Masonry Beam Question 1

[Serhiy2]

Good evening,

I'm working on a project where 8" masonry firewall needs to be added into existing building. Wall will be supported by cast in place pile foundation. I was thinking of eliminating concrete grade beam and going with reinforced masonry beam built completely above grade instead. Supported wall height is 22' in total which will be laterally supported at the top. Movement joints will be located at every second pile which are spaced 12' to 18' apart. Four courses high beam would most likely work strength wise (haven't checked deflection yet).

There are few concerns I have with this setup:
- Lateral (rotational) beam support at piles will only be provided by a dowel extending from the pile. I wanted to check this support condition and wondering what load would I need to design it to in order to achieve adequate lateral/rotational support at piles. I was going to take 2% of beam reaction and apply it laterally at the top of the beam elevation at pile.
- The reason I'm not designing it as deep beam is because deep beam will require a lot more reinforcement and consequently grouting. Also, in case of grade beam, rotational support at beam ends would also need to be evaluated for some sort of load.

Appreciate any feedback on this approach. Thanks

 

[r13]

I wouldn't support your proposal, nor would I against it, eventually you have a huge deep beam (the entire wall) over the supports, without proper reinforcing, I anticipate cracks.

Wind, earthquake and incidental eccentricity of wall are all factors to be considered in pile-wall connections.

 

[phamENG]

Serhiy2 - if your wall and associated foundation are a linear (just a single line), then at each pile cap I would expect you to have 2 piles aligned perpendicular to the wall to maintain stability. That way, any real or incidental moments out of the plane of the wall would be taken as axial loads in the two piles. If you don't do that, then your pile would need to be able to resist the moment internally and the soil-pile interaction would have to be checked accordingly, and the pile cap to pile connection would have to be capable of resisting the moment. Once you get to that point, an ordinary grade beam is restrained in torsion and you can build your wall on top of it.

Forgoing the cast in place grade beam in favor of a masonry beam creates the problems your concerned about with no good way to solve them. Using a concrete grade beam effectively solves them.