Tower Crane Foundations 1

[nutbutter]

Hello,

I've seen some tower cranes spring up lately very quickly. I never been on a site that uses tower cranes and I'm curious how these are anchored into the ground. They always carry fairly heavy loads and they seem to be installed almost overnight.

What type of foundation system do they have for these temporary tower cranes?

Peace,
NB

 

[RWF7437]

Not an expert but from what I've seen they are usually located within the building footprint where the elevator shafts and pits will ultimately be. This provides lateral bracing as the crane tower height increases from one floor to the next higher floor.

I would suppose the foundation is designed for the elevator loads or for the greatest load the crane will be required to lift during construction.

Recently, several of these have collapsed so I expect both deign and inspection practices are under review.....probably by very expensive Lawyers.

 

[bimr]

Typically, tower cranes are attached to the foundation slab and the building is built up around the tower.

 

[bimr]

here is a better description:

http://science.howstuffworks.com/tower-crane3.htm

 

[msucog]

sort of related comment here: some are freestanding on a concrete foundation (up to 30 stories i think is the cutoff for freestanding-i'm no expert but just talking with my old superintendent that did a 30 story very recently). there was nothing "anchoring" it down...made me nervous looking up knowing that it was carrying some hefty loads. even if the thing is balanced, i can imagine that it only takes one slipup by the operator or oddball event and over/down she goes!

 

[PEinc]

I've worked on a couple of tower creane foundation designs. They have been large, thick, reinforced concrete spread footings below the building slab. Sometimes the foundations are made by widening-out the proposed building footings.

 

[nutbutter]

Hey thanks for all of the insight fellas. I can't imagine a freestanding tower crane! That is nuts! I wouldn't want to be around it.
When I was just out of college I was working on a job site and I was standing about 15-20' from the crane (a regular treaded crane) and one of the cables snapped. It came flying down with tremendous force and landed about 10' away from me. I'm thinking that probably would've killed me. I don't like cranes.

NB

 

[ishvaaag]

Here (Spain) it is very usual to see freestanding cranes up to say maybe 40 m tall. Foundation usually is a slab, lost or used later for the definitive construction, and if the set of buildings develops along a line they are made on rails to travel along as echeloned construction progress. I have seen this on buildings under my direction as architect not as tall, anyway.

Of course this being the cantilever construction anyone fears, some fall sometimes, typically under wind storms say with gusts of around just 120 km/hour; maybe it is not seven days I saw the last fallen in one of these at the tv.

 

[davep043]

As a ground improvement contractor, I've worked on several crane pads recently, up to about 200 feet high. All have been freestanding, on a dedicated spread foundation just outside the limits of the future building. The allowable bearing capacity of these foundations has typically been in the 3 to 5 ksf range.

 

[dannoMD11]

As a few have already posted, tower cranes can free stand a few hundred feet. This all depends on the crane design and anticipated wind loading on the crane (locality). Foundation types can be spread footings, pile and cap, caisson and cap or special steel cross frames sitting on top of smaller spread footings. I have designed these foundation types within and outside the building footprint.

High rise buildings or taller structures that exceed the free standing height of a tower crane must be tied-in or fastened to the structure it is building. The crane then exerts lateral forces into the structure. In essence, the tie-ins reduce the crane cantilever and allow the crane to "climb" as the building is constructed.

These cranes really are very safe and have an excellent safety record. Unfortunate incidents in 2007 have unduly called into question the safety record of these cranes. A majority of incidents are a result of poor maintenance, rigging or somebody not doing what they were supposed to be doing.

 

[darthsoilsguy2]

see mostly big thick spread footing designs.... we're usually involved in signing off on the footings and concrete of the buildings for the owner. contractors are always trying to get us to do a freebie for them and inspect/test their crane footing. usually i see 3000 psf and 4000 psf designs specified. too many moments happening for my taste.

 

[dannoMD11]

Spread footings are by far the foundation of choice. When you move into the southeast you get into more of piles and caissons and even in the midwest we deal with a lot of auger cast in place piles.

You are correct in that moment typically dictates design. These cranes have anywhere from 200 to 500+ kips of vertical load but the overturning moment is on the order of several thousand foot-kips (depending on the make and model we are talking about 10,000+ foot-kips).

 

[dannoMD11]

Foundations for tower cranes can be of many sorts and often are similar to the building they are helping to construct. The crane location can be within the building footprint or outside the building footprint. The location is often chosen by the contractor based on the construction sequence, type of construction (concrete, steel, etc.), and capacity of the crane and more importantly from the crane owners perspective how to assembly and dismantle the tower crane once its job is done.

Tower cranes can freestand up to 270 feet under the hook (and some higher) depending on the crane make and model. Once you get to a certain height you begin tie-ing the crane to the building.

 

[InDepth]

Shapiro's book on Cranes and Derrick shows pads as well as matts with micro-piles and tiedowns to limit any sort of base movement, keeping the crane as level as possible.