International Concrete Abstracts Portal

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.

In the fib Model Code 2010, fibre-reinforced concrete (FRC) is finally recognized as a cement composite material for construction: this step favours significant structural applications based on new concept requirements. In the Model Code, a strong effort has been devoted to introducing a material classification in order to standardize a performance-based production and stimulate an open market for every kind of fibre, favouring the rising of a new technological actor: the composite producer. From standard classification, the simple constitutive models introduced allow designers to identify effective design constitutive laws, trying to take into account the fibres contribution in term of performance and suitably orienting its structural use. An FRC application concerning tunnelling is discussed here, focusing on the design requirements and structural advantages offered by fibres addition and on further research needs. In this application a useful combination of strain softening and strain hardening materials allowed by the unified Model Code approach can offer designers interesting opportunities and new structural challenges.

The structural use of steel-fibre reinforcement has been used as a method of reinforcement of both ground suspended slabs supported by a grid of piles and elevated slabs. About 15 million square metres (circa 165 million sq. ft) of these ground suspended slabs, and about 100 buildings including these suspended elevated slabs, have been successfully completed so far, so that the latter is still considered by the ACI to be an emerging technology. Typical applications are warehouses, plants, offices, and condominium buildings, as well as towers and sport arenas. The span-to-depth ratio is in general higher than 10 and smaller than 30. The paper summarizes the practical suitable design method used in the real cases of one elevated suspended slab reinforced with steel fibres and structural integrity rebars in Spain and another one being a ground suspended slab reinforced only with steel fibres in the USA.