Cyclic Flexure Tests of Masonry Walls Reinforced with Glass Fiber Reinforced Polymer Sheets

The research work reported here investigates the out-of-plane flexural behavior of masonry walls reinforced externally with glass fiber reinforced polymer (GFRP) sheets and subjected to cyclic loading. A full-scale test program consisting of eight wall specimens was conducted. Nine tests were performed, in which three parameters were studied. These included the level of compressive axial load, amount of internal steel reinforcement, and amount of externally bonded GFRP sheet reinforcement. Of the three parameters studied, varying the amount of GFRP sheets was the only parameter that significantly affected the behavior of the walls. The GFRP sheet reinforcement governed the linear response of the bending moment versus centerline deflection hysteresis. Increasing or decreasing the amount of GFRP sheet reinforcement either increased or decreased both the wall stiffness and the ultimate strength, respectively. Except for visible cracks, the walls maintained their structural integrity throughout the out-of-plane cyclic loading. The unloading/reloading paths for successive loading cycles were similar, indicating little degradation. Thus, the general behavior of the walls was very predictable. The system, therefore, could be used to advantageously rehabilitate older masonry structures that are inadequately reinforced to withstand seismic events. A simple model of the behavior is also presented to allow for the evaluation of the strength and deformation characteristics of these elements.     

A Further Realization of a Flexible Metamaterial-Based Antenna on Nickel Oxide Polymerized Palm Fiber Substrates for RF Energy Harvesting

In this paper, we considered a distributed antenna system (DAS) to expand the coverage of VHF maritime communication systems and analyzed its performances. To reflect the geometrical distributed antenna port placements along the coastline, we considered a linear antenna layout. By deriving the lower bounds of the expected signal-to-noise ratio (SNR), we analyzed the SNR performances for both single-ship and multiple-ship transmission schemes. Next, based on the analytical results, we present design guidelines to implement the DAS based VHF maritime communication system. From the simulation results, the coverage expansion effect of the DAS was verified by the increased expected SNR. In addition, we confirmed that the system design parameters could be found from simple numerical calculations.

     

Effect of localized KrF excimer laser treatment on fracture behaviors of freestanding <110> and <100> single crystal silicon beams

Microscale silicon structures oriented along <100> and <110> orientations were laser treated with different conditions with the cross section shape and tensile strength investigated after the treatment. Finite element simulation was performed to examine the temperature distribution at different conditions during laser treatment. Using a low energy (1.2 J/cm²) and high tilt angle (65°) led to a more preserved cross section with a slight strength improvement. The strength improvement was limited due to other surfaces that were not affected by laser treatment. An improvement of 30 % in tensile strength was achieved with a higher energy (4 J/cm²) lower tilt angle (45°) treatment that was consistent for different sample orientations. The cross section of the samples treated at such condition was significantly changed however. The effect of sample orientation on fracture behaviour was studied and unstable crack propagation was observed for <100> oriented samples that was more significant after laser treatment.     

Degenerated plate-shell elements with refined transverse shear strains

Although traditional three-dimensional plate-shell elements relax the constraint so that normal cross-sections remain normal to the neutral plane during transverse shear deformation, the section is still constrained to remain plane. The work reported here relaxes this constraint by introducing shape functions across the thickness to approximate the transverse shear strain field in the thickness direction. These shape functions are treated in the manner of generalized angles undergoing small deformations. They are added as new degrees of freedom to the ordinary displacement field of the degenerated shell elements. The field is still able to simulate large deformation behavior of the element. Each shape function yields two independent variables, one in each direction. In this work, two types of shape functions are proposed allowing a parabolic transverse shear strain, as well as an unsymmetric transverse shear strain distribution in the thickness direction. These two modes of deformation are particularly important in the case of diffused material failure in shell structures. Displacement field representation and finite element formulation based on a total Lagrangian approach are given. Examples are presented demonstrating the applicability of this element in a variety of problems.     

Fatigue life prediction of heavy mining equipment. Part 2: Behaviour of corner crack in steel welded box section and remaining fatigue life determination

Frequent fatigue failure of mining equipment has created a need for fatigue life prediction of several components that suffer from frequent recurrence of fatigue cracking. The focus of this paper is the frequent occurrence of fatigue cracks in the boom of cable shovels, which consists of a twin box girder joining together near both extremities. After the determination of load spectrum and the material fatigue properties by field monitoring and material testing, the fatigue behaviour of a cracked shovel boom was investigated. Two-tip corner cracks were of particular interest since they are commonly observed in the field. These cracks typically initiate in the flange at the toe of web to flange or flange to diaphragm welds and propagate into the web. Detailed finite element models with corner cracks were developed for the boom and stress intensity factors for various crack configurations were evaluated from the finite element analysis results. The growth behaviour of corner cracks was studied and a simplified method is presented for the fatigue life prediction. Fracture toughness tests were conducted on single edge notch bend specimens at room temperature and low temperature (−50 ^°C). The remaining life of a cracked boom is then determined based on brittle fracture or unstable crack growth.     

Skyline algorithms for multilevel substructure analysis

A matrix derivation of the method of partial decomposition for substructure equilibrium equations is given and algorithms and subroutines necessary for implementing a multi-level substructuring scheme are presented. The algorithms are based upon partial decomposition of skyline matrices by the Cholesky method. Transformation of co-ordinates and prediction of the skyline for higher level substructures are also discussed.     

Nonlinear harmonic analysis applied to axisymmetric structures

The total Lagrangian formulation for axisymmetric solids, which was introduced in an earlier paper [Comput. Struct.49, 219–230 (1993)] is investigated in more detail with a series of sample analyses. The formulation uses a cylindrical reference system to define the geometry, a Cartesian reference system for the displacement field and Fourier decomposition to describe the displacement field in the circumferential direction. Loading functions are defined in terms of the Cartesian displacement reference system and the Fourier functions. The capabilities of the formulation are further demonstrated in several examples which compare its solutions with analytical solutions, other Fourier decomposition formulations and physical test of a pipe subjected to combined axial and bending loads.     

重型采矿设备的疲劳寿命预测第一部分：疲劳荷载评估和裂纹发展速度试验

重型采矿设备的疲劳寿命预测十分重要。首先,对早已存在有慢性疲劳裂纹的铲矿机起动臂进行现场监测,从监测数据中归纳了吊杆的载荷范围。针对试验数据,建立吊杆的有限元模型来预测其压应力和应变。进行了8个裂纹发展速度试验,获得使用材料的疲劳特性。     

Evaluation of Masonry Deep Beams Externally Strengthened with CFRP Sheets

In this study, carbon fiber-reinforced polymer (CFRP) sheets were examined as a means to strengthening existing masonry walls allowing for efficient creation of doors, windows, and passage openings. The research reported here deals with eight masonry walls made with concrete blocks, subjected to three-point quasistatic loading. The parameters examined include the reinforcement configuration and their amount. While CFRP sheets were used as external reinforcement, companion studies were carried out with conventional steel rebars. Test results indicate an increase of 180% in shear strength of the reinforced walls as compared to reference unreinforced walls. Load-deflection relationships indicate that the combined plain masonry and CFRP laminate system possessed some nonlinear deformability. The use of CFRP laminates on the walls was found to have an influence on the mode of failure. Anchoring the CFRP laminates at both support regions helped in using a larger portion of the strength of the laminates. The reinforced walls exhibited diagonal shear cracks that developed at a much slower rate and were ultimately accompanied by the peeling off of the CFRP laminates.     

On the design of a reject band filter for antennas mutual coupling reduction

In this article, a novel concept for mutual coupling reduction between antenna elements is proposed at 2.45 GHz for Wi‐Fi applications. A reject band filter (RBF) is used in order to reduce the mutual coupling between two monopoles for multi‐input multi‐output (MIMO) systems. The proposed RBF inclusions are developed to have zero refractive index response over a specific frequency band. The inclusions considered here are composed of open‐loop resonators; each one with the same iteration level of Minkowski‐like pre‐fractal structures coupled with an open‐stub transmission line to increase the band selectivity. The inclusions are inserted between λ/2‐spaced monopole elements at 2.45 GHz. A significant mutual coupling reduction is realized by incorporating only two RBF cells. Such effective response is attributed to the electromagnetic wave cloaking at 2.45 GHz using the developed RBF inclusions. An extensive theoretical study using both numerical and analytical methods is invoked to obtain the best performance of the proposed MIMO antenna structure. Finally, the experimental and numerical results are agreed excellently.