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Continuous earthmoving machines, such as bucket-wheel excavators (BWEs), are the largest mobile terrestrial machines exposed to the working loads of a periodic character. This paper aims to launch a new idea regarding the preservation of the load-carrying structures of these machines by the means of implementing a controllable frequency-controlled drive of the excavating device. Successful implementation of this idea requires a detailed analysis of the dynamic response of the load-carrying structure in order to determine the domains of frequency of revolutions of the bucket-wheel-drive electromotor (FREM) where the dynamic response of the structure is favorable. The main goal of the presented research was the development of a unique three-step method for the identification of the FREM ranges, where the vibroactivity of the load-carrying structure is within the allowed boundaries. A methodologically original study of the dynamic response was conducted on a unique dynamic model of the BWE slewing superstructure that allows for continuous variation of the FREM, i.e., of the frequency of excitation caused by the forces resisting the excavation. Validation of the spatial reduced dynamic model of the slewing superstructure and the corresponding mathematical model, as well as the overall approach to the determination of the dynamic response, were performed by the means of vibrodiagnostics under the real exploitation conditions. Application of the developed method has yielded: (1) the resonant-free FREM domains; (2) the FREM domains, where the structure is not exposed to the excessive dynamic impacts; and (3) the frequency ratio ranges defining the resonant areas. Additionally, the results of the research have pointed out that the resonant-free state represents a necessary but insufficient condition for the proper dynamic behavior of the BWE slewing superstructure.

Bucket wheel excavators (BWEs) are the largest mobile terrestrial machines exposed to the working loads of a periodic character. This paper presents a small portion of the studies, conducted with the goal of proposing a new idea regarding preservation of the load-carrying structures of these machines, based on the implementation of a controllable frequency-controlled drive of the excavating device. A detailed analysis of the dynamic response of the load-carrying structure is required in order to determine the domains of frequency of revolutions of the working device's driving motor where the dynamic response of the structure is favorable, and therefore successfully implement this idea. A methodologically-original study was conducted, using a unique dynamic model of the BWE slewing superstructure that allows for the continuous variation of the frequency of excitation. This has yielded the resonant-free domains, i.e. the domains where the structure is not exposed to the excessive dynamic impacts.

Stackers-reclaimers represent the mechanization backbone of high-capacity storages for granular materials. The paper presents the design of a gantry bucket chain stackers-reclaimer for handling of crushed gypsum, as well as the working technology, finite element strength calculation for the main substructures: the working device, the trolley and the gantry. Failureless operation of the presented stacker-reclaimer represent an indirect validation of not only the presented results, but also the entire project as well as the applied technology of manufacture and montage.

Transfer bridges provide immense contribution to the efficient operation of high-capacity bulk material storages. The paper presents the design of one such system, used for transfering crushed gypsum and ash onto the barges docked in a storage facility, as well as the working technology, finite element strength and static stability analysis of the main substructures and the working devices. Due to the adjustments to the structure before its assembly, the analyses had to be repeated to account for the changes. Failureless operation of the presented transfer bridge represents an indirect validation of not only the presented results, but also the entire project, the stages of its development as well as the applied technology of manufacture and assembly.

Identification of the basic parameters of static stability (BPSS) of the slewing superstructure is the key step in solving the problem of its static stability, as well as static stability of the entire bucket wheel excavator (BWE). Specificity of the slewing superstructure examined in this paper lies in the kinematic breakdown system (KBS) which prevents the loss of static stability on the counterweight side. Development of a unique method for the formation and two-step validation of the calculation models for this particular design concept was the main objective of the presented research. A two-step validation of the analytical models is conducted based on the experimental results. As the outcome, the final calculation model formed in such manner represents an accurate basis both for the proof of static stability and for the monitoring of the BPSS during exploitation. By comparing the results of the control weighing and the referent values of the final calculation model it was concluded that the existing double-walled bucket wheel represents a 'weak point' of the considered BWE.

Predmet ove doktorske disertacije je istraživanje ponašanja zavarenih konstrukcija sa smanjenim stepenom sigurnosti prema krtom lomu i otpornost na prsline u cilju ocene njenog integriteta i veka. U tom slučaju posebna pažnja se posvećuje mestima koncentracije napona, jer se krti lomovi ovih konstrukcija po pravilu događaju upravo na takvim mestima. Radi detaljnog proučavanja nakstanka i rasta prsline, neophodna je primena principa mehanike loma, jer klasični pristup konstruisanju (projektovanju) preko faktora koncentracije napona i čvrstoće u tom slučaju nije dovoljan. Primenom parametra mehanike loma, kao što je faktor inteziteta napona, čiji opseg definiše brzinu rasta prline, a čija kritična veličina (žilavost loma) određuje kritičnu dužinu prsline. Time se obezbeđuje pouzdana procena integriteta konstrukcije (ako se dokaže da je faktor intenziteta napona manji od žilavosti loma), odnosno procena veka konstrukcije (primenom zakona mehanike loma na izračuvavanje krritičnih parametara za poznatu ili pretpostavljenu početnu dužinu prsline, njenu kritičnu vrednost, kao i izračunati opseg faktora intenzitata napona). Konzervativni pristup u svim koracima ove procedure obezbeđuje pouzdanu eksploataciju konstrukcije sa smanjenim stepenom sigurnosti., The subject of this doctoral dissertation is the research of the behavior of welded structures with a reduced degree of safety on brittle fracture and crack resistance in order to assess its integrity and age. In this case, special attention is paid to the stress concentration points, since the fractures of these structures tend to occur exactly in such places. For the detailed study of the crack and growth of the crack, it is necessary to apply the principle of fracture mechanics, since the classical approach to design (design) through the factor of stress concentration and strength is not sufficient in that case. Using the fracture mechanics parameter, such as the voltage intensity factor, whose range defines the rate of crack growth, and whose critical size (fracture toughness) determines the critical crack length. This ensures a reliable assessment of the integrity of the structure (if it is proven that the stress intensity factor is less than the tensile strength of the fracture), or the assessment of the century of construction (by applying laws of fracture mechanics to calculate critical parameters for known or assumed initial crack length, its critical value, as well as calculate the range voltage intensities factor). A conservative approach in all steps of this procedure ensures reliable exploitation of a structure with a reduced degree of safety

An original method for validation of the number of buckets on the working device of a bucket wheel excavator based on the dynamic response of its slewing superstructure (SS) is presented. A set of 16 seemingly acceptable solutions which satisfied the rigid design restrictions, based on the preservation of the existing (a) bucket wheel drivetrain, (b) theoretical capacity, (c) characteristics of the excavated soil and (d) position of the superstructure centre of gravity (CoG), was analysed. Already on the basis of the limiting vertical and lateral accelerations of the bucket wheel centre, which represents a well-grounded indicator of its dynamic behaviour prescribed by the code DIN 22261-2, 14 out of 16 analysed design variants have been discarded, reducing the set of possible solutions to only two – the originally-designed variant (with 17 buckets), and the variant with 20 buckets. Conclusions on the validity of these two design variants were derived on the basis of the dynamic response analysis of the referent points of the SS. The analysis of the impact of soiling on the dynamic response of the SS has shown that negative dynamic effects, observed in the preceding analysis of the originally-designed solution, increase with the amount of the adhered material. Although the redesigned variant with 20 buckets has proven as the only suitable solution from the standpoint of dynamic behaviour of the SS, the results have to be assessed carefully due to the fact that the reduction of the mass of the bucket wheel steel structure by more than 14% leads to the appearance of unfavourable dynamic effects, even though the SS CoG position is preserved.

A slewing superstructure (SS) represents a key functional subsystem of bucket wheel excavators (BWEs). Identification of its basic parameters of static stability (BPSS: weight and position of the center of gravity) is of equally crucial significance in design of a BWE and in its exploitation. The BPSS dominantly determine the static stability of a BWE SS and, coupled with stiffness, its dynamic response. This paper presents the results of research on the impact of the difference between the experimentally and analytically determined SS BPSS on the: (1) intensities of forces in the ropes of the bucket wheel boom hoisting mechanism; (2) maximum loads of the SS radiaxial slew bearing balls; (3) dynamic response of the SS. The presented research represents the initial stage in forming of the integral methodology for the assessment of impact of the mentioned differences on the key indicators which determine the lifespan and integrity, as well as reliability and safety of the SS of BWEs and related surface mining and material handling machines.

The design concept of temporary leaning of the gas oil storage tank bearing structure used during substitution of the worn out section of the bottom plates in the zone of the central column support is presented in the paper. On the basis of comparative analysis of the results obtained using finite element structural calculations of the designed state and the state of the central column leaning on the temporary supports, it was determined that by the implementation of the temporary support, the stress-strain state of the bearing structure, which corresponds to the designed stress-strain state of the construction, is obtained. Besides, the strength proof of the structure of temporary support including its welded joint to the central column is also presented in the paper.

An original method for validation of the number of buckets on the working device of a bucket wheel excavator based on the dynamic response of its slewing superstructure (SS) is presented. A set of 16 seemingly acceptable solutions which satisfied the rigid design restrictions, based on the preservation of the existing (a) bucket wheel drivetrain, (b) theoretical capacity, (c) characteristics of the excavated soil and (d) position of the superstructure centre of gravity (CoG), was analysed. Already on the basis of the limiting vertical and lateral accelerations of the bucket wheel centre, which represents a well-grounded indicator of its dynamic behaviour prescribed by the code DIN 22261-2, 14 out of 16 analysed design variants have been discarded, reducing the set of possible solutions to only two - the originally-designed variant (with 17 buckets), and the variant with 20 buckets. Conclusions on the validity of these two design variants were derived on the basis of the dynamic response analysis of the referent points of the SS. The analysis of the impact of soiling on the dynamic response of the SS has shown that negative dynamic effects, observed in the preceding analysis of the originally-designed solution, increase with the amount of the adhered material. Although the redesigned variant with 20 buckets has proven as the only suitable solution from the standpoint of dynamic behaviour of the SS, the results have to be assessed carefully due to the fact that the reduction of the mass of the bucket wheel steel structure by more than 14% leads to the appearance of unfavourable dynamic effects, even though the SS CoG position is preserved.

Tie-rods of the bucket wheel and counterweight booms are vital parts of the bucket wheel excavator slewing superstructure. This paper is dedicated to the problem of identifying the stress state of the critical cross-section ('net section') of the eye plates on these tie-rods. It presents the results of the experimental and numerical investigations carried out on the eyebar model. The results show the appearance of a plastic deformation in the zone near the contour of the hole even when the eye is subjected to the loads within the range of the permissible loads prescribed by the standard DIN 22261-2. Plastification in the eye net section occurs across the full thickness of the plate, but it does not jeopardize the integrity of the structure. The stress value in the eye net section, calculated in accordance with the standard DIN 22261-2, is significantly lower than the actual stress values around the hole and serves only as a comparative value for the static strength proof for the eye.

Fracture mechanics parameters have been applied to assess pressure vessel integrity. The pressure vessel analysed here was the ammonia spherical tank (volume of 1800 m(3), outer diameter 15.12 m, thickness 30 mm) where different cracks in the longitudinal and transverse butt joints were found. The finite element method was used to calculate stress and strain state and to analyse cracks and their influence on spherical storage tank integrity. Toward this end, the stress intensity factors were analytically determined, and compared with the fracture toughness to find out the critical pressure using Failure Assessment Diagram (FAD) in combination with net stress vs. critical stress.

Exploitation of bucket wheel excavators (BWEs) is accompanied by an increase of mass due to transport and adherence of a large amount of the material. Technical regulations do not account for the dynamic behaviour of BWEs. Such problems are analysed as quasi-static. A procedure and results of investigation of the influence of masses of the bucket wheel (BW) incrustation and soil in a blocked BW chute on the superstructure response are presented. Analysis of sensitivity of dynamic characteristics and the response to adherence of the material is conducted. The method and results can be used in the design stages of new and in reconstructions of obsolete BWEs.

U radu se analizira integritet konstrukcije velikog sfernog rezervoara za skladištenje tečnog amonijaka koji je izložen dejstvu unutrašnjeg pritiska, koji je izrađen zavarivanjem segmenata gornjeg i donjeg dela polusfernog omotača sa gornjom i donjom kalotom, koji su takođe izvedeni zavarivanjem prethodno deformacijom oblikovanih limova, u čijim zavarenim spojevima je otkriveno 211 grešaka ispitivanjem metodama bez razaranja. Primenom parametara elasto-plastične mehanike loma propisan je postupak određivanja kritične dubine greške u zonama zavarenih spojeva konstrukcije. Određen je adekvatan postupak obrade (geometrijsko oblikovanje) strukture u lokalnoj uskoj zoni u okolini greške kojom se postiže bezbednost konstrukcije sa aspekta čvrstoće. Pokazano je da debljina omotača sfernog rezervoara u lokalnim zonama otkrivenih grešaka može biti i manja od minimalne propisane standardom EN 13445-3:2017, a da pritom integritet konstrukcije nije narušen. Eksperimentalno-numeričkim istraživanjem propisane su granične geometrijske karakteristike greške, odnosno propisana je procedura kojom su definisane dubine grešaka koje je moguće sanirati bez primene dodatnog materijala (bez navarivanja) i kojom se obezbeđuje bezbedan rad konstrukcije., The paper analyzes the construction integrity of a large spherical storage tank for liquid ammonia exposed to internal pressure. The spherical storage tank was made by welding the previously deformed segments of sheet metal. 211 welding defects were detected performing the ultrasonic testing on welding joints. The critical depth of defect in a small zone of welded joint of a structure is defined using the parameters of elastic-plastic fracture mechanics. Adequate process of machining of the structure in the local narrow zone of detected defect is determined which achieves structural safety from the aspect of strength. It has been shown that the thickness of the spherical reservoir shell in zones of detected defects may be less than the minimum specified by standard EN 13445-3: 2017, without compromising structural integrity. Experimental and numerical investigation prescribed the boundary geometric characteristics of the defect that can be repaired without the use of additional material (without welding) and ensuring the safe operation of the structure.

Damaging of the carrying steel structure and embedding of the rejecting drum of the stacker conveyor occurred during the exploitation of the bucket-wheel reclaimer with the belonging stacker. The analysis of the cause and level of damaging led to the conclusion that damaged parts should be replaced by new ones and that methodology of repair should be based on the application of a suitable welding technology. This paper presents the methodology of repair welding performed during the replacement of the damaged carrying structure and embedding of the rejecting drum of the stacker conveyor which consist of steel sheets and profiles that’s based on the conceptual solution for damage repair through the use of program package ’Catia’ – V5 that enabled the creation of models and graphic documentation of structural parts that should be replaced by new ones. It should also be noted that geodetic survey of the lower belt of the stacker structure was performed after the substitution of damaged parts of the structure.

The method for validation of the number of buckets on the working device of a bucket wheel excavator from the aspect of dynamic behaviour of the system, partially presented in this paper, was developed on the basis of the original spatial reduced dynamic model of the bucket wheel excavator with two masts, which enables modal analysis and analysis of the dynamic response of the system for continuous variation of constructional parameters and parameters of excitation. The set of 16 seemingly acceptable solutions, all of which satisfied the rigid design restrictions which were: (a) use of the same bucket wheel drivetrain, (b) preservation of the theoretical capacity, (c) possibility of the excavation of soil of the fourth category and (d) preservation of the superstructure centre of gravity position, was analyzed. On the basis of limiting vertical and lateral accelerations, derived from dynamic coefficients prescribed by the code DIN 22261-2, of the bucket wheel centre, which for a proper geometrically-designed bucket wheel excavator structure represents a well grounded indicator of its dynamic behaviour, 14 out of 16 analyzed solutions were discarded, yielding the set of possible solutions to only 2, the originally designed one (with 17 buckets) and the solution with 20 buckets installed on the bucket wheel.

A bucket wheel with drive represents a vital subsystem of any bucket wheel excavator. A multidecadal experience in the exploitation and maintenance of bucket wheel excavators SRs 2000 has imposed a need for modernization and unification of the excavating devices of four of such machines, used for the excavation of overburden in Serbian open pit mines. This paper presents a portion of the research dedicated to the problems of strength and dynamic properties of the bucket wheel boom, static stability of the superstructure as well as installation of the unified design solution for the bucket wheel drive of the bucket wheel excavator SRs 2000. By installing a modernized design solution of the bucket wheel with drive, i.e. by the means of partial revitalization of the bucket wheel excavator, its exploitational life span is prolonged and, additionally, the level of reliability and availability of the overburden systems is increased, and a significant reduction in maintenance expenses is achieved.

Buckets are a vital substructure of all digging machines, and are intended for the realisation of the fundamental machine function - soil excavation. This paper presents the results of the experimental-numerical investigation of the cause of the bucket wheel excavator SRs 470 buckets failure. The chemical composition and mechanical properties, the impact toughness, hardness, tendency to cracks and the microstructure were determined using appropriate tests. Experimental examinations of working and residual stresses were performed using strain gauges. The superposition of the experimentally determined working and residual stresses and the calculation of the total principal stresses were conducted using the originally developed procedure presented in this paper. The bucket working stress state was calculated by applying the linear finite element method. Conclusions based on the investigation results show that the main reasons for the buckets failure were the 'design-in defects' - oversights made during the procedures of geometrical shaping and material selection. Furthermore, high values of residual stresses, as well as the cold cracking observed on the welded joint of the knife and the bucket body, suggest that the 'manufacturing-in defects' also played a significant role in the failure. The superposition of influences of the 'design-in defects' and the 'manufacturing-in defects' has conditioned the appearance and propagation of long-term fatigue cracks, leading to the total destruction of the buckets. The fact that buckets' failure appeared due to oversights made during geometrical shaping, material selection and manufacturing further points to the importance of the critical approach implementation during the design phase of the earthmoving machines working devices.

Sensitivity analysis of the dynamic response of both the designed and the actual models of a slewing superstructure with two masts to the variation of the counterweight mass and the degree of accuracy of the approximation polynomials of the digging resistance was conducted in the paper. Spatial reduced dynamic models of the bucket wheel excavator SchRs 1600 were used as a basis for the presented investigations. Based on the comparative analysis of the calculation results, the following conclusions were drawn: (a) mass of the counterweight has a significantly higher influence on the maximum intensities of accelerations of the referent points than on the spectrum of natural frequencies, (b) the accuracy of approximations of the digging resistance and the maximum values of accelerations differ by an order of magnitude, for the approximation trigonometric polynomial of the same number of harmonics.

This paper presents a methodological approach for the assessment of service life of vital welded structures of a bucket-wheel excavator Sch Rs 650/5x24 ('Thyssen Krupp', Germany) boom, subjected to cyclic loading with a variable amplitude through the use of experimental tests carried out in order to determine operational strength and growth of a fatigue crack. Realized researches and results presented in this paper offer great possibilities for the analyses of behaviour of vital welded structures of the bucket-wheel boom. By the application of the measurement device with 8 channels for registration and processing of electric signals HBM Spider 8 and measurement tapes HBM 6/350xXY31 deformations were measured at vital welded structures of the boom in the area of the bucket-wheel, made of steels St 37.2 and St 52.3 in accordance with standard DIN 17100, or steels S235J2G3 and S355J2G3 in accordance with standard EN 10025-2. The objective of the test is to determine if there is a possibility of occurrence of plastic deformations or initial cracks due to fatigue at vital welded structures. Tests that refer to the growth of the fatigue crack located at the welded joint have been carried out by bending at three points with asymmetric load R = 0.5 (R = sigma(min) / sigma(max)) at the specimen with a single edge notch. Tests were performed through the use of controlled force, ranging between F-max and F-min at the high frequency pulsator 'Cracktronic', while obtainment of data regarding the crack growth was carried out through the use of measurement gauge ARM A-10.

The complexity of the slewing superstructure (SS) balancing problem derives from the changeability of its geometric configuration, the complexity of working conditions as well as multiple limitations of the possible set of solutions. Having in mind the fact that the existing reference literature does not fully specify the procedure of static stability proof, the aforementioned procedure is presented in detail for the first time in this paper. A major contribution is represented in the classification of the slewing superstructure models into two groups which were named: the 'a priori' model (designed image of the SS) and the 'a posteriori' model (actual image of the SS). The fundamental stages of the 'a posteriori' model development method are presented in the paper. The transformation and validation of the calculation model 'a priori' to the calculation model 'a posteriori' was conducted on the basis of weighing results. A calculation of the basic parameters of the bucket wheel excavator (BWE) superstructure was conducted for both analyzed models by using the in-house developed software. The 'a posteriori' models provide a reliable calculation of the SS static stability and may be used not only for static stability proof of the machine as a whole, but also for load analysis of substructures and elements of BWE and related surface mining machines, such as spreaders. Besides that, the previously mentioned models are of extreme importance for a successful and reliable exploitation and maintenence of the machine since they present the basis for adjustment and control of limiting winch rope forces values, periodic control of mass and center of gravity position, as well as for a possible reconstruction which would be conducted in order to realize better customization of the machine versus operating conditions.

During the rehabilitation of the hydroelectric generating set A6 at hydro power plant ’Djerdap 1’, state analysis and integrity assessment were carried out for all vital components and structures. After the completion of non-destructive and destructive tests carried out on parent material and welded joints of the structure of the upper ring of guide vane apparatus as part of vertical Kaplan turbine runner, it was decided that it should be replaced with a new one, because parent material and welded joints were degraded beyond repair. Existing upper ring of guide vane apparatus was made of steel St 3, in accordance with GOST standard. New upper ring of guide vane apparatus was manufactured through the use of steel S 235, in accordance with DIN standard. During ultrasonic testing 6 mm high lack of root penetration was detected at the load carrying welded joint along the entire circumference of the guide vane apparatus. It should be noted that there is no possibility of restoring the welded joint, because the occurrence of deformations at the structure has to be avoided. In this paper the results of the check of load carrying capacity of welded joints are presented, taking into account all weakened cross-sections. Determination of load carrying capacity and fatigue strength were carried out in the usual way, as well as the stress state analysis performed through the use of finite element method in order to determine the influence of undercuts. Assessment of integrity and service life of the guide vane apparatus based on the influence of cracks on stress distribution and fracture mechanics parameters was also carried out.

Bucket wheel excavators (BWEs) are a backbone of any power industry that heavily relies on surface exploitation. As such, any failure, breakdown or collapse of the machine or its subsystems poses a serious drawback in the efficiency of an entire mining system, and is strongly reflected on costs in labour, finances, material and downtime, and is also a potential risk to the safety of workers. This, combined with lengthy lifetime of the machines operating in open cast mines of Serbia (measured in decades), places immense value on the avoidance of potentially hazardous problems during all stages of their lifespan, namely the design, manufacture and exploitation phases. Over the past decades, demand for the ever-increasing capacity and efficiency of BWEs has led to failures which may indicate a need for the reassessment of the calculation methods and guides. This paper presents few such cases, along with the discussion about causes, and suggests an approach to dynamic behaviour analysis based on reduced spatial dynamic models of BWEs which enable modal analysis and the analysis of a dynamic response for continuous variation of constructional parameters.

У раду је постављен оригинални просторни динамички модел двопорталног роторног багера који омогућава модалну анализу и анализу одзива система у условима континуалне промене конструкционих параметара и параметара побуде. Валидација математичког модела извршена је поређењем резултата модалне анализе са вредностима сопствених фреквенција добијеним научно верификованом методом коначних елемената. Резултати показују висок ниво корелације о чему најбоље сведоче релативно ниска одступања прве три сопствене фреквенције (≈1%). Параметри динамичког модела одређени су спрезањем резултата добијених на основу развијеног 3D модела горње градње са резултатима вагања извршеног након завршетка процеса монтаже. На тај начин идентификована је дистрибуција масе надградње и формиран кориговани 3D модел који омогућава да се у целокупном домену промене угла нагиба стреле ротора (СР) са довољном тачношћу одреди положај тежишта надградње. Геометријска конфигурација горње градње нема значајног утицаја на модалне карактеристике разматране конструкције па је хоризонтални положај СР усвојен као референтан. Изведена је анализа утицаја крутости ужади система за вешање СР, доминантних маса и броја кашика на ротору на динамичко понашање система. Доказано је да динамички коефицијенти прописани стандардом DIN 22261, односно из њих изведена гранична убрзања референтних тачака, представљају добру заштиту система од појаве резонанције и да конструкција која задовољава наведене критеријуме осцилује у области на коју резонанције немају утицаја. Наведена гранична убрзања коришћена су приликом формирања критичних области, односно дефинисања комбинација вредности параметара при којима може доћи до негативних динамичких ефеката. Прописан је поступак избора оптималног броја кашика на ротору са аспекта динамике., The original spatial dynamic model of the bucket wheel excavator with two masts which enables continuous variation of constructional and excitation parameters and analysis of their influence on dynamic behaviour of system was developed. Validation of mathematical model was done by comping results of modal analysis with natural frequencies obtained by scientifically verified finite element method. The results show very high level of correlation especially in the case of relative deviations of first three natural frequencies of ≈1%. Parameters of the dynamic model were determined by merging the results obtained from superstructure (SuS) 3D model and the weighing conducted after the erection. In such manner distribution of SuS masses is fully identified, and a corrected 3D model which provides enough accuracy in determining the SuS centre of gravity in the complete domain of the bucket wheel boom (BWB) inclination angle is developed. Geometric configuration of the SuS doesn’t have a significant impact on the system modal characteristics, thus horizontal position of BWB was adopted as the reference. The analysis of effects of stiffness of BWB hanging system ropes, dominant masses and number of buckets, on the dynamic behaviour was done. Limiting accelerations of the reference points, derived from the dynamic coefficients prescribed by code DIN 22261, were proven to provide adequate protection of the machine against admittance in the resonant state. Moreover, the construction which fulfills mentioned criteria oscillates in region not influenced by resonances. Limiting accelerations were used to define critical areas i.e. to determine the set of magnitudes of parameters that may cause negative dynamic effects. The procedure of optimal number of buckets adoption is prescribed.

Determining a bucket wheel excavator (BWE)'s slewing superstructure weight and its center of gravity (COG) is of extreme importance not only in the design phase, but also after the completion of the erection process and during the operation of the machine. This paper presents a critical comparative analysis of the basic parameters of the static stability of a BWE 1600 superstructure, with the parameters being obtained by both analytical and experimental procedures. The analysis shows that a relatively small difference in superstructure mass, obtained by calculation, leads to a relatively large unfavorable shifting of its COG, necessitating a significant increase in counterweight mass for balancing. A procedure for superstructure 3D model mass correction is presented based on results obtained by weighing after the completion of the erection process. The developed model provides enough accuracy to determine the superstructure's COG in the entire domain of the bucket wheel boom inclination angle, and enables accurate load analysis of the superstructure's vital parts. The importance of this analysis is reinforced by the finding that the procedure prescribed by standard DIN 22261-2 gives results which are not on the side of safety, as shown by an example of strength analysis of a bucket wheel boom stays' end eyes.

The planar response of the bucket wheel excavator superstructure is investigated by using a four degrees-of-freedom discrete dynamic model where truss-like substructures are employed to model the pillar with counterweight arm and bucket wheel boom. Excitation is due to the resistance-to-excavation. Four representative geometric configurations of the excavator are examined. The fundamental frequency of the system is most sensitive to the change of the geometric configuration, while the fourth mode frequency is the least sensitive. The maximum displacements and accelerations are observed when the bucket wheel boom is in its lowest position.

U radu je postavljen originalni prostorni dinamički model dvoportalnog rotornog bagera koji omogućava modalnu analizu i analizu odziva sistema u uslovima kontinualne promene konstrukcionih parametara i parametara pobude. Validacija matematičkog modela izvršena je poređenjem rezultata modalne analize sa vrednostima sopstvenih frekvencija dobijenim naučno verifikovanom metodom konačnih elemenata. Rezultati pokazuju visok nivo korelacije o čemu najbolje svedoče relativno niska odstupanja prve tri sopstvene frekvencije (≈1%). Parametri dinamičkog modela određeni su sprezanjem rezultata dobijenih na osnovu razvijenog 3D modela gornje gradnje sa rezultatima vaganja izvršenog nakon završetka procesa montaže. Na taj način identifikovana je distribucija mase nadgradnje i formiran korigovani 3D model koji omogućava da se u celokupnom domenu promene ugla nagiba strele rotora (SR) sa dovoljnom tačnošću odredi položaj težišta nadgradnje. Geometrijska konfiguracija gornje gradnje nema značajnog uticaja na modalne karakteristike razmatrane konstrukcije pa je horizontalni položaj SR usvojen kao referentan. Izvedena je analiza uticaja krutosti užadi sistema za vešanje SR, dominantnih masa i broja kašika na rotoru na dinamičko ponašanje sistema. Dokazano je da dinamički koeficijenti propisani standardom DIN 22261, odnosno iz njih izvedena granična ubrzanja referentnih tačaka, predstavljaju dobru zaštitu sistema od pojave rezonancije i da konstrukcija koja zadovoljava navedene kriterijume osciluje u oblasti na koju rezonancije nemaju uticaja. Navedena granična ubrzanja korišćena su prilikom formiranja kritičnih oblasti, odnosno definisanja kombinacija vrednosti parametara pri kojima može doći do negativnih dinamičkih efekata. Propisan je postupak izbora optimalnog broja kašika na rotoru sa aspekta dinamike., The original spatial dynamic model of the bucket wheel excavator with two masts which enables continuous variation of constructional and excitation parameters and analysis of their influence on dynamic behaviour of system was developed. Validation of mathematical model was done by comping results of modal analysis with natural frequencies obtained by scientifically verified finite element method. The results show very high level of correlation especially in the case of relative deviations of first three natural frequencies of ≈1%. Parameters of the dynamic model were determined by merging the results obtained from superstructure (SuS) 3D model and the weighing conducted after the erection. In such manner distribution of SuS masses is fully identified, and a corrected 3D model which provides enough accuracy in determining the SuS centre of gravity in the complete domain of the bucket wheel boom (BWB) inclination angle is developed. Geometric configuration of the SuS doesn’t have a significant impact on the system modal characteristics, thus horizontal position of BWB was adopted as the reference. The analysis of effects of stiffness of BWB hanging system ropes, dominant masses and number of buckets, on the dynamic behaviour was done. Limiting accelerations of the reference points, derived from the dynamic coefficients prescribed by code DIN 22261, were proven to provide adequate protection of the machine against admittance in the resonant state. Moreover, the construction which fulfills mentioned criteria oscillates in region not influenced by resonances. Limiting accelerations were used to define critical areas i.e. to determine the set of magnitudes of parameters that may cause negative dynamic effects. The procedure of optimal number of buckets adoption is prescribed.

Mounting and dismantling of large-scale mechanical systems is a complex engineering challenge due to several factors, such as structural diversity and size of handled structures, limited maneuvering options, and absence of related literature, to name the few, all of which make each problem unique. Numerous disasters throughout the history created a need for a safe approach to the problem of executing such procedures risk-free, while preserving the structural integrity and functionality of the structures. One of the most reliable methods is the application of unique below-the hook lifting devices and the goal of this paper is to present the benefits of their use via two examples. Case 1 deals with dismounting of dated constructions in a densely populated area, with limited structural data provided. Case 2 is focused on mounting of a large-scale roof structure in harsh boundary conditions, with limited maneuvering space. Results presented in this paper represent a contribution to the field of below-the hook lifting devices.

A slope failure was the cause of a severe accident of bucket wheel excavator (BWE) Takraf SRs 1200. This paper is dedicated to the engineering challenges that accompanied the process of returning the BWE from its after accident state to the state of full exploitation readiness. After the accident, temporary stabilization of the superstructure was carried out as well as cutting off of severely damaged parts of the bucket wheel boom (BWB) with excavating device. Successful completion of the very delicate BWE rescue and balancing operation was followed by the reconstruction of the heavily damaged slewing platform. The integrity of the slewing platform structure was preserved by removing structural parts which were seriously damaged during long-term exploitation and breakdown, and installing the newly designed elements in critical zones. The redesign of the slewing platform structure produced favorable loads and stiffness distribution while eliminating geometrical stress concentrators. Comparative analyses of the stress states pointed out that the redesigned slewing platform structure meets the strength criterion, unlike the original structure. The redesign solution enabled reconstruction in field conditions. This way the time of the reconstruction realization was drastically cut and losses due to the downtime of the machine were reduced several times over. After completing the slewing platform reconstruction, the newly manufactured BWB structural elements as well as the newly manufactured bucket wheel with drive were installed i.e. a partial revitalization of the BWE was done and by that the BWE's life was essentially prolonged.

This paper presents an investigation of the accident which occurred during startup of the extending structure from the transport position. In order to clarify the causes of crack occurrence along almost the entire surface of the lever cross-section, the authors performed visual, experimental (chemical composition, tensile properties, microhardness) as well as metallographic examinations. Stress states in the critical zone are defined by applying the finite element method (FEM). Based on the investigation results it was concluded that the lever breakdown is predominantly caused by both the 'operating-in' defect (the malfunction of the limit switch) and the 'manufacturing-in' defect (poor weld quality). The investigation results presented in this paper are important because same or similar problems could arise in supporting structures of various types of transportation, construction and mining machines.

Mounting of large-scale mechanical systems involves lifting and positioning of the so-called specific loads, namely structures of great dimensions and masses whose functionality and structural integrity should not be jeopardized during the realization of the erection procedures. Two examples of spatial truss roof construction mountings are presented in this paper as case 1, underlying the effect of unique lifting device usage on uniform load distribution on the structures being lifted. Case 2 deals with mounting of three tall vertical pressure vessels of different weights and heights with the same lifting gear and traverse specially designed to accomplish the aforementioned tasks. Case 3 is focused on the redesign of the existing traverse in order to fulfill the task of lifting and precise positioning of the bucket wheel excavator segment, a truss structure of a great span, weighing 90 t. Results presented in this paper represent a contribution in the field of below-the-hook lifting devices design, arising from the specificity of engineering problems dealing with mounting of large-scale structures.