Reliability analysis of slender columns using the general method with linear creep theory

To analyze the reliability of slender columns subjected to axial force and uniaxial bending moment, with a slenderness index between 100 and 140, 216 columns were modeled. The square cross-section was adopted, with three different configurations for longitudinal reinforcement. In the calculation, the general method with the linear creep theory was applied. Several factors were varied: slenderness index, reinforcement ratio, steel bars arrangement, compressive strength of concrete, and first-order relative eccentricity. For analysis purposes, the Monte Carlo method was adopted, followed by the First Order Reliability Method (FORM). Considering the results obtained, it was observed that the reliability index is usually higher for lower reinforcement ratios and varies according to the configuration of the cross-section.

CARRYING CAPACITY OF DAMAGED REINFORCED CONCRETE TWO-TUBE COLUMNS

The article presents the results of experimental and theoretical studies of the work, the parameters of the stress-strain state and the methodology for calculating the residual bearing capacity of reinforced concrete I-section columns damaged during operation and combat operations. The analysis of the literature on this subject made it possible to study the main factors affecting the residual bearing capacity, namely: the depth of damage; the angle of inclination of the damage front; relative eccentricity of application of external compressive force. A three-factor three-level experimental design has been developed. The conducted field tests of prototypes of damaged reinforced concrete columns made it possible to determine the parameters of the stress-strain state of damaged elements and their actual residual bearing capacity. On the basis of the performed experimental-statistical modeling, the main factors influencing the residual bearing capacity of damaged elements have been established. The prerequisites for calculating damaged reinforced concrete I-beams are proposed and equilibrium equations are drawn up. The proposals set out in the article are based on the main provisions of the current norms and expand the effect of their use. The analysis of influence of various factors on bearing capacity of the damaged I-beam reinforced concrete columns is carried out. It was found that the columns can withstand a maximum destructive load of 1738 kN at an angle of inclination of the damage front of 60о and in the absence of relative eccentricity. And the least destructive load columns can withstand in the absence of the angle of the damage front, and the relative eccentricity will be 1/8 of the applied load. On the basis of the conducted researches the technique of definition of reliably substantiated residual bearing capacity of reinforced concrete compressed elements of a T-profile profile damaged in the course of operation is developed. This makes it possible to determine the possibility of further trouble-free operation of structures or the need for their reinforcement or reconstruction.

An Investigation of Bearing Capacity of High-Strength SRC Columns under Eccentric Axial Load

This paper investigates the eccentric compression performance of high-strength steel reinforced concrete (SRC) columns. In addition, the feasibility of the calculation codes used for the load-carrying capacity of these columns is verified by eccentric compression tests on 10 high-strength SRC columns with Q460 and Q690 steels and two normal SRC columns with Q235 steel. Moreover, the influence of the steel strength, relative eccentricity, steel ratio, and stirrup spacing on the bearing capacity and ductility of the specimens is analyzed. It was found that the bearing capacity and ductility of the specimens significantly increases when the steel strength increases from 276.5 MPa to 774.2 MPa; the bearing capacity of the Q690 SRC column is slightly higher than that of the Q460 SRC column. In addition, the ductility coefficient of the Q690 SRC columns is significantly higher than that of the Q460 SRC columns. It was also found that increasing the eccentricity and steel ratio can improve the ductility of the specimens and the smaller stirrup spacing can enlarge the contribution of Q690 steel under the ultimate bearing capacity. It is demonstrated that Eurocode 4-2004 and AISC360-16 codes significantly underestimate the test results. In contrast, JGJ138-2016 slightly underestimates the test results when the relative eccentricity is 0.2 but overestimates the test results when the relative eccentricity is 0.6. Furthermore, in order to maximize the contribution of Q690 steel under ultimate bearing capacity, the expanded parameter analysis is carried out using a finite element model. Following the analysis results, the suggestions for designing high-strength SRC columns under eccentric load are provided.

Parameter Sensitivity Analysis on Dynamic Coefficients of Partial Arc Annular-Thrust Aerostatic Porous Journal Bearings

Aerostatic bearings are widely used in high-precision devices. Partial arc annular-thrust aerostatic porous journal bearings are a prominent type of aerostatic bearings, which carry both radial and axial loads and provide high load-carrying capacity, low air consumption, and relatively low cost. Spindle shaft tilting is a resource-demanding challenge in numerical modeling because it involves a 3D air flow. In this study, the air flow problem was solved using a COMSOL software, and the dynamic coefficients for tilting degrees of freedom were obtained using finite differences. The obtained results exhibit significant coupling between the tilting motion in the x-and y-directions: cross-coupled coefficients can achieve 20% of the direct coefficient for stiffness and 50% for damping. In addition, a nonlinear behavior can be expected, because the tilting motion within 3°, tilting velocities within 0.0012°/s, and relative eccentricity of 0.2 have effects as large as 20% for direct stiffness and 100% for cross-coupled stiffness and damping. All dynamic coefficients were fitted with a polynomial of eccentricity, tilting, and tilting velocities in two directions, with a total of six parameters. The resulting fitting coefficient tables can be employed for the fast dynamic simulation of the rotor shaft carried on the proposed bearing type.

Method for calculating the sliding bearing of a piston engine and compressor

A one-dimensional model for calculating the sliding bearing of a piston engine and compressor is proposed. The results of approximation of the graphs by analytical dependences of the relative eccentricity on the bearing load coefficient for different values of the ratio of the working length of the bearing to the diameter of the crankshaft journal are presented in the form of exponential functions. Keywords: sliding bearing, heat balance, piston compressor, piston engine, friction [email protected]; [email protected]; [email protected]

Computer#aided design of the pump profile with epicycloidal gearing using MathCad tools

The article discusses a method for determining the relative eccentricity , used in calculating the thermal balance of an internal combustion engine sliding bearing. When performing this calculation, a number of temperature values are set in the bearing oil layer. For each set temperature, the engine oil viscosity value and the bearing load factor Ф are determined. To determine the relative eccentricity, graphical dependencies of the load factor on the relative eccentricity are used as input data. The thermal calculation of the sliding bearing showed that the accuracy of determining the relative eccentricity is of great importance. Their inaccurate definition leads to a failure of the thermal balance in the bearing. In addition, the method of determining the value of by the accepted value of the ratio of the working length of the bearing to the diameter of the connecting rod neck of the crankshaft (graphically) for this calculation is quite time-consuming. For this reason, the graphical method for determining has been replaced with an analytical one. Relative eccentricities were obtained using the least squares method. An algorithm has been developed for automated construction of transverse and longitudinal profiles of an oil pump with epicycloidal engagement.

Influence of Natural Cavities on the Design of Shallow Foundations

When inner cavities of significant dimensions exist in natural rocks, problems arise when a shallow foundation for a building, bridge or other structure is builtonthem. Thus, taking one of the most representative cavity geometries in nature, the ellipsoidal horizontal shape, the main objective of this study is to obtain the ultimate bearing capacity of the foundation with cavities of different sizes and positions, on rock masses with different strengths and deformation characteristics. The study focuses on natural rocks of karst origin (in limestones, dolomites or gypsums) and of volcanic origin. The ultimate bearing capacity is determined relative to a situation without the existence of the cavity for different cavern positions and sizes, rock types (mi), strengths (UCS), and states (GSI) of the rock mass. The results showed that the most decisive parameter is the relative eccentricity. The influence of the rock type (Hoek’s parameter mi) is, for practical purposes, negligible (lower than 10%). The strength and condition of the rock mass (parameters UCS and GSI) have relatively little influence on the results obtained. This study aims to provide a simple design criteria for universal use, with different geometric configurations and qualities of rock masses that can be used directly without the need for sophisticated calculations by the designer.

COMPARATIVE ANALYSIS OF DIFFERENT ROTARY CONTROL SYSTEMS

This article provides a comparative analysis of various control systems for a rotor system on fluid friction bearings. The control was carried out on the basis of the criterion of the minimum friction moment, the controlled parameter was the bearing stiffness coefficients. The following control methods were compared in terms of friction torque and rotor eccentricity: STATIC, PID, DQN, DDPG, Q-Learning and SARSA. The control systems were guided by the following observed parameters: the values of coordinates and velocities along the x, y axes, as well as the frictional moment and relative eccentricity.

High-strength concrete eccentrically compressed elements

The article is devoted to the analysis of technical and economic efficiency of application of high-strength concrete (HSC) in the eccentrically compressed columns. In the first part of the paper, the effect of concrete grade on in-creasing the column stiffness depending on steel ratio at different values of the relative eccentricity is considered. According to the results of the calculation, application of HSC is most effective at low values of the relative ec-centricity because increasing the concrete strength leads to more intensive increasing of column stiffness than increasing of steel ratio. In the second part of the paper, the material cost of the 1 linear meter of the column is calculated at the fixed value of column stiffness and application domain of HSC is defined in the case under consideration. In addition, load characteristics providing the efficiency of HSC application in the eccentrically compressed columns are determined.

A new fuel-balanced formation keeping reference trajectories planning method

Purpose The purpose of this paper is to propose a new fuel-balanced formation keeping reference trajectories planning method based on selecting the virtual reference center(VRC) in a fuel-balanced sense in terms of relative eccentricity and inclination vectors (E/I vectors). Design/methodology/approach By using the geometrical intuitive relative E/I vectors theory, the fuel-balanced VRC selection problem is reformulated as the geometrical problem to find the optimal point to equalize the distances between the VRC and the points determined by the relative E/I vectors of satellites in relative E/I vectors plane, which is solved by nonlinear programming method. Findings Numerical simulations demonstrate that the new proposed fuel-balanced formation keeping strategy is valid, and the new method achieves better fuel-balanced performance than the traditional method, which keeps formation with respect to geometrical formation center. Research limitations/implications The new fuel-balanced formation keeping reference trajectories planning method is valid for formation flying mission whose member satellite is in circular or near circular orbit in J2 perturbed orbit environment. Practical implications The new fuel-balanced formation keeping reference trajectories planning method can be used to solve formation flying keeping problem, which involves multiple satellites in the formation. Originality/value The fuel-balanced reference trajectories planning problem is reformulated as a geometrical problem, which can provide insightful way to understand the dynamic nature of the fuel-balanced reference trajectories planning issue.