Structural fire design represents one important aspect of the design of reinforced concrete buildings. The work presented in this thesis seeks to elucidate the structural behaviour of reinforced concrete slabs during exposure to heating from below, as would occur in the case of a building fire, with a particular focus on structural fire modelling using finite element analysis. The focus in on validating finite element models against experimental results and quantifying the sensitivity of model outputs to relevant thermal and mechanical input parameters. A primary goal of the work is to provide recommendations to structural fire engineering analysts and designers considering the performance-based design of reinforced concrete slabs for structural fire resistance using available finite element software. A critical review of the available knowledge of the structural fire response of reinforced concrete structures in general and concrete slabs in particular is presented, along with an awareness as to the importance of understanding structural response of concrete structures exposed to fires. Current techniques for structural fire design of concrete structures are reviewed, and shortcomings highlighted. Available experimental data are presented, and various finite element models of these slabs are developed and interrogated to identify important aspects for understanding, as well as for future improvement of similar studies (both experimental and numerical) with the intention of supporting future progress in structural fire engineering, in particular as regards performance based structural fire design of concrete slabs. A range of thermal and mechanical parameters that are potentially important and influential in the structural fire design of reinforced concrete slabs is then studied, including: fire scenario, thermal properties of materials (thermal conductivity and specific heat), heat transfer parameters (coefficient of convection and emissivity) and assumptions, restraint conditions at the supports, variations of span-to-depth ratio, reinforcement detailing, as well as plan aspect ratio are all investigated; their influence on the structural fire response of reinforced concrete slabs is studied and discussed. A key issue in validating finite element models against experimental results lies in defining the temperature inputs to the structural finite element models correctly. Variation of available thermal and mechanical input parameters, as recommended in Eurocodes, influences the predictive performance of thermal and structural finite element models, however these are not the main contributing factors in obtaining a credible prediction of response from the finite element models. The most challenging aspect in performing heat transfer analysis for fire furnace tested reinforced concrete slabs lies in defining the correct thermal boundary condition. For simply supported one-way spanning and two-way spanning slabs, increasing slab's thickness (lowering span-depth ratio) does not improve fire resistance rating for the slabs when both limiting deflection criteria and limiting tensile plastic strain are set as acceptance criteria. Two-way slabs with higher span-depth ratio have better fire resistance ratings, judging from the overall trends and magnitudes of mid-span deflections. The formation of plastic hinges is likely to occur for one-way spanning slabs modelled with finite rotational spring stiffness at supports, but not for two-way spanning slabs. A yield line mechanism in two-way slabs means that the behaviour is more complex as compared to the simple flexural mechanism for one-way slabs. In one-way slabs, plastic hinges potentially occur at the location where top reinforcement is curtailed, highlighting the importance of properly understanding the nuances in response of concrete slabs in fire. Investigation of the influence of aspect ratio in two-way spanning slabs confirms that slabs with lower aspect ratios have better structural fire resistance than slabs with higher aspect ratios when both limiting deflection criteria and limiting tensile strain in reinforcing steel were used as the performance indicators. A combination of both limiting mid-span deflection criteria as well as limiting tensile plastic strain is recommended for specifying acceptance criteria for both one-way and two-way slabs, since it gives more accurate and comprehensive assessment on the structural response of the slabs under exposure to severe heating from below.

published_or_final_version / Housing Management / Master / Master of Housing Management

Indoor air quality (IAQ) has a direct impact on our health, as more than half the air we inhale throughout our lifetimes is indoor air. With an increasing trend in dampness in modern buildings due to urban expansion into wetland environments and increased use of gypsum board in construction, hydrolysis in indoor surface films has been suggested to be an important chemical process in the indoor environment. Several synthetic esters (SEs) found in building materials, electronics, and consumer products may undergo hydrolysis to produce harmful volatile organic compounds (VOCs) to which building occupants may be exposed. In this dissertation, the impact of hydrolysis on indoor air quality is explored by experiments on alkaline hydrolysis kinetics and ventilation, followed by simulations of VOC production from hydrolysis. Alkaline hydrolysis kinetics of four SEs, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate (TMPD-MIB), butylparaben (BP), bis (2-ethylhexyl) adipate (DEHA), and butyl benzyl phthalate (BBzP), in bulk solutions are investigated in chapter 2. With concentration decay profiles following pseudo first-order kinetics, the second order-rate constants were determined from measured pH values. The determined rate constants of the aforementioned SEs are compared with those of respective ester categories (e.g., parabens, phthalates), and the steric/polar effects of the ester substituents are discussed in detail. The results of this study contributed to the completion of the indoor chemistry box model GAMMA-CIE which was used for simulation studies in chapter 4. Room-level ventilation measurements in educational spaces across different US regions (e.g., Northeastern, Southeastern, Western) are presented in chapter 3. In the wake of COVID-19 pandemic, ventilation data on a room-by-room basis were critical in planning a safe reopening in schools and universities. Three major approaches to ventilation measurements are outlined in this chapter: direct flow measurement, controlled release, and passive/in-situ monitoring. The application of these approaches is presented in case studies across various educational institutions, showcasing their advantages and disadvantages. The frequently observed range of 0.5-5.5 ACH in this study is taken into account in simulation conditions in chapter 4. The predicted indoor generation of VOCs from alkaline hydrolysis of SEs occurring in surface aqueous films is discussed in chapter 4. Simulations were performed using GAMMA-CIE, which considers aqueous hydrolysis kinetics, interphase mass transport, and loss by ventilation. Three different scenarios were studied: (1) installation of PVC flooring on concrete; (2) coating of latex paint on concrete; and (3) uptake of airborne SEs by surface aqueous films. The simulation results suggested that: (1) the rate of hydrolysis of DEHA and DEHP from PVC flooring is not fast enough to generate high concentrations of 2-ethylhexanol observed during episodes of sick building syndrome (SBS); (2) fresh application of latex paint may cause acute exposure to 2,2,4-trimethyl-1,3-pentanediol (TMPD); and (3) hydrolysis of SEs diffused from indoor air is unlikely to produce significant amounts of alcohols associated with SBS.

University of Macau / Faculty of Science and Technology / Department of Electrical and Electronics Engineering

Simulation is one of the oldest and also among the most important tools available to engineers. In the building Heating, Ventilating and Air-Conditioning (HVAC) community the availability and/or functionality of simulation tools is limited and it is difficult to determine whether the simulation models accurately represent reality. The purpose of this study was to accurately verify one such a simulation model and then to extend the study to two unique applications. Comprehensive structural, comfort and energy audits were performed to construct a suitable simulation model with the aid of the control simulation package: QUICK Control. The model was then verified against measured building data to ensure an accurate representation of the actual dynamic building response. For the first application various control retrofits were evaluated and the highest potential for energy saving was found. Thereafter the model was implemented to investigate the change in indoor air conditions due to failure of HVAC equipment. Heating, ventilating and air-conditioning in buildings consume a significant portion of the available electrical energy in South Africa. Of this energy up to 30% can be saved by improving the HVAC systems currently installed in the buildings. This could result in savings of up to R400 million. For the building used in this study it was found that up to 66% of the HVAC system’s electrical energy consumption could be saved with a payback period of only 9 months. These savings could be achieved by implementing a setback control strategy with an improved time management procedure. Predicting the impact of failing equipment is a difficult task because of the integrated dynamic effect every HVAC component has on the next. With the aid of a comprehensive integrated simulation model the implications of failing can be determined and necessary assessments and precautions can be taken. The results of this study showed that the air-conditioning system under investigation was approximately 100% over designed. Failure of up to 50% was allowable in the cooling equipment before any noticeable impact could be observed in the indoor climate. With further failure the required comfort conditions could not be sustained. <p The substantial savings calculation and possibility of predicting climate deterioration would not have been possible without the aid of a comprehensive simulation package and model. This study clearly highlights the worth of integrated simulation. / Dissertation (MSc (Mechanical Engineering))--University of Pretoria, 2006. / Mechanical and Aeronautical Engineering / unrestricted

Die vorliegende Arbeit befasst sich mit datengetriebenen Modellierungsansätzen in der Gebäudetechnik zum Zweck des Entwurfs modellprädiktiver Regler. Dabei widmet sich der erste Teil (Kapitel 2 und 3) im Wesentlichen den theoretischen Grundlagen der Systemidentifikation wohingegen im zweiten Teil (Kapitel 4 bis 6) praktische Anwendungen der Identifikation sowie die Implementierung modellprädiktiver Regler im Gebäudebereich im Vordergrund stehen. Die Grundlage der Arbeit stellt die Systemidentifikation mittels der Prädiktionsfehlerminimierung (Prediction Error Minimization – PEM) dar, deren Basis stochastische Modelle dynamischer Systeme bilden. Daher wird ausgehend von den unterschiedlichen Darstellungsformen stochastischer linearer zeitinvarianter Systeme (LTI-Systeme) die Problematik der optimalen Prädiktion thematisiert, wobei ein allgemeiner Ausdruck zur Berechnung der Mehrschrittprädiktion von LTI-Systemen hergeleitet wird. Anschließend werden Implementierungsaspekte von Mehr- bzw. Multischritt-PEM-Verfahren diskutiert und der Schätzer im Frequenzbereich analysiert, wobei sich verglichen mit der 1-Schritt-PEM eine erwartungsgemäß andere Wichtung des geschätzten Modells im Frequenzbereich ergibt. Die aus diesen Untersuchungen gewonnen Identifizierbarkeitsbedingungen entsprechen im offenen Regelkreis den bekannten Bedingungen der 1-Schritt-PEM, wohingegen sich im geschlossenen Regelkreis eine restriktivere Bedingung ergibt. Die weiterhin durchgeführte Genauigkeitsanalyse führt letztlich zu einem Ausdruck für die Abschätzung der Schätzfehlerkovarianzmatrix der Modellparameter, welche wiederum für die Varianz- bzw. Konfidenzschätzung anderer Systemmerkmale genutzt werden kann. In der Gebäudetechnik spielen nichtlineare Modellansätze eine wichtige Rolle. Für diese ist die explizite Berechnung der optimalen Prädiktion, und damit eine Identifikation mittels PEM, in der Regel problematisch bzw. nicht möglich. In der Arbeit werden daher zwei nichtlineare Modellstrukturen vorgeschlagen, für welche entsprechende Ausdrücke angegeben werden können, sodass eine direkte Anwendung der PEM ermöglicht wird. Dabei hat sich im Anwendungsteil der Arbeit herausgestellt, dass einer dieser Ansätze sinnvoll in der Gebäudetechnik genutzt werden kann. Aufgrund der Ähnlichkeit zum linearen Fall können zudem die Ideen, die typischerweise für die Parametrierung stochastischer LTI Systeme genutzt werden, auf den nichtlinearen Fall übertragen werden. Im Anwendungsteil der Arbeit wird dann die Nutzung der PEM im Gebäudebereich anhand praktisch aufgenommener Messdaten einiger Demonstratoren veranschaulicht. Es werden Modell- und Identifikationsansätze für die Schätzung von thermischen Raummodellen sowie einer Gastherme und einer Wärmepumpe vorgeschlagen, wobei plausible Identifikationsergebnisse erzielt werden konnten. Weiterhin wird im Rahmen der Identifikation von thermischen Raummodellen auch auf die wichtige Problematik nicht messbarer Störungen (z. B. Raumbelegung sowie Wärmeströme aus Nachbarräumen) eingegangen und mögliche Lösungsansätze aufgezeigt. Aufgrund der umfangreichen Sensorausstattung einiger Demonstratoren konnte zudem ein direkter Vergleich eines LTI-Modells mit dem obig genannten nichtlinearen Modellansatz durchgeführt werden, wobei eine vergleichbare Prädiktionsgüte beider Modellierungsansätze festgestellt wurde. Im letzten Teil wird dann der Entwurf modellprädiktiver Regler anhand zweier typischer Beispiele aus der Gebäudetechnik veranschaulicht. Für die Demonstration des Vorgehens werden Regelstreckenmodelle mittels der Modelica Buildings Bibliothek entworfen und dann für die Generierung synthetischer Daten verwendet, welche zur Identifikation von Modellen für den MPC Entwurf verwendet werden. Die identifizierten Modelle sind in beiden Fällen in der Lage das dynamische Verhalten des Modelica Prozessmodells hinreichend gut vorherzusagen, was die Sinnhaftigkeit des gewählten Modellierungs- bzw. Identifikationsansatzes untermauert. Aufbauend wird dann für beide Beispiele auf die Formulierung einer prädiktiven Regelungsstrategie eingegangen, wobei spezielle Modelleigenschaften ausgenutzt werden. Für beide Beispiele konnten simulativ Vorteile gegenüber einer konventionellen Regelungsstrategie nachgewiesen werden.