International Concrete Abstracts Portal

In tunnels built by means of a tunnel boring machine, the use of fibre-reinforced concrete (FRC) in the precast segmental linings lead to several advantages. On one hand, FRC improves the mechanical behaviour of the segments during construction, reducing the incidence of damages. On the other hand, it contributes to a decrease of the global costs by reducing the amount of conventional passive reinforcement required. The objective of this paper is to present a real experience regarding the use of fibres as the main reinforcement in precast segmental linings in the metropolitan area of Barcelona. First, the design approach presented in the fib Model Code for Concrete Structures 2010 for fibre-reinforced concrete is adapted taking into account the mechanical requirements of the precast segments. Then, this methodology is used to assess the minimum fibre content for this application, estimated in 60 kg/m³. These results are compared with the obtained in an experimental program performed with real-scale segments simulating the critical load condition found during the most critical transient stage (stocking). The study shows an example of optimized design of FRC tunnel segments that might be useful for future tunnels.

To investigate the behaviour of precast tunnel lining segments subjected to concentrated loads on a small scale, laboratory tests on concrete prisms under partial-area loading in conjunction with numerical analyses were performed. Various parameters influencing the load-bearing and fracture behaviour of plain concrete (PC) and steel-fibre-reinforced concrete (SFRC) under concentrated loads are considered, including fibre properties (dimension, aspect ratio, tensile strength), fibre dosage and orientation, area ratio and eccentricity of load. The effects of these parameters on the ultimate bearing capacity, stress-displacement behaviour, failure mode and crack characteristics are analysed and discussed. Parallel to the experimental investigations, numerical simulations using a continuum coupled damageplasticity model for triaxially loaded cementitious material were performed. It is shown that the numerical analysis is able to realistically capture the structural behaviour and the crack pattern of partially loaded PC and SFRC specimens.

The 43.5-metre span truss footbridge over the Ovejas ravine in Alicante, made only of UHPFRC, has replaced a previous design in steel with a similar production cost, and also with improved durability and fewer maintenance costs. Thorough work was carried out in terms of material dosage, structural design and manufacturing process to minimise the total cost of the footbridge and to also make it safe, functional and pleasant. The footbridge design confers on fibres a very important role in structural behaviour. They are responsible for cracking control, ductility, confinement and, in some elements, they allow to dispense with any passive reinforcement. The most important aspects related to the structural analysis, structural design criteria, manufacturing process, cost distribution and final footbridge appearance are presented.

Steel-fibre-reinforced concrete (SFRC) has been known since the sixties and has been used for structures for the past 30 years; SFRC has therefore become a subject of intensive research and development. A Danish consortium on sustainable concrete structures was involved in several demonstration projects using steel-fibre-reinforced self-compacting concrete (SFRSCC) to prepare guidelines on design and execution of SFRC and SFRSCC structures. This paper summarizes and presents selected projects with the application of steel-fibrereinforced concrete and self-compacting concrete. The paper describes and discusses the design methodology, relevant aspects and practical experiences from the construction of bridge, tunnel and foundation projects. Special attention is paid to the cost savings, corrosion resistance and durability aspects of the SFRC application, as the demand for efficient and long-term sustainable concrete structures is rapidly growing, with the common expectation of a service life on the order of minimum 100-120 years.

Results from large-scale tests on fibre-reinforced concrete coupling beams subjected to large displacement reversals are reported. The main goal of using fibre reinforcement was to eliminate the need for diagonal bars and reduce the amount of confinement reinforcement required for adequate seismic performance. Experimental results indicate that the use of 30 mm long, 0.38 mm diameter hooked steel fibres with a 2300 MPa minimum tensile strength and in a volume fraction of 1.5% allows elimination of diagonal bars in coupling beams with span-todepth ratios greater than or equal to 2.2. Further, no special confinement reinforcement is required except at the ends of the coupling beams. The fibre-reinforced concrete coupling beam design was implemented in a high-rise building in the city of Seattle, WA, USA. A brief description of the coupling beam design used for this building, and construction process followed in the field, is provided.