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.
Highlights
Concrete structures might be subjected to low to heavy impacts during their service life.Either accidental or human-induced impact events can produce severe damage or even failure of concrete structures if the impact scenario has not been addressed in the design stage
The difference between impact force and strengthened series can be observed at the high-performance fiber-reinforced concrete (HPFRC) layer: in series Reinforced concrete (RC)-U55, debonding occurred at the total reaction clear that forces developed, which can be verified bywas thesplit acceleration interface makes betweenitHPFRC
The crack patterns of the beams strengthened with a HPFRCThe layer showed the development of to two types of shear cracks
Summary
Concrete structures might be subjected to low to heavy impacts during their service life. (a) inertia forces under dynamic loading lead to a time-dependent distribution of sectional forces different from the one under quasi-static loading; (b) material properties of concrete and steel are affected by the strain rate; (c) impulsive loading and wave propagation produce local damage near the impact zone Due to the former factors, low energy-absorbing shear failures become dominant for reinforced concrete (RC) beams. Due to the significance of crack bridging and energy absorption capacity to prevent brittle failures, the design of impact-resisting structures seems an attractive field for the application of high-performance fiber-reinforced concretes.
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