Periodica Polytechnica (Budapest University of Technology and Economics)
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An Analytical Model for the Initial Stiffness of Bearing Connections with Slotted Holes
Get PDFIn steel structures, cover plate joints are mainly used with normal round holes, but slotted holes, where the slot is oriented perpendicular to the direction of the bearing force, make it possible to release displacements in selected directions and thus better control the complex state of stresses in the connected plates. This study investigates the initial stiffness of a cover plate with a single slotted hole. The aim of this paper is to propose an analytical model that predicts the initial stiffness of slotted holes with respect to experimental results obtained on a panel of different geometries. This approach makes it possible to evaluate the effects of the end distances on the bending of the plate compared to the bearing under the bolt. A large panel of geometries is tested to quantify the experimental value of initial stiffness using Digital Image Correlation (DIC) technique compared to Linear Variable Differential Transformer (LVDT) sensors. To evaluate the initial stiffness, a method of processing experimental data is developed that allows a reproducible determination of stiffnesses. An analytical model is then proposed based on the improvement of existing models available in the literature. It is validated for different specimen geometries considering the contribution to the initial stiffness due to bending, shearing and support of the steel plate under the bolt. The comparisons show that the proposed analytical model can predict the initial stiffness of different geometries of tested specimens with slotted holes
Investigating the Effect of GNP Addition on Self-healing of ECC through Mechanical and Nondestructive Testing
Get PDFInclusion of nanomaterials is an effective method for enhancing the mechanical and durability characteristics of cement-based materials. Among various graphene-based nanomaterials, graphene nanoplatelets (GNPs) are cost-effective nanoparticles that possess graphene's key properties. Since limited information is available regarding their influence on the fresh, mechanical, non-destructive, and self-healing behavior of Engineered Cementitious Composites (ECC), this research focuses on GNP inclusion on these properties of ECC in a comprehensive way. In this research, the changes in material properties of ECC were monitored with several mechanical and nondestructive test methods. According to the results, GNP inclusion significantly enhanced flexural behavior and also promoted self-healing of ECC, with preloaded specimens exhibiting substantial or complete crack closure and similar performance to virgin specimens. Non-destructive tests and microstructural analyses also confirmed the promoting effects of GNP. A noticeable increase was observed in compressive strength when GNP was included. In conclusion, this study provides compelling evidence about the positive impact of GNP inclusion on improving the properties of ECC. The findings demonstrate the potential of GNPs to enhance the performance of cementitious materials and offer valuable insights for future research and practical applications
Empirical Punching Shear Capacity Equation for Reinforced Concrete Two-way Slabs with Openings
Get PDFThis study proposes a new equation to estimate the punching shear capacity of Two Way Reinforced Concrete Flat Slab Column (TRFSC) connections with openings. The TRFSC connections with openings in the literature were simulated using the finite element modeling technique. Then, the test results were used to calibrate and verify the finite element model. Next, the number of test data was artificially increased using the finite element model to cover a wide range of critical perimeters. Finally, the effects of several parameters such as the size of the openings in the reinforced concrete slabs, their position, and distance concerning the column on which the punching loading is applied on the variation of punching shear load capacity of TRFSC connections with openings were observed, the results showed that the proposed equation generally gave better results than the several current code equations. For the study used in the verification of the finite element model, it was observed that the ratios of the punching capacity values calculated using the experimental results and the regulations varied between 0.79 and 0.92 on average, and the regulations gave results that were not on the safe side for TRFSC connections with openings. However, with the nonlinear correction coefficient proposed in this study, the ratios of the experimental results and analytically calculated capacity values were calculated as 1.10 on average, and the standard deviation and variant values decreased much more
Validating a Two-dimensional Sediment Transport Model on a Large Danubian Floodplain
Get PDFConsidering currently operative European and worldwide regulations, preserving and/or improving the state of remnant alluvial floodplains is a high-priority goal for experts. One of the threats is the decrease of lateral connectivity: due to the erosion in the mainstem riverbed and the sedimentation of the floodplain and its channels, the bed elevation gap slowly increases between the main channel and the side branches and oxbows of the floodplain. Without revitalization measures, this progress predicts severe ecological consequences. As an example, and as a continuation of our earlier work, we considered the Gemenc floodplain forest along the Danube, in Hungary. We set up a two-dimensional coupled hydrodynamic and sediment transport computational model to describe floodplain deposition dynamics. Model validation was carried out with historical data, i.e., two ground elevation sets measured in 1990 and in 2009, respectively. Our aim was 1. to show, how coarse resolution measured data can be used for validating a large-scale model in terms of sediment deposition processes, and 2. to interpret the first results on some areas exposed to strong deposition, after validation. Showing good agreements in three pillars: magnitude of estimation, spatial tendencies and spatial patterns, the model was deemed valid. We were also able to observe a clear gradient, along which areas could be categorized with high, medium and small extent of sediment deposition. With this model, the sediment dynamics in the Gemenc floodplain forest can be assessed, with special attention to the impact analysis of restoration measures to improve lateral connectivity conditions
Strength Behavior Analysis of Self-healing Concrete Using Bacteria and Silica Gel: A Comparative Study
Get PDFConcrete cracking is a significant worry in the construction sector, and infrastructure maintenance is becoming increasingly important in the present landscape. The expenditures of inspections, repairs, and maintenance are not only unwelcome but also have negative environmental consequences. The availability of self-healing agents in self-healing concrete (SHC) may be handled in these conditions with solid integrations. Self-healing concrete has the specific benefit of detecting the emergence of fractures in SHC-made concrete pieces and initiating a self-repair process without human involvement. This paper compares two alternative concrete healing methods and offers the findings of a complete experimental examination of self-healing concrete. In this study, silica and polymer-based gels were used along with Bacillus subtilis bacteria in separate experiments as weight-based alternatives for cement. The mechanical properties of various concrete mixes were evaluated using the self-healing studies by silica-based polymers and bacillus bacteria. The optimum dose level has been identified for the usage of silica gel and bacillus bacteria in the concrete. These findings provide vital insights into deploying self-healing concrete and its potential to handle concrete cracking concerns more effectively
Influence of Key Shear Factors on the Shear Performance of Ultra-high Performance Fibre Reinforced Concrete Beam Containing Coarse Aggregate
Get PDFThis paper assesses the effect of direct and indirect factors on the shear performance of ultra-high performance fibre reinforced concrete beam containing coarse aggregate (UHPFRC-CA) using four point loading arrangement. The obtained results were used to categorize UHPFRC-CA beam's failure mode, establish the influence of key factors on shear performance, and develop UHPFRC-CA beam's compression zone resistance and first shear cracking load equations whose results were compared with those from this research, other researchers and existing equation. Findings revealed that UHPFRC-CA beam fails in cable stayed, shear partial compression, cable stayed-diagonal tension and cable stayed-partial shear tension. Shear span-depth ratio (a/d) has the most influence on the beams' failure mode. Higher percentage volume of steel fibre improves ultimate load capacity and midspan displacement resistance at failure load. Hooked-end steel fibre improves deformation (crack width and midspan displacement at failure load) resistance. Higher a/d is more beneficial to midspan displacement resistance at failure load than load capacity; while lower stirrup spacing leads to higher midspan displacement at failure load. Finally, the developed first shear cracking load equation can adequately capture the true first shear cracking load of UHPFRC-CA beam; and the developed compression zone resistance equation can be conveniently used to represent the joint contribution of compressive strength and fibre factor to UHPFRC-CA beam's shear resistance
An Experimental Investigation into the Effect of Ceramic Fiber on the Fatigue Cracking of Stone Matrix Asphalt
Get PDFFatigue cracking of the asphalt mixture is a process whereby micro-cracks in the asphalt–aggregate interface propagates into extensive coordinated cracks under repeated loads. This process is the main cause of failure in flexible pavement and reduces its serviceability. Fiber reinforcement has received significant attention in the last two decades for finding viable solutions to increase the fatigue resistance of stone matrix asphalt (SMA). Accordingly, ceramic fiber (CF) as an asphalt binder modifier was used in this study to evaluate the fatigue behavior using mechanical and rheological tests. For this purpose, asphalt binder samples with different percentages of CF were subjected to short term and long-term aging according to the rolling thin film oven (RTFO) and pressure aging vessel (PAV), and dynamic shear rheometer (DSR) test was performed at mid temperature. Also, the fatigue life test was performed by indirect tensile fatigue test at two temperatures and five stress levels on asphalt mix samples made with controlled and modified asphalt binders. Based on the results, it is observed that asphalt binder modified with CF have higher and lower complex shear modulus and phase angle, respectively, compared to control asphalt binder. Also, the results of fatigue test show that using CF up to 5% increases fatigue life of mixtures. In addition, with enhancing temperature and stress level, fatigue life decreased in all samples, with a lower rate in CF modified samples
Path Planning for Data Collection Multiagent System with Priority and Moving Nodes in a Sensing Field with Obstacles
Get PDFNowadays there is a more and more common need for one-off data collection in a specified area. For example, in case of searching for the survivors of disasters or wars, or for skiers who get into trouble. The simplest way of collecting such data is using wireless sensor network (WSN). However, data transmission within the network uses great amount of energy that may significantly reduce the lifetime and operation time of the battery-operated sensors. For this reason, the data transfer between the given sensor nodes is carried out by robots. In order to minimize the latency of data collection, it is possible to use cooperating robots. It frequently occurs that one of the nodes requires more urgent visit than the other ones, for example, the serious injuries require urgent medical attendance. The sensor nodes can also be moved to collect more usable data in a larger field. To solve this, path planning for data collection from priority and moving nodes are also presented here. The algorithm developed here to perform the one-off data collection operates so that the agents start from preliminary determined or random points and then visit all the sensor nodes, download the data from these nodes and after this arrive at a designated point where they upload the collected information. The goal here is the minimization of cost that include not only the walk-through time but also the consequences of the late visit of the higher priority nodes. The optimization is solved using the ant colony optimization
Parasitic Loaded Shorting Pin Based Compact Multi-slot LoRa Antenna for Military Application
Get PDFIn this paper, work on a compact multi-slot patch antenna with a parasitic load and shorting-pin has been presented for its use in long range (LoRa) defense applications. Initially the antenna is designed and simulated using HFSS and a parametric study has been carried out for achieving an optimized antenna configuration. This is followed by the fabrication of antenna prototype based on the optimal performances obtained from the simulated results. Further, the return loss along with free space co-polar and cross-polar radiation pattern measurements has been carried out for the fabricated antenna. The experimental results show a good comparison with that of the simulated one. The proposed antenna resonates at an operating frequency of 866 MHz, providing a -10 dB bandwidth from 856 MHz-877 MHz, which covers the wireless standard used for LoRa technology. Finally, a comparative analysis of the proposed antenna with the recently reported works is presented
Multiband SINC-slotted Patch Antenna for 5G Applications
Get PDFIn this work, we presented the design, analysis and optimization of the multiband slotted antennas based on SINC function for 5G applications. The proposed antennas are designed and modelled by CST Studio Suite software. A parametric study is performed to determine sinc function parameters that control the performance of the proposed antenna. The parametric study is implemented by varying the amplitude of the sinc function, the frequency, the location of the slot along Y-axis, the slot width and the slot window (number of cycles). The simulated results showed that the designed slotted antennas in this paper exhibits multiband operation and they offer the feasibility of controlling and adjusting the resonant frequency by changing the sinc function parameters. The proposed antennas have various resonant frequencies at around 1.5 GHz, 2.65 GHz, 5 GHz and 5.8 GHz covering the 5G sub-6 GHz band. Extensive simulation process were carried out to determine the optimum antenna performance and three antennas were selected based on the reflection characteristics and number of operation frequency bands. Finally, the three selected antennas were manufactured and their performance were measured in the lab for validation. Experimental results showed that an excellent agreement between the measured and simulated results was achieved