Experimental and analytical study on elevating working platform

Abstract This paper describes the research performed about the dynamical behavior on the mobile elevating work platform (MEWP). In particular, this research was inspired by that accident happened during a pruning operation. A big branch of three fell down and bumped the basket of MEWP. The consequent dynamical actions have made the operator jump out of the basket of MEWP. The main object of this work is to characterize the dynamic behavior of this machine (height=34 m, working load limit =200 kg) in order to estimate the actions induced by the branch on the MEWP. This load condition is not contemplated in the standards used for the design of this machine. For this purpose many experimental, analytical and numerical analyses were performed. In order to characterize the dynamical behavior of the machine (real damping, stiffness of the global arm and the sliding blocks positioned between each arms, etc.), on the similar MWEP, about 20 accelerometers and strain gauges were applied; subsequently the machine was subjected to different movements (extension and rotation the arms and the jib). The MEWP was subjected to geometrical relief with the aim to carry out the solid model necessary for finite element model (f.e.m.) analyses; which are performed using the parameters acquired in the previous step. The f.e.m. results were compared with the values obtained from the strain gauges. A lumped parameter model was created in order to apply the load condition induced by the branch to the jib. Numerical and analytical results show that in the geometrical configuration of MEWP (when the accident occurred), the acceleration of the basket is greater than gravity and it justifies the operator jumping out of the basket. The results achieved led to a revision of the standards (in a specific technical committee) both for designing this machine in order to consider this exceptional load condition and for designing the safety equipment for MWEPs operators

EVALUATING THE SEISMIC EFFECTS ON LIFTING EQUIPMENT

The purpose of this paper is to assess the dynamic behaviour of various lifting equipment (different types of cranes, elevating work platform, etc.) subjected to seismic actions, evaluating how these actions can both generate failures and affect the structural behaviour of the machine. The work is developed starting from the design of the different machines of interest (according to some classical standards and specific performance like working load, lifting speed, working area, etc.), determining their geometry. Subsequently are applied the characteristic load spectra to the structures, related to the magnitude of earthquake; the final step consist in the structural analysis of the machines, computing their maximum stresses, displacements and natural frequencies, using different finite element codes. The results show that the first natural frequencies of the structures are very low and consequently the effects of the seismic action, in general, are not dangerous. Otherwise it is important to underline that the maximum stress induced by the earthquake is detectable in different position in the lifting equipment respect to maximum stress position in the normal loading operations, therefore seismic analyses are indispensable for study these parts of machines

Numerical study of wind actions applied to a low profile container crane

Cilj predstavljene numeričke analize je da istraži probleme koji su obuhvaćeni u postupku projektovanja nisko profilnih kontejnerskih dizalica izloženih statičkom i dinamičkom dejstvu vetra, kako bi se utvrdilo da li su ova opterećenja opasna ako se uporede sa standardnim radnim opterećenjem koje se javlja u toku pretovara kontejnera. U prvom koraku istraživanje je sprovedeno pomoću različitih šema dejstva vetra koje su date u standardima; U drugom koraku je analizirano stvarno stanje (eksperimentalno dobijena brzina vetra u odnosu na vreme) i rezultati su dobijeni za konkretnu kontejnersku dizalicu lociranu u jednoj italijanskoj luci. Dobijeni rezultati u pogledu maksimalnih pomeranja na strukturi zavise od opterećenja dizalice i primene različitih šema koje se koriste da bi se obuhvatio uticaj vetra. Korišćenjem promenljivog pritiska vetra, istraživanje pokazuje da su efekti opterećenja vetrom u velikoj meri pod uticajem sopstvenih frekvencija kako noseće strukture, tako i elemenata koji čine strukturu.The target of this numerical study is to investigate the problems involved in the design of a low profile container crane exposed both to static and dynamic wind actions, in order to establish if these loads are dangerous when compared with the load induced by standard container load and unload operations. In the first step the work was performed by means of different schematizations of the wind load action allowed by the standards; the second step regarded the application of a real trend (velocity of wind versus time) obtained experimentally on a similar crane positioned in an Italian harbor. The results obtained in terms of maximum displacement depend on the crane load conditions and on the different schematizations used for the wind action. Using a variable wind pressure, the research shows that the effects of wind loads are greatly influenced by the natural vibration frequencies of both the structure and the elements that compose the structure

Numerical study of wind actions applied to a low profile container crane

Cilj predstavljene numeričke analize je da istraži probleme koji su obuhvaćeni u postupku projektovanja nisko profilnih kontejnerskih dizalica izloženih statičkom i dinamičkom dejstvu vetra, kako bi se utvrdilo da li su ova opterećenja opasna ako se uporede sa standardnim radnim opterećenjem koje se javlja u toku pretovara kontejnera. U prvom koraku istraživanje je sprovedeno pomoću različitih šema dejstva vetra koje su date u standardima; U drugom koraku je analizirano stvarno stanje (eksperimentalno dobijena brzina vetra u odnosu na vreme) i rezultati su dobijeni za konkretnu kontejnersku dizalicu lociranu u jednoj italijanskoj luci. Dobijeni rezultati u pogledu maksimalnih pomeranja na strukturi zavise od opterećenja dizalice i primene različitih šema koje se koriste da bi se obuhvatio uticaj vetra. Korišćenjem promenljivog pritiska vetra, istraživanje pokazuje da su efekti opterećenja vetrom u velikoj meri pod uticajem sopstvenih frekvencija kako noseće strukture, tako i elemenata koji čine strukturu.The target of this numerical study is to investigate the problems involved in the design of a low profile container crane exposed both to static and dynamic wind actions, in order to establish if these loads are dangerous when compared with the load induced by standard container load and unload operations. In the first step the work was performed by means of different schematizations of the wind load action allowed by the standards; the second step regarded the application of a real trend (velocity of wind versus time) obtained experimentally on a similar crane positioned in an Italian harbor. The results obtained in terms of maximum displacement depend on the crane load conditions and on the different schematizations used for the wind action. Using a variable wind pressure, the research shows that the effects of wind loads are greatly influenced by the natural vibration frequencies of both the structure and the elements that compose the structure