Grade Beam @ Column 1

[JoeBaseplate]

Situation: New addition next to existing construction. There are no documents for the existing building so we have no idea what the existing footing capacity is like. Therefore I am reluctant to place any new loads on the existing. I am proposing the attached detail, basically using a cantilever grade beam to pick up the new column. The new addition is on story so the load not really that high (max 5 kips). Do the seasoned folks here see anything in this detail that I am missing or any other avenues I should be exploring besides the grade beam? The downside of this detail is that the interior wall footing has to be at frost depth too to pick up the grade beam but since they are talking winter construction, so that might not be an issue at all.

Thank you.

 

[Teguci]

Since the HSS column is at the end of the grade beam, you will need a connection that is developed into the top of the grade beam like a haunch(ex. embedded plate with rebar welded and developed longitudinally into the plate/grade beam).

The 2" gap, if you need it, should have compressible fill spec'd. You might not need it since, depending on sensitivity of the existing structure, you could develop the grade beam into the existing footing.

 

[fancypants]

In addition to filling the 2 inch gap as mentioned, I would add some dowels from the grade be to the new footing in the front.

 

[JoeBaseplate]

fancypants: oh yeah of course, the detail is not quite finished yet but thanks for pointing that out. In essence I would have piers at each footing extending into the GB.

 

[fancypants]

Joe,

I figured as much about the dowels.

I have had to design a large number of pump handle grade beams lately with some of the cantilevers going out about 4 to 5 feet. Different jobs and different detailers.

I usually have addition bars on top at the cantilever and the detailers get it wrong every time. They put top bars on bottom and bottom bars on top. I had to go back and look at my details to make sure they were correct and they were.

best,
FP

 

[JoeBaseplate]

FP, I know what you mean. I have designed horz conc beams for wall opngs (waste.w. treat. plants) and seen the shops with the beams rotated to 90 as if it was for vertical. I intend to keep same rebar t&b for entire span.

 

[JoeBaseplate]

Teguci: Thats a good point, the existing structure is not critical enough to leave any gap actually. I can pour my new beam right next to and above it. The new g. beam is far more rigid and should theoretically not load the existing footing.I think that will make things easier in the field for the conc guys.

 

[TXStructural]

I would not connect or provide direct contact between new and existing footings since the new will likely try to compress the soil below and you will in essence load the old footing. Or simply accept that it will happen and just "enlarge" the existing. I generally preferred to stay a little ways away from existing footings when possible.

Since it appears that you are not talking about a significant quantity of these, keep the T&B bars the same, hook the top ones as deep as possible or use headed bars. Provide good confinement steel around the longitudinal steel at the end of the cantilever. This will assure that you can develop longitudinal reinforcement as close as possible to the end.

I'm not sure why you would need to use an embed rather than anchor rods if proper confinement is provided. But I would want the flexibility of a baseplate, even if you use an embedded plate.

 

[Enhineyero]

I think you might also consider the lateral force on you steel column that will be transmitted to the grade beam. I think you need to consider a gap between the existing structures (not just on the footing) and the new structure. since both structures are independent a gap is required so that in an event of a high lateral loads (Earthquake) the two structures wont be hitting each other