Papers by Amir Akhaveissy
Finite Elements in Analysis and Design, 2012
A nonlinear finite element method with eight-noded isoparametric quadrilateral elements for concr... more A nonlinear finite element method with eight-noded isoparametric quadrilateral elements for concrete and two-noded elements for reinforcement was used to predict the behavior of reinforced concrete frame structures. The disturbed state concept (DSC) and the hierarchical single surface (HISS) plasticity model with the associated modified flow rule were used to characterize the constitutive behavior of concrete in both compression and tension. The DSC model allows for the characterization of nonassociative behavior through the use of disturbance, and it computes microcracking during deformation, which eventually leads to fracture and failure. In the DSC model, the critical disturbance, D c , identifies fracture and failure. Elastic perfectly plastic behavior is assumed in models of steel reinforcement. The DSC model was validated at two levels: (1) specimen and (2) practical boundary value problem. At the specimen level, predictions are obtained by integrating the incremental constitutive relations. The finite element procedure and the DSC model are used to obtain predictions for practical boundary value problems. Based on comparisons between DSC predictions and test data, the model is capable of providing highly satisfactory predictions.
Bulletin of Earthquake Engineering, 2022
The experiences of past earthquakes show that the moment-resisting reinforced concrete structures... more The experiences of past earthquakes show that the moment-resisting reinforced concrete structures suffered damage due to the inherent brittle behaviors of concrete and lack of structural stiffness. The configuration of buckling restrained brace (BRB) in RC frame is widely increased for the development of the reinforced concrete buckling‐restrained braced (RC-BRB) dual system since the implementation of BRBs can significantly improve the dissipative capacity and lateral stiffness of the main reinforced concrete frames. On the other hand, the structural damage amount is strongly related to the induced displacements and deformations during an earthquake. Therefore, the robust design method must take into account the displacement as the main designing parameter to control the damage of the structures. To this end, researchers have proposed the direct displacement-based design (DDBD) method, which employs displacement as a main designing criterion throughout the design process. In this study, a DDBD method for dual RC-BRB frames is developed by considering the ultimate capacity of BRB elements. New yield displacement and stiffness expressions are proposed to determine the characteristics of the equivalent single-degree-of-freedom (SDOF) system. The developed method is evaluated by designing twelve RC-BRB frames corresponding to different storey numbers and two types of BRB configurations. The Numerical model is developed and validated using available experimental data to be used in the nonlinear time-history analysis (NTHA). In order to gauge the performance of the developed DDBD method, the seismic behavior of designed frames subjected to 20 real ground motions is investigated through NTHA procedure. In addition, the expressions for the design displacement profile of the RC-BRB frames are provided as a function of relative height using the average maximum displacements calculated from NTHA outputs. The developed design displacement profile leads to significant improvements in the coefficient of determination, R2, which is increased from 0.69 for low-rise to 0.98 for high-rise frames. The results indicate that the RC-BRB frames designed by the developed DDBD method can successfully achieve the desired performance objectives. Furthermore, the comparison between the estimated results and the corresponding ones obtained from NTHA indicates that the proposed displacement profile expressions can be found to be efficient and effective for estimating the displacements of the RC-BRB dual frames.
Construction and Building Materials, 2022
The current research seeks to investigate a novel method for reducing computational costs of conc... more The current research seeks to investigate a novel method for reducing computational costs of concrete modeling in the meso scale. Two separate scales, macro and meso, were used to evaluate concrete behavior. As the stress distribution at the macro scale can be a good indicator to determine the crack critical zones (onset and growth of crack), the numerical model is analyzed at the macro scale using the extended finite element method (XFEM), and then, critical zones are specified in each step using macro-optimization. Afterwards, the sum of the zones is modeled in the main model at the meso scale. At the meso scale, the three parts of aggregate are modeled with linear behavior, and cement mortar and transfer zone with nonlinear behavior. Aggregates are distributed in cement mortar by a random algorithm and Fuller curve in a circular shape. For meso-scale discretization, piecemeal discretization method was used considering the adhesive zone for all elements. Using this method, crack o...
Journal of Rehabilitation in Civil Engineering, 2020
The current article seeks to investigate the behavior of masonry wall reinforced with timber lumb... more The current article seeks to investigate the behavior of masonry wall reinforced with timber lumbers and effect of timbers on increasing the shear strength and ductility of wall. To determine the mechanical properties of the timbers, two experiments according to ASTM D143 were performed. All of the mechanical properties required for timber simulation were determined via tensile and compressive tests, and using parametric equations. The behavior of the timbers under tensile force was brittle, and under pressure was semi-ductile. Hill yield criterion was utilized for timber behavior modelling. Predictably, the location of the plastic strain formation in the tensile and compressive specimen was consistent with the location of the fracture in the experimental specimens. In the next parts of the research, the obtained parameters were used to model the mechanical behavior of the timbers. Macro and meso approaches were used for the numerical modeling of the masonry wall. The Willam–Warnke ...
Structures, 2021
Abstract While the direct displacement-based design (DDBD) method is commonly developed in seismi... more Abstract While the direct displacement-based design (DDBD) method is commonly developed in seismic design of the single frame and is extensively discussed in the technical literature devoted to this subject, the proper evaluation of this method for dual frames system has received relatively little attention. Considering excellent hysteretic behavior, buckling-restrained braces (BRBs) have been increasingly configured in reinforced concrete (RC) frame to develop the reinforced concrete buckling‐restrained braced (RC-BRB) dual system. The RC-BRB dual frame system is a new lateral-load resisting dual system aimed to minimize the time and costs of repairs after an earthquake. The one of main parameters of the DDBD method is equivalent viscous damping (EVD) proposed to represent the energy dissipation of the system due to its inelastic behavior assumption. Since in the literature no damping equation has been given for the RC-BRB dual frame, the present study aims to provide a reliable EVD equation for the RC-BRB dual system, as well as in the values of the equation verified against real earthquakes, by conducting the nonlinear time-history analysis (NTHA). To this end, first, the numerical model was proposed and validated using the results of the available cyclic test in the literature. Then, the EVD equation of the RC-BRB frames was acquired based on a new method which calibrates the obtained EVDs through nonlinear time-history dynamic analysis of the structures under real earthquake records. The comparison between the calculated results and the corresponding ones acquired from previous equations illustrates that the proposed EVD equation is appropriate for estimating the energy dissipation of the RC-BRB dual frames. Furthermore, the results show that the EVD equations presented so far can conservatively estimate the damping level for the RC-BRB dual frame structures.
Advances in Civil Engineering Materials, 2020
Fracture and crack propagation in various materials have always attracted the attention of resear... more Fracture and crack propagation in various materials have always attracted the attention of researchers. Therefore, an investigation of the fracture of construction steel as one of the most extensively used materials in the industry is of necessity. Numerical modeling has been always a complementary aid to the laboratory sample analysis. One important issue is to study the behavior of laboratory specimens based on their dimensions, which finds further significance in fracture problems. In the current research, the effect of sample thickness on the crack behavior is investigated via a compact tension specimen. Accordingly, using numerical result validation, the behavior of the numerical samples along the thickness is examined and used as a complement to the experimental results. By modeling and analyzing numerical samples with different thicknesses (0.1 < B/W < 2), an equation is proposed. The equation can be used to determine in what percentage of the thickness from the free edge the behavior is either plane stress or plane strain.
Latin American Journal of Solids and Structures, 2012
Periodica Polytechnica Civil Engineering, 2018
Strong earthquakes always occur in countries with seismic risk and can potentially cause multiple... more Strong earthquakes always occur in countries with seismic risk and can potentially cause multiple deaths. This study investigates the seismic vulnerability of RC beam-column connections. Generally, it is impractical to simultaneously set up the molds of the concrete beam, ceiling and column and achieve a uniform concrete and this can cause numerous constructional deficiencies. Usually, these deficiencies can be instrumental in the failure of RC frames. Therefore, this study investigates the performance of a defective RC beam-column connection and provides a method to improve the behavior of the connection. The defective connection studied herein belongs to a high school in the city of Kermanshah, Iran. Many factors that affect the performance of the retrofitting designs are studied. Also, all of the parameters used in the analyses were obtained based upon the actual behavior of the material through core extraction and tensile tests. Finally, an optimal design is proposed.
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Papers by Amir Akhaveissy