| ▲ | adwn 16 hours ago |
| Your explanation raises the follow-up question, which svantana already hinted at: Why don't construction cranes use hollow tubes instead of their typical truss structures? |
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| ▲ | wizardOfScience 16 hours ago | parent | next [-] |
| The crane manufacturing business case is not driven by material efficiency to the same degree. It is a tool that needs to be reliable and have performance in operations. Limit the need for man hours through ease of use etc. It should also be able to take many assembly/disassembly cycles. Thus does the amount of material not matter as much in a crane. For wind turbine towers the material cost can be >>50% of the installed cost. |
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| ▲ | majoe 9 hours ago | parent [-] | | Working for a crane manufacturing company. While raw material costs are maybe not that drastic, we consider material efficiency the most important metric for cost and a lot of brain power was spent to optimise the amount of steel used. There are multiple reasons for this. The ones I can think of are: * The margins for cranes are thin and steel is expensive.
* Thicker steel is harder to work with, increasing manufacturing cost.
* Each kg of dead weight may decrease the performance of your product, e.g. max. Live load. This is especially true for the jib.
* More weight at the top of the crane may necessitate a sturdier structure below, amplifying cost even more.
* More weight may require more ballast blocks, which are costly (especially transport)
* More weight means higher transport costs
* More weight means more wind area, which is the critical factor for high constructions.
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| ▲ | Aldipower 14 hours ago | parent | prev | next [-] |
| Because at cranes the force is not the wind that comes from any direction, but the directed payload hanging at the crane arm. Almost all cranes I now moving also the pole around. |
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| ▲ | IsTom 16 hours ago | parent | prev | next [-] |
| Certainly makes them easier to disassemble and move elsewhere. |
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| ▲ | carlosjobim 15 hours ago | parent | prev [-] |
| My guess: They want the wind to pass through the crane, while they want wind turbines to capture the wind. |
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| ▲ | majoe 8 hours ago | parent [-] | | This is the answer. Interestingly, wind/storm loads are oftentimes the limiting factor for the configuration height of a crane. This is because, when adding another tower segment, not only the total area increases but also the wind forces. The other loads stay roughly the same This is the reason why bottom-slewing cranes, which are commonly used for small buildings, sometimes are built with solid walls.
Top-slewing cranes, which are used for high buildings, always use a steel framework. |
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