Steel, polyolefin and carbon fiber reinforced concretes were combined with traditional transverse steel reinforcement in the form of steel spirals. The complete stress-strain relationship and the ductility of the concrete in compression in both the unconfined and confined states was evaluated. The compressive toughness was evaluated both according to the Japanese Standard JSCE-SF5 and according to a new method proposed in the present work. The experimental program consisted of testing concrete cylinders under compression at two different strength levels: Normal (48 Mpa) and high strength (70 Mpa), polyolefin and carbon fibers. These tests were then repeated with different volume percentages Vf (1.5, 2.0 and 3.0) of steel, polyolefin and carbon fibers. These tests were then repeated with different pitches (25 and 50 mm). It was found that by combining fibers and steel spirals it is possible: (1) to obtain a high level of fracture energy dissipation, which could previously be obtained only by using a high volume percentage of spiral steel: and (2) to improve the maximum strain of the concrete, corresponding to the first failure of the spiral steel.

It is known that Steel Fiber Reinforced Concrete (SFRC) has advantages over plain concrete. In particular, fiber reinforcement makes concrete tougher and more ductile. Although these attributes are appealing for earthquake resisting structures, design codes do not yet incorporate specifications relative to the use of SFRC for structural applications. Recent developments have indicated a good potential for SFRC in structural and seismic applications. In the first part of this paper, the beneficial effects of SFRC in the seismic design of columns are briefly reviewed. The paper then presents an overview of an ongoing research project on compression. The variables considered were the fiber content of 0%, .5% and 1.0% per volume, the amount of transverse reinforcement for confining the column core, and the confinement provided by the fibers in the cover. It is shown that SFRC improves significantly the post-peak behavior of columns for all hoop spacing and the same seismic design philosophy. Although SFRC in the cover delay its spalling confine concrete, but rather change the failure mode by limiting the progression of cracks and enhancing the aggregate interlock along failure planes.

This Symposium Publication presents 13 papers on the use of fiber reinforcement in structural applications and assembles the thoughts of some leading researchers in the field. Collectively, these writings are a snapshot of contemporary thinking in this field and provide a direction for future activity. Note: The individual papers are also available as .pdf downloads.. Please click on the following link to view the papers available, or call 248.848.3800 to order. SP182

An experimental investigation was conducted to assess the potential of steel fibers as secondary reinforcement in prestressed hollow core slabs. Following a brief laboratory study and a feasibility trial, a series of fibre reinforced extruded slabs were made at the premises of a local manufacturer and subsequently tested in shear: one of a number of potential modes of failures. The Predictive equations of other researchers were shown to accurately estimate the shear strength in the case of plain hollow core slabs, but to overestimate the shear enhancement due to adding steel fibers. Additionally, the effect of the manufacturing process, in which the concrete is compacted by rotating augers, on the fiber distribution and orientation was investigated. Whilst fibers were found to be randomly distributed within the cross-section, a tendency to align vertically within the webs was observed. This has particular relevance to the vertical shear performance.

Considerable progress has recently been achieved in strength and ductility of concretes. The use of superplasticizers and large amounts of silica fume led to densified cementitious matrices and improved adherence to the fiber reinforcement. These two properties are obtained with Compact Reinforced Composite (CRC) developed at Aalborg Portland and closely studied during a 3-year EC. The investigations reported in this paper cover the application of ultrahigh strength-fiber reinforced concrete to enhance performance of beams, columns and beam to column connections. Mechanical tests were performed on full scale structural elements. Beams of 13 m in length, columns of 2.9 m in compression with and without eccentricity of the load, and beam to column connections were tested. In all cases, concrete strengths of more than 150 Mpa were achieved. Due to CRC's high compacity and its extreme resistance to the penetration of aggressive elements, the CRC cover to the reinforcement was typically reduced from 30 mm to at least 12 mm. It has been shown that a reduction in concrete cover to the reinforcement is compatible with the requirements of structural applications. The tests carried out have shown the possibility of using ultra-high strength concrete for large-scale structural concrete elements and opens new fields of applications. This contributes to saving raw materials, weight and volume and to improving ductility and durability.