Tower crane anchorage tie back design 1

[1986ammu]

Hello,

I hope i will find some engineering solution in ENG-TIPS.com
Issue : Tower crane Anchorage tie back support forces calculations.
As a standard practice every crane manufacturer will provide crane manual along with the product.
It contains all the parts & procedure etc. It also contains Reactions on foundation , on anchorage frame etc.
Whenever the user want to increase the crane height, they will provide some anchorage tie back support between crane & the construction building. So to design tie back supports , the consultants are using the Reactions given as per manufacturer.
My i know what exactly do with these reactions & how they are going to calculate?
Can we use Staad Pro to calculate the stress & forces to design the tie back supports?

 

[oldestguy]

Not my specialty, but I'd not trust any computer program for unusual calculations. I'd instead get a licensed (PE) structural engineer for those calculations.

 

[jayrod12]

I'm not 100% sure what you are asking.

Do you want to know:

A) How to determine the forces in the tie-back?

or

B) Design the structure to support the tie-back load?

It appears you are trying to do B, i.e. check your structure for the tie-back load. In that case, yes you could use StaadPro or another program to analyze the structure for the construction loading. However that wouldn't necessarily make sure it is all ok, that would just ensure that globally the structure can resist the loading. In terms of localized failure modes, those are more often done by hand/spreadsheet. Calculations like concrete breakout at the anchorage etc.

 

[1986ammu]

Hello Jayrod12,


Sorry to reply late.


A) How to determine the forces in the tie-back?

I have attached one of the crane model of POTAIN make MCi85A.
Also attached reaction sheet at various tie levels. In the attachment in-service & out-service reactions given. May i know how to resolve the forces in each tie support & what could be the reactions on the building/construction wall.
Assume any tie level & respective reactions

 

[1986ammu]

Hello Jayrod12,

Reactions

 

[jayrod12]

I may be wrong, but I've been told that many of these companies pay for significant testing to be done to determine these forces. I don't know if you'll be able to fully replicate it. To them, with the number of installations, etc. the economics make sense to pay for some crazy wind tunnel testing in an attempt to bring the crane member sizes, and the reactions to a minimum.

 

[Craig_H]

In terms of calculating the tie-back reactions from a tower crane, I can only imagine a few unique instances where the engineering effort and assumption of risk may be justified. The tie-back forces provided by the manufacturer are envelope forces for a given configuration of the crane, calculated as per the design code for that crane. Unless your operating conditions are significantly restricted from the manufacturer's allowable conditions, you are unlikely to find significant reductions in your tie-back loads. I have done custom analyses of mobile cranes (not tower cranes) operating outside of the manufacturer's operating parameters in the past, but this is high-risk work to say the least. In order to justify doing this, I'd say:
- There must be significant benefit to performing the analysis.
- There must be good justification for operating outside of the manufacturer's parameters, if that is proposed to occur.
- If the crane's operation will be limited (limited capacity, radius, operating wind speeed, etc), then there must be safeguards in place to ensure that the crane is not operated outside of these limited parameters.
- The analysis must be peer-reviewed by a subject matter expert who is removed from the original analysis and can have fresh eyes. It may make sense from a liability perspective to have this be a separate firm.
- The crane manufacturer should be on board if at all possible, acting as an additional peer review, and also providing necessary documentation to support the calculations. I am not sure if the tower crane industry also uses proprietary materials & sections, but the mobile crane industry does, and are often secretive about these aspects, which can make analysis of the cranes quite difficult.
- I would recommend load monitoring at tie-back locations, to ensure that the predicted envelope loads are not being exceeded.
- I would be very hesitant to lower the out-of-service tie-back reactions. By my read of the news, we have too many tower cranes falling over these days, and I would hate to get involved in one where I had lowered the anticipated survivability reactions.

 

[MIStructE_IRE]

What is the purpose of your exercise? Is this a real world design?? If so, you’d want to be VERY brave to deviate from the declared values...

“Well, your honor... I just thought I could do better than the crane manufacturer on the loadings...”

Also, if I were the crane driver, I’d want to know what you’re up to and personally wouldn’t want to be the guinea pig on this.