Capacity Calculation Method Research Articles

Residual mechanical properties and numerical analysis of recycled pebble aggregate concrete after high temperature exposure and cooled by fire hydrant

In urban fire, the structure will not only be subjected to high temperature, but also cooled by fire hydrant. This paper presents the experimental results of the residual mechanical performance and the complete compressive stress–strain relationship of recycled pebble aggregate concrete (RAC) after exposure to high temperature of 20 to 600 ℃ and cooled by fire hydrant. In the experiments, five different concrete compositions were designed by substituting natural coarse aggregates with recycled coarse aggregates at the replacement ratios of 0%, 30%, 50%, 70% and 100%. Results exhibit that with the increase of exposure temperature, the surface color of the specimens changes from light to dark, the mass of RAC first increases and then decreases, and the residual mass of RAC at 200 ℃ is higher than that at room temperature. The compressive strength and the strain at the peak point decrease rapidly with the increase of temperature. The compressive strength and the strain at the peak point fluctuate with the increase of aggregate replacement percentage, and the temperature and aggregate replacement percentage have little effect on the ductility of RAC. The residual bearing capacity calculation method and constitutive equation of RAC after high temperature exposure and cooled by fire hydrant are proposed and verified. The accuracy of the constitutive equation is verified by ABAQUS finite element analysis software.

Bearing Capacity of Footings on Rock Masses Using Flow Laws

The influence of the non-associative flow law on the bearing capacity of shallow foundations on rock masses is, in general, a subject that is not discussed in the field of rock mechanics. The calculation methods of bearing capacity usually do not define which flow law is adopted and, in some methods, the associative flow rule is assumed without knowing how that hypothesis influences the bearing capacity of the rock mass. In this paper, the study of the influence of the dilatancy angle on the bearing capacity of shallow foundations on rock masses is presented. The variation of the bearing capacity with the associative flow law and the non-associative flow law with zero dilatancy angle is studied using the finite difference method and by considering the influence of the self-weight of rock material. The calculations confirm the great influence of the flow law on the bearing capacity and a correction coefficient is proposed, which makes it possible to estimate the variation of the bearing capacity of the rock mass in terms of the function of the flow law for the hypothesis of weightless rock masses.

Numerical and parametric studies on out-of-plane flexural and shear behaviour of half steel-concrete slabs

This study proposed a 3D finite element model (FEM) to investigate the out-of-plane flexural and shear behaviour of half steel-concrete (Half-SC) slabs using general software ABAQUS, simplifying the headed stud to zero-length springs in three directions. The developed FEM against fifteen Half-SC slabs test results well predicted four failure modes, namely, flexural failure, shear failure, balanced failure, and interface slippage failure. Except for the specimen in interface slippage failure, the load versus midspan deflection curves had a good agreement with the test curves. It indicated that for the slabs in partial shear connection design, the interface characteristics have a sensitive effect on their mechanical behaviour. Extensive validations of FEM were conducted on the failure mechanism of the Half-SC slabs during the loading process. Parametric studies were performed with the developed FEM to investigate the influences of main parameters on the bearing capacity of the Half-SC slabs. FEA results indicated that the increasing section steel ratio and volumetric steel ratio of the tie bar enhanced the bearing capacity of the Half-SC slabs, while there was an upper limit for both steel ratios. As the shear span ratio increased, Half-SC slabs transitioned from shear failure to flexural failure, with bearing capacity decreasing significantly. The influence of the shear span ratio, section steel ratio, and volumetric steel ratio of the tie bar on the bearing capacity decreased in order of significance. Furthermore, the bearing capacity calculation method of out-of-plane flexural and shear strength was verified based on numerical studies. A unified tie-arch model covering flexural failure and shear failure was then established. Finally, the formula for calculating out-of-plane bearing capacity was proposed based on the elastic design method.

태양광 발전의 전기차 사용 후 배터리 적용을 위한 ESS의 최적 용량 및 배터리 최대 가격 산정

Jeju Island, Republic of Korea, is the most active region for electric vehicles and renewable energy sources. However, in Jeju Island, the problems of wasted batteries from electric vehicles and the curtailment of renewable energy output already appeared. To solve this problem, there is a method to install and operate SLB(Second life battery from electric vehicle) with solar power generation. From this perspective, this paper proposes the optimal capacity calculation and maximum price calculation methods for ESS(Energy storage system) based SLB applied to solar power generation. The optimal capacity and maximum price of the SLB are derived based on the capacity and price of the new ESS. The proposed method was simulated based on the weather data actually measured in the Jeju area using the MATLAB program. As a result of the simulation, the optimal capacity of SLB was calculated as 389kWh for 200kW PV farm. To Install calculated SLB, 354SLB modules were required and its maximum price was decided as 132,000KRW.

Calculation method for the axial load-bearing capacity of steel pipe-to-sleeve grouted connections

The existing axial load-bearing capacity calculation method for the steel pipe-to-sleeve grouted connections is introduced. It is proposed that by considering the tensile strain of a grouting material along the inner cyclic direction of the sleeve reaching its ultimate tensile strain as the limit state, the limit load-bearing capacity calculation model of the steel pipe-to-sleeve grouted connections is established via:1.) the deformation coordination relationship among the cyclic strain of the sleeve, steel pipe and the grout; 2.) the overall static equilibrium of the grout; and 3.) the three-way constitutive relationship of the grout. The calculation model has a wide application range and strong applicability, In addition, the proposed model is used to calculate the axial load-bearing capacity of 82 sets of steel pipe-to-sleeve grouted connection specimens in the literature, and the calculated values agree well with the experimental values.

Examining mechanical behavior of steel-bamboo composite I-section column under long-term loading

The steel-bamboo composite structure is a novel composite structure, which is characterized by light weight and high bearing capacity of structural components, as well as excellent seismic performance and good thermal performance of fabricated buildings. To facilitate its engineering application and better understanding the deformation law of composite column during design reference period, mechanical properties of steel-bamboo composite column under long-term loads are investigated in this paper. 27 composite I-section columns were designed and fabricated, among which 18 specimens were first investigated in static loading test with steel ratio and slenderness ratio as main parameters, failure modes and effect of each parameter on the axial compression performance was observed and analyzed. Then, a self-balanced loading device was designed to perform long-term loading test on 6 specimens with loading level and steel ratio as main parameters, and the other 3 specimens were adopted to monitor the temperature effect on creep. The creep process of specimens was observed and the nonlinear fitting analysis of creep data was carried out using Burger model. Once the predetermined long-term loading duration was reached, the secondary static loading test were carried out to study the influencing factors of bearing capacity and deformation, as well as their variation laws. Further, calculation formula of yield bearing capacity was derived by analyzing yield conditions of composite column, as two calculation methods of ultimate bearing capacity were proposed based on superposition principle and limit equilibrium theory. Results show that the composite columns have good integrity, high deformation capacity and bearing capacity, which improves significantly with the increase of steel ratio and decreases with the increase of slenderness ratio. Creep deformation become basically stable after 90 days of loading, which can be accurately described by Burger model. After the long-term loading, ductility and ultimate strain of the specimens were obviously increased, while the bearing capacity was not significantly affected. The average error between the theoretical and experimental results of yield and ultimate bearing capacity is smaller than 7%, which indicates that the established calculation methods have high accuracy and are suitable for predicting the bearing capacity of steel-bamboo composite I-section columns. It is proved that scientifically designed steel-bamboo composite columns have reliable bearing capacities and controllable deformations, and can be safely applied to practical projects.

Research on the Calculation Method of Distributed Photovoltaic Access Capacity Considering Harmonic Characteristics

To raise the maximum access ability of the maximal distributed photovoltaic system, based on the metering terminal of plant and station system for many years, a nonparametric estimation method based on kernel density is proposed to calculate harmonic probability distribution, this paper proposes the calculation method of superposition index and simultaneous coefficient suitable for distributed photovoltaic grid-connection, and puts forward the capacity calculation method considering harmonic constraints. An example shows that the proposed method can increase the maximum admittance capacity by at least 15% compared with the traditional method under the condition that the harmonic emission level does not exceed the threshold value of national standard, and realize the safe, stable and economic operation.

Multi-source residual capacity collaborative dynamic compensation strategy based on robust residual generator

In this paper, a dynamic compensation strategy based on a residual generator was proposed to solve the problem of the power quality of the bus in an isolated AC microgrid. Firstly, the disturbance analysis of power quality problems such as voltage fluctuation, three-phase imbalance, harmonic wave is carried out, and the disturbance current is converted into the time domain function in the dq rotating coordinate system. Secondly, the inverter establishes the state space model under the dq rotation coordinate system. Then, the control structure based on residual generator is proposed, the voltage compensator is solved by model matching method, and the current loop secondary compensator is designed to eliminate the influence of the voltage compensator on the current loop. Thirdly, the residual capacity calculation method of the inverter is analysed, and the residual capacity is used to achieve the power quality collaborative governance on the parallel inverter system with the perturbation allocation method. Finally, the control strategy proposed in this paper is verified by the simulation built in PSCAD/EMTDC, and the results can be effectively applied to the low-level control of microgrid, and the power quality control effect of voltage fluctuation, three-phase unbalance and harmonics is good, which improves the robustness of the system to a certain extent.

실측 부하 데이터 기반 경제성 분석을 이용한 도시철도 ESS 최적 용량 산정 연구

In this paper, method to calculate the maximum capacity of Energy Storage System(ESS) connecting to urban railway substations using characteristics of load patterns is introduced. Optimal capacity of ESS was calculated using economic analysis, Prior to this, the feasibility of the capacity calculation method based on the maximum peak value was shown using the actual data analysis at the morning time when the highest peak occurs. Using the net present value method, which is one of the methods of economic analysis, the method of reducing only the morning peak and the most economical method of reducing all-day are determined and the optimal capacity of ESS is calculated accordingly.

도시철도 부하 패턴 기반 ESS 최대 용량 산정 및 동작 알고리즘 연구

In this paper, we introduce the method of reducing only the morning peak of the ESS and the method of calculating the maximum ESS capacity according to the method of reducing the entire day by using the characteristic that the load of the urban railway substation shows a different load pattern depending on weekdays, weekends, and holidays. Furthermore, an operation method suitable for urban railroad is introduced using the operation algorithm for each of the five points of time of the ESS according to the load pattern. To verify the introduced maximum capacity calculation method and ESS operation algorithm, power analysis program, PSCAD/EMTDC was used.

Centrifugal model test of post-grouting pile group in loess area

In this paper, based on the in-situ post-grouting single pile of the Wuqi-Dingbian Expressway in China, the bearing performance of the post-grouting pile groups in loess area were studied with the use of the centrifugal model test. Taking into consideration pile spacing and number of piles, nine working conditions of single pile, 2 × 2 pile group with different pile spacing and 3 × 3 pile group were designed. The settlement, ultimate bearing capacity, pile side resistance, and end resistance ratio of pile groups with different pile spacing and number of piles before and after grouting were compared and analyzed. Finally, based on the change in the group efficiency obtained before and after grouting through the model test, the group efficiency of non-grouting pile groups in code was modified and applied to the calculation of the ultimate bearing capacity of the grouting pile groups. The results show that the group efficiency will decrease after grouting, and the bearing capacity of grouting pile groups increases gradually with the increase of pile spacing, and reaches the maximum when the pile spacing is 5d. The proposed bearing capacity calculation method of grouting pile group was validated by the model test results, and the calculation results generally agree with the model results, which is valuable for pile foundation designs.

Experimental and analytical investigation on fire resistance of glulam-concrete composite beams

The timber-concrete composite beam characterized by good mechanical behavior, low susceptibility to vibration and high sound insulation has a wide application in high-rise and long-span timber structures. However, the published study on the fire resistance of TCC beam is limited. In this research, one short-term failure test at ambient temperature and five full-scale fire tests were performed on the glulam-concrete composite beams. The influences of the load ratio, presence of timber board and fire-rated gypsum plasterboard on the temperature field and fire resistance were investigated in detail. The test results showed that the fire resistance of the composite beam was decreased with the increase of the load ratio. The composite beam with timber board interlayer outperformed the beam without the interlayer in terms of fire resistance. Moreover, the fire-rated gypsum plasterboard protection on the glulam beam could effectively improve the fire resistance of the composite beam. The finite element models of the composite beams were established to predict the temperature field of composite beams under fire. The average temperature values of concrete slabs under different fire times were obtained from numerical simulations. Considering the influence of high temperature on the glulam beam, concrete slab and shear connectors, the calculation methods of load carrying capacity and bending stiffness of the composite beam under fire were proposed.

A Topology Analysis-Based MMC-HVDC Grid Transmission Capacity Calculation Method

Modular multilevel converter-based high voltage direct current (MMC-HVDC) has a broad application prospect in renewable energy transmission. With the development of converter capacity, the transmission capacity calculation for MMC-HVDC grids becomes important for power dispatching. The existing method depends on manual work and is suitable for a simple grid. However, as the grid structure and operation modes become more and more complex, it becomes difficult to calculate the transmission capacity of different operation modes for an MMC-HVDC grid. This paper analyzed and simplified affecting factors and basic topologies. On this basis, a topology-based MMC-HVDC grid transmission capacity calculation method is proposed. First, an MMC-HVDC grid is divided into sending end grid, transmission section lines, and receiving end grid. Then the power limits of these three parts are calculated. Finally, the transmission capacity is determined by analyzing the connection mode of these three parts. This method can be adapted to any kind of MMC-HVDC grid and can be easily programmed.

Comparative Study of High-Performance Concrete Characteristics and Loading Test of Pretensioned Experimental Beams

High-performance concrete (HPC) is subjected to wide attention in current research. Many research tasks are focused on laboratory testing of concrete mechanical properties with specific raw materials, where a mixture is prepared in a relatively small amount in ideal conditions. The wider utilization of HPC is connected, among other things, with its utilization in the construction industry. The paper presents two variants of HPC which were developed by modification of ordinary concrete used by a precast company for pretensioned bridge beams. The presented variants were produced in industrial conditions using common raw materials. Testing and comparison of basic mechanical properties are complemented with specialized tests of the resistance to chloride penetration. Tentative expenses for normal strength concrete (NSC) and HPC are compared. The research program was accomplished with a loading test of model experimental pretensioned beams with a length of 7 m made of ordinarily used concrete and one variant of HPC. The aim of the loading test was to determine the load–deformation diagrams and verify the design code load capacity calculation method. Overall, the article summarizes the possible benefits of using HPC compared to conventional concrete.

Calculation of Inter-Column Slabs Bearing Capacity by Kinematic Method

The method of bearing capacity calculation of the inter-column slabs of flat slab frame system is developed by a kinematic way based on the ultimate equilibrium method. The basis of the study is the kinematic method of the limit equilibrium method and its application to calculate the load-bearing capacity of the inter-column slab in flat slab structural system, as well as to select the area of the working reinforcement. Attention is also paid to establishing the location of the lines of plastic hinges formation.

Interoperability of LNG terminals and gas pipeline networks

The interchangeability between natural gas of different sources and LNG have been concerned and tackled to a certain extent at home, and the interconnection of gas infrastructures including LNG terminals and gas pipeline networks have also been lifted up to the national level since 2018. However, the research on the interoperability with overall-planning interchangeability and interconnection at a higher level is still in the blank stage at home. By extensively investigating EU's regulations and practices related to interoperability in the field of natural gas pipeline network, this paper put forward the conceptual definition of the interoperability of gas infrastructures including LNG terminals and gas pipeline networks for the first time. Then, the basic implementation framework and components of interoperability were set up. Finally, domestic latest typical cases which have presented the characteristics of interoperability in the recent two years were analyzed. And the following research results were obtained. First, interoperability and third-party access are two independent themes. Second, the target of interoperability is to realize the cross-system unimpeded flow of natural gas of all facility users between different facilities according to the uniform specification of specific technical standards, operation criteria and operation procedures of various facilities, based on interconnection, coordination and information interaction. Third, the framework of interoperability consists of 8 key elements, including gas quality standard & interchangeability, facility interconnection, facility interconnection agreement, unified measurement unit, unified electronic data exchange platform, technical capacity calculation method, approval procedure of LNG carrier entering the port and ship–shore compatibility unique to LNG terminals, and gas quality based LNG storage and tank loading rules. Fourth, it is recommended to give consideration to both target and requirement of interoperability and fully integrate 3 elements that are discussed more deeply and more crucial in EU countries (i.e., facility interconnection agreement, unified electronic data exchange platform and technical capacity calculation method) into the practice system of treatment reform of domestic natural gas industry chain.

Numerical simulation of shear capacity of lightweight aggregate concrete stud connectors

In order to study the mechanical properties of the stud connectors in lightweight aggregate concrete (LWAC), the finite element software ABAQUS was used to establish the push test models of ordinary concrete and LWAC, respectively. Through parameter analysis of 21 models, the influence of different parameters on the shear performance of LWAC stud connector was studied. Among them, concrete strength, stud diameter and stud strength have strong effects. Compared with stud connector in ordinary concrete, the LWAC stud connector enters the elastoplastic working stage earlier, the ultimate slip is slightly larger, the ductility is better, and the shear capacity is about 11% lower. Regression analysis was performed on the finite element calculation results, and the method for shear bearing capacity calculation of the stud connectors in LWAC is given.

Analysis of COVID-19 Impact on Natural Gas Supply Reliability

In this study, we have analyzed the impact of COVID-19 on natural gas supply reliability. Natural gas supply reliability is defined as the ability to satisfy the market demand and is determined by both supply-side and demand-side policy. To evaluate the gas supply reliability of the natural gas pipeline system, we have applied the method of gas supply capacity calculation based on the results of the previous gas supply reliability studies. The method combines the unsteady flow hydraulic analysis, simulation of the state transition process, and the forecasting analysis of the demand and consumption. The analysis presents a case study based on the gas pipeline system in China. The analysis results indicate that the COVID-19 consequences will cause a decrease in gas supply reliability.

Improvement of Automatic Calculation Method of CASE Bearing Capacity

Because of the reliance on the empirical parameter CASE damping coefficient Jc, the high‐strain CASE method is not recommended. The automatic bearing capacity calculation method RAU can avoid this, but it cannot be applied to friction piles. Based on the analysis of the automatic calculation method of bearing capacity RAU, considering the influence of pile side soil resistance unloading, this paper improved the RAU method through the influence of pile side soil damping on the velocity of the pile mass point during the stress wave propagation process. In this paper, we compare the collected static load test results of test piles with the improved automatic method results. The unary linear regression analysis is carried out with the help of statistical tools. The unary linear regression of the improved automatic method bearing capacity results on the static load test bearing capacity results is established. The improved automatic method solves the problem that the RAU method is only applicable to end‐bearing piles and can be applied to the quality analysis and bearing capacity calculation of the high‐strain curve of the driven pile.

Bending performance of NSTS members based on steel tube connection

This paper proposes a NSTS (new steel tube slab) structure by connecting the longitudinal steel tubes with small steel tubes in transverse, in order to decrease the construction difficulty and improve the bearing capacity of existing NTR (new tubular roof) or STS (steel tube slab) structures. Experimental study on the bending performance and influences of following parameters are carried out: the connection type of the steel tube, the diameter and eccentricity of the small steel tube, and the thickness of the bottom steel plate. The results show that the NSTS members present progressive ductile flexural failure under concentrated load. The connection type has important effect on the mechanical behavior, and the bolts fixed T-shaped plate (B+T) connection method, which provides much higher bending stiffness, is proved to be the most reliable connection type. The increase of small steel tube diameter enhances the bending performance as expected, which also confirms the effectiveness of the B+T connection, while the tube eccentricity presents little impact on the bearing capacity. The bottom steel plate significantly improves the bearing capacity and stiffness and reduces the mid-span deflection. Furthermore, the bending capacity calculation method is proposed and the calculated values show good agreement with the test results. Also, the effect rules of the diameter-thickness ratio of the small tube, the length-diameter ratio of the member and the thickness variety of the bottom steel plate on the bending capacity of NSTS members are further investigated based on the proposed theoretical method.