Maintenance management is to design, operate, and maintain the reliability and availability of assets at a required performance level using the lowest possible cost. The standby redundancy is one of the means to achieve highly reliable system with less dependable units. As commonly used performance indicator, the reliability and availability should be precisely analysed for a repairable standby system. The reliability of a standby system is mainly studied in the framework of lifetime approach. Most existing models are developed for a two-unit standby system and a Kout- of-N system with identical units. The system units are assumed to be binary-state and the failures of system units are modelled as sudden failures. The deteriorations of units are modelled as time-dependent failure rate and are assumed to be independent. In addition, most of the existing models do not consider maintenance is carried out on the system. In reality, the deteriorations and the resultant failures in real-world systems are often interactive with each other. The systems normally experience several, often imperfect, restorations before a complete renewal. Therefore, the study of different repair policies, such as opportunistic and individual policies, in multi-unit systems need also be investigated. To address the problem, the reliability and availability models for a 2-out-of-3 cold standby system will be studied in a multi-state system reliability framework. A multistate multi-path failure mode is proposed to model the interactive deteriorations. The concept of repair matrix will be adopted to model the effect of unit level restorations on system reliability. The availabilities under individual repair policy and opportunistic repair policy will be developed.

Lietuvoje įrengta 1590 tvenkinių, pastatyta daug kitokių hidrotechnikos statinių ir beveik kiekviename iš jų yra gelžbetoninių elementų ar konstrukcijų. Naudojami statiniai patiria įvairių apkrovų ir agresyvios aplinkos poveikį, dėl to jie ilgainiui nusidėvi, formuojasi pažaidos, statiniai genda ir tampa nebetinkami naudoti. Darbo tikslas – įvertinti defektų ir pažaidų įtaką naudojamų hidrotechnikos statinių gelžbetoninių konstrukcijų techninei būklei. 2006 metais tyrinėtos Marijampolės rajono naudojamų hidrotechnikos statinių gelžbetoninės konstrukcijos. Nustatyta pagrindinė konstrukcijų stiprum���� apibūdinanti charakteristika – gniuždomojo betono stipris. Užfiksuoti konstrukcijų defektai bei pažaidos, aptariamos galimos jų atsiradimo priežastys, konstrukcijų būklė įvertinta balais. Nurodyti dažniausiai pasitaikantys konstrukcijų defektai bei pažaidos, kurie atsirado dėl netinkamų sudėčių bei savybių betono, naudojimo trūkum��. / There are approximately 1590 dams and many other hydraulic structures constructed in Lithuania. Most of them have reinforced concrete elements or constructions. Due to different loads and environmental impact, condition of operational structures gets worse in time. Therefore, some deterioration may occur which leads structures to failure and makes them no longer useful for exploitation. The purpose of this work is to evaluate the influence of defects and deteriorations to the technical state of reinforced concrete hydraulic structures. In 2006, reinforced concrete constructions of hydraulic structures were investigated in Marijampole district. Compression strength is determined as the main characteristic of these constructions. Defects and deteriorations of constructions are noticed; main reasons that influence deterioration are discussed; and condition of constructions is estimated by points. It is established that most common defects and deteriorations are caused because of the use of unfit manufactured concrete and its shortage.

Vandentiekio bokštų (toliau – VB) konstrukcijos veikiamos apkrovų ir neigiamo aplinkos poveikio nudėvimos, susiformuoja pažaidos. Pavojingiausios pažaidos, mažinančios konstrukcijų laikančiąją galią. Netekus laikomosios galios kyla grėsmė statinio patikimumui ir ilgaamžiškumui, galima statinio griūtis. Darbo tikslas – įvertinti gelžbetoninių vandentiekio bokštų būklę pagal pastebėtus defektus ir pažaidas. Atlikus natūrinius ir laboratorinius tyrimus buvo nustatytas vandentiekio bokštų: gniuždomojo betono stipris naudojant E. Šmidto plaktuką; betono gniuždomasis stipris, tankis ir įgėris, ištyrus bandinius laboratorijoje. Ekspedicijų metu fiksuotos vandentiekio bokštų pagrindinės pažaidos ir defektai. Dažniausiai pasitaikančios vandentiekio bokštų pažaidos: paviršiniai plyšiai betone iki 0,2–0,3 mm pločio; paviršinio sluoksnio trupėjimas (irimas). Visiems tirtiems VB reikia atlikti remonto darbus. Pagrindiniai žodžiai: pažaidos, vandentiekio bokštas. / Water – supply towers constructions exposed of a load and a negative environmental influence are wear out, and deteriorations are formed. The most dangerous deteriorations are those reduce constructions bearing capasity. Loss of the bearing capasity reduces the reliability and durability of the structure, and the structure may collapse. The aim of the work – to estimate defects and deterioration in reinforced concrete water – supply towers. The field investigations and laboratorial studies were carried out water – supply towers features: compressive strength of concrete by using E. Christian Schmidt (Schmidt E.) hammer; compressive strength, density and volume of concrete, examinating specimens in the laboratory. The main deteriorations and defects of water – supply towers were fixed at time of expeditions. Key words: deteriorations, water – supply tower.

Magistratūros baigiamajame darbe buvo analizuojamas jūrinio transportinio laivo korpuso korozinis dilimas ir jo priežastys, pateikiami defektacijos metodai, vertinami eksperimentinių matavimų metu gauti rezultatai. Baigiamasis darbas susideda iš teorinės, eksperimentinės ir praktinės dalies. Teorinėje dalyje apžvelgtos laivo korpuso nusidėvėjimo problemos, apžvelgti klasifikacinių bendrovių reikalavimai laivo korpuso būklei, išnagrinėtos laivo korpuso remonto technologijos. Eksperimentinėje dalyje pateiktos balkerio ,,LEDI CHRIS“ korpuso konstrukcijų liekamojo storio matavimo ultragarsiniu stormačiu rezultatai, palyginti matavimų duomenys, gauti laivo korpuso defektacijos tyrimo metu 2002, 2007 ir 2012 m., nustatytos labiausiai korozinio proceso paveiktos laivo konstrukcijos. Praktinėje baigiamojo darbo dalyje buvo atlikti skaičiavimai, siekiant nustatyti laivo korpuso lakštu stipruma po korozijos poveikio ir apskaičiuota tikimybes analize. / The master‘s thesis analyses the causes of the corrosive wear in marine transport ships. It is further followed by the examples of the flaw detection methods and the assessment of the results obtained through experimental measurements. The thesis has theoretical, experimental and practical parts to it. The theoretical part entails the review of the issues related to the depreciation of the ship‘s hull. Moreover, the theory includes the overview of the requirements imposed by the classification society in regards to the condition of the ship‘s hull. The thesis also brings forth the examination of the repair technology that is being used in connection to such issues. The experimental section of the thesis entails the residual thickness measurements of the hull structures obtained through the ultrasonic calipers that were applied on the bunker „LEDI CHRIS“. The comparison of the measurements‘results is also provided, based mainly on the data taken from the flaw detection test that was administered in the years 2002, 2007 and 2012. Additionally, the thesis identifies the structures of the ship that were impacted the most by the process of the corrosion. Last but not least, the practical part of the thesis presents calculations that were conducted in order to determine the durability of the ship‘s hull plating that was affected by the corrosion. The thesis concludes with the probability analysis of the corrosion causes.

Time and circumstances for the disappearance of Neanderthals and its relationship with the advent of Modern Humans are not yet sufficiently resolved, especially in case of the Iberian Peninsula. Reconstructing palaeoenvironmental conditions during the last glacial period is crucial to clarifying whether climate deteriorations or competition and contacts with Modern Humans played the pivotal role in driving Neanderthals to extinction. A high-resolution loess record from the Upper Tagus Basin in central Spain demonstrates that the Neanderthal abandonment of inner Iberian territories 42 kyr ago coincided with the evolvement of hostile environmental conditions, while archaeological evidence testifies that this desertion took place regardless of modern humans’ activities. According to stratigraphic findings and stable isotope analyses, this period corresponded to the driest environmental conditions of the last glacial apart from an even drier period linked to Heinrich Stadial 3. Our results show that during Marine Isotope Stages (MIS) 4 and 2 climate deteriorations in interior Iberia temporally coincided with northern hemisphere cold periods (Heinrich stadials). Solely during the middle MIS 3, in a period surrounding 42 kyr ago, this relation seems not straightforward, which may demonstrate the complexity of terrestrial climate conditions during glacial periods.

Time and circumstances for the disappearance of Neanderthals and its relationship with the advent of Modern Humans are not yet sufficiently resolved, especially in case of the Iberian Peninsula. Reconstructing palaeoenvironmental conditions during the last glacial period is crucial to clarifying whether climate deteriorations or competition and contacts with Modern Humans played the pivotal role in driving Neanderthals to extinction. A high-resolution loess record from the Upper Tagus Basin in central Spain demonstrates that the Neanderthal abandonment of inner Iberian territories 42 kyr ago coincided with the evolvement of hostile environmental conditions, while archaeological evidence testifies that this desertion took place regardless of modern humans’ activities. According to stratigraphic findings and stable isotope analyses, this period corresponded to the driest environmental conditions of the last glacial apart from an even drier period linked to Heinrich Stadial 3. Our results show that during Marine Isotope Stages (MIS) 4 and 2 climate deteriorations in interior Iberia temporally coincided with northern hemisphere cold periods (Heinrich stadials). Solely during the middle MIS 3, in a period surrounding 42 kyr ago, this relation seems not straightforward, which may demonstrate the complexity of terrestrial climate conditions during glacial periods.

Approximately 75 percent (300 000 km) of the total Swedish road network and 20 percent(20 000 km) of the national road network consists of gravel roads. One of the most significantproblems associated with gravel roads is traffic-generated dust emission, which contributes tothe deterioration of the road surface and acts as a major source of particulate matter releasedinto the atmosphere, thereby involving public economics, road safety, human health, andenvironmental quality. In order to bind the fine granular material, which is prone to rise into theair, dust suppressants are applied on roads on a yearly basis. Methods for evaluating the efficiency of dust suppressants will facilitate in the selection of themost appropriate product and its optimal application rate. For example, methods forsupervision of residual dust suppressant concentration are valuable tools for estimatinglongevity and optimal application rates, and, consequently, effectiveness of different products. Application of the proper dust suppressant to a gravel road ensures road safety and ridingcomfort as well as creating a cleaner and healthier environment for residents in buildingsadjacent to the road. It also reduces the need and cost for vehicle repair, road maintenanceactivities, and aggregate supplementation. Both field-based and laboratory research were performed to evaluate the efficiency of varioussuppressants and the influence such factors as product concentration, leaching, and fine materialcontent have on the efficiency of different products. Within the field-based research, a newlydeveloped mobile methodology was used to measure dust emission on numerous test sectionstreated with various dust suppressants. In general, all dust suppressants tested, except apolysaccharide (sugar) and products, which form a brittle surface crust, i.e. lignosulphonate andbitumen emulsion, showed acceptable dust reduction. Test sections treated with a magnesium- or calcium chloride solution were the most effectivelydust suppressed. The application of solutions instead of a solid salts achieves a more uniformproduct distribution and, therefore, probably a more efficient performance. By applying acalcium- or magnesium chloride solution instead of traditionally used solids, the cost for annualdust control, as well as the environmental impact from the release of these chemicals in theenvironment, can be reduced by 50 percent. A significant problem when using dust suppressants is their tendency to leach during rainfalldue to their soluble properties. Residual chloride could be detected in the gravel wearing courseover a longer period of time than lignosulphonate and, therefore, showed more effective longtermperformance. Optimal percentages of fine material for minimal lignosulphonate andchloride leaching were found to be 15 percent by weight and 10-16 percent by weight,respectively. Ions of calcium chloride seemed to initiate flocculation of clay particles, therebypreventing them from leaching. Still, the fine material in gravel wearing courses has to be replenished regularly as indicated by studies of the longevity of fine material. Loss up to80 percent was found after two years. Toxicity tests show that dust suppressant application for dust control purposes, at traditionallyused application rates, does not constitute a threat to sensitive aquatic life. Tests on subsoilwater samples indicated elevated chloride levels, which possibly could cause corrosion to pipes,but not high enough to flavour drinking water. / QC20100616