The problem of torsion due to horizontal inertial effects is considered at cantilever beam with variable I-section. Linear variation of height is concerned as most practical one for the design of ...cantilever beams. The solution for adopted cases of beams is obtained numerically, according to the complexity of the given ordinary differential equation which deals with pure torsion along with warping torsion. The models are based on known tailor-made beams with possibility for application in design of jib cranes, as practical aspect of this work. The comparison of results is done with uniform cantilever beam models which can be used as one way for verification of stress state of variable cantilever beams subjected to bending with torsion. The obtained results show corresponding advantages of usage of variable sections.
Failures of the cranes’ structural parts unavoidably lead to serious damages or total collapses; these accidents are often followed by very high financial losses and possibly serious injuries or ...crane-related fatalities. The objective of this research was to identify the causes that led to the failure of the hammerhead tower crane (xl425C) counterjib. The crane is used for assembly works at the hydropower dam. The counterjib collapse resulted from a gusset plate failure and caused such significant damage of the whole crane structure that the crane was dismantled and removed from operation. The study of the accident includes: (1) Identification of the stress-state, where a FEM model is developed to provide a useful tool for studying stress analysis; (2) Laboratory investigations are conducted in order to define the chemical composition and mechanical properties of the material, the tensile properties, hardness, impact toughness, as well as the metallographic analyses. The analysis of the obtained results showed that the principal reasons behind the gusset plate failure originated from design and fabrication faults. The working stress was higher than the allowable one. Also, impact toughness was too low and the fabrication of welds was incorrect.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Failure analysis of the mobile elevating work platform Bošnjak, Srđan M.; Gnjatović, Nebojša B.; Momčilović, Dejan B. ...
Case studies in engineering failure analysis,
April 2015, 2015-04-00, Volume:
3
Journal Article
Peer reviewed
Open access
•Failure of the extending structure is investigated.•Experimental–numerical investigations were conducted.•Both ‘operating-in’ and ‘manufacturing-in’ defects caused the discussed failure.
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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
This work examines the dynamics of a two-dimensional jib crane structure subjected to a moving trolley with hoist and payload. Dynamic responses of the structure, both in the vertical (Y) and ...horizontal direction (X), are calculated using the finite element method and the direct integration method. Instead of the conventional moving force problem, this paper deals with the two-dimensional inertial effects due to the masses of trolley, hoist and payload. For this purpose, the moving mass matrix has been used to give contribution to the overall mass matrix of the entire system. The title problem was solved by calculating the forced vibration responses of the jib crane structure with time-dependent overall mass while subjected to an equivalent moving force. Factors as magnitude, speed and acceleration of the moving trolley were studied as well. Numerical results reveal that the approach used herein is usefull and can be used to draw conclusions for the structural design purposes of jib cranes.Original Abstract: U radu se razmatra dinamicko ponasanje ravninske konstrukcije stupne konzolne dizalice izlozene djelovanju gibanja kolica elektromotornog vitla koje nosi teret. Dinamicki odzivi konstrukcije, u vertikalnom i u horizontalnom pravcu, dobiveni su uporabom metode konacnih elemenata i metode direktne integracije. Umjesto konvencionalnog pristupa uporabe modela pokretne sile, u ovom su radu obuhvaceni utjecaji inercije masa kolica, vitla i tereta. Radi toga, koncept matrice pokretne mase je implementiran u matrici masa cijelog sustava. Odredene su prinudne oscilacije konstrukcije stupne konzolne dizalice zbog djelovanja ekvivalentnog pokretnog opterecenja pri cemu je matrica masa sustava promjenjiva u vremenu. Razmatran je utjecaj intenziteta, brzine i ubrzanja pokretnog opterecenja. Rezultati daju korisne zakljucke za konstruiranje konzolnih dizalice.
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