Load Redistribution Research Articles

Development of Creep Deformations during Service Life: A Comparison of CLT and TCC Floor Constructions

Cross-laminated timber (CLT) slabs in residential buildings need additional weight, e.g., in the form of screeds or gravel layers, to fulfill the criterion for the highest impact-sound class. The additional mass is, however, not exploited for the load bearing behavior, but adds additional weight and leads to an increased height of the floor construction. In this study, such a CLT floor construction with a construction height of 380 mm is compared with a composite slab consisting of a CLT plate with a concrete layer on top with a floor construction height of 330 mm. The timber concrete composite (TCC) slab has a different creep behavior than the CLT slab. Thus, the development of the time-dependent deflections over the service life are of interest. A straightforward hybrid approach is developed, which exploits advanced multiscale-based material models for the individual composite layers and a standardized structural analysis method for the structural slab to model its linear creep behavior. The introduced approach allows to investigate load redistribution between the layers of the composite structure and the evolution of the deflection of the slab during the service life. The investigated slab types show a similar deflection after 50 years, while the development of the deflections over time are different. The CLT slab has a smaller overall stiffness at the beginning but a smaller decrease in stiffness over time than the investigated TCC slab.

Field investigation into the performance of pipe pile in soft clay under static and cyclic axial loads

We performed a field investigation into the effective stress, the shaft friction at the pile–soil interface, and the pile-end base resistance of a 29.5 m long prestressed concrete pipe pile in soft clay under static and cyclic loadings (50 000 cycles). Our results indicate that under low-level cyclic loading (CLR ≤ 0.2, where CLR is the ratio of cyclic load amplitude to the ultimate capacity), the pore water pressure at the pile–soil interface initially accumulates with the number of cycles, followed by gradual dissipation after reaching its maximum value. The effective stress also initially decreases and then increases. The shaft friction increases after cyclic loading. Owing to axial load redistribution, the base resistance decreases with the number of cycles. When the pile is subjected to high-level cyclic loading (CLR ≥ 0.5), the pore water pressure at the pile–soil interface keeps accumulating while the effective stress continues to decrease, leading to the degradation of shaft friction. The base resistance increases as a result of axial load redistribution. In particular, we analyzed the effects of the static load level and the cyclic load level on the changes shaft friction.

Cyber-attack against heating system in integrated energy systems: Model and propagation mechanism

The integrated energy system (IES) constitutes a new kind of cyber-physical system combined with advanced information and communication technology. The coupling of the cyber system and IES improve energy efficiency while introducing the threat of cyber security. This paper highlights the significance of the cyber security of IES and figures out the weak spots of cyber security in heating systems of IES. Firstly, we propose a class of false data injection attacks against the heating systems of IES for the first time, namely, the heat load redistribution (HLR) attacks. Three specific methods and models of HLR attacks are presented, targeting indoor and supply temperatures at the secondary heating network, respectively. Based on the analysis framework combining the optimization dispatch and simulation, we find that the proposed HLR attacks have the properties of latency and transitivity and significantly affect the security, users' comfort, and economy of IES. This research provides a groundwork for future research related to the coordinated electricity-heat cyber-attack and defense in IES.

Correlation Between Avalanches and Emitted Energies During Fracture With a Variable Stress Release Range

We observe the failure process of a fiber bundle model with a variable stress release range, γ, and higher the value of γ, lower the stress release range. By tuning γ from low to high, it is possible to go from the mean-field (MF) limit of the model to the local load-sharing (LLS) limit where local stress concentration plays a crucial role. In the MF limit, individual avalanches (number of fibers breaking in going from one stable state to the next, s) and the corresponding energies E emitted during those avalanches have one-to-one linear correlation. This results in the same size distributions for both avalanches (P(s)) and energy bursts (Q(E)): a scale-free distribution with a universal exponent value of −5/2. With increasing γ, the model enters the LLS limit beyond some γc. In this limit, due to the presence of local stress concentrations around a damaged region, such correlation C(γ) between s and E decreases, i.e., a smaller avalanche can emit a large amount of energy or a large avalanche may emit a small amount of energy. The nature of the decrease in the correlation between s and E depends highly on the dimension of the bundle. In this work, we study the decrease in the correlation between avalanche size and the corresponding energy bursts with an increase in the load redistribution localization in the fiber bundle model in one and two dimensions. Additionally, we note that the energy size distribution remains scale-free for all values of γ, whereas the avalanche size distribution becomes exponential for γ > γc.

Dynamic modeling and characteristic analysis of the double-reactor and quadruple-turbine nuclear power system based on steam main-pipeline distribution characteristics

Motivated by the insufficient insights on the dynamic characteristics of the double-reactor and quadruple-turbine nuclear power system (DQNPS) and the lack of the distributed-parameter model of the steam main-pipeline (SMP), the full-system dynamic model of the DQNPS is developed based on the conservation of mass, energy, and momentum in this work, where the SMP is modeled using discrete approximate distributed-parameter modelling method. Dynamic behavior analysis is then carried out on the validated model, through which, the dynamic characteristics of key variables, such as the steam pressures in the SMP are investigated in detail under the four typical step disturbances. The simulation results show that the DQNPS is of high nonlinearity and strongly coupled among multi-variables, and that the steam pressures in the SMP exhibit obvious distributed-characteristic which is the root cause of load redistribution in the DQNPS. Furthermore, it can be obtained from the simulations that the steam generators and the SMP in the DQNPS has the strong ability of energy-storage, which is valuable for the control of the system. The simulation results in this work can provide a useful reference for research on modeling and control of multi-reactor nuclear power system.

Cyber Security Frameworks

Abstract: In this paper we attempt to explain and establish certain frameworks that can be assessed for implementing security systems against cyber-threats and cyber-criminals. We give a brief overview of electronic signature generation procedures which include its validation and efficiency for promoting cyber security for confidential documents and information stored in the cloud. We strictly avoid the mathematical modelling of the electronic signature generation process as it is beyond the scope of this paper, instead we take a theoretical approach to explain the procedures. We also model the threats posed by a malicious hacker seeking to induce disturbances in the functioning of a power transmission grid via the means of cyber-physical networks and systems. We use the strategy of a load redistribution attack, while clearly acknowledging that the hacker would form its decision policy on inadequate information. Our research indicate that inaccurate admittance values often cause moderately invasive cyber-attacks that still compromise the grid security, while inadequate capacity values result in comparatively less efficient attacks. In the end we propose a security framework for the security systems utilised by companies and corporations at global scale to conduct cyber-security related operations. Keywords: Electronic signature, Key pair, sequence modelling, hacker, power transmission grid, Threat response, framework.

Avaliação de sistemas posturais da pélvis numa pessoa com Distrofia Muscular do tipo Cinturas: resultados da análise a três almofadas na promoção do equilíbrio dinâmico

Introduction: Pressure ulcer cushions are specialised devices for pressure redistribution and management of tissue load and microclimate. They should maintain postural alignment, facilitate movement, create a stable base, relieve pain and be comfortable. They can be composed exclusively of one material such as foam, gel, air and fluid, or a combination of two or more of these materials. Research has focused on weight distribution and has neglected the dynamic behaviour of the cushion during everyday activities. Objectives: To evaluate the effectiveness in maintaining dynamic balance of three types of medium-high range cushions with different compositions. Material and Methods: Study with a female person with Girdle-Limb Muscular Dystrophy, using: a foam and air cushion (A), a foam and fluid bag cushion (B) and an air cushion (C). Data were collected in two moments: 1) anthropometric, kinematic and dynamic data collection, through direct measurement of reach, video recording and accelerometer, and pressures exerted on the cushions, employing a protocol of movements and cushion randomisation; 2) evaluation of user perception with a questionnaire and visual analogue pain scale, after four hours of staying on the cushion. Results: Cushion A revealed better results at the level of maximum reach, peak pressure in the initial position, coefficient of variation and mean pressure in frontal trunk flexion. Cushion B showed more positive results in the contact area, coefficient of variation and mean pressure in the initial position, peak pressure in frontal trunk flexion, acceleration variation and subjective analysis. Conclusion: The anti-sores cushions that combine two materials in their composition are more effective in promoting dynamic balance, with the advantage of the cushion composed of foam and fluid.

Assessment of Different Retrofitting Methods on Structural Performance of RC Buildings against Progressive Collapse

Progressive collapse refers to the spread of primary local damages within the structure. Following such damages due to removing one or more load-bearing columns, the failure spreads in a chain and causes structural failure. This study represents a report investigating the influence of various retrofitting methods on the progressive collapse resistance of multistorey reinforced concrete (RC) structures. To this end, eight different cases were considered. The first one included a thirteen-story RC moment-resisting frame (bare frame), while the others were frames upgraded with the application of X-brace, diagonal brace, inverted V-brace, the viscous damper in the central bay, viscous damper in two inner bays, viscous damper only in certain stories and carbon fiber reinforced polymer. Moreover, three different column removal scenarios were considered as a column failure at stories one, six, and thirteen of each case study structure. The analysis results indicated that the redistribution of loads after the column’s failure and the RC buildings’ collapse resistance was increased depending mainly on the type of approach used for upgrading the bare frame.

A model for cascading failures with the probability of failure described as a logistic function

In most cascading failure models in networks, overloaded nodes are assumed to fail and are removed from the network. However, this is not always the case due to network mitigation measures. Considering the effects of these mitigating measures, we propose a new cascading failure model that describes the probability that an overloaded node fails as a logistic function. By performing numerical simulations of cascading failures on Barabási and Albert (BA) scale-free networks and a real airport network, we compare the results of our model and the established model describing the probability of failure as a linear function. The simulation results show that the difference in the robustness of the two models depends on the initial load distribution and the redistribution of load. We further investigate the conditions of our new model under which the network exhibits the strongest robustness in terms of the load distribution and the network topology. We find the optimal value for the parameter of the load distribution and demonstrate that the robustness of the network improves as the average degree increases. The results regarding the optimal load distribution are verified by theoretical analysis. This work can be used to develop effective mitigation measures and design networks that are robust to cascading failure phenomena.

Finite element modelling of the progressive collapse of post-and-beam mass timber building substructures under edge and corner column removal scenarios

The structural behaviour of mass timber buildings under a load bearing element removal scenario is complex. To well understand this phenomenon and ultimately develop scientifically based design guidelines against progressive collapse for this type of buildings, there is a need to develop a Finite Element model which accurately captures the non-linear response, load redistribution mechanisms (alternative load paths) and failure modes of such buildings. As such, this paper presents for the first time how mass timber post-and-beam systems can be accurately modelled using Finite Element under edge and corner column removal scenarios. The model was validated against published 2D and 3D experimental tests performed on scaled-down substructures. The non-linear structural responses of the main structural connections were experimentally quantified and inputted into the model using the component method. Results show that the model accurately replicated load redistribution mechanisms, ultimate loads, failure modes, and strain developments. The use of the model was then illustrated by running parametric studies to quantify (i) the influence of the Cross Laminated Timber (CLT) floor panels layout and (ii) one alternative load path, typically ignored in design, on the progressive collapse resistance capacity.

Динамика объема функционирующей паренхимы и раздельной почечной функции до и после резекции почки по поводу опухоли

Objective. To assess functions of each kidney in dynamics using mathematical analysis of contrast-enhanced computed tomography findings in patients with unilateral kidney tumors. Patients and methods. We present preliminary results of a prospective study within the protocol "Assessment of the functioning renal parenchyma volume and functions of each kidney in patients with tumors before and after resection" conducted in the Institute of Urology and Human Reproductive Health, I.M.Sechenov First Moscow State Medical University. This study included 20 patients of both sexes who had undergone resection of unilateral kidney tumors with compression of the main renal artery. We performed mathematical analysis of contrast-enhanced computed tomography findings before surgery and 3–6 months postoperatively to evaluate functions of each kidney. In addition to that, we measured the dynamics of total glomerular filtration rate (GFR) using a special formula. Results. We observed no significant dynamics in any total functional renal parameters (creatinine level, total GFR, total functioning renal parenchymal volume) and in 3D-GFR of each kidney. However, there were significant differences in the dynamics of functional parameters measured for each kidney individually, including 3D renal perfusion and functioning parenchyma volume of each kidney. The volume of functioning renal parenchyma in the affected kidney decreased significantly (p = 0.006). In the subgroup with no lesions, we observed no significant dynamics (p = 0.236). Changes in perfusion affected both sides. Conclusion. We found no significant changes in the total kidney function after surgery, which suggests a sufficient reserve capacity of this paired organ. Increased postoperative perfusion in the intact kidney is likely to reflect redistribution of functional loads between the kidneys and can be considered as an adaptive mechanism. This hypothesis is also confirmed by redistribution of the functioning parenchyma volume 3–6 months postoperatively. The intact kidney probably compensates the loss of function in the affected kidney.

Quantifying the effect of macrozones on the cold-dwell fatigue response of UD-rolled Ti-6Al-4V using high-energy X-ray diffraction

High-energy X-ray diffraction is used to investigate the evolution of elastic lattice strains in rolled Ti-6Al-4V specimens during cyclic loading in-situ with and without the inclusion of a 120s dwell period. A 1mm segment of the gauge section is monitored throughout the first 100 cycles for specimens extracted along the rolling direction (RD), the transverse direction (TD) and 45° between the two, to explore the effects of texture on the evolution of the micromechanical response. Five families of lattice planes from the hexagonal α phase are analysed with emphasis on lattice strain measured at the peak of each cycle, while macroscopic strain accumulation is simultaneously monitored via Digital Image Correlation. In cyclic loading conditions including a dwell period at load, a prominent increase in elastic strains is observed in prismatic and basal lattice planes with the specimen loaded 45° from the rolling direction. In the absence of dwell, both RD and TD specimen orientations exhibited subtle cyclic hardening in all families of lattice planes probed despite negligible evolution in accumulated macroscopic plastic strain. Estimations of lattice orientation-dependent stresses are also presented using directional moduli to examine redistribution of load across sets of grains with the increasing cycle count.

Detection and Localization of Load Redistribution Attacks on Large-scale Systems

A nearest-neighbor-based detector against load redistribution attacks is presented. The detector is designed to scale from small-scale to very large-scale systems while guaranteeing consistent detection performance. Extensive testing is performed on a realistic large-scale system to evaluate the performance of the proposed detector against a wide range of attacks, from simple random noise attacks to sophisticated load redistribution attacks. The detection capability is analyzed against different attack parameters to evaluate its sensitivity. A statistical test that leverages the proposed detector is introduced to identify which loads are likely to have been maliciously modified, thus, localizing the attack subgraph. This test is based on ascribing to each load a risk measure (probability of being attacked) and then computing the best posterior likelihood that minimizes log-loss.

Robustness Optimization Method for Urban Road Networks Based on the Adjustable Load Redistribution Strategy

Robustness Optimization Method for Urban Road Networks Based on the Adjustable Load Redistribution Strategy

Invulnerability Analysis and Optimization Strategy of Sector Network Using Cascading Failure Model

Resolving the challenge of flight delays caused by air traffic congestion renders it necessary to explore the mode of congestion propagation. By applying complex network theory, this article establishes a complex network structure where airspace sectors act as nodes, and the edges represent traffic flow relationships between sectors. In addition, a cascading failure model is proposed to analyze the airspace sector network’s invulnerability. The critical threshold and the sector abnormality rate are determined according to the cascading failure measurement indexes. Based on the remaining capacity of sector nodes, two optimization strategies are proposed: adjacent load redistribution strategy and local load redistribution strategy. The simulation results demonstrate that the local load redistribution strategy greatly improves the airspace sector network’s invulnerability to cascading failure.

Impact evaluation of load redistribution on seismic response analysis of piping partially considering the plasticity of support structures

This paper describes the results of a series of seismic analyses to clarify how the plastic deformation of some support structures affects the seismic response of the entire piping system.

Study of motion amplitudes in large joints of upper and lower limbs and spine joints when using industrial exoskeletons

One of the world trends of Industry 4.0 is the introduction of exoskeletal technologies into production processes. Manufacturers of industrial exoskeletons designed to reduce the negative impact of the work process on the human locomotive apparatus provide for the redistribution of the external load on the human body by means of various technical solutions. However, there is currently no uniform methodology for assessing the operational safety of exoskeletons. A significant biomechanical factor contributing to the safety of industrial exoskeletons as promising means of personal protection of the locomotor apparatus, is possibility to work without significant restrictions on the volume of movements. In this connection, the development of a methodology for objective quantification of the influence of structural and mass dimensions of industrial exoskeletons on the biomechanics of human movements is a topical task. This article presents the results of the measurements of the amplitude of movements in the large joints and joints of the spine, when performing the tests for flexion-extension, adduction-abduction and lateroflexion. The testing of volunteers was carried out on the clinical base of Research Institute of Labor Medicine. The tests were performed both without the use of industrial exoskeletons (Group I) and with their application (Group II). The influence on the biomechanical parameters of volunteer movements by the structural characteristics of the industrial exoskeleton “Exochair” and two different models of the industrial exoskeleton «Exoatlant» was investigated. Parameters of movements of segments of the human body were measured with the help of inertial measuring sensors of the software and hardware complex «Biomechanika Trust-M». Quantitative indicators have been identified which show the limitations of movements caused by the operation of different models of industrial exoskeletons. Thus, the use of the exoskeleton “Exochair” in deep seating limits the flexion in the hip joint by 67.1%, in the knee joint by 56.1%, in the lumbar thoracic spine by 61.9%, and practically does not affect the flexion in the shoulder joint. The first model of the exoskeleton “Exoatlant” limits the amplitude of movements in the hip joint by 41.2% at flexion and by 74.5% at extension. At the same time, the second model limits the abduction of the shoulder joint by 20.5%, and in the lumbar thoracic spine limits forward flexion by 17.3%, rearward extension by 50.6%, bending to the right by 46.4%, and bending to the left by 40.3%.

Experimental study of collapse behavior of single-layer cylinder shells with infilled walls

To study the dynamic responses, dynamic characteristics and seismic performance of the single-layer cylinder shell considering the effect of infilled wall, several groups of shaking table tests were carried out. The acceleration responses, displacement responses and strain responses were measured in the tests, and the structural seismic performance was evaluated under different seismic motions and input principal directions. The mechanism of load redistribution was investigated to evaluate the local damage effect on the whole structural collapse and the progressive collapse resistance, and the test results were compared with those from the shaking table tests of the single-layer cylinder shell without the effect of infilled wall. The results show that the infilled wall changes the dynamic characteristics and dynamic behavior of the whole structure, and the damage of the infilled wall cause abrupt change of the dynamic response including the acceleration amplification effect and strain amplification effect. The collapse resistence of the structure is reduced because of the infilled walls, and the collapse pattern is also changed. The ductility of the single-layer cylinder shell structure is reduced, and this is conflict with the traditional view which believes the infilled wall will enhance the seismic resistence performance. The data and conclusion of this study will provide references to the evaluation of seismic resistance and engineering practices for cylinder shell structure.

Towards dynamic property control of bridge spans

Regulation of the dynamic properties of bridge spans is a priority field of this research, which solves the problem of increasing the obsolescence and physical periods of bridge structures manifested both at the design stage of the load redistribution in the load bearing and during long-term operation.Over the past 40 years, technical bridge diagnostics has shown that the durability and safe long-term operation can be ensured by the improved calculations, operation and stress and strain control under the excess and over-calculated live loads.The aim of this work is to control the dynamic deformation and amplitude-frequency characteristics of bridge spans under harmonic random (non-stationary) oscillations of the span-vehicle system due to changes in the energy and stress state of the structure. The dynamic behavior of the span-vehicle system is based on the control for the amplitude-frequency characteristics of random oscillations by averaged values, the required spectral density being provided.The use of dynamic dampers for the system element control and the rigidity of junctions provide antiphase oscillations of the bridge span elements such as beams and decks, that leads to the unaccounted inertial forces.Another important element of the joint work imbalance of the bridge span elements during the dynamic load, are various defects, both in the deck design and load-bearing elements. It is assumed that the deck is a transfer layer (element) of vibrations induced by a vehicle in the beams. It is shown that the control for the dynamic properties is required in the case of a coincidence between the vehicle and beam stiffness and mass at the center of the system rigidity.The attention is paid to the conditions and dependencies between the dynamic load parameters and the stress-strain state of the bridge beams at the elastic and elastoplastic stages, with respect to the additional inertia of the system. This approach is the pilot in the Russian and foreign bridge construction in terms of experimental studies and testing of bridges for continuous random traffic.The dynamic testing of bridge spans for random traffic flow contributes to the creation of vibration diagnostic express laboratories necessary for the operation and maintenance of bridges.

Experimental and numerical investigation on progressive collapse resistance of RC frame structures considering transverse beam and slab effects

In order to investigate the load carrying mechanisms in resisting progressive collapse for reinforced concrete (RC) structures while considering transverse beam and slab effects, a series of four 1/4-scale RC substructural specimens were tested and the failure modes, load-displacement relationships, and load redistribution responses are presented in this paper. Two beam-column subassemblies were tested as control specimens. The third specimen was a cross-beam subassembly composed of a transverse beam and a longitudinal beam which had the same reinforcement detailing as the control specimens to investigate the transverse beam effects excluding RC slab. The last specimen had identical beams with the third specimen, but including an RC slab to consider the slab effects, which could be used to simulate the mechanism to resist progressive collapse developed in a practical frame structure. Test results showed that the load-carrying capacity of a cross-beam system at the compressive arch stage was almost equal to the sum of the load-carrying capacities of these two crossed beams, whereas the transverse beam and slab effects could increase the capacity of a two-span beam by as much as 340%. Thus, transverse beam and slab effects should not be ignored in the simulation of progressive collapse for RC frame structures. Based on the simplified models calculating nonlinear static load-deflection responses for RC two-span beams proposed in the previous study and load-displacement relationships obtained in this test, computational models calculating load-deflection responses for cross-beam subassembly excluding or including slab were established and verified.