نشریه مهندسی عمران
سال پنجاه و ششم شماره 2 (اردیبهشت 1403)

This study aims to assess reinforced concrete moment frames designed at varying ductility levels within a typical reinforced concrete structure, from a reliability perspective. The article explores the probabilistic methods for designing different ductility levels in the current Iranian Concrete Code, focusing on reliability. Specifically, a three-story concrete moment frame structure, designed to low, medium, and special ductility levels as per the Iranian code, is studied. The reliability analysis encompasses uncertainties in loading, dimensional parameters, and evaluating structural performance functions such as floor drift and acceleration. The study utilizes horizontal earthquake components specified by the FEMA P-695 standard to analyze earthquake record uncertainties. Furthermore, a comparison of the reliability index and probability of failure for each performance function is used to assess failure uniformity. The findings reveal a maximum probability of failure in collapse damage state of approximately 9%, 5%, and 2% for low, medium, and special ductility frames, respectively.

Steel moment frames are among the structure systems for bearing gravity and lateral loads, which are more common in high-rise structures due to their lower weight than reinforced concrete moment frames. The ductility capacity of steel moment frames depends on the types of their connections, hence the moment connections are particularly important. Nowadays, in the American Steel Codes and the Iranian National Building Regulations, models have been introduced as Prequalified Connections. The ConXL modern moment connection is one of these connections and in this research that is under study. This connection is designed to create a cost-effective and resistant moment frame that allows quick installation of the frame by eliminating workshop welding. Also, WUF-W, which is known as a rigid connection in domestic codes, is a conventional connection in construction and can be a suitable reference for comparison with ConXL, which is less known in terms of seismic behavior. To do this comparison, fragility curves, which are suitable tools for determining the probability of vulnerability, are used. For this purpose, fragility curves are determined for both ConXL and WUF-W connections. The criterion of this comparison is the performance levels of IO and CP in the fragility curves of joints in a special two-dimensional bending frame. Finally, after comparing the seismic behavior of the two mentioned connections and expressing the more favorable performance and ease of implementation, it can be concluded that the modern ConXL Connection is a more suitable option for special moment frames.

In the present study, the effectiveness of a new combination of industrial wastes including calcium carbide residue (CCR) and silica-fume (SF) along with polypropylene fiber was investigated in comparison with cement for improving soft clays and increasing their durability. The results showed that in normal curing conditions, the use of CCR alone has little effect on the soil geo-mechanical performance. On the other hand, despite the initial favorable performance of cement, the W-D cycle with the failure of cement nanostructures can lead to the disturbance and even complete loss of the soil-bearing capacity. In contrast, the combination of CCR with SF had a prominent role in the stabilization process and a much lower deterioration potential was observed in the presence of the optimal ratio of CCR-SF. According to SEM-EDX and XRD analysis, expansion of solidification and reduction of voids were evaluated as the main factors of the more appropriate response of the recent system. Adding fiber to this series of samples had a significant effect on the growth of tensile strength, better absorption of energy, reduction of cracking ability, and as a result, improving the stability of the soil matrix. Following such a condition, the strength of the reinforced sample containing a 15% additive was found to be about 1.8 times the threshold allowed for successful stabilization. This can be attributed to the synergism of CCR-SF and fibers in improving the particle conjunction and reducing the access of voids for soil-water interaction. Based on the obtained results, the use of an optimal combination of CCR-SF with fiber can be recommended as a low-cost, environmentally friendly, and efficient option in improving the behavior of problematic soils and reducing their post-failure potential.

Microalgae have the potential to produce valuable substances for pharmaceutical purposes as well as serve as a food source, providing bioactive compounds and ingredients for cosmetics. However, harvesting microalgae is a crucial step in the mass production of various high-value products derived from microalgae. This process often becomes a major bottleneck in downstream processing. It is essential to find effective and cost-effective harvesting methods for industrial applications. Among several harvesting methods, magnetic flocculation offers the benefits of modest operation, energy savings, and quick separation. This study investigates the harvesting process of Chlorella sorokiniana pa.91 microalgae using a novel flocculation process involving nano-Fe3O4 coated with PACl. In this research, we have used the chemical co-precipitation method to prepare nanoparticles. Using the response surface method to optimize the most important parameters of the magnetic flocculation harvesting process to check the microalgae removal efficiency, three variables of time, concentration of nanomaterials, and pH in the culture medium obtained from municipal wastewater have been investigated. The results demonstrated that the highest harvesting efficiency, nearly 90%, was achieved under the conditions of 3.5 g/L Fe3O4, a constant concentration of 0.075 g/L PACl, a harvesting duration of 40 minutes, and a pH level of 4. On the other hand, the lowest microalgae harvesting efficiency was observed under specific conditions: a composite nanoparticle concentration of 0.5 g/L per liter, a harvesting time of 27.5 minutes, and a pH of 6.5 resulting in a mere 22% efficiency. The rate of microalgal removal increased from 53% in the most alkaline condition to 75% in the most acidic environment. The highest harvesting efficiency, reaching 80%, was achieved under neutral pH conditions with a settling time of 53 minutes. Furthermore, the investigated combined method investigated enhances the flocculation effectiveness of microalgae. Based on the findings, it can be inferred that the efficiency of microalgae harvesting rises with longer duration, higher nanoparticle concentrations, and lower pH levels

In this research, the numerical simulation of the scouring of the downstream bed of two types of trapezoidal and triangular piano key series in the same geometric and hydraulic conditions has been done using the Flow-3D numerical model. To carry out the calibration process of the desired numerical model, the laboratory study of Ghodsian et al. (2021) was used in the conditions of sediment transfer. After the software calibration, the accuracy of the R2 criterion for the longitudinal profile of scour and the maximum depth of scour downstream of the weir was equal to 0.9338 and 0.873, respectively. Eighteen numerical simulations for scour downstream of two types of trapezoidal and triangular piano key weirs were carried out under the conditions of changes in discharge and depth of abutment, and the local changes of scour in a trapezoidal piano key weir at a depth of 0.05, 0.075 and 0.1 meters and all three The flow rate of 25, 35 and 45 liters second was observed less than the weir of the triangular piano key. By doubling the depth of the weir in the trapezoidal weir up to 29% and in the triangular weir up to 26.6%, the scour depth decreases. Also, with a 44% decrease in discharge at a constant depth of the aquifer, a 40% and 37.4% decrease in the maximum scour hole depth was observed in the trapezoidal and triangular weir, respectively. The increase in the depth of the floodplain causes the loss of energy of the falling jets from the weir, and by reducing the capacity of the bed sediments carried by the water flow, it causes a decrease in the maximum scour depth downstream of the desired weirs. It was observed that with the increase of the flow through both types of trapezoidal and triangular piano key weirs in the condition of constant depth of the abutment, the scour rate in the sedimentary bed for both types of weirs approaches.

Piezoelectric materials are a type of smart materials that are of interest to many researchers in various engineering sciences due to their extraordinary properties such as converting mechanical energy into electrical energy and vice versa. In this article, the determination and control of the dynamic deformation of a one-span concrete frame with a piezoelectric layer coating on beams and columns under seismic load is discussed. In order to control the dynamic deformation of the concrete frame, a proportional-derivative controller has been used in such a way that a piezoelectric layer is considered as an actuator and a layer as a sensor. The governing equations for the beam and column components of concrete frame are obtained by using high-order shear theory, calculating energy relations, applying Hamilton's principle and considering the applied voltage on piezoelectric materials. In order to solve the dynamic coupled equations, the numerical method of differential quadrature method has been used and finally, with the help of Newmark method, the dynamic deformation of the concrete frame is calculated. After validating the results, the effect of various parameters such as voltage applied to the piezoelectric layer, piezoelectric type controller, thickness of the piezoelectric layer on dynamic deformation were investigated. Here, the optimal values of controller parameters, including proportionality coefficient and derivative coefficient, were obtained as 3.824 and 5.812, respectively. The results show that the use of the controller leads to a reduction of 72 and 65 percent of the lateral and vertical dynamic deflection of the frame, respectively.