CSA Civil Engineering Abstracts (iki 2021 m.)

Training aviation specialists is a complex and rigorous process. According to statistics, 75% of incidents negatively impacting flight safety have been caused by human error. This article analyzes the admission process to aircraft piloting studies, which has remained unchanged over the last decade.

In Lithuania, the old archival topographic maps of locations of small and medium scale and 1 : 10,000 scale contour photo plans were created on the basis of aerial images. The material of these scales provides documented records on the condition of the objects in the location and the landscape at the moment of aerial photography. Those maps can be used to restore the accurate topographic image of the terrain and buildings in 1945–1951 and in later years and perform the necessary topographic, photogrammetric, and geodetic measurements of the parameters of objects, to identify the location of objects and changes. This information is necessary for a variety of disputed property issues and for building farmhouses in reserves, in areas of forestry land parcels, and for assessment of changes in the landscape. Studies of landscape changes are needed for the assessment of renaturalization processes. This paper presents the geodetic method used for geomorphological changes at the channel of River Žalesa during the period 1942–2017, based on the collected archival cartographic materials: historical topographic maps from archive of the Lithuanian State Company Land Fund, Land Information System, and land management projects and orthophoto maps from Lithuanian spatial information portal and free open-access Sentinel-1 satellite data from the Copernicus Open Access Hub.

Experimental tests have determined the effect of slag, opoka (silica-calcite sedimentary rock), silica fume (SiO2) suspension, dolomite dust and sodium silicate solution (NaSS) together with the polycarboxylatether based plasticizing admixture on the yield stress and viscosity of Portland cement paste the rheological properties of which have been defined applying a rotational viscometer with co-axial cylinders. The tests have revealed that slag, opoka, silica fume suspension and dolomite dust added to cement paste by replacing 10% of Portland cement (by weight) have an effect on the yield stress and viscosity of the paste subject to the form and fineness of additive particles. When 10wt% of Portland cement is replaced with slag cement, the yield stress of Portland cement paste reduces by about 25.9%, and viscosity increases by about 3.5 times compared with the yield stress and viscosity of reference cement paste. The yield stress of Portland cement paste with 0.5% NaSS admixture increases insignificantly, and viscosity grows approximately twice compared with reference cement paste. The tests have also showed that the modifying admixtures of Portland cement paste enable to control the rheological properties of cement paste.

Every year, colossal amounts of used and non-biodegradable rubber tyres are accumulated in the world. Experience shows that the most efficient way to increase the concrete fracture energy GF (N/m) is to use metal or polypropylene fibres. The optimal content of fibre increases concrete resistance to stress (especially tensile stress under bending force). Concrete fracture is not brittle; concrete continues deforming after maximum stresses and is able to resist certain stresses, there is no abrupt decrease in loading. The research has proved that crumb rubber can be used in concretes as an alternative to metal and polypropylene fibres. The investigation has found that rubber waste additives, through their specific properties can partly take up tensile stresses in concrete and make the concrete fracture more plastic; besides, such concrete requires a significantly higher fracture energy and concrete samples can withstand much higher residual strength at 500 mm crack mouth opening displacement (CMOD) and deflection.

The paper considers the velocities of air movement in the ventilated air gaps of walls and focuses on pressure fields in both wall models arranged in a climatic chamber and exploited houses. The article investigates the influence of air movement on heat transfer through walls applying numerical modelling methods and conducting experiments in the climatic chamber. The thermal effects of air flows have been described with reference to the Nusselt number defined as the ratio of average convective and conductive heat fluxes and heat flux through still air.

The paper provides a new synthesis method of multiple attribute decisions (SyMAD-3 – Synthesis of Multiple Attribute Decisions using three methods) intended for combining multi-stage and multiple attribute decisions into a single common estimate. The method is applied for selecting a construction project on the basis of its structural, technological and safety decisions. To increase the reliability of the decision, three multiple attribute decision-making methods based on quantitative measurements were applied to help the person making a decision to monitor the results of a relevant decision obtained employing three methods of the same class. The algorithm of the proposed method includes methods for identifying the integrated significances of attributes and multiple attribute decision-making methods (SAW – Simple Additive Weighting, TOPSIS – Technique for Order Preference by Similarity to Ideal Solution, and COPRAS – COmplex PRoportional ASsessment) based on quantitative measurements.

Numerous alternatives exist for foundation systems and construction technologies. The systems can be described by different criteria values which are incorporated in the conventional design process. Decision on the most suitable construction technology is vital for success and depends on many effectiveness criteria. The business success depends on the right choice. The mandate of a construction management researcher is to use rational, systematic, science-based techniques to inform and improve various decisions. The paper presents multiple criteria decision making model for selection of a pile-column technology. The technological criteria are determined by an experimental study. Based on in-situ investigation of natural soil conditions, criteria values are determined. The decision making model incorporates five different methods and techniques. To solve a problem, it uses three multiple criteria decision making methods. Integrated criteria weights are determined by using the analytic hierarchy process and the expert judgement method. This model could be used to solve complicated problems pertaining to the selection of a construction technology.

Vilniaus susisiekimo problemas sukūrė ir toliau kurs gyventojų mobilumas ir pasirenkamos susisiekimo priemonės, taip pat ir gyvenimo būdas urbanistinės struktūros, gatvių tinklo ir kitokio tipo aplinkoje. Tokios visumos reguliavimas (valdymas) ir yra problemų sprendimo raktas. Dabartinėse diskusijose apie tokią visumą arba apie tramvajaus, metropoliteno funkcionavimo aplinką neužsimenama. Problemos sprendimui priskirtinos pastangos rasti tinkamas viešojo ir asmeninio susisiekimo sistemų išvystymo proporcijas. Straipsnyje nagrinėjama socialinė ir politinė susisiekimo sistemos aplinka, susisiekimo kokybė, faktinis transporto priemonių srautas ir vežimų galia, mobilumo valdymas, urbanistinės struktūros svarba apskritai ir konkrečiai Vilniaus atveju. Pateikiami pasiūlymai ir argumentai tramvajaus diegimo klausimu.

The development of fuel sort of vehicles assumes a wide spectrum of application in America and Europe. Safety assessment is needed for car exploitation using hydrogen fuel. Therefore this article covers the control methodology of defects adapting the science advancement for hydrogen fuel operation. To achieve this aim the damage prevention methodology of mechanic phenomena and damage modeling for hydrogen fuel cells is suggested. In the presented methodology the methods and steps of safety assessment are discussed.

Heat economy is a pressing issue in all countries with severe climate. The most frequent method to solve the problem is to decrease heat losses in buildings by increasing the thermal resistance of enclosures. The most popular measure to improve windows is the use of low-emissivity coatings and inert gases. The U-value of such glazing unit is mostly dependent on the possibility of coating to reflect IR (infrared) radiation. These coatings are very effective when surface temperatures are high. During service of windows with a change of outdoor conditions (mostly temperature and wind), an U-value of it will suffer changes. The aim of this article is to show an influence of outdoor temperature on thermal performance of windows with a low-emissivity glazing and to determine the differences of declared and design U-values of modern effective windows substantial enough to introduce a concept of a normative design U-value for windows in Lithuania. We have found that differences between declared and design values (under the conditions of Lithuania) reach on average up to 17 % for double glazed IG units with one low-E coating. Thus in case of very effective windows, it makes sense to introduce a concept of design U-value for windows in our country.