Pastaraisiais metais vis plačiau taikant stiprųjį betoną bei armatūrą, konst-rukcijų perdengiamos angos didėja, o skerspjūviai mažėja. Todėl projektuojant standumo (įlinkių) sąlyga vis dažniau tampa lemiamu veiksniu. Inžinieriai gelž-betoninių konstrukcijų apskaičiavimams gali taikyti empirinius normų arba skai-tinius metodus. Vieno ar kito skaičiavimo metodo parinkimas turi būti pagrįstas statistiniais tikslumo analizės rezultatais. Yra žinoma, kad adekvatus gelžbetoninio elemento pleišėjimo (ypač plyšių vystymosi stadijos) modeliavimas yra vienas sudėtingiausių netiesinės mechani-kos uždavinių. Toks uždavinys gali būti išspręstas taikant vidutinių plyšių kon-cepciją, kai pleišėjimo proceso modeliavimui naudojama tempiamojo betono vidutinių įtempių ir deformacijų diagrama. Dauguma tokių diagramų gautos, naudojant tempimo arba šlyties bandymo rezultatus. Pabrėžtina, kad šių diagra-mų taikymas lenkiamųjų gelžbetoninių elementų modeliavime duoda nemažas paklaidas. Kitas svarbus aspektas yra tai, kad gelžbetoniniuose bandiniuose, iki juos apkraunant trumpalaike apkrova, vyksta betono susitraukimas. Šiame darbe buvo siekiama sukurti metodą, leidžiantį pagal eksperimentinius lenkiamųjų gelžbetoninių elementų duomenis gauti tempiamojo betono vidutinių įtempių ir deformacijų diagramas, įvertinant betono susitraukimo įtaką. Pagrindinis diser-tacijos tikslas yra įvertinti ikieksploatacinių betono susitraukimo ir valkšnumo poveikį gelžbetoninių elementų, apkrautų trumpalaike apkrova... [toliau žr. visą tekstą] / Due to the use of refined ultimate state theories as well as high strength concrete and reinforcement, resulting in longer spans and smaller depths, the serviceability criteria often limits application of modern reinforced concrete (RC) superstructures. In structural analysis, civil engineers can choose between traditional design code methods and numerical techniques. In order to choose a particular calculation method, engineers should be aware of accuracy of differ-ent techniques. Adequate modelling of RC cracking and, particularly, post-cracking behaviour, as one of the major sources of nonlinearity, is the most im-portant and difficult task of deformational analysis. In smeared crack approach dealing with average cracking and strains, post-cracking effects can be modelled by a stress-strain tension-stiffening relationship. Most known tension-stiffening relationships have been derived from test data of shrunk tension or shear mem-bers. Subsequently, these constitutive laws were applied for modelling of bend-ing elements which behaviour differs from test members. Furthermore, such re-lationships were coupled with shrinkage effect. Therefore, present research aims at developing a technique for deriving a free-of-shrinkage tension-stiffening re-lationship using test data of shrunk bending RC members. The main objective of this PhD dissertation is to investigate shrinkage influence on deformations and tension-stiffening of RC members subjected to short-term loading. Present... [to full text]

Concrete marine structures are typically exposed to harsh marine environments where the ingress of chloride ions can lead to corrosion of steel reinforcing bars, reducing both strength and service life; therefore, concrete must be proportioned to resist these environments. Current recommendations for concrete mixtures and plastic shrinkage cracking both reduce the resistance to chloride ingress. The main objective of this thesis was to understand the benefits of fiber addition to concrete exposed to chlorides and quantify those benefits, which would lead to a concrete mixture suitable for marine structures in freeze thaw environments. The research program tested two different fibers in a total of nine concrete mixtures. The results demonstrated that fiber addition at dosages up to 0.33 % by volume resulted in significant reduction or elimination of plastic shrinkage cracking and the chloride tests determined that the ternary FRC mixtures had the best resistance to chloride diffusion.

Multivariate generalized linear mixed models (MGLMM) are used for jointly modeling the clustered mixed outcomes obtained when there are two or more responses repeatedly measured on each individual in scientific studies. The relationship among these responses is often of interest. In the clustered mixed data, the correlation could be present between repeated measurements either within the same observer or between different observers on the same subjects. This study proposes a series of in- dices, namely, intra, inter and total correlation coefficients, to measure the correlation under various circumstances of observations from a multivariate generalized linear model, especially for joint modeling of clustered count and continuous outcomes. Bayesian methods are widely used techniques for analyzing MGLMM. The need for noninformative priors arises when there is insufficient prior information on the model parameters. Another aim of this study is to propose an approximate uniform shrinkage prior for the random effect variance components in the Bayesian analysis for the MGLMM. This prior is an extension of the approximate uniform shrinkage prior. This prior is easy to apply and is shown to possess several nice properties. The methods are illustrated in terms of both a simulation study and a case example.

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This thesis which consists of four papers is concerned with estimation methods in factor analysis and structural equation models. New estimation methods are proposed and investigated. In paper I an approximation of the penalized maximum likelihood (ML) is introduced to fit an exploratory factor analysis model. Approximated penalized ML continuously and efficiently shrinks the factor loadings towards zero. It naturally factorizes a covariance matrix or a correlation matrix. It is also applicable to an orthogonal or an oblique structure. Paper II, a simulation study, investigates the properties of approximated penalized ML with an orthogonal factor model. Different combinations of penalty terms and tuning parameter selection methods are examined. Differences in factorizing a covariance matrix and factorizing a correlation matrix are also explored. It is shown that the approximated penalized ML frequently improves the traditional estimation-rotation procedure. In Paper III we focus on pseudo ML for multi-group data. Data from different groups are pooled and normal theory is used to fit the model. It is shown that pseudo ML produces consistent estimators of factor loadings and that it is numerically easier than multi-group ML. In addition, normal theory is not applicable to estimate standard errors. A sandwich-type estimator of standard errors is derived. Paper IV examines properties of the recently proposed polychoric instrumental variable (PIV) estimators for ordinal data through a simulation study. PIV is compared with conventional estimation methods (unweighted least squares and diagonally weighted least squares). PIV produces accurate estimates of factor loadings and factor covariances in the correctly specified confirmatory factor analysis model and accurate estimates of loadings and coefficient matrices in the correctly specified structure equation model. If the model is misspecified, robustness of PIV depends on model complexity, underlying distribution, and instrumental variables.

The long term goal of this research is to improve the fire resistance of gypsum wallboard (GWB). Gypsum wallboard consists mainly of gypsum, i.e. calcium sulfate dihydrate, CaSO4•2H2O. In buildings, the chemical, mechanical and thermal properties of gypsum wallboard play an important role in delaying the spread of fire. To build a fire resistant GWB, it is very important to study the thermal, mechanical, physical and chemical properties of regular GWB and various types of fire-resistant wallboards available commercially in the market. Various fire-resistant GWBs have been compared and contrasted with reference to a standard wallboard in this study. Regardless of the type of wallboard, the main component is gypsum. The fire resistance property is mainly attributed to the absorption of energy related with the loss of hydrate water going from the dihydrate (CaSO4•2H2O) form to the hemihydrate (CaSO4•½H2O) and from the hemihydrate to the anhydrous form (CaSO4) in a second dehydration. The present paper is a comparative study of commercially available standard, fire-rated Type X and firerated Type C gypsum wallboards. Type X wallboards are typically reinforced with noncombustible fibers so as to protect the integrity of the wallboard during thermal shrinkage, while the Type C wallboards are incorporated with more glass fibers and an additive, usually a form of vermiculite. These Type C wallboards have a shrinkage adjusting element that expands when exposed to elevated temperature. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), thermomechanical analysis (TMA), scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) were used to characterize and compare the materials. Various properties, such as the heat flow, weight loss, dimensional changes, morphology and crystalline structures of the gypsum wallboards were studied using these techniques.

Transverse cracking in bridge decks has been found to be a rising problem for slab-on-girder bridges. In response to the concern, this research examined the influence of structural parameters and developed an analytical truss model, based on finite element modelling responses, for predicting the condition of long term cracking. Crack widths predicted using the truss model are very similar to that measured in a recent survey of Ontario highway overpass bridges. The approach to control cracking in deck slabs through structural design decisions enables engineers to provide high cracking resistance at locations of the bridge deck that are most likely to crack. Recommendations were made, based on the findings obtained from two sets of parametric studies, to help ensure transverse cracking in bridge decks is properly controlled for typical slab-on-girder bridges designed using the empirical design method specified in the current Canadian Highway Bridge Design Code.

Transverse cracking in bridge decks has been found to be a rising problem for slab-on-girder bridges. In response to the concern, this research examined the influence of structural parameters and developed an analytical truss model, based on finite element modelling responses, for predicting the condition of long term cracking. Crack widths predicted using the truss model are very similar to that measured in a recent survey of Ontario highway overpass bridges. The approach to control cracking in deck slabs through structural design decisions enables engineers to provide high cracking resistance at locations of the bridge deck that are most likely to crack. Recommendations were made, based on the findings obtained from two sets of parametric studies, to help ensure transverse cracking in bridge decks is properly controlled for typical slab-on-girder bridges designed using the empirical design method specified in the current Canadian Highway Bridge Design Code.

The influence of drying parameters namely residence time before drying, drying temperature, drying time, relative humidity, and slip recipe on the drying rate of slip cast sanitary wares, predominantly lavatories and toilet closets, was studied. The drying temperatures were changed from 80 oC to 110 oC with an increment of 10 oC. The drying time was changed from 10 to 7 h with a decrease of 1 hour. Relative humidity of the environment was changed from 60 to 75 %. The percent weight loss, percent residual moisture and the percent shrinkage of the samples were determined by weighing and measuring the samples before and after the tests. The percent weight loss was within the range of 6.5 to 6.6 % after holding the as cast samples for 6 hours at ambient casting shop conditions while it was within the range of 17.96 to 18.10 % when subsequently dried for 10 hours at 110 oC in the dryer. The percent shrinkage was within the range of 2.9 - 3.0 % after holding the as cast samples 6 h at ambient laboratory conditions. No shrinkage was observed in the sample when it was subsequently dried for 10 hours at 110 oC in the dryer. Optimum moisture content of dried wares was obtained after drying for 8 hours at 100 oC in the dryer. It has been seen that the relative humidity of the dryer at the beginning of the drying should be lower than 75 %. As the non-plastic content in the recipe of the sanitary ware slip increased, drying shrinkage and residual moisture content decreased. The results of this study showed that through increasing the residence time up to 6h with a casting shop environment of approximately 30 oC and 60 % relative humidity, the drying time could be safely reduced from 10 h to 8 h with a drying temperature of 100 oC for the test plates. The same approach can be used for more complex shapes, e.g., WC closets, basins, tanks etc. in EczacibaSi Vitra plant. Once the drying time was reduced, the amount of natural gas per ware would be reduced to a certain extent. Aside from that the reduction in the drying time would increase the quantity of the drying cycles per week so that more wares could be dried. When all these observations were taken into account, this thesis study could also be utilized by other sanitary ware producing companies whose processes require slip cast drying.

A whole genome scan was conducted to identify and fine map QTL regions for ultrasound and carcass merit traits in beef cattle. A total of 465 steers and bulls, genotyped for 4592 SNPs, were analysed for 16 ultrasound and carcass merit traits using interval mapping, single marker regression and Bayesian shrinkage approaches. Thirty QTL and 22 SNPs associated with traits were identified by interval mapping and single marker regression respectively. In Bayesian shrinkage estimation, 218 QTL were identified, wherein 11 of the 30 QTL identified by interval mapping were confirmed. The proportions of QTL variance on the trait variations estimated by Bayesian shrinkage analysis were relatively small. They ranged from 0.1 to 4.8% compared to 6.1 to 11.7% in interval mapping because the QTL in Bayesian approach were adjusted to remove effects of other QTL in the genome. These results are useful for detection of underlying causative QTN variants. / Animal Science