Safety Coefficient Research Articles

Numerical simulation study of the failure evolution process and failure mode of surrounding rock in deep soft rock roadways

Based on the safety coefficient method, which assigns rock failure criteria to calculate the rock mass unit, the safety coefficient contour of surrounding rock is plotted to judge the distribution form of the fractured zone in the roadway. This will provide the basis numerical simulation to calculate the surrounding rock fractured zone in a roadway. Using the single factor and multi-factor orthogonal test method, the evolution law of roadway surrounding rock displacements, plastic zone and stress distribution under different conditions is studied. It reveals the roadway surrounding rock burst evolution process, and obtains five kinds of failure modes in deep soft rock roadway. Using the fuzzy mathematics clustering analysis method, the deep soft surrounding rock failure model in Zhujixi mine can be classified and patterns recognized. Compared to the identification results and the results detected by geological radar of surrounding rock loose circle, the reliability of the results of the pattern recognition is verified and lays the foundations for the support design of deep soft rock roadways.

Reliability of Foundation Pile Based on Settlement and a Parameter Sensitivity Analysis

Based on the uncertainty analysis to calculation model of settlement, the formula of reliability index of foundation pile is derived. Based on this formula, the influence of coefficient of variation of the calculated settlement at pile head, coefficient of variation of the permissible limit of the settlement, coefficient of variation of the measured settlement, safety coefficient, and the mean value of calculation model coefficient on reliability is analyzed. The results indicate that(1)high reliability index can be obtained by increasing safety coefficient;(2)reliability index will be reduced with increasing of the mean value of calculation model coefficient and coefficient of variation of the permissible limit of settlement;(3)reliability index will not always monotonically increase or decrease with increasing of coefficient of variation of the calculated settlement and coefficient of variation of calculation model coefficient. To get a high reliability index, coefficient of variation of calculation model coefficient or value range of coefficient of variation of calculation model coefficient should be determined through the derived formula when values of other independent variables are determined.

The modern evaluation method of fracture toughness of basaltplastic lining for engineering collectors

The estimation methods of fracture toughness of reinforced blocks are considered for construction for engineering collectors. There are presented the methodical accesses that make possible to numerical describe all studies of destruction process of polymer lining with regard to simultaneously action the whole complex of exploitation factors. It is stated the data of fracture toughness of the composites on organic and nonorganic matrix in normal condition in comparison with basaltplastic lining. It is reported the dates of safety and critical coefficients of composite strains intensity on organic and nonorganic base in normal conditions.

Method of Determination of Safety Factor on Example of Selected Structure

The article shows a method of determining safety factors of a frame steel structure of the dump body in a vehicle used in the agricultural transport. The focus is on the method of use of the machine along with indicating the situations where a load-bearing structure is particularly exposed to damage. The determined values of safety coefficients are confirmed with the data obtained from long-term operation of machines manufactured based on the same technology. Long-term operation has not shown any cases of damage to the structure due to an overload.

Application and comparison of stability analysis of slope using circular arc method and strength reduction method

In order to evaluate the accuracy of strength reduction method using FEM, the safety factors of the uniform clay slope and sand slope are investigated by Fellenius’s method, Bishop’s method using traditional limit equilibrium method and strength reduction method respectively. The limit equilibrium method is carried out based on the code for foundations in port engineering and the FE analysis is based on Plaxis3D. The results show that the safety coefficient obtained by strength reduction method of FEM is larger than that obtained by limit equilibrium method and the errors are 6.03% and 1.61% for clay slope and 8.54% and 3.99% for sand slope.

Reliability analysis of un-retrofitted and retrofitted concrete columns in Iran's building site conditions

The reliability analysis of built columns in Iran's building site conditions, un-retrofitted and retrofitted by CFRP, are compared with the target safety level of the Iranian Concrete Design Code and Code 345. Statistical characteristics of random variables in terms of resistance are found via field researches carried out on 60 active construction workshops and a total of 1,800 samples of concrete in Tehran and its suburbs. The results show that the CFRP materials can significantly increase the safety level of columns. Furthermore, the simulation results reveal that the safety levels of built concrete columns in Iran's building sites condition are lower than the desired level in the Iranian Concrete Design Code and Code 345. The results confirm the necessity of review on the partial safety coefficient of load and resistance in the Iranian codes. However, the results show that the target reliability index of un-retrofitted columns can significantly satisfied with the CFRP materials.

Vibration Analysis of Suspension Cable with Attached Masses by Non-linear Spline Function Method

The nonlinear strain and stress expressions of suspension cable are established from the basic condition of suspension structure on the Lagrange coordinates and the equilibrium equation of the suspension structure is obtained. The dynamics equations of motion of the suspended cable with attached masses are proposed according to the virtual work principle. Using the spline function as interpolation functions of displacement and spatial position, the spline function method of dynamics equation of suspension cable is formed in which the stiffness matrix is expressed by spline function, and the solution method of stiffness matrix, matrix assembly method based on spline integral, is put forwards which can save cost time efficiency. The vibration frequency of the suspension cable is calculated with different attached masses, which provides theoretical basis for valuing of safety coefficient of the bearing cable of the cableway.

Thickness scaled compression tests in unidirectional glass fibre reinforced composites in static and fatigue loading

Thick laminates can be found in different wind turbine blade sections, such as the root or the spar caps. However, static and fatigue design of thick laminate components is based on thin coupons tests (around 4 mm thick) and safety coefficients determined by the guidelines and standards.The aim of this work is to study the size effect in compression for unidirectional glass fibre reinforced composites. Scaled static and fatigue compression tests were performed on glass/epoxy laminates of 4 mm, 10 mm and 20 mm thick. A series of scaled coupons were designed taking into account the influence of the manufacturing process and the final testing conditions. While static tests on laminates with different thicknesses showed no significant change in the static ultimate stresses, fatigue tests showed a decrease in the fatigue life for increasing thicknesses as well as wider intervals of confidence. In addition, fatigue data were compared with the reduced fatigue capacity reported by the design guidelines showing reserve factors larger than 2.0.

Analysis on stability of an Arch Dam with interlayer shear zones

This paper focuses on the stability of arch dam abutment with interlayer shear zones, presents the experimental analysis on Lizhou Arch Dam, and implements comprehensive method by combining geo-mechanical model test with the finite element method to analyze the impact of interlayer shear zones on the stability of dam abutment. Firstly, 3D geo-mechanical model test is conducted and the model shows the impact of interlayer shear zones on stability of arch dam. According to the deformation behaviors and eventual failure form of rock mass and structure planes in dam abutment and dam foundation, the impact of interlayer shear zones unstable failure on the safety coefficient of arch dam is analyzed. Secondly, the FEM (Finite Element Method) is used for supplementary verification. As a conclusion of the analysis: Interlayer shear zones fj1 - fj4 are developing towards riverbed in the rock mass of the dam abutment of Lizhou Arch Dam, cutting through the rock mass of dam abutment and forming a bottom slide face. In the dam abutment, fault f5 and fracture Lp285 have developed and formed a side fracture plane by intersecting the interlayer shear zone. Under the effect of the resultant force of the arch abutment, with the interlayer shear zone of inferior properties as the bottom slide face, the rock mass of dam abutment slides out in the form of steps or drawers, and the stability of the dam and the foundation is influenced.

Stability of Soil Cutting and Side Slope Based on Stress Route Theory

<p>The stress route analytical method compensates for the limitation of traditional soil slope stability analytical method. Since it disregards the impact of effective stress route on the stress status and anti-shear strength of soil slope, it maps out the soil stress route drawing in the excavation process, and marks the anti-shear strength and shear stress changes under various conditions of soil. It causes the changes of the safety coefficient rules in the excavation of soil slope and affects the excavation stability of soil cutting and side slope. The result reveals: (1) The main analytical method of side slope stability which covers both the limit balance method and finite unit method fails to consider the impact of effective stress route on the existing stress status and anti-shear strength of soil slope; the stress route analytical method is able to overcome this limitation to a certain degree. (2) The stress route theory is adopted for analysis, in which, it can projected the whole stress of typical and most dangerous area of the slope, able to analyse the anti-shear strength of soil in a real-time manner, manage to express the safety coefficient changes in the stress route drawing and provides a selection of a suitable excavation plan by contrast. (3) In the overall excavation, the slope toe suffers from obvious stress concentration which expands to the surrounding areas and inconvenient for the side slope stability in the excavation.</p>

Failure analysis method of concrete arch dam based on elastic strain energy criterion

The arch dam is a type of massive water-retaining structure made of concrete. The overall failure mechanism and corresponding analysis criterion are key issues of concern in the dam engineering field. In this paper, the energy evolution of arch dams in the failure process is studied first, which can be decomposed as energy dissipation accompanied by concrete damage and elastic strain energy absorption and release during elastic deformation. An evaluation criterion for failure analysis of concrete arch dams is then established based on elastic strain energy. An orthotropic damage constitutive model for dam concrete is then proposed along with its numerical simulation method, which is established for structural failure analysis. Numerical simulations show that the elastic strain energy in elements increases with increasing overload safety coefficient and finally converges to the concrete material surface energy, at which time the locally plastic damage area develops rapidly and finally leads to cracking failure of structures. The proposed failure analysis criterion for concrete dams under integrated loads is suitable for analyzing dam instability failure, which has great operability and value in engineering applications in the future.

Stability analysis of crack slope considering nonlinearity and water pressure

The soil slopes tend to induce the appearance of tension cracks at the top of slope under various factors, which poses an adverse impact on slope stability. Based on Power-Law nonlinear failure criterion, kinematical approach is adopted in this paper to investigate the effects of underground water and vertical tension cracks on stability of slopes. Notice that the tension cracks tend to propagate vertically, and thus a novel failure mechanism composed by the tension crack and logarithmic spiral shear slide plane is postulated. Theoretically, the worst position of crack propagation makes the stability factor minimal, and the failure surfaces can be obtained under different conditions through optimization. According to the proposed mechanism and nonlinear Mohr-Coulomb strength criterion, the stability factor and safety coefficient of slopes are derived. Subsequently, sensitivity analysis with respect to specific examples is conducted to analyze the influence of tension cracks, nonlinear strength parameters and pore water pressure on the slope stability. The results indicate that slope stability weakens gradually at the presence of tension cracks, and the changing degree is more evident with the increase of the slope angle. Meanwhile, nonlinear parameters have more significant impact on the safety factor with the decreasing value of the slope angle. However, the bigger the slope angle, the greater the height of tension cracks, and therefore the more obvious influence of pore water pressure on slope stability. When the slope angle approaches to be vertical, the height of tension cracks increases sharply. As a matter of fact, the height of tension cracks is highly related to geometrical conditions, strength parameters and water effect, which build a mutual relationship to determine slope stability.

Commissioning of the cryogenic safety test facility PICARD

The sizing of cryogenic safety relief devices requires detailed knowledge on the evolution of the pressure increase in cryostats following hazardous incidents such as the venting of the insulating vacuum with atmospheric air. Based on typical design and operating conditions in liquid helium cryostats, the new test facility PICARD, which stands for Pressure Increase in Cryostats and Analysis of Relief Devices, has been constructed. The vacuum-insulated test stand has a cryogenic liquid volume of 100 liters and a nominal design pressure of 16 bar(g). This allows a broad range of experimental conditions with cryogenic fluids. In case of helium, mass flow rates through safety valves and rupture disks up to about 4kg/s can be measured. Beside flow rate measurements under various conditions (venting diameter, insulation, working fluid, liquid level, set pressure), the test stand will be used for studies on the impact of two-phase flow and for the measurement of flow coefficients of safety devices at low temperature. This paper describes the operating range, layout and instrumentation of the test stand and presents the status of the commissioning phase.

Providing safety and reliability in the design of the offshore ice-resistant stationary oil and gas structures

Safety and reliability factors, assumed in Russian and international standards, as well as the main provisions of design of offshore oil and gas structures are considered in the article. The reasons for structures destruction are classified. The analysis showed that the main design provisions and methodology of calculations related to provision of safe and reliable operation of offshore oil and gas structures by different standards are not fundamentally different: the required degree of reliability of the structure is set depending on the social and economic consequences of possible hydrodynamic accidents; calculations are based on the limit states design method using partial safety factors; etc. However, the factors accounting the degree of the structure reliability, partial safety coefficients and load combinations coefficients differ in different standards and methodologies.

The Evaluation Research of Fatigue Stress under One-Way Steady Varying Stress

At first, the unidirectional stress fatigue strength has been made the brief description, and the calculation methods about the fatigue stress under two cases also has been introduced, two cases are the symmetrical and asymmetrical cyclic stress fatigue strength. The calculation of fatigue strength is based on the fact that calculating safety factor is equal to or greater than the allowable safety coefficient. Finally, some alloy steel parts are taken as an example to carry on the fatigue strength calculation.

Use of the Failure Assessment Diagram to Evaluate the Safety of the Reactor Pressure Vessel

Analysis of multiple failure modes is the key element of the integrity evaluation of the nuclear reactor pressure vessel (RPV). While the simple single-criterion failure code provides the guidance for structural integrity, the guidance ignores the interaction between fast fracture and plastic collapse. In this paper, the differences between the reserve factor (RF) in the R6 two-criteria failure procedure and the safety coefficient (SC) in the single-criterion failure code were compared. Based on 3D finite element (FE) analyses, the option 3 failure assessment diagram (FAD) of the beltline of the RPV was established according to the R6 basic route and alternative approaches, respectively. Also, the nonconservation of the secondary stress correction parameter ρ was reviewed. In this paper, it was shown that the effect of crack sizes on the FAD is considered to be limited, and the influence of the thermal stress on the FAD is obvious in the transition region of the failure assessment curve (FAC). The FAD only considering the mechanical load encloses the FAD considering the thermal–mechanical load for the Lr smaller than 1, but it is contrary when the Lr is bigger than 1. It is not enough to just satisfy the requirement in the IWB-3612 of the ASME code because the risk of plastic-collapse failure is ignored. And in this study, the maximum nonconservation of the fracture toughness RF is more than 7% due to the approximate value of ρ. Accordingly, the accurate method in the R6 procedure should be used in the integrity assessment of the RPV under the faulted transient.

Research of vehicle flow based on cellular automaton in different safety parameters

In this paper, the cellular automaton model is put forward to evaluate the effect of the different drivers’ psychology in the two-lane highway. Each value of safety parameter βji, used to reflect the jth vehicle driver’s psychology in the ith lane, represents his or her cautious or risky preference. Assuming that βji follows normal distribution, whose mathematical expectation is β, we generate a stochastic safety coefficient for each driver in the simulation area. Based on different values of β, the vehicle flow and density are contrasted under some different traffic rules such as driving on the right, free overtaking and non-overtaking with low speed limitation. Through the cellular automaton simulation, the results demonstrate that safety parameter has less influence on the traffic flow under the lightest and heaviest traffic. Meanwhile, non-overtaking with the lowest speed limitation can increase the traffic flow in the light traffic. Free overtaking can improve the usage of the highway. With the increase of vehicle, non-overtaking with the lowest speed limitation will be of benefit to improving the traffic flow.

Research on a probabilistic assessment criterion of casing deformation in an incomplete borehole in deep salt formation

Drilling and completing wells through complex salt formation is technically challenging and costing. Field data demonstrates that well casings designed by traditional safety coefficient criterion occurring failure in deep salt formation though their safety factors are greater than 1. To reveal the failure mechanism, a probabilistic computational model coupled with salt formation, defective cement and worn casing is established and analyzed using Monte Carlo simulation method. On the basis of reliability theory, the results calculated by 5000 times simulations show that the traditional safety coefficient criterion has been unable to adapt to the safety assessment of well casings under salt creep conditions. To gain a sophisticated evaluation, a new assessment criterion is established and applied to assess the security of well casings under salt creep conditions. This study provides a new perspective for revealing the failure mechanism and solutions of evaluation on well casings under salt creep conditions, which may be an alternative method to study and predict the life of well casings in deep complicated formation.

Design of composite tank covers

The problem of design and failure analysis of composite tank covers is discussed in the paper. Covering systems consist of segmental parts of tanks, independently on tank structure. Composite covers have several advantages connected with structure, transport and assembly. Additionally, the construction divided into several sections enables repair and inspection improving. However, on the one hand, failure of the tank covers, which are occurred sometimes, and on the other hand new applications, make it necessary to develop design, analysis and optimization of these structures. In this study, the main advantages of the GRP covers are shown against other covers and roofs systems. The construction of the representative rectangular composite tank cover, segments and joints are described. Failure analysis of the covering segment under combined loading is presented. The exemplary cover was built in the sewage treatment plant in Poland. The cover is built of repetitive two-wave segments with flanges overlapping one another. The segments are made of mixed glass-fiber reinforced plastic laminates. The cover is subjected to the following static loads: dead load, technological vacuum, snow and ice and local load (workers with tools). Static analysis of the exemplary cover was conducted using the finite element code MSC.Marc. The considerations include shell geometry of the cover, structural GRP laminates with specified ply sequences, segment connections of rivet nut–bolt and anchor–nut types, friction at the interface between flanges and between flanges and tank walls. Safety coefficients have been analyzed for the different elements of the exemplary composite cover.

Stability Analysis on High and Steep Slope of Open-Pit Based on Limit Equilibrium Method

The stability of slope in open-pit affects the economic benefits and safety production of mining enterprises. From the two aspects of internal factors and external factors, this paper analyses the factors affecting the slope stability of open-pit, discusses the basic theory of slope stability analysis, and puts forward the criterion of slope stability based on the safety coefficient. The limit equilibrium method is chosen to analyze the stability of the high and steep slope of open-pit in this paper, and the SLIDE software is used for numerical simulation according to the actual slope model of certain open-pit. The simulation results show that the slope safety coefficient of the instance is 1.01, which is unstable slope. When the number of the slope blocks is more than 40, the safety coefficient tend to be stable. Blasting vibration has a great influence on slope stability. The results of slope stability analysis provide a scientific guidance for the prevention and control of the slope instability.