Abstract:Ultra-high performance fiber-reinforced concrete (UHPC) is a new class of concrete that has been developed in recent years. UHPC results from the addition of either short discrete fibers or continuous long fibers to the cement based matrix. When UHPC compared with high performance concrete (HPC), UHPC exhibits superior properties in terms of compressive behavior, tensile behavior, workability, toughness, ductility and durability. UHPC has exceptional mechanical and transport properties including a very high tensile strength, strain hardening, and a density leading to a very low permeability. In this research, tests were carried out on a total 42 cubes, 84 cylinders and 21 prisms of UHPC samples to study the effect of adding steel fibers on the mechanical properties of UHPC such as, compressive strength, modulus of elasticity, poisson's ratio, flexural strength and tensile strength. The major parameters included in this research were the volume fraction of steel fibers and aspect ratio. The test results showed that the increase of volume fraction of steel fiber from 0% to 3% for UHPC causes maximum increase in compressive strength by 18.2%, flexural strength by 40% and tensile strength by 66.1% for higher side of aspect fiber ratio. Furthermore, adding steel fiber to UHPC can change the crack patterns, delay the crack appearance and restrain the crack expansion in concrete specimen.
The developed Strut-and-Tie Model (STM) has no unique shape for each load case of a given structural problem as long as the selected idealized internal load-resisting truss is in equilibrium with boundary forces, and also stresses in its components "struts, ties, and nodes" are within acceptable limits. However, the optimal shapes are the well-designed with best ordinal weight number of conditional factors as the rebar amount, the load factor, and the structural concrete ductility. The current study investigates numerically based on FE method stress flow contours and micro truss techniques many alternatives with different shapes of struts and ties that transfer the flow of forces from top of the deep beam with opening to both right and left supports. Then, these alternatives with different concrete characteristics are analyzed by strut-and-tie computational tools using different code provisions for verifying its results accuracy with the numerical nonlinear finite element analysis results for studying the structure performance under applied service loads and over loading till failure. The chosen alternative produce load factor to reach capacity greater than 1, therefore the strut-and-tie method always give demand collapse load lower than the true capacity collapse load. This implies that the solution obtained from STM usually lies on the safe side with conservative sense for concrete structures subjected to service loads. That's why the STM is emerging as an increasingly popular code-worthy methodology for the design and detailing of concrete structures D-Regions.
Powder metallurgy (PM) approach was utilized for the preparation of Ti porous material mixed mechanically with different percentages of sodium chloride salt from 10 to 40 % with stirring speed 100 rpm and ball to powder ratio 10:1 for milling time 24 h. The Ti -NaCl mixed samples were compacted under 600Mpa, then sintered at 1450 ᴼC for 90 min in a vacuum furnace. The phase composition and microstructure of Ti samples are investigated through X-ray diffraction analysis and scanning electron microscope (SEM). All the prepared samples were characterized by measuring the porosity percentage, Vickers hardness, and compression strength. Microstructure indicated that porosity was found to increase with increasing salt percent while the highest hardness (380) and the compression strength (45MPa) were recorded for the lowest ratio of salt (10%NaCl). Biocompatibility test was estimated for the prepared samples, which exhibited the high viability for cell with good growth of the life cells on the sample's surface, and low adhesion.
This paper presents an analytical model to construct the interaction diagrams (normal force and moment) for the RC column strengthened using the steel jacket technique. The proposed model is defined using the strain distribution block by determining the location of the neutral axis in the concrete section. The proposed analytical formulation is verified by experimental results performed by previous researches and numerical models using the nonlinear program ANSYS. The factors affecting the capacity of the strengthened column are taken into consideration, such as the amount of loads resisted by the steel cage, steel strips spacing, and the effect of concrete confinement. The results of the proposed model are in good agreement with the results from the experimental and numerical work used in verification. A practical design formula has been presented for strengthened columns.
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