<p>Electron beam therapy represents an underutilized area in radiation therapy. While electron radiation therapy has existed for many decades and electron beams with multiple energies are available on linear accelerators – the most common device to deliver radiation therapy – efforts to advance the field have been slow. In contrast, photon beam therapy has seen rapid advancements in the past decade, and has become the main modality for radiation therapy treatment. </p><p>This doctoral research project comprises the development of a novel treatment modality, dynamic electron arc radiotherapy (DEAR) that seeks to address challenges to clinical implementation of electron beam therapy by providing a technique that may be able to treat specific patient subsets with better outcomes than current techniques. This research not only focused on the development of DEAR, but also aimed to improve upon and introduce new tools and techniques that could translate to current clinical electron beam therapy practice. </p><p>The concept of DEAR is presented. DEAR represents a new conformal electron therapy technique with synchronized couch motion. DEAR utilizes the combination of gantry rotation, couch motion, and dose rate modulation to achieve desirable dose distributions in patient. The electron applicator is kept to minimize scatter and maintain narrow penumbra. The couch motion is synchronized with the gantry rotation to avoid collision between patient and the electron cone. </p><p>First, the feasibility of DEAR delivery was investigated and the potential of DEAR was demonstrated to improve dose distributions on simple cylindrical phantoms. DEAR was delivered on Varian’s TrueBeam linac in Research Mode. In conjunction with the recorded trajectory log files, mechanical motion accuracies and dose rate modulation precision were analyzed. Experimental and calculated dose distributions were investigated for a few selected energies (6 MeV and 9 MeV) and cut-out sizes (1x10 cm2 and 3x10 cm2 for a 15x15 cm2 applicator). Our findings show that DEAR delivery is feasible and has the potential to deliver radiation dose with high precision (RMSE of <0.1 MU, <0.1° gantry, and <0.1 cm couch positions) and good dose rate precision (1.6 MU/min). Dose homogeneity within ±2 % in large and curved targets can be achieved while comparable penumbra to a standard electron beam on a flat surface can be maintained. Further, DEAR does not require fabrication of patient-specific shields, which has hindered the widespread use of electron arc therapy. These benefits make DEAR a promising technique for conformal radiotherapy of superficial tumors.</p><p>Next, an accurate dose calculation framework for DEAR was developed since current commercial dose calculation systems cannot handle the dynamic nature of the DEAR. Comprehensive validations of vendor provided electron beam phase space files for Varian TrueBeam linacs against measurement data were assessed. In this framework, the Monte Carlo generated phase space files were provided by the vendor and used as input to the downstream plan-specific simulations including jaws, electron applicators, and water phantom computed in the EGSnrc environment. The phase space files were generated based on open field commissioning data. A subset of electron energies of 6, 9, 12, 16, and 20 MeV and open and collimated field sizes 3×3, 4×4, 5×5, 6×6, 10×10, 15×15, 20×20, and 25×25 cm2 were evaluated. Measurements acquired with a CC13 cylindrical ionization chamber and electron diode detector and simulations from this framework were compared for a water phantom geometry. The evaluation metrics include percent depth dose, orthogonal and diagonal profiles at depths R100, R50, Rp, and Rp+ for standard and extended source-to-surface distances (SSD), as well as cone and cut-out output factors. Agreement for the percent depth dose and orthogonal profiles between measurement and Monte Carlo were generally within 2% or 1 mm. The largest discrepancies were observed for depths within 5 mm from the phantom surface. Differences in field size, penumbra, and flatness for the orthogonal profiles at depths R100, R50, Rp, and Rp+ were within 1 mm, 1 mm, and 2%, respectively. Simulated and measured orthogonal profiles at SSDs of 100 and 120 cm showed the same level of agreement. Cone and cut-out output factors agreed well with maximum differences within 2.5% for 6 MeV and 1% for all other energies. Cone output factors at extended SSDs of 105, 110, 115, and 120 cm exhibited similar levels of agreement. The presented Monte Carlo simulation framework for electron beam dose calculations for Varian TrueBeam linacs for electron beam energies of 6 to 20 MeV for open and collimated field sizes from 3×3 to 25×25 cm2 were studied and results were compared to the measurement data with excellent agreement. </p><p>DEAR uses the superposition of many small fields for its delivery, as such accurate planning requires the knowledge of accurate small field dosimetry. Prior research has shown that previous versions of the clinically used eMC dose calculation algorithm (Varian Medical Systems, Inc., Palo Alto, CA) cannot accurately calculate small static electron fields, leading to discrepancies in the dose distributions and output. Further, the clinical treatment planning system, Eclipse, currently does not support the planning of dynamic electron radiation therapy. Therefore, the aforementioned validation was extended to small fields and compared to dose calculations from the treatment planning system.</p><p>Subsequently, small field optimization was explored. Monte Carlo simulations were performed using validated Varian TrueBeam phase space files for electron beam energies of 6, 9, 12, and 16 MeV and square (1x1, 2x2, 3x3, 4x4, and 5x5 cm2) and circular (1, 2, 3, 4, and 5 cm diameter) fields. Resulting dose distributions (kernels) were used for subsequent calculations. The following analyses were performed: (1) Comparison of composite square fields and reference 10x10 cm2 dose distributions and (2) Scanning beam deliveries for square and circular fields realized as the convolution of kernels and scanning pattern. Preliminary beam weight and pattern optimization were also performed. Two linear scans of 10 cm with/without overlap were modeled. Comparison metrics included depth and orthogonal profiles at dmax. (1) Composite fields regained reference depth dose profiles for most energies and fields within 5%. Smaller kernels and higher energies increased dose in the build-up and Bremsstrahlung region (30%, 16 MeV and 1x1 cm2), while reference dmax was maintained for all energies and composite fields. Smaller kernels (<2x2 cm2) maintained penumbra and field size within 0.2 cm, and flatness within 2 and 4% in the cross-plane and in-plane direction, respectively. Deterioration of penumbra for larger kernels (5x5 cm2) was observed. Balancing desirable dosimetry and efficiencies suggests that smaller kernels should be used at the target edges and larger kernels in the center of the target. (2) Beam weight optimization improves cross-plane penumbra (0.2 cm) and increases the field size (0.4 cm) on average. In-plane penumbra and field size remain unchanged. Overlap depends on kernel size and optimal overlap results in flatness ±2%. Dynamic electron beam therapy in virtual scanning mode is feasible by employing small fields to achieve desired dose distributions and acceptable efficiencies.</p><p>Further, tools to generally improve upon limitations in Monte Carlo simulations for electron beams were investigated. The phase space file contains a finite number of particle histories and can have very large file size, yet still contains inherent statistical noises. A characterization of the phase space file was investigated to overcome its inherent limitations. To characterize the phase space file, distributions for energy, position, and direction of all particles types were analyzed as piece-wise parameterized functions of radius. Subsequently, a pseudo phase space file was generated based on this characterization. Validation was assessed by directly comparing the original and pseudo phase space file, and by comparing the resulting dose distributions from Monte Carlo simulations using both phase space files. Monte Carlo simulations were run for energies 6, 9, 12, and 16 MeV and all standard field sizes 6x6, 10x10, 15x15, 20x20, and 25x25 cm2. Percent depth dose and orthogonal profiles at depths R100, R50, and Rp were evaluated. Histograms of the original and pseudo phase space file agree very well with correlation coefficients greater than 0.98 for all particle attributes. Dosimetric comparison between original and pseudo dose distributions yielded agreement within 2%/1mm for PDDs and profiles at all depths for all field sizes 6x6, 10x10, 15x15, 20x20, and 25x25 cm2 and energies 6, 9, 12, and 16 MeV. Phase space files were found to be successfully characterized by piece-wise distributions for energy, position, and direction as parameterized functions of radius and polar angle. This facilitates generation of sufficient particles at any statistical precisions.</p><p>Additionally, new hardware for improved DEAR capability was investigated. Few leaf electron collimators (FLEC) or electron MLCs (eMLC) are highly desirable for dynamic electron beam therapies as they produce multiple apertures within a single delivery to achieve conformal dose distributions. However, their clinical implementation has been challenging. Alternatively, multiple small apertures in a single cut-out with variable jaw sizes could be utilized in a single dynamic delivery. A Monte Carlo simulation study was performed to investigate the dosimetric characteristics of such an arrangement. Investigated quantities included: Energy (6 and 16 MeV), jaw size (1x1 to 22x22 cm2; centered to aperture), applicator/cut-out (15x15 cm2), aperture (1x1, 2x2, 3x3, and 4x4 cm2), and aperture placement (on/off central axis). Three configurations were assessed: (a) single aperture on-axis, (b) single aperture off-axis, and (c) multiple apertures. Reference was configuration (a) with the standard jaw size. Aperture placement and jaw size were optimized to maintain reference dosimetry and minimize leakage through unused apertures to <5%. Comparison metrics included depth dose and orthogonal profiles. Configuration (a) and (b): Jaw openings were reduced to 10x10 cm2 without affecting dosimetry (gamma 2%/1mm) regardless of on- or off-axis placement. For smaller jaw sizes, reduced surface (<2%, 5% for 1x1 cm2 aperture) and increased Bremsstrahlung (<2%, 10% for 1x1 cm2 aperture) dose was observed. Configuration (c): Optimal aperture placement was in the corners (order: 1x1, 4x4, 2x2, 3x3 cm2 for quadrants I, II, III, and IV) and jaw size were 2x2, 2x2, 3x3, and 7x7 cm2 and 7x7, 7x7, 10x10, and 10x10 cm2 for apertures: 1x1, 2x2, 3x3, 4x4 cm2 and energies 6 and 16 MeV, respectively. Asymmetric leakage was found from upper and lower jaws. Leakage was generally within 5% with a maximum of 10% observed for the 1x1 cm2 aperture irradiation. Multiple apertures in a single cut-out with variable jaw size can be used in a single dynamic delivery, thus providing a practical alternative to FLEC or eMLC.</p><p>Based on all the results from this project, DEAR has been found to be a feasible technique and demonstrates the potential to improve electron therapy.</p> / Dissertation

Pyrochlore-type oxides (A2B2O7) and glass-ceramic composites have been investigated for nuclear waste sequestration applications due to the remarkable compositional diversity and structural flexibility of these materials. These properties can enhance the incorporation of radioactive waste elements and resistance to radiation induced structural damage. Radiation induced structural damage can be simulated by bombarding materials using high-energy heavy ions. The study has shown how the metal-oxygen bond covalency, cationic radii ratio (rA/rB), and oxygen vacancies of pyrochlore type oxides affect the resistance of these materials to radiation induced damage. RE2Ti2O7 (RE=La–Lu), Yb1.85Ca0.15Ti2O7-δ, Yb2Ti1.85Fe0.15O7-δ, and Gd2Ti2-xSnxO7 were synthesized by the ceramic method and investigated by X-ray absorption near edge spectroscopy (XANES), which allows for the study of the effect of elemental substitution on the electronic structure of materials. Surface sensitive glancing angle and total electron yield XANES (GA/TEY XANES) spectra have been used to study the damaged surface of the materials, as the high energy ions can only implant in the near-surface region (~ 450 nm) of the pellets. These measurements have allowed for an investigation of how the local structure of the materials changed after ion implantation and discussed in terms of coordination number and bonding environment. After investigating the ceramic materials, the glass-ceramic composite materials containing Gd2Ti2O7 pyrochlore type crystallites in a (borosilicate- and Fe-Al-borosilicate) glass were investigated. These glass-ceramic materials were synthesized and analyzed by backscattered electron (BSE) images and XANES spectra. The study has shown how the Gd2Ti2O7 crystallites interact within a glass matrix depending on glass composition, pyrochlore loading, and annealing temperature. Further, the GA-XANES spectra from these materials have shown that the glass ceramic composite materials show a similar response to ion implantation as pure ceramics (i.e., Gd2Ti2O7). All of these studies and techniques could provide a better understanding of how to develop and design materials for nuclear waste sequestration applications.

This research experimentally shows the effect of sediment roughness characteristics on the acoustic reflection coefficient. This information is useful when trying to classify various types of sediment over an area. This research was conducted in an indoor laboratory tank at Applied Research Laboratories (ARL) at the University of Texas at Austin. A single beam echo-sounder (SBES) system was developed to project and receive a wideband (3 kHz to 30 kHz) acoustic pulse. A method was developed using the system transfer function to create a custom pulse that would minimize the dynamic range over the wide frequency band. A matched filtering and data processing algorithm was developed to analyze data over the full frequency bandwidth and over smaller frequency bands. Analysis over the smaller frequency bands showed the effect of the roughness on the reflection coefficient with respect to frequency. It was found that the reflection coefficient is significantly lower at the higher frequencies (above 20 kHz) than at the lower frequenices [sic] due to off specular scattering. It was also found that the variability of the reflection coefficient was significantly higher for the rough sediment than for the smooth sediment. / text

Significant diagonal cracking in reinforced concrete inverted-T (IT) straddle bent caps has been reported throughout the State of Texas. Many of the distressed structures were recently constructed and have generally been in service for less than two decades. The unique nature of the problem prompted a closer look into the design and behavior of such structural components. A preliminary investigation highlighted outdated design requirements and a scarcity of experimental investigations pertaining to inverted-T bent caps. This research project (TxDOT Project 0-6416, Shear Cracking in Inverted-T Straddle Bents) aims to improve current understanding of the behavior of inverted-T caps, while providing updated design provisions. In order to develop strength and serviceability guidelines for inverted-T beams, an extensive experimental program was developed. This series of large scale tests was used to evaluate the strength and serviceability of IT deep beams in relation to the following parameters – shear span-to-depth (a/d) ratio, web reinforcement ratio, ledge height, ledge length, number of point loads, and member depth. This report focuses mainly on results from a first series of tests conducted within this experimental program. / text

Theory, design, fabrication and characterization of on-chip optical beam steering systems are presented in this dissertation. Silicon photonics is being considered for integration with conventional CMOS technology for large-band width and low loss on and off-chip communications. We choose silicon nanomembrane, or silicon-on-insulator (SOI) substrates for implementation of large-angle and agile beam steeres. While working on the targeted device, we contributed to the theory, modeling, engineering and implementation of different building blocks. Multimode-interference couplers (MMIs) constitute important parts of this dissertation. These devices are commonly used as on-chip beam splitters, optical switches and on-chip static phase shifters. The MMIs’ principles of operation are suited in more details and design rules are derived for the first time. MMI based beam splitters with number of outputs as large as 12 are fabricated and tested on SOI wafers. Traditionally, MMIs devices were designed by means of computationally expensive numerical simulations. Numerically and experimentally, we show that our analytical design rules make design of MMIs with low insertion loss and highly uniform outputs possible without additional optimization processes. Optical phased arrays include phase shifter blocks. In the first prototype, we use micro-heaters for tuning the optical phase. The bread-loafing effect, which is generally considered an undeniable phenomenon in the silicon industry, is engineered to realize a mechanical structure to efficiently direct heat toward the silicon waveguides. We also investigate slow light photonic crystal based delay lines to be used as phase shifters. An important drawback of such devices is the low coupling efficiency between slow-light photonic crystal waveguides and fast light strip waveguides. We numerically and experimentally investigate the coupling efficiency, and show for the first time that a few-period long fast-light photonic crystal waveguide without any group index tapering suffices for efficient coupling. The prototype is fabricated, packaged and tested and optical beam steering angle over ±30degrees is demonstrated. Finally, preliminary investigations for 3D implementation of the beam steerer system are presented to clarify the approaches to take for future works. / text

Continual scaling of devices and on-chip wiring has brought significant challenges for materials and processes beyond the 32-nm technology node in microelectronics. Recently, three-dimensional (3-D) integration with through-silicon vias (TSVs) has emerged as an effective solution to meet the future interconnect requirements. Among others, thermo-mechanical reliability is a key concern for the development of TSV structures used in die stacking as 3-D interconnects. In this dissertation, thermal stresses and interfacial reliability of TSV structures are analyzed by combining analytical and numerical models with experimental measurements. First, three-dimensional near-surface stress distribution is analyzed for a simplified TSV structure consisting of a single via embedded in a silicon (Si) wafer. A semi-analytic solution is developed and compared with finite element analysis (FEA). For further study, the effects of anisotropic elasticity in Si and metal plasticity in the via on the stress distribution and deformation are investigated. Next, by micro-Raman spectroscopy and bending beam technique, experimental measurements of the thermal stresses in TSV structures are conducted. The micro-Raman measurements characterize the local distribution of the near-surface stresses in Si around TSVs. On the other hand, the bending beam technique measures the average stress and viii deformation in the TSV structures. To understand the elastic and plastic behavior of TSVs, the microstructural evolution of the Cu vias is analyzed using focused ion beam (FIB) and electron backscattering diffraction (EBSD) techniques. To study the impacts of the thermal stresses on interfacial reliability of TSV structures, an analytical solution is developed for the steady-state energy release rate as the upper bound of the driving force for interfacial delamination. The effect of crack length and wafer thickness on the energy release rate is studied by FEA. Furthermore, to model interfacial crack nucleation, an analytical approach is developed by combining a shear lag model with a cohesive interface model. Finally, the effects of structural designs and the variation of the constituent materials on TSV reliability are investigated. The steady state solutions for the energy release rate are developed for various TSV designs and via materials (Al, Cu, Ni, and W) to evaluate the interfacial reliability. The parameters for TSV design optimization are discussed from the perspectives of interfacial reliability. / text

The aim of the present research is to identify human subjective response (health and comfort) to the micro-thermal environment established by integration of individually controlled localized chilled beam and chilled ceiling (LCBCC) system and to compare its performance with the performance of mixing ventilation combined with chilled ceiling (CCMV).Experiments were carried out in mock-up of an office (4.1 m × 4.0 m × 3.1 m, L× W× H) with one person under two summer temperature conditions (26 °C and 28 °C). To mimic direct solar radiation in the room, five radiative panels on the wall together with electrical sheets on the half of the floor were used. The test room was set-up with two desks, as two workstations, and one laptop on each table. The main workstation (WS1) was located close to the simulated window. The second work station (WS2) was placed in the opposite side of the room. The room was equipped with two types of ventilating and cooling systems.  The first system consisted of a localized active chilled beam (LCB) unit together with chilled ceiling (CC) panels. The LCB was installed above the WS1 to create micro-environment around the occupant sitting at the desk. The supply flow rate from the LCB could be adjusted by the occupant within the range of 10 L/s to 13 L/s by means of a desk-mounted knob. The integration of mixing ventilation (MV) system and chilled ceiling panels was the second ventilating and cooling strategy. Twenty- four subjects (12 female and 12 male) were exposed to different indoor environment established by two cooling systems. Each experiment session lasted 120 min and consisted of 30 min acclimatization period and 90 min exposure period. The performance of the systems was identified and compared by physical measurements of the generated environment and the response of the human subjects. The study showed that perceived air quality (PAQ), overall thermal sensation (OTS) acceptability and local thermal sensation (LTS) acceptability clearly improved inside the micro-environment by using LCBCC system. Moreover, at the main workstation, OTS and LTS votes were close to “neutral” thermal sensation (ASHRAE seven point scale) when LCBCC system was used. However, OTS and LTS votes increased to the “slightly warm” side of the scale by applying CCMV system which implied the better cooling performance of the LCBCC system. Acceptability of work environment apparently increased under the room condition generated by LCBCC system. In agreement with human subjective study, the results from physical measurements and thermal manikin study showed that uniform thermal condition was generated all over the room. Air and operative temperature distribution was almost uniform with no difference higher than 1 °C between the measured locations in the room. Thus, both LCBCC and CCMV systems performed equally well outside of the micro-environment region. The use of the chilled ceiling had impact on the airflow interaction in the room and changed the airflow pattern. It can be concluded that the combination of convective and radiative systems can be considered as an efficient strategy to generate acceptable thermal condition in rooms.

The beam-foil method was used to determine mean-lives of excited atomic states. Initial studies were done on states. Initial studies were done on states of the helium- and hydrogen-like ions B IV and B V, with the mean-lives determined by fitting the decay curves to sums of exponential terms. Since theoretical values of the mean-lives are very precise in these simple atomic systems, our results indicate the accuracy of the experimental method. A series of measurements was made of the low lying 2s 2p⁴ states in nitrogen-like Ne IV, Na V, Mg VI, Al VII, and Si VIII. The experimental results were compared to theoretical calculations of Fawcett and Sinanoglu, and showed excellent agreement with Sinanolu's nonclosed-shell many electron theory. The lifetimes of the 4p ²P₁/₂ and 4p ²P₃/₂ states in copper-like Br VII were determined by measuring decay curves for both the primary and cascade decays and then analyzing the curves jointly. Our resulting mean-life values are considerbly shorter than those of previous experiments which analyzed only the primary decay curve. Comparison with theoretical calculations showed excellent agreement with those which include core polarization effects.

This thesis describes the development of an empirical model of focus beam reflectance measurements (FBRM) and the application of the model to monitoring batch cooling crystallization and extracting information on crystallization kinetics. Batch crystallization is widely used in the fine chemical and pharmaceutical industries to purify and separate solid products. The crystal size distribution (CSD) of the final product greatly influences the product characteristics, such as purity, stability, and bioavailability. It also has a great effect on downstream processing. To achieve a desired CSD of the final product, batch crystallization processes need to be monitored, understood, and controlled. FBRM is a promising technique for in situ determination of the CSD. It is based on scattering of laser light and provides a chord-length distribution (CLD), which is a complex function of crystal geometry. In this thesis, an empirical correlation between CSDs and CLDs is established and applied in place of existing first-principles FBRM models. Built from experimental data, the empirical mapping of CSD and CLD is advantageous in representing some effects that are difficult to quantify by mathematical and physical expressions. The developed model enables computation of the CSD from measured CLDs, which can be followed during the evolution of the crystal population during batch cooling crystallization processes. Paracetamol, a common drug product also known as acetaminophen, is selected as the model compound in this thesis study. The empirical model was first established and verified in a paracetamol-nonsolvent (toluene) slurry, and later applied to the paracetamol-ethanol crystallization system. Complementary to the FBRM measurements, solute concentrations in the liquid phase were determined by in situ infrared spectra, and they were jointly implemented to monitor the crystallization process. The framework of measuring the CSD and the solute concentration allows the estimation of crystallization kinetics, including those for primary nucleation, secondary nucleation, and crystal growth. These parameters were determined simultaneously by fitting the full population balance model to process measurements obtained from multiple unseeded paracetamol-ethanol crystallization runs. The major contributions of this thesis study are (1) providing a novel methodology for using FBRM measurements to estimate CSD; (2) development of an experimental protocol that provided data sets rich in information on crystal growth and primary and secondary nucleation; (3) interpretation of kinetics so that appropriate model parameters could be extracted from fitting population balances to experimental data; (4) identification of the potential importance of secondary nucleation relative to primary nucleation. The protocol and methods developed in this study can be applied to other systems for evaluating and improving batch crystallization processes.

Στόχος της παρούσας εργασίας είναι η δημιουργία ενός προγράμματος ηλεκτρονικού υπολογιστή για τη μελέτη της συμπεριφοράς δοκών ενισχυμένων με πρόσθετες στρώσεις σκυροδέματος, στο εφελκυόμενο και στο θλιβόμενο πέλμα. Η διατριβή αυτή αποτελείται από οκτώ κεφάλαια τα οποία συνοπτικά περιλαμβάνουν τα εξής: Το πρώτο κεφάλαιο είναι εισαγωγικό και κάνει μια αναφορά στις βλάβες των δοκών οπλισμένου σκυροδέματος, στους τρόπους επισκευής και ενίσχυσής τους καθώς και στον τρόπο εξασφάλισης της σύνδεσης στη διεπιφάνεια παλιού και νέου στοιχείου. Στο δεύτερο κεφάλαιο γίνεται περιγραφή του προβλήματος με το οποίο πραγματεύεται η παρούσα εργασία. Γίνεται αναφορά στη συμπεριφορά των σύνθετων μελών, στον τρόπο προσομοίωσης της διατμητικής τάσης στη διεπιφάνεια καθώς και μια σύντομη βιβλιογραφική ανασκόπηση. Στο τρίτο κεφάλαιο περιγράφεται το αναλυτικό μοντέλο που δημιουργήθηκε για τη μελέτη δοκών ενισχυμένων με νέες στρώσεις σκυροδέματος. Περιγράφονται αναλυτικά οι θεωρητικές εξισώσεις που χρησιμοποιήθηκαν, δίνονται τα διαγράμματα ροής των προγραμμάτων που γράφτηκαν σε γλώσσα προγραμματισμού FORTRAN για τη μελέτη ενισχυμένων και μονολιθικών δοκών, καθώς και κάποιες εφαρμογές των προγραμμάτων αυτών. Στο επόμενο κεφάλαιο γίνεται ένας έλεγχος της αξιοπιστίας των προγραμμάτων που αναφέρθηκαν προηγουμένως, με σύγκριση με πειραματικά αποτελέσματα. Επίσης γίνεται και μία παραμετρική διερεύνηση για τα συγκεκριμένα πειραματικά δοκίμια. Η γενίκευση των αποτελεσμάτων που προέκυψαν από την παραμετρική διερεύνηση του τέταρτου κεφαλαίου γίνεται μέσω της παραμετρικής διερεύνησης του κεφαλαίου πέντε και που αφορά ένα πλήθος δοκιμίων ενισχυμένων με διάφορους τρόπους. Στο έκτο κεφάλαιο πραγματοποιείται έλεγχος κάποιων θεωρητικών εξισώσεων που δίνουν τη διατμητική τάση στη διεπιφάνεια του ενισχυμένου δοκιμίου καθώς και μιας ακόμη εξίσωσης που υπολογίζει τον οπλισμό ενίσχυσης. Στο έβδομο κεφάλαιο παρουσιάζονται κάποιες θεωρητικές εξισώσεις που προέκυψαν στα πλαίσια της παρούσας διατριβής, από την προσπάθεια να εκτιμηθεί η κατανομή της ολίσθησης κατά μήκος της ενισχυμένης δοκού. Η εργασία τελικά ολοκληρώνεται με το όγδοο κεφάλαιο που παρουσιάζει συγκεντρωτικά όλα τα συμπεράσματα. / The object of this thesis was the creation of computer programs to predict the behaviour of reinforced concrete beams strengthened by placing additional layers in the tensile and compressive regions. This thesis consists of eight chapters. By way of introduction, the first chapter describes the damage sustained by reinforced concrete beams, outlines methods of strengthening and describes techniques used to connect between old and new elements. The second chapter presents a literature review. The behaviour of composite members and a method that simulates the shear stresses that develop at the interface between the old and the new concrete are described. The analytical models that were created to model the strengthening of reinforced beams is described in the third chapter. An analytical description of the theoretical equations that were used is presented as well as a flow chart of the programs that were created in FORTRAN in order to predict the behaviour of monolithic and strengthened beams. Some applications of the programs are also presented in this chapter. The fourth chapter conducts reliability study of the programs that were created and results are compared to experimental results. In addition, there is a parametric study of experimental beams. An additional parametric study of several specimens that were strengthened by using different methods is performed in the fifth chapter in order to generalize the results from the fourth chapter. In the sixth chapter theoretical equations that calculate the shear stress at the interface of the strengthened specimen and the amount of the reinforcing steel that is required are examined. Theoretical equations that have been derived from this thesis are presented in the seventh chapter. These theoretical equations can be used to calculate the distribution of sliding along the interface of a strengthened beam. Finally, all conclusions of this thesis are presented in the eighth chapter. It was found that the programs gave results that are very close to experimental results. In addition, the program that was written for strengthened elements can also be used for the monolithic elements by using a large value for the stuffiness factor of the interface. This program also gave results very close to those of the theoretical equations that calculate shear stress at interface presented in chapter six, especially when a new layer is added to the compressive region of the beam. The theoretical equations that are derived in chapter seven need further examination and the modification of the programs to use these equations could be a part of a future work.