Experimental analysis of a mechanical shear connector in concrete filled steel tube column

ABSTRACT This work includes an analytical and experimental study of the structural behavior of shear connectors in composite columns, composed of concrete-filled circular hollow section. For this study was adopted a structural bolt like a shear connector in order to verify the validity of the analytical expressions in ABNT NBR 16239: 2014 [1]. Was carried out a series of push-out tests, fixing the outer diameter of the hollow section and varying the thickness, the bolt diameter, the strength of concrete and the hole dimension. Analysis of the results shows that is possible to use this type of shear connector. The Brazilian prescriptions results are conservative and may be adjusted to provide strength capacity value closest to the experiment.

Punching shear in reinforced concrete flat slabs with hole adjacent to the column and moment transfer

The structural behavior and the ultimate punching shear resistance of internal reinforced concrete flat slab-column connections, with one hole adjacent to the column, with or without flexural moment transfer of the slab to the column was investigated. Main variables were: the existence whether or not hole, flexural reinforcement layout and ratio, the direction and sense of the moment transferred and the eccentricity of the load (M (moment transferred to column) / V (shear)) ratio at the connection - 0,50 m or 0,25 m. Seven internal slab-column joining were tested and ultimate loads, cracking, deflections, concrete and reinforcement strains were analyzed. The existence of hole adjacent to the smaller column dimension, the hole dimension, flexural reinforcement rate and placing, the variation of relation Mu/Vu in function of the load, and, than, of eccentricity of the load, influenced the slabs behavior and rupture load. Test results were compared with the estimations from CEB-FIP/MC1990 [7], EC2/2004 [12], ACI-318:2011 [1] and NBR 6118:2007 [5]. ACI [1] and EC2 [12] presented most conservative estimates, although have presented some non conservative estimates. Brazilian NBR [5], even though being partly based in EC2 [12], presented smaller conservative estimates and more non conservative estimates. A modification on all codes is proposed for taking in account the moment caused by the eccentricity at the critical perimeter for slabs with holes.

New Instrument PFT for Powder Flow Researching

Researching of Powder flow behavior is an important issue in many new material industries. But the familiar method used does not meet the requirement actually. This article introduced the PFT (Powder Flow Tester) from Brookfield Engineering Laboratories Inc. It complies with the ASTM D 6128. The basic function includes the measurement and calculation of Flow Function, Wall Friction, Bulk Density, Time Consolidation Test with Flow Function, Arching Dimension, Rat-hole Dimension, Hopper Half Angle etc.

Cobalt Silicidation on Sub 100nm Hole Patterned Vertical Diode Formed by Silicon Epitaxial Growth and Its Electrical Properties

ABSTRACTSelf-aligned Cobalt silicide as ohmic contact layer on sub 100 nm hole patterned Si vertical diode formed by silicon epitaxial growth (SEG) is investigated and silicon epitaxial growth of higher than 4000 Å thickness and good crystalinity for PN diode has been successfully developed. Also, electrical isolation of 100 nm pitch size between diode and diode, and removal of unreacted Co/Ti/TiN layer have been realized by dip-out process without CMP simultaneously. Through the mechanism of void formation due to the variation of Si consumption rate during silicidation at limited hole pattern dimension, critical Co and Capping Ti thickness are investigated as various hole dimensions (80∼120 nm), and then with p+ type dopant species (49BF2, 11B). The ratio of Co thickness to hole dimension demonstrates void free cobalt silcidation on various pattern sizes of silicon epitaxial growth. Silicon epitaxial growing PN diodes including void free CoSi2 show excellent electrical performance, especially lower than 10 pA reverse off leakage current.

A RSS Method for Estimating Hole Dimension Error in a Batch Micro-EDM Process

In an attempt to estimate the spread of errors in an EDM hole making process, a new Root-Sum-Square (RSS) method is proposed to combine the dimensional spread of a batch of electrodes with the over-cut variation in the micro-EDM process. Two sources of errors are commonly associated with an EDM process and contribute to the dimensional accuracy of the EDMed hole: the dimensional variation of the electrodes and the process over-cut error and its variation. Especially in a micro-EDM process, it is often difficult and time-consuming to measure the geometric dimension and tolerance of either a batch of electrodes or holes of small dimensions. By quantitatively establishing the relationship among the spreads in geometric errors of the electrodes and holes and the process capability, this new method provides an analytical tool in predicting hole error and allows allocating the tolerance budget when selecting the appropriate electrode making process, the EDM machine and process parameters. A series of experiments are carried out to establish and verify the RSS method. Given a set of EDM parameters and a batch of electrodes, the process error in the average over-cut and its spread is first obtained by the RSS method. The process error is then verified by separate experiments with electrodes of fixed dimension under the same EDM conditions. The validity of RSS method is further confirmed by experiments under different electrode dimensions. The RSS method is shown to well represent the contribution of both electrode and process errors to the statistical characteristics of the hole dimension. The establishment of this statistical error model should facilitate the design and control of hole quality by balancing the requirements for the dimensional accuracy of the electrodes and the process accuracy in a batch production environment.

Crystal Morphology and Decalcification Patterns Compared in Rat and Human Enamel and Synthetic Hydroxyapatite

The purpose of this investigation was to compare morphology and dissolution patterns by ultrastructural examination of rat and human enamel crystals as well as synthetic apatite crystals. Mature enamel crystals were of particular interest, since crystal maturation appears to be inhibited in amelogenesis imperfecta. Specimens were isolated from developing and mature rat incisor enamel. Rat enamel, mature human enamel, and synthetic apatite were thin-sectioned without decalcification and examined by transmission electron microscopy. Some sections were exposed to acid, and selected synthetic apatite sections were further treated for removal of embedding plastic, followed by vacuum-shadow-coating with carbon. Results showed that cross-sections of rat, human, and synthetic crystals had a distortion in the flattened hexagonal outline in regions where the growth of one crystal impinged on another. Crystal dissolution occurred preferentially along the c-axis, producing a central defect or hole in the crystals. Preliminary studies with weak acid on mature human enamel indicate that the relatively soluble crystal core is quickly dissolved, while the outer shell remains intact over a much longer period of time. In the mature rat and human enamel, this crystal hole formation had a consistent dimension of approximately 10-nm thickness. The crystal hole dimension was the same size as crystals that are formed during the early secretory phase in rat amelogenesis. Acid-treated synthetic apatite also showed dissolution of the crystal core along the c-axis, but dimensions of the hole were not consistent. Shadowed grids showed that the defective hole penetrated the entire section thickness. Mature human enamel showed a unique variation to acid at rod borders where larger, isohexagonal crystals were resistant to acid dissolution. It was concluded that (1) crystals of rat and human enamel show evidence of diphasic growth that may affect their dissolution properties, and (2) unique acid-resistant crystals in human enamel at rod borders may be a result of long oral exposure.