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Tensile Force (tensile + force)
Selected AbstractsTragverhalten von Flachdecken aus Stahlfaserbeton im negativen Momentenbereich und Bemessungsmodell für das GesamtsystemBETON- UND STAHLBETONBAU, Issue 8 2010Julien Michels Dr. Baustoffe; Berechnungs- und Bemessungsverfahren; Versuche Abstract Der vorliegende Artikel befasst sich mit dem Tragverhalten von Flachdecken aus Stahlfaserbeton im negativen Momentenbereich. Zugkräfte werden allein von den in der Betonmatrix eingebetteten Stahlfasern aufgenommen, letztere ermöglichen in einer Dosierung von 100 kg/m3 (1.3 % des Volumens) eine hohe Rotationsfähigkeit bei gleichzeitig hoher Tragfähigkeit. In einer ersten Phase kann anhand von Laborversuchen an Deckenausschnitten gezeigt werden, dass bei Flachdecken mit reiner Faserbewehrung und unter rotationssymetrischer Belastung kein Durchstanzen auftritt und sich ein Biegeversagen mit deutlicher Bruchlinienbildung einstellt. Neben den erhaltenen Informationen über Versagensart und -last konnte ebenfalls eine abfallende Faserwirksamkeit mit steigender Plattendicke festgestellt werden. Kombiniert mit den experimentellen Untersuchungen kann anhand nicht-linearer FE-Simulationen der Einfluss von Aussparungen bei lokalem Plattenversagen im Stützenbereich auf die Traglast beschrieben werden. Anhand der Festigkeitsstreuungen und einem semi-probabilistischen Sicherheitskonzept wird ein Sicherheitsfaktor hergeleitet, welcher es ermöglicht, einen Bemessungswert der Querschnittstragfähigkeit zu berechnen. Wegen dem experimentell festgestellten Biegeversagen wird die Bruchlinientheorie als Rechenmodell angewendet. Bearing Capacity of Steel Fiber Reinforced Concrete (SFRC) Flat Slabs in the Negative Bending Moment Area and Design Model for the Complete System The present paper deals with the bearing behaviour of steel fibre reinforced concrete (SFRC) flat slabs in the negative bending moment area. Tensile forces are carried only by steel fibers. The latter allow, due to a dosage of 100 kg/m3 (1.3% in volume), a high rotation capacity with simultaneously high bearing capacities. In a first step experimental analysis showed that under symmetrical loading no punching shear failure occurred. A bending behaviour with creation of yield lines was observed for all test specimens. Furthermore, a decreasing fibre orientation with growing plate height could be noticed. The effect of openings in the column area on the bearing capacity loss in a local failure were evaluated with the use of non-linear finite element software. Scatter in bending tensile strengths was used to calculate a safety factor by the means of a semi-probabilistic safety concept. Eventually, slab design is performed by using yield line theory. [source] Column restraint in post-tensioned self-centering moment framesEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 7 2010Chung-Che Chou Abstract Gaps between beam-to-column interfaces in a post-tensioned (PT) self-centering frame with more than one column are constrained by columns, which causes beam compression force different from the applied PT force. This study proposes an analytical method for evaluating column bending stiffness and beam compression force by modeling column deformation according to gap-openings at all stories. The predicted compression forces in the beams are validated by a cyclic analysis of a three-story PT frame and by cyclic tests of a full-scale, two-bay by first-story PT frame, which represents a substructure of the three-story PT frame. The proposed method shows that compared with the strand tensile force, the beam compression force is increased at the 1st story but is decreased at the 2nd and 3rd stories due to column deformation compatibility. The PT frame tests show that the proposed method reasonably predicts beam compression force and strand force and that the beam compression force is 2 and 60% larger than the strand force with respect to a minor restraint and a pin-supported boundary condition, respectively, at the tops of the columns. Therefore, the earlier method using a pin-supported boundary condition at upper story columns represents an upper bound of the effect and is shown to be overly conservative for cases where a structure responds primarily in its first mode. The proposed method allows for more accurate prediction of the column restraint effects for structures that respond in a pre-determined mode shape which is more typical of low and mid-rise structures. Copyright © 2009 John Wiley & Sons, Ltd. [source] Shaking table tests on seismic response of steel braced frames with column upliftEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 14 2006Mitsumasa Midorikawa Abstract Previous studies have suggested that rocking vibration accompanied by uplift motion might reduce the seismic damage to buildings subjected to severe earthquake motions. This paper reports on the use of shaking table tests and numerical analyses to evaluate and compare the seismic response of base-plate-yielding rocking systems with columns allowed to uplift with that of fixed-base systems. The study is performed using half-scale three-storey, 1 × 2 bay braced steel frames with a total height of 5.3 m. Base plates that yield due to column tension were installed at the base of each column. Two types of base plates with different thicknesses are investigated. The earthquake ground motion used for the tests and analyses is the record of the 1940 El Centro NS component with the time scale shortened by a factor of 1/,2. The maximum input acceleration is scaled to examine the structural response at various earthquake intensities. The column base shears in the rocking frames with column uplift are reduced by up to 52% as compared to the fixed-base frames. Conversely, the maximum roof displacements of the fixed and rocking frames are about the same. It is also noted that the effect of the vertical impact on the column associated with touchdown of the base plate is small because the difference in tensile and compressive forces is primarily due to the self-limiting tensile force in the column caused by yielding of the base plate. Copyright © 2006 John Wiley & Sons, Ltd. [source] Modeling cell adhesion to a substrate with gradient in ligand densityAICHE JOURNAL, Issue 11 2009Alireza S. Sarvestani Abstract Surface density profile of bioadhesive ligands greatly influences spreading and migration of cells on substrates. A 1D peeling model is developed to predict the equilibrium adhesion strength and peeling tension of a cell membrane, adhered on a substrate with linearly increasing density of ligands. Cell membrane is modeled as a linear elastic shell subjected to a tensile force applied at the free extremity and adhesive traction due to specific receptor-ligand interactions with the substrate. Membrane peeling tension increased with gradient slope and reached an asymptotic limit independent of gradient slope but proportional to receptor-ligand interaction energy. Peeling tension from substrates with negative gradient slope, at the rear edge of adhesion zone, was considerably lower than the tension from substrates with positive gradient slope at the leading edge, indicating that detachment is more likely to be initiated at the rear edge. This prediction leads to a possible mechanism for experimentally observed haptotactic locomotion of motile cells toward the direction of higher ligand density. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] A biomechanical effect of wide implant placement and offset placement of three implants in the posterior partially edentulous regionJOURNAL OF ORAL REHABILITATION, Issue 1 2000Y. Sato To prevent loosening or fracture of screws retaining the prosthesis to the implants in the posterior partially edentulous region, the use of staggered buccal and lingual offset placement or wide implants is suggested. However, it is not known how this usage compensates for the torque produced by lateral occlusal forces. This study evaluated the effectiveness of offset placement of three implants and a wide implant placement at the most posterior site. Three-dimensional geometric analysis was used to calculate the tensile force applied to gold screws in clinical situations with buccal or lingual loading perpendicular to cuspal inclination (10 or 20°). Four variations of the placement of three implants (, 3·75 mm) are: (1) straight; (2) buccal offset of the second implant; (3) lingual offset of the second implant; (4) a wide implant (, 5 mm) placement at most posterior site. The offset placement did not always decrease tensile force at the gold screw, but wide implant placement and decrease in cuspal inclination did. [source] The Retention of Cast Metal Dowels Fabricated by Direct and Indirect TechniquesJOURNAL OF PROSTHODONTICS, Issue 1 2010MDentSci, Wael M. Al-Omari BDS Abstract Purpose: To explore the effect of fabrication technique, cement type, and cementation procedure on retention of cast metal dowels. Methods and Materials: Eighty intact single-rooted teeth were selected. The clinical crown was removed at the cementoenamel junction level. Each root was prepared to receive a cast metal dowel of 10-mm length and 1.45 mm in diameter. The 80 specimens were divided into two major groups of 40 based on fabrication technique (direct and indirect). Each group was further divided into four subgroups of ten based on the cement type (zinc phosphate and glass ionomer), and cementation procedure (with and without lentulo spiral). The dowels were subjected to a constantly increasing tensile force, in a universal Instron testing machine, at crosshead speed of 5 mm/min until failure. Results: The most significant factor to affect retention was the cementation procedure, as cementation with lentulo spiral produced greater retention than cementation without the use of lentulo spiral (p < 0.05); however, there seems to be a close interaction between fabrication technique, cement type, and cementation procedure (p= 0.051). The least retentive group was the one fabricated by direct technique, cemented with zinc phosphate without the use of lentulo spiral. Conclusion: Fabrication technique does not affect retention of cast dowels, except when zinc phosphate was the luting agent and placed in the canal space without using a lentulo spiral. The cementation procedure had a significant effect on retention; thus, it is recommended that cementation should be done using the lentulo spiral. [source] Tests and calculations of short-circuit forces and displacements in high-voltage substations with strained conductors and droppersEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 3 2000N. Stein Forschungsgemeinschaft für Elektrische Anlagen und Stromwirtschaft FCH and DKE UK 121.2 have recently completed an extensive systematic programme of short-circuit tests on substation bus bars of stranded conductors with and without droppers. The present test series, in continuation of the former studies, comprises 100-kV and 400-kV arrangements, applying the relevant parameters of the former. Apart from other variations, different current paths were studied for the arrangements with droppers. The present paper is confined to giving a survey of the 100-kV arrangements, parameter variations, measurements and test results, as far as they presently relate to the calculation procedure oflEC, CENELEC and D/V/VDE. It is further reported on studies with the Finite-Element Method (FEM) which show a remarkable comparative accuracy. Finally, the standardized method of IEC 60865-1 and EN 60865-1 for the calculation of short-circuit tensile forces is extended onto arrangements with droppers. [source] Restraint of fire-exposed concrete floor systemsFIRE AND MATERIALS, Issue 2-4 2004Linus Lim Abstract This paper describes the numerical analyses of restrained concrete floor slabs exposed to fire. The analyses of the slabs were carried out with the SAFIR finite element program considering a 200 mm thick slab, spanning 5 m between two end supports. The slabs were exposed to the ISO standard fire for up to 4 h and were analysed with pinned and rotationally restrained supports. Different heights of the line of thrust at the supports and different levels of axial restraint were also investigated. The analyses show that fully restrained pin-supported slabs can survive the 4 h ISO fire without collapse if the position of the line of thrust is located near the soffit of the slab. If the position of the line of thrust is located much above the soffit of the slab, the slabs will rapidly undergo large deformations and sag into a catenary, imposing axial tensile forces at the supports. The analyses have shown that even if the line of thrust is located close to the soffit, the slab can still deform into a catenary if there is insufficient horizontal axial restraint. In this study, rotationally restrained slabs experience much smaller vertical deflections than pin-supported slabs when exposed to fires. Rotationally restrained slabs with low levels of horizontal restraint do not collapse, due to the beneficial effects of moment redistribution. However, high levels of horizontal restraint can be detrimental, causing slabs to collapse at advanced stages of the fire. Copyright © 2004 John Wiley & Sons, Ltd. [source] Application of crosslinkers to dentin collagen enhances the ultimate tensile strengthJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2007Ana Karina B. Bedran-Russo Abstract The stabilization of dentin collagen with biocompatible crosslinking agents may be of clinical importance to improve dentin bond strength. The present study aimed to evaluate the effect of three collagen crosslinking agents on the ultimate tensile strength (UTS) of undemineralized and demineralized dentin. Ten freshly extracted sound molars were sectioned into 0.5 × 0.5 mm2 thick beams. The beams were either demineralized or kept undemineralized. Then, specimens were subdivided into four groups according to treatments,PBS solution (control), 5% glutaraldehyde (GD), 0.5% proanthocyanidin PBS solution (PA), and 0.625% genipin PBS solution (GE). Specimens were kept in their respective solutions for either 4 or 40 h. To assess UTS, specimens were subjected to tensile forces at a crosshead speed of 1 mm/min. Statistical analysis was performed using two-way ANOVA and Fisher's PLSD test (p < 0.05). Statistically significant increases in UTS were observed for demineralized dentin after PA and GE dentin treatment, when compared with those of the control group. Dentin treated with GD showed no statistically significant differences in UTS when compared with that the control. Undemineralized dentin revealed no significant differences as compared to that of the control, regardless of the collagen crosslinkers. The application of two naturally occurring crosslinkers, i.e., PA and GE, to dentin collagen significantly improves UTS, indicating its potential value in restorative dentistry. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2007 [source] | |||||||||||||