Push-out tests of shear dowels

Continuous shear connectors in a shape of dowels are one of the newer shapes of composite steel-concrete bridges. In this article results of push-out tests of such a dowel with geometry designed at Faculty of Civil Engineering, Technical University of Kosice are presented and compared to the previous research.

Material characteristics of push-out tests

Two types of push-out tests were carried out at the Centre of Research and Innovation in Construction, the Technical University of Košice - one at a composite based on steel continuous shear connector and the second one at the same connector, however made of glass-laminate material. For further research, the material characteristics of the material used needed to be found. In this article, the material tests performed as well as their results are presented.

Push-Out Test and FEM Analysis of Continuous Shear Connector

Composite steel concrete bridges with embedded continuous shear connectors are one of the newer popular options for short span (up to 20 m) bridges. They can be used for both road and railway bridges and due to their low structural height, nowadays, they are also a welcome alternative for bridge reconstructions – the concrete part serves as the bridge deck as well as the main structure. Unfortunately, In the Slovak Republic, no such bridges have been built as of yet (2020). At Technical University of Kosice, Department of Steel and Timber Structures, an extensive research regarding the steel shear connectors have been launched. Its goals are to bring new, easier for construction (due to prefabrication process), more resistant with even lower structural height, and more economical (due to lesser usage of materials and quick construction) geometrical solutions for composite steel concrete bridges as well as to open and popularize this solution for developers in the Slovak Republic. In this article, one of the new types is presented. It has a cross-section in a shape of a trapezoid, with holes in all its sides, except the bottom flange. Their purpose is to create concrete studs and secure full shear transmission with higher shear resistance, but they also serve to create space for transverse reinforcing bars. Its geometrical and material characteristics are closely specified. Results and process of push-out tests performed in Laboratory of Excellent Research onto three specimens are described and compared to results of finite element analysis simulation performed in Abaqus software.

Permeability Analysis of Hydrate-Bearing Porous Media Considering the Effect of Phase Transition and Mechanical Strain during the Shear Process

Summary The permeability characteristics of hydrate-bearing reservoirs are critical factors governing gas and water flow during gas hydrate exploitation. Herein, X-ray microcomputed tomography (CT) and the pore network model (PNM) are applied to study the dynamic gas and water relative permeabilities (krg and krw) of hydrate-bearing porous media during the shear process. As such, the dynamic region extraction method of hydrate-bearing porous media under continuous shear is adopted by considering deformation in the vertical direction. The results show that krw and krg of hydrate-bearing porous media are influenced by the effect of disordered sand particle movement under axial strain. Declines in the critical pore structure factors (pore space connectivity, pore size, and throat size) contribute to the reduction in krw and the increase in krg. However, krg decreases during the shear process at a high water saturation (Sw) because of the high threshold pressure and flow channel blockage. In addition, the connate water saturation (Swc) continuously increases during the shear process. Swc is influenced by pore size, throat size, and flow channel blockage. Moreover, the preferential flow direction of krg and krw changes during the continuous shear process. The results of dynamic permeability evolution during the continuous shear process under triaxial stress provide a reference for pore-scale gas and water flow regulation analysis.

FE analysis of continuous shear connector

<p>Composite bridges with encased steel beams, or nowadays, rather encased steel continuous shear connectors are a welcome option for short span railway or road bridges. With lower construction height and easy construction of prefabricated composite beams it brings a new, complex, solution for replacement of older, overserved bridges, as well as for new tasks. At Technical University of Košice, Faculty of Civil Engineering a new designed of the steel perforated strip was developed. At Laboratory of Excellent Research several experiments for resistance finding were carried together with material tests. In this article the numerical analysis of push-out tests performed is closely described and the shear resistance of finite element model developed in Abaqus/CAE is compared to experimental results.</p>

On the Cutting of Metals: A Mechanics Viewpoint

The mechanics of large-strain deformation in cutting of metals is discussed, primarily from viewpoint of recent developments in in situ analysis of plastic flow and microstructure characterization. It is shown that a broad range of deformation parameters can be accessed in chip formation—strains of 1–10, strain rates of 10–105/s, and temperatures up to 0.7Tm—and controlled. This range is far wider than achievable by any other single-stage, severe plastic deformation (SPD) process. The resulting extreme deformation conditions produce a rich variety of microstructures in the chip. Four principal types of chip formation—continuous, shear-localized, segmented, and mushroom-type—as elucidated first by Nakayama (1974, “The Formation of ‘Saw-Toothed Chip’ in Metal Cutting,” Proceedings of International Conference on Production Engineering, Tokyo, pp. 572–577) are utilized to emphasize the diverse plastic flow phenomena, especially unsteady deformation modes that prevail in cutting. These chip types are intimately connected with the underlying flow, each arising from a distinct mode and triggered by an instability phenomenon. The role of plastic flow instabilities such as shear banding, buckling, and fracture in mediating unsteady flow modes is expounded, along with consequences of the flow modes and chip types for the cutting. Sinuous flow is shown to be the reason why gummy (highly strain-hardening) metals, although relatively soft, are so difficult to cut. Synthesizing the various observations, a hypothesis is put forth that it is the stability of flow modes that determines the mechanics of cutting. This leads to a flow-stability phase diagram that could provide a framework for predicting chip types and process attributes.