Current Load Factor Research Articles

Analysis of 38 kW class agricultural tractor engine load rate according to agricultural operation

This study was conducted to analyze the engine load ratio of a 38 kW agricultural tractor to calculate national emissions. Engine output was calculated using engine CAN (Controller area network) data measured through a load measurement system. In this study, plow tillage (PT) and rotary tillage (RT), which are the main agricultural tasks of small and medium horsepower tractors, were selected and performed three times for each stage. The engine load ratio was calculated as the ratio of the engine power generated during work and the engine rated power, and weights (25% each for PT M1, PT M2, RT L3, and RT L4) according to the agricultural work ratio were applied. The engine load ratio was found to be an average of 0.68 and 0.75 for the M1 and M2 stages of plow tillage work, respectively, and an average of 0.57 and 0.65 for the L3 and L4 stages of rotary tillage work, respectively. The weighted load ratio was 0.17, 0.19, 0.14, and 0.16 for plow tillage operation M1, M2, and rotary tillage operation L3 and L4, respectively. The integrated load factor was found to be 0.66, which is approximately 1.38 higher than the current domestic load factor of 0.48.

Temperature Dependence of Optimal Shape and DC Current Transport Characteristics of 3 T Whole Body REBCO MRI Magnet

This paper reports the optimum design results of REBCO high-temperature superconducting magnets for 3 T-whole-body magnetic resonance imaging (MRI). The REBCO magnet consists of a main coil, compensation coil, and shield coil, and optimum design is carried out using an immunogenetic algorithm. A magnetic field uniformity of 20 ppm was observed in the uniform sphere inside the coil, and a 5-gauss region of 2.67 m in radial length and 4.50 m in axial length was realized. The local magnetic field vector distribution of the designed coil was also calculated for the designed magnet using electromagnetic field analysis, and the local voltage was obtained using the magnetic field/temperature dependence of the electric field vs. current density properties evaluated with the REBCO short sample. Then, the voltage vs. current characteristics of the magnet were evaluated by adding it over the entire coil length. Defining the current load factor (operating current/critical current) of the designed magnet using the above analysis results makes it possible to clarify the relationship between the operating current, optimized magnet shape, and required wire length for the operating temperature. In particular, we found that the required HTS tape length and transport current have a simple linear relationship in the operating temperature range below approximately 50 K.

The Influence of Load on the Vibration and Noise Characteristics of Transformer

In order to further understand and grasp the impact of load on the vibration and noise characteristics of the transformer, this article analyzes the impact of load factors, power factor, harmonic current, three-phase unbalance and other load factors on transformer vibration and noise from the perspective of transformer vibration mechanism. A 10kV/200kVA three-phase oil-immersed distribution transformer was used as the object. Experiments were conducted to study the changes in the spectrum distribution, noise intensity and A-weighted sound pressure level of the transformer vibration and noise under the influence of different load factors. The results show that: when the frequency increases, the amplitude of the 100Hz fundamental frequency in the vibration noise signal increases, and the noise level increases accordingly; when the power factor increases, the amplitude of the odd frequency components in the vibration noise signal gradually decreases with the increase of the power factor. There is no obvious fluctuation in amplitude except 100Hz. When the harmonic current and the three-phase are unbalanced, the spectral components become complicated and accompanied by a large number of odd-order frequency multiplication components. With the increase of harmonic content, the amplitude of vibration noise signal and A-weighted sound pressure level increase significantly; the degree of unbalance and the occurrence of unbalance have a greater impact on the amplitude of vibration noise signal and A-weighted sound pressure level. The research in this paper provides a reference for the noise suppression of power equipment and the fault diagnosis technology based on vibration and noise signals.

Reliability Assessment of Steel Bridges for Specialized Hauling Vehicles

Specialized hauling vehicles (SHVs) are short heavy trucks within the legal weight limits but induce higher load effects than routine commercial loads. The Manual for Bridge Evaluation (MBE) adopted a series of single-unit trucks (SUs) to represent this type of vehicle. However, the SUs were introduced without rigorous reliability-based analysis due to the lack of data on SHVs. With the availability of vast amounts of data on weigh-in-motion (WIM) truck weights and configurations, the reliability of steel bridges under the SHVs should be evaluated in a more robust and quantitative manner. Through the utilization of WIM data, the authors quantified the SHVs in terms of percentages of SHVs among all truck traffic, daily average counts of SHVs, and number of axles. The gross vehicle weights (GVWs) and typical configurations of SHVs were investigated. In addition, their load effects were determined and normalized by the corresponding SUs. The maximum live loads corresponding to a return period of 5 years were also extrapolated using normal probability paper (NPP). To evaluate the effectiveness of current load-rating procedures for SHVs, the authors investigated the relationship between the load-rating factors and the corresponding reliability indices for existing bridges using the developed live load parameters based on the WIM data. Results indicated that the current live load factors were not able to provide a uniform and appropriate reliability index at different average daily truck traffic (ADTT) scenarios. This paper thus proposes new live load factors and weight adjustments of SU trucks to provide an adequate and uniform safety margin for the evaluation of steel bridges.

Theoretical evaluation of the screening-current-induced magnetic field in superconducting coils with tape wires

We theoretically investigate the physical mechanism of the screening-current-induced field (SCIF) in solenoid coils wound with superconducting tape wires. We derive the direct relationship between the SCIF and the magnetization of tape wires, and a scaling law for the SCIF and the coil dimensions is demonstrated. A simple analytical expression of the SCIF is obtained as functions of current load factor, tape wire width, and the coil dimensions. We verify that the published data for the precise numerical computation of SCIF are roughly fitted by our theoretical results for flat coils where the height is smaller than the outer diameter.

A Review of Current and Historical Occupant Load Factors for Mercantile Occupancies

The determination of the occupant load of a building is often necessary as part of a fire engineering design assessment. Designers often use occupant load factors (or other equivalent terminology) to carry out this calculation typically using values taken from various published guidance or deemed-to-satisfy documents. This paper examines past and current values for mercantile occupancies that are specified in documents that are used in various jurisdictions around the world. In general three approaches are used; the occupant load factors are defined by the floor level of the building, by the type of mercantile activity within the spaces or through the application of uniform values throughout the occupancy. A simple six-storey exemplar building is used to illustrate the differences in the total occupant load and the relative number of occupants per floor when the different occupant load factor approaches are employed. Even for this simple building the occupant load differs by a factor of 4.1 and the distribution of the occupants varies noticeably between upper and lower levels depending on the particular document selected for the calculation.

Estimation Method of Optimal Amount of Overshooting Current for Temporal Uniform Magnetic Field in Conduction-Cooled HTS Coils

We investigated a suitable excitation method to suppress the shielding magnetic flux density attenuation using only the one-time excitation of a REBCO coil, which was cooled by a refrigerator. We investigated the operating temperature and current load factor dependences of the variation rate of the shielding magnetic flux density immediately after an overshooting process. Regardless of the operating temperature and current load factor, the variation rate of the shielding magnetic flux density decreases with the magnitude of overshooting current and changes from a positive value to a negative value. In each current load factor, the ratio of the optimal overshooting current to the critical current of the REBCO coil becomes almost identical regardless of the operating temperature. Based on these results, we devised a suitable overshooting current waveform to suppress the shielding magnetic flux density attenuation in the REBCO coil cooled by the refrigerator. The overshooting current was repeated to the coil in a one-time excitation; the amount of overshooting current was gradually increased until the variation rate of magnetic flux density was changed from positive to negative. Using this current waveform, we can suppress the shielding magnetic flux density attenuation in the conduction-cooled REBCO coil using only a one-time excitation.

A tunnel magnetoresistive effect wattmeters-based wireless sensors network

In the present work a wireless sensors network (WSN) for smart energy metering is presented using the ZigBee protocol as the communication link. Each network node process the electrical power by means of a Wheatstone bridge sensor based on the tunnel magnetoresistive (TMR) effect working as analogue multiplier. The electrical power is acquired and processed by a digital signal processor that extracts various parameters of interest like current and voltage load, active power and power factor by means of Fourier analysis. All the obtained electrical parameters at each node are served and shown in a web page that can be easily accessed by authorized users.

AC Loss Characteristics in kHz frequency band of a High Temperature Superconductor Coil for a Wireless Power Transmission System

Improvement of transmission efficiency is an important issue in a large-capacity wireless power transmission (WPT) system using copper coils for automobiles and electric railways. We have investigated the application of a high-temperature superconducting (HTS) coil to a high-power WPT system operating in the frequency region of 10 kHz. We measured the transport current losses of GdBCO and Bi2223 tapes and the total ac losses of GdBCO and Bi2223 coils in the kilohertz frequency band. We analyzed the current distribution within the tape using a finite element method (FEM) program. When the current load factor was low and the frequency was above 1 kHz, the ac losses per cycle increased with the frequency. This is because the eddy current loss in stabilized layers was larger than the hysteresis loss at the frequency of above 1 kHz. One the other hand, the ac losses per cycle were constant regardless of the frequency at the high-current load factor. This is because the hysteresis loss was larger than the eddy current loss regardless of the frequency. We investigated the maximum transmission efficiency at a resonance frequency in an HTS WPT system and a Cu WPT system. Although the quality factor of the HTS coil gradually decreased with the frequency and the operating current, the maximum transmission efficiency of the HTS WPT system was much higher than that of the Cu WPT system. We believe that the HTS coil is suitable for a large-capacity and high-efficiency WPT system in the frequency region below 10 kHz.

Wind load factors for dynamically sensitive structures with uncertainties

The current recommendations for the load factors on wind load in ASCE Standard 7 are based on an analysis of performance of rigid buildings, which may not be adequate for dynamically sensitive structures. In light of the uncertainties associated with dynamic characteristics of flexible buildings such as natural frequency and damping ratio, the load factors for such buildings may deviate from that in ASCE 7. This study investigates the efficacy of the current wind load factor for dynamically sensitive structures in the presence of uncertainties. A systematic analysis is performed using Monte Carlo simulations. Uncertainties associated with each component of the wind load effects such as the wind speeds, natural frequency and damping ratio of a building are incorporated in the load effects based on both ASCE Standard 7-05 and ASCE Standard 7-10. In addition, a database-enabled design (DED) procedure is utilized to support the analysis of the wind load factor, especially for the acrosswind case where ASCE 7 does not offer any guidance. In addition, the effects of terrain conditions, amplitude-dependent frequency and damping, and negative aerodynamic damping on the wind load factor are also discussed. Recommendations are made for wind load factors for dynamically sensitive structures both in the alongwind and acrosswind directions and for non-hurricane and hurricane winds.

Simplified Uniform Hazard Liquefaction Analysis for Bridges

Many bridge designers currently rely on the design specifications provided by AASHTO to evaluate liquefaction hazards for foundations and embankments. These guide specifications recommend a pseudo-probabilistic approach (i.e., an approach in which probabilistic estimates of seismic loading are incorporated into a deterministic liquefaction hazard analysis) for most conventional projects. A more consistent approach for the assessment of liquefaction hazards would involve a performance-based or uniform hazard evaluation of liquefaction potential. However, a performance-based liquefaction analysis is complex and difficult to implement in practice. This paper describes a simplified procedure for uniform hazard liquefaction analysis that uses the standard penetration test to closely approximate the results of a performance-based liquefaction analysis at a desired uniform hazard level. The simplified procedure is compatible with current AASHTO load and resistance factor bridge design specifications and is intended for use on bridges and other transportation-related structures. The procedure is summarized and shown to produce more consistent results for liquefaction hazards across different seismic environments than the existing AASHTO pseudo-probabilistic procedure. An example application of the simplified procedure is presented and discussed, and limitations for the procedure's proper use are provided.

Towards establishing practical multi-hazard bridge design limit states

In the U.S., the current Load and Resistance Factor Design (LRFD) Specifications for highway bridges is a reliability-based formulation that considers failure probabilities of bridge components due to the actions of typical dead load and frequent vehicular loads. Various extreme load effects, such as earthquake and vessel collision, are not considered on the same reliability-based platform. Since these extreme loads are time variables, combining them with frequent, nonextreme loads is a significant challenge. The number of design limit state equations based on these failure probabilities can be unrealistically large and unnecessary from the view point of practical applications. Based on the opinion of AASHTO State Bridge Engineers, many load combinations are insignificant in their states. This paper describes the formulation of a criterion to include only the necessary load combinations to establish the design limit states. This criterion is established by examining the total failure probabilities for all possible time-invariant and time varying load combinations and breaking them down into partial terms. Then, important load combinations can be readily determined quantitatively.

Reliability evaluation of axially loaded steel members design criteria in AASHTO LRFD bridge design code

Reliability based structural design insures a uniformly designed structure, in terms of safety. By considering an adequate reliability index (or probability of failure) for different parts of a structure, a reasonable balance between cost and safety of the structure can be achieved. In this study, the reliability of steel tension and compression members designed with AASHTO LRFD bridge design specifications (2007) is evaluated. These members are prevalent in different types of truss or arch bridges. Various conditions such as redundancy, ductility and importance of the bridge are taken into account by changing the load modification factor, η. To include the effect of the span length, a variable ratio of dead load to total load is considered. Current load factors in AASHTO LRFD code are accepted due to their verification in a comprehensive study for reliability of girder-type bridges. Furthermore, load and resistance distribution models are chosen based on the latest existing experimental data. The Monte Carlo simulation technique with randomly generated samples is applied in numerical calculations. For tension members, analysis results show relatively high reliability indices in yielding design, while having slightly low reliabilities for the fracture mode. For fracture design of steel tension members, an increase in vehicular dynamic load allowance (IM) from 33% to 75% is suggested to insure a safer behavior. Also, it is shown that the resistance factor for yielding of gross section, φy, can be increased from 0.95 to 1.00 while maintaining enough safety for designed tension members. In addition, obtained reliability curves for steel compression members show a safe behavior of designed compression members with conservative response in some cases. More results and plotted curves are discussed in detail and possible adjustments in code criteria are presented in this paper.

Mechanical Performance of Steel-Concrete Composite Beams Subjected to a Hogging Moment

Limited experimental results have been reported in the literature on the fatigue and ultimate static loading behavior of composite beams subjected to negative bending moment. This paper examines experimentally the behavior of composite steel-concrete beams. Eight composite specimens were tested to study the various aspects of composite beams under a negative bending moment, including the effects of repeated loading, shear connectors (studs and PBLs), rubber-latex mortar coating, and steel fiber-reinforced concrete (SFRC) on their structural performance. Load versus midspan deflection, crack formation and its developing process, slip distribution on the steel-slab interface, and the flexural strain results of shear connectors were measured and studied. The test results show that the initial cracking-level repeated load did not show obvious effects, while the stabilized cracking-level repeated load can reduce the rigidity and loading capacity of composite beams. The experimental results indicate that the plastic bending moment criteria in the current AASHTO load and resistance factor design specifications are typically conservative for composite beams under a negative bending moment. In addition, the effects of SFRC on crack width control and adhesion bonding effects of rubber latex on the steel-slab interface were confirmed in the testing.

Towards multiple hazard resilient bridges: a methodology for modeling frequent and infrequent time-varying loads Part II, Examples for live and earthquake load effects

The current AASHTO load and resistance factor design (LRFD) guidelines are formulated based on bridge reliability, which interprets traditional design safety factors into more rigorously deduced factors based on the theory of probability. This is a major advancement in bridge design specifications. However, LRFD is only calibrated for dead and live loads. In cases when extreme loads are significant, they need to be individually assessed. Combining regular loads with extreme loads has been a major challenge, mainly because the extreme loads are time variable and cannot be directly combined with time invariant loads to formulate the probability of structural failure. To overcome these difficulties, this paper suggests a methodology of comprehensive reliability, by introducing the concept of partial failure probability to separate the loads so that each individual load combination under a certain condition can be approximated as time invariant. Based on these conditions, the extreme loads (also referred to as multiple hazard or MH loads) can be broken down into single effects. In this paper, a further breakdown of these conditional occurrence probabilities into pure conditions is discussed by using a live truck and earthquake loads on a bridge as an example.

Towards multiple hazard resilient bridges: a methodology for modeling frequent and infrequent time-varying loads Part I, Comprehensive reliability and partial failure probabilities

The current AASHTO load and resistance factor design (LRFD) guidelines are formulated based on bridge reliability, which interprets traditional design safety factors into more rigorously deduced factors based on the theory of probability. This is a major advancement in bridge design specifications. However, LRFD is only calibrated for dead and live loads. In cases when extreme loads are significant, they need to be individually assessed. Combining regular loads with extreme loads has been a major challenge, mainly because the extreme loads are time variables and cannot be directly combined with time invariant loads to formulate the probability of structural failure. To overcome these difficulties, this paper suggests a methodology of comprehensive reliability, by introducing the concept of partial failure probability to separate the loads so that each individual load combination under a certain condition can be approximated as time invariant. Based on these conditions, the extreme loads (also referred to as multiple hazard or MH loads) can be broken down into single effects. In Part II of this paper, a further breakdown of these conditional occurrence probabilities into pure conditions is discussed by using a live truck and earthquake loads on a bridge as an example. There are three major steps in establishing load factors from MH load distributions: (1) formulate the failure probabilities; (2) normalize various load distributions; and (3) establish design limit state equations. This paper describes the formulation of the failure probabilities of single and combined loads.

공동주택 변압기용량 적정 산정을 위한 수용률 개선 및 사례 연구를 통한 경제성 평가

Interest in energy efficiency and savings have been rising internationally. For this reason, the domestic housing construction in the area of power equipment is being actively studied. Currently approximately 400,000 per year of domestic housing is being built. Applies to housing construction during the current transformer capacity low utilization and load factor has been applied has been designed. In other words, excessively high reserve capacity has been applied. According to this problem, initial facility costs and power losses will cause because transformer low utilization be appropriated. Thus, the energy efficiency drops. In this paper, analysis of past utilization of the housing transformer, and applying an appropriate demand factor has been analyzing the energy loss reduction. this analysis of current domestic conditions for the proper housing transformer scheme is to calculate the capacity.

Convenient Method for On-Site Check of Single Steel I-Girder Stability during Erection

The behavior of a single steel I-girder during erection is quite different from that of a girder under service: the girder during erection usually has limited or no lateral bracing along the span. Elastic lateral torsional buckling of the steel girder may occur if the girder span becomes too large. Rules of thumb have been used to check girder stability during erection by using the ratio of unbraced length L to compression flange width b; this is based on experience. For any longitudinally unstiffened girder section, formulas were developed on the basis of the current AASHTO load and resistance factor design code for the unique maximum L/b ratio. Parametric studies were then conducted to calculate Lmax and the (L/b)max ratio for a variety of girder sections that cover the range of practical design in order to identify dominant section parameters on the (L/b)max ratio as well as girder stability during erection and to develop simplified formulas for the upper and lower bounds of the (L/b)max ratio for all girder sections within the range of practical design. On the basis of the simplified formulas, an on-site check of single steel I-girder stability during erection could be conducted by checking the girder L/b ratio against the (L/b)max ratio for that given section or, even more easily, by checking the girder L/b ratio against the upper and lower bounds of the (L/b)max ratios for all girder sections.

Adjustment of Load and Resistance Factor Design Live Load Factors Using Recent Weigh-in-Motion Data

Traffic loads on bridges exhibit significant variations regionally, from state to state, and from site to site. Accounting for actual live loads in the bridge design process is important to improving the overall reliability and safety of bridges. In some cases, the code-specified live loads may underestimate traffic loading on a bridge. The current load and resistance factor design (LRFD) live load calibration is based on a biased sample of truck weights collected as part of an Ontario, Canada, truck weight survey conducted in 1975. In the past 35 years, truck traffic has significantly increased in volume and weight, which may necessitate adjusting the LRFD live load factors in certain cases on the basis of current truck traffic conditions. Although the quality and quantity of traffic data being collected by highway agencies has improved since 1975, it has not been used to update the bridge design loads. NCHRP Project 12–76 was initiated in 2006 to develop a set of protocols and methodologies using recent truck traffic data to update live loads for LRFD bridge design. Various levels of complexity are available using the site-specific truck weight and traffic data to calibrate live load models. One simplified calibration approach focuses on the lifetime maximum live load for updating the live load model or the load factor for current traffic conditions. Another, more robust, reliability-based approach for calibration is proposed in the protocols. The models are applicable for the design of bridge members, for both ultimate capacity and cyclic fatigue, and are implementable for both main structural members and the design of bridge decks.

Shear Tests on High-Strength Prestressed Bulb-Tee Girders: Strengths and Key Observations

Although a prestressed concrete section cast with high-strength concrete (HSC) can support larger loads or span longer distances in comparison to the same section cast with normal-strength concrete, current AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications limit the cylinder compressive strength of concrete to 10 ksi (69 MPa) due to a lack of experimental evidence to justify the use of higher strength concretes. This paper summarizes results from a study on the HSC limits of shear design provisions that was part of a larger project aimed at permitting the use of concrete strengths much higher than 10 ksi. To examine the 10 ksi (69 MPa) limit for shear design, ten 52 ft (16 m) long and 73 in. (1.8 m) deep prestressed concrete bridge girders were load tested to failure in shear. The primary test variables were concrete strength, 10 to 18 ksi (69 to 124 MPa); maximum design shear stress, 0.7 to 2.5 ksi (5 to 17 MPa); strand anchorage details (straight, unbonded, and draped); and end reinforcement detailing (bar size, spacing, and level of confinement). A total of 20 tests were conducted to evaluate various combinations of the most critical mechanisms of shear resistance. The results from this research, along with those from other experimental test programs of the project, indicate that the limit on the compressive strength of concrete can be raised safely from 10 to 18 ksi.