Analisa Perilaku Pushover pada Pengujian Balok Beton Bertulang

Beams are part of the building structure that is important to consider when designing the structure. Some failures that occur in beams due to beam reinforcement are not installed such as planning/ design procedures, this problem can cause structural failure. Knowing the behavior of the beam structure due to the given load can help predict the strength of the structural beam and the comfort of the planned structure. To determine and predict the strength and comfort of the reinforced concrete beam structure due to the received load, experimental and simulation tests are carried out. VecTor2 simulation is used to predict shear, crack, and displacement forces in reinforced concrete beams when displacement loads are applied. The bond stress-slip effect (0.139) has a good effect on the strength and hysterical response of reinforced concrete beams. From the results of pushover testing and simulations, it is obtained that the ratio for load capacity ranges from 1.00-1.095. In addition, the installation of 135˚ hooks on stirrups shows that the crack behavior that occurs forms an angle of 45˚, this indicates that the bond between concrete and reinforcement is going well, this can be seen from the analogous behavior principle of reinforced concrete beams.

Bond parameters for peeling and debonding in thin plated RC beams subjected to mixed mode loading – Framework

Studies have primarily focussed on predicting mode-II debonding failure; whereas, in real-case-scenario, flexurally strengthened reinforced concrete (RC) beams observe premature failure mechanisms under mixed-mode loading conditions engaging geometrical and material variations. Peeling is a consequence of flexural crack as debonding is of interfacial shear crack. Under bending, peeling failure is considerably catastrophic over debonding due to the nature of crack formation; therefore, this needs to be distinguished in predictive analysis. In this paper, a new numerical modeling methodology is approached using eXtended finite element method (xFEM) for flexural cracks and Cohesive Zone Model (CZM) for shear cracks without predefining crack locations. The parameters of the constitutive models are identified through comparing finite element results with the experimental data. These parameters are related to key material properties. Based on proposed framework, the models provide a good estimation of plate strain distribution, cracks and failure type, in terms of mode and load of failure. Bilinear bond-slip curve is a closer match over exponential crack evolution at interface.

Punching Shear Strength Prediction for Reinforced Concrete Flat Slabs without Shear Reinforcement

Failure of flat slabs usually occurs by punching shear mode. Current structural codes provide an experience-based design provision for punching shear strength which is often associated with high bias and variance. This paper investigates the effect of adding a horizontal reinforcement mesh at the top of the slab-column connection zone on punching the shear strength of flat slabs. A new equation considering the effect of adding this mesh was proposed to determine the punching shear strength. The proposed equation is based on the Critical Shear Crack Theory combined with the analysis of results extracted from previous experimental and theoretical studies. Moreover, the equation of load-rotation curves for different steel ratios together with the failure criterion curves were evaluated to get the design points. The investigated parameters were the slab thicknesses and dimensions, concrete strengths, size of the supporting column, and steel ratios. The model was validated using a new set of specimens and the results were also compared with the predictions of different international design codes (ACI318, BS8110, AS3600, and Eurocode 2). Statistical analysis provides that the proposed equation can predict the punching shear strength with a level of high accuracy (Mean Square Error =2.5%, Standard Deviation =0.104, Mean=1.0) and over a wide range of reinforcement ratios and compressive strengths of concrete. Most of the predictions were conservative with an underestimation rate of 12%. Doi: 10.28991/CEJ-2022-08-01-013 Full Text: PDF

Strengthening flat slabs without shear reinforcement against punching shear by concrete overlay

Research in this paper presents a theoretical study of increasing in punching shear capacity of the strengthened flat slab by concrete overlay. The parametric study is based on comparison of three different relevant standards design models and presents results how Eurocode 2 (EN 1992-1-1), Model Code 2010 and draft of second generation of Eurocode 2 (prEN 1992-1-1) take into account strengthening by concrete overlay. A reference specimen is represented by a fragment of a flat slab supported by circular column. Influence of concrete toppings depends on thickness and also on reinforcement ratio. In Eurocode 2 and new generation of Eurocode 2 the increase of punching shear resistance of the slab with concrete topping can be taken into account only by reinforcement ratio and thickness of the slab considering the perfect connection and bond between the original slab and new layer of concrete overlay. Model Code 2010 is based on Critical shear crack theory and the reinforcement ratio in concrete topping was considered in equation of moment of resistance and punching shear resistance is calculated by considering the rotation and deformation of the slab. Estimation of results by parametric study are compared by non-linear model from Atena software.

Application of critical shear crack theory on punching of flat slabs

This article deals with the punching capacity of a flat slab fragment supported by an internal atypically elongated column. Based on the results of this analysis and the application of Critical Shear Crack Theory, the reliability of two design models was determined. The CSCT model is a mechanical model where the shear force transferred by concrete in shear crack can be determined by accounting for the roughness and opening of a critical shear crack. The crack width is proportional to the slab rotation, which was obtained from a nonlinear program Atena and from experimental test and shear capacity was obtained by integrating the shear strength along the control perimeter. The aim of this analysis was to compare the application of CSCT in non-linear analysis and experimental test to point out the significant difference between obtained results, which shows the importance of experimental tests realization. Non-linear analyses provided unsafe results. Contrary the currently used EC2 model provided safe results when reduction of the control perimeter was applied. The best results were obtained in a combination of the CSCT model with measured rotations of the slab specimen.

Optimal hole shape for arrest of longitudinal shear crack

Рассматривается задача об отыскании оптимальной формы отверстия в вершине трещины продольного сдвига. Искомая форма отверстия удовлетворяет условию минимальной концентрации напряжений на его контуре. Исследуется влияние отверстия оптимальной формы на торможение трещины. Дается критерий и метод решения задачи по предотвращению хрупкого разрушения тела, ослабленного прямолинейной трещиной продольного сдвига. Используется минимаксный критерий. Получено условие хрупкого разрушения. The problem of finding optimal hole shape at the tip of a longitudinal shear crack is considered. The desired hole shape satisfies the condition of the minimum stress concentration on the contour. The effect of the optimal hole shape on deceleration of a crack is studied. A criterion and solution method for the problem of preventing brittle fracture of the solid weakened by rectilinear longitudinal shear crack is given. The minimax criterion is used. The brittle fracture condition is obtained.

Three-dimensional fluid-driven stable frictional ruptures

We investigate the quasi-static growth of a fluid-driven frictional shear crack that propagates in mixed mode (II+III) on a planar fault interface that separates two identical half-spaces of a three-dimensional solid. The fault interface is characterized by a shear strength equal to the product of a constant friction coefficient and the local effective normal stress. Fluid is injected into the fault interface and two different injection scenarios are considered: injection at constant volume rate and injection at constant pressure. We derive analytical solutions for circular ruptures which occur in the limit of a Poisson's ratio ν=0 and solve numerically for the more general case in which the rupture shape is unknown (ν≠0). For an injection at constant volume rate, the fault slip growth is self-similar. The rupture radius (ν=0) expands as R(t)=λL(t), where L(t) is the nominal position of the fluid pressure front and λ is an amplification factor that is a known function of a unique dimensionless parameter T. The latter is defined as the ratio between the distance to failure under ambient conditions and the strength of the injection. Whenever λ>1, the rupture front outpaces the fluid pressure front. For ν≠0, the rupture shape is quasi-elliptical. The aspect ratio is upper and lower bounded by 1/(1-ν) and (3-ν)/(3-2ν), for the limiting cases of critically stressed faults (λ≫1, T≪1) and marginally pressurized faults (λ≪1, T≫1), respectively. Moreover, the evolution of the rupture area is independent of the Poisson's ratio and grows simply as Aᵣ(t)=4παλ²t, where α is the fault hydraulic diffusivity. For injection at constant pressure, the fault slip growth is not self-similar: the rupture front evolves at large times as ∝(αt)⁽¹⁻ᵀ⁾ᐟ² with T between 0 and 1. The frictional rupture moves at most diffusively (∝√(αt)) when the fault is critically stressed, but in general propagates slower than the fluid pressure front. Yet in some conditions, the rupture front outpaces the fluid pressure front. The latter will eventually catch the former if injection is sustained for a sufficient time. Our findings provide a basic understanding on how stable (aseismic) ruptures propagate in response to fluid injection in 3-D. Notably, since aseismic ruptures driven by injection at constant rate expands proportionally to the squared root of time, seismicity clouds that are commonly interpreted to be controlled by the direct effect of fluid pressure increase might be controlled by the stress transfer of a propagating aseismic rupture instead. We also demonstrate that the aseismic moment M₀ scales to the injected fluid volume V as M₀ ∝ V³ᐟ².

Study On The Effect of Bond Strength On The Failure Mode of Coarse-Grained Sandstone In Weakly Cemented Stratum

Bond strength is one of the most important parameters and can affect the macroscopic mechanical properties and the damage state of the rock to some degree. The coarse-grained sandstone with strength of less than 40 MPa was studied by the controlled variable method. The influence of parallel bond strength on the peak strength and failure mode of coarse-grained sandstone was simulated, the evolution law of peak strength and failure mode of bond strength were comprehensively analyzed. The results show that the peak strength of rock was positively correlated with the bond strength, the difference value between tensile and shear crack was negatively correlated with tensile bond strength and positively correlated with shear bond strength. Tensile-shear bond strength ratio less than 0.5, the peak strength of the rock was usually stable at the certain extreme value under a constant tensile bond strength. Tensile crack was negatively correlated with the tensile-shear bond strength ratio, shear crack was positively correlated with the tensile-shear bond strength ratio. The failure mode of coarse-grained sandstone is shear failure. The research results can be used to guide the ground control of other mine stopes or roadways with weak cementation lithology.

Research on Microscopic Evolution Laws of Sandstone Deformation and Failure Based on the Particle Discrete Element Method

The fracture of sandstone is closely related to the condition of internal microcracks and the fabric of micrograin. The macroscopic mechanical property depends on its microscopic structures. However, it is difficult to obtain the law of the microcrack growth under loading by experiments. A series of microscopic sandstone models were established with particle flow code 3D (PFC3D) and based on the triaxial experiment results on sandstones. The experimental and numerical simulations of natural and saturated sandstones under different confining pressures were implemented. We analyzed the evolution of rock deformation and the rock fracture development from a microscopic view. Results show that although the sandstones are under different confining pressures, the law of microcrack growth is the same. That is, the number of the microcracks increases slowly in the initial stage and then increases exponentially. The number of shear cracks is more than the tensile cracks, and the proportion of the shear cracks increases with the increase of confining pressure. The cracking strength of natural and saturated sandstones is 26% and 27% of the peak strength, respectively. Under low confining pressure, the total number of cracks in the saturated sample is 20% more than that of the natural sample and the strongly scattered chain is barely seen. With the increase of the confining pressure, the effect of water on the total number of cracks is reduced and the distribution of the strong chain is even more uniform. In other words, it is the confining pressure that mainly affects the distribution of the force chain, irrespective of the state of the rock, natural or saturated. The research results reveal that the control mechanism of shear crack friction under the different stress states of a rock slope in the reservoir area provides a basis for evaluating the stability of rock mass and predicting the occurrence of geological disasters.