Quasi-static Calculation Research Articles

Stress-strain state of building structures taking into account possible local failure of the element

The issue of choosing a structural design and material for supporting structures is an important technical and economic task at the stage of developing a design solution. It depends on a number of factors: consequence class of the structure, reliability of the design solution, savings in basic building materials. The publication provides a classification of design schemes and types of load-bearing structures used in the corresponding solutions. The disadvantages and advantages of using prefabricated and monolithic structures for the installation and subsequent operation of the structural scheme of buildings and structures are considered. Modern design requirements include ensuring the ability of a damaged structure to adapt to new conditions while continuing to function while ensuring the integrity of human life, property and equipment. New conditions mean the consequences of the occurrence of a certain emergency situation, accompanied by weakening or overloading of the load-bearing structures of a structure or soil foundation: a change in the structural design, a combination of new existing loads and a redistribution of internal forces. The publication reflects the results of assessing the redistribution of the stress-strain state of the elements of the “base - foundations - load-bearing structures” system as a result of the implementation of a hypothetical emergency situation with the exclusion of the load-bearing structure from operation. The case of the collapse of one of the vertical load-bearing elements (local failure of the pylon) of an underground floor, which can be used as a dual-use structure, is considered. Calculations for the stability of the structure against progressive collapse were carried out by numerical modeling in the LIRA SAPR-2019 software using a quasi-static calculation and the method of direct integration of dynamics over time. It has been demonstrated that the method of numerical modeling the joint work of a building with a soil base affects the results of a calculation of the progressive collapse of the building frame. The influence of local collapse of a vertical load-bearing element on the redistribution of stresses and strains in the foundation structures of a building section is assessed. The load on the piles under the pylons around the element removed under the local failure scenario is expected to increase by 15...25%.

ANALYSIS OF CALCULATION METHODS FOR PROGRESSIVE COLLAPSE OF SINGLE-STOREY FRAME INDUSTRIAL BUILDINGS AND SEARCH FOR OPPORTUNITIES TO IMPROVE THE ACCURACY OF CALCULATIONS

The issues of analysing the progressive collapse of buildings have become an inseparable part of design. However, design standards still do not provide clear criteria for the calculation algorithm in the analysis of instantaneous collapse of building structures. The article discusses the problems and uncertainties of formulating the problem of analysing the instantaneous collapse of structures. To illustrate the uncertainty of applying applying building analysis methods to progressive collapse in accordance with the requirements of various standards, examples of calculations of existing one-storey frame industrial buildings are given. SCAD Office and LIRA-SCAD software packages are used for the analysis. The results of the solution of the dynamic problem in the time domain are compared with the setting of different times of redistribution of the reaction and the results of the quasi-static calculation with different dynamic coefficients. A comparison is made between the theoretical results of predicting disproportionate destruction and the actual collapse of the structures of the industrial building that was damaged by missile strikes. The presence of important discrepancies in the calculation results and their causes are analyzed. The purpose of the article is to analyze the main features that arise when designing (reinforced) structures of industrial buildings, taking into account the possibility of their local destruction. Conclusion. The article considers some problems that must be solved during the design or reconstruction of industrial buildings, the operation of which may be associated with one or another local destruction of the bearing structures. Prospective constructive ways of effectively solving these problems are presented.

Load Calculation and Strength Analysis of the Deepwater Landing Drill Pipe-Lowering Operation

A landing string is directly exposed to seawater and subjected to significant stresses and complex deformations due to environmental loads such as wind, waves, and ocean currents during the phase in which the drill string carries the casing to the wellhead. Meanwhile, as the water depth increases, the weight of the drill string increases, leading to an increase in the tensile loads borne by the drill string, which can easily cause a risk of failure. Therefore, a quasi-static load calculation model for the deepwater insertion of the pipe column was established. Using the Ansys platform, simulations were conducted for average wind, wave, and ocean current conditions during different months throughout the year. The ultimate loads and stress distributions of the string were derived from theoretical analyses and numerical simulations for different operational sea states, and the suggested safe operating window and desired BOP trolley restraining reaction force for landing strings’ lowering are given according to the existing industry standards. The research findings can help in identifying the potential risks and failure modes of the deepwater landing string under different working conditions.

Способы расчета несущих конструкций на устойчивость к прогрессирующему разрушению

Introduction. Calculation methods and current normative documents used in the calculation of buildings for resistance to progressive collapse are considered. The key methods of analysis are listed and fundamenta.rules of each of them are stated. The advantages and disadvantages of these methods are analyzed. Materials and methods. The calculations of stability to progressive collapse have been carried out for a multi-span flat frame at the failure of the middle post of the ground floor. The software complex LIRA-SAPR 2021 R1.2 was used to perform calculations. The task was solved by several methods: the static calculation, quasi-static calculation and dynamic calculation. The nonlinear functioning of construction and material was considered by step-methods with using the flow curve from SP 16.13330.2017. Quasistatic calculation was performed in two variants: pulldown and pushdown analysis. The dynamic calculation was carried out by direct integration of the equations of motion using the module “Dynamics in Time”. Two variants with different element elimination time were considered. Results. The results are analyzed and summarized in Table 2. The static calculation yields force and displacement values that are clearly underestimated as compared to other methods. Forces and displacements obtained by quasistatic analysis are greater than those obtained by dynamic analysis. The results obtained in the pulldown and pushdown analyses are close in value. Conclusions. Quasistatic calculations give higher forces and displacements than dynamic calculations. The results of pushdown analysis correlate better with the results of calculations in the dynamic formulation. In order to determine forces more accurately when using quasi-static calculation, a justification of the dynamical coefficient is necessary.

Bearing Capacity of Steel Trusses with Local Damage Considering the Exclusion Time

To ensure the safety of buildings and structures, they must maintain their bearing capacity in case of local damage. The article is devoted to the study of the robustness of damaged steel trusses, as well as the time during which local destruction of the trusses occurs. Finding a solution to this problem is one of the key stages in the development of a practical methodology for calculating steel trusses’ resistance to the local destruction of elements. The time from the beginning of destruction to the complete failure of the element is proposed to be called the exclusion time. Based on the performed theoretical and numerical studies, for the quasi-static calculation it is recommended to use the values of the dynamic coefficient for the considered steel trusses. In the numerical formulation, the work of steel trusses as part of the building frame was investigated along with local destruction of individual elements of the truss. Numerical studies have shown that the shorter the failure time of the truss element, the greater the dynamic forces arising in the structure. The frame of the building is considered as a spatial system. A numerical dynamic analysis of the spatial coverage is carried out, taking into account the local failure of one of the truss elements. The distribution of the dynamic coefficient over the steel trusses is obtained. This made it possible to study the effect of local failure on the intact load-bearing structures. The article presents the results of a series of experimental studies of flat trusses aimed at determining the time of failure of a steel truss element. Based on the results obtained, the failure time of the damaged rod and the redistribution of efforts to the neighboring elements of the truss were calculated. In accordance with the calculated failure time, recommendations were formulated to reduce the value of the dynamic coefficient used in the static calculation, depending on the types of damage to the truss.

Progress in understanding seismic wind noise

Previous work at NCPA on predicting and measuring wind noise in the ground used a quasistatic calculation employing Shield’s wind noise correlation function. This method predicted the vertical displacements at the surface well, but under predicted the horizontal displacement and predicted a rapid decay of levels with depth that was not observed in the measurements. A new measurement of the wind noise correlation coefficients using flush mount microphones was presented at the Seattle Meeting (2aPa1). In this talk additional measurements and improved methods for evaluating the coefficients are described. An improved calculation of the seismic levels due to wind induced pressures at the ground has been developed based on the wavenumber-frequency analysis developed for studying airframe noise due to turbulence. This calculation correctly predicts the surface vertical component and the near constant seismic level in the first 40cm of the ground. It still under predicts the horizontal component, but the under prediction is smaller than that predicted by the quasistatic calculation. [This research was sponsored by the Department of the Navy, Office of Naval Research under ONR Award No. N00014-18-2489.]

Post-buckling loads of a horizontal pipe string with variable length

Horizontal well is one of the main measures to improve oil and gas production capacity. However, with the extension of horizontal section, the risk of pipe string buckling will be increased. In the quasi-static finite element calculation, it is difficult to identify the contact with the cylindrical wellbore due to the jumping changes of the sinusoidal and helical buckling configurations of the pipe string. Therefore, this method is difficult to solve the calculation convergence problem, especially with the increase of horizontal pipe string length and greater flexibility, this problem becomes particularly prominent. We propose a finite element calculation strategy, namely, using the dynamic relaxation method, to transform the static buckling of the horizontal pipe string into a virtual dynamic problem. We put forward the identification methods of sinusoidal and helical post buckling modes, as well as their critical load determination methods. The research results show that the use of large damping in the dynamic relaxation method can significantly restrain the vibration phenomenon of alternating contact and separation between the horizontal pipe string and the cylinder wall, reduce the response time to reach the stable buckling mode, and also can significantly improve the calculation efficiency. The change trend of critical load is the same when the length of horizontal pipe string is extended for a certain length. Within the extended length range, the horizontal pipe string has the same half sine wave or helix number, and the critical loads of sine and helix buckling will gradually decrease with the extension of the string length, and eventually tend to be constant. This trend is more obvious when the number of half sine waves or helixes of horizontal pipe string is more. The dimensionless critical loads of sinusoidal and helical buckling tend to 1.00 and 2 respectively, and the corresponding dimensionless string lengths are 3.73π and 6.21π, respectively. However, other researchers underestimated the effect of length on the critical load of helical buckling. We have verified the critical loads for sinusoidal and helical buckling of short and long pipe strings. The results of this paper are practical for post-buckling analysis of horizontal wells with various lengths of pipe string.

From quasi-static calculation of an aerial tramway system to traveling cycle time optimization

From quasi-static calculation of an aerial tramway system to traveling cycle time optimization

An iterative algorithm for studying forced vibrations of a nanotube conveying fluid

A dynamic analysis of the fractional viscoelastic nanobeam conveying fluid, resting on a viscoelastic foundation, with simply-supported boundary conditions and uniformly loaded, is performed. The existence of a significant internal damping of the nanotube led to the choice of a nonlinear and fractional Zener model for the nanotube material. Solving of the integral-differential governing equation is done using Galerkin’s method and an iterative method that uses the Laplace transformation techniques, Bessel functions theory and the binominal series. The effects of the nonlocal parameter and of the fractional order on the transverse displacements of the nanotube conveying fluid are studied. In order to validate the approached iterative method, the results of the dynamic analysis were compared with those of the quasi-static calculation of the structure. The proposed algorithm for solving the governing equation and the accompanying graphical data are useful in the engineering design of the nanotubes conveying fluid.

Dynamic simulation analysis of rail track and track structure based on SIMPACK and ABAQUS

With the continuous improvement of China's railway construction level, the requirements for the quality of train operation are also improved. For the mixed passenger and freight railway, it is necessary to transit from the simple design concept of safety to the design concept of the unity of comfort and safety. Therefore, modern numerical calculation method or simulation software method is used to replace the traditional quasi-static calculation method, and SIMPACK, ABAQUS and other related software are mainly used to analyze the operation quality and track structure dynamics of the line design scheme. The derailment coefficient, vertical acceleration and other evaluation indexes are used to evaluate the safety and comfort of the line, and the dynamic analysis of the track structure is carried out based on the vertical force. The research shows that under the condition of this line, when the passenger and freight train run at the designed speed per hour in the curve section, they can meet the specification requirements of various indexes, and there is still room for increasing speed, and the stress and strain value of the track structure can meet the specification requirements.

STIFFNESS ANALYSIS AND OPTIMIZATION OF STEPPED COLUMNS UNDER COMBINED BENDING AND COMPRESSION

The paper presents the stiffness analysis and optimization of stepped columns constituting the core frame of the industrial building. The two-span cross section of a one- storey industrial building is investigated herein. The quasi-static calculation is performed using the limited load approximation method for the cross-section of the most loaded middle column. The critical Euler characteristic of the compressive longitudinal load is determined by the differential bending equations at the bifurcation instability in the column sections. The parameter optimization of the column cross-section is achieved through the nonlinear mathematical programming. The optimization of medium column cross-section is considered using the proposed calculation when setting a set of constraints for the optimization task.

A Bandpass Filter Based on Dielectric Layers with a Strip Conductor Subwavelength Grating at Their Interfaces

The design of a multilayer bandpass filter has been investigated, in which each of the half-wavelength resonators consists of two dielectric layers with outer strip conductor gratings in the form of square grids and inner ones in the form of square patches. The grids serve as mirrors with specified reflective properties, which ensure optimal couplings of the outer resonators with free space and optimal coupling between the resonators. The patch gratings make it possible to tune the resonator eigenfrequency during the filter synthesis. The efficiency of the quasi-static calculation of the frequency response for the layered structure is shown for the case of a lattice period smaller than the wavelength in the dielectric and much smaller than the layer thickness. Since the calculation does not require much computing power, the parametric synthesis of the device can be performed on a conventional personal computer. The measured characteristics of the prototype of the synthesized third-order filter with a fractional passband width of ∼10% and a central passband frequency of ∼10.6 GHz are in good agreement with the calculation. The proposed design allows one to fabricate multilayer panels radio transparent in a certain frequency band for hiding microwave antennas.

55 Mn-based fiducial markers for rapid and automated RF coil localization for hyperpolarized 13 C MRI.

To use fiducial markers containing manganese 55 to rapidly localize carbon 13 (13 C) RF coils for correcting images for B1 variation. Hollow high-density polyethylene spheres were filled with 3M sodium permanganate and affixed to a rectangular 13 C-tuned RF coil. The relative positions of the markers and coil conductors were mapped using CT. Marker positions were measured by MRI using a series of 1D projections and automated peak detection. Once the coil location was determined, coil sensitivity was estimated using a quasi-static calculation. Simulations were performed to determine the minimum number of projections required for robust localization. Phantom experiments were used to confirm the accuracy of marker localization as well as the calculated coil sensitivity. Finally, in vivo validation was performed using hyperpolarized 13 C pyruvate in a rat model. In simulations, our algorithm was accurate in determining marker positions when at least 6 projections were used (RMSE 1.4 ± 0.9 mm). These estimates were verified in phantom experiments, where markers locations were determined with an RMS accuracy of 1.3 mm. A minimum SNR of 4 was required for automated detection to perform accurately. Computed coil sensitivity had a median error of 17% when taken over the entire measured area and 5.7% over a central region. In a rat, correction for nonuniform reception and flip angle was able to normalize the signals arising from asymmetrically positioned kidneys. Manganese 55 fiducial markers are an inexpensive and reliable method for rapidly localizing 13 C RF coils and correcting 13 C images for B1 variation without user intervention.

Detection and Localization of Interference and Useful Signal Extreme Points in Closely Coupled Multiconductor Transmission Line Networks

This study highlights the importance of detecting and localizing useful and interference signal extreme points in multiconductor transmission lines (MCTL) by developing a new approach for detecting and localizing signal extreme points in MCTL networks of arbitrary complexity. A radio-electronic component is presented as a network consisting of a number of connected MCTL sections. Each MCTL section is divided into segments and the number of segments is set by the user. The approach is based on a quasi-static calculation of signal waveforms at any point (segment) along each conductor of an MCTL. The block diagrams of the developed algorithms are presented. Using the approach, a number of investigations have been done which include the following: the signal maximum detection and localization in the meander lines with one and two turns, the influence of ultrashort pulse duration on localization of its extreme points in the printed circuit board (PCB) bus of a spacecraft autonomous navigation system, the influence of ultrashort pulse duration on localization of crosstalk extreme points in the PCB bus, and the simulation of electrostatic discharge effects on the PCB bus. There are also some investigations with optimization methods presented. A genetic algorithm (GA) was used to optimize the influence of ultrashort pulse duration on localization of the pulse and crosstalk extreme points in the PCB bus. Furthermore, the GA was used to optimize the PCB bus loads by criteria of the peak voltage minimization. A similar investigation was carried out with the evolution strategy. The obtained results help us to argue that the signal extreme points can be detected both in structures with different configurations and applying different excitations.

Research Onquasi-Static Calculation for Seismic Response of Underground Rock and Soil

This paper analyzes the common quasi-static calculation error sources for seismic design of underground rock structure cross-section. For the current seismic underground rock response, the finite element reaction displacement method and the finite element reaction acceleration method are used for comparative calculation to a specific geological condition. The structure of the metro station changes the applicability of seismic wave, structural stiffness, coating stiffness and structural depth to the quasi-static actuarial. It is found that the finite element response stress method is the closest to the dynamic analysis results. It is a quasi-static calculation method with high precision and applicability, which can be used for seismic response analysis of underground geotechnical structures.

Contributions of poroelastic-wave potentials to seismoelectromagnetic wavefields and validity of the quasi-static calculation: a view from a borehole model

Contributions of poroelastic-wave potentials to seismoelectromagnetic wavefields and validity of the quasi-static calculation: a view from a borehole model

New methodology for fast prediction of wheel wear evolution

ABSTRACTIn railway applications wear prediction in the wheel–rail interface is a fundamental matter in order to study problems such as wheel lifespan and the evolution of vehicle dynamic characteristic with time. However, one of the principal drawbacks of the existing methodologies for calculating the wear evolution is the computational cost. This paper proposes a new wear prediction methodology with a reduced computational cost. This methodology is based on two main steps: the first one is the substitution of the calculations over the whole network by the calculation of the contact conditions in certain characteristic point from whose result the wheel wear evolution can be inferred. The second one is the substitution of the dynamic calculation (time integration calculations) by the quasi-static calculation (the solution of the quasi-static situation of a vehicle at a certain point which is the same that neglecting the acceleration terms in the dynamic equations). These simplifications allow a significant reduction of computational cost to be obtained while maintaining an acceptable level of accuracy (error order of 5–10%). Several case studies are analysed along the paper with the objective of assessing the proposed methodology. The results obtained in the case studies allow concluding that the proposed methodology is valid for an arbitrary vehicle running through an arbitrary track layout.

CALCULATION-EXPERIMENTAL SUBSTANTIATION OF VIBRATION STRENGTH OF NUCLEAR POWER PLANT PIPELINES BASED ON THE QUASI-STATIC APPROACH

In accordance with NP-096-15 [1], management of equipment and pipelines resources at the stages of design, operation and decommissioning should be based on the evaluation of the technical condition and residual life; identifi cation of the dominant (controlling) mechanisms of aging, degradation and damage of equipment and pipelines of nuclear power plants (NPP); the constant improvement of monitoring processes of aging, degradation and damage of equipment and pipelines of nuclear power plants. Despite the progress in computer development in recent decades, its capabilities are still insuffi cient to solve equations of hydrodynamics when high Re numbers are of practical interest (solution instability: arbitrarily small perturbation radically alters the stability of the solution of the Navier-Stokes equations). Challenges remain in the verifi cation of CFD codes. Due to the complex spatial confi guration of diff erent functional purpose piping systems of NPPs, as well as the specifi cs of the hydro-elastic interaction of the fl ow and tubing, calculation methods to evaluate the dynamic stress-strain state can be selected only based on the results of experimental measurements of vibration parameters of pipelines. The vibration parameters of the pipelines are the vibrational acceleration, velocity and displacement. Vibration of piping from the point of view of resource is classifi ed as high cycle fatigue, which, due to its specifi cs, requires adopting conservative approaches in substantiation of vibration strength of pipelines. As the pipelines are operating within the elastic deformation, the strength test with time-dependent load can in some cases be replaced with a quasistatic calculation. A numerical experiment illustrates the application of the quasistatic approach that gives satisfactory results. Substantiated application of the quasistatic approach is based on the analysis of the spectral density of the pipeline vibration at diff erent points of measurement and can be eff ectively used to assess vibrostresses, fracture toughness and substantiation of vibration strength of NPP pipelines.

Loads and Stress Analysis Cycle Automation in the Automotive Suspension Development Process

The article describes the use of the Multi-Body Dynamics (MBD) models, the Finite Element Analysis (FEA) and the CAD-modelling process in the automotive suspension development. Automation of maximum quasi-static loads calculation with the automatic two-way geometry update between MBD/CAD-models and automatic load transfer to the finite element analysis allows performing numerous analysis of suspension during development without significant time consumption, and, hence, provides an increased accuracy and reliability of stress analysis results.

PECULIARITIES OF CALCULATION OF MAGNETIC SYSTEMS WITH SHORT-CIRCUITED SECONDARY WINDINGS IN IN-PLANE FORMULATION

Introduction. A feature of quasi-static calculation of plane electromagnetic fields is unlimited volume occupied by the current. This condition imposes certain requirements on the choice of boundary conditions for solving such problems (the vanishing of the algebraic sum of the currents flowing through the cross section of all wires), failure of which leads to incorrect results. Purpose. The mathematical formulation of the boundary conditions corresponding to real physical processes in solving problems of plane quasi-static field by Kelvin transformation and development of a technique for calculating the induced currents in closed circuits in the calculation of AC electromagnet in the quasi-static mode. Methods. Investigation of nonlinear model of the current transformer in in-plane electromagnetic field calculation and the AC electromagnet is carried by the finite element method using a specific software package. Results. A possible error in the boundary conditions and summarizes the estimated model corresponds to the physics of the process using the Kelvin transform, proposed method of calculating currents in closed loop AC electromagnet in the calculation of plane problems of the field. Conclusions. The specificity of the problem of calculating the electromagnetic field in in-plane formulation requires a special approach to the assignment of boundary conditions and calculation of the currents induced in a closed loop.