Mohammad Taghi Kazemi’s research while affiliated with Sharif University of Technology and other places

Earthquakes are natural phenomena that damage structures and buildings and their equipment. Preventing the transfer of earthquake vibration to the buildings is important to protect the residents and reduce the damage. Base isolation with lead rubber isolator is one of the desirable methods to prevent the transfer of seismic to buildings. Many parameters are involved in the design of these isolators and some of them are unknown at the beginning of the design. Therefore, iterative methods are required to design these isolators. This research described two procedures for isolator design, First, usual design procedure based on AASHTO and ASCE7 codes and second, design based on the performance point that completely presented in this paper. Non-linear time history analysis was done for building analysis. Results show that the performance point method (PPM) is more accurate than the previous usual method. Also, base shear force and relative displacement of a fixed base and the isolated building were calculated and compared.

In the past three decades, several experiments were conducted to investigate the seismic behavior of composite plate shear walls (C-PSW) because of their advantages to conventional reinforced concrete (RC) and steel plate shear walls (SPSW). Numerical studies, however, are limited due to the complexities for the finite element modeling of the steel and concrete material behaviors and their composite action. Herein, the cyclic behavior of various C-PSW with and without boundary elements (BE) is investigated numerically. The effects of design parameters such as aspect ratio, axial load ratio, and the length of the BE on the response of C-PSW are investigated. The advanced finite element software LS-DYNA is utilized to develop the cyclic model of C-PSW. The LS-DYNA model is validated using the available experimental data in the literature. Numerical analyses indicate that the‌‌ BE has a significant impact on the stiffness, strength, and energy absorption of C-PSW especially in high aspect ratio walls. A simplified method is proposed to estimate the peak shear strength of C-PSW with BE using the results of the numerical and experimental study.

To date, many researchers have developed various types of macro models to simulate the general response of conventional steel plate and reinforced concrete shear walls. Although extensive numerical and experimental studies have been conducted to assess the seismic response of steel-plate concrete composite shear walls, a robust macro-model for simulation of the cyclic response of such systems has not been developed yet. Herein, a fiber-based model is proposed to simulate the nonlinear seismic response of SC walls using PERFORM-3D program. The details of the proposed model, including material properties, element type, and boundary condition, are presented. The proposed model is validated using the available test data of seventeen SC wall specimens with and without boundary elements. Based on the analysis results, this novel approach can capture the global response of SC shear walls including initial stiffness, peak shear strength and its corresponding displacement, stiffness and strength degradation, and pinching behavior accurately. The proposed macro model for SC shear walls can be considered as a reliable tool to extend the engineering application of SC walls in the building industry.

The vertical stiffness of elastomeric bearing is a dominant parameter of the base isolation design. Several empirical relations have been used to calculate the vertical stiffness of the elastomeric bearing systems, although, in certain conditions such as the presence of rotation, these relations are not accurate enough. In this paper, by using a nonlinear finite element program, the effect of rotation on the vertical stiffness investigated. It was observed that the vertical stiffness of the isolator could be increased or decreased depending on the amount of rotation and the value of lateral displacement limit.

Structural response to near field earthquake has been taken into consideration by researchers in recent years. This response, considering specific characteristic of near field earthquake including forward directivity, high-frequency content and fling step, could be completely different and mostly more destructive compared to far field earthquake. Although the near field effect is significant on global behavior of structures, the same approach is employed to scale both near filed and far field earthquake records in old codes and near field and far field earthquakes alike, were scaled and applied to structure by same method. To have a more accurate assessment of structures, quite different criteria for scaling near field earthquake is addressed in recent codes. The purpose of this paper is to investigate and compare different criteria for scaling near field earthquake records and also determine effects of this difference on damage in RC moment frame buildings. To achieve this goal, two 3 and 8 story reinforced concrete moment frame buildings with moderate and high ductility were modeled numerically. It was found that, employing appropriate scaling method from new code, components of structures suffered from sixteen percent more of damage, on average, compared to using former scaling method. Some components of structures passed moderate damage limits and reached heavy damage range, using new scaling method instead of old methods. This considerable difference shows the necessity of considering methods to check and in case of need rehabilitation of structures which were designed and built based on old criteria.

Observations from past earthquakes in reinforced concrete buildings show that the masonry partitions can endanger the life of buildings occupants and lead to significant damage and loss. The most present codes of practice do not consider the effects of nonlinearity and higher modes of the structure and three-dimensional behavior of partitions on the out-of-plane seismic demands of these components simultaneously and the main purpose of this study is to investigate the effect of these cases together. This research involves assessing the seismic performance of partitions made of the hollow brick located in different stories of 3-, 7- and 11-story buildings containing 3D reinforced concrete special moment frames and subjected to a suite of 7 appropriate earthquakes. A finite element program, OpenSees, has been used for nonlinear seismic response history analysis. The average of the peak of responses of partition, under the seismic excitations, was computed for any model and the forces obtained using the analytical method, which some of them verified with existing studies results, were compared with the values from the code. For the majority of the models, the results show that the analytical seismic demands on partitions, in the lower half, are higher than those calculated using the code provisions because of the effect of higher modes of the structures and the peak values is even up to 1.54 times the computed value based on the code. The code provisions are conservative for the partitions in the upper half of the buildings.

In this manuscript, an advanced damage-plasticity model is utilized to simulate response of concrete structures under high-velocity impact. Due to presence of large deformations, it is necessary to incorporate the damage-plasticity model into the finite deformation framework. In high-velocity impact, severe numerical problems could be encountered while updating stress values due to the sudden increase in their levels, especially for the complicated material model used in this study. To overcome these obstacles, an enhancement is made in the nonlinear system of equations of stress- updating procedure. In addition, an adaptive multi-step numerical algorithm is introduced which improves the performance and stability of stress updating. Some computed results of the damage-plasticity model used in this study was compared with existing experimental tests and good agreement was observed. Furthermore, to prove the strength and efficiency of the proposed stress-updating framework, several numerical examples of high-velocity impact to composite steel-concrete structures are provided. It is shown that by using the proposed framework, complicated impact problems could be simulated in a robust and stable fashion.

Considering the interaction of flexural moment and shear force in the steel frames with haunch or intermediate beam length and eccentrically braced frames with intermediate link length is a major concern of the structural analysis and design. This article contains two stages. In the first stage, to investigate the moment–shear interaction for the highly ductile steel I-sections, a study is carried out using finite element analysis and a simple and practical relationship is developed. In the second stage, a simple approach based on virtual work method for assemblage of interconnected rigid bodies is employed to consider collapse mechanisms with mixed hinges. Using this approach, the applicability of the proposed relationship is demonstrated for a one-bay portal frame by considering all possible collapse mechanisms including those containing mixed hinges. Some numerical examples are presented using the proposed approach. Results indicate that, in general, the effect of moment–shear interaction on the load capacity of the structures cannot be ignored, and the capacity could be estimated, without using step-by-step analysis. Finally, by satisfying kinematic compatibility requirements and normality condition, simplified relations are derived to estimate post-mechanism deformations of plastic hinges for a prescribed lateral drift.

An effective method utilizing the differential evolution algorithm (DEA) as an optimisation solver is suggested here to detect the location and extent of single and multiple damages in structural systems using time domain response method. Changes in acceleration response of structure are considered as a criterion for damage occurrence. The acceleration of structures is obtained using Newmark method. Damage is simulated by reducing the elasticity modulus of structural members. Three illustrative examples are numerically investigated, considering also measurement noise effect. All the numerical results indicate the high accuracy of the proposed method for determining the location and severity of damage.