Probabilistic Seismic Performance Assessment of Tall RC Special Moment-resisting Frame Buildings Equipped with Buckling-restrained Braces under Near-field Excitations

Many tall buildings have already been constructed near faults throughout the world, several of which have sustained casualties and economic losses during strong ground motions. This study investigates the effect of near-fault excitations on the vulnerability of tall, reinforced concrete (RC) special moment-resisting frame (SMRF) buildings equipped with buckling-restrained braces (BRBs) using seismic fragility curves. After attaining the structure’s response modification factor (R), three-dimensional (3D) models of 15-, 25- and 35-story frames were developed by the OpenSees software according to the Iranian code provisions. Thus, the seismic response of the elements was obtained. Subsequently, incremental dynamic analysis (IDA) was conducted by selecting a suitable number of compatible accelerograms in two near-field and far-field groups. Considering the maximum story drift as the demand parameter and selecting the interstory drift ratios (IDR) for the slight, moderate, extensive, and complete collapse seismic performance levels proposed by Hazus, IDA curves were plotted. Then, the seismic fragility curves were produced using the structural reliability relations. The median fragility at complete collapse damage level reduced from 0.73g, 0.62g, and 0.61g to 0.68g, 0.59, and 0.57g for the 15-, 25, and 35-story near-field and far-field earthquake models, respectively. This was attributed to increasing vulnerability and seismic fragility of the structures as a result of both height increase and distance reduction from fault. Based on the results, the most vulnerable structure, i.e., the 35-story near-fault model, experienced a 40, 17, 18, and 6% increase in median fragility at slight, moderate, extensive, and complete collapse damage levels, respectively

A Substructure-based Model Updating Method to Damage Detection for Large-scale Structures

The health monitoring and damage detection of structures are major scientific issues that the civil engineering discipline, which made great achievements in the 20th century, has bequeathed to the 21st century. Despite the installation of health monitoring systems in many large structures, implementing damage detection through finite element model updating is often time-consuming or even infeasible due to the size of the model and the presence of numerous uncertain parameters. To address this issue, this paper proposes a substructure-based model updating method. The entire structure is divided into substructures with reduced degrees of freedom, allowing for the simplification of the motion equation by employing only a small number of low-order modes from each substructure. Consequently, the analysis scale of the structure is effectively reduced. The discarded higher modes are compensated by residual modes to ensure the accuracy of structural response and sensitivity. Subsequently, a damage identification program substructure-based model updating is developed, which is applied to component mode synthesis and damage identification for large structures. By precisely detecting damage in critical areas, accurate diagnosis and evaluation of the global structural safety are achieved. The results validate the implementation, computational efficiency, and accuracy of the proposed substructure-based model updating method. This approach shifts the focus from model updating of the entire structure to model updating of substructures, with the aim of fundamentally resolving the technical challenge of accurate damage detection of large and complex structures. Furthermore, it provides theoretical support for the practical application of damage detection in large civil structures

Improved Droop Controller for Distributed Generation Inverters in Islanded AC Microgrids

Stability in island microgrids is crucial for efficient power distribution among distributed generation (DG) inverters. Conventional droop control, while effective in power sharing, poses challenges with voltage stability due to frequency and voltage deviations resulting from changing load power. Such deviations can lead to system instability, impacting power flows within each inverter. Therefore, this paper introduces a proposed droop control approach that effectively tackles the issues of frequency and voltage deviation, aiming to restore them to their rated values and significantly enhance transient response in power flows among inverters. The novel method incorporates integrating controllers for frequency and voltage, coupled with the utilization of virtual impedances. These virtual impedances, comprising virtual positive/negative-sequence impedance (VPI/VNI) loops at the fundamental frequency and a virtual harmonic impedance (VHI) loop at harmonic frequencies, play a crucial role in overcoming mismatched line impedance conditions, ultimately improving overall system performance. Simulation results demonstrate the effectiveness and outstanding performance of inverters operating in parallel within an island AC microgrid. The proposed approach ensures stable voltage and frequency levels in all operational states, regardless of varying load conditions

Processes Towards Sedimentation around a Reed Island in a Shallow Lake

There are many studies on the hydromorphological impacts of emergent aquatic vegetation, but many of these focus on gravity-driven flows in riverine or tidal environments. However, an added effect of emergent vegetation in lakes is that it reduces the main external force (wind) significantly and in a spatially coherent way. We performed long Monte Carlo simulations using a 2D hydrodynamic model and a spectral wind wave model to study resuspension dynamics around a 100-m-wide reed island in southern Lake Fertő/Neusiedl. Wave-current interaction, computed in a post-processing step, was found to enhance maximum bed shear stresses only on the leeward side of the reed island, and even there to a small extent. We have found evidence that the present bed topography is close to an equilibrium where simulated combined wave-current shear stresses have a reasonably uniform exceedance probability over the critical shear stress of the bed sediment. We also found that an artificially flattened lakebed around the reed island would start evolving towards the present bed topography and grain size distribution (both of which were surveyed in the field). Despite the limitations of our modelling framework, our results illustrate the importance of how wind climate is translated to an uneven distribution of sediment entrainment around the reed island, explaining tendencies of sediment accumulation and sorting. Our results lead to a better understanding of the complicated processes involving interaction among wind, vegetation, circulation, wind waves, sediment and bathymetry

Optimization of Breakpoint Chlorination Technologies for Drinking Water Treatment: a Hungarian Case Study

Ammonium ion is one of the major pollutants found in drinking water sources in Hungary, especially in deep aquifers. under oxidative conditions, ammonium can transform into nitrite ions in the water system, posing potential health risks. In Hungary mostly biological process or breakpoint chlorination are used to eliminate ammonium ion from raw water during the drinking water treatment process. When breakpoint chlorination is applied, harmful by-products are formed. Trihalomethanes concentrations have long been regulated in Hungary, therefore during the design and optimization of the breakpoint technologies trihalomethane concentrations have been considered. However, haloacetic acids (HAA5) and chlorate ion have been recently regulated in accordance with EU Directive 2020/2184. Chlorate is a by-product that appears in treated water when sodium hypochlorite is used in breakpoint chlorination.Experiments were carried out at four Hungarian case study areas to determine the optimal strategy for breakpoint chlorination: applying higher chlorine dosages with lower contact times, or lower chlorine dosages with higher contact times. The investigations concluded that the preferable dosing strategy is to use lower chlorine concentrations and longer contact times. This approach reduces chemical demand (cost-effective) and has a neutral effect on THMs formation. it can be concluded that when the raw water contains ammonium ion concentrations above 0.5 mg/l, the use of sodium hypochlorite may raise concerns due to elevated chlorate ion levels in the treated water, particularly during summer. Further research is required to expand the optimization strategy, considering not only ammonium and trihalomethane concentrations but also chlorate concentrations

Geometric Parameter Optimization of Switched Reluctance Machines for Renewable Energy Applications using Finite Element Analysis

The choice of SRM design depends on the specific application and performance requirements. Factors such as power output, torque characteristics, and efficiency will all influence the choice of SRM design. To find an optimal geometry, it is therefore necessary to determine the effect of each parameter such as rotor pole angle, stator pole angle, stator external diameter, rotor diameter, air gap length, rotor yoke, stator yoke and shaft diameter on the machine performance. For this reason, this paper discusses a comparative study of the geometric parameters influence on SRM performance. The analysis is performed by finite element simulations based on the variation of rotor inclination, air gap length, stator and rotor polar arc variations of three machine topologies such as the three-phase 12/8 SRM, three-phase 6/4 SRM and four-phase 8/6 SRM. For a reliable comparison, these machines must have the same basic dimensions (stator outer diameter, rotor outer diameter and length) and operate in the same magnetic circuit saturation. Graphical and numerical results of torque and magnetic flux for three SRM topologies are highlighted. The presented study aims to provide reliable results on the dimensions to be adjusted for various applications

Heat Recovery Variable Refrigerant Volume System Installation and Experiences from its Summer Operation

Variable refrigerant volume (VRV) systems operate on the principle of a cooling machine. They extract heat from one side and return it on the other, enabling them to function as a source of heat for both heating and hot water preparation, as well as a source of cold for cooling within a single building. These systems efficiently remove unnecessary excess heat outside and only introduce the required amount of heat from the outside into the building. With an appropriate configuration and setting, a VRV system can transfer heat in both directions within one system, eliminating the requirement for waste heat to be removed without use in the building. Instead, it is transferred to the desired locations where it is needed. This principle necessitates the adjustment of not only the refrigerant temperature but also its flow rate. Consequently, the VRV system can fulfil tasks that are otherwise handled by several individual systems in a building.A heat recovery VRV system was installed in a small retail store to extract waste heat generated by baking ovens during the baking process. This report provides a brief summary of electricity and energy consumption measurements taken during the summer period for cooling purposes. Sequential logic is observed and coherence is ensured, with active voice predominating for clearer and more direct communication. The parameters of interest include cooling setpoints, cooling outside of working hours, and capacity assessment

A Comprehensive Investigation of Performance Characteristics, Mechanical Properties and Durability Parameters of Self-compacting Concrete Containing Iron Slag as Coarse Aggregate

In this paper, iron slag is used as partial coarse aggregate substitution in Self-compacting concrete (SCC). The SCC samples tests were conducted after 28 days of water curing for samples with 0%, 10%, 20%, 30%, 40%, 50%, and 60% iron slag as coarse aggregate substitutes. This paper evaluates slump flow, V-funnel, L-box, compressive strength, flexural strength, splitting tensile strength, surface water absorption, capillary water absorption, electrical resistance, acid resistance, and ultrasonic pulse velocity (UPV) of concrete samples. Furthermore, scanning electron microscopy (SEM) of samples was investigated for evaluating cement paste microstructure. Samples containing 20%, 60%, and 60% iron slag as coarse aggregate substitute have higher compressive, flexural, and splitting tensile strength than control samples (about 18.4%, 28.6%, and 16.9% higher, respectively). In addition, using 10%, 20%, 30%, and 40% iron slag as coarse aggregate increased the compressive strength. Moreover, incorporating iron slag as a coarse aggregate decreased the mass loss of samples which were exposed to the acid environment compared to control specimens. Using iron slag as partial coarse aggregate substitution reduced the porosity of the cement matrix compared to control samples (based on SEM images)

Shear Strength Evaluation of Concrete Beams with FRP Transverse Rebar

Rebar corrosion in traditional reinforced concrete (RC) components may lead to a decrease in service life and carrying capacity. This condition is one of the reasons of the growing popularity of Fiber Reinforced Polymer (FRP) rebars as a corrosion-resistant alternative, particularly in RC infrastructure projects. Because the material properties and behavior of FRP rebar are very different from conventional steel rebar, the calculations used for reinforced concrete with conventional steel reinforcement should be updated for this material. The aim of this study is to propose a new shear strength prediction model for RC beams with transverse steel rebar in order to calculate the shear strength of RC beams with FRP transverse rebar according to TS-500, which is the Turkish Building Code. To achieve this goal, Finite Element Method (FEM) models were created for 27 RC beams with FRP transverse rebars and 9 RC beams without transverse rebars. Furthermore, for RC beams with FRP transverse rebars, a prediction model has been developed. Additionally, 13 prediction models obtained from regulations or scientific studies were compared to the proposed prediction model using a database of 105 tests obtained from previous experimental studies. It was observed that the proposed prediction model provides more consistent results with the test database from the literature compared to the models suggested by other regulations or studies. Therefore, by modifying the shear strength relations recommended in TS-500 for RC beams with transverse steel rebar, they can also be applied to RC beams with transverse FRP rebars

Simulation of Eddy Current Losses in Twisted Wires

Twisted wires made of insulated strands, known as stranded conductors or litz wires, are used in various areas where the eddy current loss within the wire needs to be reduced. These areas include induction heating, resonance-based wireless energy transfer, and certain radio frequency devices. Some litz wires consist of thousands of individual conductor strands that are twisted together in multiple stages, creating a hierarchical bundle structure. Computer simulations (typically using finite element analysis) are used in the optimal design of the bundle structure. However, detailed three-dimensional models are computationally demanding. In this work, a two-dimensional finite element model was presented for simulating the eddy current loss in cables made of twisted wires. The key element of the model is considering the bundle structure (generally referred to as 3D configuration conditions) within the cross-sectional model domain. The accuracy of the proposed model is tested against 3D finite element simulations. The new method is shown to be accurate, and its computational cost is by orders of magnitude lower than that of 3D models