Presence Of Slabs Research Articles

Collapse-resistant mechanism of RC beam-slab substructures using kinked steel plates under two-adjacent-edge-columns removal scenario

To improve the progressive collapse resistance of reinforced concrete (RC) frame structures without basically affecting their seismic performance, the authors have proposed a novel method of adding locally debonded kinked steel plates (KPs) at the beam-ends of the RC frames. This method has been verified through quasi-static tests on the RC beam-column assemblies. Considering the presence of slabs, this paper investigated the collapse-resistant mechanism and resistance improvement for the RC beam-slab substructures using locally debonded KPs. First, quasi-static tests were conducted on two RC beam-slab substructures under the scenario of removing two-adjacent-edge-columns. One substructure was configurated with the KPs and the other without the KPs for comparison. Test results demonstrated that, by adding the KPs, the ultimate resistance and deformability of the beam-slab substructure improved by 76% and 40%, respectively. Second, the high-fidelity finite element (FE) models were created to analyze the load transfer path of the substructure and the resistance contribution at the stage of catenary mechanism. Combining the test and FE analysis results, the collapse-resistant mechanism was revealed, i.e., the KPs could fully mobilize and develop the catenary action in the edge-beams and the tensile membrane action in the slabs along the edge direction. Finally, an analytical model was developed for predicting the ultimate resistance of the RC beam-slab substructures with or without the KPs under the scenario of removing two-adjacent-edge-columns.

Assessing the impact of eccentricity, slabs, and transverse beams on the behavior of reinforced concrete beam-column joints

In this study, a cyclic lateral load experiment was performed to assess the behavior of reinforced concrete (RC) beam-column joints with non-seismic detailing. For the experiment, eight full-scale joint specimens were prepared; the experimental variables were eccentricity, presence of slabs, and number of transverse beams. Most experimental objects showed joint shear failure after beam yielding, and their eccentricity reduced the joint shear strength. Although the joints had non-seismic details, the presence of the slabs and increased number of transverse beams strengthened the confinement within the joints, thereby enhancing the joint shear strength. The joint shear strength that was calculated based on the equation suggested in ASCE 41-17 showed a substantial discrepancy from the actual measurement, primarily because the calculation neglected the impact of the slabs and number of transverse beams. Therefore, to improve the performance prediction, an actual three-dimensional shape of the joints must be considered. Additionally, based on further research outcomes, more factors that affect joint behavior must be considered in future relevant standards.

Using coupling slabs to tailor surface-acoustic-wave band structures in phononic crystals consisting of pillars attached to elastic substrates

The propagation of surface acoustic waves (SAWs) in two-dimensional phononic crystals (PnCs) with and without coupling-enhancement slabs was theoretically investigated using a three-dimensional finite element method. Different piezoelectric substrates, for example, lithium niobate (LiNbO3), gallium nitride (GaN), and aluminium nitride (AlN), were taken into account. Compared to the PnCs without coupling-enhancement slabs, the coupling between each pillar and its nearest neighbor was largely enhanced in the presence of slabs. The bandwidth of the first directional band gap increased markedly compared with its initial value for the PnCs without a slab (within square symmetry). In addition, with increasing thicknesses of the slabs bonded between neighboring pillars, the first directional band-gap and second directional band gap of the PnCs tend to merge. Therefore, the structure with coupling-enhancement slabs can be used as an excellent electrical band elimination filter for most electro-SAW devices, offering a new strategy to realize chip-scale applications in electroacoustic signal processing, optoacoustic modulation, and even SAW microfluidic devices.

Experimental and Numerical Investigations on the Seismic Behavior of Lightly Reinforced Concrete Beam-Column Joints

The experimental and analytical investigations carried out on lightly reinforced concrete beam-column joints subjected to seismic loading are presented in this paper. Five 3/4-scale reinforced concrete beam-column joints were tested to investigate the seismic behavior of the joints. The variables in the tested specimens include column orientations and the presence of slabs on the top of beams. The specimens were subjected to quasi-static load reversals to simulate earthquake loadings. Experimental results obtained include joint shear stresses, joint shear strains, observed cracking and initial stiffness. The test results provided some information about the seismic behavior of the specimens. However, due to the unique nature of the specimens, several key parameters could not be varied. Therefore, to elucidate further information, a numerical study consisting of three-dimensional nonlinear finite-element (FE) models was carried out. The FE models were then validated with the experimental results. This was followed by parametric studies, carried out to understand the effects of several critical factors, including column axial load, ratio of column depth to beam reinforcement bar diameter, and effective slab width, on the complex behavior of the joints.

Synthesis, crystal and magnetic structure of a novel brownmillerite-type compound Ca 2Co 1.6Ga 0.4O 5

The novel compound Ca 2Co 1.6Ga 0.4O 5 with brownmillerite (BM) structure has been prepared from citrates at 950 °C. The crystal structure of Ca 2Co 1.6Ga 0.4O 5 was refined, from neutron powder diffraction (NPD) data, in space group Pnma , a = 5.3022 ( 6 ) Å , b = 14.884 ( 2 ) Å , c = 5.5276 ( 6 ) Å , χ 2 = 1.798 , R F 2 = 0.0455 , R wp = 0.0378 and R p = 0.0292 . On the basis of the NPD refinement the compound was found to be a G-type antiferromagnet (space group P n ′ m ′ a ) at room temperature, with the magnetic moments of cobalt atoms directed along chains of tetrahedra in the BM structure. Electron diffraction and electron microscopy studies revealed disorder in the crystallites, which can be interpreted as the presence of slabs with BM-type structure of Pnma and I 2 mb symmetry.

The phase transitions and crystal structures of Ba3RM2O7.5 complex oxides (R = rare-earth elements, M = Al, Ga).

The structures of alpha-Ba(3)RAl(2)O(7.5) and beta-Ba(3)RM(2)O(7.5) complex oxides (R = rare-earth elements, M = Al, Ga) have been studied by a combination of X-ray diffraction, electron diffraction (ED) and high-resolution electron microscopy (HREM). The alpha and beta forms have cell parameters related to the perovskite subcell: a = 2a(per), b = a(per)(2)(1/2), c = 3a(per)(2)(1/2), however, the alpha form has an ortho-rhombic unit cell whereas the beta form adopts monoclinic symmetry. The crystal structure of monoclinic Ba(3)ErGa(2)O(7.5) was refined from X-ray powder data (space group P2/c, a = 7.93617(9), b = 5.96390(7), c = 18.4416(2) Å, beta = 91.325(1) degrees, R(I) = 0.023, R(P) = 0.053), the structure of the alpha form (space group Cmc2(1)) was deduced from ED and HREM data. The important feature of the alpha and beta structures is the presence of slabs containing strings of vertex-sharing tetrahedral Al(2)O(7) pairs. Two almost equivalent oxygen positions within the strings can be occupied either in an ordered manner leading to the low-temperature beta phase or randomly resulting in the high-temperature alpha structure. The critical temperature of this order-disorder phase transition was determined by high-temperature X-ray diffraction and by differential thermal analysis (DTA). In situ ED and HREM observations of the second-order phase transition confirmed the symmetry changes and revealed numerous defects (twins and antiphase boundaries) formed during the phase transformation.

The effects of methane seepage at an intertidal/shallow subtidal site on the shore of the Kattegat, Vendsyssel, Denmark

The effects of methane gas seepage were studied at an intertidal/shallow subtidal site on the Kattegat coast of Denmark. A 30 m wide zone, containing approximately 65 gas seeps, extended over 70 m seawards from the shore. This was characterised by the presence of slabs, pavement and small pillars of carbonate-cemented sandstone which formed a partially buried reef. The escaping gas contained 91-100% methane with some carbon dioxide, 0.6--0.9%, and hydrogen sulphide. The hydrogen sulphide concentration varied over time and between individual seeps. Gas flow rates of individual seeps ranged up to 211 h-1 and the estimated total flow was 110 I h-1• Seeps were often stopped by sand movement, but the overall gas flow from the site appeared to be constant. The escaping gas generated an interstitial water circulation and drew overlying seawater into the sediment. Water pumped out by the seeps was enriched in phosphate and ammonia. Sulphate reduction rates in the seep area were 1.1-17.1 m moles sulphate reduced and aerobic methane oxidation rates were 0.2 - 5.5 m moles methane consumed m-2 day-1• The composition of the flora and fauna surrounding the seeps was affected by the presence of hard substrate (the cemented sandstone). Epifauna was more abundant in the seep zone than else­where, whereas the macrobenthic infauna was reduced in the seep zone, possibly due to the cementation. The sediment was almost devoid of meiobenthic organisms, except nematodes. Nematode species numbers, abundance and biomass were lower at the seeps than 5-20 cm away. The nematode fauna penetrated deeper into the sediment close to the seeps than at the seeps themselves. This is explained by the interstitial water circulation at and close to the seeps. 14C measurements showed that little methane carbon was entering the food web surrounding the seeps.

Explicit eigenmodes for anisotropic media

An exact computational algorithm that solves steady-state Maxwell equations for fields produced by electric currents in the presence of slabs with biaxial anisotropy is developed. Eigenmodes are computed explicitly and are used to study unattenuated propagation and transverse modes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>