Tower crane peer review
Tower crane peer review
(OP)
I am new to doing peer review on tower cranes. The tower crane stands 260ft tall with a massive foundation. I see the designer has used crane dead load & weight of crane footing in arriving at reactions and overturning moment. In my opinion wind loads should be included to obtain base reactions, i could be wrong. Please share your valuable input.. If i am supposed to check for wind loads what would be a quick way to get the reactions without having to do the entire calculations myself, because this is only peer review. I just want to get a feel for structural capacity of footing with wind loads on tower crane.
Thanks,
SKM
Thanks,
SKM





RE: Tower crane peer review
Dik
RE: Tower crane peer review
RE: Tower crane peer review
RE: Tower crane peer review
RE: Tower crane peer review
http://www.biggetowercrane.com/tower_crane_charts....
Thanks
RE: Tower crane peer review
RE: Tower crane peer review
A widely accepted standard is to take a crane out of service when wind speed reaches 20 meters/second (45 miles per hour). When higher wind speeds are predicted, the crane may be secured with guy wires, or even lowered.
Don't perform wind speed analysis as if the crane is a fixed, unchanging structure (for example, a building). Find out what steps are taken in windy conditions for this crane model. Because action is taken, wind loads are too low to govern.
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RE: Tower crane peer review
Dik
RE: Tower crane peer review
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RE: Tower crane peer review
Yet to read thru FEM 1004 to find out what wind loads have been used in arriving at the base reactions.
Thanks,
RE: Tower crane peer review
Not sure where you are but in NZ/Australia we have a code (AS 1418) that outlines all the load combinations that a tower crane foundation must be designer for, there are about 7 load combinations to consider all with varying load allowances. I'm sure where ever you are based there is a similar code with similar load cases.
The thing is usually you have no idea what the loads the manufacturer gives you are based on. They can give you specific loads for specific loadcase, but usually you pay for their engineering team to look at it.
See below for example
RE: Tower crane peer review
The "TOWER" schematic you posted gives requirements for bracing the crane to the building (A, B, C).
RE: Tower crane peer review
Maybe a 6'-0" thick footing can get the job done from a shear perspective, but I have no gut feel to rely upon due to the magnitude of this crane and loading coming down on it.
RE: Tower crane peer review
Thanks
RE: Tower crane peer review
In normal spread footing its not common to use vertical stirrups. Advise !!.
Thanks,
RE: Tower crane peer review
1. Did you receive the geotechnical report? Design load of 150 tons is a lot for an HP 14x73... especially when any settlement will cause major problems. Also have the 15 tons uplift per pile. Would be nice to see the backup for these high values.
2. Will any to these piling, or similar piling on the jobsite, be load tested to verify accuracy of the geotech recommendations (testing for both for bearing and uplift)?
3. How many piles are there? I see six, if that is all or anywhere close to to all, there is essentially no pile redundancy. Not all driven piling perform as expected.
4. The 15 tons uplift / tension pile is resisted by 2 each #6 rebar in tension... not much steel. At a minimum review the connection of the rebar to pile and rebar (tension) anchorage in the concrete.
5. An HP 14x73 has a crossectional area of 21.4 in2. With the 150 ton design load the pile is (theoretically) compressing the 6 ksi concrete with 14 ksi of pressure. There is controversy if this type loading is a problem, or not. I believe that this type high loading is ok... under the right conditions. This design does not meet what I would consider the "right conditions". Steel plates on the pile tops are another solution... but one that has it's own set of serious drawbacks.
6. Let's move on to rebar, the designer has selected #11 bars for what appears to be one reason - the largest bar size where lap splices are permitted. This foundation is begging for #14 or maybe #18 bars... with their mechanical or welded splices. Using #11 rebar results in a foundation "choked" with a large number of rebars. Look at the bottom rebar mat - #11 @ 4" O.C., Each Way. All the concrete that goes below that mat, to the critical pile bearing area, has to pass though a "screen" that has "hole's just over 2 1/2" square. Yes that probably meets code on concrete aggregate clearance. But don't count on getting well consolidated concrete below the bottom mat.
7. The top mat, #11 @ 8" O.C., Each Way, is better, but considering virtually all the concrete has to pass though this mat, expect problems. Problems made worse since the concrete placement under the bottom mat (See #6, Above) has to be worked though this mat, too.
8. The #11 lap splices are troublesome. First, is a 42" inch (3' 6") long enough - that's a question, I don't recall the answer. The top mat #11 bars @8" are turned down. The bottom mat #11 bars @4" are turned up. The perimeter is a virtual wall of rebar, and there are twice as many upturned bars as downturned bars. Ok, just upturn every other bar in the bottom mat - but that is just a half-way solution to the rebar crowding.
9. The top rebar mat weights about 9 tons, the bottom mat about 18 tons. Has the designer addressed the structural support system for these mats? Better still, is the Contractor required to submit (for approval) detailed plan on how to do this? Note that any reasonable support method for the top mat will affect rebar placement locations of the bottom mat.
10. Along with the rebar mat support, consider how will the soil under the foundation carry the temporary load from the rebar supports. The designer shows a small "Rat Slab" (mud mat), but a full-size (structural) mud mat will probably be needed for the construction loads. Again, a design for the Contractor to submit for approval.
11. Now to the concrete, 6 ksi. Probably a lot of cement in the mix which means high heat of hydration for what is clearly mass concrete (6 feet thick). What controls are inplace for those issues? There is a lot of concrete (190+ yd3) for one pour considering the rebar congestion. Cold joints are quite likely.
12. That's all I can think of for now. In summary, believe this foundation would benefit from more piling, larger size rebar, and lower strength concrete.
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RE: Tower crane peer review
Thanks everyone for sharing your valuable knowledge. Really appreciate all of you !!.
I have reviewed and sent a letter to client. I need to wait for them to address all comments and get back to me.
Thanks,
SM89
RE: Tower crane peer review
Thanks
RE: Tower crane peer review
Concerning what multiplier to use, I assume this crane is not a permanent installation but will be used for a limited time then taken down. If so, criteria and factors from ASCE 37 "Design Loads on Structures During Construction" may be more appropriate than more strict requirements of ASCE 7 or building codes for permanent structures.
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RE: Tower crane peer review
I believe that 15t is allowable uplift capacity of pile and it may have reserve capacity for ultimate. The crane will be used for about an year. Based on RISA model maximum uplift in pile is 26k. Am concerned that by multiplying the 26k with 1.5 overturning safety it exceeds the allowable uplift capacity. And the crane is already in job site. Don't know if I should hit the panic button!!.
But even with 1.5 safety factor it is still within ultimate capacity which Twice the allowable. So 30t or 60k.
Any suggestion is welcome.
Thanks.
RE: Tower crane peer review
Number One is getting that rebar spacing increased, especially the bottom rebar mat. One way would be to use two complete bottom mats stacked on top of each other. That is (#11 @ 8" O.C. Each Way) x 2. Another way is use larger rebar (#14). IMHO, the foundation is not really constructible as shown. Getting 6000 psi concrete under and around the bottom mat (#11 @4" Each Way) without serious honeycomb is doubtful.
Number Two is getting more piling. For a heavily loaded 27'x 32' mat I would expect to see maybe 30+ driven piling. With more piling, required bearing value and uplift capacity per pile go down.
What safety factor to use is pretty far down the priority list. But, for now let's accept the proposed 30 ton ultimate uplift capacity per pile. That is the value (30 tons) to be verified by an uplift field pile test... this is one reason, of several, why more piling (lower loading) is the way to go. Of course test for the 150 tons bearing, too. These tests are not of the steel piling themselves, they will be fine, it for the soil/pile interaction.
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