نشریه مهندسی سازه و ساخت
سال نهم شماره 7 (پیاپی 60، مهر 1401)

With the increasing urbanization and expansion of cities, the implementation of development plans and proper implementation of urban projects that meet all aspects of urban life and the needs of citizens, is an inevitable necessity. In urban projects, as in other construction projects, the success and satisfaction of all stakeholders is the most important thing in project management. The purpose of this study is to evaluate the development projects of Karaj and provide solutions for their better and more appropriate implementation. Therefore, a researcher-made questionnaire was prepared based on the components extracted from previous studies and distributed among civil engineering experts in Karaj Municipality. The data were used using one of the new decision-making methods based on the mental characteristics of decision-makers. Risk management criteria have been analyzed. The results of the study showed that among the risk factors in urban development projects, the factor of financial and economic resources as the most effective and the factor of rules and regulations as the weakest factor in the success of construction projects from the perspective of risk-averse managers. Using Friedman test, among the 10 areas of the American Project Management Standard, cost management with a coefficient of 8.24, time management with a coefficient of 8.15 and integration management with 7.75 were recognized as the highest areas of knowledge. Finally, by identifying and ranking the risk factors, a model with detailed solutions for the success of urban development projects is presented.

The acidic and corrosive environments have necessitated the need for more research on the new concrete that uses cement or aggregates substitutes in their mixing design. The use of waste tires in concrete as part of concrete aggregates has been evaluated and researched in recent years. In this paper, the strength and permeability of concrete containing crumbed tires exposed to sulfuric acid were investigated. For this purpose, 5, 10, and 15% of the sand of the concrete mixing design were replaced with the crumbed tire. After making the concrete, the samples were cured in standard conditions for up to 7 days and then placed in water containing 5% sulfuric acid to continue the curing. The compression strength and water penetration depth tests were performed on the samples at 28 and 90 days. Although the compressive strength of the samples has decreased with increasing the percentage of crumbed-tire, the percentage of crumbed-tire has not had much effect on the amount of difference due to changing curing conditions. The permeability of the concrete increased with increasing the percentage of crumbed-tire and also the samples stored in sulfuric acid showed more permeability. Permeability increased by 13% by changing the curing environment to sulfuric acid.

In this paper, the main purpose is to investigate the behavior of a reinforced section with vertical stiffeners and circular stirrups of Concrete filled double-skin steel tube (CFDST) columns under cyclic and fixed axial loading. So, the proposed reinforced section with a simple section (not reinforced) in this type of columns with a length of 200 cm has been loaded and examined in the structural laboratory and then modeled in ABAQUS software and their displacement- force cycle diagram has been extracted. In this research, by designing a new reinforced cross section of this type of columns and comparing it with a simple cross section, the improvement of seismic behavior of this type of columns, including ductility, bearing capacity, and energy absorption capacity, has been investigated. To ensure the accuracy of finite element modeling, the results of numerical analysis were compared with laboratory results and the modeling accuracy was also ensured. In addition, the column with reinforced cross section has a significant improvement in its cyclic behavior compared to the simple cross section of this type of column, so that vertical stiffeners and circular stirrups prevent a sharp drop in column strength after the outer wall of the steel pipe deteriorates.

Regular structural systems have been designed based on supplying sufficient ductility in seismic events, which lead to considerable permanent deformation after major earthquakes. Buildings with Large permanent deformation usually are unusable or require extensive repairing. Therefore, low damage structural systems are recently focused. The present study aimed at introducing a new self-centering structural system having frictional sliding in their braces. It is compared with common dual steel moment frames. In the proposed system, post-tensioned cable is used in beam to column connections to provide self-centering. The frictional sliding connections in the braces are utilized as well, to provide energy dissipation capability for the system. Connections are modeled in OpenSees software and validated using previous experimental results. Then, Incremental dynamic analyses are carried out on some frame models under some real earthquake records. Then, their fragility curves are achieved for different performance levels and compared with those of regular dual systems. The results indicate that supplying post-tensioned cables and frictional sliding connections in dual moment frames, reduces the inter story drift, permanent relative displacement and vulnerability of the frames. Therefore, construction of such system for new buildings is recommended, regarding its high performance in earthquakes and repairability after intensive seismic events.

Numerous advantages of concrete-filled steel tubular (CFST) columns have led to the widespread of such column sections in highly important specific structures such as high-rise buildings, piers, and bridges in recent years. The major drawback of CFST columns is the uncoated steel tube, causing the loss of concrete confinement and sudden strength decline against external loads exerted on the steel tube such as impact, explosion, fire, and so on due to the weakness of it. A novel upgraded section designed and introduced using the internal steel mesh, acting as a double-skin tube along with the external steel tube to prevent the destruction of the concrete core and sudden decline of column load-bearing capacity by the internal steel mesh when the external steel tube was destructed. The columns with the newly designed section and those with the conventional section were tested under axial and seismic loads. The experimental results were validated by the results of the nonlinear finite element analysis of the columns. Other columns were modelled using different internal steel meshes, and the results were compared. In the novel section proposed for the CFST columns, concrete core confinement was improved by the internal steel mesh, leading to an increase in the load-bearing capacity and progressive collapse duration of CFST columns against sudden loads such as impact and fire. The results of the research confirm a significant increase in the strength and ductility of the upgraded sections compared to the usual sections.

Dynamic shear stiffness is a key parameter for determining the soil behavior for site analysis under strong ground motion. The dynamic shear modulus reduces during cyclic loading due to the loss in the soil shear strength. Besides, the soil behavior depends on the loading direction due to the anisotropic nature of the soil. Thus, the anisotropic shear stiffness should be determined for accurate modeling of the soil in the models able to incorporate the anisotropy to estimate the soil's behavior. The models based on the dissipated energy are appropriate for determining the model parameters at different loading conditions. In this study, the shear stiffness of dense Babolsar and Toyoura sands obtained from torsional shear apparatus have been compared, and the effect of major principal stress has been evaluated. The specimens were similarly prepared to the relative density of 75% and then isotopically consolidated before shearing. The shear stress was applied in a stress-controlled manner under a unique deviator stress ratio but at different major principal stress directions. The variation of shear stiffness under different loading direction were evaluated. Results indicated that the major principal stress direction has a significant influence on the dynamic shear stiffness. On the other hand, a unique relationship for the evolution of shear stiffness can be obtained using the dissipate energy approach.

Today, extensively eccentrically braced structures are used to absorb seismic energy using link beam elements on beams. The function of this system is defined as yielding this beam elements during an earthquake and remaining safety and elastic of other structure elements. The length of the link beam is expressed as an effective parameter determining the type of behavior of it as shear or flexure, which determines the seismic performance and the amount of seismic energy absorbed by this element in this type of braced frames. In this research, using incremental dynamic analysis on steel frames under far field records and by performing modeling steps in Python version 3.8 and using of OpenSeesPy documentation, the variables of failure and frame reliability have been investigated. In this research, two samples of 6 and 12-story frames with changes the link beam length from 0.4, 0.6 and 0.8 m have been studied. The results show that the behavior of link beams is affected by the characteristics of the earthquake record and the capacity of the link beams with the same length is various for each record. The results of incremental dynamic analysis on the mentioned frames with different link lengths have shown that the length of short shear link beam in medium height frames has resulted in better seismic behavior and the optimal length of the link beam should be selected after seismic evaluation under different records. The maximum acceleration of the median collapse in this research has been obtained for 6-story frames and the link with 0.6 m length is 5.10, and for 12-story frame with the link of 0.6 m length, 4.20 times the acceleration of the earth's gravity.

Chloride ions cause the most common corrosion, so chloride ions can enter the concrete through contaminated aggregates and additive materials or infiltration from external sources, such as seawater. If the concrete is exposed to the aforementioned ions, there will be severe loss of durability and expansion of corrosion. In this case, there will be a tangible effect on the development process of resistance reducing the concrete's strength. Therefore, the extant study was conducted to compare the effect of fly ash and micro silica on the development, compressive strength, and electrical resistance of concretes exposed to chlorinated waters. The plans of this study included two types of ordinary concretes and concretes containing pozzolanic material. Concrete mixing plans in chloride medium were divided into 11 groups, which included 8 plans with substitution of micro silica and fly ash powders with different percentages in exchange for cement. The first group included no additive material as a cement substitute and included one plan as the base plan. Accordingly, 81 plans that each consisted of 4 samples were constructed and examined to test compressive strength in 7, 14, 28, and 42-days ages (N=324 plans). According to the results of laboratory samples in chloride medium, there was an increase in the development process of compressive strength, and electrical resistance of concrete while using concrete with standard aggregates reinforced with micro silica and fly ash by selecting the optimal mixing plan and lower cost. The above mentioned case was cost-effective for project implementation.

 In the FEMA-P695 report, there is an applied method for evaluating the collapse of structures designed by seismic regulations under the most severely expected earthquake, in which the collapse of special concrete frames without considering the effect of soil-structure interaction is studied. In this study, soil-structure interaction analysis is used directly to evaluate the seismic performance of buildings. For this purpose, 4 and 8-storey reinforced concrete buildings with special bending frame system, on medium (D) and soft (E) soils classified according to ASCE7-10, have been modeled and analyzed by Opensees software. Incremental dynamic analysis has been used to accurately evaluate the collapse performance of the frames for both rigid base and flexible base. The results of the analysis show that the soil- structure interaction, especially with softer soil and increasing the number of building floors, can play a key role in the behavior of building frames including increasing system period, reducing floor drift, increasing performance and changing probability collapse of the structure. On the other, the results at first glance show an increase in the probability of collapse for frames placed on flexible supports at the same spectral acceleration, but using the modified flexible fragility curve, it is observed that the soil-structure interaction reduces the likelihood of collapse. Therefore, not considering the soil-structure interaction leads to unrealistic evaluation of the performance of structures.

The use of pozzolans to make concrete with suitable and durable mechanical properties has found a special place in the last decade; because the use of these materials reduces the consumption of cement and consequently reduces environmental pollution. In the meantime, knowing the optimal amount as well as the effect of pozzolans has been an important and challenging aspect that many researchers have focused on. In this study, an attempt was made to make concrete with suitable mechanical properties using three types of high-consumption pozzolans, namely microsilica, rice husk ash and furncae slag. The compressive strength of 7, 28, and 90 days, as well as the three-point flexural strength of the experiments, was performed separately and in combination to investigate the effect of the use of these pozzolans. In this study, a wide range of alternative values of pozzolan was considered so that in addition to knowing how these pozzolanes are affected, the optimal percentage for each of the pozzolanes used can also be determined. Experimental results have shown that the effect of using microsilica separately from furncae slag is more severe. In addition, the effect of the utilization of pozzolans in combination is positive in improving the compressive strength of concrete specimens and only reduces the compressive strength at an early age. With the exception of samples containing low levels of pozzolan, other specimens cause a decrease in compressive strength at an early age. The potential for pozzolans can be an important factor in reducing resistance to overus. The electrical resistance of concrete samples containing pozzolan was higher than the control specimen, which indicates a denser structure of concrete at the age of 90. The proposed artificial neural network based on the experimental data was able to predict the compressive strength of concrete containing different pozzolan in various ages.

Evaluation of maintenance system in the building is one of the key factors in improving the quality of maintenance and repair processes. It can be stated with certainty that all buildings need maintenance and scientific and technical repair after construction, and therefore how to define this system and determine the appropriate indicators and strategies for it will play an important role in the cost and longevity of the building during operation. The purpose of this paper is to identify and prioritize the indicators affecting the maintenance and repair system (R&M) of Residential buildings and determine the most appropriate policy related to it using a combination of multi-criteria decision-making method. In the presented method, first the weight of the indicators was calculated and then the indicators were prioritized based on multi-criteria fuzzy and non-fuzzy decision-making methods.Finally, considering the ranks obtained from those methods, the final ranking of indicators was calculated using the Average rating and Copeland method. The results showed that the indicators of safety, health, accessibility and proper utilization are in the highest priority respectively and reliability are in the last rank. This issue indicates the importance of safety indicator in evaluating the maintenance and Repairs system of buildings. in order to perform maintenance and repair operations, by identifying and prioritizing effective indicators, they can be used to evaluate the maintenance and repair system of the building based on them.Finally, according to the results and with the help of ARAS method, Breakdown Maintenance Strategy was selected as the most appropriate maintenance policy for buildings.The results of this study show that the application of multi-criteria decision-making methods can help the construction industry professionals to select the key effective indicators in the repair and maintenance system and determine appropriate strategies. Finally, suggestions for future research were provided.

One of the most important components in steel structures is their joints. It is a matter of correct design of steel members, especially fittings. Since the beam flange is not connected to the column flange in the side plate connection system, all the vulnerabilities and uncertainties of the brittle behavior of conventional joints that in the full penetration welding behavior of the beam flange to the column wing are eliminated. Today, the use of composite sections filled with concrete has been widely considered in many structures. One of the steel joints that has been proposed in the past years is the use of side plates, which to some extent guarantees the linear behavior of the connection spring. In this research, the behavior of side joints with side panels in composite steel and concrete frames has been investigated. Thus, after ensuring the modeling process by validating a steel connection in Abacus software, a U-shaped steel beam composed of a CFT column with a side plate is modeled and parameters has been investigated.The effects of compressive strength of concrete were also investigated. The results showed that except for the diameter of the screws, other factors affect the strength, hardness and ductility . Increasing the width of the plate has increased the strength, stiffness, ductility and energy absorption. By decreasing the d / t ratio of the column, the strength, stiffness and energy absorption are increased and the ductility is reduced. As the compressive strength of concrete increases, the amount of strength, stiffness, ductility and energy absorption increases. The arrangement of the screws, the diameter of the screws, the d / t ratio of the beam and the addition of the thickness of the side plate do not have much effect on the strength, stiffness and ductility and energy absorption of the joint.