جستجوی مقالات مرتبط با کلیدواژه "concrete structures" در نشریات گروه "عمران"

Building and their related activities are important sources of the environmental pollutants, regarding the fact that during the process of building and materials manufacturing a considerable amount of carbon is produced and disposed to the atmosphere. Virtual carbon footprint related to this industry is not confined to the process of building and manufacturing, it actually includes the operation time and dismantling too. In this study, the per capita energy consumption and the carbon footprint of three buildings in Mazandaran province during one year of operation have been estimated and compared with each other. So, a house, two-story, and five-story apartments with the same structure in Babolsar have been modeled in Design-Builder, and energy consumption and carbon footprint during one year of operation have been assessed comparatively. The results of modeling indicate that along the one-year operation of the house, two-story and five-story apartments, 8490, 4878, and 4881kg carbon (kg per occupant) have been produced and released into the atmosphere. Furthermore, the per capita, energy consumption of the house has been estimated more than those of apartments significantly, and this fact illustrates a vast difference between the detrimental effects of houses and those of apartments during operation time on the environment.

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.

Increasing study and research on the components of concrete structures has led to the availability of materials, the use of which in turn has been able to have a tremendous impact on concrete production. Concrete is undoubtedly the most important building material, the production and consumption of which is increasing day by day and it is used in almost all structures. The performance of cement as one of the main components of concrete products has always been considered and with the increasing development of Iran's cement industry in terms of quantity in the production of cement, cement quality control by examining physical and chemical properties is very important. In this study, we tried to investigate the factors affecting the strength of hydrated cement used in concrete structures in Shiraz and the results indicate a decrease in concrete strength due to increasing the ratio of water to cement and also C3S and C2S are the two main compounds causing cement strength are hydrated.

The aggregates as a prominent part of concrete mixture have significant impact on durability and strength of concrete. One of the most important problems attributed to some part of aggregates in Iran are reported to possibly deleterious alkali silica reaction between the hydroxyl ions (OH−) in the pore solution and reactive silica in the aggregate over the time. So, investigation of alkali-silica reaction potential for aggregate in this area is so invaluable because of high consumption of these suspicious materials in the construction of varied hydraulic structures.In present study, alkali silica reactivity of aggregate in a number of mines in West of Iran including Zanjan, Kermanshah and Kordestan province has been investigated comprehensively. In this regard, in order to evaluate alkali silica reactivity of aggregates, petrography examination of aggregate according to ASTM C295, alkali silica reactivity mortar bar testing according to ASTM C1260 and determination of length change of concrete due to alkali silica reaction according to ASTM C1293 was used. Based on results obtained in present study, it was concluded that alkali silica reactivity was observed at a number of aggregates placed in every three studied province and in order to using of these aggregate at concrete structures exposed to water, preventive action including using low alkali cement or pozzolan could be useful.

Identifying and examining the types of cracks in concrete structures is one of the challenging engineering issues. Detection of crack bifurcation is very important because it detects high-intensity surfaces in concrete structures. In this paper, a new architecture based on convolutional neural networks is presented for crack classification in concrete structures. The proposed architecture detected and classified crack bifurcation in less time and with higher accuracy than other conventional and authentic deep learning architectures. In this paper, the cracks in 12000 images of concrete structures were investigated by the proposed algorithm, which resulted in 99.3% accuracy in categorizing as non-cracked images, images with simple cracks, and bifurcated crack images. Moreover, the analysis of the confusion matrix showed an accuracy of 99.3% and a recall of 99.5%, which confirmed the proper performance of the proposed algorithm. The sensitivity analysis of the proposed algorithm also showed the need for proportionality between the number of data, the number of neurons in the fully connected layer, execution time, and the expected percentage of accuracy according to the application of the problem.

One of the most important issues for engineers regarding concrete structures has been the greater stability of these types of structures. Most reinforced concrete structures deteriorate over time due to environmental conditions or the impact of external loads on them, such as earthquakes, traffic loads, explosions and other sources that cause vibration in the structure. Structural damage causes adverse changes in the performance of the structure. Therefore, monitoring the health of structures and diagnosing their damage in the early stages has always been one of the topics of concern. Due to the destructive factors and Deterioration of concrete structures, it was necessary to address the set of factors that cause partial and general damage to the structure, and to provide solutions to address these problems. These factors include: improper design of the structure, overloading on the structure, cracking, improper substructure, fire and corrosion of rebars, which are among the mechanisms of causing damage in concrete structures. In this article, an attempt has been made to review each of the mentioned factors and provide appropriate solutions to increase the life of concrete structures and reduce the effects of destructive factors.

In this paper effects of the placement of various stiffeners and opening on the interaction behavior of steel plate shear walls and precast concrete frame, has been investigated. Steel plate shear walls has been bolted to concrete frame, by use of embedded plate in boundary concrete elements. Push over and dynamic analysis under seven earthquake acceleration in ABAQUS software, was done.
The results showed that the proposed connection, by keeping up its stability and strength, showed appropriate function in the route of load bearing of shear wall. Also it was observed that adding steel plate shear wall to concrete frame increased initial stiffness, base shear and dissipated energy 4, 4.3 and 340 times, respectively. The sample with opening in diagonal line and horizontal and vertical stiffeners, had maximum dissipated energy (22% increased). This sample showed the maximum relative displacement (increased 2 times) and minimum base shear force (decreased by 10%). Adding horizontal and vertical stiffeners to simple sample, increased dissipated energy by 16% while, the sample with diagonal stiffeners decreased dissipated energy by 25%. This model showed the minimum relative displacement (decreased by 15%) and maximum base shear force (increased by 7%). Placing the opening at the middle of sides in this model, increased dissipated energy by 35%.

The buildings structures around the world suffer from terrorist attacks and bombings. This justifies the need to study the effect of blast loading on structures and the methods to prevent collapse of structures in order to save human lives and minimize financial losses. In this study, effects of the passive viscous dampers and base isolators on structures which are subjected to blast loading are separately investigated. Blast load is applied on the structures with a pressure wave. This pressure wave has many uncertainties specified in different codes. For the sake of simplicity, this pressure wave is applied on different faces of the structure. Herein, only loading on the fa\c{c}ade or the structure is considered and the loading on the other faces of the structure are neglected as the structure doesn't have any severe irregularities. In the 1st case, viscous dampers are added to the structure adding damping of the structure between 5 to 25\% and the effect of this added damping is studied through the paper. For the 2nd case, base isolators are designed according to UBC-1997 code. Numerical simulations are carried out in the SAP environment using nonlinear time-history analysis. Moreover, they are studied with different stiffness coefficients and the uncertainties in yielding force of these tools have been considered in numerical simulations. These passive control devices are mainly designed such that they can perform well under earthquake loads. Viscous dampers conform to the first mode of vibration of the structure and base isolators are designed according to seismic codes. Numerical simulations show that base shear in the optimum specifications of viscous dampers and base isolators compared to bare frame showed 60\% increase and 50\% decrease, respectively. However, drifts are minimized to 1.7\% for added damping values of 25\%. This value is hard to reach with base isolators as the values of drifts in this case have a minimum value of 2\%.

Buildings in high seismic regions are prone to severe damage and collapse during earthquakes due to large lateral deformations. The use of superelastic shape memory alloys (SMAs) as reinforcements in concrete structures is gradually gaining interest among researchers. the effect of SMAs as reinforcement in concrete structures is analytically investigated for 3, 6 and 8-story reinforced concrete (RC) buildings. Each building has five bays in both directions with the same bay length of 5m. For each concrete building, three different reinforcement details are considered: (1) steel reinforcement (Steel), (2) SMA bar used in the plastic hinge region of the beams and steel bar in other regions (Steel-SMA), and (3), beams fully reinforced with SMA bar (SMA) and steel bar in other regions. For each case, columns are reinforced with steel bar. Results obtained from the analyses indicate that the value of Sa in Steel-SMA frames are higher than SMA frames, and its recovery capacity is almost similar with SMA frames. the SMAs materials are expensive, and the use of Steel-SMA frames can be reasonably effective in seismic zones. The comparison between frames with various reinforcements details shows that Sa of 3-story frames with various reinforcements are almost identical. but, in 6- and 8-story frames, Sa of Steel frames are higher than others. frames with SMA bars in the all length or plastic hinge region of the beam have reached a same level of seismic demand under lower spectral acceleration which can be resulted from the decreased stiffness caused by SMA bars. results indicate that structural behaviour factor in 3 and 6 story buildings with different types of reinforcement is not much change, but this change is perceptible in the 8-story frame. In the case of residual drift in all cases, the use of shape memory alloys will reduce this drifts.