H.R. Naseri's scientific contributions

In the design process of a moment resisting frame (MRF), the principle of weak–beam and strong–column should been considered because of the occurrence of plastic hinge in the beams. This mechanism is caused because the frame is capable of dissipating significant energy and remaining stable in the inelastic region. Stability is defined as the ability of the frame to maintain its elastic level of resistance throughout the entire inelastic range of response. Using this principle, plastic hinges can be developed in the beams adjacent to the connections and usually very close to the column face. This mechanism allows the cracks to be caused by the plastic hinging. The cracks can also propagate into the connection core region, and initiate a brittle failure mechanism. Furthermore, the mechanism has not been established in many existing MRFs - designed based on the previous codes. Hence, the methods have been proposed and developed in order to relocate the plastic hinges away from the column face. Fiber Reinforced Polymer (FRP) has been used as a strengthening solution of beam–column connections and successfully reported for retrofitting existing structures. In fact, the web–bonded FRP retrofitting system can control the mechanism of plastic hinge and provide the strong–column weak–beam concept. Due to many advantages, such as high strength, low weight, endurance and convenience, Carbon Fiber–Reinforced Polimers (CFRPs) have been used in strengthening concrete structures. However, the strength and stiffness of CFRP are severely reduced at elevated temperatures, which will affect the strengthening effect seriously. In this study, six schemes are proposed for strengthening concrete beam–column connections using CFRP and the seismic performance of strengthened connections is investigated. In order to achieve this purpose, seven downscaled RC exterior joint of a typical ordinary MRF are chosen, and modeling this strengthened connection is implemented in a general finite element program, ABAQUS software. In the finite element model of strengthened concrete beam–column connection, the concrete is modeled using the damaged plastic model. The sheets of CFRP are also considered as the elastic and orthotropic model. These schemes of strengthened concrete beam–column connections are tested under moderately monotonic/cyclic loads. In order to verify the finite element model of the connection, the analysis results of this model is compared with the experimental investigation on the external beam–column connection repaired using CFRP. The results demonstrate the verification of the finite element model. Selection of the best scheme of strengthened concrete beam–column connection using CFRP is based on the improvement of the seismic performance of connection such as the load–carrying capacity, the energy absorption, the initial stiffness and changing failure mechanism of connection. The nonlinear results show that the proper layout of CFRP sheets can increase the load–carrying capacity, the energy absorption and the initial stiffness of connections. Furthermore, the proposed schemes of strengthened concrete beam–column connection cause the failure to relocate from the column face and locate in beam. Therefore, the best proposed scheme of strengthened concrete beam–column connection using CFRP can be recommended and utilized in the practical projects of concrete structures.

The paper deals with the reliability–based design optimization (RBDO) of concrete gravity dams subjected to earthquake load using subset simulation. The optimization problem is formulated such that the optimal shape of concrete gravity dam described by a number of variables is found by minimizing the total cost of concrete gravity dam for the given target reliability. In order to achieve this purpose, a framework is presented whereby subset simulation is integrated with a hybrid optimization method to solve the RBDO approach of concrete gravity dam. Subset simulation with Markov Chain Monte Carlo (MCMC) sampling is utilized to estimate accurately the failure probability of dams with a minimum number of samples. In this study, the concrete gravity dam is treated as a two–dimensional structure involving the material nonlinearity effects and dam–reservoir–foundation interaction. An efficient metamodel in conjunction with subset simulation–MCMC is provided to reduce the computational cost of dynamic analysis of dam–reservoir–foundation system. The results demonstrate that the RBDO approach is more appropriate than the deterministic optimum approach for the optimal shape design of concrete gravity dams.

This study focuses on the shape optimization of concrete gravity dams considering dam–water–foundation interaction and nonlinear effects subject to earthquake. The concrete gravity dam is considered as a two–dimensional structure involving the geometry and material nonlinearity effects. For the description of the nonlinear behavior of concrete material under earthquake loads, the Drucker–Prager model based on the associated flow rule is adopted in this study. The optimum design of concrete gravity dams is achieved by the hybrid of an improved gravitational search algorithm (IGSA) and the orthogonal crossover (OC), called IGSA–OC. In order to reduce the computational cost of optimization process, the support vector machine approach is employed to approximate the dam response instead of directly evaluating it by a time–consuming finite element analysis. To demonstrate the nonlinear behavior of concrete material in the optimum design of concrete gravity dams, the shape optimization of a real dam is presented and compared with that of dam considering linear effect.