مقالات رزومه محسن ایزدی نیا

Production of construction waste In this research, the factors affecting waste production have been identified from previous articles, preliminary questionnaires and interviews.aste is one of the most important factors affecting performance and cost increase in construction projects. In the next step, the final questionnaire was prepared. Then, the relationship between the variables and the cause-and-effect relationships was carried out through the system thinking approach and Dimtel technique to confirm the cause-and-effect relationships according to the pairwise comparison questionnaire among ten identified experts. Also, lean construction was used as a solution to reduce waste production. Lean construction follows new rules and without using new technologies or updating equipment with minimum use of resources, minimum waste and maximum productivity in construction projects. The main purpose of this article is to use the concept of lean construction and the system dynamics method to identify the main causes of waste production in construction projects. The main focus of lean construction is to analyze waste production processes, improve activities to reduce waste production and increase performance in construction projects. First, the effective factors on reducing the production of construction waste were identified through previous researches, and then a survey (interview and questionnaire) was conducted with experts in the case study of the waste management organization in the metropolis of Isfahan. In the next step, 52 questionnaires were prepared and distributed in the case study of the research. After collecting the information, the data obtained from the questionnaire was analyzed using statistics after checking its validity and reliability. In the last stage, after confirming the effective factors in the production of construction waste and how they are related, in order to develop a conceptual framework, cause-and-effect diagrams were drawn. The statistical results showed that the first to third most important factors affecting the reduction of construction waste with lean construction approach, flow perspective, identification of waste from the point of view of transformation and identification of waste from the point of view of value were the most important according to the experts in the waste management organization. Also, cause-and-effect relationships were confirmed through Dimtel's method. As a result, considering the relationship of correlation as well as cause and effect relationship, the way of communication between variables has been rooted through cause and effect circles and systemic thinking

Advanced analysis refers to a method in which the strength and stability of the system and structural members are recognized in an integrated manner and there is no need to separately check the capacity of the structural members. This approach is a suitable method for evaluating the real behavior of structures and makes structural designers better understand the main characteristics affecting the actual behavior of structures. Undoubtedly, one of the most widely used structural systems in the construction industry is Concentrically braced frames (CBFs). Mainly, these kinds of frames collapse because of a soft story formation in one or more stories in which excessive brace buckling occurs. Using second order inelastic analysis, this study provides an intuitive understanding of the collapse mechanism of CBFs with 6 and 18 stories subjected to mainshock-aftershock sequences. Such understanding will support development of design methods that preclude low-capacity collapse modes specially under multi-shock excitations. This paper assesses the collapse mechanism as a stage in which the imposed seismic energy fails to dissipate and eventually leads to uncontrolled kinetic energy in structure. The investigation focuses on the role and distribution of the various energy measures and different dissipating mechanisms throughout the structures. Collapse mechanism is identified for various combinations of the utilized 32 mainshock-aftershock pairs that are gradually scaled following the incremental dynamic analysis (IDA) process. The distribution of input and dissipated energies along various stories reveals the role of upper stories in damping the imposed energy. Furthermore, the similarity between the height profile of the residual drifts and the story imposed energies highlights the characteristics of the structures in adapting their drift response to a mode with the highest energy absorption.

In recent years, self-centering concrete walls have been utilized as modern structures. The mechanism of these structures is such that the focus of energy dissipation is on the dampers, and the role of the concrete wall and tendons is to create stiffness and provide the self-centering capacity in the system resulted in the reduction of residual deformation in the system. The jointed self-centering concrete walls are a type of self-centering wall system where dampers are placed between two concrete wall panels. The most important point that should be considered in these structures is the optimal use of dampers in them. In the present research, a new system has been introduced, which is a combination of self-centering concrete walls with gravity columns. In such a way that the friction dampers were placed in the middle and side positions of the concrete wall. This research aimed to investigate the optimal numerical value for the "slip load of friction dampers" in the middle and side positions of the Self-centering concrete wall based on the "amount of prestressing force" in the friction screws of the dampers. In the current study, the resistance of damper materials, their shape and dimensional size are not considered as variable parameters and they are considered without influence in determining the optimal damping. In total, the optimal sliding load based on the prestressing force in the friction bolts has been simultaneously determined by two-way sensitivity analysis by OpenSEES software. Based on the results, applying the method of determining the percentage of the minimum response coefficient (R) based on parallel (two-way) sensitivity analysis can be recognized as a very efficient method for determining the most optimal friction damper in Self-centering jointed concrete wall systems. Furthermore, the prestressed and optimal force for the dampers indicated that the dampers located between the two walls (set of middle dampers) exhibit a specific optimal value and other dampers (set of side dampers) also present a different optimal value.

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.

Advanced analysis refers to a method in which the strength and stability of the system and structural members are recognized in an integrated manner and there is no need to separately check the capacity of the structural members. This approach is a suitable method for evaluating the real behavior of structures and makes structural designers better understand the main characteristics affecting the actual behavior of structures. Undoubtedly, one of the most widely used structural systems in the construction industry is Concentrically braced frames (CBFs). Mainly, these kinds of frames collapse because of a soft story formation in one or more stories in which excessive brace buckling occurs. Using second order inelastic analysis, this study provides an intuitive understanding of the collapse mechanism of CBFs with 6 and 18 stories subjected to mainshock-aftershock sequences. Such understanding will support development of design methods that preclude low-capacity collapse modes specially under multi-shock excitations. This paper assesses the collapse mechanism as a stage in which the imposed seismic energy fails to dissipate and eventually leads to uncontrolled kinetic energy in structure. The investigation focuses on the role and distribution of the various energy measures and different dissipating mechanisms throughout the structures. Collapse mechanism is identified for various combinations of the utilized 32 mainshock-aftershock pairs that are gradually scaled following the incremental dynamic analysis (IDA) process. The distribution of input and dissipated energies along various stories reveals the role of upper stories in damping the imposed energy. Furthermore, the similarity between the height profile of the residual drifts and the story imposed energies highlights the characteristics of the structures in adapting their drift response to a mode with the highest energy absorption

Adopting risk management is a must, inevitable in all construction projects. Risk management is very important in retrofitting of the projects. Strengthening the reinforced concrete beams with respect to their type and how they are made is assessed in this study. Although both of the near-surface mounted (NSM) and externally bonded reinforcement (EBR) methods have advantages and disadvantages and it depends on the reinforced member and the project conditions, but in general, the NSM method outperforms the EBR while somehow (EBR) is adopted more. A researcher-designed questionnaire consists of ten restrictive factors regarding NSM implementation. The responding persons consist of skilled experts with at least five years of experience in this field. The execution of risk management in NSM, obstacles on the way of implementation, and the effect of risk management on the functionality of these factors are of concern here. The obtained data is assessed through statistical tests. The factors of more execution time, lack of experts, high volume, low knowledge on the client, uninformed employers, consultants and contractors about the existence of this method, complexities in the calculation, big calculating mass, concrete cover 5-7 cm, FRP rebar needed in NSM, high implementation cost and high FRP implementation cost are considered as the restrictive factors affecting NSM implementation. The initial assumption that the ten factors were restrictive as to NSM implementation led to proving that the factor of lack of information about this method within the client, contractor, and consultant was the most effective as a restriction. This proof was obtained through the statistical tests conducted on the assumptions.

The progressive collapse in building frames refers to the spread of an initial localized chain collapse in all or some parts of the structure. This phenomenon occurs following the removal of one or more load-bearing elements and eventually leads to the total or partial collapse of the structure. In previous studies, the progressive collapse has been analyzed mainly using the method proposed in building codes under gravitational loading with a defined load combination. This study aims to investigate the progressive collapse of steel moment-resisting frames equipped with gate (hat) bracing under seismic loading. For this purpose, the effect of the seismic properties of the acceleration records such as peak ground acceleration (PGA), Arias intensity, frequency content, and a vertical component are examined, following the introduction of several acceleration groups. Next, progressive collapse analysis with side and middle column removal is simulated under various scenarios during an earthquake. The results showed a high effect of about 66% PGA and predominant period on frame responses and, at the same time, a slight effect of the vertical component application on frame responses.

In this paper, in order to improve the seismic behavior of BRBs, buckling-restrained braces with three parallel cores with different yield stress have been suggested and introduced. The buckling restrained braces were made in one and three steel core with the same tensile and compressive capacity. These braces were subjected to cyclic tensile and compressive loads in the laboratory under the ATC-24 loading protocol. Hysteresis cyclic performances of each brace were obtained and examined. Then, the one and three core buckling braces were placed diagonally in a steel moment frame and their seismic performance and response modification factors were obtained using adaptive pushover analysis. The results indicated that the three core brace has 16.3% and 8.8% higher energy absorption and damping capacity. In addition, the damping in the three-core brace in drift 2.5% is 8.8% higher than the one core brace. Mean value of response modification factors for steel moment frame with one-core brace is 8.11 and steel moment frame with three-core brace is 9.14. In conclusion, the three-core brace has higher energy absorption and damping capacity and the ductility of the steel moment frame with the three core brace is higher than that of the frame with the one core brace, which presented the three-core brace has more acceptable seismic performance and is highly recommended for rehabilitation

Hollow structural sections (HSS) have been used in many structural applications, owing to their efficient structural performance and suitable appearance. However, due to the lack of access inside the HSS column for bolting purposes, it has been difficult to develop a practical bolted moment connection. Thus, field welded beam-to-HSS column connections have been the only viable method. Recently some blind fasteners are developed to be used in application which access for installation is only from one side of the connection. At the moment different blind bolts were designed for use in one side connections. In this project, comparison of the test result of an article and three dimensional finite element modeling of the blind bolted end plate joint with concrete-filled square hollow section columns to steel beam and Lindapter blind bolt (Hollo-Bolt) under monotonic loading indicates that the finite element analyses can be used to predict the connection behavior with sufficient accuracy. After that studied parametric investigation under cyclic loading into the end plates thickness, bolt diameter and bolt pretension force for the blind bolted extended and flush end plate connections of steel beams to hollow section column with ABAQUS and got moment-rotation hysteretic curve of each ones. Results have shown that the end plates thickness, bolt diameter and bolt pretension force have influenced on the connection behavior.

In order to solve the problem of access to inside of hollow columns for tightening bolts and achieving a suitable connection both in terms of rigidity and stiffness and in terms of the proper behavior, various solutions have been suggested by researchers. One of these solutions is steel beam to hollow column connection by an angle and blind bolts. This connection can be made in different types with different number of blind bolts. Connection with flange angle and blind bolts have showed proper and semi-rigid behaviour.In this research, the effect of changing various parameters on the behavior of steel beam-hollow column connection with angle and blind bolts was investigated under monotonic loading. The nonlinear finite elements method and Abaqus software was considered and solid three-dimensional elements as continuum elements was supplied in connection models. The behavior of connection was studied by changing various parameters such as beam height, column thickness, length of angle leg and number of blind bolts. The results show that increasing height of the beam, thickness of the column and length of angle leg raises the connection’s rigidity. Also, increasing the above mentioned parameters leads a simple connection toward semi-rigid connection. Also, by studying the models, the rigidity degree of most models except a few of them, which is less than 20%, is between 20% and 90%. Considering the rigidity degree, studied models behaved as semi-rigid connections.

As a passive control system, braces have an effective role in creating structural resistance to lateral forces such as earthquakes and winds. One of the ways to make the braces more economical is to use their inelastic capacity. Ordinary braces perform well in tension; however they buckle under pressure and exhibit undesirable behavior. This problem can reduce dissipated energy due to lack of plasticity, which plays an important role in cyclic loading such as earthquakes. For this reason, buckling-restrained brace (BRB) have become increasingly popular in different countries. BRBs include yielding steel core and an outer steel hollow section. Although the yielding steel core has a low compressive capacity, its capacity in pressure can be increased by limiting its buckling due to the outer steel hollow section. So far BRBs introduced as mentioned have a single yielding core, however In this paper, in order to improve the seismic behavior of BRBs, buckling-restrained brace with three parallel cores with different yield stress have been suggested and introduced. The buckling braces were made in one and three steel core with the same tensile and compressive capacity. These braces were subjected to cyclic tensile and compressive loads in the laboratory under the ATC-24 loading protocol. Hysteresis cyclic performances of each brace were obtained and examined. The experimental results show that: 1) the hysteresis loop of the 3-core brace is thicker and higher than the 1-core brace, 2) indicating that the three core brace has 16.3% and 8.8% higher energy absorption and damping capacity, respectively compared to that of the single core brace. Furthermore, it has better seismic performance.

This paper describes a numerical method for the full-range analysis of prestressed concrete flexural beams strengthened with prestressed glass fiber-reinforced polymper (GFRP) sheets, focusing on ductility and flexural strength behaviour. Prestressing concrete structures cause increased flexural strength of these structures thus increased resistance of structures, increased span length, and reduced displacements of beams are resulted, which is very effective and economically feasible. The study of ductility of these structures that have been used a lot nowadays, has a great importance because it expresses the capability of structure in inelastic deformations before destruction of members. Present paper attempts to investigate the effect of prestressed GFRP sheets on ductility and deformation of beams strengthened by this method. Regarding to this, the modelling of three sample of beams in different conditions was studied using finite element software ANSYS. After comparing the results of numerical analysis of concrete beam with GFRP sheet and the numerical results of two types of prestressed concrete beam with wire and proofing the efficiency of presented model, the displacement and energy ductility index, deformation, resistance and the amount of displacement of concrete beams have been investigated. Three beams with 160mm*280mm*3600mm dimensions have been modelled. In summary, the results express that the application of prestressed GFRP sheet may cause the least displacements of beam and an increase of 10% and 10.4% will be achieved in the flexural stiffness and ductility.

Extensive damages in a large number of existing buildings under in-plane shear has shown the need of structural strengthening techniques for masonry structures. FRP and shotcrete are strengthening techniques which can be used to repair or strengthen masonry structures. Masonry walls strengthened with FRP and shotcrete can greatly increase some behaviour parameters such as strength, energy absorption and stiffness, but the comparison and effect of single-faced FRP and shotcrete layers on shear behavior of masonry walls under lateral loads have not been studied so far. In this research in order to evaluate and validate numerical modelling approaches, two kinds of experimental masonry wall models made by clay bricks and concrete blocks strengthened by FRP and shotcrete were introduced. At the end, modelling and analysis of six walls under lateral loads using the nonlinear analysis of pushover in Abaqus software has been investigated. The results of the analysis show the feasible effect of strengthening unreinforced walls with single-faced shotcrete and FRP, so that the stiffness and strength of the wall increases significantly due to the addition of shotcrete to one side of the wall. Also, amount of energy absorption increase for FRP is 60-70% and for shotcretes 70 to 90%. Therefore strengthening by single-faced shotcrete has a more feasible effect.

The present study tries to examine the seismic behavior of a new type of beam-column connection having yielding damper with circular placement pattern. The main purpose of the proposed system is to use yielding dampers in a space as high as the beam depth in order to occupy much lesser space, and not to reduce the useful height of the story  in the beam-column connection, so that the inelastic deformations from cyclic loading is restricted to the dampers. Three samples were made in the laboratory and were loaded up to 0.05 radian rotation under the cyclic loading. In order to evaluate the numerical modeling techniques and analyses in predicting the cyclic behavior of the proposed connections, finite element models of  laboratory samples were made and were analyzed based on corresponding  loading pattern. Based on the numerical and experimental results, inelastic deformations  were concentrated  in the dampers for all proposed connections and  the beam and the column remained within the elastic range. It is also possible to achieve a higher resistance that of the plastic moment of the beam in the proposed connection with a suitable design.

Extensive damages in welded unreinforced flange connections (WUF) in the Northridge 1994 earthquake led to the development of reduced beam section (RBS) moment connections to prevent premature brittle failure modes in welded connections. This paper investigates the seismic performance of recently developed drilled flange (DF) moment resisting connections as a simple and efficient alternative to RBS connections in seismic regions. DF connections are established by a series of holes made by drilling on the top and the bottom flanges of the beam (along the main axis) to create an intentional weak point, which can prevent stress concentrations at the connection edges. In this study, a series of analytical studies based on previous experimental researches were carried out to evaluate cyclic behaviour of DF,WUF and RBS beam to column connections. Different drilled flange hole configurations and panel zone shear strength ratios were used to obtain an optimum design and prevent premature failure modes in complete joint penetration groove welds. Results show optimum configuration of drilled flange holes in DF connections reduce the rapture index and equivalent plastic strains of critical points on welded joints and comparing with WUF and RBS connections provide an appropriate seismic performance. The diameter of holes increase by distance from column face for the optimum configuration of DF connections.