Biaxial-Bending on a Masonry Pier
Biaxial-Bending on a Masonry Pier
(OP)
Hey Everyone,
Here's a new one.
I have a 16x16 masonry pier. Not a pier block, but (2) 8x16s, with the courses alternated as it goes up. The pier is 10ft tall. The (4) cells each have (2) #5 bars in each cell (probably just thrown in there), and they are fully grouted. No lateral ties installed in-between courses. This pier is already constructed.
Of course I have an eccentric point load coming down. 16k DL/25k LL (unfactored) The center of the column is offset in the +y direction by 4.5", and in the -x direction by 2.75". The column is sitting on a steel base plate as well. Also already erected.
Individual (not biaxial but x eccentric or y eccentric) give me stress ratios of 0.55 and 0.813. I'm worried about the combined (biaxial).
Option#1: It's all good and no reinforcement required. Any good way of calc'ing this? I know the neutral axis shifts...
Option#2: Reinforce the pier. How? Add another 8x16 on the side of the worst case eccentricity, reinforce the pier and grout solid, and dowel the new pier to the old with (2) #3 bars into the joint of the existing pier and into the joint of the new pier to tie the two together?
Any thoughts would be appreciated, as well as comments on are there any calc differences when using a pier block over alternating 8x16s.
I'm Stressing....Thanks!
Here's a new one.
I have a 16x16 masonry pier. Not a pier block, but (2) 8x16s, with the courses alternated as it goes up. The pier is 10ft tall. The (4) cells each have (2) #5 bars in each cell (probably just thrown in there), and they are fully grouted. No lateral ties installed in-between courses. This pier is already constructed.
Of course I have an eccentric point load coming down. 16k DL/25k LL (unfactored) The center of the column is offset in the +y direction by 4.5", and in the -x direction by 2.75". The column is sitting on a steel base plate as well. Also already erected.
Individual (not biaxial but x eccentric or y eccentric) give me stress ratios of 0.55 and 0.813. I'm worried about the combined (biaxial).
Option#1: It's all good and no reinforcement required. Any good way of calc'ing this? I know the neutral axis shifts...
Option#2: Reinforce the pier. How? Add another 8x16 on the side of the worst case eccentricity, reinforce the pier and grout solid, and dowel the new pier to the old with (2) #3 bars into the joint of the existing pier and into the joint of the new pier to tie the two together?
Any thoughts would be appreciated, as well as comments on are there any calc differences when using a pier block over alternating 8x16s.
I'm Stressing....Thanks!






RE: Biaxial-Bending on a Masonry Pier
Calc it as...
Max stress = P/A + P*ex/Sy + P*ey/Sx
RE: Biaxial-Bending on a Masonry Pier
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Biaxial-Bending on a Masonry Pier
I thought the calc was a little more complicated than that, no? Am i overthinking?
RE: Biaxial-Bending on a Masonry Pier
I don't know that there is any difference. Your f'm is based on the weak link in the block/grout/mortar assembly so you should be good to go. With a pier block, you have the option of ignoring the block and mortar and just treating it as concrete column with some junk on the outside. That's another kettle of fish however.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Biaxial-Bending on a Masonry Pier
RE: Biaxial-Bending on a Masonry Pier
I remember doing that method in my Masonry Class. The senior engineer I work with, however, once recommended the P/A + M/Sx + M/Sy method.
Not to challenge you, but out of curiousity, what is incorrect about the latter method? Doesn't take into account slenderness, or tension only resisted by reinforcing?
RE: Biaxial-Bending on a Masonry Pier
Challenge away. I live for technical debate.
Exactly this. At least in general, If the column doesn't actually crack, M/Sx starts to look a whole lot better.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Biaxial-Bending on a Masonry Pier
Dick
Engineer and international traveler interested in construction techniques, problems and proper design.
RE: Biaxial-Bending on a Masonry Pier
Just outta curiosity, if it didn't work and it was indeed over-stressed, how would you recommend reinforcing it? The method i mentioned above?
Thanks for everyone's input!