External blast load factors for dome structures based on reliability

Dome structures have been used extensively for industrial,residential,and military infrastructure.Therefore,it is necessary to understand the damage risk potential for such structures for blast-resistant design considerations.This paper investigates the effect of blast load variability on the design value and the structural dynamic response.Therefore,the sources of uncertainty in the external blast load on dome structures were discussed firstly.Then based on the probabilistic blast load model for the dome,the rationality of a deterministic mass-increase safety method was assessed.It was found that previous deterministic design method cannot provide a consistent and sound assurance factor or reliability index on the entire dome roof.In addition,it was also proved that the assurance-based load method fails to ensure compliance with structural safety design standards on the dome roof when compared with the reliability-based blast method.A sensitivity analysis on the probabilistic blast load was conducted,and the results indicate that stand-off distance and explosive mass both act as dominant sources to influence the mean and variability of blast load.Therefore,based on the Latin hypercube sampling method,a reliability-based external blast load factor technique was proposed.This technique was further used to estimate structural damage levels of a single-layer reticulated dome under different reliability requirements,associated with a low,medium,and high level of protection grades for a specific explosion scenario,and it indicated that this technique can be useful in the building design to achieve a higher structural anti-explosion capacity.This study herein can serve as a reference for the calculation method of designed blast load.

R-Factor Analysis of Data Based on Population Models Comprising R- and Q-Factors Leads to Biased Loading Estimates

Effects of performing an R-factor analysis of observed variables based on population models comprising R- and Q-factors were investigated. Although R-factor analysis of data based on a population model comprising R- and Q-factors is possible, this may lead to model error. Accordingly, loading estimates resulting from R-factor analysis of sample data drawn from a population based on a combination of R- and Q-factors will be biased. It was shown in a simulation study that a large amount of Q-factor variance induces an increase in the variation of R-factor loading estimates beyond the chance level. Tests of the multivariate kurtosis of observed variables are proposed as an indicator of possible Q-factor variance in observed variables as a prerequisite for R-factor analysis.

Calibration of LRFD Format for Steel Jacket OffshorePlatform in China Offshore Area(2): Load, Resistance and Load Combination Factors

Adopting the load and resistance factor design format, the design method for steel jaeket platform structures is developed. Firstly, the limit state equations and design format for steel jacket platform structures are introduced. Then, the ratio of live load effect to dead load effect is estimated. The target reliabilities for design of offshore structures in China offshore area are calibrated by past practice in API RP2A-WSD code. The load and resistance factors are optimized by minimizing the difference within the target reliability and the resulting reliability over the range of load effect ratios. Considering the concurrence of different loads, load combination factors are obtained through an optimization process, and the relation between the load combination factor and load correlation coefficient is established. Finally, the design formulae for steel jacket structures in China offshore area are recommended.

Experimental study on dynamic load magnification factor for ballastless track-subgrade of high-speed railway

The magnitude of dynamic load produced by high-speed trains depends on many factors,of which train speed is the most critical one.However,it is quite difficult to determine the effect of train speed on dynamic load using the theoretical methods due to the complexity of the interaction between vehicle and track-subgrade.Thus large-scale model test has gradually become an important approach for studying dynamic responses of ballastless track-subgrade of high-speed railway.In this study,a full-scale model of ballastless track-subgrade was constructed in accordance with the design and construction standards for Shanghai-Nanjing intercity high-speed railway line firstly.Then,the dynamic strain of slab and the dynamic earth pressure of subgrade were measured by conducting single wheel axle excitation test.In addition,the relationship between the dynamic load magnification factor（DLF） and the train speed was obtained.Finally,the DLF of track-subgrade under different train speeds was proposed,similar to that given by German Railway Standard.

EFFECT OF GEAR WIDTH AND HELIX ANGLE ON FACTOR OF DYNAMIC LOAD OF DOUBLE CIRCULAR ARC HELICAL GEARING

Based on theory of mechanical dynamics, meshing characteristic as well as thedynamic model of double circular arc helical gearing, an analysis approach and a computer programhave been developed for studying the state of dynamic load and factor of dynamic load of thegearing, the changing situation of dynamic load and dynamic load factor vs some affecting factorssuch as gear width, helix angle and accuracy grade etc are investigated. A series of conclusions areobtained: ①With the increasing in the values of gear width, the dynamic load factor appears slowdecreasing tendency in most region of gear width. ②When the accuracy grades of the gearing areimproved, the values of dynamic load factor decrease. ③The value of dynamic load factor appears adecreasing tendency with the increasing of value of helix angle at the same ratio of criticalrotational speed.

Reliability-Based Load and Resistance Factors Design for Offshore Jacket Platforms in the Bohai Bay:Calibration on Design Factors

For the fulfillment of the probability-based structural design for the offshore jacket platforms in the Bohai Bay, the design factors of loads, resistance and load combinations are much necessary to be calibrated according to the proposed target reliability index. Firstly, the limit states function for the offshore jacket platforms is introduced. Then, four approaches to calibrate the factors of load and resistance are presented and compared. Afterwards, the methods to calibrate the load combination factors are developed. Finally, the factors of load, resistance and load combination for the offshore jacket platforms in the Bohai Bay are calibrated and the corresponding design formulae are recommended. The results are proved to be rational in practice, and also illustrate that the proposed target reliability index for offshore jacket platforms in the Bohai Bay is also appropriate.

Measurement of the cavity-loaded quality factor in superconducting radio-frequency systems with mismatched source impedance

The accurate measurement of parameters such as the cavity-loaded quality factor(Q_(L))and half bandwidth(f_(0.5))is essential for monitoring the performance of superconducting radio-frequency cavities.However,the conventional"field decay method"employed to calibrate these values requires the cavity to satisfy a"zero-input"condition.This can be challenging when the source impedance is mismatched and produce nonzero forward signals(V_(f))that significantly affect the measurement accuracy.To address this limitation,we developed a modified version of the"field decay method"based on the cavity differential equation.The proposed approach enables the precise calibration of f_(0.5) even under mismatch conditions.We tested the proposed approach on the SRF cavities of the Chinese Accelerator-Driven System Front-End Demo Superconducting Linac and compared the results with those obtained from a network analyzer.The two sets of results were consistent,indicating the usefulness of the proposed approach.

Closing law and stress intensity factor of elliptical crack under compressive loading

The solution of surface displacement of an elliptical crack under compressive-shear loading was obtained by using the complex function method. The closing mode was established by analyzing the geometrical condition of closing crack, and the corresponding critical stress was solved. The result corrects the traditional viewpoint, in which there exist only open or close states for an elliptical crack, and points out that the local closing is also one of crack states. Based on them, the effect of the closed crack on stress intensity factor was discussed in detail, and its rational formulae are put forward.

Effect of Load Power Factor on Electromechanical Wave Propagation in Ring Power System

One-dimensional ring power system is discredited to a number of nodes each containing a generator with internal reactance and load branch of resistance and reactance with a certain power factor. When a disturbance occurs at any machine in the power system, simulative analysis is performed to verify how the variation of load power factor affecting the behavior of electromechanical wave propagation by using the MATLAB package, from which different situations are presented and discussed. These results show the type of load has no effect on the behavior of electromechanical wave propagation.

DYNAMIC STRESS INTENSITY FACTORS AROUND TWO CRACKS NEAR AN INTERFACE OF TWO DISSIMILAR ELASTIC HALF－PLANES UNDER IN－PLANE SHEAR IMPACT LOAD

Transient stresses around two collinear cracks which lie in parallel with theinterface of the two dissimilar half-planes are studied in this article.The surfaces ofthe cracks are sheared suddenly. Application of the Fourier and Laplace transforms technique reduces the problem to that of solving dual integrai equations.To solvethese,the differences of.the crack surface displacements are expanded in a series offunctions which are automatically zero outside of the cracks. The unknown coefficients accompanied in the series are determined by the Schmidt method. The stress intensity .factors are defined in the Laplace transform domain and these are inverted numerically in the physical space .As an example ,the dynamic stress intensity factors around two cracks in a ceramic and steel bonded composite are numerically calculated.

THE THREE-DIMENSIONAL STRESS INTENSITY FACTOR UNDER MOVING LOADS ON THE CRACK FACES

The dynamic stress intensity factor history for a half plane crack in an otherwise unbounded elastic body,with the crack faces subjected to a traction distribution consisting of two pairs of combined mode point loads that move in a direction perpendicular to the crack edge is considered.The analytic expression for the combined mode stress intensity factors as a function of time for any point along the crack edge is obtained.The method of solution is based on the application of integral transform together with the Wiener-Hopf technique and the Cagniard-de Hoop method. Some features of the solution are discussed and graphical results for various point load speeds are presented.

Factors Associated with the Unsuppressed Viral Load of Children on Antiretroviral Therapy Followed Up in the GbêkêRegion (Côte d’Ivoire)

Introduction: Unsuppressed viral load (VL) in immunocompromised children on antiretroviral therapy (ART) increases the risk of child morbidity and death. The aim of the study was to identify factors associated with unsuppressed viral load in children on ART for the improvement of prognosis. Patients and Methods: this is a retrospective, descriptive and analytical study carried out from July 2015 to December 2019 in the 28 pediatric HIV/AIDS treatment centers supervised by the NGO IRAA in the region of Gbêkê. It Included children from 0 to 15 years who were HIV positive, on ART for at least 6 months with at least one viral load. The variables studied were socio-demographic, diagnostic and evolutionary. Data analysis was descriptive and analytical with a significance level of p < 0.05. Results: out of 329 children included, 118 (62 boys, 53 girls) had a non-suppressed VL, i.e. a prevalence of 36%. The mean age at diagnosis was 61 months. The mother was a small trader (36.4%), illiterate (45.8%). Unsuppressed viral load was significantly associated with poor nutritional status at the start of treatment (p < 0.001), non-compliance with treatment (p < 0.001), poor maternal education (p = 0.011) and the lack of follow-up of the mother in the context of PMTCT (p = 0.03). Conclusion: Unsuppressed viral load is common in children on ART in the Gbêkê region. It mainly concerns the child who did not comply with ART, and whose mother was not followed within the framework of PMTCT. Strengthening early detection, early initiation of ART, PMTCT and increased therapeutic education strategies would improve the prognosis of children infected with HIV.

THE 3-D STRESS INTENSITY FACTOR FOR A HALF PLANE CRACK IN A TRANSVERSELY ISOTROPIC SOLID DUE TO THE MOTION OF LOADS ON THE CRACK FACES

Three-dimensional analysis of a half plane crack in a transversely isotropic solid is performed. The crack is subjected to a pair of normal point loads moving in a direction perpendicular to the crack edge on its faces. Transform methods are used to reduce the boundary value problem to a single integral equation that can be solved by the Wiener-Hopf technique. The Cagniard-de Hoop method is employed to invert the transforms. An exact expression is derived for the mode I stress intensity factor as a function of time and position along the crack edge. Some features of the solution are discussed through numerical results.

冲击载荷下圆柱形锂离子电池的动态响应预测

为提高径向冲击载荷下圆柱形锂离子电池的安全性,基于膜力因子法研究了大变形下电池的动态响应特性。将电池首先简化为包括内芯和外壳的夹层梁结构,根据抗拉屈服强度建立了电池横截面的塑性屈服准则和膜力因子,进一步将膜力因子引入运动方程实现了大变形下动态响应的求解。此外,基于拉压试验测定了电池构件的力学性能,进一步建立了电池整体有限元模型。研究表明:电池位移响应和速度响应的理论结果和有限元结果具有一致性;冲击载荷下电池初始速度越高,轴力效应对动态响应的影响越大;电池最大挠度随初始速度近似线性增加,且实际的响应时间具有饱和性;电池最大挠度随内芯和外壳屈服强度之比的减小而增大,电池外壳越薄,屈服强度的影响越显著;电池最大挠度随外壳厚度的增大而减小,屈服强度比越大,外壳厚度的影响越显著。

Investigation of Excavator Performance Factors in an Open-Pit Mine Using Loading Cycle Time

This study presents the effect of excavator model, loading operation location, shift availability and truck-shovel combination on loading cycle time and productivity of an open-pit mine. The loading cycle time was used to assess the material loading system performance which is one of the key components of the total cycle time for material transportation in an open-pit mine. Loading is among the components of cycle time during which material is being handled. The data analyzed?was?collected from a computerized dispatch system at GGM from which 62,000 loading dispatches per month involving several shifts, 14 excavators and 49 trucks were loaded. About 4465 dispatches per excavator and 1276 dispatches per truck were assessed using loading cycle time data for each dispatch for a period of four months (between August and December). Under fixed tonnage loaded and waste type (33 t of non-acid forming waste rock),?it was observed that loading cycle time depends on excavator model, location and truck being loaded. Average cycle times, PDFS?and CDFS of loading cycle time series were used to identify differences in performance under different situations. It was concluded that shift availability for excavators, loading location, excavator model and truck-shovel combinations strongly affect the productivity during loading process in an open-pit mine.

Progressive collapse resisting capacity of reinforced concrete load bearing wall structures

Reinforced concrete(RC) load bearing wall is widely used in high-rise and mid-rise buildings. Due to the number of walls in plan and reduction in lateral force portion, this system is not only stronger against earthquakes, but also more economical. The effect of progressive collapse caused by removal of load bearing elements, in various positions in plan and stories of the RC load bearing wall system was evaluated by nonlinear dynamic and static analyses. For this purpose, three-dimensional model of 10-story structure was selected. The analysis results indicated stability, strength and stiffness of the RC load-bearing wall system against progressive collapse. It was observed that the most critical condition for removal of load bearing walls was the instantaneous removal of the surrounding walls located at the corners of the building where the sections of the load bearing elements were changed. In this case, the maximum vertical displacement was limited to 6.3 mm and the structure failed after applying the load of 10 times the axial load bored by removed elements. Comparison between the results of the nonlinear dynamic and static analyses demonstrated that the "load factor" parameter was a reasonable criterion to evaluate the progressive collapse potential of the structure.

考虑气象因素的高速公路服务区电动汽车充电负荷预测

天气对交通流量的影响显著,而交通流量状态直接影响着电动汽车充电负荷的时空分布,为了探究天气对高速公路服务区电动汽车充电负荷时空分布的影响,提出了一种考虑气象因素的高速公路服务区电动汽车充电负荷预测方法。分析导致电动汽车高速行驶产生里程衰减的因素,建立能耗模型以分析高速行驶状态下电动汽车的能源补给需求;分析天气对交通流量的影响,基于能耗模型,建立电动汽车充电负荷与天气之间的关系;根据地理信息系统建立高速公路路网模型,采用交通起讫点分析法模拟电动汽车的行程轨迹,结合高速公路气象状况对高速公路服务区电动汽车充电负荷进行预测。以某高速公路实际路网为算例,预测各种天气下服务区充电负荷的时空分布,分析天气对各服务区充电负荷的影响规律,验证所提方法的可行性。

基于有限元分析的液压启闭机稳定性折算系数研究

为了获得更符合实际的液压启闭机稳定性折算系数,文章系统分析了现有两端铰支液压启闭机等效力学模型和理论公式等,探究了适用于液压启闭机稳定性计算的有限元方法,并基于有限元计算结果提出了新的计算公式,进而分析了中部铰支液压启闭机临界载荷计算方法。研究表明:考虑油压作用于活塞的稳定性折算系数理论公式计算值与沿轴线方向施加油压的有限元计算结果相差较小,说明了该力学简化模型的合理性;基于油压始终垂直于活塞的有限元计算结果提出了新的稳定性折算系数计算公式;中部铰支液压启闭机可转化为铰点距相同的两端铰支模型计算临界载荷,液压启闭机临界载荷仅与活塞杆两端的约束有关。上述研究成果可为液压启闭机的设计及校核提供理论依据。

计及冷负荷启动时变特性的弹性配电网供电恢复

极端灾害事件引发配电网停电后,利用分布式电源构建孤岛微电网恢复重要负荷供电,能有效提升配电网弹性。现有研究在制定配电网供电恢复策略时大都采用恒定负载模型,未考虑冷负荷启动时负载峰值引起的三相电流不平衡,无法保证孤岛微电网的安全运行。该文提出一种计及冷负荷启动时变特性的弹性配电网供电恢复方法。首先,考虑冷负荷启动特性与停电时间之间的关系,建立与时间相关的冷负荷启动模型,并通过采样法生成负荷功率需求曲线;其次,以加权负荷恢复量最大为目标,考虑微电网功率平衡、电流不平衡度等约束,建立协同区域划分、恢复路径和负荷投运时序的配电网供电恢复模型;再次,对模型进行线性化处理,将其转换为混合整数规划问题进行求解;最后,采用IEEE 37节点配电系统,对所提方法的有效性进行验证。

光伏接入机房的功率因数节能分析及应用

在双碳目标的背景下,节能减排是一项重要任务指标,通信运营商积极开展机房的各种节能措施,包括光伏绿色能源、高效的电源设备、变频空调等。而机房在低负荷的情况下,光伏发电导致机房的功率因数低于电网考核标准,产生了以电量总额一定比例的罚款。分析机房的负荷特性,调整光伏逆变器的无功输出,可以使机房电网的功率因数在合适区间,降低机房的电费实现绿色节能。