CTU Open Journal Systems (Czech Technical University, Prague / České vysoké učení technické v Praze)
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Experimental investigation of polyurethane-coated HPFRC panels under direct contact blast
Get PDFHigh-performance fibre-reinforced concrete (HPFRC) exhibits exceptional resistance to dynamic loading, making it a promising material for structures exposed to blast or impact events. However, when used to produce thin panels, it can experience scabbing under extreme loads. To address this and enhance the blast resistance, this study explores the application of a polyurethane (PU) coating to the HPFRC panels. Coated and uncoated panels undergo direct contact blast testing and various factors, such as crater area, rear fragment formation, cracking, and residual flexural strength, are analysed. Our study indicates that applying a PU coating to the panels could effectively prevent scabbing and mitigate the risk of complete perforation, while it appears that it results in the panel absorbing more energy during blast, leading to increased damage and a subsequent decrease in residual flexural strength compared to bare panels
CO2 capture in pilot-scale unit using solid adsorbent in biomass fluidised bed boiler flue gas
Get PDFThe search for methods to capture carbon dioxide (CO2) emissions from solid fuel combustion processes has led to the development and subsequent testing of alternative innovative CO2 capture technologies. Vacuum Pressure Swing Adsorption (VPSA) method is a promising technology for efficient CO2 capture using solid sorbents. This article introduces CO2 capture using the VPSA technology, providing description of the selected VPSA method and the construction of a pilot-scale unit for VPSA CO2 capture. The main goal of this article is to present experimental results, including a description of the pilot-scale unit used for the VPSA adsorption tests using zeolite 13X, an industrially proven sorbent for CO2 capture. The measured adsorption values were compared with theoretical isotherms, allowing the assessment of VPSA method efficiency and accuracy in practical conditions. Results indicated discrepancies between the experimental unit and the theoretical adsorption models, attributed to non-ideal conditions, non-optimised processes, incomplete drying of the sorbent, and temperature variations affecting the adsorption efficiency. The conclusion confirms the VPSA lab unit’s ability to adsorb CO2 using solid sorbents, suggesting that further research and additional tests with new alternative sorbents is needed
3U CubeSat mechanical design and subsystems
Get PDFIn this paper, an in-depth analysis of the mechanical design and integration of the 3U CubeSat subsystems is presented, a common form factor in the small satellite community. The study summarises recent research and emphasises developments in material selection, structural integrity, thermal management, and computer-aided design (CAD) techniques. In addition, it explores the integration of crucial subsystems, such as power, communication, and payloads, highlighting the challenges and solutions encountered. This paper aims to provide a comprehensive understanding of the state-of-the-art 3U CubeSat mechanical design and subsystem integration by compiling and evaluating current developments. The insights offered here are essential for researchers and engineers, laying the groundwork for further advancements in CubeSat technology
Vortices in the wake past adjustable car spoiler in open and closed configuration studied experimentally by PIV
Get PDFA complex adjustable car spoiler opens or closes in dependence on ride properties: the closed state increases negative lift (better for curves), while the open state ensures lower drag (better for straight segments of the road). Both these configurations are studied by using Particle Image Velocimetry method in a wind tunnel at model scale. The three measured planes are perpendicular to the main flow. The wake is characterised by upwind (stronger past the closed variant) and by a pair of wing-tip vortices, although the spoiler wing has no end, it is rounded downwards instead. These vortices are stronger past the closed variant, they migrate towards each other, while their positions correlate by about 30 %. The circulations of both vortices are strongly correlated by about 90 % for the closed case, while this correlations is much smaller (∼25 %) for the open case
Analysis and optimisation of reinforcing materials for wood adhesives
Get PDFAdhesives are very important in the field of glued timber elements. In recent years, more and more attention has been paid to innovations in the field of adhesives for wood materials. Not only in terms of mechanical properties but also in terms of environmental aspects. Wood remains a popular material in the construction industry, but the challenge remains how to ensure the long-term stability and durability of its glued joints. The designed elements must withstand various changes of moisture as well as elevated temperatures throughout the lifetime of the structure. Optimising wood adhesives through appropriate fillers or fibres selection is a step towards more sustainable building materials. The aim of the work was to select suitable fillers or fibres for adhesives based on optimisation through the pairwise comparison method. According to the results obtained, glass (99.98 %) and carbon (95.92 %) fibres can be considered as the most suitable reinforcement material. Basalt fibres, nanocellulose and montmorillonite particles achieved an average of 56 %. TiO2, SiO2 and Al2O3 particles can be considered as unsuitable fillers for adhesives based on the weight of the selected criteria
Flexural behavior of timber-high-performance concrete experimental slabs
Get PDFIn general, one of the possible future paths of the building construction industry is the development of robotization and prefabrication of individual building components. Presented article continues the development of prefabrication using traditional effective ombination of two often used materials in construction – timber and concrete in the form of a slabs. The traditional concept of combining these materials is used for ceiling structures – slabs, panels, floor panels, where timber is most often in the form of beams and a concrete slab is applied over the beams as a material transmitting compressive stress. The key to functionality for this system is the shear connection of both materials. The presented study presents a thin concrete layer made of high-performance concrete, which is connected to a wooden board from glulam using an adhesive bridge. The aim of this presented study is to improve the bending load-bearing capacity and bending stiffness of the glulam slab with a small amount of high-performance concrete and thus achieve a more favorable environmental profile of the ceiling panel. The individual variants differ in thickness, the presence and number of ribs. These variants are compared with a variant of the same thickness of glulam slab without the layer of concrete
CASE STUDY: ROCKFALL MITIGATION AT A HIGHWAY SLOPE IN SUICHUAN COUNTY, CHINA
Get PDFProper stability analysis of potential rockfall and appropriate prevention measures are essential for ensuring highway safety. This study investigated a rock slope along the G105 National Highway in Suichuan, Jiangxi, China. The stability evaluation of the slope was carried out through theory analysis combined with on-the-site surveys. The slope is stable under normal conditions but exhibits a state of basic stability-to-unstable or instability during extreme weather condition or seismic activities, necessitating protective design. Numerical simulation was conducted to assess the risk of rockfall movements. The translational velocity, bouncing height, kinetic energy, and deposition distribution of different rock volumes during the falling process were simulated. The kinetic energy of rockfall is primarily related to the volume of rock mass, while translational velocity, bouncing height, and deposition distribution are closely associated with the cross-sectional conditions. Based on the evaluation results, suitable reinforcement measures were selected, and the slope was monitored using InSAR technology and automatic monitoring technology. The combination of drone scanning, modeling, automated monitoring techniques, and InSAR technology effectively reduces uncertainties in risk assessment. Based on the evaluation results, the application of active energy-absorbing protection nets and other preventive measures were proposed, demonstrating a satisfactory protective effect. The case study will provide valuable engineering guidance for rockfall analysis and prevention along highway slopes
KEY TECHNOLOGY OF SUPER-LARGE DIAMETER SHIELD PILE FOUNDATION REPLACEMENT CONSTRUCTION
Get PDFThis paper takes Guangzhou Haizhu Wan shield tunnel project as the background to study the key technology of large-span pile foundation replacement construction under the condition of super-large diameter shield. Research on key technology of large span pile foundation replacement construction under super-large diameter shield conditions was carried out. Formation of spanning 20.8 m large-span buttress structure with buttress piles, double buttress beams and bearing platforms, active buttressing, and truncation of existing pile foundations construction methods. Research focused on the active buttressing phase, which directly affects the deformation of the superstructure. At the same time, the existing building settlement, tilt and stress-strain of the joist were monitored during the joist construction. It shows that the maximum settlement value is -6.1 mm, the overall uneven settlement does not occur, and the monitoring results do not exceed the warning value. Monitoring results show that the large-span prestressed double-beam buttress pile foundation can effectively control the settlement of the superstructure, and have good construction effect
Analysis of reticulated dome with universal connector
Get PDFIn order to investigate the stress-strain state of a 4 m diameter reticulated dome model, four series of glued wooden rods were prepared for centric and eccentric compression tests. The tests were carried out in the laboratory of the Department of Metal Wood and Plastic Structures. The stresses at the specific points of the elements were determined through the deformations using the strain gauges. The feature of the prismatic specimens was the stress concentrators in the bearing areas in the form of holes for the arrangement of universal connectors. These areas were also reinforced with steel sleeves. The general conclusion of the study is the high load bearing capacity of the tested samples. The destruction of the samples occurred in the bearing zone due to wood crushing. The next research tasks will be to optimise the dimensions of the elements and test the dome model. The cross-section of the elements, in addition to providing the load-bearing capacity, is also influenced by the need to obtain certain thermal characteristics of the enclosure, i.e. the dome elements should have dimensions that allow placing a layer of an effective insulation in their plane. A special task is to choose a roofing that can be considered only as a part of the constant load on the load-bearing system or as a continuous shell that unbinds the frame
Rheology properties of metakaolin activated by lithium water glass
Get PDFAlkali-activated materials play an important role in the current industry, because they offer alternative way towards low carbon technologies. However, their crucial utilization still lays in the field of composites resistant to high temperatures, especially in the heavy machinery and chemical industry. The current paper documents rheological properties of set of pastes on the basis of Czech metakaolin as precursor, which was activated by lithium water glass exhibiting various silicate modulus. The rheological properties were studied in terms of standard flow test and optimized composition exhibiting similar workability were subsequently investigated by using rotary rheometer. The rheology was monitored in time to document performed changes during the geopolymerization. The attained flow curves were fitted by Herschel-Bulkley model and basic rheological characteristics of optimized pastes were derived. The research confirmed prolonged workability of the studied paste activated by lithium water glass and better. The pastes activated by lithium water glass of lower silicate modulus exhibited lower values of yield stress