The resulting improvements in model accuracy, forecasting capability, and energy efficiency were published in eight journals. By unifying the results of eight publications, this dissertation presents a comprehensive and coherent study that advances the state-of-the-art building energy research.
  • Response of long-span and high-strength steel beams to nonuniform temperature fields induced by fire
    (2023) Shakil, Saani
     School of Engineering | Doctoral dissertation (article-based)
    This thesis explores the effects of nonuniform temperature fields on the behaviour of long-span structures and compares the responses of members made of mild and high-strength steel (HSS). Advanced nonlinear analyses of structural members using the finite element (FE) method and fire simulations using computational fluid dynamics were conducted. Comprehensive steady and transient state tensile tests at elevated temperatures were carried out to determine the mechanical properties of S700 MC grade HSS, which were used to establish its material model for numerical analyses. The FE calculations were carried out using the Abaqus programme, while the Fire Dynamics Simulator (FDS) programme was used for fire simulations. The coupling between FE and FDS analyses was based on adiabatic surface temperatures and was carried out using the FDS2FEM programme. The study indicates that the EN 1993-1-2 material model with reduction factors based on the results of transient state tests reasonably describes the S700 MC material. Moreover, its strain hardening at large strains can be modelled using the Ramberg-Osgood equations with the reduction factors derived from steady state test results. Responses of beams and frames exposed to the nominal fire indicate that the critical temperatures of structures made of HSS are higher than those of structures made of mild steel with similar loads. However, at equal load ratios, the use of HSS can only be promoted if the displacements are allowed to be larger for its structures. The developed five-stage mechanism indicated that heating-cooling cycles of travelling fire and higher strength of HSS beams increased fluctuations in the axial force response. At load ratio of 0.5, these fluctuations activated catenary action at a much lower temperature than the critical temperatures based on the EN 1363-1. This means that the catenary action temperatures should be considered in structural design. The analyses of 31 m span truss beams pointed out that the orientation of the beams with respect to the travel path of fire affects their temperature fields and mechanical responses. Depending on the orientation, the structural failure may occur due to large local or global deflections. The simulation of fire intervention with a duration of 360 s decreased the temperature and overall deformation of the truss beam locally. However, with insufficient water, the fire intervention transferred the flames to one of the ends of the beam span. The results point out that efficient fire-fighting tactics can be developed with the methods used in the study. Fire and fire intervention cause three-dimensional and time-dependent temperature fields in long-span steel structures. The structural fire-safety design of these structures should be based on methods capable of calculating highly nonlinear responses. The study also highlights the need for experimental investigations of the mechanical properties of HSS at elevated temperatures during and after fires considering the effects of different heating and cooling rates.