Crane Foundation Next To Existing Wall

[klipper]

Hi all,
I have been getting a number of requests for new crane system foundations to be installed into existing facilities lately. The crane system vendors sell to customers by placing the new crane columns as close to exterior walls as possible (face of column just inches from wall face). It has been my practice in the past (maybe too conservatively) to locate the columns so I can install a new rectangular footing next to the existing wall's spread foundation and also to match the bottom of the existing wall foundation. Customers do not like to hear that I would like them to move the columns away from the wall after the have been sold a bill of goods from the crane contractor showing the columns right against the wall. I know I have seen other engineers design a foundation for a column tight to the wall where a new pier is installed and then a foundation is poured over the top and along side the wall's strip footing and the new foundation is doweled to the old. I suppose if the proposed new foundations were small enough, you could undermine the wall footing and pour the new foundation under the wall footing if you design the new for the wall load as well. I have also heard of people cutting the existing wall's strip footing flush with the wall to allow the installation of the new crane foundation. What are you guys doing as common practice and what are your theories on the best practice?

Thanks in advance.

 

[JAE]

You mention many valid alternatives (although I wouldn't cut away the existing footing unless you intend to do this in short phases and then provide additional new footings to deal with the crane AND the existing wall loads).

If the need is to get the columns tight to the existing footings, then I see two basic philosophies that could apply:

1. Use deep foundations placed as close to the edge of the existing footings as possible. These could be helical piles, drilled auger-cast-piling, or drilled piers. Other kinds of micro-piling could be considered....depends on your locale and what is typical for your region.

2. Use a cantilevered footing system where you set new footings inside the building (but as close as practical to the existing footings) and another set of buried footings further inside the building. These pairs of footings are then linked with an underground grade beam that spans from the inside footing out to the outer footing and then cantilevers beyond it to the exterior wall where the crane column would load it. This option could get pricey.