Non matching slots of anchor bolts in base plate

[tubsdua]

Dear All,

I am facing a typical problem at site and would like to seek guidance from experienced engineers here who have faced similar problem.

We are casting 8 steel columns for erecting a door structure. The foundation for columns is pile foundation and the anchor bolts have been casted in the pile cap. Please refer to the image attached for layout of the columns.

Due to involvement of different agencies there is a mismatch in the distance between the already casted anchor bolts and the trusses for the door structure. Hence the Steel columns supporting the trusses have to be shifted resulting in non matching slots on the base plate (20 mm thick) of the columns. The base plate of the columns will be concreted subsequently.

We are looking at two things to be done:-

(a) For the outer columns the mismatch is 10-15 mm. For this we are planning to increase the slot dia and provide a 40x 40 mm plate (15 mm thick) between the base plate and the nut. This plate is gas welded to the base plate.

(b) For inner columns the mismatch is outside the base plate. Would it be prudent to increase the base plate by welding an additional plate of same dia (as shown in the attached mail)? OR Second option is to prepare a new base plate with correct slots and weld the existing column + base plate on it.

I hope I am going in the right direction.

I am also skeptical about the eccentricity that will set in due to this shift. Any comments on this?

Best.

 

[MikeHalloran]

{
I've had masons involved in placing anchor bolts exactly twice.
The first time I had specified deep anchors with floating plates that would accomodate a lot of eccentricity. ... and in truth the mason's only mistake was removing the red felt washers intended to centralize the bolts while the concrete set. ... so some of the anchors were a little eccentric but we were okay because of the float. ... and we were planning to use washers anyway.

The second time, the guy _really_ screwed up the placement of short rigid anchor bolts for a plastics machine's cast base. We had to design a spacer frame with studs on top and holes on the bottom and install the machine three inches higher than originally planned. Couple buckets of grout made it look like some kind of custom raised foundation.
}
... back to your problem...

a) Thick washers sound okay, if everything else clears, etc.

b) Definitely replace the plates; much easier than splicing a plate's edge. If maintaining the length over the plates is critical, as I suspect, it might work better to cut a square hole in the old plate around the column and a central-ish square hole in the new plate. Then you make a full-pen weld while holding the bottom of the new plate flush to the bottom of the piece of old plate that's still welded to the column.








Mike Halloran
Pembroke Pines, FL, USA

 

[TLycan]

tubsduo,

1- the second option is O.K.

2-from the structural safety point of view:

if the columns are in compression no eccentricity need to be taken into consideration. refer to BS specs as they design the compression column base plate according to the effective width method, which 90% will be safe with your column

if the columns are in tension you have to redesign your base plate(s)

if your base plate is under bending then shear-flow

 

[asixth]

For rectifications I have allowed/specified washers welded to the baseplate or use post installed anchors. This happens all the time.

 

[tubsdua]

Thanks for the views Mike, TLycan and asixth.

For rectifications I have allowed/specified washers welded to the baseplate or use post installed anchors. This happens all the time.

asixth can you point me to some literature on post installed anchors?

Best.