huangyhg

modifying strip footing on 9 storey building
working on a project, 9 storey building with two way slabs and exterior icf walls. foundation wall is poured with the strip footing for exterior walls. problem is the client wants to change the exterior walls to concrete columns which the strip footing obviously cannot support. anybody have any suggestions on how to "economically" retrofit the strip footing for the column loads?
what kind of soil/rock?
another question: do they want to demo the entire wall and then install new concrete columns? or...is the idea to chop out big parts of the wall, effectively leaving "columns" behind?
3rd question :
your how question is about the design or execution?
first question, the soil varies around the bldg the bearing capacity is 5ksf for half the bldg, 8 ksf at middle, and 10ksf for remainder.
second question, no, i do not want demo wall i'm thinking of pouring columns tight to adjacent walls that have already been pouring. my issue is primarily with the footing.
calculor,
if there were intended to be bearing walls all the way up and you are replacing them with columns, then there is obviously already plenty of capacity in the strip footings to carry the load. to distribute the load to the strip footings, you would need to design the floor above to transfer the new column loads onto the already constructed wall.
if that is not an option, then you will have to either 1)demolish part of the wall and strip footing at each column to allow construction of a column footing, or 2) dig under the wall footing and construct the column footing, probably not requiring much in the way of underpinning since there is not much load from above as yet.
with the varying bearing capacity, the changes could cause significant differential settlement... can you cut out the lower portion of the wall to provide a stiff spandrel?, provide more frequent column supports and use steel to stiffen the strip footing?
dik
adding steel to stiffen the footing is not an option as is cutting the lower portion of wall. however, reducing the column spacing and transferring the load to the wall as hokie mentioned may work. my problem is the foundation wall is only 10" thick, which limits the dimension of my column.
how big are the columns above? are they partly over the wall? you may be able to counter the eccentricity with an equivalent couple in the floor if you have enough depth. use strut and tie analysis.
from the geotech side of it: someone gave you from 5ksf to 10ksf in soil for the bearing capacity across the building foundation? yikes...i hope someone is on top of their game when giving recommendations like that for foundation support on soil. i would think differential settlement would kill recommendations like that even if the soil was good to 10ksf, but that's just me not knowing anything about the site conditions...i would enlist the help of the geotech to evaluate the settlement to see if your structure can tolerate it.
hokie,
i'm looking at 12x24 columns centered over the walls with 24" dimension parallel to the wall. i'm thinking about increasing the thickness of the wall in this area to 12". placing the columns over the wall i can take of the wall to distribute to column loads more uniformly. problem with this approach i vaguely recall seeing a new section in csa a23.3 cl 14 which restricts the amount of wall that be considered part of the column when cast integral. i don't have a copy of the code near but if my recollection is incorrect this is will be the approach i will consider.

__________________
借用达朗贝尔的名言：前进吧，你会得到信心!
[url="http://www.dimcax.com"]几何尺寸与公差标准[/url]