Journal of Civil Engineering Researchers
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Numerical Development of a Re-centering Damper with High Seismic Performance, Including Friction Wedges and SMA Rods
Re-centering dampers, developed using shape memory alloy (SMA)-based dampers and their superelasticity capability, absorb earthquake energy and provide a re-centering capability for the structure. In this study, the laboratory sample of Zhang's re-centering damper was first validated using ABAQUS software, followed by parametric analysis involving changes in the number and diameter of SMA rods, the friction coefficient of the wedges, and the placement configuration of two dampers, which were numerically investigated. The results indicated that increasing the diameter and number of rods, as well as the friction coefficient, enhances seismic resistance and stiffness but reduces ductility; excessive increase in friction only boosts the stiffness and ductility of the damper's compressive section while reducing seismic resistance. A friction coefficient of approximately 0.12 is recommended, whereas Zhang assumed 0.09. Additionally, the results showed: in parallel configuration, resistance and stiffness are higher but ductility is lower, whereas in series configuration, all three parameters decrease.
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Numerical investigation of a steel frame braced with a central-cylinder cable system using shape memory alloy
Conventional steel braces increase the risk of structural damage during earthquakes due to compressive buckling. In this study, the performance of a steel frame equipped with a memory alloy cable brace with a central cylinder is investigated through numerical modeling in ABAQUS. This system is expected to exhibit superior seismic performance compared to traditional braces due to characteristics such as superelasticity, self-centering, and energy dissipation, and to return to its initial state after an earthquake. It can significantly enhance the seismic performance of steel frames with minimal construction interference and reduced construction time. After model validation, this study evaluates the effects of cable type, memory alloy properties, and cable diameter on the lateral performance of the steel frame with central cylinder cable braces. The results indicate that even using steel cables in this system significantly increases strength, stiffness, and energy absorption compared to a frame without braces, although ductility decreases by 25%. Replacing the steel cable with a memory alloy cable simultaneously improves strength, stiffness, energy absorption, and ductility (by 10%) compared to the steel-cable specimen, compensating for the ductility reduction. Furthermore, enhancing the superelastic properties of the memory alloy increases the load-bearing capacity and absorbed energy, while increasing the memory alloy cable diameter (from 6 to 16 mm) improves all performance indicators, especially stiffness and strength, without significant loss of ductility. Overall, the results demonstrate that using memory alloy cables, along with optimizing their properties and diameter, is an effective approach for simultaneously improving strength, stiffness, ductility, energy dissipation, and seismic behavior of structures.
A Comparative Analysis of Ensemble NWP Models for Flood Forecasting
This study presents the first application of gamma quantile mapping to bias-correct ensemble precipitation forecasts from seven global NWP models (ECMWF, NCEP, UKMO, CMA, JMA, ECCC, NCMRWF) in the data-scarce Saliyan Basin, Iran. The integration of these models with advanced bias correction techniques significantly improves flood forecasting accuracy. To address systematic biases in the raw forecasts, gamma quantile mapping was applied, significantly enhancing the reliability of the precipitation inputs. These bias-corrected forecasts were then used as inputs for the GR4J hydrological model to simulate river flow and predict flood events. The study period included a major flood event in March 2019, which was used to evaluate the performance of the ensemble forecasting system. Results demonstrated that bias correction using gamma quantile mapping substantially improved the accuracy of flood forecasts, with the ECMWF and UKMO models showing the highest skill scores. The ensemble approach effectively captured the uncertainty in flood predictions, providing valuable insights for risk assessment and decision-making. This research highlights the importance of bias correction in ensemble forecasting and offers a robust framework for flood prediction in data-scarce regions. The findings have significant implications for improving flood early warning systems and mitigating flood-related damages in similar basins worldwide.
Ensemble Numerical Weather Prediction (NWP)
Simplified Unified Model for Flexural Capacity of Ductile HPC Beams with A Low Reinforcement Ratio
There is no specific model to predict the flexural capacity of ultra-high-performance concrete (UHPC) beams with a low reinforcement ratio. Accordingly, a comprehensive experimental database containing 162 datasets was gathered from literature to propose an explicit analytical model containing various critical features, including fiber volume fraction, fiber aspect ratio, fiber strength, water-to-binder () ratio of mixture, and reinforcement ratio. Additionally, a supplementary experimental study involving a large-scale UHPC beam with a very low reinforcement ratio (almost negligible) was conducted to verify the model's performance. The findings revealed that the proposed bending model achieved an IAE of 10.8% and a COV of 1.04, indicating its high accuracy in comparison to a comprehensive experimental dataset comprising 162 large-scale beam tests. Furthermore, the comparison between the experimental results of the tested beam and the proposed model showed a deviation of 4.5%, which supports the effectiveness of the flexural capacity formulation. A parametric statistical analysis was conducted using Minitab software to evaluate the influence of key parameters affecting the roles of fiber and matrix.
Mechanical Performance and Freeze–Thaw Durability of Expansive Clay Stabilized with Graphene Oxide and Fly Ash: A Laboratory Study
Expansive clay soils are characterized by their high water affinity and significant volume changes, which frequently result in structural issues such as swelling, settlement, and cracking, particularly under freeze–thaw (F–T) conditions. This study investigates a dual-stabilization method using fly ash (FA: 5–15%) and graphene oxide (GO: 0.05–0.15%) to enhance the mechanical strength and durability of such soils. After 28 days of curing, samples underwent 3, 6, and 9 F–T cycles, followed by unconfined compressive strength (UCS) testing. Results show that the GO–FA combination significantly improved soil performance, with the optimal mix (10% FA + 0.1% GO) achieving a 76% increase in UCS at zero cycles and reducing strength loss after nine cycles by over 45% compared to untreated soil. These outcomes demonstrate the promise of GO–FA stabilization as a sustainable and effective solution for expansive soils in cold-region geotechnical engineering.
Damage Identification in Beams and Plates Using Wavelet Theory and Firefly Optimization Algorithm
Identifying the location and severity of structural damage represents one of the most critical challenges in civil engineering. The ability to identify damage in its earliest stages cannot be overstated in terms of importance. Among the most powerful tools available for damage detection and generally structural health monitoring can name signal data processing. This study uses a two-step procedure based on wavelet theory and an optimization method to identify the location and severety of damage in beams and plates. The damage simulates through the introduction of cracks at targeted locations. Acceleration responses obtained from a dynamic analysis using finite element method undergo wavelet transformation, enabling detailed analysis of the dynamic response signals. Through filtering processes, the structural response signal details are extracted. Disturbances appearing in the signal detail plots indicate the presence of damage, leading to the development of a quantitative index for determining probable damage locations. The second phase is used to properly determine the location and magnitude of the damage using firefly optimization algorithm. To assess the effectiveness of the proposed method, five numerical examples including three beams with varying characteristics and 16, 27, and 20 elements, respectively, and two plates with different support conditions—one with two-edge fixed supports and another with four-edge fixed supports are considered. Different damage scenarios are considered for structures. The findings indicate that the proposed method shows outstanding results in terms of identifying the location and severity of damage using acceleration responses with considering noise interferences.
Optimal Placement of Viscoelastic Layers in Sandwich Beams for Maximum Vibration Attenuation and Minimum Creep Deflections
Until now, various mathematical models have been proposed to characterize the behavior of viscoelastic materials and facilitate their implementation in finite element software. However, it remains unclear which configuration of the viscoelastic layer along the thickness and length of the beam yields the lowest creep deflection and highest damping effect under applied forces. To fill this literature gap, efforts are undertaken in this study to identify the optimal placement of the viscoelastic layers in the sandwich beam. To reach this aim, the creep and dynamic behaviors of sandwich beams with different boundary conditions and various configurations of the viscoelastic layer along the thickness and length were investigated using a finite element model. The obtained results indicate that the damping capability and creep deformations of the sandwich beam are strongly affected by the position of the viscoelastic layers.
Optimizing Date Seed Utilization in Green Concrete: A Methodological Evaluation
Concrete is one of the most widely used construction materials globally; however, its production contributes significantly to carbon dioxide emissions. In the Middle East, annual date production is substantial, and date seeds, as a byproduct, are typically discarded. This study investigates three methods for incorporating date seeds into concrete: (1) Cement replacement: Using powdered date seeds (PDS) as a partial substitute for cement at 5%, 10%, 15%, and 20% levels; (2) Aggregate replacement: Replacing coarse aggregates with crushed date seeds (CDS) at 10%, 20%, and 30% ratios and (3) Hybrid approach: Combining PDS (0%, 5%, 10%, and 20%) with fly ash (fixed at 20%). Mechanical tests revealed that replacing cement with up to 10% PDS had no significant impact on compressive strength, whereas higher replacement levels reduced strength. Similarly, increasing the aggregate replacement percentage led to a decline in concrete strength. In contrast, the hybrid approach—combining PDS with 20% fly ash—enhanced compressive strength. Based on these findings, the third method emerged as the most effective for improving both the strength and sustainability of concrete. The optimized hybrid mixture was selected for further comprehensive evaluation, including tests for tensile strength, flexural strength, water absorption (porosity), sulfate resistance, and freeze-thaw durability. These assessments aimed to verify not only the mechanical properties but also the long-term durability of the modified concrete under diverse environmental conditions.
2D Equivalent Linear Seismic Site Response Analysis in SBFEM
Understanding the dynamic behavior of soil layers under seismic loading is pivotal for accurate seismic design and risk assessment. This study conducts a two-dimensional equivalent linear site response analysis using the Scaled Boundary Finite Element Method with Rayleigh damping to enhanced modeling accuracy. SBFEM combines the advantages of finite and boundary element methods, offering high efficiency in simulating wave propagation and stress concentrations in semi-infinite domains. A MATLAB implementation of the method was validated against previous studies, confirming consistent accuracy across various soil profiles and seismic scenarios. The method demonstrates convergence, accuracy, and stability, requiring fewer elements due to boundary-only discretization. This reduces both computational cost and time while accurately modeling the infinite domain condition. The findings highlight the method’s effectiveness for site response analysis under diverse seismic inputs and layered soil configurations, combining the equivalent linear method with SBFEM as a robust and practical tool for dynamic geotechnical applications.
3D free vibration analysis of nanocomposite beams carbon nanotube reinforced FGM using DQ method
Beams are always noteworthy as an engineering structure due to their wide application in industry such as bridges, railway tracks, floors and ceilings of buildings and many other cases. Therefore, considering the wide application of these materials in industry, the analysis of this category of structures becomes important in the overall design process of these parts in a structure. With the increasing use of beams in industry and the need to increase their efficiency and ensure their proper functioning, the use of new materials such as functionally graded materials[1]has increased. The use of composite materials, shape memory alloys, piezoelectric materials, etc. and the expansion of the scope of use of these materials has led to increased efforts by researchers to achieve the construction and design of structures and parts with better efficiency and quality. On the other hand, conducting experimental analyses on these materials is associated with problems such as size, price, complexity of the laboratory model, etc., hence the presentation of general theoretical models­. More suitable for ‌In this research, the vibration analysis of a nanobeam is considered. Unidirectional FGM (functional properties along the beam thickness) with carbon nanotubes and a layer‌ Metal and ceramic supports on various types of supports ‌Sometimes. ‌The solutions, including simple, complex, etc., were discussed. The solution method in question was the mixing method, and in line with the thickness of the numerical method, the differential function. It has been DQ based on this, relationships have been extracted regarding how to increase the natural frequency and the lowest natural frequency, as well as the length-to-thickness ratio, natural frequency changes, and dimensionless natural frequency changes in the beam.
Retaining Structures in Slope Stabilization: A Comparative Analysis on Safety and Cost Effectiveness
This study evaluates slope stabilization methods using gravity stone walls, reinforced concrete cantilever walls, and pile shoring systems. Stability and economic performance of these systems were compared through analyses conducted with Plaxis 2D and İstCAD software on a model slope subjected to increasing excavation depths. Results show that gravity stone walls are more economical up to 5 m, while cantilever walls are preferable between 5–9 m. Beyond 9 m, both methods become inadequate, and pile shoring systems provide the most effective solution. Each method's advantages and limitations were assessed based on field applicability, cost, and stability.
Evaluation of Seismic Response of Multi-Story Structures: A Comparative Study of Buckling Restrained Braces and Viscous Dampers
In buckling restrained bracing systems, earthquake-induced elongation problems are solved, and BRB-equipped structures have a much more effective performance in energy absorption in addition to high lateral stiffness. Systems equipped with viscous dampers (VD) also have great potential to absorb seismic energy. To assess the vulnerability of structures equipped with buckling restrained bracing (BRB) and VD systems, three structures (6-, 10- and 15-story) were chosen as representatives of mid-rise, high-rise and super high-rise buildings and modeled in four states of moment-resisting frame (MRF): the frame equipped with VD, the frame equipped with BRB, and the frame equipped with BRB and viscous damper simultaneously (BRB+VD) using OpenSees-2.4.6 software under incremental dynamic analysis (IDA). Seven seismic records were applied, and the maximum inter-story drift response and fragility curves were determined. The results indicated that although the simultaneous application of BRB+VD causes a significant decline in the response of all structures, each of these two systems is able to provide structural safety at various levels in mid-rise structures. It is required to apply both systems simultaneously to provide safety for slight and moderate levels of damage in high-rise buildings, while super high-rise buildings are vulnerable to whole levels of damage, and their structural safety involves the simultaneous use of both systems.
The Effect of Employing a Thermal Insulation Layer in the Building Façade on Energy Consumption (A case study of a residential building in Tehran)
Although currently, a large part of the existing buildings are considered inefficient in terms of energy, the ability to save energy consumption up to 80% has been proven in residential and commercial buildings. This study aims to calculate energy consumption during the operational phase caused by various scenarios of thermal insulation combinations in a building's exterior shell. The simulation was conducted using Design Builder software, with a five-story residential building in Tehran as the case study. Initially, the building was modeled in Design Builder, and keeping all other characteristics constant, ten scenarios were defined: nine using different types of thermal insulation and one without insulation. The software outputs for each scenario were analyzed. Results showed that the best thermal insulation layer is polyurethane foam, which saves 1070.15 kilowatt-hours of energy during one year of the building's operation. This article can help designers and construction engineers optimize the energy consumption of buildings by deciding the right materials. © 2017 Journals-Researchers. All rights reserved
Laboratory Study of Weight Loss and Ultrasonic Wave Propagation Velocity in Conventional Concrete Under High Temperature, Along with Validation by SEM and XRD Analysis
In this laboratory study, a mixed concrete design containing Portland cement type 2 with a grade of 500 kg/m3 was made. Weight loss and ultrasonic pulse velocity (UPV) tests were performed on concrete samples at a curing age of 90 days at room temperature (21 ℃) and under a temperature of 600 ℃. In order to further investigate and verify the results, scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses were performed on concrete samples at a curing age of 90 days. The results of the tests in this study were evaluated together and compared and analysed with the results of other researchers. Applying high heat to concrete samples caused a decrease in results. In this regard, in the weight loss test of concrete samples, the weight of the concrete sample decreased from 2378 to 2225 grams, which was a decrease of 72.6%, and in the UPV test, the speed of ultrasonic waves decreased from 6179 to 3411 m/s, which was a decrease of 79.44%. At the end of this study, the results of SEM and XRD analysis at room temperature and under high temperature, while coordinating with each other, overlapped with the results of the weight loss test and the ultrasonic wave velocity test in concrete samples.
The Evaluation of the bond strength of heavyweight concrete containing iron pellets
Heavyweight concrete incorporating iron aggregates is widely utilized as a radiation-shielding material in environments with harmful radiation due to its high density. Although this material is also employed as a structural component, certain mechanical properties, such as the bond strength between concrete and reinforcing steel bars, remain insufficiently studied. This paper investigates the bond strength of concrete containing varying percentages of iron pellets and its interaction with steel reinforcement. For this study, 25%, 75%, and 100% of the concrete aggregate was replaced with iron pellets, ensuring an appropriate grain size distribution. After curing under standard conditions, the specimens were subjected to direct pull-out tests. The results indicate that, except for the sample with 25% iron pellets, the inclusion of iron pellets slightly reduces compressive strength but enhances bond strength across all samples. Notably, adding 25% iron pellets combined with 5% micro silica in heavyweight concrete significantly improves compressive strength by 20% and bond strength by 43%.
Forensic Investigation and Petrographic Analysis of Concrete Apron Distresses; A Case Study in Nashville, Tennessee
This study presents a forensic investigation into pavement distress in a concrete apron located in Nashville, Tennessee. The investigation involved detailed engineering observations and a comprehensive pavement condition survey in accordance with ASTM D5340. To identify the underlying causes of deterioration, petrographic examinations were conducted on three concrete cores extracted from the apron, following ASTM C856 guidelines. The analysis revealed consistent aggregate distribution, primarily composed of micritic limestone and quartz-based sand, with air content (total of entrapped and purposefully entrained air) ranging from 3.9% to 5.2% and air void spacing factors exceeding American Concrete Institute (ACI) recommendations for freeze-thaw durability. No carbonation was detected in the cores, but moderate to abundant ettringite, calcium hydroxide, and alkali-silica gel resulting from Alkali-Silica Gel (ASG) were observed lining voids and fractures. The findings indicate that Alkali-Silica Reaction (ASR)-related damage, exacerbated by cyclic wetting and drying, is a primary contributor to the pavement deterioration. Freeze-thaw damage due to inadequate air entrainment was also identified as a contributing factor. Based on the results, recommendations for improving the long-term performance and durability of the concrete apron include using low-alkali cement, selecting better-graded and less reactive aggregates, increasing the percentage of purposefully entrained air to reduce air void spacing and improve freeze-thaw durability, and incorporating supplementary cementitious materials (SCMs) to reduce alkali availability and enhance ASR resistance. We note the use of lithium nitrate has also been proven to mitigate ASR in new concrete. However, the mechanism of mitigation is not fully understood, and the relatively high cost and limited availability of lithium introduces challenges for this alternative. This study underscores the importance of petrographic examination in understanding concrete deterioration mechanisms and developing targeted repair strategies to enhance infrastructure durability.
Investigation of the Effect of High Temperature on the Microstructure of Conventional Concrete Containing High Grade of Portland Cement
In this laboratory study, a mixed concrete design containing 500 kg/m3 Portland cement was prepared, and elastic modulus testing, X-ray diffraction (XRD) analysis, and scanning electron microscope (SEM) image analysis were performed on concrete samples at 21 and 600 °C after a curing age of 90 days to investigate and evaluate the microstructure of concrete at room temperature and under high temperature. The results of the tests indicate that high temperature causes a decrease in the results, so that the elastic modulus of concrete experienced a decrease of 71.63% from 73.33 GPa at 21°C to 24.12 GPa at 600 °C, and in the XRD analysis, a decrease in the height of the peaks of hydrated elements is observed. The low peak height of calcium hydroxide in the XRD spectrum indicates a proper polymerization process in conventional concrete. In SEM analysis, at a temperature of 21 °C, due to the completion of a large part of the polymerization process, the tree structure, pores and unhydrated particles are seen in their minimum amount, but after applying a temperature of 600 °C to the concrete sample, with damage to the microstructure of the concrete and the hydrated calcium aluminum sulfate (C-A-S-H) and hydrated calcium silicate (C-S-H) gels, an increase in the tree structure, pores and cracks is evident in the concrete sample.
Viscoelastic damper connected to adjacent structure with seismic isolation system
Base isolation solutions are efficient alternatives for seismic protection of buildings and for enhancing resilient capacity. Currently, seismic isolation is focused principally on the critical infrastructure of public health, transportation, education, etc. The seismic response of multi storied base-isolated structure to various types of isolation systems connected using viscoelastic dampers to the adjacent dissimilar base isolated or fixed base structure is investigated. The multi- storied structures are modelled as a shear type structure with lateral degree of freedom at each floor, which are connected at different floor levels by viscoelastic dampers. The variation of top floor absolute acceleration of both the buildings and bearing displacement under different real earthquake ground motions is computed to study the behavior and effectiveness of resulting connected system. It is concluded that connecting the two adjacent base isolated buildings with the viscoelastic dampers is useful in controlling large hearing displacements in the base isolated structures thereby eliminating the isolator damages arising due to instar billet at these large displacements or pounding with adjacent ground structures during earthquakes. The viscoelastic damper connection between adjacent structures is found to be most effective when the adjacent base-isolated and fixed base buildings are competed. Such scheme is hence useful in upgrading the seismic performance of existing fixed base structures adjacent to a base isolated structure.
Methodology for Evaluating and Optimizing the Selection of Concrete Structure Demolition Methods Based on Cost, Time, and Quality (Safety)
Nowadays, with the aging of old structures and the advancement of construction technologies, demolition projects for outdated structures have seen significant growth. this paper focuses on demolition methods in detail. In a case study conducted in Iran, this paper evaluates the demolition methods for a concrete silo using the Analytical Hierarchy Process (AHP) to select the optimal method based on cost, time, and quality (safety). Time evaluation is performed using MSP software, while cost assessment for each method is estimated based on resources allocated to the activities within the Work Breakdown Structure (WBS) of each approach. Safety evaluation employs a combined application of the AHP and Data Envelopment Analysis (DEA) methods. Required data for constructing pairwise comparison matrices were gathered through questionnaires completed by domain experts. The results reveal that the demolition method using concrete wire saws scores the highest among the methods evaluated. Furthermore, based on modeling results in Sap2000 software, it is shown that single-stage toppling of the silo by removing its main columns is not feasible. Subsequently, the site layout design and lifting plan calculations for the selected method were carried out. All outcomes were compared with real-life execution, and the project's success demonstrated the effectiveness of the chosen method due to comprehensive consideration of all construction management aspects of a demolition project. This paper is written with the aim of simplifying technical concepts in the management of demolition methods.
Numerical investigation of the parameters influencing site effects
One of the most important topics in geotechnical earthquake engineering is the examination of site effects. This phenomenon alters the characteristics of seismic waves, leading to amplified vibrations and consequently increasing financial and human losses. Today, various methods exist for assessing site effects, among which numerical methods are among the most widely used due to their reasonable costs, reduced time, and high accuracy. In this research, a problem was subjected to the effects of three different earthquakes (Bam, Naghan, and Tabas). By comparing the results of each earthquake, the site effects were identified in terms of changes in peak gorund acceleration (PGA), frequency content, and shaking duration. Additionally, to investigate the effects of soil layering, the position of the layers was altered, revealing significant impacts of layer changes on seismic wave characteristics. Finally, to assess the effect of earthquake source type, one earthquake was evaluated at two different stations (near/far field). Results indicated a significant influence of the epicentral distance on the amplification and attenuation of waves.
Analysis of Box-Girder Bridge Considering Translational and Rotational Components of Earthquake
Due to the importance of bridges as vital arteries and the huge investment of countries in building bridges, the need for more accurate seismic analysis of bridges to better understand their structural behavior is inevitable. Like many structures, the effect of the rotational components of the earthquake on bridges has been less noticed by researchers and designers. This research has evaluated the effect of the rotational components of the earthquake to better understand the seismic behavior of bridge. For this purpose, in addition to three translational components, the rotational components of the earthquake, including two rocking components and one torsional component, have been considered in the three-dimensional seismic analysis of box-girder concrete bridges. By creating the rotational component of the earthquake by the Hong-Nan Li method, three box-girder bridges with pier heights of 12, 30, and 45 meters were subjected to the combined effect of six translational and rotational components, as well as three translational components were separately subjected to under a far-field earthquake with different soil and shear wave velocity. The results of the analysis show that the effect of the earthquake's rotational components on the response of stresses and displacement, depending on the type of earthquake and the characteristics of the bridge structure, can be particularly important.
Comparison of the Mechanical Behaviour of Concrete Reinforced with Industrial Metal Fibres and Recycled Chips in Acidic Environments
In recent years, most of the laboratory research on the comparison of the mechanical behaviour of reinforced concrete containing industrial metal fibres and recycled chips has been carried out abroad, and it is necessary to carry out special studies on reinforced concrete with domestic materials, so that we can produce a recycled reinforced concrete from metal waste and recycled chips that is resistant to acid attack and can be used in the construction industry. First we prepare the materials and fibres required for the test, then we design an optimal mixing plan in which industrial metal fibres and recycled chips are used in different percentages. The recycled chips are added to the concrete mix in such a way that the amount of chips we add reduces the amount of fine-grained sand, and the chips replace a small percentage of the sand. Concrete samples are then taken according to the mix design and tested after curing at a specified age. We compare concrete samples containing industrial metal fibres and recycled chips after exposure to an acidic environment with a concrete sample without fibres exposed to an acidic environment to understand how much the presence of fibres and chips in the concrete mix has increased the resistance of the concrete to acid.
Numerical Investigation of the Seismic and Axial Performance of Circular Steel Columns Filled with Double-Layer Concrete with Inner Bracing
Concrete-filled double-shell circular steel columns consist of two concentric steel tubes with the space between them filled with concrete. These columns are a suitable option for high-rise construction due to their lower weight and also allow the passage of cables and utilities. In this research, modelling was carried out in Abaqus software and parametric analysis was performed based on variables such as the shape and dimensions of the stiffeners. The results show that concrete-filled double-shell columns perform better against axial and seismic loads than columns without concrete. The total and square stiffeners give the best performance, but it is not possible to increase their number due to space constraints. Trapezoidal stiffeners are also effective in improving axial and lateral performance, but result in a reduction in ductility. Circular stiffeners have the greatest reduction in ductility and their use is limited. In general, the choice of stiffener type has a significant effect on the performance of double shell columns.
Numerical Investigation of the Impact of Steel Profiles and Embedded Stiffeners in Circular and Square Concrete-Filled Steel Columns under Axial and Lateral Loading
Concrete-filled steel tube (CFST) columns are widely used in high-rise buildings around the world due to their numerous structural advantages, including high load-bearing capacity, favorable inherent ductility, substantial energy absorption capabilities, and the elimination of the need for formwork. However, in Iran, these structures have not yet been widely implemented in practice, highlighting the need for further research in this area. Additionally, challenges such as buckling and local delamination between the concrete and steel under loading remain key issues for these columns. Research indicates that circular CFST columns provide the strongest confinement for concrete, whereas square CFST columns exhibit higher local buckling under loading. Furthermore, embedded steel profiles significantly enhance the overall performance of these columns. In this study, a finite element model of CFST columns with embedded cruciform profiles is validated using Abaqus software and subsequently analyzed parametrically. The objective of this study is to evaluate the seismic and axial performance of the "primary column cross-sections" and the "embedded steel profiles" with equivalent areas. The findings of this research demonstrate that filling the internal space of steel columns with concrete substantially improves axial and lateral performance, although it slightly reduces lateral ductility. Additionally, stress analysis reveals that the type of embedded steel profile directly influences the enhancement of load-bearing capacity and lateral performance. Results also show that square CFST columns outperform their circular counterparts in terms of axial strength and stiffness, though they exhibit lower axial ductility. Moreover, the results indicate that embedded profiles with concentrated mass at the center (central profiles) significantly enhance axial performance, whereas those with mass concentrated along the perimeter (peripheral profiles) exhibit the lowest axial performance but the highest lateral performance criteria.
Physical and Chemical Surface Modifiers of Carbon Nanotubes on the Mechanical and Physical Properties of Concrete
This study utilizes nanofilament-based nanotechnology, such as carbon nanotubes (CNTs), to improve the mechanical characteristics of concrete as a building material. One of the important and effective factors in adding carbon nanotubes to cement composites is their proper dispersion in the mixture. Therefore, in this research, different methods of dispersing carbon nanotubes in cement mortar have been investigated. They were first functionalized through covalent bonding to prevent carbon nanotubes from accumulating in the water. To achieve the appropriate distribution of carbon nanotubes in water and maintain the stability of their dispersion, different surfactants including Polycarboxylate (PCE), Sodium dodecyl sulfate (SDS), Cetyltrimethylammonium bromide (CTAB), Polyethylene glycol (PEG) were employed. At that point, utilizing visual perception and UV test, PCE/PEG surfactant was presented as a reasonable surfactant for the scattering of carbon nanotubes. Once the most suitable dispersal technique was identified, the impact of incorporating multi-walled carbon nanotubes into concrete was investigated with varying weight proportions. The study revealed that even at low concentrations (0.015%, 0.030%, and 0.045%) relative to the cement weight, the inclusion of carbon nanotubes decreased the porosity of the concrete nanocomposite, resulting in a denser and more compact composite. As a result, it increases the concrete samples' compressive, tensile, and bending strength.
The Effect of Ash from Burning Industrial Waste on the Physical and Mechanical Properties of Ordinary Portland Concrete
One of the ways to dispose of urban waste is to burn it in incinerators. In this research, it was tried to use the ash obtained from the waste incineration plant of Saveh city (Iran) as a substitute for part of the consumed cement in concrete production. To achieve this goal, the effects of waste ash on compressive strength, abrasion resistance, flexural strength, water absorption and unit weight of concrete were investigated using experimental methods. The concrete used was made with a compressive strength of 30 MPa. The results obtained from the laboratory tests showed that the addition of waste ash as a partial substitute of the cement in the amounts of 10, 20, and 30% in the tested concrete samples caused to decrease the compressive strength by 21, 42, and 49%, the flexural strength by 5, 15 and 22%, and the unit weight of concrete by 3, 5 and 7% respectively, and to increase the water absorption by 3, 6 and 12% respectively, compared to the control sample. Also, there is a slight decrease in the abrasion resistance of concrete including waste ash. However, the obtained strengths were still acceptable for the construction of concretes that require less strength. On the other hand, the use of this ash as a part of the cement used in concrete not only removes the concern of waste incineration plants to dispose of this pollution, but also reduces the consumption of cement and consequently reduces greenhouse gases caused by cement production.
Exit Strategies for Commercial Complexes in Economic Recession Periods (Case Study: Roya Mall Kish Commercial Complex)
The primary aim of this article is the identification and selection of the optimal strategy for the exit of a significant capital volume invested in the construction of commercial centers in the face of investment risk in the construction of commercial complexes, along with influential factors in challenging economic conditions such as exchange rate fluctuations, transregional power sanctions, stagflation, excessive supply and growth in commercial complex construction in the country, etc., specifically focused on the Royal Mall Kish project. Indeed, the effectiveness and reliability of formulating and selecting exit strategies based on successful implementation and the creation of a sustainable economic cycle for a commercial complex are deemed essential and prerequisite. The research method employed is qualitative. In the qualitative section of this study, through interviews, we identified the relevant factors affecting exit strategies, considering the current conditions and business environment to achieve ultimate goals. These factors are ultimately categorized into three dimensions: structural, behavioral, and contextual. The qualitative sample population includes active experts in this project. At theoretical saturation point, 8 experts were identified as participants in the research. Ultimately, 43 influential components on strategy selection and 5 exit strategies were identified in this project that can be determined as suitable strategies in the appropriate situation for decision-making regarding exit.
Optimizing Slope Stability Assessment Using Hybrid BPSO - SVC with Kernel Function Evaluation
The complex nature of slope engineering presents considerable challenges in accurately predicting slope stability using traditional methodologies. Due to the serious implications that can arise from slope failures, it is crucial to implement the most effective techniques for assessing slope stability. This study investigates a hybrid approach that integrates BPSO with SVC to enhance predictive accuracy in slope stability assessment. The methodology employs BPSO to optimize the selection of features that are critical to the prediction process. Additionally, grid search technique is utilized for fine-tuning the hyperparameters of the SVC. The research evaluates the performance of three SVC kernel functions: linear, polynomial and rbf. For the predictive analysis, six features identified as potentially influential were selected: height of the slope (H), pore water ratio (ru), unit weight of the soil (Ƴ), cohesion of the soil (c), slope angle (β), and angle of internal friction (ɸ). To enhance the generalization capability of the classification models, a 5-fold cross-validation (CV) approach was implemented. The effectiveness of the models was evaluated using various metrics, including the area under the curve (AUC) and overall accuracy of the predictions. The findings of the study indicate that the hybrid approach, particularly the SVC employing the rbf kernel, significantly outperformed the other models in terms of prediction accuracy, achieving an AUC of 0.735 and an accuracy rate of 0.725. This underscores the potential of the proposed hybrid method as a valuable tool for accurately predicting slope stability and mitigating risks associated with slope failures in engineering applications.
Investigating the Effect of Silica Foam on the Mechanical Properties of Concrete Containing Recycled Glass Shards
Recycled glass waste is one of the most attractive waste materials that can be used to create a concrete mix.Therefore, researchers focus on the production of concrete using recycled glass as an abrasive or as a pozzolanic material, but the use of recycled glass in the form of coarser particles to replace sand in concrete increases the alkali-silica reaction and this causes Unfavorable performance in the mechanical properties of concrete.To prevent this, microsilica is used to improve the strength and mechanical properties of concrete.In this research, after building the control mixing design, recycled glass was replaced with sand and silica foam as microsilica in four designs with a fixed ratio of 5% by weight of cement.The compressive strength test was performed at the ages of 7 and 28 days, and three samples were taken in each test, and a total of 24 cubic samples were tested.Tensile test, like compressive strength test, were tested at the ages of 7 and 28 days, which included two cylindrical samples in each test, and a total of 16 cylindrical samples were tested.The presence of silica foam in concrete causes adhesion and reduction of slump fluidity, and the highest slump fluidity was observed at 5% ratio.The result of testing the compressive strength and tensile strength of the concrete containing glass shards and silica foam had decreased in quality compared to the control mixing plan, which shows the unfavorable performance of coarse glass particles in the concrete structure.
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Evaluation of Shape Memory Alloys in the Performance of Reinforced Concrete Frames under Near-Fault Earthquakes
This study investigates and compares the performance of reinforced concrete buildings containing SMA bars and steel bars as longitudinal reinforcement of column.The use of this type of material is to reduce permanent deformation in the structure due to the reversible properties of these materials.First, a laboratory specimen of a reinforced concrete column with shape memory alloy bars was modeled in the OPENSEES software and the modeling method was validated.Then, 3- and 5-story concrete frames, in two states, reinforced with steel bars and SMA bars, under nonlinear static and nonlinear time history analyses with near-fault records were analyzed.The results of the time history analyses showed that, although the use of SMA bars significantly reduces the residual deformation of the structure, it does not show a significant effect on reducing the maximum displacement of the structure.The maximum rotational deformation of columns in frames with SMA bars is greater than of frames with steel bars.However, SMA bars have greatly reduced the permanent rotational deformation of columns and reduced it to zero.The maximum drift of floors in frames with SMA bars increases slightly.The permanent drift of the structure in frames with SMA bars is significantly reduced.