---

---

Understanding the impact of masonry infill walls on the behavior of moment frames is of paramount importance in the field of structural engineering. A thorough investigation is essential to gain insights into the complex interplay between various parameters and their effects on the flexural frames surrounding masonry infills. Unfortunately, the current state of knowledge is hindered by the absence of comprehensive exploration, partly attributed to constraints in existing numerical models and the prohibitively high costs associated with experimental studies. There is an urgent need to delineate the influence of diverse parameters on the dynamic interaction between frames and masonry infill walls. This understanding is critical for optimizing the accuracy of structural and component designs, ultimately leading to a reduction in project costs and an enhancement of resident safety. Although numerical models have been employed in the past, these models have limitations, and experimental studies, on the other hand, are costly, creating a need for a fast, accurate, and comprehensive method to evaluate masonry infill walls under in-plane loading. To address these limitations, there is a pressing demand for a swift, precise, and comprehensive evaluation method specifically tailored to assess the performance of masonry infill walls under in-plane loading conditions. Such a method would not only overcome the drawbacks of existing numerical models but also provide a cost-effective alternative to traditional experimental studies, allowing for a more expansive exploration of the multifaceted interactions between moment frames and masonry infills. The development of such a methodology holds the key to advancing our understanding of structural dynamics and ensuring the resilience and safety of built environments. The current research aims to develop a model that explores the nonlinear behavior of masonry infill walls and their interaction with the surrounding frame. The proposed model utilizes truss elements and material homogenization, allowing for modeling and analysis in commercially available software. The idea of this method is to simplify the typically 2D problem of masonry infilled frames under in-plane loading and reducing the infill and the surrounding frame to assemblages of braces and axial members, which is called piers, both exhibiting a mono-dimensional non-linear behavior with softening. Despite its simplicity and minimal input requirements, this method delivers comprehensive results on the structure's state in the nonlinear stage, including load-displacement curves and failure mechanisms. The method's ability to determine responses of masonry infill walls with ease and high accuracy is an innovative aspect of this research. Moreover, the proposed method can be readily implemented in widely used commercial software, displaying remarkable robustness in handling non-linear behavior and demonstrating swift convergence, even when significant global softening occurs. In the proposed method, the masonry infill is modeled as a regular set of vertical and inclined bracing members. Vertical members are referred to as "piers" and inclined members are known as "braces". The outcomes of this research have the potential to enhance the engineering community's understanding of masonry infill walls and their interaction with structural frames, shedding light on influencing factors. Furthermore, these results may contribute to the future development of regulations and standards for masonry structures, offering improved insights into the behavior of masonry intermediate frames.
 

---

Horizontally curved bridges have been observed to suffer severe structural damage during past earthquakes so determining the seismic performance of curved bridges is crucial due to the complex dynamic behavior of these structures because of their irregular geometry and non uniform mass and stiffness distributions. Analyzing and plotting the capacity curve of these structures can be costly and time-consuming. As a result, many efforts have been made to simplify the structural models of these bridges and reduce the computational workload required for their analysis. This article presents a straightforward method to convert the multi-degree-of-freedom system of these structures into an equivalent single-degree-of-freedom system, ensuring that the capacity curve of the equivalent structure closely matches that of the original structure with minimal error. In this study, the OpenSees program was used to extract the stiffness and mass matrices of a curved bridge structure. These matrices were then condensed into one-by-one matrices for mass and stiffness using dynamic condensation equations. The characteristics of these matrices were applied to a single-degree-of-freedom stick model. In this model, the obtained mass is placed at the top of a stiff rod (stick), which is connected to the ground by a spring (zero-length element) with the equivalent stiffness obtained. A nonlinear static pushover analysis of the bridge structure was performed to obtain the capacity curve. An equivalent bilinear curve was then drawn, and the yield shear force and yield displacement were determined. The nonlinear behavior of the single-degree-of-freedom structure was modeled using the Steel02 material available in the OpenSees library by zero length element utilizing the yield shear force and yield displacement magnitudes of the curved bridge. The capacity curve of the stick model, which has a single degree of freedom, showed an error percentage of 7% compared to the bridge's capacity curve. This indicates acceptable compliance with the capacity curve of the main structure, making the stick model a viable alternative for repeated analysis of the curved bridge structure. This study also included a sensitivity analysis to investigate the effects of increasing the curvature radius and decreasing the curvature angle of the bridge on its capacity and effective mass. Due to the dynamic condensation of the curved bridge structure, the influence of all degrees of freedom was considered in the stiffness and mass matrices, unlike methods that rely solely on the first vibration mode for dynamic condensation. Comparing the capacity curve of each structure with that of an equivalent single-degree-of-freedom system revealed that the structure's capacity increases with a larger curvature radius. In contrast, the lowest capacity was observed in the straight bridge scenario. Additionally, modal analysis of the studied models showed that increasing the bridge's curvature radius leads to a longer structural period, while a decreasing curvature angle has a similar effect. However, the period of the straight bridge was longer than all the other models. Furthermore, as the curvature radius increased, the mass contribution percentage of the first mode in the translational x-direction decreased, whereas the translational mass contribution percentage in the y-direction and the rotational mass contribution around the z-axis increased.

---

The graphical technique for nonlinear circuits was described that enable us to optimize circuits to obtain maximum output power, maximum efficiency or minimum intermodulation. According to this method a high power amplifier in the Ka band was designed. Using a nonlinear model of the transistor, optimum slope for load-line was determined so that maximum power at the output was obtainable, then the output matching circuit was synthesized. Finally, the nonlinear network of the high power amplifier was analyzed by the harmonic balance method and the output load cycles were optimized by modification of the bias point or output matching network.

---

Research Subject:

Polymer melts show complex response under the act of deformation. This response has direct relation to their molecular structure. The purpose of this study was to investigate the rheological behavior of branched polymers and the effect of branching on linear and nonlinear viscoelastic flow for usage in various industrial applications.

 
Research Approach:

For this purpose, the  tests such as frequency sweep and extensional for two polyethylene (LDPE) with long branches have been used. From these tests we obtained storage and loss moduli, complex viscosity and extensional viscosity. Molecular models in nonlinear  regions can also be used in this regard. 

Main Results:

Linear  tests can partly show the presence of branch in LDPE, while nonlinear  tests show strain hardening behavior for branched sample. One of the  models for branched polymers is the Multimode Pom-Pom (MPP) model which can be used to predict the strain hardening phenomenon in extensional flows. In this study, the average number of lateral branches was also calculated using this model.

---

---

---

Thyristor-Controlled Series Compensator (TCSC) is one of the electric power lines series compensators. TCSC increases transmission system capacity and improves system dynamic and voltage stability. Several controllers have been proposed, but most of them generally improve one of TCSC capabilities. In this paper a TCSC robust controller is designed based on Nonlinear Quantitative Feedback Theory (QFT). This controller improves both of small signal and transient stability of power system.

---

In this paper, optimum location of power system stabilizers in order to damp inter-area oscillations has been investigated by using modal series method. Nonlinear effects grow in dynamical behaviors of heavily loaded stressed power systems significantly. Hence linear based methods and techniques no longer present clear and exact response of the systems. In this article by defining new nonlinear participation factors and a nonlinear interaction index in modal series frame, location of PSS is determined and its effectiveness has been analyzed. For two various operating conditions, low and high stress cases proper site of the controller is determined by using both the conventional methods such as mode shapes, participation factors and residues in one side and the proposed nonlinear participation factors in modal series frame in other side. The obtained results are compared with each other and with nonlinear time domain simulations. Studies carried out on IEEE 50-generator test case system and selected machines to locate PSS by modal series method are validated by time domain simulations. Also nonlinear interaction index shows increasing of nonlinear interaction between fundamental modes of the system when PSS placement has been selected properly and its design has been done well. This shows a high influence of PSS on damping inter-area oscillations and improving system oscillatory stability. Nonlinear time domain simulation shows that improper selection of PSS location may result in poor performance of system and deterioration of oscillatory response of the system.

---

In restructured power systems and in a wholesale power market, a distribution company as a market player intends to maximize its profit by utilizing its options. Hence determining an optimal energy acquisition strategy for a distribution company is vital, for attaining to this goal. However an important challenge for determining these strategies is forecasting other competitors and Generation companies' strategies and competitors' incomplete information must be considered as uncertainties in the problem. In this paper, an energy acquisition model for a distribution company with considering distributed generations, interruptible loads and information's uncertainties in a day-ahead electricity market has been presented. In the proposed method, distribution company energy acquisition strategy has been modeled as a two-level multi-objective optimization problem and has been solved by using nonlinear complementarities and L-P metric methods and then, the uncertainties in the competitors' information, has been applied to the model by using Monte Carlo method. An 8-bus system is employed to illustrate the proposed model and algorithm.

---

Abstract Low height beams in concrete moment frames, decrease the ability of beams in controlling lateral displacement of buildings. Because of that, in the sixth subject from Iranian Regulations of Buildings and its following, in the 3rd edition of Standard 2800, the height of buildings with low height beams has been limited to 3 floors or 10 meters. According to that, in this study, concrete buildings with different amount of stories and moment frames, with medium ductility and the height of beams in 30 centimeters, have been analyzed (with linear equivalent static and spectral dynamic analysis Methods)and designed on the basis of seismic principles in the 2nd and 3rd edition of Standard 2800. Finally, studies continued with nonlinear static analysis and the performance point of structures determined (with capacity spectrum and displacement coefficient methods) in 4 levels of different seismic risks. Studies show that only one or two story buildings that designed with 2nd edition of Standard 2800 have enough safety in design base earthquake level (DBE) and also higher buildings, should go under rehabilitation.

---

This paper presents a finite element solution for the static analysis of a multi-layers beam with and without piezoelectric layers. The beam is under large deformation. The virtual work principle and the Lagrangian update method (LUM) have been employed to study the static behavior of piezoelectric beams. Four-nodes element with two displacement degrees of freedom and one electrical degree of freedom has been used in this analysis. Finally, in order to prove the validity of the presented formulation and the solving process, the results are compared with the other available data.

---

Abstract The stiffness of soils is not constant and it is highly strain dependent. Some nonlinear models such as Fahey's model for sands have been proposed for sands but these models can not be the representative of the behavior of most coarse-grained soils such as alluvial sediments of Tehran. In this paper, firstly some data of deformation modulus of several coarse-grained soils such as Tehran's soil are presented as a function of strain. Then the weakness of nonlinear models such as Fahey's model in predicting the behavior of these kind of geo-materials is presented. In next step, a new proposed model, which is in fact a type of corrected Fahey model, is explained and then a comparison is done for Tehran soil. The foundation of Milad tower is modeled using FLAC software incorporating new model and then calculated settlement is compared with measured one using micro-geodetic method.

---

Abstract Due to its simplicity, the structural engineering profession uses the nonlinear static analysis or pushover analysis. Modeling of such analysis requires the determination of the nonlinear properties of each component in the structure, quantified by strength and deformation capacities depending on the modeling assumptions. Pushover analysis is carried out for either user-defined nonlinear hinge properties or default-hinge properties, available in some programs based on the FEMA guidelines. While such documents provide the hinge properties for several ranges of detailing, the programs may implement averaged values. The user needs to be careful; becduse the misuse of default-hinge properties may lead to unreasonable displacement capacities for existing structures. This paper studies the possible differences in the results of push-over analysis due to default and user-defined nonlinear component properties. Four- and eight-story buildings were considered to represent low- and mediumrise buildings for this study. Plastic hinge length and transverse reinforcement spacing were assumed as effective parameters in the user-defined hinge properties. The observations showed that plastic hinge length and transverse reinforcement spacing have no influence on the base shear capacity, while these parameters have considerable effects on the displacement capacity of the frames. The comparisons pointed out that an increase in the amount of transverse reinforcement improves the Frames displacement capacity. Also Our findings clearly showed that the user-defined hinge model is better than the default-hinge model in reflecting the nonlinear behavior compatible with the element properties. However, although the default-hinge model is preferred due to its simplicity, the user should be aware of the circumstances provided in the program and thus should avoid the misuse of default-hinge properties.

---

Abstract In this paper, using Artificial Neural Networks (ANNs) and Finite Element Method (FEM), health monitoring of damaged cantilever beams having longitudinal cracks is discussed. The main focus is devoted to the nonlinear behavior (breathing) of crack, which, to our knowledge, is taken into account in the crack detection of structures using ANNs, for the first time. Thus nonlinear behavior of crack is modeled using FEM.The changes in the natural frequencies (due to crack) of various vibration modes were implemented as input for training and testing of ANNs. By producing various scenarios for sound and damaged beams (with different damage location and severity), two specific classes of ANNs were trained to predict the location and length of longitudinal cracks. The Results showed a promising prediction for the length of cracks by the proposed methodology. Also a considerable approximation observed in the prediction of cracks location.

---

The objective of this research is to develop nonlinear constitutive models for performance evaluation of masonry members on the basis of continuum model and fixed smeared crack approach. The finite element program called "WCOMD", which has basically been developed for modeling and analyzing the reinforced concrete, is used as the basis for modeling and analyzing in this paper. Constitutive laws and yield criteria according to the available experimental results on masonry panels are improved, so that it would have the capability of modeling nonlinear anisotropic behavior of masonry. The post-cracking behavior of masonry in direction normal to the crack (tension softening) is calculated according to crack band theory and in terms of fracture energy and element size in finite element. Also, the effect of cracking on compression behavior of masonry is considered on the basis of compression field theory. The validity of behavior models and analysis methods is measured via analyzing available experimental results in field of masonry panels and masonry walls.

---

Abstract Studying the response details of steel moment connections is very important due to the role of connections in moment resisting frames. The aims of this research were: i) to study the damage indices of steel material including: Pressure Index, Mises Index, Equivalent Plastic Strain Index, Triaxiality Index, and Rupture Index and ii) to compare these indices at connections of steel moment frames under earthquake loads. To achieve this, time history nonlinear dynamic analysis is performed using selected earthquake records on 2D model of special steel frame with ten storey and one bay to determine maximum rotations of connections. Then, damages indices of the selected connections under maximum rotation of records are investigated with selecting two types of moment connections. The results indicate that damage indices are dependent on type of connection, location of surveying, and rotations caused by earthquake movements. This dependency is very considerable for Equivalent Plastic Strain Index and Ruptureindices

---

There are a lot of approximation techniques for structural optimization. Among them, four outstanding approximation methods have been selected for trusses optimization. These approaches have been developed or modified by previous ones. Based on these schemes, a lot of trusses have been optimized by author's program. This study shows that the abilities of the mentioned methods are not the same and some of them have deficiencies. Reaching a better solution, lesser analysis time, oscillation of response, numerical stability and also using a variety of the design variables are among the findings of this work. A brief of these obtained results has been given in the conclusion part. Keywords: Nonlinear programming, Global optimum, Approximation methods, Convex approximation, Structural analysis, Two and three dimensional trusses

---

There are a lot of approximation techniques for structural optimization. Among them, four outstanding approximation methods have been selected for trusses optimization. These approaches have been developed or modified by previous ones. Based on these schemes, a lot of trusses have been optimized by author's program. This study shows that the abilities of the mentioned methods are not the same and some of them have deficiencies. Reaching a better solution, lesser analysis time, oscillation of response, numerical stability and also using a variety of the design variables are among the findings of this work. A brief of these obtained results has been given in the conclusion part.

---

Abstract: Implementation of 3D panels in buildings is increasing due to the importance of lightening, optimizing and reduction of fuel consumption. These panels are used as interior, outer, load bearing and partitioning walls beside the structural frame without considering the frame-panel interaction. Steel frames act in shear mode and panel frames act in flexure; hence, combining the two systems will change the structural behavior of each system. So, investigation of the seismic behavior of combined systems using nonlinear dynamic methods seems to be mandatory. In this article, frames with 3, 5 and 10 stories (filled in different bays by panel) were modeled in ANSYS. These frames were then analyzed under Elcentro, Tabas and Naghan seismic records. The results illustrated that using panel not only results in more acceptable drifts, but also it lets the system to have a better seismic behavior and more energy dissipation. For example, the displacements of the structures in the highest level decrease more than 35% by using one bay panel for filling steel frames. This amount of filling also leads to more than 100% increase in the area under the base shear-displacement diagram of a steel frame.

---

In this paper, with the assumption of constant material properties, the nonlinear behavior of beams is studied using the finite element method. To this end, two approaches are represented: in the first approach, the beam is modeled by one dimensional elements of second order that is formulated according to continuum mechanics relationships based on the Lagrangian strategy, while in the second approach based on the Eulerian strategy the nonlinear behavior of the beam is investigated by making use of two dimensional elements. In both approaches, the second configuration, strains and stresses in the beam are obtained via the calculation of deformation gradient