Load Combination Considering Crane Load

[StructuralAddict]

How do we account for crane load in load combinations? The crane load consists of both dead load and live load (both increased by a certain percentage as shown in Sections 4.9.3 through 4.9.5 of ASCE 7-16 to account for vertical impact force, lateral force, and longitudinal force, respectively).

 

[SJBombero]

Everything except the lifted load is considered a dead load
The lifted load is considered a live load
The VIF and lateral forces are considered live loads.

 

[StructuralAddict]

Thanks pvchatbot.

So, considering the following:

[ASCE7-16/Section 4.9.2]
Maximum Wheel Load acting on the runway beam includes the following:
1- Weight of the crane bridge (Dead Load)
2- Weight of the trolley (Dead Load)
3- Rated Capacity of the Crane (Live Load)

[ASCE7-16/Section 4.9.3]
Vertical Impact Force (VIF) = (Percentage based on Crane Type) x (Maximum Wheel Load)
So, do we consider the entire VIF as Live Load? Or should we split it as both Dead and Live Loads as follows:
VIF1 = (Percentage based on Crane Type) x (Maximum Wheel Load due to Weight of crane bridge and weight of trolley)
VIF2 = (Percentage based on Crane Type) x (Maximum Wheel Load due to the rated capacity of the crane)
Then deal with VIF1 as dead load and VIF2 as live load?

 

[GC_Hopi]

Since the VIF is a dynamic force, my preference is put it as a live load and use the 1.6 factor. Also you calculate the VIF in the live load chapter so its considered a live load.

 

[topsisu]

I look at as:
Since a crane moves by definition, the only real dead load is the weight of its runway. The dead load of the crane bridge can move to different portions along the support structure and may or may not be present.

Therefore I treat the entire crane as a live load, no point in trying to economize on these types of structures. IE use 1.6 x Max Wheel Load. The vertical and lateral impacts should be 1.6 (if using LRFD) x ASCE-7 specified % of the max wheel load.

 

[CanuckPE]

The CISC's "Crane-Supporting Steel Structures: Design Guide" has a really elaborate load combinations. They're very useful. It helps with things like multiple cranes, lateral loads, wheel tractions, etc. It's $40 in CND (i.e. play money) on amazon.

 

[StructuralAddict]

Thanks guys, that was very helpful.
It seems that just the maximum wheel load may be split into dead and live loads (or conservatively consider it as live load). However, it is reasonable to consider the full VIF and the full lateral forces as live loads.

 

[SJBombero]

Therefore I treat the entire crane as a live load, no point in trying to economize on these types of structures.

My understanding of a live load is that there is some uncertainty of its true value and that is why there are additional factors added to it in the load combinations. There is no uncertainty in the weight of a crane, only the lifted load. The maximum wheel load from the crane itself (without lifted load) already takes into account any permutations of movement.

ASCE 7-16 3.1.1 also specifically defines the weight of a crane as a dead load.

 

[Settingsun]

Curious that it's filed under the live load section if it's mostly dead load.

 

[StructuralAddict]

It seems the crane load is split into dead and live loads as follows:
- The crane weight is considered a dead load.
- The rated capacity of the crane is considered a live load.

So, crane load will show up as both dead and live in the load combos. For example 1.2(DL + weight of crane) + 1.6(LL + rated capacity of crane)

Of course, there are the other loading cases that are all live loads: (Vertical impact force, Lateral Force and Longitudinal Force)

That's my understanding of crane loads...