CDP Model Research Articles

Investigations on web-shear behavior of deep precast, prestressed concrete hollow core slabs

Shear tests were conducted on four precast, prestressed concrete hollow core (PCHC) slabs with depths ranging from 320 mm to 500 mm, resulting in two distinct modes of failure, i.e., web-shear and flexural-shear. Shear strength results of the specimens obtained from the experimental program were compared to those predicted by EN 1168 and ACI 318-14. The comparisons showed that in some instances, these codes overpredict shear capacity of the tested specimens. Furthermore, an finite element (FE) model aimed to simulate web-shear responses of PCHC slabs was developed using Abaqus/Explicit (2014). Concrete Damage Plasticity model (CDP model) was employed to model nonlinear behavior of concrete. The sensitivity of the numerical analyses was calibrated against four plastic parameters in the CDP model. The calibrations showed that web-shear behavior of PCHC slabs is not sensitive to three out of the four plastic parameters. However, the last parameter, dilation angle, significantly affects the predicted failure loads. The validity of the developed FE model was verified by 2 shear tests in the experimental program and another 8 shear tests from the literature. Parametric studies based on the verified model were then performed. The influence of design variables including concrete strength, slab geometry, and level of prestressing force, on web-shear behavior of PCHC slabs was examined. The parametric studies showed that concrete strength plays a dominant role in the web-shear performance. However, the choice of angular or smoother-surface void shapes does not lead to a noticeable difference in web-shear capacity. Besides, web-shear strength increases with web thickness. Most importantly, a high level of prestressing force increases additional shear stresses in concrete webs due to changes in strand stress within the transmission length region. In addition, it leads to higher compressive forces in concrete diagonal struts. The presence of such a higher compression force reduces the resistance in tension of concrete webs in the direction of maximum principal tensile stress. As a result, the web-shear strength of PCHC slabs decreases with increasing prestressing force.

Numerical study of the effect of concrete cover and the friction of steel concrete interface

The work presented in this paper resume a numerical analysis of the concrete cover effect, on the resistance of the steel-concrete interface. The effect of friction on the interface behavior is also included. For this, a brief description of the experimental steps generally used for the characterization of the steel-concrete interface is presented. Also, the CDP model, Concrete Damage Plasticity, is illustrated. The results of the numerical simulation using the Abaqus code are presented with different diameters of coatings with and without friction.

Experimental Test and Numerical Simulation of the Initial Crack Reinforced Concrete Beam in Bending

Based on the concrete constitutive relations provided by the concrete structure design specifications, a three-point bending beam numerical analysis was performed by introducing a damage plastic damage model and using ABAQUS to add a concrete parameter plug-in. The three-point bending test of the beam was carried out by the fatigue test machine, and the results of theoretical calculation and numerical simulation were compared to verify the correctness and reliability of the plastic model of concrete damage (CDP model). At the same time, the shortcomings of the theoretical calculation were pointed out, which can be used as a reference for the later engineering calculation and the research of concrete.

A micro-electromechanical systems based vibration energy harvester with aluminum nitride piezoelectric thin film deposited by pulsed direct-current magnetron sputtering

Piezoelectric vibration-based energy harvesting is a promising alternative for the durable and reliable power supplies for the low-powered wireless sensor networks nodes. However, improving the piezoelectric vibration-based energy harvester’s energy conversion efficiency related closely on the structure parameters and materials become significant and urgent. In this paper, a micro-electromechanical systems (MEMS) cantilever-based aluminum nitride (AlN) vibration energy harvester is presented, modeled, optimized and fabricated. The c-axis oriented AlN piezo thin film is deposited by the pulsed direct-current magnetron sputtering with the optimized process parameters. Furthermore, the coupled distributed parameter model is derived in detailed, verified by using the ANSYS finite element analysis, and applied to the optimization of structural parameters and load resistance. Finally, the prototype of the device is fabricated by the standard bulk-silicon technology. As a result, at 1g and 210.85 Hz, the maximum output root mean square (RMS) voltage can reach to 4.66 V, the output average power and output average power density of the prototype is up to 56.4 μW and 854.55 μW/(cm3·g2) at a load resistance of 146.6 kΩ, respectively. The experimental results agree well with theoretical analysis. The derived CDP model has an important and effective guiding role in cantilever based piezoelectric vibration energy harvester for structural design and performance optimization, especially for the device with long tip mass. The prototype has wide application prospects in the fields of the wireless sensor network node such as the structural health monitoring system.

EFFECT OF STRESS PATH, SIZE AND SHAPE ON THE OPTIMUM PARAMETERS OF A BRITTLE-DUCTILE CONCRETE MODEL

The main purpose of this study is to investigate the effects of the stress path, size and shape of the specimen, on the optimum values of the plastic input parameters of Concrete Damaged Plasticity-CDP- model of the ABAQUS software. This study concentrates on eccentricity, dilatation angle and viscosity input parameters. To finding optimum values of the mentioned parameters, an objective function which estimates the error of the model predictions was defined and tried to minimize. For evaluating the effect of the stress path on this optimization procedure, four different standard tests were simulated by the ABAQUS software: uniaxial compression, dual compression, dual-border cut specimen and three-point bending tests. For studying the effect of the size of the specimen, the three-point bending test, with three different sizes of the beam were modeled in the ABAQUS software. Furthermore, for investigating the effect of the specimen shape on the input parameters, a notched disk in a tensile stress field was modeled. Obtained results demonstrated that the path of the stress can influence significantly on the optimum values of the input parameters, while it was revealed that the CDP model can automatically take into account the size and shape effects in the simulation.

Modification of Concrete Damaged Plasticity model. Part II: Formulation and numerical tests

A refined model for elastoplastic damaged material is formulated based on the plastic potential introduced in Part I [1]. Considered model is an extension of Concrete Damaged Plasticity material implemented in Abaqus [2]. In the paper the stiffness tensor for elastoplastic damaged behaviour is derived. In order to validate the model, computations for the uniaxial tests are performed. Response of the model for various cases of parameter’s choice is shown and compared to the response of the CDP model.

Best Combinations of Software Practices from CDP Model by using Crystal Ball Tool to Achieve Quality Goals of an Organization

Best Combinations of Software Practices from CDP Model by using Crystal Ball Tool to Achieve Quality Goals of an Organization

칼슘 용출 열화에 의해 표면이 손상된 콘크리트 부재의 구조적 거동에 관한 해석적 연구

다양한 열화 인자에 의해 저감된 콘크리트의 내구성은 구조물의 구조적 성능과 사용 수명에 부정적인 영향을 미치게 되며 콘크리트 연구 분야 중에서도 매우 중요하고 매력적인 주제라고 할 수 있다. 이러한 이유로 콘크리트의 내구성과 관련된 많은 연구들이 발표되었으나 물리-화학적 열화에 기인하는 콘크리트의 본질적인 물성 변화에 주된 초점이 맞춰져 왔으며, 콘크리트 내구성과 구조물의 구조적 성능 사이의 관계 정립은 아직 미흡한 실정이다. 본 연구에서는 콘크리트의 강도 감소에 원인이 되는 칼슘 용출 열화를 적용하였으며, 열화 정도에 따른 구조적 거동을 평가하기 위하여 열화 손상을 입은 콘크리트 부재의 압축 및 휨 거동 실험을 수행하고 그 결과를 비선형 유한요소해석 결과와 비교 분석하였다. 연구 결과에 따르면 칼슘 용출 열화는 콘크리트의 압축 강도를 저하시키며, 열화가 진행됨에 따라 취성 거동에서 연성 거동으로 변화되는 경향을 나타냈다. 또한 열화에 의한 압축 영역의 손상 정도가 심화될수록 RC 부재의 내하력과 강성은 저하되었으며, 이러한 구조적 거동은 ABAQUS의 CDP 모델을 사용한 비선형 유한요소해석의 결과와도 비교적 잘 일치하였다. Durability is one of the most important and attractive subjects in concrete research field because not only durability of concrete is reduced by various degradation factors but also its reduction adversely influences the structural performance and service life of concrete structure. For this reason, a considerable amount of papers associated with concrete durability have been published and those researches were mainly focused on the changes of intrinsic properties of concrete due to chemicophysical degradations. However, the relationship between durability of concrete and structural behavior of concrete member has not been well established yet. In this study, calcium leaching degradation, a cause of concrete strength reduction, was dealt with. The experiments of compressive and flexural behavior of degraded concrete member were performed to evaluate the characteristics of structural behavior according to degradation level. Finally, the results from the experiments were compared with those obtained from nonlinear FEM analysis. The results from this study clearly showed that leaching degradation leads to decrease in compressive strength and compressive behavior evolves from brittle to ductile failure pattern during the degradation process. Load capacity and flexible rigidity of the degraded RC member decreased when the degradation level increased, in compressive zone. Additionally, it was found that the values from nonlinear FEM analysis, CDP model in ABAQUS, coincided well with the experimental results.

The ‘trainer in your pocket’: mobile phones within a teacher continuing professional development program in Bangladesh

Examples of mobile phones being used with teachers to provide continuing professional development (CPD) in emerging economies at scale are largely absent from the research literature. We outline English in Action’s (EIA) model for providing 80,000 teachers with CPD to improve their communicative language teaching in Bangladesh over nine years. EIA’s CPD program is delivered face to face and supported through open distance learning (ODL). This innovative model of teacher CPD is supported through peer learning and self-study using a variety of print, audio and video resources. Drawing on the success of EIA’s pilot studies, where internal and external evaluation reported significant improvement in teachers’ and students’ English-language competence after one year, the current phase is using low-cost mobile phones, or the ‘trainer in your pocket’ to deliver CPD to 12,500 teachers through 2015. We believe EIA’s teacher CDP model is best suited to assist the project in achieving one of its primary goals: to increase the English-language proficiency of 12 million students, allowing them to access greater social and economic opportunities in the future. We argue EIA’s use of mobile phones for the provision of teacher CPD – at scale – is timely and replicable in both developed and developing contexts.

Modelling of copper precipitation in iron during thermal aging and irradiation

The cluster dynamics model for precipitation (CD-P model) described in [J. Nucl. Mater. 245 (1997) 224] has been improved and applied to copper precipitation in Fe–Cu and Fe–Cu–Ni during thermal aging at different temperatures. The CD-P model was tested on atom probe measurements [Mater. Sci. Eng. A 250 (1998) 49] and small angle neutron scattering (SANS) measurements [J. Nucl. Mater. 245 (1997) 224; Springer Proc. Phys. 10 (1986) 73]. Copper diffusivity was found to be a little higher than that proposed by Salje and Feller-Kniepmeier [J. Appl. Phys. 48 (1977) 1833]. The binding energy proposed in [J. Nucl. Mater. 277 (2000) 113] was also tested and it was concluded that little change occurs compared to the classical capillary model. Assuming a constant vacancy concentration (in other words a constant Cu diffusivity), the CD-P model was then applied to electron and neutron irradiation at 290 °C. In a second step, the CD-P model and the cluster dynamics model for vacancy and interstitial clustering (CD-VIC model) described in [J. Nucl. Mater. 302 (2002) 143] were mixed so as to really describe precipitation under irradiation by taking into account the evolution of vacancy concentration with time. The result is that the agreement between modelling and experimental data is better, specially in the case of neutron irradiation.