Accidental Loads Research Articles

Design of the monorail crane system for remote handling of the ITER neutral beam cell

This paper describes the preliminary design result of the Monorail Crane System (MCS), which is a subsystem of the ITER Neutral Beam Remote Handling System. Since the concept design of the MCS, the design is elaborated further detail considering new maintenance requirements, updated interfaces with the components to be maintained, and the latest configurations in the NB cell. The main design updates are described as follows. First, the railway is changed from the one monorail with two side reaction rails to a dual rail system, which has better load distribution within the crane trolley and the building mountings. Second, additional railway and a switching mechanism are added between the HNB#1 and #2 to access to the VVPSS components, which are newly added in the NB cell. Third, the mounting of the transversal beams supporting the dual rails onto the embedded plates are updated and further elaborated. Forth, the crane trolley is designed to have independent redundant kinematic chains so that it is recoverable from a single point failure. Fifth, series of braking systems such as a service brake, an auxiliary brake, and an emergency brake are integrated in each kinematic chain to cope with normal and accidental loads. Sixth, seismic uncoupling devices are integrated to protect the mechanical components of the crane itself and the building structure. Lastly, detailed cabling design is implemented from the control cubicle to the locations where the subcomponents are located.

Tensile Behaviour of FRCM Composites for Strengthening of Masonry Structures-An Experimental Investigation.

This paper presents the results of direct tensile tests performed on six different FRCM (fabric reinforced cementitious matrix) strengthening systems used for masonry structures. The emphasis was placed on the determination of the mechanical parameters of each tested system and a comparison of their tensile behaviour in terms of first crack stress, ultimate stress, ultimate strain, cracking pattern, failure mode and idealised tensile stress-strain curve. In addition to the basic mechanical tensile parameters, accidental load eccentricities, matrix tensile strengths, and matrix modules of elasticity were estimated. The results of the tests showed that the tensile behaviour of FRCM composites strongly depends on the parameters of the constituent materials (matrix and fabric). In the tests, tensile failure of reinforcement and fibre slippage within the matrix were observed. The presented research showed that the accidental eccentricities did not substantially affect the obtained results and that the more slender the specimen used, the more consistent the obtained results. The analysis based on a rule of mixtures showed that the direct tensile to flexural tensile strength ratio of the matrixes used in the test was 0.2 to 0.4. Finally, the tensile stress–strain relationship for the tested FRCMs was idealised by a bi- or tri-linear curve.

Risk‐based explosion hazard analysis and building upgrades in industrial facilities to prevent blast failures

AbstractAccidental loadings such as blast loadings constitute the great majority of potential and actual fatalities in industrial facilities. To prevent human loss and injuries, and for a safe design or blast assessment of an industrial building, the risks of these accidental loadings should be quantified in terms of both probability/frequency and consequence aspects. In this paper, we propose a combined risk‐based approach for the assessment of all accidental loadings. The study includes a newly developed risk‐based method that can be used for blast analyses of buildings in industrial facilities. The methodology is introduced for blast design/analysis of structures in industrial facilities with explosion hazards. Within this scope, the paper presents an evaluation of explosion hazards in industrial facilities. The study also focuses on a series of vital phases in the analysis and design stages, including explosion modeling, building screening analysis, detailed structural analysis, conceptual structural upgrade design, and final upgrade design. Finally, upgrade techniques for buildings in industrial facilities against explosions are also provided to minimize the individual risk.

Development of simplified method for prediction of structural response of stiffened plates under explosion loads

During their lifetime, marine structures may be exposed to accidental loadings such as from collisions or explosions, as well as environmental loadings such as from slamming, sloshing and green water. Such loadings can cause damage to structures. Therefore, to minimize such damage, advanced and robust design guidelines should be formulated. Among those loads, in this study, explosions imparting an impulsive pressure loading containing a rapid increase in pressure and a short duration that can cause serious casualties, property losses, and marine pollution were considered. In this paper, a practical and robust method for damage assessment of marine structures exposed to explosion loads based on a single degree of freedom (SDOF) system and numerical simulations is proposed. The SDOF method was improved by introduction of new and better idealization resistance for the system and consideration of the effect of strain-rate, and subsequently was verified by a numerical method developed using the commercial ABAQUS software package. The numerical method was itself validated by comparison with relevant pulse pressure test data available in the open literature (good correlation was shown). Based on the validated numerical models, a rigorous parametric study of the structural response of stiffened plates having actual scantlings of offshore structures was performed. The numerically obtained maximum deformations were compared with the results from the improved SDOF method in a parametric study, and the variation of both methods was verified. Finally, simple yet accurate and reliable formulations for prediction of structural response were empirically derived. These formulations are expected to be usefully employed as a first-hand tool for prediction of damage extent of marine structures (including offshore structures) due to explosion loads.

Dynamic response analysis of submerged floating tunnel subjected to underwater explosion-vehicle coupled action

The submerged floating tunnel (SFT) is a novel type of ocean structure that is expected to be built in the 21st century. The Underwater explosion (UNDEX) is an extreme accidental load may occur during the operation of SFT. To study the dynamic response of SFT system subjected to the UNDEX, the semi-empirical formula of the Cole shock wave and the Geers–Hunter bubble motion formula are used to established the UNDEX load formula, and the transient fluid–solid interaction effect of the structure is considered according to the retarded potential formula (RPF), a coupled model that considers the explosion and vehicular loads is developed using D'Alembert's principle and the Runge–Kutta method. Additionally, the established load and coupled model are verified using existing test data and methods. The influence of the load and structural parameters are analyzed based on the parameters of the proposed SFT. The results reveal the impact of vehicle-explosion coupled on the SFT system response and the relationship between the structural parameters and the system response, and some significant conclusions are presented.

Structural assessment of a whole toroidal sector of the HELIAS 5-B breeding blanket

The European roadmap for the realization of fusion energy considers the stellarator line as a possible long-term alternative to a tokamak DEMO. In this context, from the plasma physics standpoint, the most promising option is a five-field period power plant called HELIcal-axis Advanced Stellarator (HELIAS) 5-B. In order to allow the electricity production, the HELIAS 5-B reactor must be endowed with a breeding blanket (BB). Hence, in this paper, the advancements in the HELIAS 5-B BB design are reported. In particular, the structural assessment of a whole BB period, extending along toroidal direction for 72 °, is depicted. A geometric configuration encompassing dummy BB segments has been set up to verify the feasibility of the proposed BB segmentation strategy for the whole sector. Both the Helium Cooled Pebble Bed (HCPB) and Water Cooled Lithium Lead (WCLL) BB concepts have been considered. Results have shown that, in principle, the occurrence of overlapping between adjacent segments depends on the BB-Vacuum Vessel connection mode, regardless of the considered BB concept, and on their mutual thermal expansion. Then, focusing only on the HCPB BB concept, a preliminary detailed geometric design of two BB segments, located at the inboard region of a bean shaped ring, has been carried out in order to investigate their structural behavior under steady state accidental loading conditions. To this end, the stress field arising within the structure of the two segments has been assessed following the RCC-MRx structural design rules. Results have shown that the proposed design works quite well under the assumed loading conditions. The study has been performed adopting the Finite Element Method and using the Ansys v.19.1 commercial code. The obtained results will be presented and critically discussed.

Large deformation coupled analysis of embedded pipeline – Soil lateral interaction

Subsea pipelines buried in the seabed may undergo large lateral displacement under environmental, operational, and accidental loads at different interaction rates and hence different drainage conditions. The undrained shear strength is commonly used in practice to assess the pipe-soil interaction assuming a sufficiently high displacement rate. This approach neglects consolidation effects and the rate-dependent response of the soil and may significantly underestimates the lateral resistance for a pipeline moving slowly relative to the ground. In this study, a coupled large deformation finite element (LDFE) framework is developed via a remeshing and interpolation technique with small strain (RITSS). A Modified Cam-Clay (MCC) model with efficient numerical integration is used. The proposed coupled LDFE framework is verified against selected physical model tests. Effects of the interaction rate and hence drainage condition on the p-y curve, excess pore pressure generation and dissipation, and failure mechanisms are discussed. An empirical relationship between the ultimate resistance and the normalized velocity of the pipe (denoting the drainage condition) is proposed, which may be applied for the integrity and safety analysis of buried pipes in landslide or fault-crossing regions.

Experimental and Numerical Investigation on the Dynamic Responses of the Remaining Structure under Impact Loading with Column Being Removed

The dynamic response and stability of building structures under accidental loads such as earthquake, explosion, and impact have been focused by experts. The significant influence will be induced once the damaged structure begins to collapse. In this study, a reinforced concrete frame structure model was designed and tested to study the dynamic response law of the structure under the condition of the failure of the middle column of the model structure, the remaining structure successively failed the load-bearing column and continued to be subjected to impact load and uniform load. The analytical method was used to calculate the ultimate uniform load subjecting to the structure under the failure of four load-bearing columns, because its value was less than the load in this test, the structure collapsed. The finite element calculation model was established, and compared the simulation results to the test results to verify its rationality. Then, the influence of the impact energy and the structural stores on the dynamic response of the structure were analyzed. The results showed that the peak value of the dynamic response of the damaged structure did not increase strictly with the increase of the number of failure columns, which may be related to the sequence of failure columns.

The simulation research on the natural circulation operation characteristic of FNPP in rolling and inclined condition

Abstract Recently, the FNPP (Floating Nuclear Power Plant) has got more and more attention and rapid development due to very wide prospect application on remote areas or islands. In general, the IPWR (Integral Pressurized Water Reactor) is adopted to meet the requirements of the limited space, the nuclear safety and the maneuverability in marine. The IPWR could depend on natural circulation operation to remove the residual heat of core under accident or low load operation condition. Because the driving head is low, the natural circulation flow is likely to be influenced by rolling and inclined condition. To clarify the natural circulation flow characteristics of the core in FNPP rolling motion and inclined condition, based on the modified THEATRe code by adding the ocean motion module and spatial coordinate convert module, the main thermal-hydraulic parameters variation in rolling and inclined condition were obtained. The effect of inclined angle, rolling amplitude and period on the natural circulation flow were discussed. The natural circulation flow in the core fluctuates periodically with rolling motion. And the inclination and rolling will also cause the degree of steam superheat of OTSG secondary side fluctuate, which could impact on the stable operation of secondary side system.

Dynamic Punching Assessment of Edge Columns after Sudden Corner Column Removal

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Towards limiting potential domino effects from single flammable substance release in chemical complexes by risk-based shut down of critical nearby process units

The explosion load is a significant escalation factor possibly influencing the potential occurrence of domino accidents in chemical plants. It is not economical to install explosion isolation systems (e.g., extinguishing barrier) for all equipment or process units across a chemical plant. Although shutting down all equipment or process unit can prevent an explosion, it may also cause further economic losses. To prevent domino accidents, the process unit that needs to be shut down accurately should be selected, and the normal operation of other units needs to be ensured. A method to select the process unit to be isolated based on the Dimensioning Accidental Load (DAL) is proposed. By calculating the occurrence probability and consequences of the accident scenarios, the DAL of the surrounding units is determined. DAL is used as the impact intensity of the accident unit on the surrounding units. The probit model is used to calculate the damage probability of surrounding units. The case analysis results show that the method of selecting the process unit to be isolated based on DAL quantifies the impact intensity of the exploded unit on surrounding units from probability and consequence. Under the premise of meeting the acceptable risk criteria, the method can determine which units should be shut down and which units can operate normally when a release accident occurs. While preventing domino accidents, economic losses caused by the shutdown of all process units are reduced and a theoretical basis for accident prevention and safe operation of the plant is provided.

Progressive collapse of RC flat slab substructures with unbonded posttensioning strands after the loss of an exterior column

Reinforced Concrete (RC) flat slab structures are mainly composed of load-bearing columns and RC slabs, which are vulnerable to collapse once one or several local load-bearing columns fail due to accidental loads such as terrorist bomb attack or vehicle collision. To investigate the progressive collapse performance of flat slab structures after the loss of an exterior column, static collapse tests were conducted on three 1 × 2 bay RC flat slab substructures. Effect of prestress and layout of the unbonded posttensioning strands (UPSs) on the progressive collapse of flat slab structures was discussed. Experimental results showed that punching shear failure (PSF) foremost occurred at the slab-column connection (SCC) of the failed exterior column during collapse, and then successively occurred at the SCCs close to the corner column and the exterior column adjacent to the failed column. Primary cracks on the top slab surfaces around the failed exterior column generally presented arc-shaped distribution; while primary cracks on the bottom slab surfaces radially propagated from the failed exterior column. Comparing with the flat slab substructure without UPSs in the slabs, the load-bearing capacity of the substructures with UPSs in the slabs significantly improved. Flexural action was the fundamental collapse resistance mechanism in the initial collapse stage, and tensile membrane action gradually formed during collapse. The flexural action, the tensile membrane action, as well as the post-punching behaviors of the slabs resisted the collapse load together before the final collapse occurred. Most of the load applied on the failed exterior column mainly transmitted along the shorter slab bay under the exterior-column-removal scenario. Arranging posttensioning strands in the slabs contributed to reducing vertical deformation of the slabs. The UPSs in the column strip passing through the failed column played a more important role in resisting collapse load than those arranged in the middle strip. The residual flat slab substructures still possessed satisfactory load-carrying capacity even if PSF occurred in one or several SCCs.

Ensuring the Structural Safety of Overhead Transmission Lines by Design

During service, transmission lines (TLs) will be subjected to unbalanced longitudinal loads due to events such as conductor breakage, insulator failure, and sudden ice shedding, which may damage TLs and subsequently hinder reliable power supply. Although unbalanced longitudinal loads are considered in current design codes, damage to TLs still occasionally occurs. This paper reviews the literature from the last 20 years pertaining to the response of TLs induced by the abovementioned events and associated tower failures. It comprises four main sections in relation to the sources of large unbalanced accidental loads: conductor breakage, sudden ice shedding, insulator breakage, and tower failure. Structural analysis methods to investigate these accidents are reviewed, and the latest research progress on modeling tower failure is discussed. Chinese code, American code and International Electrotechnical Commission code are compared to analyze the differences in accounting for longitudinal loads in these codes. In the end, several recommendations are provided for future design and research to ensure the structural safety of TLs.

Methods for failure assessment of NPP pressure boundary under severe accident loading

During postulated high-pressure core melt accidents, high temperatures can be reached by the reactor coolant system (RCS) pressure boundary due to hot gases from the core melt process, which may lead to failure in terms of leak or break and subsequent depressurization. Location, time and size of the failure can have large implications on the further accident progression. Nevertheless, not for all possibly affected components and failure modes suitable integrity assessment methods, in-depth structure mechanical analyses or in some cases even simple models for the integration into severe accident codes are available. Investigations on the events in Fukushima Daiichi emphasize the importance of methods for RCS failure assessment within severe accident analysis.This work concentrates on the assessment of gross boundary failure, e.g. of the RCS piping, from a mechanical point of view. First, failure modes of RCS components as well as the deformation and fracture behavior of typical RCS materials in the relevant loading regime are discussed. Established assessment methods based on linear damage accumulation and the use of Finite Element (FE) codes as well as a newly developed method based on a zero-dimensional approach are presented. The methods are compared among each other and to a large-scale experiment with a DN700 pipe and international benchmark analyses within the OECD/NEA Components and Structures under Severe Accident Loading (COSSAL) activity. Results of the application to an exemplary severe accident scenario in a PWR and corresponding parametric studies are summarized. An outlook is given on the analysis of local boundary failure of components, potentially responsible for small early leaks.

Structural integrity assessment for ITER lower VS coil feedthrough

The ITER vertical stabilization coil system is designed to provide fast plasma stabilization in all scenarios with elongated plasma cross-section. It consists of two water-cooled coils located in upper and lower portions of the vacuum vessel (VV), with feedthroughs responsible for the transfer of electricity and cooling water across the vacuum boundary of VV. Depending on location, the feedthroughs can be divided into upper port feedthroughs (UPR feedthroughs) and lower port feedthroughs (LWR feedthroughs), each family sharing the same design. Both designs are subject to demanding operation scheme, a severe working environment and the presence of interfacing components, which impose important thermal, electromagnetic and seismic loads on the components. In particular, the LWR feedthrough, object of present paper, is more impacted by seismic loads due to the more flexible structure compared to the UPR feedthrough. During the worst seismic event, it is subjected to a vertical acceleration of 28.8 m s−2, acting on an effective mass of 249.9 kg at its first order modal mode. Furthermore, the current circulating in the conductor of the LWR feedthrough, impose significant linear forces, up to 27.7 kN m−1 during normal operation and 30.3 kN m−1 during categories I & II abnormal plasma events, respectively. Finally, the effect of differential thermal expansions of interfacing structures imposes a relative displacement between the supports up to 32.9 mm in X (radial) direction and up to 14.67 mm in Z (vertical) direction, during baking. Being part of the vacuum boundary, the feedthrough must assure confinement function under all normal and accidental loading conditions, with proper structural integrity assessment by applying analysis approach and design criteria foreseen by the applicable nuclear codes. The paper details the load types and categories, the analysis methodologies, the structural design criteria, and the assessment results in views of static stress and fatigue for the LWR feedthrough. This study could be a comprehensive reference for the structural integrity assessment of other similar components in fusion devices.

Experimental stand for internal pressure testing of pipes

The experimental programs carried out on the stands for the research of mechanical stress behaviour typically target the following objectives: to determine the behaviour of the pipes at internal pressure and / or other mechanical stresses (which may secondary occur as accidental loads during exploitation), to establish the processes and factors of in-service degradation and to determine the load carrying capacity of pipes and other components of pipelines systems with defects of different types and configurations. For this paper an experimental stand was designed and developed for the purpose of determining the behaviour of the pipes with different types of imperfections / defects. The experimental results were verified and validated using the finite element method.

Use of high strength technical textiles in strengthening of reinforced concrete structural elements

A structure may show sign of deterioration earlier than its design life due to poor designing, change in the occupancy of the structure and the damage caused by abnormal and accidental loading. In order to avoid economic loss, the structural elements i.e. beams, slabs, columns are usually retrofitted and/or strengthened such that they can withstand the applied load during their operational life. Among many strengthening techniques used, use of high strength technical textiles, more commonly referred as fiber reinforced polymers (Carbon, Glass, Aramid, Kevlar, etc.) have proved to be beneficial in improving the overall performance of the ageing and damaged structural elements. Therefore, in this investigation, aim was to study the behaviour of the reinforced concrete beams and columns externally wrapped with carbon fiber reinforced polymers (CFRP) fabrics under static loading. For this purpose, different types of wrapping techniques were adopted to strengthen reinforced concrete (RC) columns and beams with CFRP wraps. The uniaxial compression tests were carried out on the columns investigated, whereas, four-point loading setup was used for the RC beams. Based on the detailed investigation, it was observed that the use of CFRP wraps proved to be significantly beneficial in improving the overall performance of beams and columns, as load carrying capacity, ductility and stiffness exhibited by CFRP wrapped specimens were found to be higher when compared with identical specimens without CFRP wraps.

Применение алгоритма обнаружения изменения сигнала в системе контроля гидроамортизаторов

During nuclear power plant (NPP) operation, the reactor plant main equipment can show displacements when subjected to the effect of various external and internal loads. These displacements are mainly caused by thermal expansion of the metal and seismic loads. To cope with these phenomena, the reactor plant components that are most susceptible to these types of loads are fastened with hydraulic shock absorbers (HSAs) to limit their displacements under the effect of seismic or accident dynamic loads, as well as to ensure thermal displacements in increasing or decreasing the power unit output. For monitoring the HSA operation and indirectly monitoring the displacements of the reactor plant equipment items fastened with hydraulic shock absorbers, the dedicated hydraulic shock absorber monitoring system (HSAMS) is used, which is equipped with linear displacement sensors installed directly on the HSAs. If the displacements go beyond the predetermined limits, the HSAMs algorithms produce an appropriate alarm. The information from the HSAMS is also used by the automated residual lifetime monitoring system (ARLMS) to calculate the steam generator connection pipe displacement criteria parameters. However, during the operation of a number of NPP power units, a problem associated with numerous failures of the HSAMS linear displacement sensors has been faced. These failures manifested themselves in that the sensor signals went beyond the valid range or frozen under the effect of external influencing factors. As a result, the HSAMS and ARLMS operation was complicated by a large number of unreliable measurements and the functions of these systems were not performed in a proper way. To solve this problem, it has been proposed to use an algorithm for tracking signal changes, which can improve the credibility of HSAMS indications by determining unreliable data in the online mode and by performing statistical processing of the already available array of indications.

Assessment of Fenestration Security as Part of Railway Infrastructure

The safety of train stations can be affected by many internal and external threats. Train stations or stations in generally can be classified as soft targets. It can be assumed a potential target for many, especially terrorist attacks. In elevated number of railways stations, large glass surface as facades and stained-glass windows are presented. They present vulnerable part of construction, affected by various type of accidental loads (as blast and impact) in case of terrorist attacks. In this terrorist attack, the biggest cause of injuries and deaths are caused by debris from glass parts of structure. The paper is focused on the glass used in modern construction of train stations. Based on this, several methods of loading condition are described and the resistance of fenestration on such loads is assessed. The practical part of the paper is focused on two types of window systems and the resistance to dynamic loads was evaluated. The experimental testing was performed using a pendulum test. The results showed the resistance of selected types of windows without, as well as, with the use of security protective film. The paper also interprets possible glass failure under dynamic loading.

Research Status of Impact on Concrete Structures

Concrete is currently the most widely used material in civil engineering structures. In addition to being subjected to dead loads and live loads during its service, it may also encounter accidental loads such as impacts and collisions. Previous research has shown that the forced characteristics of concrete structures under dynamic loads such as impacts and collisions are very different from those under static loads. In order to summarize the dynamic characteristics of concrete structures and measures to reduce its impact damage, this article firstly introduced the mechanical characteristics of concrete structures under impact loads, including the dynamic force characteristics of concrete structures under high-speed, low-speed impact loads and confining pressure; Then reviews the achievements and development of domestic and foreign scholars on concrete impact research in recent years: the research status of concrete dynamic constitutive structure is summarized from the aspects of the sensitivity of concrete strength strain rate and the dynamic constitutive model; the research status of impact resistance of concrete structure is carried out from the aspects of high-speed, low-speed impact load and measures to reduce its impact damage. Finally the development trend of concrete structure impact is summarized and prospected, which will provide some references for the subsequent research on concrete structure impact.