Residual Load Research Articles

Impact of renewable energy generation on power reserve energy demand

With increasing shares of renewable energy generation, the evolution of reserve needs may represent an important challenge for the power system. The evolution of reserve capacity needs in this context has been extensively studied in the literature (Hirth and Ziegenhagen, 2015). On the other hand, reserve energy needs have been less studied. This work focuses on analysing the relationship between reserve energy demand and load, wind, and solar generation. To this end, autoregressive models with exogenous variables are estimated on 2019 data of the French power system. We find a positive impact of renewable energy generation on downward reserve energy demand and a negative impact on upward reserve energy demand. These results can be interpreted through the relationship between the level of residual load and the probability to find a counterpart on the intraday market to balance forecast errors, thus allowing to reduce the imbalance of the system in real-time and thus the need for reserve energy.

Environmental carrying capacity and ecological risk assessment of pesticides under different soil use types in the Central Plains Urban Agglomeration (CPUA), China

Soil environmental safety has received much attention during the past few decades due to its significance in agricultural production and human health. Special attention is required for soil pesticide residues and ecological risks. This study examined 197 soil samples from industrial, residential and agricultural areas for the presence of 12 organophosphorus pesticides (OPPs) and 8 synthetic pyrethroids (SYPs) in the 16 cities in Henan Province, and the center of CPUA, based on the Central Plains Urban Agglomeration (CPUA) concept proposed by China. The total average concentrations of ∑12OPPs in industrial, residential and agricultural soils were 194, 217, 267 ng/g dry weight, and those of ∑8SYPs were 26.8, 35.7, 25.5 ng/g dry weight, respectively. The two pollutants with the greatest concentrations in the soils were malathion and fenpropathrin, respectively, the dominant components of OPPs and SYPs. The soil environmental carrying capacity (SECC) analysis, representing the maximum residual load that can be supported, shows that acephate and cyhalothrin were overloaded, with a predicted period of over 500 years. Among the 16 cities of CPUA, a higher frequency of high ecological risk could be observed only in Shangqiu. The OPPs in children had total non-carcinogenic risk values of more than 1.0. Similarly, the non-carcinogenic risks of SYPs in adults and children in the residential areas were more than 1.0. The study provides knowledge on how to effectively manage soil safety in Henan Province, which is the center of the CPUA, with a large population and grain province to protect ecosystems and reduce the risks of soil pesticide residues in humans.

Optimizing pumped-storage power station operation for boosting power grid absorbability to renewable energy

Optimizing peak-shaving and valley-filling (PS-VF) operation of a pumped-storage power (PSP) station has far-reaching influences on the synergies of hydropower output, power benefit, and carbon dioxide (CO2) emission reduction. However, it is a great challenge, especially considering hydro-wind-photovoltaic-biomass power inputs. This study proposed a novel optimization operation framework for a PSP station driven by the PS-VF operation for boosting power grid absorbability to renewable energy inputs. An optimization operation model based on a grasshopper optimization algorithm was developed to minimize the residual load volatility. A PSP station in the Hunan Province of China constituted the case study, and the practical operation scheme formed the benchmark. The findings underscore the effectiveness of the proposed approach in fostering remarkable synergy, evident in substantial improvement rates of 61% for power output, 58% for power benefit, and 62% for CO2 emission reduction compared to the practical operational scheme. This study not only furnishes valuable scientific and technical backing for the PS-VF operation of the PSP station, enhancing the interplay between hydropower generation, financial benefits, and CO2 reduction, but also provides policymakers with well-informed strategies that consider potential load volatilities and advantages. These strategies are geared towards enhancing the power grid's capacity to assimilate hydro-wind-photovoltaic-biomass power inputs, aligning with the goals of sustainable renewable energy development.

Performance of rubberized reinforced concrete columns at ambient and high temperatures

The proliferation of discarded rubber tires is rapidly increasing at a concerning pace. Driven by the significant movement towards promoting environmental sustainability and mitigating the adverse environmental impact associated with non-biodegradable waste rubber tires, the objective of this study is to identify a viable and ecologically responsible resolution to the issue of discarded tires. This study experimentally focuses on the structural response and load-carrying capacity of reinforced concrete (RC) short columns containing crumb rubber as a partial replacement for fine aggregate after being exposed to temperatures of 27 °C, 300 °C, and 500 °C. Four concrete mixes were produced in which the natural fine aggregate (NFA) was partially replaced by CR with ratios of 0%, 5%, 10%, and 20% in volume. Twelve columns (three columns from each mix) were cast and tested under concentric loading. The experimental results showed that the workability and compressive strength of the concrete mixes decreased with increasing the CR replacement ratio. The residual failure load of columns decreased with increasing CR quantities and heating temperatures. The CR quantity had a more considerable impact on the decline of the column capacity than the heating temperatures. Analytical equations from international standards ACI 318–14, CSA A23.3, and previously existing equations were applied to study the validity of these equations in predicting the failure load of heated rubberized RC columns. Finally, a proposed equation for predicting the failure load of the columns is developed. The predicted failure loads obtained from the proposed equation were compared to the experimental results. The predictions from the proposed equation were in good agreement with the experimental data. Different statistical tests were done to compare the predictions from the proposed equation and previously existing equations for predicting the failure load of heated rubberized RC columns.

Thermal storage power plants – Key for transition to 100 % renewable energy

Transition from fossil/nuclear towards renewable energy supply can be achieved in three phases: firstly, variable renewable electricity (VRE) can be fed into the electricity grid just as available, while its fluctuations are balanced by thermal power plants fired by fossil fuels. Secondly, after achieving grid saturation with VRE, the residual load gaps must be covered and grid stability must be secured by highly flexible thermal power stations that generate dispatchable renewable electricity (DRE) without using fossil fuels. Thermal Storage Power Plants (TSPP) that integrate solar- and bioenergy are proposed for that purpose. Finally, in the third phase, renewable power supply can be extended to other sectors via power-to-X technologies, reducing fossil fuel consumption for transport, heat and industrial purposes. The phases of energy transition are described in the frame of a model scenario of the German electricity sector with TSPP as central element for the realization of Phase 2.

Passivity and underactuated modeling-based load energy coupling control for three-dimensional overhead crane systems

The conventional control strategies and methods with the three-dimensional model of overhead crane system are excessively dependent on model parameters and lead to the controllers design complex on position and anti-swing of overhead crane systems. With analysis on the coupling relationship among various state variables of overhead crane, the three-dimensional dynamic model of overhead crane based on mechanical virtual displacement and Lagrangian equation is constructed. A novel control strategy based on load energy coupling is designed to realize system positioning and eliminate the problem of residual load swing. The passivity of the three-dimensional overhead crane system is judged, and the energy composition of the system is deduced. The energy coupling function based on load displacement and swing angle is built. The control strategy of three-dimensional overhead crane system based on load energy coupling is designed by the Lyapunov stability theory and function construction method. The stability of the system is verified by the Lasalle invariance principle. With the experimental and programming, the proposed method is compared with different control methods. The results show that this method can realize the accurate positioning of the trolley more quickly and restrain the load swing more effectively.

Evaluation of residual flexural behavior of corroded fiber-reinforced super workable concrete beams

This study investigates the effect of macro synthetic fiber (MSF) volume and crack widths on corrosion of the reinforcing bars and residual flexural behavior of fiber-reinforced super-workable concrete (FR-SWC) beams exposed to accelerated corrosion. FR-SWC beams prepared with 0, 0.33%, and 0.66% MSF were pre-cracked at 0.2-, 0.4-, and 0.75-mm widths before corrosion testing. The controlled crack width was initiated in one set of beams that were then unloaded. The crack width was maintained for another set of beams during corrosion testing by inserting a shim. Test results showed that the use of 0.33% and 0.66% MSF reduced crack development and crack propagation, delayed corrosion initiation time, and significantly increased the residual flexural strength of beams subjected to accelerated corrosion. The beams reinforced with 0.66% MSF enhanced residual ultimate load, residual yield load, and residual flexural toughness by 10%–45%, 38%–113%, and 42%–150% compared to the corresponding non-fibrous beams. The improved flexural performance of beams made with MSF after accelerated corrosion can be attributed to the ability of MSF to reduce crack width due to corrosion damage. Crack width lower than 0.2 mm showed no significant effect on the residual flexural behavior of beams after corrosion testing. However, the pre-crack width over 0.2 mm showed a significant influence on the crack initiation and residual flexural behavior after accelerating corrosion. The pre-cracked beams with a 0.75 mm crack width retained the ultimate load of 65%–76%, yield load of 47%–80%, and toughness of 38%–83%, respectively, compared to their corresponding uncracked beams subjecting to accelerated corrosion. The un-shimmed beams allowed partial closure of cracks due to the presence of MSF after initial loading and increased the residual ultimate load, yield load, and flexural toughness by 7%–45%, 27%–82%, and 3%–56%, respectively, compared to their corresponding shimmed beams. A correlation between the residual flexural behavior and the rate of cross-sectional area loss of reinforcing bars due to corrosion was developed. Furthermore, a mechanism was proposed to explain the effect of MSF in improving the residual flexural performance in the cracked FR-SWC beams.

Multi-objective solution and decision-making framework for coordinating the short-term hydropeaking-navigation-production conflict of cascade hydropower reservoirs

The transformation of energy structure motivates hydropower to participate in peak shaving operations for grid stability, which conflicts with the multiple uses of cascade hydropower reservoirs. To coordinate the principal contradictory tasks of peak shaving, ship navigation, and power generation in day-ahead scheduling, a mixed integer linear programming model for the short-term multi-objective optimal scheduling is constructed. Specifically, a novel power release-based indicator is adopted to describe the navigation objective, while the minimization of the peak-valley difference of the residual load and the total water released are taken as the other two objective functions. Constraint aggregation and rectangular meshing methods are employed to handle the challenging nonlinear and nonconvex constraints. Subsequently, the Normalized Normal Constraint method, integrated with the mathematical optimization solver Gurobi, generates a set of well-distributed Pareto solutions, each representing a scheduling scheme. Finally, the Combined Weighting - Technique for Order Preference by Similarity to Ideal Solution is utilized as a decision-maker to trade off and determine a compromise solution for final implementation. Case studies on the cascade hydropower reservoirs of the Wujiang River in China demonstrate that the proposed model can adequately characterize the demands of various stakeholders, and the suggested framework can obtain an even and extensive Pareto front, mediate conflicts, and make reasonable decisions. Compared to the original peak-shaving scheme, the finalized compromise scheme reduces the peak-shaving effect by just 27.82% but offers simultaneous boosts of 96.54% in navigation benefits and 10.88% in power generation benefits. Consequently, the presented framework can be a promising alternative for conflict resolution of cascade hydropower reservoirs.

An efficient UV-C device for photoinactivation of human Corona and Influenza virus: Solution for small-scale reuse of personal protective equipment (PPE)

The world has recently witnessed a significant surge in the use of non-recyclable items such as Personal Protective Equipment (PPE) due to the COVID-19 pandemic. This has increased environmental pollution and caused a massive burden on the global waste management system. Hence, an effective strategy to address the demand-supply disparity and provide road map for sustainable management of used PPE are the need of the hour. In the present work, we aimed to develop a cost-effective, convenient, and effective strategy to safely reuse PPE by engineering an in-house UV-C-based Sanitization Device (UVSD) and systematically evaluating its potential to disinfect virus-contaminated PPE. To this end, we tested the capacity of the UVSD to disinfect single-use PPE and N95 face masks, experimentally soiled with the human Influenza (A/PR/8/1934/H1N1) and human Coronavirus (HCoV-OC43). For this, the UV-C-based photoinactivation of both viruses was assessed by in vitro cell protection, quantification of viral gene transcript, and residual viral load by plaque-forming assay. Further, Indirect immunofluorescence and viral hemagglutination assays were also performed to visualize and quantify the viral titers at different post-exposure (UV-C) time points. Our results demonstrate that 15 min exposure to the virus-contaminated simple or complex PPE within the UVSD cabinet could effectively inactivate both the H1N1 and HCoV-OC43 viruses.

Towards Feasible Solutions for Load Monitoring in Quebec Residences.

For many years, energy monitoring at the most disaggregate level has been mainly sought through the idea of Non-Intrusive Load Monitoring (NILM). Developing a practical application of this concept in the residential sector can be impeded by the technical characteristics of case studies. Accordingly, several databases, mainly from Europe and the US, have been publicly released to enable basic research to address NILM issues raised by their challenging features. Nevertheless, the resultant enhancements are limited to the properties of these datasets. Such a restriction has caused NILM studies to overlook residential scenarios related to geographically-specific regions and existent practices to face unexplored situations. This paper presents applied research on NILM in Quebec residences to reveal its barriers to feasible implementations. It commences with a concise discussion about a successful NILM idea to highlight its essential requirements. Afterward, it provides a comparative statistical analysis to represent the specificity of the case study by exploiting real data. Subsequently, this study proposes a combinatory approach to load identification that utilizes the promise of sub-meter smart technologies and integrates the intrusive aspect of load monitoring with the non-intrusive one to alleviate NILM difficulties in Quebec residences. A load disaggregation technique is suggested to manifest these complications based on supervised and unsupervised machine learning designs. The former is aimed at extracting overall heating demand from the aggregate one while the latter is designed for disaggregating the residual load. The results demonstrate that geographically-dependent cases create electricity consumption scenarios that can deteriorate the performance of existing NILM methods. From a realistic standpoint, this research elaborates on critical remarks to realize viable NILM systems, particularly in Quebec houses.

Endovascular Thrombectomy for Acute Iliofemoral Deep Venous Thrombosis Through a Jugular Approach with a Rotational Device.

To report the effectiveness of pharmacomechanical catheter-directed thrombolysis (PCDT) in the management of acute iliofemoral deep venous thrombosis (DVT) via the jugular vein using a slow rotation and large-tip device (SRD) in a large cohort of patients. From 2011 to 2021, 277 patients (mean age 45years, 59.2% women) were treated in 6 centres with PCDT for ilio-fémoral DVT. PCDT was performed via the jugular vein and consisted of one session of fragmentation-fibrinolysis, aspiration and, if needed, angioplasty with stenting. The aim of PCDT was to achieve complete clearance of the venous thrombosis and to restore iliofemoral patency. Residual thrombotic load was assessed by angiography, venous patency by duplex ultrasound and clinical effectiveness by the rate of post-thrombotic syndrome (Villalta score > 4). All patients were treated via the jugular vein using an SRD, and all but one were treated with fibrinolysis. Angioplasty with stenting was performed in 84.1% of patients. After the procedure, the residual thrombotic load at the ilio-fémoral region was < 10% in 96.1% of patients. The rate of major complications was 1.8% (n = 5), the rate of minor complications was 4% (n = 11), and one patient died from pulmonary embolism (0.4%) At a median follow-up of 24months, primary and secondary iliofemoral patency was 89.6% and 95.8%, respectively. The rate of PTS was 13.8% at 12months. PCDT via the jugular vein using an SRD is an efficient treatment for acute iliofemoral DVT and results in high long-term venous patency and low PTS rates. Level of evidence Level 4, Case series.

Microalgae growth using treated domestic effluent added to emerging pollutants: Removal mechanism and generation of by products

The objective was to assess the efficiency of microalgae metabolism in removing BOD5, COD, N, P, and emerging pollutants (EPs) from pretreated domestic effluent. Spirulina platensis and Scenedesmus obliquus were cultivated in standard medium with the addition of 5 % and 10 % pretreated domestic effluent every 5 d. The growth parameters, biochemical composition, and removal efficiencies were evaluated. Spirulina was scaled up to 10 L tanks with an open reactor, here using 10 % effluent and 20 μg/L of EPs (caffeine, fluoxetine, and acetylsalicylic acid) every 5 d. EP concentrations and the generation of degradation byproducts were monitored. Microalgae exhibited significant growth in both effluent additions, achieving biomass concentrations exceeding 1 g/L. After 30 days, all the physical-chemical parameters of the effluent were reduced (removals <80 %). The scaled-up experiments demonstrated removal of 39 % caffeine and 80 % fluoxetine after 30 d. EP degradation byproducts (theobromine and norfluoxetine) from caffeine and fluoxetine degradation showed EP biodegradation as a mechanism. Microalgae cultivation proved effective as a posttreatment method for the residual loads remaining after conventional treatment, and it can also target new fractions of pollutants in wastewater, reducing the risk to aquatic organisms. Moreover, the biomass of Spirulina platensis obtained after treatment exhibited high carbohydrate and protein contents (55 % and 29.18 %, respectively), showing potential as a source of bioenergy and biofertilizer products.

German atlas of Thermal Storage Power Plants (TSPP) - A first approach

The paper assesses the potential of transforming conventional power plants to Thermal Storage Power Plants (TSPP) in Germany on a macro scale. The resulting atlas is based on a scenario of the power sector published before that assumes that current conventional power plants will be transformed to TSPP with a capacity of 70 GW in 2040, providing reliable power supply for the residual load. In order to achieve this, several criteria are introduced that rank all power plants in Germany in terms of suitability for such conversion. Moreover, a method of finding the necessary land areas for PV and biomass required as primary energy sources for the TSPP is described with the help of a geographic information system. The analysis is divided into 2 parts: The first part is to consider the whole country as a single entity, and all power plants are analyzed according to their ranking list in order to find out if the scenario is consistent with existing PV and biomass potentials. The second part focuses on individual power plants without considering the ranking list, in order to find the best potential PV and biomass supply areas for each potential power plant that could be transformed on a first-come-first-save basis. The findings of this study include mapping of the transformation potential of individual power plants, and also provides an integrated framework for a TSPP transition at the national level. By providing a comprehensive overview of the TSPP-atlas across the country, these maps may serve as a helpful tool for policymakers and power plant owners in making decisions regarding the deployment of TSPP.

Cell-filling reinforced materials for improving the low-velocity impact performance of composite square honeycomb sandwiches: Polymethacrylimide foam vs. aluminum foam

In this study, PMI foam and aluminum foam are used as reinforcement materials for filling the cells of carbon fiber-reinforced composite square honeycomb sandwiches (CSHSs), forming two new sandwich structures, namely, PMI foam-reinforced CSHS (PRCSHS) and aluminum foam-reinforced CSHS (AFRCSHS). The impact resistance and residual flexural performance of the composites is compared by using low-velocity impact (LVI) and three-point bending (3 PB) experiments. The different impact energy levels of 25 J, 50 J, 65 J, and 100 J are applied. The impact and bending failure process and failure mechanism are analyzed using a combination of industrial computed tomography (ICT) and scanning electron microscopy (SEM). PRCSHS and AFRCSHS are compared for various enhancement effects and their resulting lightweight features. The residual flexural and impact resistance properties of the two sandwiches improved significantly. Compared with CSHS, the maximum impact load of PRCSHS and AFRCSHS increased by 115.6% and 78.9%, respectively. Moreover, the impact energy absorption, residual flexural load, and residual flexural energy absorption increased by 30.9% and 21.3%, 80.7% and 58.5%, and 173.1% and 84.3%, respectively. The PRCSHS was noticeably lightweight, but AFRCSHS was not sufficiently lightweight. The qualitative results of comparison of the two reinforcement materials in this study can be extended to other carbon fiber-reinforced all-composite 2D honeycomb sandwiches.

Design and Verification of Deep Submergence Rescue Vehicle Motion Control System.

A six degree-of-freedom (DOF) motion control system for docking with a deep submergence rescue vehicle (DSRV) test platform was the focus of this study. The existing control methods can meet the general requirements of underwater operations, but the complex structures or multiple parameters of some methods have prevented them from widespread use. The majority of the existing methods assume the heeling effect to be negligible and ignore it, achieving motion control in only four or five DOFs. In view of the demanding requirements regarding positions and inclinations in six DOFs during the docking process, the software and hardware architectures of the DSRV platform were constructed, and then sparse filtering technology was introduced for data smoothing. Based on the adaptive control strategy and with a consideration of residual static loads, an improved S-plane control method was developed. By converting the force (moment) calculated by the controller to the body coordinate system, the complexity of thrust allocation was effectively reduced, and the challenge of thrust allocation in the case of a high inclination during dynamic positioning was solved accordingly. The automatic control of the trimming angle and heeling angle was realized with the linkage system of the ballast tank and pump valve. A PID method based on an intelligent integral was proposed, which not only dealt with the integral "saturation" problem, but also reduced the steady-state error and overshooting. Water pool experiments and sea trials were carried out in the presence of water currents for six-DOF motion control. The responsiveness and precision of the control system were verified by the pool experiment and sea trial results and could meet the control requirements in engineering practice. The reliability and operational stability of the proposed control system were also verified in a long-distance cruise.

Residual load capacity of HVFA reinforced concrete after elevated temperature heating: Experimental and analytical study

High volume fly ash (HVFA) is used as structural concrete's main constituent in the current concrete construction practice. The residual load capacity of HVFA reinforced concrete after elevated temperature heating is needed for retrofitting compression members after fire exposure. In this experimental study, an effort has been made to estimate the axial load capacity of concrete containing HVFA after 28 and 90 days of curing after elevated temperature heating at 200 °C, 400 °C and 600 °C. The 35% and 50% amount of cement was partially replaced by fly ash. The weight loss and crack pattern in reinforced HVFA concrete were also studied. It has been observed that after heating at elevated temperature, the compression behavior of fly ash concrete is better than that of plain concrete. The analytical models are proposed to estimate the residual load capacity of HVFA concrete columns after exposure to elevated temperature. The model predictions are reasonably good. These models can be used to assess the load carrying capacity of columns in concrete buildings containing HVFA after elevated temperature exposure for deciding strengthening schemes.

Impact performance of fire-damaged hybrid steel-BFRP reinforcement concrete beams: Influence of area ratio and arrangement of BFRP bars

Hybrid steel-BFRP reinforced concrete (HRC) beams have demonstrated their ability to meet the rigorous demands for both strength and serviceability. However, the mechanical properties of HRC beams under fire accompanied by impact loadings are not yet clear. In order to delve into the impact resistance of HRC beams under high temperatures, a three-dimensional numerical model was crafted to account for both the effects of strain rate and temperature degradation. The study aimed to examine how the impact resistance of HRC beams is influenced by varying area ratios and arrangements of BFRP bars. The model's reliability was ascertained through a comparison between its simulation outcomes and the results of physical tests. The results show that HRC beams exhibit a significant reduction in stiffness, impact and internal force under fire conditions (39 %, 38 % and 72 % for a fire duration of 45 min, respectively). Furthermore, the damage is concentrated in the mid-span. The impact performance of HRC beams at room and high temperatures is between those of pure steel-RC beams and pure-BFRP beams. The variations under the same fire conditions in the displacement and internal force of beams with different BFRP bars area ratios reach 70 %, while with different arrangements of BFRP bars do not differ much (within 20 %). The dynamic to static stiffness ratio and ultimate load ratio is reduced following the growth of BFRP bars area ratio (max. gap up to 56 % and 25 %) and fire time (max. gap up to 15 % and 20 %). Therefore, specimen design prioritizes the bar arrangement with better corrosion resistance. Additionally, the residual bearing capacity of HRC beams is only 10–40 % of the original under 45 min fire duration. The association of residual load capacity and displacement with fire time shifted from linear to nonlinear with rising temperature.

Parameters Affect Flexural Mechanism to Prevent Progressive Collapse of RC Buildings

This study investigates the effect of spans length, reinforcement ratio and continuity of flexural reinforcement on the progressive collapse performance of double span beams over failed columns. The investigations focus on initial flexural resisting mechanism to prevent the progressive collapse. Detailed nonlinear finite element simulation of double span beam-column sub-assemblages subjected to residual gravity loads that initially carried by the failed column is adopted for the investigations. Nonlinear static pushover analysis is conducted in which capacity curves are derived and compared with demanded capacities. The effect of spans length, reinforcement ratio and number of continuous bottom flexural reinforcement on progressive collapse are considered in the investigations. Analysis results show that the strength to resist progressive collapse has decreased by 25.4 % and the ductility increased by 103 % following the increasing in span length from 5 m to 7 m. On the other hand, increasing reinforcement ratio of top flexural reinforcement from 0.447 to 1.089 leads to 26.27 % increasing in strength accompanied with a decrease in ductility equal to 16.42 %. In addition, extending all bottom bars rather than the minimum specified two bars resulted in 12 % increasing in strength and 40.28 % decreasing in ductility.

Effect of Fire Flame (High Temperature) on the Behaviour of Axially loaded Reinforced SCC Short Columns

Experimental research was carried out to investigate the effect of fire flame (high temperature) on specimens of short columns manufactured using SCC (Self compacted concrete). To simulate the real practical fire disasters, the specimens were exposed to high temperature flame, using furnace manufactured for this purpose. The column specimens were cooled in two ways. In the first the specimens were left in the air and suddenly cooled using water, after that the specimens were loaded to study the effect of degree of temperature, steel reinforcement ratio and cooling rate, on the load carrying capacity of the reinforced concrete column specimens. The results will be compared with behaviour of columns without burning (control specimens). The results showed that, the ultimate load capacity of columns exposed to fire decreases with increasing the fire flame temperature. At burning temperature 300 Co , 500 Co and 700 Co , the average residual ultimate load capacity for gradually cooled specimens were 91%, 81% and 71% respectively. By increasing the ratio of longitudinal reinforcement 44% , the maximum improvement in the ultimate load capacity was 24% and 17% for the gradually and sudden cooling respectively at Co 500 . For the same longitudinal reinforcement ratio and fire burning temperature, the ultimate capacity for the sudden cooling specimens was less than that of gradually cooled specimens by about 10%.

Effects of double-arched geometry and tensile strength on the pullout resistance of fibers

This study evaluated the pullout resistance performance of a developed double-arched steel fiber. Pullout experiments were conducted to assess the resistance load, bond strength, and energy absorption capacity of the fiber according to the geometry and tensile strength of the fiber. Double-arched (DA) steel fibers demonstrated peak and residual resistance loads approximately 36–112% and 29–163% higher than hooked-end and single-arched steel fibers, respectively. The DA steel fiber also significantly increased the bond strength and energy absorption capacity by approximately 58–159% and 125–130%, respectively, compared to the hook-end and single-arched steel fibers. Moreover, the DA fiber exhibited a more significant increase rate in pullout resistance load, bond strength, and energy absorption capacity with increasing tensile strength. A prediction model was also developed to incorporate the influence of plastic bending and friction resistance on the pullout behavior of the DA fiber. The resistance loads and decreasing trend obtained from the prediction model exhibited a very close agreement with the experimental results.