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FINITE ELEMENT SIMULATION ANALYSIS OF CURVILINEAR CONTINUOUS BEAM BRIDGE JACKING AND TRANSLATION CONSTRUCTION
Get PDFThis paper investigates the issue of beam misalignment in curved continuous beam bridges. Taking the D0 to D6 spans of the Gongbin Road viaduct as the basis, the main influencing factors causing misalignment in curved beam bridges are analyzed and the causes of transverse and longitudinal misalignment in curved beam bridges are calculated and analyzed using Midas/Civil finite element simulation software. The results indicate that the main influencing factor causing misalignment in the operation of curved continuous beam bridges is the system temperature, with the displacement caused by it being larger than the cumulative displacement caused by self-weight, construction phase, gradient load, vehicle load, and bearing settlement. During operation, the failure of expansion joints changes the boundary conditions of the beam, preventing the bridge from freely expanding and contracting longitudinally under temperature load. As a result, the transverse displacement increases to 2-3 times the normal working state of the expansion joint, leading to beam misalignment
GEOTECHNICAL ANALYSIS AND REMEDIAL DESIGN OF A POTENTIALLY UNSTABLE CUTTING
Get PDFThe article deals with the analysis of a potentially unstable cutting in weak rocks and a design of its remediation. It is described here the collection of information, its interpretation and stability analysis of the cutting, which focuses on deeper than just surface slip surfaces to assess the risk of slope movements with significant safety and economic impact. Based on the results of the evaluation, appropriate remediation measures are proposed
Outdoor performance investigation of a thermoelectric cooler-integrated solar air heating collector
Get PDFSolar air heating systems are continuously being improved by combining them with other energy conversion technologies. In this paper, outdoor tests were carried out on a thermoelectric heat-pumping solar air heater (TE-SAH), with four (04) TECs (TEC1–12706) attached to the backside of the absorber plate, and powered by a 40Wp mono-Si PV module to pump heat from the absorber plate into the heated air. The thermal energy production, energy efficiency, heat loss coefficients, and heat removal factor were evaluated and compared with a reference system without TECs. The heat collection and energy efficiency of the solar air heater were improved by 7.14 % and 66.71 %, respectively, with the integration of TECs. Heat losses also decreased by 0.46 MJ. Furthermore, the estimated heat removal factor for the TE-SAH was 0.55, higher than 0.49 obtained for the reference SAH. These results showed that PV-TE heat-pumping is a viable means of improving the thermal performance of solar air heaters
Parametric optimisation of laser welding of stainless steel 316L
Get PDFThis paper presents numerical and experimental studies focused on the optimisation of laser welding parameters for AISI 316L stainless steel. The focus of the numerical studies was to obtain the mathematical model with the least time complexity and the highest fidelity. Based on the comparison of different mathematical models, a combination of two models, double ellipsoidal and conical models, was found to be optimal for the numerical simulation of the laser welding process. The studies were also complemented by material characterization studies for validation purpose. A pulse duration of 8 milliseconds and a current of 400 amperes with an average power of 380W were found to be the optimum parameters for laser welding of standard gauge 12 sheet of stainless steel AISI 316L. In addition, the effect of duty factor of the pulsed laser beam on the weld profile was also investigated and was found to be a major contributor to the optimisation process. The properties of the sample welded with the optimised set of parameters were also compared with the base metal, and based on the mechanical characterisation studies, it was found that the yield strength and hardness of the welded sample were improved, but the overall ductility was slightly reduced as compared to the base metal. The average weld zone size was also reduced by increasing the power density due to multiple reflections of the beam
Problems with reinforced concrete industrial floors with regard to subsoil swelling
Get PDFMost of the problems associated with open cracks in reinforced concrete industrial floors do not arise from technological indiscipline in the execution or exceeding the permitted floor load, but from the geotechnical profile beneath the floor. In the presence of swelling soil in the subsoil, the floors can then be shifted upwards by centimeters and create open cracks. This article describes regression relationships for the prediction of swelling pressure and deformation of reinforced concrete industrial floors based on indirect measurements. These relationships were obtained by evaluating a large database of measurements carried out by the company GeoTec-GS and the Czech Technical University in Prague using neural networks, multiple correlation, regression analysis, and sensitivity analysis. The article also presents the actual classification of the risk of surface damage of reinforced concrete floors due to swelling of the subsoil and an example of its application is given
Hydrothermal and mechanical performance of mortars containing waste brick powder
Get PDFIt is widely recognised that green building, environmental sustainability, and technical performance have recently become requirements in the field of civil engineering. For this reason, the new trend in research is to focus on the recycling and recovery of materials, even if some of them such as industrial waste are still underexplored. In this perspective, the main objective of this work is to study the influence of brick powder on the thermophysical and mechanical properties of mortars containing this type of waste, in different environments, and within the temperature range between ambient temperature and 50 °C. To this end, a number of mortar mixtures, in which cement was replaced by brick powder in different proportions, were studied and characterised according to technical standards in order to define the optimal substitution percentage. Three batches of samples were examined at different ages, i.e., 3, 7, 28, and 90 days. The samples of the first batch were kept in water at a temperature of 20 ± 2 °C with a relative humidity RH = 100 %, while those of the second batch were immersed and stored in water at 50 °C in order to simulate a hot and humid climate. As for the samples of the third batch, they were kept in a dry oven at 50 °C in order to investigate the effect of the hot and dry climate. The results obtained revealed that the partial replacement of cement by brick powder makes it possible to improve the thermal insulation characteristics but reduce the mechanical strength of the mortar. In addition, it was shown that in a hot and dry environment, the mechanical characteristics of the different mortars decrease as the rate of weight substitution of cement by brick powder rises. However, in a hot and humid environment, a reverse trend is observed. The findings also suggested that the optimal recommended rate of substitution of cement by brick powder is 20 %
Experimental investigation of an entropy production in a linear blade cascade
Get PDFThe vortical structures in turbomachinery are crucial phenomena that significantly impact the machine’s efficiency. Therefore, investigating them is essential for a better understanding of the machine’s operation.The presented paper focuses on an experimental investigation of entropy production in a linear blade cascade composed of prismatic blades for two pitch-to-chord ratios, t/c = 0.6, and 0.9. The effects of the inlet flow angle, α1 = −20°, 5°, 30°, and outlet isentropic Reynolds number, Re2,is = (0.8, 1.2, 2.5, and 4.5) × 105, are examined based on pressure measurements.Entropy production is evaluated as a balance of fluxes through the inlet and outlet boundaries of the control volume. The paper provides a detailed discussion of the local distribution of entropy production and vorticity in the flow field, as well as their evolution with the tested parameters. The correlations between the integral values of entropy production and the tested parameters are also given
General quality of urban greenery as a city indicator in Brazil in comparison with central Europe
Get PDFThe evidence for climate change and its associated consequences, such as severe droughts, floods, and storms, exposed the need to investigate the ways that countries can cope with them, especially Brazil, which is a continental nation. Moreover, the COVID-19 pandemic contributed to the urgency to consider global uncertainties. To audit it, the Pondělíček method, an indicator of the general quality of urban greenery (IOKZM), was employed. This approach considers four factors to indicate if one city is sustainable: city altitude [m], average annual temperature [°C], average annual precipitation [mm], and the total greenery area [km2] per inhabitant per year. The outcomes demonstrate that, regardless independently of the Brazilian region, geographic localization, estimated altitude range, or precipitation range may not strongly influence the BIOKZM. The impact measured in the indicator is significantly influenced by the greenery areas in Brazil. Those estimated areas are much smaller than European Union ones. Teresina’s Fkes demonstrates that if the greenery area is more than 5 (i.e., more than 50 percent), the IOKZM will be a positive outcome. The IOKZM calculated for Brazilian cities is interesting precisely because of their location in the southern hemisphere, as all the evidence of climate change subtly suggests that the climate in the southern hemisphere changes in a different way. Hence, this article can be used as an initial tool to assess whether the chosen Brazilian cities (Belém, São Luís, Guarulhos, Campinas, Porto Alegre, Teresina, and João Pessoa) can be considered “smart cities”. It is a step towards guiding mayors and other public figures in charge to create and maintain smart cities in Brazil. In addition, further studies should be conducted to contribute to this collaborative effort
Cities in transition: Krakow‘s social, economic and spatial transformation within the last thirty years (selected aspects)
Get PDFKrakow is a city that has undergone an immense transformation in recent years. At the end of the 1980s, the period of communism ended and Polish local governments began to operate based on the principles of subsidiarity, decentralisation and independence. In 2004, Poland joined the European Union, which opened up new prospects for development, including in regional and local terms. The world has become a networked and digitized entity susceptible to the influence of innovation. Due to metropolitisation processes, cities, especially those offering above-average earnings, a diversification of economic resources and a relatively high quality of life, began to develop even more dynamically, which had and still has negative consequences. In Poland, there are five cities in which development dynamics have a highly specific dimension. Apart from the capital city of Warsaw, these are Krakow, Wrocław, Poznań and the agglomeration of the so-called Tri-city (Gdańsk, Sopot and Gdynia). The aim of this study is to show how Krakow, the second-largest city in Poland, has evolved over the last three decades at the level of demographics, urban development and economy; how it changed in the historical “milestones” indicated above. Therefore, depending on the availability of statistical data, several time periods were selected and compared with each other in the most important areas of Krakow’s functioning. The research hypothesis is as follows: Krakow’s development policy in key areas optimally uses the opportunities resulting from contextual conditions (social, economic and cultural changes that have taken place in recent decades). The study focuses on the three main problems of the city’s development (the abovementioned key areas of the city’s functioning and development): socio-demographic, spatial and economic changes. The analysis assessed data from the literature, city reports and other available sources, as well as public quantitative data (assessment of data from the National Census for the years 1988, 2002, 2011, 2022; Local Data Bank of Statistics Poland and otherrepositories and reports)
Dowel bars – reinforcing elements of cement concrete pavements
Get PDFOur aim is to analyze the function of reinforcement elements (dowel bars) in cement concrete pavement to highlight the influence of these elements on the service life of the pavement as a whole and to find possible alternatives to existing products that are freely available on the Czech market. That is, how these elements in the form of dowel bars should work properly so that the function meets the design assumptions of a rigid pavement. We describe the procedure for inserting dowel bars during paving, which is directly related to the possibilities of using different dowel bars. Finally, we summarize the possibilities of using alternative materials, shapes, or sizes of dowel bars and the possibilities of their use in the Czech Republic