Dynamic analyses of gantry crane under several trolley and payload movements

Izučava se dinamičko ponašanje realne portalne dizalice izložene većem broju pokreta kolica i korisnog tereta. Razvijen je poseban numerički postupak koji je primenjen metodom konačnih elemenata na simulaciju različitih načina kretanja glavne grede. Rezultati jasno pokazuju da pomeraj krana, naročito longitudinalni, u velikoj meri zavisi od ubrzanja kako u početnoj tako i u fazi zaustavljanja, čemu su kolica izložena za vreme kretanja glavne grede krana. Poslednji deo rada prikazuje simulaciju iznenadnog zaustavljanja kretanja kolica i potonjeg ljuljanja korisnog tereta; u ovom slučaju, dužina užeta koje zaustavlja koristan teret na kolicima ima glavnu ulogu u određivanju kretanja i maksimalnog longitudinalnog pomeraja dizalice.The aim of this research is to study the dynamic behaviour of a real gantry crane subjected to the actions induced by the trolley and payload movement. A specific numerical procedure was developed and implemented in the finite element method in order to simulate different trolley movement modes on the crane's main beam. From the results, it is clear that the crane displacement, especially the longitudinal one, is strongly dependent on the acceleration both in the starting phase and in the stopping phase to which the trolley is subjected during its movement on the crane main beam. The last part of this research simulates the sudden stop of the trolley movement and subsequent payload swinging; in this case, the length of the rope that suspend the payload to the trolley has a fundamental role in the trend and maximum longitudinal crane displacement value

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

Estimation of the dynamic effect in the lifting operations of a boom crane

The paper describes a model for the study of the dynamic behavior of lifting equipments. The proposed model proposed allows to evaluate the fluctuations of the load arising from the elasticity of the rope and from the type of the motion command imposed by the winch. A calculation software was developed in order to determine the actual acceleration of the lifted mass and the dynamic overload inside the rope during the lifting phase. In the final part of the article an application example is presented, with the aim of showing the correlation between the magnitude of the stress and the type of the employed motion command