mohammad ghanooni bagha

Today, the use of energy-dissipating system such as yielding metal damper in structures can improve the seismic performance of structures. One of the characteristics of metal yielding dampers is the ability to dissipate high energy and increase the ductility of the structural system, which can improve the ductility and energy absorption characteristics of the metal frame equipped with braces and prevent the brace from buckling during an earthquake. The purpose of this research is introduce a new form of yielding dampers called honeycomb yielding damper (HYD) with different dimensions and thickness along with evaluating and comparing the force-displacement diagrams and investigating the seismic parameters of this type of yielding damper. All modeling and validation of numerical samples were done by Ansys software. Non-linear analysis method is used in this research. The hysteresis curves are obtained under in-plane cyclic loads. The mechanical parameters such as ductility ratio, initial hardness, effective hardness and damping coefficient can be determin. The results of this research showed that the effective stiffness increases by increasing the length and thickness of the sample. The ductility ratio decreases by increasing the height of the sample. the effective stiffness decreases by increasing the height of the sample. The ductility ratio increases by increasing the height of the sample. Also, the effective damping coefficient decreases with the increase in the height of the samples, the effective damping coefficient increases with the increase in length and thickness of the samples.

According to the technical literature, the amount of chloride that is transported by air from the sea surface depends on the amount of salt in the seawater in that area, the speed and direction of the wind, and the distance from the sea. Accordingly, data on the highest annual wind speed and direction of the wind are collected in several reinforced concrete structures (RC structures) in southern cities near the Persian Gulf at different distances from the sea. In this paper, by applying probabilistic modeling and utilizing the Hasofer–Lind and Rackwitz–Fiessler (HL-RF) method of reliability by aligning the enhanced Colliding Bodies Optimization method (ECBO) algorithm, and utilizing the data from the National Meteorological Organization, for concrete structures located in different distances with different speeds and directions of the wind from the Persian Gulf, the time of chloride corrosion initiation in reinforced concrete structures and the durability of these structures has been surveyed.

Corrosion is one of the crucial damages that may occur to reinforced concrete structures. It also may affect the expected performance of the structure during the possible earthquakes. Onshore reinforced structures, bridges exposed to deicing salts in winter and also the pillars of marine structures under tidal waves, all of which are examples of corrosion damages. Corrosion mostly occurs due to two main reasons: chloride and carbonation which cause pitting corrosion and uniform corrosion, respectively. Corrosion starts with reaching of those two ions to the bar surface, passing by the physical and chemical passive covers. Corrosion also affects the mechanical properties of the steel and the concrete and reduces the seismic performance of the structure. One of the most important parameters in studying the corrosion and its effects on the seismic performance and life cycle of the structure is the corrosion initiation time. According to Fick’s law, the initiation time is a function of surface and critical chloride, chloride diffusion coefficient and concrete cover on armatures. In the present study, the chloride-based corrosion is considered. Besides, corrosion initiation time is determined by deterministic and probabilistic Monte-Carlo methods considering the uncertainties in the effective parameters. In the end, by comparing these two methods, the effect of uncertainties in the possibility of corrosion initiation time is presented. Furthermore, parameters like the distance from the sea and the water to cement ratio are discussed in a parametric study.

It is unavoidable to prevent serious damage to the structure and to reduce the casualties and damage caused to it. For this purpose, structural control systems can be used. The study used a viscous damper. The Endurance Time method (ET) is a simple method of analyzing history when the structure is exposed to a gradual accelerating function. The advantage of this method is that with only one analysis of the structure under the acceleration function of endurance time, the performance of the structure can be evaluated at different functional levels. In this study, the application of endurance time method in nonlinear seismic analysis of steel structures equipped with viscous dampers has been investigated. The parameter of engineering demand is the maximum drift of the floors, which is calculated in structures with and without viscose damper. Finally, using curves of endurance time, it was found that the use of viscous dampers reduced the maximum drift of the floors. Non-linear time history analysis (NTH) has also been used to validate the results of the (ET), which showed that the (ET) results are well matched to the nonlinear time history analysis. Finally, the results demonstrated that utilizing of ET method can be replaced in structural building which the viscous damper was utilized.

Steel braced frames are among the most effective lateral load resisting systems. The eccentrically braced frame has a higher ductility, less stiffness, and a better serviceability (limited retrofitting needed after the seismic excitations) compared to concentrically braced ones. Static indeterminacy is generally considered as the number of extra constraints or members in a structural system. In other words, redundancy is the ability of a structure to keep its stability after the onset of the failure or removal of its lateral load resisting elements, preventing it from collapse in the initial stages of loading. The redundancy of a system depends on the “dynamic” characteristics of its structure and properties of the applied earthquake excitations as well as its structural geometric features and details. This indeterminacy is called dynamic redundancy.In this study, the effects of the number and location of braced bays on redundancy were investigated to obtain the best pattern for regular 5 and 8-story buildings using nonlinear analysis. It also develops a relationship for the redundancy factor of the dual structural systems. Results show that position of braced bays is more effective on redundancy than the number of bays. It is also concluded that the building’s height affects the required number of bracing bays. The study also showed that the dynamic redundancy is different from the over-strength. According to the results of this research, for dual structural systems, it is recommended not to arrange the braces only in the perimeter of the plan

Seismic retrofit of concrete columns with FRP composites is a well-known method for enhancing their strength and ductility. Behavior of rectangular concrete columns confined with FRP composites depends on several parameters, including unconfined concrete strength, confinement level, aspect ratio of cross-section (defined as the depth /width of the cross-section), and the sharpness of the section corners. For proper design of rectangular concrete columns confined with FRP composites, a good understanding of the stress–strain behavior of FRP-confined concrete prism under axial monotonic compression is necessary. In recent years many design oriented stress-strain models with simple closed-form expressions have been developed for FRP-confined concrete columns. Also some analysis oriented models are proposed in which the stress-strain behavior of circular columns is generated with an incremental process. But to the best knowledge of authors, there is not an analysis oriented stress-strain model for FRP-confined rectangular columns in the literature. Thus in this paper a base model for actively confined concrete is used to develop a new analysis stress-strain model for rectangular concrete columns confined with FRP. This model considers all parameters that affect behavior of rectangular columns. The procedure for generation of analysis oriented stress–strain curves for FRP–confined concrete based on active confinement model is as follows:1) For a given axial strain, find the corresponding lateral strain according to the lateral-to-axial strain relationship; (2) based on force equilibrium and radial displacement compatibility between the concrete core and the FRP jacket, calculate the corresponding lateral confining pressure provided by the FRP jacket; (3) use the axial strain and the confining pressure obtained from steps (1) and (2) in conjunction with an active-confinement base model to evaluate the corresponding axial stress, leading to the identification of one point on the stress–strain curve of FRP–confined concrete; (4) Repeat the above steps to generate the entire stress–strain curve.      It is obvious from above procedure that the main relations in analytical modeling are the lateral-to-axial strain relationship, lateral confining pressure provided by the FRP jacket, peak axial stress on the stress–strain curve of actively confined concrete, axial strain at peak axial stress, and stress–strain equation. Thus in this paper these relations for rectangular sections are presented and when these relations be defined, the stress-strain curve can be generated using above mentioned procedure. In this paper an experimental database containing 167 axial compression test results of externally confined rectangular columns is assembled and used for stress-strain modeling. The proposed model considers different parameters that can affect the behavior of rectangular columns, including aspect ratio, corner radius, confinement ratio, and unconfined concrete strength. Also both the strain hardening and strain softening behavior of rectangular columns can be modelled by the proposed formulation. Comparison between experimental results and those of model predictions indicates that the proposed model provides good predictions for different parts of stress-strain curve such as compressive stress and strain also ultimate stress and strain. Also the shape of predicted stress-strain curve is in a good agreement with the test results.

Chloride ion ingress into concrete causes steel corrosion over time, thereby ending the service life of structures. Sometimes, it severely reduces the loading capacity of reinforced concrete and may even cause the sudden destruction of concrete structures. Concrete cracking stems from different factors, such as shrinkage and tensile stress due to thermal loading and under loading. Modeling and estimating chloride ion ingress into cracked concrete over different periods can aid the appropriate determination of structural lifetime and maintenance of reinforced concrete structures. Accordingly, this research investigated the effects of the width and depth of concrete cracks on the rate of chloride ion diffusion and rebar corrosion. To this end, different concrete specimens characterized by various cracking conditions were modeled in COMSOL Multiphysics. Analytical results showed that the critical crack that reflected the highest extent of chloride ingress into a specific region at different times was not necessarily the defect with the largest thickness and depth. This finding highlights the importance of investigating crack behavior in the appropriate estimation of structural service life. Nevertheless, over time, considerably wide and deep cracks may ultimately be a reflection of substantial rate of ingress.

One of the most concerns about design and maintenance of structures in civil engineering is the safety of structures in the events of natural disasters, including earthquakes, which requires adequate resistance and providing expected performance of structures. Different factors can have an impact on the occurrence of damage and the damage content in structures and, consequently, the loss of economic assets as well as human health and life safety during earthquakes. Normally, high alkaline property of concrete, PH about 13, forms a protective oxide layer on the reinforcement steel surface. The Carbon dioxide in the atmosphere or the chloride ion in the concrete environment especially in the coastal zone, along with the moisture and the oxygen can penetrate through the concrete pores and micro-cracks and can reach the rebar surface. Then, they cause rebar corrosion inside the concrete by destroying the protective oxide layer on the steel surface. Chloride ions reach the passive layer according to the explained pattern and they begin to react in the passive layer when the amount of chloride ions exceed the critical value and cause the perforation corrosion. Therefore, the performance of deteriorating structures can be different from the desirable performance of pristine structures. Corrosion of steel reinforcement in reinforced concrete (RC) structures is one of the main factors in increasing the vulnerability of RC structures. Due to corrosion, mechanical properties of steel involving yield and ultimate stresses, their corresponding strains, and the elasticity modulus of steel will change. Also the cross-sectional area of steel reinforcement decreases. Furthermore, after cracking, the mechanical properties of concrete will change. In this study, in order to investigate the seismic fragility and vulnerability of RC structures due to steel reinforcement corrosion, two buildings involving a 3-storey and a 7-storey RC moment frames are modeled based on the lumped plasticity model for considering nonlinearity. Two corrosion scenarios of 10 and 20 percent reduction of steel reinforcement cross section and their effects applied to the structural members of these RC frames. Then, seismic performance and the fragility of these two RC frames are investigated using nonlinear static analysis (pushover analysis) and incremental dynamic analysis. Fragility analysis results show that the probability of failure and seismic fragility of RC structures increased due to reinforcement corrosion. Therefore, fragility curves shifted to the left due to corrosion, illustrating the increase in the probability of damage at different spectral accelerations. The safety margin of the collapse of the 3 and 7-storey structures also decreased due to corrosion. For example, as a result of 20 percent corrosion scenario, safety margin of three-storey structure decreased by 16.5 percent and the safety margin of seven-story structure decreased by 28 percent. Results also illustrate that the collapse margin ratios of both structures (CMR) are reduced for 10 percent corrosion scenario. Although the probability of failure increased for 3-storey RC frame, it remains below 10 percent. However, for 7-storey RC frame, the probability of failure exceeds 10% (allowable failure probability adopted by the code) and the frame needs to be rehabilitated.

With the increasing global population in recent decades and the increasing number of construction projects in the world, researchers and scientists from various sciences are thinking about restoration of civil engineering structures, which has reached to useful life of many of these structures. The failure of part of these structures leads to the destruction of the entire structure, which results in the wasting of large amounts of capital from owners and owners of these structures. Destruction and rebuilding of such structures are not at all cost-effective. Therefore, the science of health monitoring of structures in order to solve these problems has attracted researchers in recent years. So far, various methods, including X-rays and ... have been used to find the damaged member, but these methods can only be used on members of the structure that is available. And they are not comprehensive for the whole structure. For this purpose, vibration-based methods were introduced. Among the vibration-based methods, modal field methods have been of major interest to the researchers for their simplicity in performance. One of these methods is the mode shape curvature method, whose intrinsic ability to detect and locate damage is obvious to everyone. In this study, taking into account the noise generated by the mode shape data acquisition, more careful attention is needed in the field of damage detection. For this reason, the damage index was used as an indicator of the damage. The results indicate high accuracy of the method in identifying low-intensity damage and high noise level in higher modes.

When the discussion is about the destructive effects of salt spray on the coastal structures, the distance between RC structures and the sea is considered as an important parameter. This parameter allows considering the distance influence on structural durability in order to make a proper decision to protect the structure against the corrosive chloride agent. Since probabilistic methods and modeling    at the design stage can save the costs of repair and reconstruction of structures, in this paper, through probabilistic modeling and using Monte Carlo simulation, the probability of reinforcement corrosion initiation has been considered at different distances from seawater as a chloride source. Considering a structure in Caspian Sea condition, the effect of surface chloride reduction is investigated with increasing distance from the sea and its effect on corrosion probability is studied. The results of this study show that by increasing the distance from the sea after 200 meters, the chloride concentration will be significantly reduced. It is also observed that, after 2000 meters, the effect of chloride. Also, it can be seen that with increasing distance, chloride corrosion will not have a significant effect on the durability of reinforced concrete structures. However, further studies are needed regarding the change in the rate of reduction of chloride due to distance from the sea.

The effect of intelligent semi-active thermal exchange-fuzzy controller in structural rehabilitation by attenuating seismic responses of structural systems is investigated. In the suggested structural controller, MR dampers and their sensors are employed as a semi-active controller. Resultant control forces of MR damper are administrated by providing external voltage supply during the earthquakes and high intensity winds. Moreover, a novel evolutionary algorithm of thermal exchange (TE) is applied to compute the optimal location and the quantity of Magnetorheological (MR) dampers and their sensors with regard to minimizing resultant vibration magnitude. An optimal semi-active Thermal Exchange-Fuzzy Controller (TE-FC) has been suggested to administrate MR damper ingeniously. Results of numerical simulations illustrate the efficiency of suggested control system. The TE-FC can determine the optimal control arrangement and forces during a reasonable number of iterations. In comparison of the performance of various control strategies, the TE-FC demonstrates that economical cost and rehabilitation properties of the building could be optimized simultaneously. The TE-FC managed the optimal control forces online during strong ground motion, to attenuate the excessive responses in several rehabilitated buildings. Consequently, the TE-FC could improve the reliability of rehabilitated structure in comparison with passive and offline controllers. The significant efficiency of optimal arrangement of dampers and sensors over uniformly distribution of damper and sensors is presented as well.

Carbon dioxide and carbonation in concrete structures after several years may leads to corrosion of the reinforcements, and consequently reduces the life of concrete structures. According to reports of IPCC, uncertainty to predict the weather conditions is very high. The annual growth rate of carbon dioxide concentrations from 1.4 ppm during the period of 1960 to 2005 has increased to 1.9 ppm during the period of 1995 to 2005. Two predictions of A1F1 and A1B are presented for changes in carbon dioxide concentrations. In A1F1 high economic growth, population growth will continue in the mid-21st century with high speed, and the use of fossil fuels will also continue as before. In A1B, using clean energies is common. In fact, A1F1 and A1B are respectively pessimistic and optimistic predictions for the concentration of carbon dioxide in the environment. According the analysis results base on Monte Carlo simulation, global warming and climate change lead to an increase in average temperature of Earth and atmospheric carbon dioxide concentrations, and finally, it can reduce the durability of concrete structures. Also, it was observed that ignoring changes in concentration of carbon dioxide can have a significant effect on the results obtained for carbonation depth. It was also observed that considering each of predictions for changes in carbon dioxide concentrations does not substantially influence the depth of carbonation.

Reinforcement inside the concrete is protected from corrosion and its damages until several years after the construction. After corrosion initiation, the Cross Section of Reinforcement begins to reduce and often load bearing of the reinforced concrete structure will be reduced significantly. Corrosion of reinforcements in concrete in polluted and contaminated areas can be occurred in two ways: Chloride and Carbonation. Chloride ion ingress is one of the major problems that affect the durability of reinforced concrete structures such as bridge decks, concrete pavements, and other structures exposed to harsh saline environments. Corrosion occurrence and development in reinforced concrete structures increase the steel volume and produce products with volume of about 2-7 times the steel initial volume. This volume increase, which is due to cracks, reduces the compressive and tensile strengths in reinforced concrete structures. Therefore, durability based design of concrete structures in marine areas has gained great significance in recent decades and various mathematical models for estimating the service life of reinforced concrete have been proposed. In spite of comprehensive researches on the corrosion of reinforced concrete, there are still various controversial concepts. Effect of environmental conditions on durability of concrete structures is one of the most important issues. Hence, regional investigations are necessary for durability-based design and evaluation of the models proposed for service-life prediction. The Persian Gulf is one of themost aggressive regions of the world because of elevated temperature and humidity as well as high content of chloride ions in seawater. Corrosion of reinforcement due to chloride ions attack causes enormous damages to structures in severe condition of marine environments. Normally, high alkaline property of concrete (PH≈13) forms a protective oxide layer on the steel surface. This is called a passive protection. The dioxide existing in the atmosphere or the chloride in the concrete environment along with the moisture and the oxygen can penetrate via the concrete pores and cracks and can reach the armature surface; then, by reducing concrete alkalinity, they cause armature corrosion inside the concrete by destroying the protective oxide layer on the steel. Chloride ions reach the passive layer according to the explained pattern and they begin to react in the passive layer when the amount of chloride ions go beyond the critical value and cause perforation corrosion. Since each influencing factor in the life time of the structure is subject to random variability and inherent uncertainties, a stochastic approach is utilized to predict the time for initiation of the corrosion. Based on Fick’s law, time for corrosion is a function of surface chloride, critical chloride, concrete cover thickness, and diffusion coefficient. The most common models service-life prediction of reinforced concrete structures under load chloride, only produce a limited definite time for the start of corrosion. In this paper monte carlo simulation use for service-life prediction of reinforced concrete structures of predict the time of corrosion initiation, and shown the influence of mean and standard deviation variations for each of the parameters that affect the occurrence of corrosion, on the time of initiation corrosion and impact of these factors on the probability initiation corrosion.

Today is a common method of seismic design of structures in the regulations are based on the static method equivalent and Determine the base shear design by using The linear spectrum. To determine the base shear, a coefficient called earthquake coefficient is used. In this article first, Methods of calculation and factors affecting the behavior of factors are investigated. Then a number of steel structures with lateral load systems MRF and CBF, with the number of floors 3, 7 and 10 Irregular on the plan is evaluated. By performing a non-linear static analysis under the influence of lateral loads، Ductility and their coefficient of resistance in different angles Due to the limitation of local ductility in structural elements (Based on maximum drift) and finally the behavior coefficients (Given the values obtained from the analysis) will be counted. It is assumed that the angular behavior coefficients follow a rectangular rule so that the values of the angular behavior coefficient with the length of the line from the origin with the desired angle in a rectangle whose sides are the coefficient of behavior of the main structure of the structure is equal. Then, the values of the angular behavior coefficient obtained from this rule are compared with the values obtained from nonlinear static analysis. According to the results, it is also observed that the angular behavior coefficients obtained from this type of analysis are slightly higher than their values from the rectangular base, and follow this rule well. As well as structures at these angles relative to the main directions shows better behavior.

Aggressive marine environments and tidal conditions due to chloride ions attack and subsequent wetting and drying concrete, lead to excessive corrosion of reinforcing steel that creates destruction. Simulating behavior of corrosion can be effective in reducing the damage, regional investigations are necessary for durability-based design and evaluation of the models proposed for service-life prediction. In this paper Monte Carlo simulation use for service-life prediction of reinforced concrete structures in tidal zone. This study evaluates the influence of mean and standard deviation variations for each of the parameters that affect on the time of corrosion initiation. In tidal condition that studied in this paper, in the case of 10 mm convection depth with respect to non tidal zone, the service life of the structures decrease about 15 years. So it is found the effect of corrosion occurrence to standard deviation of concrete cover that must be noticed in constructions of marine structures.