The dynamic compression deformation of an in‐house cast concrete (average aggregate size of 2–2.5 mm) was modelled using the finite element (FE), element‐free Galerkin (EFG) and smooth particle Galerkin (SPG) methods to determine their capabilities of capturing the dynamic deformation. The numerical results were validated with those of the experimental split Hopkinson pressure bar tests. Both EFG and FE methods overestimated the failure stress and strain values, while the SPG method underestimated the peak stress. SPG showed similar load capacity profile with the experiment. At initial stages of the loading, all methods present similar behaviour. Nonetheless, as the loading continues, the SPG method predicts closer agreement of deformation profile and force histories. The increase in strength at high strain rate was due to both the rate sensitivity and lateral inertia caused by the confinement effect. The inertia effect of the material especially is effective at lower strain values and the strain rate sensitivity of the concrete becomes significant at higher strain values.
Ib value analysis was applied to investigate effect of the steel fiber on Ib value. Damage in steel fiber reinforced concrete beam was evaluated by AE parameter analysis. Ib value distribution is affected after post-peak because of higher amplitude values due to steel fiber activities. There are numerous nondestructive testing methods that are used to determine damages within structures. Acoustic Emission (AE), being one of these methods makes it possible to obtain significant pieces of information such as origin time, location and type of damage formed in a material during loading by analyzing AE data using various algorithms. Ib value analysis is one of these algorithms which is based on AE signal and this analysis enables to have information on formation of new cracks or propagation of existing cracks by scaling the magnitude of AE activities. In this study, in order to investigate effect of the steel fiber in concrete matrix on Ib value, two reinforced concrete beams were tested under simple bending while one of them was the reference. Afterwards, AE parameters obtained were analyzed, Ib value analyses were applied to amplitude values and these parameters were associated to each other. Furthermore, effect of steel fiber existence on behavior of the beam and distribution of Ib value were examined. Figure A. Ib value vs time distributions of the test specimens Purpose: In this study, it was aimed to evaluate AE activities of plain and steel fiber reinforced concrete beams by Ib value analysis and to reveal effects of steel fiber presence on Ib value distribution. Theory and Methods: Ib value analysis is a technique to evaluate Acoustic Emission (AE) data for scaling failure mechanisms. While higher Ib values indicate more activities having lower amplitude (micro activities), lower Ib values show less activities having higher amplitude (macro activities). Results: Figure A indicates the lowest Ib values in Test Specimen-1 at 41 st and 114 th sec when the beam reached up to 56% and 82% of its ultimate capacity. Likewise, the lowest Ib values in Test Specimen-2 were observed at 69 th and 112 nd sec when the beam reached up to 59% and 75% of its ultimate capacity. These states point out that Ib value gives a warning before macro failures. Decrease of Ib values reveals cracking of concrete matrix in pre-peak region. However, presence of steel fiber affects the Ib value distribution at post-peak region due to higher ductility. Conclusion: Increase in AE energy and amplitude causes lower Ib values because of macro damages. Thus, Ib value can be used as a damage parameter for AE analysis. While higher Ib values indicate micro activities, lower Ib values show macro activities. Presence of steel fiber increases ductility of reinforced concrete beam; thus Ib value distribution is affected after post-peak because of higher amplitude values due to steel fiber activities in this region.
Eight slabs with two different longitudinal reinforcement ratios and varying steel fiber ratios were tested Steel fibers increased the ultimate load capacity for all slabs Contribution of steel fibers to the displacement capacity was more significant for slabs with higher longitudinal reinforcement ratio Addition of steel fibers in concrete mixture is known to increase the punching resistance of slabs. There are numerous studies, both analytical and experimental, in the literature investigating the effects of steel fibers on the punching behavior of steel fiber reinforced concrete slabs. Figure A. Load-displacement curves for slabs Purpose: This study is concentrates on the effects of steel fibers on the punching behavior of reinforced concrete slabs with different longitudinal reinforcement ratios. Experimental studies on the subject were usually performed with either no or constant longitudinal reinforcement. This study aims to investigate the coupling effects of steel fibers with varying longitudinal reinforcement ratios. Theory and Methods: Reinforced concrete slabs in two groups, having 0.004 (D1 series) and 0.002 (D2 series) longitudinal reinforcement ratios in two orthogonal directions, were cast with concrete mixes containing 0%, 0.5%, 1% and 1.5% steel fiber ratios in volume. Slabs were 2150x2150x150 mm in dimensions. Eight slabs were tested in total under static loads applied at their midpoints. An analytical study of the test specimens were also performed using Critical Shear Crack Theory and based on comparisons of experimental and analytical results some improvements in the model were proposed. Results: For slabs without steel fibers, the slab with higher reinforcement ratio showed punching failure before the yielding of longitudinal bars, whereas the slab with lower reinforcement ratio displayed a significantly higher ductility before final punching failure. Addition of steel fibers increased the punching load capacity up to two times. However, although addition of steel fibers also increased the maximum displacements in D1 series slabs, it did not make any significant effect on the maximum displacements of D2 series slabs. Maximum displacements were still controlled by the yielding of longitudinal reinforcement. Increasing the steel fiber ratio increased both the punching capacity and the maximum displacements in D1 series slabs, but it did not make a significant difference in behavior of D2 series beyond 1% fiber ratio (Figure A). Conclusion: Role of steel fibers on the behavior of slabs is dependent on the longitudinal reinforcement ratio. For slabs with low reinforcement ratio, steel fibers increase the load capacity but do not have a significant effect on the displacement capacity since displacement capacity is still controlled by the yielding of the longitudinal reinforcements. For slabs with high reinforcement ratio, which do not show yielding before punching, steel fibers increase both punching capacity and displacement capacity. Increased punching capacity in these slabs allows yielding...
The lack of a complete understanding of shear behavior under high dynamic conditions hindered the efforts for accurate prediction of impact behavior, since severe shear mechanisms may dominate the behavior of RC structures when subjected to impact loads. This current study involves a well-instrumented experimental program that was undertaken to contribute to our understanding of the effects of shear mechanisms on the behavior of reinforced concrete (RC) structures under impact loads. The test results showed that the shear characteristics of the RC beam specimens played an important role in their overall behavior. All specimens, regardless of their shear capacity, developed severe diagonal shear cracks, forming a shear-plug under the impact point. Furthermore, the application of the Disturbed Stress Field Model (DSFM) as an advanced method of modeling shear behavior under impact conditions is also investigated. A two-dimensional nonlinear finite element reinforced concrete analysis program (VecTor2), developed previously for static loads, was modified to include the consideration of dynamic loads such as impacts. VecTor2 analyses of the test specimens were satisfactory in predicting damage levels, and maximum and residual displacements. The methodology employed by VecTor2, based on the DSFM, proved to be successful in predicting the shear-dominant behavior of the specimens under impact.
Çelik fiber katkılı betonarme elemanların kullanımı son yıllarda artmakla birlikte bu elemanların yapısal davranışlarının modellenmesinde mevcut analitik yöntemler yetersiz kalmakta ve doğrusal olmayan sonlu elemanlar yöntemi gibi sayısal yöntemlere ihtiyaç duyulmaktadır. Bu çalışmada üç noktalı statik yükleme altında Anahtar kelimeler: Doğrusal olmayan sonlu eleman analizi, Çelik fiber katkılı beton, Eğilme davranışı
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