Moving loads in structural dynamics of cranes: Bridging the gap between theoretical and practical researches

Problematika pokretnog opterećenja je jedno od osnovnih poglavlja dinamike struktura. Tokom poslednjih sto godina sprovedena su mnoga istraživanja koja se bave analizom dinamičkih odziva struktura, najpre kod železničkih i drumskih mostova. U poslednje vreme predmet ovih istraživanja postaju i strukture dizalica. u poslednjih nekoliko godina istraživanja iz oblasti uticaja pokretnog opterećenja na strukture dizalica su privukla pažnju nekolicine istraživača. Pa ipak, nezavisno od teorijskih dostignuća u ovoj oblasti, nakon provere usvojenih parametara dizalica, očigledno je da dobijeni rezultati u mnogim radovima nisu relevantni za praktičnu primenu na postojećim dizalicama. Sa druge strane, izazov za inženjere i naučnike je upravo konverzija teorijskih ideja u praktičan pristup, koji se može iskoristiti za projektovanje dizalica. Međutim, ponekad je potrebno pretpostaviti parametre koji prevazilaze trenutni nivo tehničkih rešenja, posebno imajući u vidu da se performanse dizalica konstantno poboljšavaju, što će i dalje biti nastavljeno. Na primer, današnje obalske kontejnerske dizalice i portalne dizalice su trostruko povećale raspone, nosivosti i brzine kolica u poređenju sa istim napravljenim pre 50 godina. Zbog toga je neophodno razmatranje dinamičkih modela dizaličnih kolica. U poslednje vreme velika pažnja je posvećena boljem razumevanju dinamičkog ponašanja i vibracija kod struktura obalskih kontejnerskih dizalica i portalnih dizalica usled dejstva kretanja kolica. Jedan od osnovnih problema u istraživanjima jeste usvajanje odgovarajućeg modela pokretnog opterećenja. Cilj ovog rada je da da osvrt na širok spektar najvažnijih objavljenih radova iz ove oblasti u odnosu na budući razvoj struktura dizalica i da naglasi kako se može premostiti jaz između 'čistog' teorijskog pristupa (njihove korisnosti) i praktičnih potreba konstruktora koji projektuju dizalice visokih performansi.The moving load problem is one of the fundamental problems in structural dynamics. A lot of work has been reported during more than a century ago dealing with the dynamic response of structures at first in the field of transportation such as railway bridges, later on highway bridges and finally various constructions such as are cranes, under the influence of moving loads. Research discussing the moving load effects on structural dynamics of cranes attracted the interest of several authors in the past years. However, regardless of the theoretical accomplishments in, after checking the adopted crane's parameters it is obvious that the obtained results in many papers are not relevant for practical considerations for already existing cranes. On the other hand, one of the challenges for engineers and scientists is the conversion of theoretical ideas and researches into practical and efficient approaches that can be used by designers of mechanical equipment. However, sometimes it is needed to move from research findings of existing machines to future systems, particularly having in mind that cranes performances have increased over the years and this intension is not yet finished. For instance, high-performance mega quayside container cranes (QCCs) and gantry cranes have already tripled in outreach, capacity and trolley velocity compared to the machines built more than 50 years ago. This reason makes the investigations on mathematical models of a crane moving trolley necessary. In recent years, considerable efforts have been made to better understand the dynamic behavior and vibration of large QCCs and gantry cranes under a moving trolley. The other direction in research is how to adopt the most appropriate moving load model. The goal of this paper is to discuss a wide spectrum of the most significant published papers in this field with respect to the future perspective of cranes structures development and to point out how to bridge the gap between 'pure theoretical researches' (their usefulness) and practical requirements that are imposed by the structural engineers who are involved in the design of high-performance cranes