Experimental and numerical investigations on I-shaped UHPC-beams with combined reinforcement under shear load

Abstract eng:
On account of its compounding, ultra-high performance concrete exhibits a very high compression strength ranging from 150 to over 200 N/mm², as well as having an exceptionally high density. The high compressive strength of UHPC comes along with a high brittleness of the matrix. Adding fibers to UHPC with conventional or prestressed reinforcement improves the deformation and crack developing behavior of UHPC-members in the softening range. At the same time, fibers take an influence on the load bearing behavior of structures. A safe and economic design of UHPC-members requires exact knowledge of the load bearing behavior. In this respect, the presented research project concentrates on I-shaped UHPC-beams under shear load. 3-point-bending tests on beams of UHPC with a standard I-section and a shear slenderness of a/d = 4 were carried out. The identical beams varied only in type and amount of shear reinforcement. The tests showed the dependence of the shear bearing behavior from the type of shear reinforcement. Compared to beams made of UHPC without fibers or stirrups, test specimens of fiber-reinforced and combined reinforced UHPC showed a significantly higher shear bearing capacity in tests, although the selected fiber contents led to a softening behavior in the post-cracking range. Based on the results of the experimental and analytical investigations, a mechanically consistent model was developed to describe the shear bearing behavior of structural elements made of UHPC, reinforced with steel fibers, and combined reinforced with steel rebars and fibers, respectively. By doing so, existing design rules referring to Normal (NSC) and High Strength Concrete (HSC) are examined in terms of their validity for and their transferability to UHPC.

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