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The impact strength of reinforced concrete beams without shear reinforcement is studied in this paper, with emphasis on the improvement of the impact performance achieved by using steel fiber-reinforced concrete (SFRC). Drop-weight and companion quasi-static tests have been completed on 2000 × 125 × 250 mm beams containing ordinary longitudinal steel bars. Seven SFRC mixes have been studied, including three fiber types (smooth, hooked and prismatic) and three volumetric fractions (0% i.e. plain concrete, 0.5% and 1.0%). The study has confirmed the brittle impact behavior of beams without fibers, which failed by shear. With the addition of 0.5% steel fibers, shear failures were obtained with hooked and prismatic fibers but not with smooth fibers. Finally, all beams with 1.0% steel fibers developed a flexural failure mode. The improvement of the impact behavior of beams with SFRC is also confirmed by the fact that most of the specimens which developed a flexural failure had thin diagonal cracks in the webs of the shear spans, but such cracks did not progress due to the fiber-bridging capacity. In the paper, the study is completed with an analysis of the rate sensitivity of the shear strength and the capacity for energy absorption of tested beams.

The research presented in this paper deals with the impact behavior of steel fiber-reinforced concrete (SFRC). An experimental campaign on unnotched prismatic specimens has been carried out, covering three types of steel fibers (smooth, hooked and prismatic), two volumetric contents (0.5 and 1%), and companion unreinforced plain concrete specimens. Impact tests have been performed with an instrumented drop weight testing machine recently installed at the Technical University of Madrid (UPM), Spain. According to experimental results, the peak strength and fracture energy of tested SFRC mixes are strain-rate dependent, showing dynamic increase factors (DIF) well larger than 1. On the one hand, the analysis has shown that the DIF of the peak bending strength of SFRC reinforced with smooth and prismatic fibers is higher than the DIF of the tensile strength of plain concrete and increases with the fiber content. SFRC reinforced with hooked fibers presented higher DIF with 0.5% fiber content than with 1.0%. The influence of rate-dependent size effect in the former results is discussed in the paper. On the other hand, the DIF of the fracture energy showed the highest rate sensitivity for plain concrete specimens and decreases with the addition of fibers due to the rate dependence of the mechanisms involved in the fiber-matrix interaction.

Interest in precast construction system has been growing due to the emphasis on improving work zone safety, reducing construction time and environmental impact, while maintaining quality. This experimental study aimed to develop a method to connect precast elements avoiding the use of complex reinforcing details and inefficient construction processes. For that purpose, the outstanding properties of ultra high performance fibre reinforced concretes (UHPFRC) were used to develop continuity connections between precast elements. A two-stage experimental program was defined to study the behaviour of precast elements connected using short reinforcement splice lengths. In the first experimental stage, flexural beam tests were carried out to assess the use of short reinforcement splice lengths in continuity connections. In the second experimental stage, an alternative beam–column connection for precast construction using UHPFRC was proposed and tested. The configuration proposed avoids the interference between longitudinal and transversal reinforcement, reduces the in situ work and makes it possible to define an efficient and safe construction process.