Column end Conditions
Column end Conditions
(OP)
I have a edge column with following end conditions, what you use in design:
Bottom: 550mm square columns with starter bars that were cast into a 1000mm diameter pile. The pile designer says that the pile would be able to carry 50kNm in bending.
Top: 550mm square column tied into a 550mm deep slab.
The column is tied into a hoist and stair shaft, but this shaft comprises concrete columns and ring beams, no concrete shear walls, with infill brick work that is tied to the columns with hoop irons and a 20mm soft joint between column and wall.
I am not sure if this would provide sufficient restraint, as in for the column to be designed as braced.
What effective length would you use for a column in this case as the end conditions and braced or unbraced condition are a bit of an uncertainty. The column is 8.25m tall.
Bottom: 550mm square columns with starter bars that were cast into a 1000mm diameter pile. The pile designer says that the pile would be able to carry 50kNm in bending.
Top: 550mm square column tied into a 550mm deep slab.
The column is tied into a hoist and stair shaft, but this shaft comprises concrete columns and ring beams, no concrete shear walls, with infill brick work that is tied to the columns with hoop irons and a 20mm soft joint between column and wall.
I am not sure if this would provide sufficient restraint, as in for the column to be designed as braced.
What effective length would you use for a column in this case as the end conditions and braced or unbraced condition are a bit of an uncertainty. The column is 8.25m tall.






RE: Column end Conditions
RE: Column end Conditions
But, it depends on the degree of restraint provided by the pile. It is providing rigid lateral restraint against translation? Is it providing rigid restraint against rotation?
RE: Column end Conditions
"Structural Engineering is the Art of moulding materials we do not wholly understand into shapes we cannot precisely analyse, so as to withstand forces we cannot really assess, in such a way that the community at large has no reason to suspect the extent of our ignorance." Dr. Dykes, 1976
RE: Column end Conditions
RE: Column end Conditions
RE: Column end Conditions
RE: Column end Conditions
I would just use the nomograph tables (Ga, Gb vs K) that are given in the AISC manuals. I think some copies of ACI have these nomographs as well.
If the column stiffness exceed 4 times the rotational stiffness of the grade beam connection, then I would tend to use a K value of between 1.5 and 2.0.
If, however, the column is weak compared to the grade beams moment resistance then I would use a K of between 1.0 and 1.5.
RE: Column end Conditions
RE: Column end Conditions
If you design the pile caps to prevent rotation then you can use k = 1.0. However I find this an expensive solution. For a little bit of concrete on the stair shaft you
can remove the requirement for these ground beams,
Regards,
"Structural Engineering is the Art of moulding materials we do not wholly understand into shapes we cannot precisely analyse, so as to withstand forces we cannot really assess, in such a way that the community at large has no reason to suspect the extent of our ignorance." Dr. Dykes, 1976
RE: Column end Conditions
RE: Column end Conditions