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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

A dynamic damping device for payload pendulations of construction cranes

Holk, Michael A. 02 May 2009 (has links)
As a material handler, the crane plays a vital role within the operations of the manufacturing, construction, and shipping industries. Objects of all shapes and sizes are conveyed with the crane to improve productivity and reduce worker fatigue. The crane's capacity to operate efficiently and safely however, suffers from payload pendulations. This cyclic motion of crane cable and payload produces schedule delays, property damage, and high risk to personnel. Current pendulation reduction systems have typically been applied to overhead cranes within the manufacturing and shipping industries. The construction industry in contrast, has failed to innovate tower and mobile cranes. This can be traced to the complexity of the construction operation and the conditions under which the construction crane performs. This thesis aims to improve productivity and safety within the construction industry through the application of damping systems on construction cranes. To achieve this goaL an experimental model will be developed and tested. The design process will include an analysis of operational constraints, theoretical design, and physical testing. Tuned mass damping will be investigated as the basis for the damping control method. Theory will be detailed and incorporated in a mathematical simulation. The tuned mass damper, a cantilevered rod, will be designed and tested for application. The system will then be coupled to a scaled crane model for testing. Data analysis will be used to define the models effectiveness. From the theoretical analysis and physical testing, a conceptual model will be defined. Subjects for future research will also be presented. / Master of Science
2

Časové posouzení využití zdvihacích mechanismů v pozemním stavitelství / Time Assessment of Lifting Mechanisms Efficiency in Civil Engineering

Štěrba, Martin Unknown Date (has links)
The dissertation thesis deals with the time assessment of designed lifting mechanisms in monolithic constructions in Civil Engineering. The main reason for choosing this subject matter is a current trend in construction that in terms of administrative and housing construction tends to build monolithic buildings. Lifting mechanisms are crucial in such buildings nowadays. The efficiency of lifting mechanisms is often neglected in the preparatory phase of construction time schedules, which leads to inefficient capacity utilization of the machine. Nevertheless, this is directly related to meeting the agreed deadlines, which in turn leads to complications that often result in a considerable financial loss for the contractor. In order to solve this subject matter it was necessary to perform monitoring on an appropriate sample of constructions. In the case of this work it was a total of six buildings, four of which were further analysed. Furthermore, individual partial construction processes requiring tower crane operation were analysed. A time assessment methodology including a proposal of possible prioritization of selected activities has been developed. Based on the knowledge gained from the monitoring of the buildings as well as from the analysis of individual items, a simulation model was developed. This model mathematically and graphically evaluates the ability of the designed tower crane to serve a given number of partial construction processes within a specified evaluation section in which the smallest evaluated section equals to one work shift. The benefit of this work is to enable efficient deployment of the tower crane in the preparatory phase of construction. Another benefit is also a prompt operative assessment of the load of the tower crane by a works foreman within a given shift. This should lead to a more efficient deployment of tower cranes during construction and as a consequence it should result in keeping the agreed terms. This is closely associated

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