Theoretical Analysis of Beams Combining Ultra High Strength Concrete and Normal Strength Concrete

In general, the structural engineer should concentrate towards the structural as wellas functional design of the structure. So by keeping in mind the structure safety andeconomy, lead us to the concept of Composite structures or partial elements. Thebasic idea for this concept is combining the normal strength concrete and UHSC orany recent advanced cementitious material in composite structures in order toexploit the advantages of the two materials in an optimal way. Recently Ultra-highStrength concrete (UHSC) is the most famous advanced cementitious materials thathave exceptional properties, however their material costs are significantly higherthan those of normal strength concretes. UHSC is characterized by extraordinarymechanical and durability properties, The UHSC-Matrix is very brittle materialbehavior, and it provides flexural strengths up to 50 MPa and compressive strengthsup to 200 MPa. This research is considered a supplement research for anexperimental previous one that was carried out in parallel by the same author [1]. Itmainly aims to predict theoretically the behavior of the UHSC, NSC and compositeconcrete beams similar to the previous experimental program tested specimens,under the effect of the same parameters. This prediction was carried out bysimulation of three models by using the first principle concepts. The materialswhich were used were the Ultra-High Strength Concrete (UHSC) (141MPa) andNormal strength concrete. By using the three simulated models a comparisonbetween the theoretical beams behavior and the experimentally tested beamsbehavior was presented, in order to confirm the validity of these three models uponUHSC and Composite concrete beams. The previous experimental program wasconsists of ten reinforced concrete beams. The main parameters of this programwere: longitudinal reinforcement ratio, the type of used concrete and the thicknessof UHSC layer. A small parametric study was carried out through a prediction ofanother 12 beams that weren’t tested experimentally, in order to confirm one of theprevious experimental research related to the optimum use of the UHSC thicknesslayer in concrete. Finally, the three models give an acceptable prediction for each ofNSC, UHSC and composite concrete beams. This models leads to the sameValuable conclusions that were obtained previously. It was concluded that in caseof high reinforcement steel ratios the optimum thickness of UHSC in the concretebeams cross section should be not less than the third of the cross section depth onlyin order to achieve the economic point of view. In contrast, of the lowreinforcement steel ratio the UHSC layers thickness can be decreased more than thethird cross section depth.