Papers by Keyword: Shear

Abstract: The historical masonry buildings are generally characterized by a load-bearing structure constituted by walls that should resist to both gravitational and horizontal actions. In several existing constructions, masonry panels are made by two external leafs with higher mechanical properties and an inner core with very low, or even negligible, mechanical characteristics. In some cases the connection between the external leafs was provided by inserting a certain number of bricks in the transversal direction (namely diatones); while sometimes, the leafs were totally independent. Often in the case of horizontal forces, as those due to earthquakes, the multi-leafs walls collapse has been observed, because of the leafs separation. Nowadays, there are different connecting systems available in the market and utilized to guarantee the collaboration of the external leafs, in order to finally improve the wall bearing capacity.In this scenario, the present paper is aimed to investigate the shear strength of small-scale multi-leafs panels, coupled with different types of connector, such as: diatones, L-shaped glass; glass and steel rope and helical steel bars. In plane shear tests have been performed in order to evaluate the shear stress-strain relationship. The results are herein reported and discussed, aiming to determine the effectiveness of the different connections systems.

Abstract: The aim of this study was to evaluate the influence of shear and micro-shear tests on adhesive resistance and on defects in restorations in human dentin. The teeth were sectioned and embedded. The dentin surface was treated with universal system adhesive and the samples were divided into two groups. In the first, composite resin pins were fixed with 1 mm diameter and in the second, pins with 2 mm. After mechanical tests the samples were taken to the SEM for analysis of fractures. Tensile strength on G1 was 16 MPa and on G2 20 MPa. The fractures occurred after shear were mostly mixed and cohesive in dentin. On micro-shear adhesive and mixed, no cohesive. It can deduce that, the diameter of the pin influenced the adhesive resistance and the type of failure. Therefore, for evaluation of adhesive strength in dentin the test indicated is micro-shear.

Abstract: The effect of point defects on the shear rupture resistance in titanium aluminide is investigated by the density functional theory and pseudopotential methods. Vacancies, as well as substitution atoms – tungsten and chromium were considered as points defects. The shear was simulated in the(111) slip plane for two directions, namely [110] and [11-2]. It is shown that for a {111}<110> sliding system, vacancies significantly reduce the shear resistance. However, when alloying element occupies a titanium vacancy, it can partially compensate for this negative effect.

Abstract: Dibenzylidene Sorbitol is a very effective clarification additive for isotactic polypropylene. It is not effective with polyethylene although recent studies have shown that it can act as an effective nucleating and directing agent. We employ small-angle neutron scattering measurements to more fully understand the behavior of dibenzylidene sorbitol in a polyethylene matrix. The small-aangle neutron scattering clearly shows that the disappearance of the DBS fibrils is concentration dependent and for 2% DBS the midpoint of the dissolution is at 145°C and for 1% is ~ 20°C lower

Abstract: One of the main ways to improve product quality, obtained by forging, is implementing shear and alternating deformation (severe plastic deformation) during deformation process, which allows manufacturing products with required mechanical properties and less forging reduction. In practice, it is possible to implement shear and alternating deformation by improving the design of the ingots or the billets, forging tools, heating modes and forging method. In this paper newly designed forging die, which allows implementation of shear and alternating deformation without sufficient changes of the billet sizes, is proposed. By the research results of the new forging technology influence in the proposed tools on the microstructure evolution, it was found, that the use of the newly designed step-wedge dies has more potential for manufacturing high-quality forgings with required level of mechanical properties.

Abstract: According to the common design methods of calculation of the stress state induced by torsion of massive prismatic concrete structural elements, the structural system is reduced to a simple cage consisting of ties and struts. This model has, however, a number of principal shortcomings, the major of them is the fact that all of simultaneously acting effects like axial forces, bending moments and shear forces are not taken into account – the compressive axial forces increase very significantly the torque capacity of structural members, while due to action of tensile forces, bending moments and shear forces the torque capacity is reduced. These phenomena, applying non-linear approaches, are analysed and assessed.

Abstract: This paper presents an experimental study on the shear behavior of concrete beams with fiber-reinforced (FRP) composite grating as shear reinforcement. Corrosion resistance and non-magnetic properties of FRP reinforcement allows its use in places where application of regular steel reinforcement would face difficulties. The use of FRP composites can increase the life span of constructions and reduce its maintenance costs. Shear stirrups are more susceptible to harsh conditions, due to their placement at the outer face of the reinforcement, and the use of FRP materials can lead to lower concrete cover thickness and therefore to a more effective design of an element. FRP reinforcements are highly anisotropic material with low strength in the direction perpendicular to the fibers. This causes the strength of a FRP stirrup to be limited by its strength in the bends (corners) of a stirrup. The tensile strength in the corner of the bent stirrup is around 40 to 60% of the strength of the straight bar. FRP grating doesn’t contain a bent section limiting its strength, but its behavior as a shear reinforcement is unknown. The paper contains the results of own experimental research on concrete beams with shear reinforcement made of FRP gratings done at the Faculty of Civil Engineering at the Brno University of Technology. Test specimen consisted of nine beams with different shear reinforcement ratios. Presented experimental data are then compared with the results of tests on beams with regular shear FRP stirrups found in literature.

Abstract: In this paper, possibility to detect damage on post-tensioned concrete girders was investigated through an experimental program with 6 m long specimens containing smart tendons where FBG (Fiber Bragg Grating) sensors were embedded. Total six specimens were fabricated and tested, and test variables were prestressing tendon’s profile and web thickness. All the specimens were subjected to 3-points loading, and they exhibited shear failure. Through the test, it was observed that tendon strains were successfully measured through FBG sensors regardless of the test variables. It was also observed that tendon strains within the pure span significantly increased while ones nearby the anchors beyond the pure span were constant. When the specimen was cracked, FBG sensors nearby cracks showed relatively drastic increase on tendon strain. Since strain variation along tendons cannot be detected by conventional equipment such as a load-cell, the test results indicated that actual tendon strains can be easily measured with FBG sensors. These results showed that FBG sensors can be useful to check whether prestressed concrete members were significantly damaged. In addition, it is expected that FBG sensors can be helpful on more reasonable maintenance of PSC girders.

Abstract: Degradation of reinforced concrete (RC) element could lead to a reduction of its strength and serviceability. The degradation may be identified in the form of spalling of concrete cover. For the case of RC beam, spalling of concrete cover could occur at the web of the shear span due to corrosion of the web reinfocements. The shear strength of the damaged-RC beam possibly will become less conservative compared to the corresponding flexural strength with a risk of brittle failure. Patch repair could be a choice to recover the size and strength of the damaged-RC beam. This research investigates the shear failure of patched RC beam without web reinforcements with a particular interest to compare the shear failure behaviour of patched RC beam and normal RC beam. The patch repair material used in this research was unsaturated polyester resin (UPR) mortar. The results indicate that the initial diagonal cracks leading to shear failure of patched RC beam occur at a lower level of loading. However, the patched RC beam could carry a greater load before the diagonal crack propagates in length and width causing the beam to fail in shear.

Abstract: In recent years, different strengthening techniques adopting composite materials have been proposed. Among these, FRP strengthening technique, which adopts Fiber-Reinforced Polymers strips, has become quite popular for the rehabilitation and seismic improvement of existing buildings. In this paper, this composite material is adopted to design the strengthening of an existing Reinforced Concrete (RC) frame. Firstly, its behavior is considered up to failure condition by performing a Finite Element (FE) analysis that incorporates a non-linear constitutive relation for the material named 2D-PARC. Then, based on the obtained FE analysis results, a strengthening design of the frame by adopting composite materials is developed and discussed.