Abstract:Designing protective reinforced concrete (RC) beams against impact loadings is a challenging task. It requires a comprehensive understanding of the structural response of RC beams subjected to impact loads. Significant research efforts have been spent to unveil the impact response of RC beams by using analytical models, experimental testing, or numerical investigations. However, these studies used various assumptions in the analytical derivations and different test setups in the impact testing, which led to si… Show more
“…During impact loading, it is therefore possible to initiate global shear failure (static flexural shear failure) and local shear failure (shear plug) for statically flexure-critical RC beams. The same conclusions are reported in the review of the impact response of RC beams, presented in [5]. The local shear failure was explained as an effect of only part of the beam resisting the impact force by its inertia in the early stages of the response, where the stress wave propagation has a significant influence.…”
Impact loads in previous research showed to induce brittle responses of statically flexure-critical reinforced concrete (RC) beams designed for ductility. The impact load may produce flexural shear damage modes similar to that observed during quasi-static loads and local shear damage under the impact zone. The occurrence of shear damage modes during impact tests has been investigated extensively, but their effect on the residual quasi-static and dynamic capacity is not fully understood. For this aim, an initial high-velocity impact test initiated severe shear damage to RC beams. The beams were then tested quasi-statically and by sequential impact testing using the same setup as the initial tests. The results indicate a flexure-dominated response during sequential impact tests for beams containing extreme shear reinforcement amounts, favouring the energy-absorption capacity. Significant shear and flexural damage occurred for beams with less shear reinforcement, indicating a hybrid response that varied throughout the tests. The tests for the residual quasi-static capacity indicated severe consequences from initial local shear damage on the capacity, as shown by the brittle response of the beam with the most shear reinforcement. However, wide initial flexural cracks instead showed a favourable effect, as there was an indication of transfer from brittle to ductile failure. For beams showing both global and local shear damage, it was concluded that global shear damage modes were critical for the residual static and dynamic shear capacity.
“…During impact loading, it is therefore possible to initiate global shear failure (static flexural shear failure) and local shear failure (shear plug) for statically flexure-critical RC beams. The same conclusions are reported in the review of the impact response of RC beams, presented in [5]. The local shear failure was explained as an effect of only part of the beam resisting the impact force by its inertia in the early stages of the response, where the stress wave propagation has a significant influence.…”
Impact loads in previous research showed to induce brittle responses of statically flexure-critical reinforced concrete (RC) beams designed for ductility. The impact load may produce flexural shear damage modes similar to that observed during quasi-static loads and local shear damage under the impact zone. The occurrence of shear damage modes during impact tests has been investigated extensively, but their effect on the residual quasi-static and dynamic capacity is not fully understood. For this aim, an initial high-velocity impact test initiated severe shear damage to RC beams. The beams were then tested quasi-statically and by sequential impact testing using the same setup as the initial tests. The results indicate a flexure-dominated response during sequential impact tests for beams containing extreme shear reinforcement amounts, favouring the energy-absorption capacity. Significant shear and flexural damage occurred for beams with less shear reinforcement, indicating a hybrid response that varied throughout the tests. The tests for the residual quasi-static capacity indicated severe consequences from initial local shear damage on the capacity, as shown by the brittle response of the beam with the most shear reinforcement. However, wide initial flexural cracks instead showed a favourable effect, as there was an indication of transfer from brittle to ductile failure. For beams showing both global and local shear damage, it was concluded that global shear damage modes were critical for the residual static and dynamic shear capacity.
“…This observation is in accordance with the findings observed by other researchers (Cotsovos, 2010; Pham and Hao, 2017a; Zhao et al, 2017). Some suggested that the negative reaction force was caused by the stress wave propagation (Cotsovos, 2010; Pham and Hao, 2017a; Pham et al, 2021; Saatci and Vecchio, 2009). However, the up-to-date investigation has proven that the negative reaction force is more likely to be induced by the high modal responses (Hao et al, 2021), which is determined by the natural frequencies (geometric and physical parameters) and the impact energy.Figure 14.Illustration of time histories of impact and reaction forces.…”
Discrete short steel fibres were proposed to be mixed with concrete for arresting cracks and enhancing the post-cracking resistance. It has been proven in previous tests that spiral steel fibres possessed markedly higher bonding to concrete matrix, leading to significantly improved performance of steel fibre reinforced concrete (SFRC) in terms of crack controllability, impact resistance, deformability and energy absorption capability. However, at the initial stage of cracking, SFRC reinforced with spiral fibres has relatively lower resistance to crack opening as compared to that reinforced with other types of steel fibres because of spiral shape stretching. To overcome this shortcoming, in the present study, short hooked-end steel fibres that exhibit high pull-out resistance at the crack initiation stage were mixed with spiral steel fibres in the normal-strength concrete matrix. A total volume fraction of 1% of hybrid steel fibres was mixed to cast SFRC specimens. With various mix ratios between spiral and hooked-end fibres considered, five batches of SFRC specimens were tested. Uniaxial compressive tests and four-point bending tests were carried out to compare the mechanical properties of SFRC materials with hybrid fibres while three-point bending tests on SFRC structural beams under static, drop-weight impact and post-impact static loading tests were conducted to investigate the structural performances. An equal dosage of hooked-end and spiral fibres was found to outperform other blend proportions to provide synergetic reinforcement to concrete matrix in terms of post-cracking resistance, energy absorption capacity and post-impact performance.
“…The connection configurations had a limited effect on the peak impact force under the first impact because of the same impact energy and contact stiffness at the impact zone as summarized in Ref. [46]. However, in the subsequent impacts, the peak impact force acting on the specimens were different because the joints with different connection configurations experienced different residual deflections of beam and damage after each impact.…”
Section: Discussion Of the Impact Performance Of Different Wet Connec...mentioning
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