Im forming a concrete pier. I expect 20k lbs of weight every 10 ft. I have 5 2x12x16s spaced about 14in apart. How can i determine the weight tolerance. The boards are bolted at 10ft to concrete piling with 2 5/8x8in lag bolts on each end

  • 2
    Hi Sean, welcome to the Home Improvement site. It would be really helpful if you could provide a sketch and/or photos of your plan. It is possible to imagine a lot of different configurations from your short question. – Michael Karas Apr 7 '19 at 14:11

You have a couple of issues: 1) load that the lumber can support, and 2) fasteners that will support such a load.

1) Depending on the species and grade of lumber, a 2x12 spanning 10’ will support a total of about 3550 lbs. on a 10’ span. (Thats a No.1 grade or Select structural grade.) So, your 5 boards will support about 5 x 3550 lbs. = 17,750 lbs.

However, that’s based on “Working Stress” design in a repetitive installation. “Working Stress” means the load will be there permanently. That load can increase significantly if it’s an “impact load” like snow for less than 30 days, a deck that is occasionally used, etc.

2) You indicate the joists will be fastened with 2 - 5/8” LAG bolts. Assuming the correct spacing between bolts and correct end distance from the end of the 2x12’s, the 2 - 5/8” THROUGH bolts will support about 1,000 lbs. at each end. (For Working stress design with perpendicular to grain loading.)

That means the 5 boards would support about: 5 boards x 1,000 each end x 2 ends = about 10,000 lbs.

So, I’d increase the bolting or provide end bearing for each joist and not rely only on shear from the bolts.

Alternate Idea: You indicate the boards are 16’ long, which I assume about 6’ is being cut off each board. Is there a way the 6’ board could be cut in half and each 3’ piece installed under each end of the 10’ joists to help support it? If the 3’ pieces are installed with the grain running up and down your concrete supports, the allowable load is about double, or about 1,000 lbs. for each 5/8” thru bolt. That could add up fast with just 2 bolts in each 3’ piece.

| improve this answer | |
  • Ok its a pier so there are two rows of 14in concrete piling spaced 5ft apart outside to outside 10ft on center. Each row of 2x12x16s are lapped about 3 ft on each end as its a 100ft long pier. There are 5 rows of 2x12x16s in total across the 5ft span. 4 of them are bolted with 2 5/8 lags at each piling the fith one is resting on 2- 2x12x8 lagged to the piling one on each side of the pile with 2 5/8 x 8in lags and shields on each end. The lower 2x12 is under all 5 rows. – Sean Felicello Apr 7 '19 at 23:55
  • @SeanFelicello Ok, so are these all the changes: 1) only 4 joists are bolt, not 5, 2) there are 2 rows of piers, 3) there are 2 - 2x12’s lagged to concrete piling, 4) the 2 - 2x12’s only span 5’, not 10’ , 5) You say “the lower 2x12 is under all 5 rows”. Don’t you mean the lower 2 - 2x12’s ? 6) 4 of the 5 - 2x 12’s spanning 10’ have end bearing. – Lee Sam Apr 8 '19 at 20:02
  • Ok let me see if i can explain better. – Sean Felicello Apr 10 '19 at 1:39
  • 2x12 sub stringer spanning 4'-6" between two concrete piling with 2 5/8 lags on each end. I have one of these on each side of the 14in concrete pile. Atop of these rests 5 2x12x16 beams aprrox 14in apart. The outer 2x12x16 is lag bolted with 2 5/8 lags on each end. The next 2x12x16 is bolted to the other side of the piling. Then one rests solely on the bottom 2x12 sub – Sean Felicello Apr 10 '19 at 2:04
  • Then the next 2x12x16 is lag bolted as the others. Then on the out side of the pile the final 2x12x16 is bolted. – Sean Felicello Apr 10 '19 at 2:07

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.