Abstract:The effect of the loading-rate on the dynamic response of reinforced concrete members under impact loading is investigated numerically through the use of three-dimensional dynamic nonlinear finite element analysis. The package employed is capable of realistically accounting for the triaxiality and the brittle nature characterising concrete material behaviour as well as the characteristics of the problem at hand, a wave propagation problem within a highly nonlinear medium. Due to the availability of tests data,… Show more
“…Under static load, on the contrary, no top cracks appeared. These observations are consistent with the understandings that (1) under impact loads, the failure mode of beam changed from pure flexural damage mode under static loading to combined flexural and shear damage mode owing to inertial resistance of the beam which changed the shear span of the beam, (2) impact load induced negative bending moment owing to inertial resistance, which caused negative flexural damage on the top of the beam (Madjlessi and Cotsovos, 2016; Pham et al, 2018; Pham and Hao, 2017b; Saatci and Vecchio, 2009). Figure 12.Typical cracking pattern of SFRC structural beam under impact loading.…”
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.
“…Under static load, on the contrary, no top cracks appeared. These observations are consistent with the understandings that (1) under impact loads, the failure mode of beam changed from pure flexural damage mode under static loading to combined flexural and shear damage mode owing to inertial resistance of the beam which changed the shear span of the beam, (2) impact load induced negative bending moment owing to inertial resistance, which caused negative flexural damage on the top of the beam (Madjlessi and Cotsovos, 2016; Pham et al, 2018; Pham and Hao, 2017b; Saatci and Vecchio, 2009). Figure 12.Typical cracking pattern of SFRC structural beam under impact loading.…”
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.
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