Impact Resisting Mechanisms of Shear-Critical Reinforced Concrete Beams Strengthened with High-Performance FRC

Abstract

Reinforced concrete (RC) structures typically present brittle failures by shear or punching under impact loading. High-performance fiber-reinforced concrete (HPFRC) has great potential due to its superior strength and energy absorption. The higher price and environmental cost of HPFRC compared to conventional RC can be effectively overcome by partially strengthening impact-sensitive RC members with HPFRC. To study the feasibility of this technique, HPFRC was applied as a tensile layer at the bottom of RC beams. Drop weight impact tests were carried out on beams with two values (35 and 55 mm) of HPFRC thickness, in addition to companion RC beams. Results show that the impact response can be divided into two stages: a first stage governed by local effects and shear plug formation at midspan, and a second stage governed by global beam behavior with formation of shear web cracks. A new resisting mechanism was observed for beams strengthened with HPFRC, as the strengthening layer worked similarly to a stress ribbon retaining the damaged RC and reducing fragmentation-induced debris. Such mechanism was fully achieved by the specimens with 35 mm HPFRC layer but was limited for the specimens with 55 mm HPFRC layer due to impact-induced interface debonding.

Effect of Strengthening Methods on Two-Way Slab under Low-Velocity Impact Loading

“…This was calculated from the section where the maximum deflection occurred in the load-deflection curve to the point where it fell vertically. In this study, the energy dissipation capacity of a reinforced concrete slab was calculated based on the first blow because the deflection is excessively large at the final blow, resulting in a reliability problem in obtaining the overall energy dissipation capacity [33]. At the first blow, the energy dissipation capacities for all reinforced concrete slabs were approximately 1.79 kJ, 3.70 kJ, 3.64 kJ, 2.3 kJ, and 2.88 kJ, respectively ( Figure 6).…”

“…High-performance-fiber-reinforced-cement composites (HPFRCCs) exhibit high strength and are being studied and widely applied [33][34][35][36][37]. Among these HPFRCCs, no-slump high-strength and high-ductility concrete (NSHSDC) offers excellent adhesion with conventional concrete owing to its high viscosity, excellent load resistance, and ductility [35,36].…”

Composite Behavior of RC-HPFRC Tension Members under Service Loads

“… Possible schemes for strengthening a reinforced concrete cross-section with high-performance fiber-reinforced concrete (HPFRC) layers, abstracted from [ 4 , 5 , 6 , 7 , 8 , 9 ]. …”

“…In the last years, the use of high-performance fiber-reinforced concrete (HPFRC) as strengthening material for existing concrete structures has increased significantly [ 1 , 2 , 3 ]. The most common strengthening technique has been based on the application of thin HPFRC layers on the old concrete surface, either longitudinally [ 4 , 5 , 6 , 7 ] or transversely [ 8 , 9 , 10 ], to improve the tension/bending or shear capacity of structural members, respectively ( Figure 1 ). In order to ensure that the superior properties of HPFRC in tension and compression contribute to the global capacity of strengthened members, an adequate bond between the HPFRC and the old concrete is required, which can be achieved by surface treatments on the old concrete layer before the application of the fresh HPFRC or by adhesive bonding of precast HPFRC strips on the old concrete [ 11 , 12 , 13 ].…”

“…The present paper represents a step forward in the authors’ research towards a better understanding of the composite behavior of RC-HPFRC members. Previous research [ 6 , 25 ] has focused on the behavior of beam elements under bending or combined shear-bending forces. In Ref.…”