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Received Dec 28, 2017; Accepted May 6, 2018
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1. Introduction
In order to overcome the low tensile and flexural strengths of conventional concrete, study is being actively conducted worldwide on steel fiber-reinforced ultrahigh performance concrete (UHPC) developing compressive strength higher than 120 MPa through the admixing of steel fiber in high performance concrete [1–3]. While, the flexural behavior of fiber-reinforced concrete can be influenced by specimen size, concrete casting method, and support devices [4]. Such steel fiber reinforced UHPC is known to present improved deflection, flexural strength, and postcracking ductile behavior compared to conventional concrete.
Composite structures are probably the most appropriate application enabling to take full advantage of the outstanding properties of UHPC, and various solutions combining a UHPC slab and a steel girder were successfully developed [5, 6]. In addition, numerical expression for flexure of UHPC beam has been successfully derived by the strain compatibility relation [7].
Yoo and Yoon [8] carried an extensive review for the behavior of various UHPFRC structures under different loading conditions, such as flexure, shear, torsion, and high-rate loads (impacts and blasts), with practical applications of UHPFRC in architectural and civil structures.
Among the latest achievements and to increase the economy in the material, Europe through the European Commission EUR 25321 developed the preco-beam, a composite beam combining a UHPC deck and an inverted-T steel girder of which the top is worked to have puzzle, fin or clothoidal dowel shape [9]. This dowel shape is obtained by oxycut of the web that may affect the fatigue behavior of steel [10]. Following the same idea and in order to ease the fabrication of the composite beam and to prevent this fatigue problem, the composite beam combining a slab made of steel fiber-reinforced UHPC and a steel girder without the top flange shown in Figure 1 was proposed [11, 12]. This composite beam was conceived considering the fact that the top flange of the steel girder might be superfluous when the composite beam is formed by composing a UHPC slab with the steel girder considering the high stiffness developed by the...