Stress Ratio Method Research Articles

Identification and analysis of evolution characteristics of flash drought based on three-dimensional perspective: A case study in the Jialing River basin

Flash drought is an extreme hydrological event, with a short foreseeable period and high destructive force, and it is difficult to monitor. Flash drought aggravates the risk of extreme disasters and seriously threatens agricultural production and urban water security. To explore the temporal and spatial dimension evolution and identifiable characteristics of flash drought, the present study proposed a comprehensive flash drought intensity (FDI) index to evaluate the severity of flash drought in the Jialing River Basin (JRB) based on the standardized evaporative stress ratio (SESR) method. In addition, the Normalized Area-Time Accumulation (NATA) curve was used to describe the three-dimensional continuous spatiotemporal evolution process of flash drought in the basin. The results showed that flash droughts lasted longer and were more severe in the highly urbanized southern part of the basin. In the past 40 years (1980–2020), the frequency, duration, and severity of flash droughts in the JRB increased. According to the susceptibility to flash drought, the JRB can be divided into four drought centers. Drought Center No. 1 is situated in the mountainous region in the northwest of the basin, exhibiting a high frequency of occurrence but affecting a relatively small area. In contrast, Drought Centers No. 2, 3, and 4 are located within urban areas, showing lower occurrence frequency but affecting a wider geographical expanse. Drought events with different developmental characteristics were compared using the NATA curve. Overall, the FD1 flash drought type, occurring in the early stages of drought, accounted for a significant proportion. Meanwhile, the accumulated area affected by FD3 and FD4 flash drought events in the later stages exceeded that of the FD2 flash drought type. In the later period, FD3 and FD4 flash drought events exhibited stronger growth momentum, thereby increasing the complexity and challenges of drought monitoring. The present study provides a theoretical basis for understanding the process, shape and evolution model of drought development under environmental changes as well as enables an enhanced early warning for flash droughts to improve management of water resources.

Evaluating the Service Performance of Heavy Axle Load Ballasted Railway by Using Numerical Simulation Method

To evaluate the service performance of the track substructure of heavy axle load (HAL) railway transportation, an inverse analysis was performed to estimate the resilient modulus values of the track substructure, based on the deflection data obtained from light falling weight deflectometer testing. Subsequently, a three-dimensional finite element model was developed to simulate the effect of the train speeds (v) and axle loads (F) on the typical dynamic responses in the railway track system. The results convincingly indicated that increasing v or F can amplify the track vibration. Finally, a critical stress ratio method was adopted to evaluate the service performance based on the numerical results. A recommended range of v and F was determined to maintain the long-term stability of the HAL railway line. The findings can provide guidance for designing the track and maintenance plans to avoid track support failures and ensure track infrastructure resiliency.

Application of an improved spatio-temporal identification method of flash droughts

Flash droughts are regional phenomena that can manifest in large areas with rapid intensification for a period of time. Few studies have considered the spatial pathways of flash droughts or their drought period. This study uses the five criteria based on the standardized evaporative stress ratio (SESR) method to identify flash droughts, and when a SESR value recovers to the 20th percentile, the flash drought is considered to terminate. To define spatially continuous flash droughts accurately, the usual order of first calculating drought patches and then identifying flash droughts is reversed to first identify flash droughts on the grid and then determine flash drought patches. In addition, this study tracks the spatial paths of flash droughts via centroid transfers of flash drought patches. Using MOD16 data, the methodology is evaluated by analyzing the regional characteristics of flash droughts in the Huaibei Plain of China from 2001 to 2019. The flash droughts in this region most frequently tracked in the northeast and west. The average flash drought duration was 31 days, of which the rapid intensification period was 18 days and drought period was 14 days. Flash drought events in this region mostly occurred in May, August and October, and east to west transition and non-transitions, which accounted for 44% and 22%, respectively, were the main spatial track paths. Only 26% of flash drought events transitioned to long term drought events. This study expands our knowledge of the evolution process of flash droughts to space-time dimensions, which is essential for flash droughts early warning and agricultural water management.

Circular steel tubes strengthened by welding angle steel under preloading condition

Thermal effect and preload are significant factors affecting the mechanical properties of strengthened members in engineering structures. This study concerns the welding thermal effect and mechanical properties of circular steel tubes strengthened by welding angle steel under the preloading condition. The mechanical properties of circular steel tubes strengthened by welding angle steel under the preloading condition were studied with the axial compression tests. The indirect thermal-structural coupling method was proposed and verified by finite element analysis, further compared with the tests. At last, a series of parametric studies were conducted to investigate the influence of loaded strengthening on mechanical properties of circular steel tubes strengthened by welding angle steel under the preloading condition. The corresponding permissible stress ratio and calculation method for the ultimate earing capacity and the axial thermal deformation were proposed. The results provide a basis for the strengthening design of the circular steel tube under the preloading condition.

Stress Ratio Method to Predict Fracture Pressure Gradient in Southern Iraqi Deep Wells

This research presents a method for calculating stress ratio topredict fracture pressure gradient. It also, describes a correlation andlist ideas about this correlation.Using the data collected from four wells, which are the deepestin southern Iraqi oil fields (3000 to 6000) m and belonged to four oilfields. These wells are passing through the following formations: Y,Su, G, N, Sa, Al, M, Ad, and B. A correlation method was applied tocalculate fracture pressure gradient immediately in terms of bothoverburden and pore pressure gradient with an accurate results.Based on the results of our previous research , the data were usedto calculate and plot the effective stresses. Many equations relatinghorizontal effective stress and vertical effective stress are obtained foreach well and used to calculate fracture pressure gradient. Similarequations are found for group of formations that calculate fracturepressure gradient and to find the most accurate correlation amongthem.

Stability Analysis of Slope and Nearby TransmissionTowers in a Hub project Based on Flac3D

Aiming at the problem that the construction process of a water conservancy and hydropower project will affect the stability of the slope and its surrounding buildings, a numerical simulation method is used to carry out a numerical analysis of the displacement and stress diffusion of a junction engineering slope and its nearby transmission tower. The results show that: the deeper the excavation depth of the slope, the greater the rebound of the excavated surface; after excavation, the horizontal displacement of the facing surface of the slope under the support of the continuous wall is small, and the slope can maintain stability. The stress ratio method determines the distance between the excavation surface and the tower foundation, and the slope excavation can be carried out smoothly while ensuring the stability of the tower foundation.

Stress Analysis and Structure Improvement on Arm of Ladle Turret

Static stress analysis on arm of ladle turret is based on finite element (FE) theory and shell theory by finite element software ANSYS. In this paper, an arm subjected to a multi-axial state of stress is examined both numerically and experimentally. The hot spot strains and stresses in the connection are determined through a detailed finite element analysis (FEA) of the joint. The arm geometry is accurately modeled using FE. Check the dangerous position on the side of the arm by different safety factor. For the experimental study, a test rig is designed and used to validate the FE model. Gain the impact factor of the arm. According to finite element calculations, assesses the fatigue strength by stress ratio method and stress amplitude method on the weld.Structural improvement is performed with increasing thickness and changing the location of the force.

Truss Optimization Based on the Evolutionary Structural Optimization

The Evolutionary Structural Optimization (ESO) as an important structural topology optimization method has been widely used in many fields of engineering optimization. However, due to some technical constraints, the use of ESO for the truss optimization is relatively less. A method for truss optimization that combines the ESO method and the Stress Ratio method is proposed in this paper. This method solves the problems of ESO for truss optimization that the sectional area of bars cannot be changed and the speed of optimization cannot be easily controlled. It can be widely used in truss optimization and can get the same good result as other methods (such as GA and SA, etc.). Furthermore, the method proposed in this paper has the advantage that it can be easily programmed in the commercial software (such as Ansys and Abaqus, etc.) owing to its relatively simple optimization principle.

Transformed Stress Method for Generalizing Soil Constitutive Models

AbstractIt is important to generalize constitutive models from the triaxial compression state to the three-dimensional stress state for soils. However, there are some deficiencies in the existing methods, e.g., the using failure criteria method, the generalized shear stress ratio method, and the shape function approach using Lode’s angle or reduced Lode’s angle, for generalizing either isotropic or anisotropic constitutive models. For example, the critical state curve may be misshapen and the yield surface will appear to be curvature discontinuous if the constitutive model is generalized with the shape function approach using reduced Lode’s angle. The transformed stress (TS) space has been proposed in the authors’ former work based on the spatially mobilized plane (SMP), the Lade’s, and the generalized nonlinear strength criterion. In this paper, the TS method based on an arbitrary failure criterion is proposed. It is a simple approach to generalize constitutive models without introducing any extra parame...

Multiple fully stressed designs of steel frame structures with semi‐rigid connections

AbstractA fully stressed design of a frame structure, in which each member is performing to its maximum safe level under at least one loading case, is a common goal in structural design. When multiple fully stressed designs are possible, the designer must make some decisions regarding the desired load path because the outcome of the iterative fully stressed design computation depends upon the initial starting design selected. When steel frame structures are modelled as having semi‐rigid beam‐to‐column connections, the connection flexibility has a significant impact on the nature and diversity of potential fully stressed designs. This paper presents a computational study of how the variety of potential fully stressed designs is affected by connection flexibility. A numerical algorithm, which combines the stress ratio method and Newton's method to avoid problems associated with each method when used alone, is applied to generate sets of distinct fully stressed designs as connection flexibility is varied. It is found that as the connections become increasingly flexible, the variety of fully stressed designs diminishes. Load paths that are efficient with rigid connections are not realizable with semi‐rigid connections because of limited bending moment transfer capacity and, consequently, limited alternate load paths. Copyright © 2003 John Wiley & Sons, Ltd.

Experimental and predicted fatigue crack growth resistance in Al2124/Al2124+35%SiC(3 μm) bimaterial

When a fatigue crack approaches perpendicularly to the macroscopically planar interface of an Al2124/Al2124+35%SiC(3 μm) bimaterial, the fatigue crack growth resistance is affected by the elastic–plastic mismatch, thermal residual stresses and the direction of crack approach to the interface. The main purpose of this work is to compare experimental and predicted behaviour to evaluate how such parameters affect the fatigue crack growth resistance in an Al2124/Al2124+35%SiC(3 μm) bimaterial. Results show that the effective stress ratio method (R′) alone cannot predict the fatigue crack growth resistance of such bimaterials accurately and the effects of the elastic-plastic mismatch must therefore be taken into account.

Fully Stressed Design of Frame Structures and Multiple Load Paths

Fully stressed design is an optimization heuristic that is widely practiced for member sizing of frame structures. When performed iteratively, such as with the stress-ratio method, it usually converges rapidly and yields a reasonable structural design. A previous paper has demonstrated that some frame structures are capable of being proportioned in many different ways, each of which is a distinct fully stressed design with a unique load path. Furthermore, many of these fully stressed designs are unstable fixed points under the stress-ratio iteration, and are consequently unobtainable by conventional methodology. This paper relates this behavior to Hardy Cross’s notion of normal, hybrid, and participatory action. Parameter studies reveal that certain combinations of lateral-to-gravity load ratios and height-to-width ratios tend to produce a greater multiplicity of fully stressed designs. The multiple designs are classified according to eight commonly observed material distribution patterns, and their load ...

Multiple Fully Stressed Structural Designs and the Stress Ratio Method

Abstract: Some structures are capable of being proportioned in several different ways such that each one is a fully stressed design. This paper investigates the nature of these multiple fully stressed designs, the relationships that exist between them, and the behavior of the stress ratio method when applied to the sizing of such structures. “Basins of attraction” constructions are used to graphically portray the behavior of the stress ratio method and to compare it with those of alternative design techniques. It is shown that both attracting and repelling fully stressed designs coexist in the design space under the action of the stress ratio method. A simple modification of the stress ratio method is suggested for transforming repellers into attractors. Instances of limit cycle and chaotic behavior of the stress ratio method are also presented.

Global convergence of the stress ratio method for truss sizing

It is proved that if the well-known stress ratio method is applied to a “perturbed” stress-constrained minimum weight problem for truss structures, then the generated sequence of iteration points always converges to a global optimum.

Using a stress ratio method and F. E. analysis for establishing geometry correction factors in fracture mechanics

When designing stressed-skin structures, one of the prime objectives is to determine accurate stress intensity factors for the specific components in question, which, in turn, depends on the production of accurate geometry correction factors. For an irregularly shaped component, this usually means applying a specific analytical theorem or using a devoted facility such as may be found in relatively sophisticated finite element packages. An alternative technique, however, is proposed whereby stress intensity/geometry correction factors can be readily evaluated using the most rudimentary of finite element programs. The method is potentially very powerful, since it uses the magnitude of the stress at the crack tip which can be obtained using a surprisingly coarse finite element model of the cracked component. It has been found to produce very accurate results when compared with alternative, more widely established method buts is, nevertheless, very easy to apply. In addition, consideration of the relevant theory indicates that although the method is only applied here to the relatively simple case of a thin centre-cracked sheet, it should be sufficiently versatile to be generally applicable to a wide variety of different structural shapes. This paper describes the technique and compares results using different mesh densities with results obtained by other methods.

Phase‐space representation of iterative design processes

AbstractA large variety of design optimization methods have been proposed in recent years. Comparison of the relative performance of each method is a difficult task, and attempts to do so are often based on a limited number of numerical experiments. Recently, a ‘basins of attraction’ construction has been proposed as a graphical tool for investigating global performance of iterative design optimization methods, and as a basis for comparison of different methods. The phase‐space representation presented in this paper is a companion to the basins of attraction construction. Basins of attraction reveal the relationship between starting design and final outcome of the solution process; the phase‐space construction reveals that nature of the paths connecting the starting design and final outcome. The two constructions complement one another in summarizing the performance of design optimization processes. Both constructions are demonstrated in this paper, applied to the optimal design of an elastic grillage structure using Newton's method and the stress ratio method.

Structural Optimization with Stiffness and Frequency Constraints

Abstract Automated preliminary design algorithms for large aerospace structures require an efficient and reliable method to economically minimize weight, while satisfying multiple types of constraints. Often structural optimization is started with a few cycles of Fully Stressed Design, using the stress ratio method, because of its simplicity and computational efficiency. The present approach is to generalize more sophisticated optimality criteria for more than one type of constraint. The goal is to account for more than just stress constraints, while retaining the computational efficiency of the simple stress ratio method. Previous optimality criteria methods for static and frequency constraints are combined in a new algorithm that handles both types of constraints simultaneously. Two trusses and one wing structure are used to demonstrate the validity of an Optimality Criteria method for multiple behavior constraints.

Sensitivity analysis of truss structures and its application to the fully stressed design

Based upon the theorems of structural variations this paper derives a set of expressions for calculating partial derivatives of internal forces, stresses and joint displacements with respect to bar areas for truss structures. Compared with the known formulas for finding the gradients of structural behaviours the calculation effort with the proposed expressions in this paper is usually smaller because the additional virtual loadings needed are relatively fewer. It is of practical significance to various optimization methods in which the calculation of gradients of behaviours is widely used. Moreover, applying the derived formulas to the fully stressed design (FSD), we obtain an improved iterative method for FSD. The numerical examples show that the new method considerably reduces the reanalysis number required to converge to an FSD in comparison with the simple stress ratio method.

Convergence of Stress-Ratio Method

The stress-ratio equations can be derived from fully-loaded conditions. The technique is therefore always a first order iterative method and under certain conditions, second order. All intermediate designs are within the iterations subspace which constitutes a small part of the design space. Convergence characteristics of the stress-ratio method are discussed and illustrated with numerical examples.

Discrete Sizing of Trusses for Optimal Geometry

The optimal configuration and discrete member sizes are automatically determined to minimize the cost of three-dimensional indeterminate truss structures under multiple loading conditions. Member areas and joint coordinates are used as design variables. Design constraints include Euler buckling and specified limits on member stresses, member sizes, and joint displacements. Design variables may be linked and members can be deleted. The design process is separated into geometry modifications using the complex method and suboptimization using the stress ratio method and an analogous scaling procedure for displacement constraints. For each geometry change, discrete member sizes are selected from a table of allowable values. The method is applied to the cost minimization of a 25-member space truss using discrete steel angle sections that are chosen from a table satisfying AISC code requirements, and comparisons are made with minimum weight designs and with continuous variable methods.