Thin UHPFRC slabs without conventional reinforcement as light-weight structural elements
Ultra-High Performance Fibre-Reinforced Concrete (UHPFRC) is a material characterised by significantly improved mechanical and durability properties compared to other concretes. In recent years, an important research effort has been made to identify appropriate structural forms and to provide practical design rules allowing efficient UHPFRC structures to be conceived. This paper presents the results of an experimental and theoretical study on the structural behaviour of thin UHPFRC slabs without conventional reinforcement. It is shown that these elements can provide high bending resistance, and, applied in an appropriate structural arrangement, lead to strong and light-weight structures that cannot be built with ordinary reinforced concrete. The favourable behaviour of thin UHPFRC members results from material mechanical properties: high compressive strength and significant ductility in tension of thin UHPFRC members lead to a ductile bending response, even when conventional reinforcement is not provided. It is demonstrated that the theory of plasticity can be safely used to assess the bending failure load for thin UHPFRC slabs. A practical expression is proposed to define the resistant plastic moment, allowing an easy estimation of the bending load-bearing capacity of thin statically indeterminate UHPFRC elements. The results are compared with experimental data on slabs of various thicknesses, showing good agreement.
Characterization of Punching Shear Capacity of Thin Uhpc Plates
UHPC (ultra-high performance concrete) is a relatively new type of concrete that exhibits mechanical properties that are far superior to those of conventional concrete and in some cases rival those of steel. The main characteristics that distinguish UHPC from conventional reinforced concrete are the improved compressive strength, the tensile strength, the addition of steel fibers, and the resistance to corrosion and degradation. The mechanical properties of UHPC allow for smaller, thinner, lighter sections to be designed while strength is maintained or improved. The use of UHPC has been limited to a few structural applications due to the high cost of the materials and the lack of established design guidelines. A proposed material model based on material and finite element models has served as the foundation of this research effort. The model was used to minimize the dimension of an optimum section in order to limit the material usage and maximize the performance. In the model, the top flange served as the riding surface and contained no reinforcing steel to resist shear. The lack of steel reinforcement allowed for the possibility of a punching shear failure to occur from the application of a point load such as a wheel tire patch load. The model and optimized section served as the foundation for this research, the characterization of punching shear capacity of thin UHPC plates. A total of 12 UHPC slabs were tested to failure to determine the boundary between a flexural failure and a punching shear failure. The variables considered were the slab thickness and loading plate dimensions. The results of the testing were compared to
Punching Shear Strength of Steel Fiber Reinforced Concrete Flat Plates
The primary objective of this experimental study was to determine whether addition of steel fibers to the concrete mix could significantly increase the punching shear strength of reinforced concrete slabs. Thirteen slab specimens and their companion cylinder specimens were tested. Fiber concentrations in the slabs ranged from 0 to 6.4 percent by weight of concrete. Test results of this study indicate that the addition of steel fibers to the concrete mix does significantly enhance the punching shear strength of slabs. A modification of the standard code design equation for shear punching strength of slabs is suggested to reflect the strength increase produced by the fibers. The tests also provided information on the shape and inclination of the fracture surface, and indicated that only a small, shallow region of the slab in the vicinity of the slab-column intersection is highly stressed in tension before rupture. This means that punching shear failure occurs in a progressive manner.