International Concrete Abstracts Portal

Using steel fibres for primary reinforcement in structural elements requires design methods based on meaningful material properties and good construction practices. In recent years, worldwide research efforts have brought the knowledge on these two aspects to a level which allows steel fibres to be considered for primary reinforcement for structural applications. Experiences in Canada have shown that using steel fibres in bridge deck design is a sound and economical solution that can solve several issues related to conventional reinforced concrete (R/C) design. This paper presents the proposed solution for bridge deck design in which SFRC is considered for primary reinforcement. It describes the concept and the main steps of the research program that supported its development. The performance of the proposed approach is shown in service and ultimate conditions. The design of a real bridge deck with reduced reinforcement illustrates the application of a proposed simplified design method. Recommendations for designing bridge elements made with SFRC are suggested.

The use of fibres as the main reinforcement for concrete pipes is recognized as an attractive alternative to steel bars, especially for smaller diameters. Nevertheless, the use of fibre reinforcement has not been consolidated yet. The lack of more reliable procedures for systematic quality control of the steel-fibre-reinforced concrete pipes is one of the reasons for that condition. In addition, there are no reliable technical data to support durability evaluation. A numerical simulation of the pipe crushing test can be used, with the goal of reducing this lack of knowledge. This paper presents a new solution based on a numerical simulation of steel-fibre-reinforced concrete pipes using constitutive equations derived from Barcelona tests. An experimental campaign was carried out to confirm the suitability of both the model and the constitutive equation to simulate the pipe response subjected to crushing test. This is an important tool to support evaluations of the ultimate limit state and serviceability limit state of fibre-reinforced concrete (FRC) precast elements. This is of particular relevance when the new concepts of the fib Model Code for Concrete Structures 2010 are taken into account.

This paper reports the full-scale production and testing, for the first time in Canada, of precast concrete pipes fabricated with dispersed steel fibres as the only reinforcement. Two types of steel fibres having rounded cross-sections and hooked ends were used. Steel fibres had lengths and aspect ratios of 35 mm and 65, and 60 mm and 80, respectively. The steel fibres content ranged from zero to 60 kg/m³. Steel fibre reinforced concrete (SFRC) pipes with internal diameters of 300, 450, and 600 mm were cast and tested under the continuous threeedge-bearing test (TEBT) according to ASTM C497 standard and the cyclic TEBT according to the European standard EN 1916. Plain concrete (PC) and conventionally reinforced concrete (RC) pipes were also tested for comparison. Vertical deformations of the pipes cross-section were monitored using displacement transducers. Results showed that SFRC pipes achieved ultimate loads substantially higher than the required strength for class V pipes according to the ASTM C76 standard. Moreover, the post peak behaviour of SFRC pipes was similar to or higher than that of RC pipes, depending on the fibre content. These findings confirm the ability of steel fibres to replace regular steel rebar reinforcement, leading to desired economic benefits.

Nonlinear finite element simulation has big potential in the field of fibre reinforced (FRC) structures. Special material models accounting for the high toughness and ductility are available for modelling of FRC material. Input material parameters for the numerical models are of crucial importance here. They are identified from the measured responses of four-point bending beams using inverse analysis. The optimal material input data sets are utilized for nonlinear modelling of segmental tunnel lining. The utilization of steel-fibre-reinforced concrete (SFRC) for segmental tunnel lining promises potential advantages in comparison to the traditionally reinforced concrete (RC) structures: faster manufacturing, lower risk of corrosion, less damage during transport. Results from the experimental and numerical investigations for RC and SFRC segments are presented. The response of the structural members under service loads and their damage under limit loads are evaluated in order to check and confirm the suitability of the SFRC segments for practical utilization.

In the last few years, several research projects were realized at the University of Rome “Tor Vergata” on precast tunnel lining made with fibre-reinforced concrete without any other traditional reinforcement. The proposed technique exhibited several advantages with respect to the traditional reinforced concrete solution related not only to minor construction costs, but also (and more importantly) to high performance of the structure. The use of fibre reinforcement increases the impact strength of the segments, enhances the durability properties and reduces crack openings. Furthermore, it is possible to increase the quality of the production process in the precast plant and reduce the labour cost. The first experience was made in Panama with two hydraulic tunnels having a “small” diameter: “Monte Lirio Tunnel” and “Pando Tunnel” with an internal diameter of 3.2 m. A wide research effort on the definition of optimal fibre-reinforced concrete was developed during the design phase, with a series of full-scale tests. Eventually, the technology was applied on a hydraulic tunnel with a greater diameter: “El Alto Tunnel” with an internal diameter of 5.8 m. All these tunnels were designed according to the prescriptions of the fib Model Code for Concrete Structures 2010. This paper discusses some aspects related to the use of fibre-reinforced concrete in tunnels with different diameters and thicknesses.