| المستخلص: |
In general, the structural engineer should concentrate towards the structural as well as functional design of the structure. So by keeping in mind the structure safety and economy, lead us to the concept of "Composite structures or partial elements. The basic idea for this concept is combining the normal strength concrete and UHSC or any recent advanced cementitious material in composite structures in order to exploit the advantages of the two materials in an optimal way. Recently Ultra-high Strength concrete (UHSC) is the most famous advanced cementitious materials that have exceptional properties, however their material costs are significantly higher than those of normal strength concretes. UHSC is characterized by extraordinary mechanical and durability properties, The UHSC-Matrix is very brittle material behavior, and it provides flexural strengths up to 50 MPa and compressive strengths up to 200 MPa. This research is considered a supplement research for an experimental previous one that was carried out in parallel by the same author [1]. It mainly aims to predict theoretically the behavior of the UHSC, NSC and composite concrete beams similar to the previous experimental program tested specimens, under the effect of the same parameters. This prediction was carried out by simulation of three models by using the first principle concepts. The materials which were used were the Ultra-High Strength Concrete (UHSC) (141MPa) and Normal strength concrete. By using the three simulated models a comparison between the theoretical beams behavior and the experimentally tested beams behavior was presented, in order to confirm the validity of these three models upon UHSC and Composite concrete beams. The previous experimental program was consists of ten reinforced concrete beams. The main parameters of this program were: longitudinal reinforcement ratio, the type of used concrete and the thickness of UHSC layer. A small parametric study was carried out through a prediction of another 12 beams that weren’t tested experimentally, in order to confirm one of the previous experimental research related to the optimum use of the UHSC thickness layer in concrete. Finally, the three models give an acceptable prediction for each of NSC, UHSC and composite concrete beams. This models leads to the same Valuable conclusions that were obtained previously. It was concluded that in case of high reinforcement steel ratios the optimum thickness of UHSC in the concrete beams cross section should be not less than the third of the cross section depth only in order to achieve the economic point of view. In contrast, of the low reinforcement steel ratio the UHSC layers thickness can be decreased more than the third cross section depth
|
