This paper presents an overall evaluation of the observed behavior of fiber reinforced concrete under dynamic loading. The term dynamic loading is used to describe either high strain rate monotonic loading (impact) or cyclic loading under high stress range, high strain rates (simulating earthquake loading). Particular emphasis is placed on the evaluation of the fracture energy (or toughness) and fatigue life of this composite. The research program comprises four related parts dealing re-spectively with: 1) the effect of strain rate on the pull-out behavior of fibers in mortar, 2) the surface energy of fiber reinforced mortar prisms in tension, 3) the energy absorbed by fiber reinforced mortar beams subjected to impact loading and 4) the behavior in compression of fiber reinforced concrete cylinders under high strain rates monotonic and cyclic loadings. While Parts 2 and 3 of the program deal with steel fibers only, Parts 1 and 4 involve also glass, polypropylene and polyester fibers.

Plain and mesh reinforced shotcrete have been used for many years for ground support in tunnels, mines, excavations and rock slopes. Since the early 1970's steel fiber shotcrete has enjoyed increasing use in such applications. The question has often been asked how steel fiber reinforced shotcrete performs under loading in such applications compared to plain and mesh reinforced shotcrete. There is a dearth of published literature on this subject and this study seeks to help fill this void. In this study, 1.52 m x 1.52 m x 64 mm (5 ft. x 5 ft. x 21/2 in.) shotcrete panels were fabricated using plain shotcrete, plain shotcrete reinforced with 2 in. x 2 in. x 12/12 wire mesh, and shotcrete with two concentrations of steel fiber. The panels were anchored at 1.22 m (4 ft.) centers with two different conditions of restraint and loaded to destruction with continuous monitoring of the load versus deflection and fracture characteristics of the panels. Under the conditions of test, the improved residual load carrying capacity of the mesh and steel fiber reinforced shotcrete after first cracking, compared to the plain shotcrete, was well demonstrated. The steel fiber reinforced shotcrete panels also displayed improved residual load carrying capacity after first crack compared to the mesh reinforced shotcrete at deformations up to 10 mm (1/2 in.), and equivalent residual load carrying capacity at deformations up to 50 mm (2 in.). The inherent toughness and ductility characteristics of the steel fiber reinforced shotcrete were enhanced by increasing the volume concentration of steel fiber from 0.75 percent to 1.25 percent by volume.

Experiments concerning the bearing capacities of thin steel fiber-reinforced concrete (SFRC) slabs which are most important in using SFRC for over-lays on asphalt pavements are reported and installation operations and serviceabilities of actual overlays are described. According to loading tests, SFRC slabs with crushed-rock and asphalt-concrete bases possess bearing capacities of about 17 to 22 tons and it is thought actual traffic loads can be amply supported. Consequently, it is considered the use of SFRC immune to rutting and distortion would Drovide excellent resurfacing, smooth and durable, and economical as well. It is further shown that the "Yield Line Theory" can be applied to design of resurfacing using SFRC. Actual overlays were constructed on asphalt pave-ments in the northern city of Sapporo where extreme de-formation occurs due to wear in winter and plastic flow in summer. The overlays were of fiber contents of 2 percent and 1.4 percent measuring 3x130x0.05 and 3x200x 0.05 meters, respectively, and were among the first SRFC overlays in Japan. Until the fall of 1981 they had been in service 4 years and 2 years (5 and 3 win-ters), respectively, and worn down 1 to 2 centimeters, with a fair amount of cracks traversing the overlays. However, most of the cracks are connected well by steel fibers, while the wear is of a degree not to impede traffic. Overall, it may be judged that serviceability under traffic is good and that economic losses due to repairs of asphalt pavements at least every 2 to 3 years can be alleviated to a considerable extent.

The main purpose of this project was to explore the feasibility of using newly developed polypropylene (PP) fibers as reinforcement for portland cement concrete and to compare their reinforcing effectiveness with asbestos, glass and steel fibers. The PP fibers used were made of a high tensile strength (up to 80 ksi), high modulus (up to lo6 psi), high stretch ratio (up to 12 to 1) polypropylene ribbon yarn supplied by AMOCO Synthetic Fabrics. The fibers were cut from a continuous strand obtained by properly twisting two PP ribbon yarns together. Twisting led to a substantial increase in the bonding properties of the fibers (mechanical bond) and their rigidity considered important during mixing. Different fabrication procedures and mortar mixes are described. Salient results of an extensive series of tests on flexural beams and pull-out tests to improve bonding properties are reported. Because steel, glass, asbestos and polypropylene have substantially different specific gravities, performance com-parison is made not only on the basis of volume fraction of fibers but also weight fraction and related costs. It stresses the potential merits of using PP or equivalent organic fibers in concrete matrices and suggests exciting research directions to pursue.

Six two span continuous type beam-column specimens of span 1.75 m (5 ft.06.9 in.) each were tested to failure. The specimens had beam section of 150 x 250 m m (6 x 10 in.) and column section of 150 x 150 mm (6 x 6 in.). The beam section had 2 bars each of 12 mm (l/2 in.) diameter. two test specimens (Type A) were of reinforced concrete, having steel stirrups as shear reinforcement. In other two specimens (Type B) steel fiber reinforced concrete (SFRC), having steel fibers of size 25 x 0.25 mm (1.0 x 0.01 in.), 2% by weight of concrete was used throughout the specimens. In the remaining two specimens (Type C) SFRC was provided in the connection region only. An axial compressive load of 18000 kgf (40 kips) was applied to the column section by post tensioning high strength steel. Vertical load was applied to each of the beams at a distance of 1.175 m (46.26 in.) fran each end. Test results showed an increase of 19% and 9.9% in shear and moment capacities respectively of SFRC connections over that of RCC connections. SFRC connections failed in ductile mode of failure. SFRC was found to be very effective in the connection region in specimens tested for low cycle fatigue.