نشریه مهندسی سازه و ساخت
سال دهم شماره 6 (پیاپی 71، شهریور 1402)

The purpose of this research is to reduce cement consumption by replacing nano fly ash (NFA) in the concrete mixture and increase the compressive strength of concrete by strengthening the interfacial transition zone (ITZ). Thus, four proportions of NFA with values of 0.1, 0.5, 1 and 5% by weight were selected in the concrete mixture and the compressive strength of concrete was evaluated within 7 and 28 days. A scanning electron microscope (SEM) equipped with an X-ray energy diffraction spectrometer (EDS) was used to detect the compounds resulting from the reaction between particles. Based on the results, in the sample containing 1% NFA (optimal sample), compared to the samples without NFA, the 7-day compressive strength of concrete increases by 97% and the 28-day compressive strength increases by 61%; which shows the NFA has a better performance in increasing the strength of concrete at early ages. Also, the amount of water absorption in the sample containing 1% NFA decreased to 33%, therefore, the permeability of concrete against destructive agents is improved. These results show that the interfacial transition zone (ITZ), which is the weakest link in the concrete chain and the limiting factor of concrete strength, is strengthened in the presence of NFA, and leads to an increase in durability and compressive strength of concrete.

Cost is considered as one of the main challenges for each project manager in the construction industry and one of the criteria that measure the success of the project is the comparison between the cost of the project with the planned budget at the beginning of the project. For this purpose, an accurate forecast in the early stages of the project can greatly assist the decisions that are taken in the feasibility phase. This accurate cost estimate will help us choose the best implementation systems in different parts of the building according to the budget we plan, and avoid the options that may not lead to our main objectives in the project. in this study, we intend to design a model to predict the cost of construction in a feasibility stage using artificial neural network (ANN) as one of the tools of artificial intelligence field, whose error is less than traditional methods and calculation time is much faster than methods such as bottom-top cost estimation. for this purpose, we have identified the most important factors that affect construction cost by experts in housing investment group and then we have collected data from the past projects. In the next stage we have used MATLAB program to build the construction cost estimation model using ANN based on data gathered from past projects on housing investment group. In the end, the model based on the obtained results has a precision of 89.56 %. Finally, a graphic user interface is designed as an EXE. file, which facilitates the use of the model for users to estimate the cost of new projects and eliminates the need for a MATLAB application to use the model.

Studies on behavior of structures under the effect of earthquakes in the near-field earthquakes, compared to far-field earthquakes, have shown more effects of this type of earthquake on the structure. Most of these effects depend on the characteristics of forward-directivity and flip-step with permanent displacement effect. The characteristics of near-filed earthquakes should be considered in the design and analysis of structures. The present research, aimed to investigate the effect of directivity characteristics of near-field earthquakes on the response of concrete structures. To this aim, first the different records of ChiChi earthquake in different stations have been determined as the basis for selecting accelerograms. Then, using analytical methods, the response spectrum of these records, considering the effect of forward-directivity and without it (removing dominant pulses) in the east-west and north-south directions was determined. Next, using time history analysis on two concrete structures of 10 and 15 stories, the drift (relative displacement) and the inter-story base shear in the structures was investigated for seven records of ChiChi earthquake. The results showed that due to the unpredictable nature of the earthquake, the drift and base shear responses of stories in both structures have been increased or decreased in different directions in some cases. Therefore, it can be seen that directivity does not always have a uniform effect on the behavior of the structure and does not follow a fixed pattern. Also, the results showed that by increase in the height of the structure and as a result of increasing its period, the effect of forward-directivity on the response of the structure increases. This is despite the fact that in many cases of shorter structures, the directivity does not have much effect on the response of the structure and even in some cases; it has caused a decrease in the response.

Today, the production of high-quality construction materials with low production costs is one of the needs of the construction industry. By using geopolymerization technology, it is possible to produce construction materials such as mortar, concrete, and geopolymer bricks with high mechanical strength and desirable quality. One of the aluminosilicate minerals that can be used to produce geopolymeric adhesive material is laterite. To improve the mechanical strength, durability, and physical characteristics of the geopolymer product, its reinforcement using different fibers such as glass fibers has been considered by various researchers. In the current research, using laboratory tests, the effect of reinforcing geopolymer mortar based on laterite powder using glass fibers was studied. The alkaline solution containing 6, 10, and 14 M sodium hydroxide was used to make samples of geopolymer mortar with laterite powder, without and containing glass fibers after 5 minutes of complete mixing, The samples were poured into 50 × 50 × 50 mm wooden molds and 40 × 40 × 160 mm prism molds and vibrated on a vibrating machine. After processing for 3 days in the greenhouse, the compressive and bending strength of the geopolymer samples as well as the water absorption percentage of the samples were measured. The results showed that the concentration of activating solution and glass fibers has a significant effect on the compressive and bending strength of geopolymer samples based on laterite powder with glass fibers. According to the obtained results, the increase in 3, 7, and 28 days compressive strength of geopolymer samples containing fibers varies between 10.9 and 47% compared to geopolymer samples without fibers. According to the results of this research, it is recommended to make geopolymer building materials based on laterite powder containing glass fibers with relatively high strength.

Because of the development of wind turbine farms in seismic areas, such as East Asia, southern Europe, and the United States, as well as the importance of the foundation of the wind turbines in the design and implementation, it is necessary to study the seismic behavior of wind turbine foundations. In this study, the seismic behavior of monopile foundation of a simplified offshore wind turbine model under a specific earthquake record was evaluated by using finite element method in OpenSees software. At first, the proposed numerical model was validated by the results of a dynamic centrifuge modeling of a steel pile located in sandy soil. Then, the effects of various parameters such as dimensions of monopile (diameter and length), soil relative density, end bearing pile effect and wind load effect were evaluated. The results of this study showed that the changes of these parameters have significant effects on the seismic behavior of the monopile of offshore wind turbines. Increasing dimensions of monopile (diameter and length) and soil relative density improves the seismic performance of the structure and foundation system and reduces lateral displacement at the top of tower and reduces settlement and rotation of the monopile. Chang of behavior of the monopile from frictional pile to end bearing pile, improves the behavior of the wind turbine structure and foundation under seismic loading. Also, wind loading causes more displacement and rotation to the structure, and static wind load creates more critical conditions than the dynamic wind load.

In this article, seismic vulnerability of one of the ancient monuments ‎in Iran, Falakol aflak Castle, located in ‎Lorestan, is evaluated. In this ‎regard, by conducting field surveys, the damages in different parts of ‎the ‎building were categorized. The results of these investigations ‎indicated erosion and cracking in the ‎construction of the building, ‎settlements of parts of the building that caused cracks in some parts ‎of the building, ‎and rising dampness due to the presence of water ‎flow in the foundation of the building. Next, by modeling the ‎building ‎in Abaqus software, the seismic vulnerability of the building was ‎studied through incremental analysis. The ‎results of this analysis ‎indicated the vulnerability of different parts of the building, which ‎indicated the necessity of ‎presenting a seismic improvement plan. By ‎using in-situ piles and micro piles in the soil as well as vertical ‎reinforced ‎cores in the walls, the results of numerical analysis showed ‎that a significant improvement in the seismic ‎performance of the ‎building has occurred. The intensity of the original maximum plastic ‎strains and its extent were ‎much less compared to the unretrofitted ‎building. Also, the force-displacement diagrams of the building in ‎different ‎directions indicated a significant decrease in the ‎deterioration of the building's stiffness, which indicates the ‎reduction ‎of its vulnerability due to the addition of the proposed improvement ‎system. ‎

In many practical applications of structural reliability analysis, one of the preferred sciences is the sensitivity analysis of failure probability based on design parameters under the limit state function. This information is needed, for example, in design optimization based on reliability. The design parameters are calculated by first- and second-order reliability methods FORM\SORM to sensitivity analysis of the probability of failure approximately. Therefore, in many cases, these methods are very inaccurate or difficult to solve problems. Accordingly, the Monte Carlo simulation method is very useful for determining the reliability sensitivity parameters. The derivation probability of failure into the parameters of the limit state function is calculated by integrating the surface of the performance function. By using the Monte Carlo simulation to determine this integral will not be efficient due to the small portion probability of failure and will have a high computational cost. Hence, some methods can be used to estimate Monte Carlo simulations that reduce the computational cost. One of these methods is linear sampling method. In this paper, an approximate method is used to determine the surface integral in terms of a domain integral. The integration domain can be calculated using standard Monte Carlo simulations or importance sampling simulations. This article presents two practical examples of sandwich panels to determine the effectiveness of parameters random variables are used in the design.

Composite prestressed joist floors are one of the economical roof systems, which are increasingly used in Iran. In this research, the composite behavior of prestressed joists in composite joist floors has been experimentally evaluated. What can prevent the composite behavior of the prestressed joist and the in-situ concrete slab is the lack of proper transfer of horizontal shear at the contact surface of the prestressed joist and the in-situ concrete. In prestressed joist floors, unlike truss joist floors, it is difficult to install horizontal shear reinforcement between precast and in-situ concrete. This research was carried out in two stages and in each stage the final load as well as the cracking load and moment were evaluated. In the first stage, two prestressed joist samples were tested and the quality of the joists was ensured by matching the laboratory results and the calculated values. In the next stage, samples of composite joist slabs without horizontal shear reinforcement and with the proposed shear reinforcements were made and tested in the laboratory. Based on the results, the slab samples without shear reinforcement were able to resist the fast laboratory loading up to the calculated load based on the bending strength, but they almost immediately suffered brittle failure due to horizontal shear slip, which makes their use under long-term loading in the structure problematic. The proposed reinforcements were able to improve the composite behavior of the joist and in-situ concrete by improving the horizontal shear strength and improve the bearing capacity of the slab up to 27 percent.

In this article, the analysis of a simply supported viscoelastic Bernoulli beam under a dynamic transverse loading combined with a compressive axial load was discussed. The applied dynamic transverse load was considered a non-harmonic load with an exponential decreasing function over time, and the applied axial load was considered constant compressive. This study investigated the effect of a specific decreasing transverse load and introduced, formulated, and proved the phenomenon of non-harmonic resonance of the viscoelastic beam, for the first time. The stress-strain relationship of the linear viscoelastic material was expressed according to the Boltzmann integral law. The relaxation function of the viscoelastic material was defined based on two terms of the Prony series. The displacement field was approximated by the product of two functions, a known spatial function and a time function with unknown coefficients. Using the principle of virtual work, the formulation of the viscoelastic beam was extracted. Then, utilizing the Laplace transform, the unknown coefficients of the time function were calculated. Finally, the displacement field of the viscoelastic beam was expressed in the time and space domains. To validate the results, Abaqus software was used for beam modeling. In the numerical results section, the effect of different viscoelastic material parameters and different loads on the displacement of the viscoelastic beam was investigated. Also, the occurrence time of the non-harmonic resonance, and the ratio of the maximum displacement at the resonance time to the displacement at time zero were calculated

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.

Today, a huge amount of data is transmitted around the world through the high capacity of optical telecommunication networks. In railways, optical transmission telecommunication networks play a very important role in the transmission of vital rail data and the safety of movement. Reliability stability of telecommunication infrastructure is essential in increasing productivity, maintaining safety and reducing maintenance costs. In this article, the existing reliability level and all relevant parameters (the number of network outages and the duration between network failures, MTBF) of the railway optical transmission telecommunication network to obtain the number of blocked railway lines through the block diagram method (Reliability block diagram model) created and simulated through the Monte Carlo method and then optimized with the aim of reducing line blocking, considering that with each network failure, rail lines are blocked, the number of network outages is equal to line blocking. Therefore, with optimization, the reliability of the line blocking network is reduced. Also, predicting the behavior of the network and obtaining the probability of its failure is done through perceptron three-layer neural networks and its results are presented. The network implemented in this article is an optical telecommunication transmission network. The railway zone of Azerbaijan is 654 km long.

Self-compacting composite concrete is known as a cement composite with high performance and adhesion. This composite has a lot of psychological capability and efficiency. Concrete failure depends on the formation of cracks and microcracks. As the load increases, the microcracks join together to form cracks. To solve this problem and also to create homogeneous conditions, in recent years, thin fibers of fiber in the entire volume of concrete are used. Fiber concrete is actually a type of cementitious composite that increases its tensile and compressive strength by using reinforcing fibers inside the concrete mix. In this study, the effect of adding materials (Microsilica Fume, Fly Ash, GGBFS) and sinusoidal steel fibers (corrugated) on the mechanical properties of self-compacting cement composite was investigated in 9 mixing designs. For this purpose, cement alternative additives in the amount of 10% by weight of cementitious materials and steel fibers in the amount of 1% of the volume of cement composite were used in the mixing design. In the compressive strength test, the sample with 1% steel fibers had a 4.5% increase in strength compared to the reference sample, which showed a very low effect of steel fibers on the compressive strength. Also, the use of microsilica by 10% by weight of cement substitute increased the amount of compressive strength by 6.6%, which due to the property of microsilica in increasing resistance, this result was not far from the eye. In general, the use of steel fibers had no effect on the results of compressive strength, capillarity, and water absorption, but the changes in other test results compared to the reference sample were quite noticeable and expected due to the use of steel fibers.