• Structural Engineering and Mechanics
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• 제86권6호
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• pp.793-815
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• 2023

The current study looks at the experimental and numerical performance of ferrocement RC channel slabs reinforced with welded steel mesh, expanded steel mesh, and fiber glass mesh individually. Ten RC channel slabs with dimensions of 500 mm×40 mm×2500 mm were subjected to flexural loadings as part of the testing program. The type of reinforcing materials, the number of mesh layers, and the reinforcement volume fraction are the key parameters that can be changed. The main goal is to determine the impact of using new inventive materials to reinforce composite RC channel slabs. Using ANSYS -16.0 Software, nonlinear finite element analysis (NLFEA) was used to simulate the behavior of composite channel slabs. Parametric study is also demonstrated to identify variables that can have a significant impact on the model's mechanical behavior, such as changes in slab dimensions. The obtained experimental and numerical results indicated that FE simulations had acceptable accuracy in estimating experimental values. Also, it's significant to demonstrate that specimens reinforced with fiber glass meshes gained approximately 12% less strength than specimens reinforced with expanded or welded steel meshes. In addition, Welded steel meshes provide 24% increase in strength over expanded steel meshes when reinforcing RC channel slabs. In general, ferrocement specimens tested under flexural loadings outperform conventional reinforced concrete specimens in terms of ultimate loads and energy absorbing capacity.

• Computers and Concrete
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• 제17권1호
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• pp.1-27
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• 2016

Final construction project cost is significantly determined by construction rate. The Industrialized Building System (IBS) was promoted to enhance the importance of prefabrication technology rather than conventional methods in construction. Ensuring the stability of a building constructed by using IBS is a challenging issue. Accordingly, the connections in a prefabricated building have a basic, natural, and essential role in providing the best continuity among the members of the building. Deficiencies of conventional precast connections were observed when precast buildings experience a large induced load, such as earthquakes and other disasters. Thus, researchers aim to determine the behavior of precast concrete structure with a specific type of connection. To clarify this problem, this study investigates the capacity behavior of precast concrete panel connections for industrial buildings with a new type of precast wall-to-wall connection (i.e., U-shaped steel channel connection). This capacity behavior is compared with the capacity behavior of precast concrete panel connections for industrial buildings that used a common approach (i.e., loop connection), which is subjected to monotonic loading as in-plane and out-of-plane loading by developing a finite element model. The principal stress distribution, deformation of concrete panels and welded wire mesh (BRC) reinforcements, plastic strain trend in the concrete panels and connections, and crack propagations are investigated for the aforementioned connection. Pushover analysis revealed that loop connections have significant defects in terms of strength for in-plane and out-of-plane loads at three translational degrees of freedom compared with the U-shaped steel channel connection.

• Steel and Composite Structures
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• 제42권4호
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• pp.513-538
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• 2022

This paper reports on experiments addressing the buckling and collapse behavior of an innovative built-up cold-formed steel (CFS) columns. The built-up column consists of four individual CFS lipped channels, two of them placed back-to-back at the web using two self-drilling screw fasteners at specified spacing along the column length, while the other two channels were connected flange-to-flange using one self-drilling screw fastener at specified spacing along the column length. In total, 12 experimental tests are reported, covering a wide range of column lengths from stub to slender columns. The initial geometric imperfections and material properties were determined for all test specimens. The effect of screw spacing, load-versus axial shortening behaviour and buckling modes for different lengths and screw spacing were investigated. Nonlinear finite element (FE) models were also developed, which included material nonlinearities and initial geometric imperfections. The FE models were validated against the experimental results, both in terms of axial capacity and failure modes of built-up CFS columns. Furthermore, using the validated FE models, a parametric study was conducted which comprises 324 models to investigate the effect of screw fastener spacing, thicknesses and wide range of lengths on axial capacity of back-to-back and flange-to-flange built-up CFS channel sections. Using both the experimental and FE results, it is shown that design in accordance with the American Iron and Steel Institute (AISI) and Australia/New Zealand (AS/NZS) standards is slightly conservative by 6% on average, while determining the axial capacity of back-to-back and flange-to-flange built-up CFS channel sections.

• Steel and Composite Structures
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• 제50권5호
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• pp.515-529
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• 2024

Cold-formed steel (CFS) is a popular choice for construction due to its low cost, durability, sustainability, resistance to high environmental and seismic pressures, and ease of installation. The beam-column connections in residential and medium-rise structures are formed using self-drilling screws that connect two CFS channel sections and a gusset plate. In order to increase the moment capacity of these CFS screwed beam-column connections, stiffeners are often placed on the web area of each single channel. However, there is limited literature on studying the effects of stiffeners on the moment capacity of CFS screwed beam-column connections. Hence, this paper proposes a new test approach for determining the moment capacity of CFS screwed beam-column couplings. This study describes an experimental test programme consisting of eight novel experimental tests. The effect of stiffeners, beam thickness, and gusset plate thickness on the structural behaviour of CFS screwed beam-column connections is investigated. Besides, nonlinear elasto-plastic finite element (FE) models were developed and validated against experimental test data. It found that there was reasonable agreement in terms of moment capacity and failure mode prediction. From the experimental and numerical investigation, it found that the increase in gusset plate or beam thickness and the use of stiffeners have no significant effect on the structural behaviour, moment capacity, or rotational capacity of joints exhibiting the same collapse behaviour; however, the capacity or energy absorption capacities have increased in joints whose failure behaviour varies with increasing thickness or using stiffeners. Besides, the thickness change has little impact on the initial stiffness.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제10권7호
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• pp.2992-3009
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• 2016

The performance of D-MIMO systems is not only affected by multipath fading but also from shadowing fading, as well as path loss. In this paper, we investigate the ergodic capacity of D-MIMO systems operating in non-correlated K fading (Rayleigh/Gamma) channels. With the aid of majorization and Minkowski theory, we derive analytical closed-form expressions of the upper and lower bounds on the ergodic capacity for D-MIMO systems over non-correlated K fading channels, which are quite general and applicable for arbitrary signal-to-noise ratio (SNR) and the number of transceiver antennas. To intuitively reveal the impacts of system and fading parameters on the ergodic capacity, we deduce asymptotic approximations in the high and low SNR regimes. Finally, we pursue the massive MIMO systems analysis for the lower bound and derive closed-form expressions when the number of antennas at BS grows large, and when the number of antennas at transceivers becomes large with a fixed and finite ratio. It is demonstrated that the proposed expressions on the ergodic capacity accurately match with the theoretical analysis.

• Steel and Composite Structures
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• 제25권6호
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• pp.727-734
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• 2017

This paper describes a quasi-static finite element analysis, which uses the explicit integration method, of the apex joint of a cold-formed steel portal frame. Such cold-formed steel joints are semi-rigid as a result of bolt-hole elongation. Furthermore, the channel-sections that are being connected have a reduced moment capacity as a result of a bimoment. In the finite element model described, the bolt-holes and bolt shanks are all physically modelled, with contact defined between them. The force-displacement curves obtained from the quasi-static analysis are shown to be similar to those of the experimental test results, both in terms of stiffness as well as failure load. It is demonstrated that quasi-static finite element analysis can be used to predict the behavior of cold-formed steel portal frame joints and overcome convergence issues experienced in static finite element analysis.

• Structural Engineering and Mechanics
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• 제78권4호
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• pp.473-484
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• 2021

Similar to other structures, ultimate strength values showing the maximum load that the structure can resist without damaging has great importance on ships. Therefore, increasing the ultimate strength values will be an important benefit for the structure. Low carbon steels used in ships due to their low cost and good weldability. Improving the ultimate strength values without interfering with the chemical composition to prevent of the weldability properties of these steels would be very beneficial for ships. Grain refinement via severe plastic deformation (SPD) is an essential strengthening mechanism without changing the chemical composition of metallic materials. Among SPD methods, equal channel angular pressing (ECAP) is one of the most commonly used one due to its capacity for achieving bulk ultrafine-grained (UFG) materials. When the literature is examined, it is seen that there is no study about ultimate strength calculation in ships after ECAP. Therefore, the mean purpose of this study is to apply ECAP to a shipbuilding low carbon steel to be able to achieve mechanical properties and investigate the alteration of ship hull girder grillage system's ultimate strength via finite element analysis approach. A fine-grained (FG) microstructure with a mean grain size of 6 ㎛ (initial grain size was 25 ㎛) was after ECAP. This microstructural evolution brought about a considerable increase in strength values. Both yield and tensile strength values increased from 280 MPa and 425 MPa to about 420 MPa and 785 MPa, respectively. This improvement in the strength values reflected a finite element method to determine the ultimate strength of ship hull girder grillage system. As a result of calculations, it was reached significantly higher ultimate strength values (237,876 MPa) compared the non-processed situation (192,986 MPa) on ship hull girder grillage system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권5호
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• pp.2357-2380
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• 2019

In this paper, we investigate the impact of hardware impairments (HWIs) on the performance of a downlink massive MIMO system. We consider a single-cell system with maximum ratio transmission (MRT) as precoding scheme, and with all the HWIs characteristics such as phase noise, distortion noise, and amplified thermal noise. Based on the system model, we derive closed-form expressions for a typical user data rate under two scenarios: when a common local oscillator (CLO) is used at the base station and when separated oscillators (SLOs) are used. We also derive closed-form expressions for the downlink transmit power required for some desired per-user data rate under each scenario. Compared to the conventional system with ideal transceiver hardware, our results show that impairments of hardware make a finite upper limit on the user's downlink channel capacity; and as the number of base station antennas grows large, it is only the hardware impairments at the users that mainly limit the capacity. Our results also show that SLOs configuration provides higher data rate than CLO at the price of higher power consumption. An approach to minimize the effect of the hardware impairments on the system performance is also proposed in the paper. In our approach, we show that by reducing the cell size, the effect of accumulated phase noise during channel estimation time is minimized and hence the user capacity is increased, and the downlink transmit power is decreased.

• 전기전자학회논문지
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• 제27권4호
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• pp.411-417
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• 2023

무인 항공기(UAV) 지원 중계는 분포가 쉽고 통신 채널이 양호하며, 이동성이 뛰어나 기존 지상 중계에 비해 높은 무선 연결성을 가질 수 있다. 본 논문에서는 무선 주파수(RF) 대역을 활용하여 소스로부터 에너지를 수확하고 테라헤르츠(THz) 대역을 활용하여 2차 송신기와 해당 수신기 간에 정보를 전송할 수 있는 UAV 지원 중계 네트워크를 설계한다. 그 후, 릴레이 채널 용량을 최대화하는 UAV의 최적 위치를 결정하기 위한 최적화 문제의 해를 유도하고, 유도된 해를 활용하여 두 가지 UAV 궤적(직선 궤적과 타원 궤적)을 설계하는 알고리즘을 제안한다. 시뮬레이션 결과, 제안된 알고리즘은 UAV 직선 궤도가 수확된 에너지 및 채널 용량 측면에서 더 나은 시스템 성능을 제공할 수 있음을 보여준다.

• Journal of Communications and Networks
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• 제17권3호
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• pp.265-266
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• 2015

In a recent paper [1], the authors investigated the maximum stable throughput region of a network composed of a rechargeable primary user and a secondary user plugged to a reliable power supply. The authors studied the cases of an infinite and a finite energy queue at the primary transmitter. However, the results of the finite case are incorrect. We show that under the proposed energy queue model (a decoupled M/D/1 queueing system with Bernoulli arrivals and the consumption of one energy packet per time slot), the energy queue capacity does not affect the stability region of the network.