pre eng buildding no floor no frade beams 1

[rittz]

I have a client who wants to put up a pre-eng building on cast in place concrete piles without grade beams and without a concrete floor. On an existing asphalt paved area. The frames span 60 ft and spaced at 25 f oc t. I don’t like it. Am I right?

 

[JedClampett]

I see a couple of problems that might be solvable. It will be extremely difficult to design the anchor bolts in the cast in place piers (piles?) due to edge distance restrictions. The PEMB supplier could care less about this.
However, if the PEMB designer can design the building knowing the supports (cast in place piers) are likely to have limited lateral capacity, then it's doable.

 

[hokie66]

Use a pair of bored piles at each column, connected with a pile cap. I don't really see what the floor slab has to do with the structure, as I don't like the concept of tying the columns to a thin slab on grade which may not stay where you put it, or later be chopped up with trenches. There was a thread about this same issue recently.

 

[ztengguy]

I dont see it any different than a PEMB on a spread footing, just make sure the piles have the lateral and vertical capacities needed to resist the loads.

 

[a2mfk]

I've designed a lot of PEMB foundations, but never with piles. I think if this is early enough in the design, you can do a couple of different things. Both are economic decisions and should involve input from the owner and his contractor if he has one.

1. Coordinate with the PEMB designer and have them at least do a preliminary design where you transfer minimal base shear from the columns to the piles. This would allow you to use a relatively normal auger-cast or similar concrete pile for high uplift but low shear. It will lead to more of an expensive design in terms of the steel moment frames.

2. Plan on doing what Hokie suggested with a pile cap to deal with fully restrained bases and large base shear loads. More money on concrete and pile installation, but a more efficient steel design. But maybe the PEMB designer can do a quick and dirty frame or two for cost engineering purposes.


The owner has to pay for the structure one way or the other, so maybe a side by side comparison is worth it. I think a little bit beefier moment frame system and a simpler pile system would be more economical, but that is a gut reaction and not based on experience.

 

[TLHS]

If you are in an area with any significant seismics, check your code. You may be required to tie your piles together. Even if you aren't required to, it's generally a good idea to tie your foundations in a seismic area so you hold your foundation together as a single unit and not a half dozen independant piles all deflecting in different directions.

 

[ArtBang]

With a Moment Frame Pre-Engineered Building with a pinned base, you need at least 2 piles per column pile cap to resist the transverse lateral loading and gravity loading.
For Longitudinal Loading Condition, you either add a grade tie beam between pile caps or add another pile in triangular pattern. Also, for seismic area, tie or grade beams are
required to resist a minimum axial load of 10% of the total vertical column loads.

 

[TLHS]

I don't know. While I'm not a huge fan of sustained lateral loading on single piles because of the possible long term deflection, you actually might be able to make a single augured pile work. They can make those things pretty big.

Alternatively, there are ways to do tension ties to the pile on the opposite side of the building that wouldn't require grade beams. However, since I suspect the reason for not wanting grade beams is that they want flexibility for the slab, cutouts, trenches, equipment foundations and other items at grade most of those probably wouldn't work either.