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Experimental study on dynamic elastic modulus of reinforced concrete bridge deck panels in salt-freeze environment
No full textReinforced concrete structures are the most widely used structural form today. In the western salt-alkali areas and in road and bridge engineering environments where de-icing agents are used in the northern regions, chloride ions penetrate the concrete, causing steel reinforcement to lose its passivation and corrode, resulting in durability damage to the reinforced concrete structure. Among all bridge components, the bridge deck panels of reinforced concrete bridges are most severely and directly affected by salt-frost damage. Predicting the service life under salt-frost conditions is an urgent issue to be addressed in the durability design, evaluation, and structural maintenance decision-making of reinforced concrete bridge deck panels. In this study, 15 beam specimens and 75 steel reinforcements were subjected to freeze-thaw tests, and 300 freeze-thaw cycles were performed on the concrete beam specimens to analyze the variation of their dynamic elastic modulus. Freeze-thaw tests were conducted on the steel reinforcement specimens with freeze-thaw cycles of 50 times, 100 times, and 150 times. After the freeze-thaw tests, pull-out tests were conducted to measure the changes in bond strength between the steel reinforcement and concrete, relative slip between the steel reinforcement and concrete, and other data
EFFECT OF ELECTRODE BELT USED FOR LUNG MONITORING WITH ELECTRICAL IMPEDANCE TOMOGRAPHY ON TIDAL VOLUME IN HEALTHY SUBJECTS
Get PDFElectrical impedance tomography is a radiation free, non-invasive lung monitoring method that is increasingly coming to the forefront of the interest of researchers and clinicians. The most frequently used EIT system PulmoVista 500 (Dräger Medical, Germany) uses stiff silicone electrode belt that is applied around the patient’s thorax to monitor the distribution of ventilation. To achieve proper electrode-skin connection and obtain high-quality signal, the electrode belt needs to be placed tightly at the level of 4th to 6th intercostal space. There is a possibility that tightly placed belt affects the compliance of the chest wall, tidal volume, and respiratory effort of the patient. In this study, we monitored tidal volumes using spirometer in 10 healthy, spontaneously breathing volunteers with and without the electrode belt applied around the thorax. Potentially clinically significant, but not statistically significant changes occurred in 70% of the subjects during calm breathing and in 90% of the subjects during forced breathing. The study did not determine whether the use of the electrode belt increases or decreases the value of tidal volume. However, when monitoring lung ventilation with EIT system, the possible influence of the stiff electrode belt on chest wall compliance and tidal volumes should be considered
Assessing the efficacy of flat-plate solar collectors using nanofluids in the climatic context of Kirkuk city, Iraq
Get PDFSolar energy is a key renewable energy source. Research and development have focused on enhancing the heat transfer coefficient, heat gain, and practical efficiency of solar systems. The aim of this study is to evaluate the performance of a flat solar panel collector using a nanofluid under conditions in the city of Kirkuk/Iraq, 35° latitude and 45° longitude, in terms of practical calculation of thermal efficiency. The study included making two solar collectors, one traditional and the other improved using a nanofluid (CuO). The CuO/Water nanofluid was prepared with a volumetric concentration of 0.25 % by mechanical mixing and then ultrasonic mixing to homogenise the particles and eliminate the agglomerations that form inside the fluid. Practical testing was conducted for the two solar collectors, one using distilled water and the other using the nanofluid, during four months (January, February, March, and April) of the year 2023. The experiments revealed that the efficiency progressively improves from 9:00 a.m. to 1:00 p.m. This increase is attributed to solar radiation’s decreasing intensity post 12:00 p.m., while thermal storage and minimised thermal losses continue to contribute. After 2:00 p.m., the efficiency dwindles due to the declining solar radiation intensity. The practical efficiency of a 0.25 % nanofluid (CuO) attains its zenith at a mass flow rate of 0.015 ls−1. Higher mass flow rates enhance heat transfer within fluid-filled tubes. The collector efficiency at this flow rate ranges from 31.66 % in January to 44.44 % in April
Investigation the plastic flows in the metal stamping-drawing process at the die corner
Get PDFThe present investigation covers the study of the influence of metal-plastic flow on the die corner for the deformed state of the blank and energy-power parameters during stamping-drawing. The influence of workpiece size and material on stress intensity and maximum deformation force has also been investigated both experimentally and theoretically. In addition, simulation of the stamping and drawing process was also presented. One type of die, with variations in diameter are considered different in the drawn part size and for each standard size four types of workpiece materials have been considered. The stamping process continued until the part failed structurally. The predicted test results show a dependence of the maximum load and stress intensity on both the diameter of the blank and the yield strength of the alloys and these data are in agreement with the actual measured values. Then, the method for calculating the processes of plastic deformation of metals based on a closed set of equations of continuum mechanics is proposed for the theoretical study of energy-power parameters of the technological processes. Comparison of the results of a full-scale experiment, simulation of metal flow at the die corner and theoretical calculations shows that the proposed theoretical model gives satisfactory results and can be effectively used for engineering calculations
P-LDPC coded image transmission with OFDM over underwater acoustic channel
Get PDFUnderwater environment is still an attractive area to explore and exploit by human beings. However, underwater characteristics limit communications due to harsh channel conditions, and efficient channel codes are essential to deploy. This study presents an underwater system based on protograph low-density parity check (P-LDPC) codes and orthogonal frequency division multiplexing (OFDM) for image transmission. The system proves a successful reconstruction of P-LDPC coded images with different levels of comparison. The performance of the proposed system is evaluated using nine objective measures such as bit error rate (BER) and peak signal to noise ratio (PSNR). Firstly, the proposed system performance is evaluated with different block lengths of P-LDPC code. Then, the implemented system shows a coding gain of approximately 1.75 dB for applying P-LDPC when compared to polar with cyclic redundancy check at 0.0001 BER. Additionally, image subjective assessment is obtained to demonstrate how the P-LDPC outweighs polar and turbo product codes in terms of estimated image quality. Lastly, further investigation is performed to study the effect of varying fast Fourier transform (FFT) size and cyclic prefix (CP) length on image reserved quality. The results show that the received image is better reconstructed for larger FFT sizes since that produce longer CP and symbol duration, and that in turn helps the system to combat the multipath fading introduced by the underwater channel
Czechoslovak and Polish intelligence (cryptologic) services at the time of the institutionalisation of both states and their armies after 1918
Get PDFIn the course of historical development, the intelligence or cryptologic departments of individual states, usually associated with military structures, have influenced the outcomes of (military) conflicts (especially during the 19th century, World War I and II, and the Cold War), as well as political events. For this reason, it is important to examine not only their political and historical impact, but also the technologies (codes and ciphers, production of cipher machines etc.) used in their operations. To find out the form and extent of the education of intelligence (cryptologic) personnel, which takes place at different types of higher (technical, military) schools in theoretical and practical fields, and their results applied in the activities of most of the state-controlled power apparatuses (foreign, interior, army-defense, National Security Bureau etc.), as well as in the communication (secure) channels of the state.Later, especially in the 1990s in Europe, these practices have been used outside the state apparatus in the commercial sphere. There was a demand for encryption devices and for programs for data protection (ensuring computer security, e.g. in banks, mobile operators, in the ICT industry, in the fight against international terrorism and organised crime, in ensuring the protection of individual rights, etc.), and for activities in applied cryptology. In the last five years, several cryptology conferences have been held each year to exchange knowledge in the field and to characterise and understand the constant struggle between the creators and the crackers of ciphers, as this connection has in the past led to many scientific discoveries applicable to the everyday life of individual societies. The paper focuses on the analysis of the creation and organisation of intelligence services within the Czechoslovak and Polish armies after 1918
Analysis on the mechanics and deformation of side pile structure in metro station with the PBA method
Get PDFThere are few researches on the interaction mechanism between the buckling load of the side pile top and the soil pressure behind pile (SPP) and the side pile structure. While the side pile structure is the key component of the lining structure of the metro with pile-beam-arch (PBA) method, which plays a very important role in the mechanical stability and deformation control of the lining system of station. Therefore, relying on the metro project about Guangzhou Metro Line 11, this paper investigates the influence law of mechanical characteristics and deformation of the side pile structure of the station with PBA method, taking into account the factors such as different buckling loads (including horizontal load of arch (HLA) and vertical load of arch (VLA)) and SPP, and puts forward corresponding construction suggestions. It is found that the lateral displacement and deformation of side pile structure are controlled by the HLA, and the optimal HLA is 1200kN. The influence of HLA on the bending moments about side pile are greater than that of the axial force. The VLA has more significant effect on vertical settlement of side pile, but little effect on lateral deformation about pile body. The SPP has significant impact on the stability of side pile structure, so it is recommended to take appropriate lining measures to ensure the stability of side pile structure when the SPP is too large
The application of UHPC on the monolithic part of the Štvanice footbridge
Get PDFThe use of UHPC with fibers is becoming an increasingly common topic in the world. This material is used for its superior mechanical and physical properties and long service life. However, the production cost is high, hence UHPC is used for special applications or for smaller prefabricated parts. This paper focuses on UHPC application for the construction of the Štvanice Footbridge, Prague, the Czech Republic. A monolithic part of the structure was made of UHPC from fresh transport concrete, which was produced by Skanska Transbeton. The special feature is that about 126m3 of fresh concrete was industrially prepared. This concrete achieved the properties of SCC and the final 28 day compressive strength was 120MPa with tensile strength of 18.6 MPa. Due to high hydration heat release rate, an internal water cooling system was designed and sucessfully appled using water from Vltava River
Verification of material characteristic of natural fibers for concrete reinforcement
Get PDFThe topic of the article is the verification of the tensile mechanical characteristics of selected natural fibres commonly available on the Czech market. Due to their high tensile strengths, some natural materials have a certain potential for use in specific engineering applications such as concrete reinforcement. Additionally, natural fibres are renewable materials, making them an environmentally friendly material. Potentially, its use as a reinforcement in the form of technical textiles for textilereinforced concrete could help create more sustainable reinforced concrete elements. This article deals with tensile tests of chosen available natural fibre materials, such as flax, hemp, jute, and sisal, both pure and impregnated (homogenised) using epoxy resin. In this article, the results and comparisons of tensile strengths and Young’s modulus are presented
Production of concrete pavements using mixed cements
Get PDFCurrently, great importance is attached to the reduction of emissions in industrial production, especially in the production of cement, when it is indicated that during production 1 ton of cement produces approximately 0.6 ton of CO2. Reducing emissions is possible thanks to secondary raw materials, which are produced in large quantities in the Czech Republic volumes for which a suitable use is sought. Some secondary raw materials are suitable for use in concrete mixes, which are used to improve the rheology of the fresh concrete mixture as well as the properties hardened concrete. Currently, there is an effort to eliminate the production of cement, to which its partial replacement by admixtures could also contribute. Therefore it is necessary determine the optimal admixture that could be used to replace part of the cement in concrete mix. A large consumer of concrete mixes are transport structures, where it is possible for some of the cement used to be replaced by an admixture