Iranian Journal of Science and Technology, Transactions of Civil Engineering最新文献

In this paper, the mechanical properties and microstructure of hybrid basalt-brucite fibers reinforced low heat cement concrete were investigated, including compressive strength, splitting tensile strength, hydration products, microstructure, and pore. The results showed that the composite effect of hybrid fibers could effectively affect the failure mode of specimens, and improve the mechanical properties of low heat cement concrete that under optimal dosage conditions, it reached the maximum value, which were 40.2% for compressive strength and 70.6% for splitting tensile strength higher than the benchmark group. Based on microscopic techniques, hybrid fibers was found that it had a good bonding effect with the mortar. The failure modes of hybrid fibers in mortar included pull-out, tensile failure, and torsional failure. Meanwhile, mineral fibers could effectively promote hydration reaction, enhance the interface transition zone between fibers and concrete, and improve the compactness of concrete by compensating for small pores in concrete. Based on the theory of composite materials, the reinforcement mechanism of hybrid fibers on low heat cement concrete was elucidated.

One of the most significant factors affecting the durability of concrete is sulfate attack. In this paper, to predict the compressive strength (CS) of concrete under sulfate attack, three coupled machine learning methods (SSA-BP, PSO-BP and NGO-BP) were developed by coupling BP neural networks (BPNN) with three swarm intelligence algorithms, which are sparrow search algorithm (SSA), particle swarm optimization algorithm (PSO) and northern goshawk optimization algorithm (NGO), respectively. Twelve influencing factors related to material composition, erosion medium and exposure conditions are chosen as inputs, and the CS of concrete subject to sulfate attack is selected as the output. The database of 591 samples collected from published literatures is divided into three parts. Performance indexes are used to evaluate the three coupled models and BP independent model. Finally, the influence of each input on the CS of concrete under sulfate attack is examined using the Grey relational analysis approach. The following findings are reached: (1) all coupled models can predict the CS of concrete under sulfate attack with higher accuracy and achieve better performance than BP independent model, and the best one is SSA-BP model. Benefitted both from the strong nonlinear mapping ability of BPNN and from the global search and fast convergence ability of SSA, SSA-BP model has strong potential in predicting the CS of sulfate attack concrete. (2) Grey relational analysis shows that, among the twelve inputs considered, the initial compressive strength of concrete has the highest correlation (almost one) with the CS of concrete under sulfate attack. The robustness of the suggested model is confirmed by the relational analysis of all input parameters. (3) In addition, this model can provide an innovative way to assess the durability of concrete under complex or harsh environmental conditions.

Multiple treatment phases are involved in a water treatment plant (WTP), but coagulation and disinfection are the most crucial for producing safe and clear water. Determining the optimal coagulant and chlorine doses in the laboratory is time-consuming and poses a significant challenge in water treatment. To streamline this process, artificial neural network (ANN) models have been developed to predict the chlorine dose based on the coagulant dose. Studies comparing various ANN models indicate that the radial basis function neural network (RBFNN) model provides excellent predictions (R = 0.999). In modeling with radial basis function neural networks (RBFNN) and generalized regression neural networks (GRNN), the spread factor was varied from 0.1 to 15 to achieve a stable and accurate model with high predictive accuracy. Employing soft computing models to define the coagulant and chlorine doses has proven highly beneficial for the management of WTPs, significantly enhancing the efficiency and accuracy of dosing predictions.

Use of steel slag in asphalt mixtures has proved to be economically and environmentally beneficial. However, still some aspects of this application need more investigation. This study aimed to investigate the aging effect on some properties of asphalt mixture made by SSA and its comparison with conventional limestone aggregates (LA). Asphalt concrete mixtures with the same binder were made with SSA and LA, and were subjected to different aging conditions. Aging conditions included short-term on loose mixture, and long-term in 2 conditioning times of 5 and 7 days on compacted specimens. Then, the specimens were evaluated by Marshall test, indirect tensile strength (ITS) test, Cantabro abrasion loss test and semicircular bending (SCB) test to evaluate their resistance against rutting, moisture damage, raveling and fracture, respectively. Results reveal that the mixture made by SSA has more Marshall stability, Marshall quotient and ITS, and is more resistant against moisture damage and raveling and has higher fracture toughness and fracture energy than the mixture made by LA. Results also show that aging results in increase of Marshall stability, Marshall quotient and ITS and decrease of flow, moisture damage resistance, raveling resistance, fracture energy and fracture toughness. The effect of aging on the properties was found to vary with the type of aggregates. In general, the mixture containing SSA is less affected by aging than the mixture made by LA. However, for some properties the aging is more effective on the mixture containing SSA.

Accurate and simple determination of baseflow is an extremely important issue. In this study, the baseflow levels of Göksu station number 1805 in the Seyhan basin were determined by calibrating the Lyne and Hollick, Chapman, Chapman and Maxwell methods available in the literature using meta-heuristic optimization methods. The meta-heuristic algorithms used for calibration in the study were run thirty times each. Thus the reliability, the reliability of the algorithms was tested with the standard deviations obtained. The study also measured the temporal performance of the algorithms. In addition, the baseflows of Göksu station were determined and their percentage rates were found separately according to all three methods and intuitive methods, and the results obtained were compared. By examining the results obtained in this section, the average baseflow rate of the basin was also determined. Furthermore, each phase of the study was repeated over a five-year period, with the objective of measuring its sustainability. Consequently, it has been demonstrated that the method can be employed over extended periods.

Addressing the increasing demand for concrete due to advancements in the construction sector and population growth, this research explores the critical intersection of waste management and sustainable construction practices. By incorporating recycled coarse aggregate (RCA) derived from construction and demolition waste into concrete, waste reduction and natural resource conservation is achieved. An innovative standard compaction method is utilized to investigate the complex dynamics of RCA's influence on concrete properties. Key parameters examined include workability, compressive strength, flexural strength, split tensile strength, microstructural characteristics (XRD, SEM, EDAX), and modulus of elasticity. A distinctive feature of this research involves systematically replacing conventional coarse aggregates with RCA at varying proportions: 0, 25, 50, 75, and 100%. The comprehensive analysis reveals significant improvements in the fresh, hardened, and microstructural properties of concrete. Results indicate a nuanced relationship between RCA replacement levels and concrete strength, with the optimal mixture at 25% RCA replacement (RCA 25) demonstrating notably higher compressive (11.56%), flexural (3.06%), and split tensile (5.17%) strengths compared to the control concrete. Additionally, RCA 25 exhibits an 8.91% increase in modulus of elasticity. XRD, SEM, and EDAX analyses provide insights into the underlying mechanisms, indicating that pozzolanic activity enhances strength at lower RCA replacement levels by producing more hydration products, while strength may decrease at higher replacement levels. The significance of this research lies in its novel methodology, addressing a critical gap in understanding the intricate relationships between RCA content and concrete performance. The findings strongly advocate for the judicious use of recycled materials in concrete, contributing to environmental conservation and the long-term resilience of construction materials.

The new staggered story isolated structure (NSSIS) is a new structure developed from the base isolated structure and mid-story isolated structure. In this paper, a finite element model of an NSSIS was established and the dynamic response of the NSSIS under three-dimensional (3D) long-period earthquake waves was analyzed. As the tensile and compressive stress of the isolated bearings exceeded the limit value under the 3D long-period earthquake waves, the 3D isolated bearings were introduced and compared with the traditional horizontal isolated bearings. The results show that the earthquake response of the NSSIS under long-period earthquake waves were larger than ordinary earthquake wave. The earthquake response of structure under 3D earthquake waves was larger than that under one-dimensional (1D) and two-dimensional (2D) earthquake waves. After setting 3D isolated bearings, the earthquake response of the structure was reduced, the shock absorption performance of the structure was improved, the compressive and tensile stress of isolated bearings met the requirements. It can provide a reference for the study of the NSSIS under 3D long-period earthquake waves.

This research investigated the suitability of gray water as a non-conventional water source in the concrete production. The findings showed that both gray and tap water can be considered as mixing water, but based on water quality indicators for industry usage, gray water cannot be used without restrictions to build reinforced concrete structures due to its high corrosive ability. Gray water had no significant effect on the slump and setting time of the concrete. The compressive strength of concrete made with tap water increases from 7 days to 28 days, while gray water concrete, after an increasing trend from 7 days to 14 days, reached its lowest value at 28 days (28.1 MPa). This decrease is due to high TDS values and impurities, which can lead to a decrease in compressive strength. Gray water concrete showed a significant loss in tensile strength compared to tap water concrete after 28 days of curing. The P-wave velocity of the tap water concrete sample increased with the increase in curing time, while the gray water sample decreased by 13% in 28 days. Microscopic studies revealed the formation of carbonate halos around carbonate aggregates due to alkaline reactions in both tap and gray water concretes. The carbonate halo has developed to the inner parts of the aggregates in the gray water sample, indicating greater intensity of alkaline reactions. This means the long-term strength of the concrete will likely suffer a significant loss.

Steel plate shear walls (SPSWs) are efficient options for lateral load-resisting systems in buildings. However, introducing opening(s) in the SPSWs results in a significant drop in their performance. To investigate the effects of introducing openings and adding stiffeners around them on the performance of SPSWs, thirty-three finite element-based models of stiffened SPSWs with full height opening were analyzed. These models had different steel plate thicknesses, opening aspect ratios, and stiffener configurations. Numerical results of this study agreed with the Plate-Frame Interaction (PFI) theory. It was found that adding stiffeners considerably increased shear stiffness and shear strength of SPSW. Furthermore, improvement in the shear load carrying capacity of the SPSW is significantly influenced by cross-sectional shape and even arrangement of the stiffeners. Finally, it was shown that SPSWs with a thicker steel plate are more sensitive to both the presence of the opening and its widening.

This study presents an analytical methodology for predicting the natural frequencies of hollow-core slab panels, addressing a significant research and application need in structural engineering. The study suggests a numerical–experimental calibration utilizing the Finite Element Method (FEM) via ANSYS software to assess the modal response of hollow-core slabs validated according to literature study. Through the development of Irvine’s equation, this research proposes a simplified methodology for determining the natural frequency of slabs. The slabs were modeled as simply supported beams, and Irvine’s equations have been applied to simplify several degrees of freedom structure (SDOF) and determine the natural frequencies for various spans. The validation of the numerical–experimental model indicates a maximum error of 8.32% in the third vibration mode, demonstrating the accuracy and practicality of the proposed analytical method. This approach could be useful in determining the vibration serviceability presented in Brazilian Standard Procedure for the Design of Concrete Structures. It can help engineers and manufacturers to estimate structural compliance and vibration serviceability.