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Showing 5 results for Abbasnia

R. Abbasnia, M. Kanzadi, M. Shekarchi Zadeh, J. Ahmadi,
Volume 7, Issue 2 (June 2009)

Drying shrinkage in concrete, which is caused by drying and the associated decrease in moisture content, is one of the most important parameters which affects the performance of concrete structures. Therefore, it is necessary to develop experimental and mathematical models that describe the mechanisms of drying shrinkage and damage build up in concrete. The main objective of this research is the development of a computational model and an experimental method for evaluation of concrete free shrinkage strain based on the internal moisture changes. For this purpose and for modeling of moisture losses in concrete members a computational program based on finite element approach and the modified version of Fick's second law in which the process of diffusion and convection due to water movement are taken into account, is developed. Also the modified SDB moisture meter was used to measure the internal moisture changes in concrete. Based on the obtained results, calculated humidity is in good agreement with measured data when modified Fick's second law with diffusion coefficient from Bazant method were used, and are very reasonable for determining the moisture gradient. Also, the predicted value of shrinkage strain from the proposed method is in good agreement with measured data and also the established relationship can be used for determine the distribution of shrinkage strains in concrete members.
Reza Abbasnia, Neda Mirzadeh, Kamyar Kildashti,
Volume 9, Issue 3 (September 2011)

In recent years, different damage indexes have been introduced in engineering literature. The most prominent one among other

counterparts is the 1985 Park and Ang's damage index (DIPA), which demonstrates well calibration against experimental

results. Hence, it has traditionally had broad application in the field of structural engineering. Commonly, in DIPA relevant

parameters are assessed based on plastic-hinge approach, which is not well suited to consider the coupled response between

stress resultants (axial force and flexural moment) especially in grossly nonlinear domain. The reason is that named approach

is utilized constant shape plastic moment-curvature curve, which is not capable of varying the shape throughout loading history.

Another drawback of plastic-hinge method is the difficulty of representing precisely partial yielding of the cross-section. To

remedy the situation, the fiber discretization technique is used in this paper. Based on the fiber discretization strategy, not only

have the stiffness and strength degradation been characterized more accurately, but also the distribution of plasticity along the

plastic zone has been considered. Besides, the multi-directional effect of axial force and flexural moment is considered to assess

DI parameters. Additionally, this strategy directly incorporates the effect of transverse confinement into cross sectional

constitutive behaviour.

R. Abbasnia, A. Holakoo,
Volume 10, Issue 3 (September 2012)

One important application of fiber reinforced polymer (FRP) is to confine concrete as FRP jackets in seismic retrofit process

of reinforced concrete structures. Confinement can improve concrete properties such as compressive strength and ultimate axial

strain. For the safe and economic design of FRP jackets, the stress-strain behavior of FRP-confined concrete under monotonic

and cyclic compression needs to be properly understood and modeled. According to literature review, it has been realized that

although there are many studies on the monotonic compressive loading of FRP-confined concrete, only a few studies have been

conducted on the cyclic compressive loading. Therefore, this study is aimed at investigating the behavior of FRP-confined

concrete under cyclic compressive loading. A total of 18 cylindrical specimens of FRP-confined concretewere tested in uniaxial

compressive loading with different wrap thickness, and loading patterns. The results obtained from the tests are presented and

examined based on analysis of test results predictive equations for plastic strain and stress deterioration were derived. The

results are also compared with those from two current models,comparison revealed the lack of sufficient accuracy of the current

models to predict stress-strain behavior and accordingly some provisions should be incorporated.

R. Abbasnia, A. Farsaei,
Volume 11, Issue 3 (Transaction A: Civil Engineering, September 2013)

Corrosion of reinforcing steel and other embedded metals is the main cause of severe deterioration in reinforced concrete structures which subsequently imposes adverse effects on ultimate and serviceability limit state performance of the whole structure. In this paper, a new corrosion detection method for reinforced concrete beams, based on wavelet analysis is presented. To evaluate the capability and efficiency of the method, a simply supported RC beam was modeled in 3-D taking into account the behaviors of concrete, steel and bond degradation. Deflection profile and mode shapes were extracted numerically and analyzed by wavelet transform. From the findings of the modeling, it can be concluded that this wavelet-based method is capable of detecting corrosion at its earliest stage. It is also concluded that both discrete and continuous wavelet transforms can be used and mother wavelet type has no significant effect on the results.
R. Abbasnia, M. Aslami,
Volume 13, Issue 3 (Transaction A: Civil Engineering, September 2015)

A new model is proposed for two-dimensional simulation of the concrete fracture in compression. The model generated by using the Voronoi diagram method and with considering random shape and distribution of full graded aggregates at the mesoscopic level. The aggregates modeled by combining irregular polygons, which then is placed into the concrete with no intersection between them. By this new modeling approach, the simulation of high-strength concretes with possible aggregates fracture is also feasible. After generation of the geometrical model, a coupled explicit discrete element method and a modified rigid body spring model have been used for solution. In this method, all the neighboring elements are connected by springs. The mortar springs have Elasto-plastic behavior and considering normal concrete, the aggregate springs behave only elastically without any fracture. The proposed model can accurately predict the mechanical behavior of concrete under compression for small and large deformations both descriptively and quantitatively

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