Application of bi-directional static loading test to deep foundations

Bi-directional static loading test adopting load cells is widely used around the world at present, with increase in diameter and length of deep foundations. In this paper, a new simple conversion method to predict the equivalent pile head load-settlement curve considering elastic shortening of deep foundation was put forward according to the load transfer mechanism. The proposed conversion method was applied to root caisson foundation in a bridge and to large diameter pipe piles in a sea wind power plant. Some new load cells, test procedure, and construction technology were adopted based on the applications to different deep foundations, which could enlarge the application scopes of bi-directional loading test. A new type of bi-directional loading test for pipe pile was conducted, in which the load cell was installed and loaded after the pipe pile with special connector has been set up. Unlike the conventional bi-directional loading test, the load cell can be reused and shows an evident economic benefit.

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.

Evaluation of vertical impact factor coefficients for continuous and integral railway bridges under high-speed moving loads

In the railway bridge analysis and design method,dynamic train loads are regarded as static loads enhanced by an impact factor(IF).The IF coefficients for various railway bridges have been reported as a function of span length or frequency of the bridges in Eurocode(2003).However,these IF coefficient values neglect the effects of very high speeds(>200 km/h)and soil-structure interaction(SSI).In this work,a comprehensive study to assess the impact factor coefficients of mid-span vertical displacements for continuous and integral railway bridges subjected to high-speed moving loads is reported.Three different configurations,each for the three-dimensional(3D)continuous and integral bridge,are considered.Also,single-track(1-T)and two-track(2-T)“real train”loading cases for both these bridge types are considered.Subsequently,finite element analysis of the full-scale 3D bridge models,to identify their IF values,considering the effects of SSI for three different soil conditions,is conducted.The IF values obtained from the study for both bridge types are comparable and are greater than the values recommended by Eurocode(2003).The results reveal that with a loss of soil stiffness,the IF value reduces;thus,it confirms the importance of SSI analysis.

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.

Analysis of Geometrical Parameters of Tubular TY-Joints on Stress Concentration Factors Due to Axial Loads

In this paper,the influence of geometric parameters on the stress concentration factors due to three different types of axial loading on 81 TY tubular structures is studied.Our results reveal that,geometric parameters have a considerable impact on the variation of stress concentration factors on tubular TY-joints under axial loads.Thus,the highest stress concentration factor values are observed on the vertical brace than on the inclined one.The finite element results of the tubular structures were verified by parametric equations and experimental data.A parametric study was carried out by analyses using the nonlinear regression method to obtain parametric equations.These equations are used to calculate stress concentration factors and to analyse the fatigue resistance of TY-joints due to axial loads.

Factors Analysis of Affecting Loading and Reinforcing Scheme of Large Goods in Railway

Large goods transported in railway are kinds of special goods and they are very important in national construction. In order to transport safely, loading and reinforcing schemes must be made first. How to design a reasonable scheme will be affected by many factors. This paper presents the characteristic of the large goods, summarizes the process of designing a loading and reinforcing scheme of large good, then probes the factors of affecting the loading and reinforcing scheme and gives a detail analysis. It’s considered that those out-of-gauge and overweight degree of goods, center-of- gravity height of a loaded wagon, position of center-of-gravity of goods, type of wagon for using, reinforcement material and reinforcement method, transport expense and transport organization could affect a scheme in the aspects of safety, economy, rapidity and convenience. This conclusion will instruct and help to make a good scheme.

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.

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.

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.

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.

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.

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.

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 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.

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.

A novel approach to the dynamic response analysis of Euler-Bernoulli beams resting on a Winkler soil model and subjected to impact loads

This work presents a novel approach to the dynamic response analysis of a Euler-Bernoulli beam resting on a Winkler soil model and subjected to an impact loading.The approach considers that damping has much less importance in controlling the maximum response to impulsive loadings because the maximum response is reached in a very short time,before the damping forces can dissipate a significant portion of the energy input into the system.The development of two sine series solutions,relating to different types of impulsive loadings,one involving a single concentrated force and the other a distributed line load,are presented.This study revealed that when a simply supported Euler-Bernoulli beam,resting on a Winkler soil model,is subject to an impact load,the resulting vertical displacements,bending moments and shear forces produced along the span of the beam are considerably affected.In particular,the quantification of this effect is best observed,relative to the corresponding static solution,via an amplification factor.The computed impact amplification factors,for the sub-grade moduli used in this study,were in magnitude greater than 2,thus confirming the multiple-degree-of-freedom nature of the problem.

Load Forecasting Technique for System Expansion in Isolated Area Using Time Invariant Socio-Economic Factors of Identical Agglomerations

Load forecasting is a critical issue for operational planning as well as grid expansion to ensure an uninterruptable electric power system. Being a small but densely populated country in South Asia, Bangladesh has many isolated places which are not connected to national grid yet. If concern authority opts to expand grid to those areas, they need reliable demand data for designing and dimensioning of different power system entities, e.g., capacity, overhead line capacity, tie line capacity, spinning reserve, load-shedding scheduling, etc., for reliable operation and to prevent possible obligatory redesigning. This paper represents an analysis to forecast the electricity demand of an isolated island in Bangladesh where past history of electrical load demand is not available. The analysis is based on the identification of factors, e.g., population, literacy rate, per capita income, occupation, communication, etc., on which electrical load growth of an area depends. Data has been collected from the targeted isolated area and form a grid connected area which is similar to target area from social and geographical perspective. Weights of those factors on load have been calculated by matrix inversion. Demand of the new area is forecasted using these weights factors by matrix multiplication.

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.