نشریه آنالیز سازه - زلزله
سال بیستم شماره 2 (تابستان 1402)

Owing to the common use of infill walls in conventional buildings, it is a practical and important topic to investigate the effect of infill walls on the behavior of structures during earthquakes. One of the disadvantages of infilled frames is the presence of large window openings in some of the reinforced concrete frame buildings, which results in the short column phenomenon. The part of the column that is adjacent to the wall is almost integrated with the wall and leads to a reduction in the height of the column. Therefore, the lateral stiffness increases considerably. With increasing stiffness, the lateral force applied to the column also increases. In this study, a 4-story, 3-span reinforced concrete model with a different arrangement of infill walls in the stories and considering short walls on the ground floor, the short column phenomenon has been investigated in ETABS software. Also, the seismic capacity of the structure has been calculated by valid methods based on the capacity spectrum method proposed by ATC40. The results indicate that with increasing stiffness, the maximum shear force applied to the column due to the presence of the infill wall under the designed earthquake load will increase by about 50% compared to the frame without the infill wall. Furthermore, the amount of stiffness difference in the frame with and without infill wall in the analyzed models is about 70%, which can prevent irreparable damage by predicting this event and proper design.

The goal of the present research is to propose a novel adaptive fractional order PID (AFOPID) controller whose parameters are tuned online by five exclusive multilayer perceptron (MLP) neural networks using the extended Kalman filter (EKF). An MLP neural network that is trained using the Back Propagation (BP) error algorithm is considered to identify the structural system and estimate the plant. The Jacobian of the model estimated online is utilized to apply to the controller. Considering the adaptive interval type-2 fuzzy neural networks (IT2FNN) and this issue that the compensator is tunned by EKF and feedback error learning strategy (FEL), the stability and robustness of this controller are increased against the estimation error, seismic disturbances, and some unknown nonlinear functions. In order to validate, the performance of the proposed controller is investigated on a 3-story nonlinear benchmark building equipped with semi-active dampers under far and near field earthquakes. In order to evaluate the effectiveness of the proposed controller equipped with a compensator in reducing seismic responses, the evaluation indices were discussed and compared with previous studies. The numerical results represent the substantial efficiency of the proposed adaptive controller (AFOPID) over the previous controllers such that J2 in the Hachinohe and Northridge earthquakes enhanced by up to 35% and more than 40%, respectively. In general, all indices ( J3  to J6 ) have experienced a considerable enhancement using the proposed method.

Strengthening reinforced concrete beams using fiber reinforced polymer (FRP) materials compared to other strengthening methods due to its low weight and easy transportation, high resistance with less manpower has been accepted as a common practice in most countries. Externally bonded reinforcement (EBR) and near surface mounting (NSM) reinforcement are common methods for FRP installation. In this research the strengths, weaknesses, opportunities and threats of these two methods are identified as the strengths, weaknesses, opportunities, and threats (SWOT) method from the perspective of construction management and then the structural equations modeling (SEM) method is used to investigate the relationship between each of these variables. Two separate models were used in the EBR and NSM methods that identify the relationship between strengths, weaknesses, opportunities and threats as hidden variables and then questionnaire questions related to each of these variables as explicit variables. Also, confirmatory factor analysis and Cronbach's alpha coefficient were used to assess the validity and reliability of the questionnaire, respectively. The results of this study showed that each of the EBR and NSM methods has different advantages and disadvantages and then management solutions were evaluated using SWOT technique and structural equation modeling.

By increasing the risk of explosive terrorist attacks and threats to all types of structures and buildings, a careful study of the behavior of structures under explosive loading is considered as an important matter. A simple method to protect important structures against explosive loads is to improve the security of the environment by using protective perimeter walls against explosive loading. In this research, the effect of reinforced concrete perimeter walls with and without canopy has been investigated. Different parameters such as the geometrical shape of the perimeter wall, the element removal and degradation rate, wall displacement, the scaled distance change and the explosive mass have been investigated. Finite element software (LS-DYNA (R11.1.0) has been used for modeling. For this purpose, the perimeter walls were designed in three different shapes and conditions. The results indicate that the existence of canopies for the perimeter walls under explosive loading has positive effects, so that the canopied perimeter walls with a canopy angle of 90 degrees compared to other types of wall, at different station distances and in the same conditions, reduce the displacement rate in the protected structure by about 11 percent. Furthermore, the location of perimeter walls and obtaining a safe distance in placing these walls is very effective in enhancing safety and reducing the vulnerability of the facilities and structures protected by these walls.

There is little evidence of the formation of plastic zones in damagd structures in diffrent types of earthquakes. Most of the conducted studies have focused on creating a plastic hinge in a part of the beam making irreparable damage to the beam.  If the plastic joint in the beam does not occur, a force will be created which is more than the plastic moment of the beam and will be transferred to the connection and finally to the column. This will either cause the brittle failure of the connection or damage to the panel zone of the column. Therefore, in this research, four connections with new geometry have been proposed aimed at reducing damage in beams and columns and creating the possibility of replacing damaged parts. In general, the presented connections are suggested by replacement of an H or I-shaped cross section along with or replacing of an end-plate, as a short stub column. In this reserch, first, a finite element model of the end-plate connection, which is a combination of welding and screwing subjected to cyclic loading was selected. Then, after the validation of Abaqus software, a study was carried out on the proposed connections. The results indicate that the stub region, with its nonlinear behavior, creates a controlled limited joint with extraordinary ductility. Yielding in the stub causes its fusion behavior and prevents damage to beams and columns. It also significantly reduces the plastic stress and strain in the panel zone of the column.

Among the countless methods that have been proposed in the field of structural damage detection, the finite element model updating method has been very popular. However, the accuracy and efficiency of this method decrease drastically when the number of variables in the problem increases, and this is a problem when dealing with large structures with a large number of elements. In this research, a two-step method is proposed, which is capable of reducing the size of the damage detection problem introduced to the updated model by identifying damaged structural members through a damage index based on static strain energy in the first step. Therefore, only a few variables are introduced to the second step, which include a process of updating the finite element model. This second step actually consists of an iterative process of updating the model, which uses a new and damage-sensitive objective function to detect the severity of damage in the elements identified in the previous step. Also, a meta-exploratory optimizer named equilibrium optimizer is utilized to determine the value of the unknown variables of the problem, which are the damage values ​​of the elements introduced by the first step. The proposed method has also been tested on a number of numerical samples to check the effectiveness of the method in the presence of external disturbing factors such as measurement noise. A comparative study has been done to compare the results. According to the results, the proposed method is able to detect the location and severity of damage in different structures, and measurement noises and modal information only from the first few vibration modes do not have much impact on the accuracy of the results. A laboratory study has also been conducted to find out the efficiency and accuracy of the proposed method in real structures, and according to the results, the proposed method is well able to detect damage.

This paper presents the results of an experimental study on the flexural performance of reinforced concrete beams made of fibrous concrete under the corrosion of tensile steels. Fifteen reinforced concrete beams were prepared in three groups; in two groups, two types of steel and polyolefin fibers were utilized to construct the beams. Four beams from each group were subjected to accelerated corrosion to create corrosion percentages of 3.5, 7, 15 and 30% in tensile steels. Then the beams were subjected to a four-point bending test, and the parameters of yield strength, ultimate strength, yield deflection, ultimate deflection, failure mode and ductility of the beams were investigated. The results indicated that up to the corrosion level of 15%, with the development of general corrosion, along with the reduction of stiffness and resistance of the beams, the ultimate deflection of the beams increased, and at the corrosion level of 30%, with the development of local corrosion, the ultimate strength and ultimate deflection of the beams were greatly reduced. The level of corrosion in tensile steel of beams containing steel fibers was lower than that of in the other beams, which was caused by the sacrificial anode effect of steel fibers. Under the corrosion conditions of tensile steel, the reduction of strength and stiffness in fibrous concrete beams were less than those in the plain concrete beams, and the performance of steel fibers in this field was significantly better than their polyolefin counterparts. Furthermore, the fibers used for this purpose, had significantly positive effect on the ductility of reinforced concrete beams with tensile steel corrosion.